Comparative leaf morphology spectra of plant ...

Journal of the Royal Society of New Zealand

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Comparative leaf morphology spectra of plant communities in New Zealand, the Andes and the European Alps S. R. P. Halloy & A. F. Mark To cite this article: S. R. P. Halloy & A. F. Mark (1996) Comparative leaf morphology spectra of plant communities in New Zealand, the Andes and the European Alps, Journal of the Royal Society of New Zealand, 26:1, 41-78, DOI: 10.1080/03014223.1996.9517504 To link to this article: http://dx.doi.org/10.1080/03014223.1996.9517504

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© Journal of The Royal Society of New Zealand, Volume 26, Number 1, March 1996, pp 41-78

Comparative leaf morphology spectra of plant communities in New Zealand, the Andes and the European Alps

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S. R. P. Halloy*, A. F. Mark1

Leaf morphology of native vegetation has often been interpreted as a sensitive indicator of environmental conditions, presumably as a result of natural selection. If environmental pressures act as a selective force on community leaf morphology, then we would expect a high degree of similarity in similar environments, regardless of biogeographic origin of the flora. A comparative study of full regional floras of alpine vascular plants was undertaken to test the sensitivity of leaf morphology to macro-environmental conditions. Five alpine sites and one lowland (control) site were selected in southern New Zealand spanning 1.5° latitude and 2323 m. Three sites with equivalent alpine environments were selected in South America across a 60° latitudinal and 4200 m altitudinal span with subtropical forest used as a control. A further alpine site from the European Alps was included as an outlier. Twenty leaf parameters were obtained for 2143 taxonomic entities x sites. Both the mean and the frequency distribution of leaf size and shape parameters were distinctive for each locality. Several morphological trends were found. Means of New Zealand contiguous low-alpine and high-alpine site pairs differed in: length -33%, width -14%, length/width -20%, leaf area -44%, entire margin - 2 % (variable), coriaceousness -18%, folded +22%, pubescence +40%. At higher elevations, leaves become smaller but rounder, considerably softer, are more often folded into crypts or similar structures and are more often pubescent. These changes corresponded to reductions of 2-3°C in mean annual air temperature, c. 10% in mean minimum relative humidity and 7% in CO2 partial pressure. Despite the biogeographic and environmental differences, New Zealand and South American low-alpine sites were consistently similar in their morphological parameters and consistently different from high-alpine sites (except in Tierra del Fuego). High alpine sites were also consistently similar across the Pacific. Several parameters were found to have multimodal frequency distributions that were not significantly different in widely separate localities with different floras. The results suggest that plant community morphology is an emergent property, the magnitude of which is environmentally constrained. Keywords: alpine. Andes, biodiversity patterns, community structure, ecophysiology, environmental constraints, evolutionary ecology, frequency distribution, functional ecology, leaf morphology, monocharacter spectra, New Zealand, South America

INTRODUCTION This paper attempts to analyse leaf characteristics of relatively complete regional vascular floras (florulas), without regard to taxonomic groups or life forms, covering reasonably homogenous climatic zones as externally defined by vegetation and geomorphic boundaries. By quantifying the variation in leaf morphology between different environments, we intend to demonstrate any functional relationship between the two.

*Invermay Agricultural Centre, P.B. 50034, Mosgiel, New Zealand †

University of Otago, P.O.Box 56, Dunedin, New Zealand


42

Journal of The Royal Society of New Zealand, Volume 26, 1996

Leaves perform a basic function for most plants: the capture of light energy and carbon molecules. These functions can best be fulfilled by a flat, thin surface full of chlorophyllous cells such as is achieved by many liverworts and prothalli. However if such a surface (leaf) is connected by a stem to a group of other leaves (as in vascular plants and many bryophytes), then it is subject to a series of architectural and physiological constraints that will affect the optimum size, shape and orientation of each leaf (e.g., Parkhurst & Loucks 1972; Gates 1980; Givnish 1986). Architectural constraints include aspects of support, resistance, leaf distribution, shape and weight. The size and shape of the leaf are also related to the life form of a plant and its life strategy. Physiological constraints centre around the water-use efficiency, gas-exchange requirements and thermal characteristics of the present environment. These constraints affect size within the limits of inherited shape, and they relate to environment, particularly temperature, humidity and wind (Salisbury & Ross 1969; Parkhurst & Loucks 1972; Larcher 1977; Box 1981; Napp-Zinn 1984; 1988; Woodward 1987; Korner & Larcher 1988; Korner et al. 1989). Biotic pressures may also affect leaf morphology (e.g. Cooper et al. 1993). Constraints on plant form should lead to convergent forms in floras of different origin (e.g. Raunkiaer 1934; Hedberg & Hedberg 1979; Halloy 1983; Orshan 1986). The complex interaction between environmental factors and plant form is clouded even more by historical factors (e.g. Vuilleumier 1994). By designing experiments where history is different but environment is similar we expect to shed some light on this problem. The main hypotheses addressed in this paper are that: 1. the environment selects not only each plant species but also the full community, producing a repeatable frequency distribution between sites with similar climates but different floras; 2. a certain subset of each flora can give adequate information if taken at random; 3. a single major selective factor should produce a unimodal frequency distribution curve of a character state; 4. the frequency distribution of leaf area by species in a community forms a lognormal curve; 5. two alternative (but not exclusive) hypotheses with respect to abundance or cover are tested: a) the mean character state of the most important species should be close to the community mean if adaptive pressure is operating b) more species are competing close to the community mean (for other resources); thus species close to the mean may be less abundant; 6. If species assemblages function as systems, they should exhibit emergent properties. Leaf form frequency distributions and community means may represent such properties. METHODS Sites Testing hypotheses by searching for information in natural ecosystems is subject to many problems. In this study these include practical limitations on number of sites and variability between sites. New Zealand low-alpine and high-alpine (Wardle 1964) floras (Mark & Adams 1986), were compared with vegetation at equivalent levels in the Andes, and with "control" or benchmark sites in different environments. Sites were defined by vegetation - climatic criteria, encompassing regions or biogeographic provinces. The macroscopic scale of such a study means that a range of micro-habitats, micro-climates, soil types and plant associations were assessed at any one site. Such heterogeneity could allow us to assess whether macroenvironmental constraints could still be strong enough to override this "noise" and produce repeatable morphology patterns. Site selection was based on a comparative approach (Halloy 1983, 1989) in an attempt to isolate three effects:


Halloy - Leaf morphology comparison between alpine communities

43

1. environment: by using floras of similar origin in different environments (e.g. southern New Zealand sites). 2. phylogeny-biogeography: by using different floras in similar environments (e.g. New Zealand alpine vs Neotropical paramo). 3. variance: by using similar floras in similar environments (e.g. New Zealand alpine sites) to evaluate within sampling unit variance. A total of 21 sites was analysed as follows: 7 high-alpine (4 New Zealand, 3 South America), 8 low-alpine (5 New Zealand, 2 South America, 1 Austria), 1 temperate subalpine (New Zealand), 4 montane forest (grouped into one, South America), 1 lowland temperate mire (New Zealand). Table 1 shows the characteristics of the sites. Parallel designs allow cross checking and estimates of consistency and variability of data. In some cases it may also allow the separation of interacting factors. Three parallel nested experimental designs were used for these purposes. A All 21 sites were used to attempt to establish purely altitude related trends from possible local trends related to altitude only in some areas. This is an unreplicated design. However, variable by variable comparison in a factorial type arrangement provides insights into some trends and correlations. B Nine New Zealand low- and high-alpine sites were used to restrict variability of intercontinental origin, such as latitude and biogeographic origin. This data set is replicated (five low-alpine and four high-alpine sites) and acts as classical altitudinal transects. Unknown sources of global variation are also reduced in such a set. It provides a crosscheck of any conclusions obtained from A. C Paired comparisons between six pairs of low- and high-alpine sites (two in South America, four in New Zealand) were used to reduce known sources of variation such as latitude, biogeographic origin, regional climatic effects on pressure, radiation, precipitation as well as allowing an estimate of the variation between the six replicates. Trends and correlations appearing consistently in all three data sets were considered to be a possible indication of real effects justifying further research. These are discussed in the text. A contingency table was built to compare the mean values of variables for all sites and the significance of the differences (t-test). A conceptual factorial design was used as well to eliminate interaction effects between altitude and temperature. Biogeographic origin At the scale of this study, all the New Zealand sites can be considered as having a common origin (Godley 1975). However, on a smaller scale the Mt. Burns subalpine and the Waituna Bog floras contain distinct lowland elements. Tierra del Fuego (Moore 1983) has several elements in common with New Zealand, particularly at the generic level, but it is classified by Cabrera and Willink (1973) as belonging to the High Andean Province of the Neotropical realm. Although Huaca-Huasi is also High Andean, it is substantially different from Tierra del Fuego (Halloy 1985). The Colombian paramo has a flora of mostly neotropical origin with some definite nearctic and subantarctic affinities (Chardon 1938; Cuatrecasas 1968; Cleef 1978) and the super-paramo is related more closely to the High Andean biogeographic elements. Calilegua is Amazonian montane forest (Yungas) close to its southern limit. Obergurgl is palaearctic alpine. Environment We analysed those environmental factors that have been presumed to have physiological morphological consequences in plants, and that show elevational variations. Radiation, predation, competition and other biotic interactions were not evaluated in this study but have been covered elsewhere (Caldwell et al. 1980; 1982; Oksanenet al. 1981; Korneretal. 1983; Halloy 1985; Callaghan 1987; Edwards 1988; Cooper et al. 1993). A Stevenson screen with recording thermohygrograph was installed at 6 of the sites, one South American (Huaca-Huasi) and five in New Zealand (Waituna, Blue Mountains, Old

Table 1

Environmentalcharacteris 1 characteristics of study sites Blue Mts lap

Latitude Altitude (m) 2

Area (km )

Old Man Ra lap hap

45°53'S 940-1031 970

45°20'S 1630

905

27-168

35

Pressure mode (mbar) (926) 920 848 Days meas. 288 181 Air temperature (°C) Annual mean 5.2 55.0-3.5 2.2-0.2 "Summer" mean 1 9.2 5.7 "Winter" mean1 2.4 -2.4 Avg Ampl. 6.4 6.9 Max 25.0 17.4 *Min -6.0 -11.7 Relative humidity (%) Mean 84.7 79.3 Mean max 97.9 97.5 Mean min 71.4 56.6 Max 100 100 Min 24 9 + Max days Min < 20% 0 11 Vapor pressure deficit (mbar) Mean air 1.35 1.38 Mean max air 3.33 3.98 Surface max 42.8 51.2 Precipitation (mm) Annual 1342*" 1034-1500 719xS Summer,, , 703" 524 . . .. f\J 1I1U11U 639M ]9617.4

3.0 6.3 10.8 6

3.5 6.7 -0.1 4.1^4.8

4.6 7.3 2.0

7.5 8.5 17.4 10

4.2 6.3 20.8 12

5.7 41.1 55.6

5.7 6.3 9.7 11

3.1 5.8 11.1 5.9 8.6 14.0 0.3 2.7 8.1 4.7-5.8 3.9-5.4 4.3-7.3

3.2-8

2.4 7.7 25.0 3.6 8.1 -1.0 5.2-7.1

3.1 8.1 12.0 10.0 -11 -9 H 34.0-5.1

low-alpine high-alpine high andean Data from Mark ( 1974). Data from Bliss and Mark (1974). Soil temperature at -10 cm, relative humidity based on four months only. Obergurgl climate station at 1938 m. Data extrapolated from Punta Arenas and Co. Guido at lapse rate of-0.7°C/100 m for °C (from Pisano 1974, 1975). Paramo, based on El Angel 3650 m and Cotopaxi 3850 m plus data from Guhl (1968), Lauer (1979), Acosta-Solis (1984). Super-paramos based on Chimborazo 5,000 m and Antisana 4,600 m. Montane forest, represented for climate by Villa Nougues, 1390 m. is that encompassing the given vegetation type and all species found. The area for Mt Burns hap is only 1.9 km. Summer and winter are defined as the three warmest and three coldest months, respectively. Data interpolated. Temperatures in Stevenson screen, at ground level minima may be up to 5°C lower than this. Max number of days (in %) of a month where humidity reaches to or goes below 20%.

4.5-6.2

I §

I a

Precipitation xS.

Wind: M.

n days: B.

Slight underestimates due to rain gauge problem. Large underestimate. Large underestimate due to snow. Mark (1974) gives 1,616 mm as the total precipitation for this area with over 50% falling in winter. Values for TF are from Punta Arenas at 4 m above ground. Mark (1974) gives a value of 5.7 for 2 years measurement in same area. Spread evenly throughout year and only if different from days measured. 3 month summer averages at 0.6 m, the mean for one year for 1390 m at 2 m = 7.79 m/s. Excluding azonal lake bottoms which reach 10.6 (Halloy 1985).

TO

1 s SS


46


Man high-alpine, Mt Burns alpine, Remarkables high-alpine). Data from Halloy (1985) was used to complement the South American measurements and data from Meurk (1978), Mark and Bliss (1970) and Mark (1974) was used to complement the New Zealand data, also giving the values for Rock and Pillar Range. Vapour pressure deficit (VPD) was estimated from temperature and relative humidity in three ways with decreasing precision but increasing biological relevance: 1. Mean air VPD was calculated from mean annual temperature and mean relative humidity. 2. The driving force behind transpiration or ET (evapotranspiration) is the vapour pressure gradient between leaf and air. Lowest air humidities tend to occur with highest day temperatures and give more biologically significant values of VPD. A maximum air VPD, ignoring complexity of the boundary layer, microhabitat and leaf temperature and humidity gradients (e.g. Gates 1980; Cernusca & Seeber 1981) can be approximated by a VPD calculated with respect to mean summer temperature and mean minimum humidity. 3. For alpine plants closely appressed to the ground, these may be underestimates. A maximum VPD for ground level can be calculated with the maximum soil surface temperature used as a ceiling for leaf temperature and with the absolute minimum humidity. Although clearly exaggerated, as it does not take into account the higher humidity at ground level, this gives us a maximum reference point. Soil temperatures (temperature probes or mercury thermometers introduced through plastic conduits, Halloy 1985), wind speed (cup anemometer at 1.5 m) and precipitation (standard rain gauge) were also measured. Pressure was measured with aneroid barometers and verified by the temperature of boiling distilled water. The same measurements were made at Ecuadorian paramos (Cotopaxi, El Angel, Antisana) and super-paramos (Antisana, Chimborazo) during 1980 (Halloy 1980). As these gave values within the range of published information for these environments (e.g. Guhl 1968; Mills 1975; Lauer 1979; Acosta-Solis 1984), they are considered representative also of the Colombian paramo for which the morphological data are presented. For Tierra del Fuego, approximations were made based on lowland stations, estimated lapse rates and the effects of mountain ranges on wind and precipitation. All other site data were extrapolated from neighbouring standard meteorological stations. Our interest in broad patterns directed at a global perspective rather than detailed descriptions explains the very large scale geographic and ecosystem basis of this study. Short term environmental records (Huaca-Huasi excepted) are justified firstly by all New Zealand measurements being simultaneous and secondly because the differences between life zones exceed multi-annual variance within a zone (e.g. Bliss & Mark 1974; Halloy 1985). Morphological characters Because we are concerned with functional relationships, leaf characters were defined functionally. A "leaf is thus a photosynthetic lamina, whether morphologically a leaf, leaflet or phyllode (e.g. the photosynthetic unit). Threshold values to discriminate between a lobed and a compound leaf, or various degrees of leaf crowding, were based on the Fibonacci series (see Halloy 1990b), which produces a numerical proportion well known in phyllotaxis. A total of 44 characters were recorded, of which the following 14, together with 6 ratios, are reported here: Leaf length (L), Width (W) and Area (one sided or for cylindrical leaves, 1/2 the total area of the cylinder); Petiole length (Pet, if present, otherwise listed as sessile); Number of leaves per 10 mm length of stem (NL per 10 mm); Length of green support (LGrS: stem length supporting living leaves); Repetitions (Rep: number of live leaves on a shoot); Group distances between tips (GDT: distance between stem apices or tips of compound leaves, e.g. leaf groups); Margin (entire vs dentate, serrate, undulate);

Halloy — Leaf morphology comparison between alpine communities

47


Division (morphological leaf simple vs compound); Consistence (leaf rigid to subcoriaceous vs membranous); Section [folded (U or V in section, leaves appressed to stems, revolute and involute margins, crypts) vs flat (including cylinders)]; Vestiture (hairy includes ciliate, lanate, pubescent, puberulent or tomentose on either or both surfaces but does not include scabrid or with sparse hairs or confined to the margin vs leaf glabrous); Sessile: (leaves sessile, often with sheathing bases vs leaves with distinct petioles). The following six ratios were analysed: L/W, Pet/L, NL per L, NL per W, LGrS/L, GDT/L. Measurement protocols Individual plants are the functional units of adaptation and therefore of measurement. Where a species has clearly distinct life forms at the same site, these are considered separate measurement entities (e.g. Halloy 1990b). In cases of leaf polymorphy, such as in plants with brachyblasts or juvenile stages, the most common type of leaf was sampled (in alpine plants, generally the short stem leaves). Five individual leaves on five individual branches were sampled from one or several individual plants, and all the above measures were taken on fresh field material (with some exceptions, see below). The mean of five was taken to represent each morpho-species (the species form/s at a given site). Individual plants were subjectively selected as healthy, average-looking plants. Leaves and branches within a plant were selected in the same way. Leaf characters within a single individual and between individuals may vary substantially, even at a same site (e.g. Coleman et al. 1994). Although five replicates does not begin to address the within-species variation, it gives a reasonable representation of each morpho-species. The within-morpho-species variation is important when we are looking at the individual species, but at the community level it becomes a minor noise, relative to the community whole. Even apparently large variations such as a doubling of leaf area would still fall within a single logarithmic size class. Community means are the average of all the morpho-species means. As a result, the possible error created by one set of five measurements having been chosen too large should be compensated by others being chosen too small. A species growing at several localities was measured in the different localities, with the exception of some rare species. The few rare species which we could not find on a site but had been cited in previous surveys or were in herbaria, were represented in the measurements of that site by the values for the same species in the field from the most similar site. Although not precise, this approach gives results closer to reality than disregarding those species. The experimental unit is thus the community as it stands; not imaginary species but the individuals of those species as they have genetically and phenotypically adapted to a site. Validation of the community means and frequency distributions is obtained by the independent sampling of different communities with similar species composition in similar environments (five low-alpine and four high-alpine New Zealand communities were compared in this way). These did not differ significantly, showing that even though the odd individual larger or smaller than average plant may have been chosen, the effect which would have been substantial on a species comparison, is insubstantial at a community level. A similar validation was obtained for field data compared to published information on the same or similar floras (see discussion). For the New Zealand and Huaca Huasi sites, all species in an area were noted and their morphological characters recorded, either by direct measurements and observations of live specimens or in a few cases (< 5%) from published data (e.g. descriptions and illustrations in Cheeseman 1925; Allan 1961; Moore & Edgar 1970; Mark & Adams 1986; Poole & Adams 1980; Wilson 1982). To ensure as many species as possible were considered for each site, herbarium samples and published surveys were also consulted (Heads 1985 for Blue Mts; Mark & Bliss 1970 for Old Man Range and Remarkables; West 1967; Kelly 1968 and Dept of Lands & Survey 1985 for Waituna). Data from the literature were from the same regions


48


as the live specimens. Quadrat and point sampling of vegetation provided values for cover and frequency. Sites where less than the total number of species was sampled are noted in the tables. Other sites were treated less comprehensively: for Calilegua and Obergurgl, time allowed only the most common and readily available species to be measured (129 and 78, respectively). This corresponds in practice to the abundance-weighed sampling described later for Mt Burns. For Tierra del Fuego all values are from Moore's (1983) Flora; for Colombian Paramos data are based on recalculations of Cuatrecasas' (1968) frequency values for c. 290 spp in addition to the first author's observations in Ecuador, Colombia and Venezuela, to Acosta-Solis (1968) and to Vareschi's (1970) flora of the Venezuela paramos. In all, a total of 2143 taxonomic entities x sites were identified and measured. For New Zealand, 387 alpine species (62% of all alpine species described, Mark & Adams 1986) were measured; 168 species were used for Waituna; 150 for Tierra del Fuego and 201 for Huaca-Huasi. A total of 1340 species were analysed in the study. Nomenclature for New Zealand species follows Connor & Edgar (1987) and references therein. For Tierra del Fuego, it follows Moore (1983). Since no comprehensive taxonomic revisions are available for other areas, nomenclature for them has been based on specific revisions, species lists and herbaria. Full species lists are available from the senior author. Analysis Continuous characters (Length, Width, L/W, Area) being skewed, were log transformed (log base 10). Mean (±SD) values were obtained, as well as frequency distributions. Differences between means were subjected to t-tests. Means of logs were transformed to antilogs in Table 3 and in text so as to express values in a more intuitively understandable way. However, from a statistical point of view this produces a biased estimate of the mean (Miller 1984), so that all comparisons, graphs and tests are based on logarithms. The precision of mean values obtained from a sample number of species (as opposed to the total flora) was determined for leaf area, to establish some guidelines as to what proportion of the flora would provide a reliable mean. This was done in ten-species increments both: (1) with a random selection from the full species list of the richest New Zealand alpine site, i.e. Mt Burns (162 species) and (2) by selecting from the same list on the basis of abundance in the field, and at random within a given abundance. This procedure was meant to imitate incomplete species collection in a normal field situation (e.g. Calilegua and Obergurgl) and thus give an indication of the validity of such sampling. To allow for the fact that rare species are also chosen in the field, the choice for each 10-species sample was weighed as follows: 3 very common species (frequency of occurrence >40%), 3 common (20-39%), 2 scarce (6— 19%), 1 rare (1-5%) and 1 very rare (15 % of species) is at a logarithm of L = 0.9 (7.9 mm), with two subsidiary ones at logarithm L = 1.7 (50 mm) and 2.3 (200 mm), and a minor one at 2.7 (501 mm). In contrast, Calilegua peaks at logarithm L = 1.9 (79.4 mm) with over 25 % of species in that class. Frequency distributions of leaf width at four New Zealand high-alpine sites have three almost equal peaks at log W = -0.1 (0.8 mm), 0.3 (2) and 0.7 (5). The five New Zealand lowalpine sites show two peaks identical to the high-alpine at -0.1 (0.8 mm) and 0.7 (5) but a trough at 0.3 (2). Other sites show multimodal distributions but their peaks shift to different positions. The mean leaf length/width ratio (Fig. 6) was lowest for the Calilegua sites (2.53) and the



54

Fig. 3 Frequency distributions of morphological parameters in the Mt Burns alpine flora ( 162 species, except for e and f) (a) Leaf length, (b) Leaf width, (c) Leaf area, (d) Leaf length : width ratio. Representative leaf types in each ratio class are illustrated in their appropriate shapes but not to size scale. 1, Ranunculus lyallii; 2, Hebe odora; 3, Brachyglottis revoluta; 4, Abrotanella caespitosa; 5, Celmisia viscosa; 6, Luzula rufa\ 7, Chionochloa pallens; 8, Schoenus pauciflorus; 9, Chionochloa teretifolia. (e) Frequency distribution of relative petiole length (petiole length/leaf length) in all petiolate species of the Mt Burns alpine florula (64 species). 98 species had no petiole and 23 of those had a sheathing base. Characteristic species for a few classes are illustrated with correct proportions but not to scale. 1.Celmisia viscosa (as an example of no petiole); 2,Epilobium melanocaulon;3,Coprosma cheesemanii; 4,Hebe odora; 5,Brachyglottis bellidioides; 6,Gentianella montana; 1',Ranunculus lyallii. (f) Relative leaf crowding expressed by the number of leaves inserted in a length of stem equivalent to the length of one leaf (NL per LfL). n = 67. Schematic diagrams show selected species in some classes. These highlight the fact that although leaves may be very crowded, this is not the full picture. The number of leaves that remain alive at any one time (Rep) completes the picture and shows that in several species, the length of stem with green leaves is very short. 1, Phyllocladus alpinus, 2, Hebe odora, 3, Abrotanella caespitosa, 4, Brachyglottis bellidioides; 5, Dracophyllum. menziesii; 6, Phormium cookianum; 7, Dolichoglottis scorzoneroides


Hallox — Leaf morphology comparison between alpine communities

Fig. 4

55

Mean leaf area (log of mm2) for all species at each site, ranked by altitudinal zone and leaf area.

Mt Burns subalpine site (3.47), with a maximum at the sea level bog site (Waituna, 10.07). This ratio is a convenient expression of "grassiness" of the vegetation: graminoids (sedges, rushes and grasses) were abundant in Waituna. With the exception of Mt Burns, L/W tends to decline consistently with elevation between paired sites (-20%, Table 5) as graminoids give way to shorter leaved rosettes, cushions and dwarf shrubs. LAV showed a significant negative correlation with mean temperature over the total range of sites, but a positive non-significant correlation for New Zealand alpine sites (Table 4). Figs 3d and 7 show the frequency distribution of LAV, which is distinctly multimodal and right-skewed with peaks repeating at most sites, even the subtropical outlier. Even very small samples show similar peaks, e.g. Huaca-Huasi at log LAV = 0.2 (1.6), 1.0 (10) and finally an inflexion at 1.4 (25). The same three peaks, with similar relative sizes, are found in the New Zealand high-alpine communities. In contrast, the Tierra del Fuego high-alpine shows a wide plateau running from log LAV = 0.2 (1.6) to 0.6 (4), with a second clear plateau at 1.8 (63) to 2.0 (100) in the same position as the New Zealand high-alpine values. Although peaking at log LAV = 0.4 (2.5), Calilegua has a suggestive small peak at 1.4 (25) as in the New Zealand low- and high-alpine sites (Fig. 3d and 7). Leaf petiole, margins, pubescence, etc. Petiole length increases 13% with elevation between low- and high-alpine pairs (Table 5). Together with a decreasing leaf length, this shows that the petiole length/leaf length ratio also increases (+15%), although two site pairs (Remarkables and Mt Burns) show slight decreases. On the other hand the number of species with a petiole actually decreases with altitude: there are fewer species with a petiole, but the average length of those with a petiole increases. The proportion of sessile species thus increases between 5.2 to 8.4 % from low- to high-alpine, with two exceptions (Tierra del Fuego and Rock & Pillar). The petiole length and petiole

ON

Table 3 Community means of morphological character states. Antilog of average log of each character, oi:%


Site Life Zone

BM lap

n° species 154 n° genera 88 Leaf L (mm) 18.2 Leaf W (mm) 3.21 Leaf area (mm2) 45.5 n° species for NL 55 Petiole (mm) 3.27 NL per 10 mm 10.89 LGrS (mm) 8.07 Rep 8.13 GDT (mm) 13.41 LAV 5.69 Pet/L 0.28 NL per L 13.1 NL per W 3.13 LGrS/L 0.62 GDT/L 1.12 77.2 Entire (%) Simple (%) 86.4 Coriac (%) 50.0 Folded (%) 29.2 Hairy (%) 25.3 Sessile or sheathing (%) 61.0

OM lap

RP hap

lap

hap

lap

Rem hap

sap

MB lap

hap

Wai Ob Coast lap+hap

TF lap

hap

HH Hand

Col

Par

37* 156 32 77 22.1 11.3 3.00 2.50 51.9 21.4 15 69 1.81 3.67 15.47 22.17 3.97 4.42 5.74 9.55 11.75 8.88 7.36 4.65 0.20 0.36 16.4 28.0 4.24 5.69 0.22 0.64 0.84 1.19 73.0 69.2 78.4 86.0 51.4 37.8 43.2 40.4 10.8 29.5

47* 112 64 40 15.4 9.91 2.56 2.47 29.6 18.7 11 59 1.89 2.58 8.97 23.12 8.09 4.47 9.17 10.49 13.90 9.15 6.01 4.20 0.22 0.26 17.9 17.5 1.73 6.18 0.62 0.62 1.38 1.30 76.6 73.2 85.1 83.9 48.9 40.2 31.9 37.5 12.8 29.5

59* 43 15.3 2.38 29.7 21 5.16 17.25 5.37 7.39 9.36 6.45 0.37 21.1 4.42 0.44 0.92 69.5 88.1 61.0 27.1 16.9

124 44* 67 35 11.38 21.1 2.31 6.08 20.2 97.9 68 22 3.25 3.18 19.49 9.01 4.86 9.37 9.10 10.47 8.92 22.95 5.12 3.47 0.33 0.19 15.6 18.9 4.93 5.60 0.64 0.45 1.18 1.21 71.8 56.8 84.7 86.4 46.0 61.4 39.5 22.7 14.5 18.2

162 85 21.3 3.68 60.7 67 3.99 11.45 7.32 8.28 15.79 5.99 0.23 24.8 4.44 0.39 0.84 73.3 88.2 58.6 35.4 20.5

82 41 17.5 2.82 36.1 40 4.10 17.71 4.70 8.46 8.10 6.25 0.22 27.4 4.01 0.32 0.71 76.5 80.2 54.3 45.7 23.5

168 112 30.6 3.05 73.5 25 3.60 9.71 11.42 6.88 12.28 10.07 0.32 13.3 2.08 0.70 0.88 78.6 85.1 44.6 19.6 16.1

74 201 >183 78* 148 57 93 53 13 21.8 19.2 16.51 5.39 1.16 2.56 3.08 3.23 42.3 43.9 40.6 -11.48 69.4 3 14 54 12 6.2 6.53 4.79 5.71 10.24 10.40 6.21 46.54 5.88 10.06 5.41 1.62 5.62 10.76 3.73 8.03 6.63 14.63 12.27 3.37 4.66 8.50 6.23 5.11 0.34 0.44 0.54 0.92 25.3 7.49 2.98 25.1 2.65 1.73 0.80 5.38 0.30 0.24 1.39 1.13 0.24 2.23 2.56 0.67 82.0 66.2 59.5 92.9 85.3 85.1 81.1 57.1 79.8 13.1 32.4 28.4 35.7 45.4 27.8 34.5 39.2 50.0 24.1 19.7 32.4 39.2 42.9 54.6

62.9

70.2

69.5

70.2

61.1

75.6

63.7

70.5

Calil. Spar M For >214

129*

67.9 26.8 40.7 1,362.2 123 0.80

Ia (^

-? ? Si' >

2.53 5.51 2.11

88.5 11.5 11.5 58.3

49.0 67.6

N !v o a" a. Ci

PN

ON

70.5

65.2

34.1

68.2

67.6

92.9

HH: All measurements are for 14 species only, except for leaf area, estimated from frequency distribution for all vascular species (201 ), area for 14 species was 4.68 Col: Data from Cuatrecasas ( 1968) Petiole: Average of those that have one, remainder are included in % of sessile and sheathing. GDT: Excluding solitary species. Folded:Includes U and V sections and appressed leaves but not cylinders. Hairy: Includes ciliate, lanate, pellucid, pubescent, puberulent, tomentose (either on 1 or 2 surfaces), but not scabrid or sparse hairs or few hairs on margin *: Number of species measured is below the maximum obtainable for florula. lap: low-alpine



J2

57

^

length/leaf length ratio has a polymodal distribution, with a high peak at log Pet/L 0.8 (0.16) for the latter at low-alpine sites (Fig. 3e). Leaf margin and division do not vary in a consistent way. Entire margins are least common in forest sites (Calilegua, 49% and Mt Burns subalpine, 56.8%), with values commonly above 70% for alpine sites and up to 93 % in Huaca-Huasi. In spite of this clear increase with lower temperatures and increasing elevation, the overall trend between alpine pairs is a slight decrease with elevation (-1.7 %), with three sites declining and two increasing. There is a significant decrease of entire-leaved species at higher temperatures over data set A (all sites) but a non-significant increase in data set B (New Zealand alpine, Table 4, Fig. 2d). Because temperature and altitude are also correlated, the proportion of entire leaves also shows some correlation to altitude (only in data set A). The same applies for the correlation with mean minimum relative humidity. The proportion of simple leaves in the flora is within a very narrow range for all sites, from 78 to 88 %, with only two exceptions at both thermal extremes: Huaca Huasi (57%) and Calilegua

I

(68%).

r| (j g ^ £ °£? § ^ ^ -2! 35 ^ •;• ••£ -^ I a H--S

Coriaceous or sclerophyllous leaves, contrary to popular belief, show a very clear and consistent decrease with elevation (-18 to -27% depending on the number of sites taken into account). All site pairs declined with elevation. Overriding this trend, Obergurgl has a much lower value (13.1%) than any New Zealand site, possibly related to shorter leaf longevity in the short European summer. Tierra del Fuego also had lower values than New Zealand sites. The high andean, with its many winterdormant species, is at the lower end of the ^ew Zealand range, with 35.7%, while the paramo, more predominantly evergreen, has a value similar to New Zealand sites. In contrast, the super-paramo, although still evergreen, declines to 11.5%. Two possibly related characters, leaf folding and pubescence, increased substantially and consistently with elevation. As a consequence, both characters are also inversely correlated to temperature and mean

g c .£ 5 > « ^ § "g o '•g < ^ S "g § [5 si á a c -Q N w u < SJ*1 •§ Ü u .2 5 ,g - j ^ 3 t> " "E 1 « I 1 u ^ u s g1! | c § ~ 3 j S o " c l z ^ u r,-! o ^ § ^ 2- -3 f 3 I '£ M 1 & ^ — a "= I cc" c ^ _-§ •§ S , | £ « ,c ^ í í a c ^ o t c i - S a ' ^ es "^ J ^ l 0 ^ ^ Si1! G j¿ o.g§-a v c | " | J S ^ O Q ^ I w'-l|'5"j " ^_g^i-:|(i;«n_; across the range of sites 1 : Among environmental variables Altitude Pressure " 0.973 Mean minimum Altitude relative humidity*" 0.959 Altitude* 0.600 Latitude Precipitation Mean minimum relative humidity* 0.753 Precipitation Altitude 0.459 2: Between environment and plant characters 0.872 Mean temperature Leaf area" Mean winter temperature Leaf area" 0.817 Leaf area* Precipitation 0.712 Mean temperature LAV* 0.608 Mean temperature Entire leaves * 0.571 Mean winter temperature Entire leaves * 0.530 Mean minimum relative humidity Pubescence" 0.762 Mean minimum relative humidity Leaf areat x 0.725 Mean temperature Folded leaves" 0.484 Altitude Entire leaves 0.469 B — Trends withinNew Zealand low- and high-alpine 1 : Among environmental variables Pressure* Altitude 0.999 Mean winter Altitude temperature" 0.830 Altitude Mean temperature" 0.796 Latitude Altitude* 0.650 2: Between environment and plant characters Precipitation Leaf area* 0.829 Alitude Leafareat x 0.761 Mean Minimum Relative Humidity Entire leaves * 0.888 Mean Minimum Relative Humidity Folded leaves* 0.886

p value < intercept x coefficient

9

0.001

1021

8 21

0.001 0.01

0.843 3415

-0.0001 -47.56

8 19

0.05 0.05

0.234 1357

0.0003 -0.129

21

0.001

1.192

0.115

21 19 19 19

0.001 0.001 0.01 0.02

1.565 0.551 0.805 0.759

0.114 0.001 -0.020 -0.013

19

0.02

0.712

-0.013

8

0.05

0.606

-0.533

8 17 19 site

0.05 0.05 0.05

0.575 0.396 0.590

1.505 -0.018 0.0001

6

0.001

1039 8.49 9.88 35884

-0.099

-0.118

10 10 10

0.01 0.01 0.05

-0.006 -O.005 -759.5

8 10

0.02 0.02

0.971 2.251

0.0005 -0.0005

5

0.05

0.461

0.417

5

0.05

0.773

-0.635

Found significant in both A & B data sets. Giving a correlation of at least P < 0.1 in the other data set (A or B). Showing opposite slope with alternative data set (A or B). Showing similar trend in pairwise data set (C, table 5)

minimum relative humidity (Table 4, Fig. 2e and f). The proportion of leaves folding into U shapes, and generally forming barriers to air flow (crypts) increases between 9 to 22% between low- and high-alpine floras. The two exceptions to this trend can be put in doubt given sample size (Old Man Range) and methodology (Colombia). Moreover, the actual proportion of folded leaves, disregarding paired sites and Colombia, shows a clear overall


Halloy — Leaf morphology comparison between alpine communities trend with the lowest values at sea level (Waituna, 19.6 %), increasing to 22.7 % in the subalpine forest (Mt Burns), 27-43 % in low-alpine, 3746 % for high-alpine and up to 50 % for Huaca-Huasi. The proportion of pubescent species showed a similar consistent increase with elevation (increase between pairs = 31 to 40%), and less clearly, with precipitation. Thus the proportion of pubescent species in the flora goes from 16% at sea level (Waituna) to 18 % for subalpine forest (Mt Burns), 11—32 % in the temperate low-alpine, 15-39 for the temperate high-alpine, 43 % for Huaca-Huasi and 55-58 % for Colombia. Within elevational zones, the highest proportions of pubsecence are found in the wettest sites (e.g. low-alpine: Blue Mountains and Mt Burns; contrary to the overall trends shown in Fig. 2f) and the lowest in the driest sites (Old Man and Rock & Pillar, low-alpine). This generalization is less clear in the highalpine New Zealand data but is consistent with the increase from Huaca-Huasi to the paramos.

59

.,.oo .o.si 0.03 o.*» 0.92 1.40 i.aa 2.35 2.33 3.31 3 J B 4.26 4.74 Log leaf area

Fig. 5 Leaf area frequency distributions, (a) In four

Leaf group architecture high-alpine floras of New Zealand. *—T Mean for 4 New Most of the characters of leaf groups Zealand high-alpine sites covering a total of 474 species, show expected trends. Leaf number • r•- ±1 SE for the former. s> 4 Mean for Old Man Range per 10 mm of stem (NL) and high-alpine (156 species) as a test of fit. (b) In five lowrepetitions increase, and length of alPine floras of New Zealand and one from Tierra del for 5 New Zealand low-alpine sites green support and group distance tips Fue§0 - ~ ^ covering a total of 459 species. •+ 1 SE for the former, decrease with both elevation and • • ^ ^ for J i e m ^ Fuego low.alpine, 148 species. decreasing temperatures. Smaller sample sizes for the leaf group measurements (Table 3) make the results less reliable. NL increased 65% between New Zealand pairs. Excluding Tierra del Fuego, NL ranged from 0.8 leaves/10 mm at Calilegua, through 9.7 at Waituna and 9 in the subalpine forest (Mt Burns), 9 to 17 for lowalpine sites, 18-23 for high-alpine sites and 47 for Huaca-Huasi. On the other hand, due to the disproportionate reduction in leaf length, NL per L actually decreases with elevation (— 7.9% on average) for most site pairs, with the exception of Mt Burns. Nonetheless, the combined elevation and temperature trend is still an increase, from 5.5 NL per L for Calilegua, 13 Waituna, 19 subalpine, 13-28 low-alpine (TF excluded), 16-27 high-alpine and 25 for Huaca-Huasi. The NL per leaf length has a polymodal, rather flattened frequency distribution, with peaks at log NL per L = 0.6-0.8 (NL per L = 4-6.3), 1.2 (15.8), 1.8 (63) and 2.4 (251) (Fig. 3f). The characteristic peaks repeat at different sites and may correspond to adaptive zones or morphological types like those classified in Halloy (1990b).

60


Table 5 Morphological and environmental trends between mean logs of all (6) contiguous pairs of low-alpine and high-alpine sites (C data set) from table 1 and 2. * P < 0.05, ** P < 0.01. Higher variation for all sites than for New Zealand may be due to less stringent sampling. New Zealand results are thus more detectable statistically. Environmental factor trends are taken from the difference between the means of low-alpine and high-alpine. Only those environmental factors shown here displayed a definitive trend, while others varied widely. Mean 9< ]Mean % change of antilog no. of ishange 4


Character

or%

pairs

Range NZ pairs Max Min

-30 Leaf length 5 Leaf width -9 5 -38 Leaf area 6 PetL + 16 5 +31 NLper 10 5 -28 LGrS 5 -3.7 Rep 5 GDT -27 5 Leaf LAV -21 5 Pet/L + 18 5 -29 5 NL per L + 17 5 NL per W LGrS/L +23 5 GDT/L + 10 5 Leaf margin (entire) -2.3 5 Leaf division (simple) -0.1 6 Leaf consistence (Coriaceous)-27 6 Leaf section (folded) +9.0 6 Vestiture (pubescent) +31 6 Sessile +5.2 5 COn partial pressure -7 6 (total range -44) Total exchangeable bases (9 low-alpine vs 3 high alpine sites) Mean annual temperature-2 to -3°C 3 Minimum humidity -5to-10%RH 5 Mean air VPD +67 unpaired Max air VPD + 11 unpaired Surface VPD +46 unpaired

-33 -14 -A4 + 13 +65 -27 +23 -31 -20 + 15 -7.9 +51 +25 +6.3 -2.3 -1.8 -18 +22 +40 +8.4 -6.7

-14 +4.7 -7.3 + 103 + 158 +11 +66 -A.I +4.4 +82 + 10 +257 +189 +41 +4.4 + 10.9 -8.9 +46 + 173 +24 -4.9

-49 -23 -59 -37 -40 -46 -66 -49 -37 -10 -60 -54 -19 -15 -10 -9.1 -75 -52 -14 -7.2 -8.4

Obs ** at all pairs * at 1 pair (MB), 4- and 1 (TF) + ** 4 pairs (except TF, Rem) 4+, 1 (Rem) 4+, 1 (TF) 4-, 1 (OM) + 4+, 1 (TF) all * 2 pairs (OM, RP), 4 -, 1 (MB) + 3+, 2 (Rem, MB) 4-, 1 (MB) + 3+, 2 (MB, TF) 3+, 2 (MB, TF) 3+, 2 (RP, MB) 3 - 2 (Rem, MB) + 4-, 2 (OM, Col) + all 4+, 2 (OM, Col) 5+, 1 (Rem) 3+, 2 (RP, TF) all -

-51.7 some variation, no pairs -3.1' 3C -2.0°C -3.3°Call -10.5%RH all-4.3 + 16.4 +22.5

Notes in observations provide the abbreviation of sites where increases (+) or decreases (-) occurred between low- and high-alpine pairs. Numbers give the numbers of pairs increasing or decreasing.

More importantly, NL per W shows a clear increase of 51 % between altitudinal pairs, with exceptions at Mt Burns and Tierra del Fuego. Over the whole range of sites the trends are not so certain: however, disregarding the sites with smaller sample sizes, the increasing trend with elevation is still clear. Generally speaking, New Zealand alpine leaves are more crowded than those in equivalent environments in Tierra del Fuego and the European Alps and are more similar in this respect to the subtropical Huaca-Huasi flora. The number of leaves held in live leaf groups (Rep) clearly increases with elevation (+23 % between New Zealand pairs), possibly in relation to leaf longevity and stem growth rates. Only Tierra del Fuego decreased, and given the very small sample size there, this can be disregarded. Over all the sites however, this trend is not clear, with Waituna (6.9 rep) and



61

Fig. 6 Mean leaf LAV ratios (log) for all species at each site, ranked by altitudinal zone and LAV ratios.

Huaca-Huasi (8.0), well within the range of low- (5.7-9.2) or high-alpine sites (8.5-10.5). Obergurgl (5.6) and Tierra del Fuego high-alpine (3.7) again show the lowest values. The length of green support (LGrS) declined 27 % with elevation, decreasing for all pairs except Old Man Range (small low-alpine sample size). The overall pattern confirms this trend, with values of 11.4 mm for Waituna, 9.4 for subalpine forest, 4-8.1 for low-alpine, 4.4_4.9 for high-alpine and 1.6 for Huaca-Huasi. The LGrS/L trends in the opposite direction, increasing 25% between low- and high-alpine site pairs, with two sites decreasing (Mt Burns and Tierra del Fuego). The decreases are probably related to an even stronger decrease in leaf length. Nevertheless, disregarding Tierra del Fuego, the highest value is again from the lowest/warmest site (Waituna, 0.7). The distance between group (GDT) decreases for all low- to high-alpine pairs, on average -31 %. The overall picture is not as clear, since Waituna (12.3 mm) is well below the Mt Burns subalpine (23 mm) and several low-alpine (range 9.4-15.8) values. This, together with the LAV ratios show Waituna's close eco-morphological relation with the alpine zones. New Zealand high-alpine values of GDT range from 8.1 to 9.2, with 12.3 mm at Tierra del Fuego. Huaca-Huasi is clearly lower, at 3.4, while Obergurgl again differs from New Zealand alpine sites by being lower (6.6). The ratio (GDT/L) increases slightly with elevation (+6.3 %), with two pairs decreasing (Rock and Pillar and Mt Burns). This is again an overriding effect of the decreasing leaf length. Outlier comparisons Despite the different biogeographic backgrounds, the high number of unrelated species, and the variations in environment (particularly latitude), low-alpine sites were consistently similar (i.e. not significantly different) in their morphological parameters and consistently different from high-alpine sites (except in Tierra del Fuego) which were in turn consistently similar amongst themselves. Among alpine sites, the relatively dry high-andean Huaca-Huasi environment differed the most from all others in the magnitudes of the morphological features of its flora although in terms of form (ratios) it is closely related to New Zealand high-alpine sites. Of the outlier sites, Waituna had some similarities to wetter low-alpine sites


62


(Blue Mts, Mt Burns low-alpine, for leaf area frequency distribution; Mt Burns subalpine, Paramo, Mt Burns low-alpine, Old Man low-alpine, Superparamo for leaf area mean) and other low-alpine sites for L/W frequency distributions (Old Man, Remarkables, Rock & Pillar). With respect to mean leaf width, Waituna was similar to all low-alpine and highalpine sites and differed significantly from Remarkables high-alpine and Huaca Huasi. The frequency distribution of leaf width showed similarity with Blue Mountains, and to a lesser degree with Tierra del Fuego Fig. 7 Frequency distribution of leaf length/width ratio (low- and high-alpine). Waituna had in five low-alpine florulas of New Zealand compared to values of coriaceous leaves close to that of a coastal bog and subtropical montane forest. ew^ Mean for 5 New Zealand alpine sites covering a those in the lower end of the New eoffa' of 4K59 s P e c f •"" ±] SfE for the former. » - Mean Zealand alpine sites but had one of for 4 subtropical montane forest sites at Catilegua ( 129 the lowest values in both folded and ldedand Representative leaf types for the most abundant hairy leaves, consistent with its sea adasses are illustrated for the Calilegua site (not to scale). level position. 1 _ proc/t/a crucis, 2 — Myrcianthes pungens. Calilegua was altogether different from other sites, with the exception of LAV frequency distribution. Despite the differences in magnitude, the similar position of peaks in this multi-modal curve (Fig. 7) resulted in similarities with all New Zealand low- and high-alpine sites (means of 5 and 4 sites). Obergurgl, being an incomplete sample, and including low-alpine and high-alpine, still showed a generally good fit to the alpine sites, particularly Tierra del Fuego low-alpine and Blue Mountains. It differed in having the largest petiole length and one of the highest number of sessile leaves, plus one of the lowest values of length of green support (L GrS), repetitions (Rep) and group distance tips (GDT). As expected it also has one of the lowest levels of leaf crowding (number of leaves per leaf width, NL/W), LGrS/L and GDT/L (typical differences between páramo and Nearctic alpine). It had a high proportion of entire leaves and low proportion of coriaceous leaves (and a predominance of short-lived leaves). Tierra del Fuego, both low-alpine and high-alpine, were closer to Obergurgl than to New Zealand sites in NL, petiole length, Rep, NL/W and coriaceousness. In terms of leaf-area frequency distribution, Tierra del Fuego was generally similar to New Zealand but showed some distinct differences (Fig. 5b for low alpine). These characters may be important for temperate, short summer alpine zones. Huaca Huasi was at the opposite end of the scale with respect to NL, Rep and NL/W, a possible indication of the tropical affinity of its environment. Paramos were similar (i.e. not significantly different at P < 0.05) in mean leaf area (69.4 mm2, the only meristic data for these sites) to the New Zealand coastal site of Waituna (73.5 mm2) and the low-alpine sites of Mt Burns (60.7) and Old Man Range (51.9). The super-paramo was similar to many New Zealand sites. In terms of mean leaf area it was similar to Blue Mountains, Mt Burns (low- and high-alpine), Old Man (low- and high-alpine) and Tierra del Fuego (low- and high-alpine). More surprisingly, because it implies a much closer fit, the super-paramo was also similar in the frequency curves for leaf area with Mt Burns high- alpine and Remarkables low-alpine sites and less similar to the Rock & Pillar low-alpine site. Colombian paramos were generally similar to New Zealand alpine sites in terms of proportion of entire margins, simple leaves and, for low- alpine only, folded leaves.

Halloy — Leaf morphology comparison between alpine communities

63


As these characters were also similar in outliers (Tierra del Fuego, Obergurgl, Huaca Huasi) they are probably of little discriminating value for this set of data. On the other hand, Colombian sites had a much higher proportion of pubescent species and, for super-paramo, a lower proportion of coriaceous species. Relation between abundance and morphology Table 6 shows that common species tend to be more different from the mean than are rare species. Also, common species tend to be skewed in a definite direction; in this example, their values for area and length are both clearly larger than average (Fig. 8 showing all species on the leaf area gradient in relation to their abundance). This is particularly true for the four most common of the ten species and may be a prerequisite for a common species (larger leaves may compete more successfully, e.g. Knapp & Fahnestock 1990) or might be a hint of an evolutionary trend in the community such as a reaction to increasing temperatures. It also explains why small samples of a flora based on abundance are liable to depart significantly from the mean (methods). The four most frequent species in the Mt Burns lowalpine (Chionochloa teretifolia, C. crassiuscula, Schoenuspauciflorus and Celmisiapetriei) also depart from the mean L/W, all having elongated narrow leaves. DISCUSSION The value of community analysis Function-environment variations have been investigated by other authors within a species or groups of species along an environmental gradient (e.g. Baruch 1979. Korner, et al. 1983, 1986; Rada et al. 1987). Such an approach is analytically clear and usually gives straightforward results. Yet it has disadvantages: the sample size is evolutionarily and genetically very small. Variations on a restricted genetic sample over a transect may answer the question "what happens to a particular genome when subject to a particular environmental gradient", but not "what would tend to happen to any vascular plant genome when subject to a particular environmental pressure". It is thought that one can extrapolate from the first to the second, but this has to be demonstrated Table 6 Relative distance to the mean of (e.g. Manly 1985). 162 species [(Sp value-Mean)/SD] of 10 At a community scale, it is common to abundant species and 10 rare species from Mt find exceptions to general trends: leaf area Bums low-alpine zone. All values based on of many species decreases on a gradient of logarithms. increasing elevation yet some species with very large leaves may appear at very high Area L W L/W elevations (eg. Espeletia species in the equatorial Andes, Cuatrecasas 1968; Abundant tspp Dendrosenecio and Lobelia species in East Avg dist. 0.205 0.608 -0.389 0.866 Africa, Hedberg 1964; Ranunculus lyallii to mean and Celmisia species in New Zealand, Mark SD 1.248 1.392 0.763 1.042 & Adams 1986). Do these exceptions 1.752 Max dist. 2.030 0.900 2.546 negate the apparent trend? The answer must Min dist. -1.67 -1.31 -0.47 -1.17 come from a community synthesis n° spp > 1 SD 4 4 5 0 considering all taxonomic groups (e.g. n° spp < - 1 SD 2 2 2 0 Westoby et al. 1992 regarding seed Rare spp characters and Leishman & Westoby 1992). Avg dist. -0.049 -0.216 0.156 -0.338 to mean If environmental pressures act as a selective SD 0.935 0.873 0.415 0.749 force on leaf morphology, then a high Max dist. 0.69 1.946 1.36 1.91 degree of form repetition would be expected -0.99 -0.85 Min dist. -1.08 -1.08 over similar gradients regardless of the n° spp > 1 SD 2 1 2 0 biogeographic origin of the flora. On the n° spp < - 1 SD 2 1 0 0 other hand, whole floras in different


64


continents may not react in the same way, considering the heterogeneity of microclimates, microhabitats, soils, history and phylogenetic lines (Billings 1974). It is repeatability that will provide the strongest arguments for convergence (Halloy 1983; Schluter & McPhail 1993). Much work has been done comparing whole floras in terms of either averages or frequency distributions of certain morphological characteristics (from Raunkiaer 1934 onwards). Such studies involve determination of a wide range of characteristics in hundreds of species. It has the drawback of comparing ill-defined (from an environmental perspective) geographical units such as countries, with possibly many different environments. Raunkiaer's life form system has encountered criticism due to its lack of precision, particularly in the southern hemisphere (Allan 1937). To increase precision, plant form has been subdivided into modules (Halloy 1990b) or into individual characters (the "monocharacter" approach, Orshan et al. 1984). However Raunkiaer also worked with simple characters such as leaf size. Such analyses have also tended to reduce the area to a relatively homogeneous environment such as a climatic zone, a soil type or a small island (e.g. Werger & Ellenbroeck 1978; Orshan et al. 1984; Campbell & Werger 1988; Turner & Tan 1991). Often the choice of species has also been restricted (e.g. only trees, or trees and shrubs). Some of this work has implied that the character-environment relations are clearly apparent, following Bailey and Sinnot (1915, 1916) and Raunkiaer (1934), and that it therefore can be applied to predict some features of paleo-environments based on characters such as leaf margin or size (Dilcher 1973; Dolph 1978; Wolfe 1971, 1978, 1979). The parameters used were means or frequency distributions of the character states considered. The procedure for sample selection, as well as the variation in sampling methods, is partly due to practical constraints given the scale of the study, and partly motivated by an attempt to compare data obtained from the field and from the literature. The log transformations have shown the method to be rather robust, with data from measured floras being comparable to fresh field data. This is not to say that individual plant leaf sizes (for example) do not vary in dried and fresh specimens, or from one individual plant to another. This variation exists and can be very large, when the unit of comparison is the species. But the fact is that the variation introduced by these effects is small when compared to the overall community range of variation. The within species variation is such that it does not tend to exceed the size classes used. As a result, the frequency distributions remain robust. The present paper has combined full flora analyses in well defined replicated macroenvironments, thus allowing a focus on evolutionarily meaningful relationships between plant and environment characters. The environmental trends In mountainous situations both the soil and climate vary considerably through different micro and meso-habitats over the total areas studied (e.g. Cernusca & Seeber 1981). This variation is not taken into account here since total floras, rather than those of single micro- or mesohabitats, are considered. If a total flora really averages out the plants' "perception" of the environment, then macro-environmental factors should be correlated to the community morphological parameters. Of all factors measured, two (pressure, minimum humidity) showed a consistent trend and close correlation with elevation (Korner et al. 1983: option 2, factors applicable to all mountains) and two (temperature, total exchangeable bases) showed a decrease with elevation within a narrow range of latitude (regionally determined) (Table 4). The very close correlation of pressure and altitude on a macro scale allow us to use altitude as a replacement for pressure in our correlations with morphological characters (however, on a regional scale pressure may vary substantially at equivalent altitudes, Halloy 1985). Some environmental factors not considered in this study may have influenced community life forms. Among them is herbivore pressure, with New Zealand distinguished by an absence (until recently) of mammalian herbivores and the past presence of large herbivorous



65

ratite birds (Cooper et al. 1993). Korner (pers. com. 1993) suggested that herbivory, by discriminating against all species with higher buds, should favour an abundance of rosettes, rhizomatous shoots and tussocks. These life forms translate to high leaf crowding (NL/W) and low length of green support/leaf length, (LGrS/L) and group distance tips/L (GDT/L). However, Obergurgl, with the highest herbivore pressure, shows the lowest levels of leaf crowding (NL and NL/W), but a low value of LGrS. GDT/L is the lowest at this site. Here the leaves are less crowded, fewer, on shorter supporting stems and the stems are closer together, compared to the other alpine sites in the study. Thus if mammalian herbivory is effective at all, its effects may be overridden by other factors or is acting in different ways. Radiation, particularly UV-B radiation, has a strong latitudinal gradient (Caldwell et al. 1980) relating to gradients in epidermal transmittance (Robberecht et al. 1980), but not to pubescence. The extreme sites in this study show an atmospheric pressure reduction of over 44% and a range of mean annual air temperatures over 14°C. Stratifying pairs of alpine sites by vicinity, we obtained, from low-alpine to high-alpine, a decrease in pressure of 7%, 2 to 3°C reduction in mean annual temperature, c. 10% reduction in mean minimum relative humidity, and close to 52% reduction in total exchangeable bases (Table 5). Other environmental factors did not show consistent trends with elevation. The decreasing partial pressure of CO2 resulting from the lower atmospheric pressure may have effects on life form, productivity and vegetation limits (Halloy 1985, 1989). Mean air VPD decreased with elevation in New Zealand sites (—4.3%) but maximum air VPD increased (11 to 16%). The latter is a better approximation to leaf VPD. Although increasing with elevation, this parameter is still low compared to wet tropical forest values above 20 mbar (e.g. Walter 1977, 21 mbar). The effective diurnal VPD for the leaf should be intermediate between the summer air VPD and the maximum soil surface VPD, as leaves cool below soil temperature and both leaves and soil are enveloped by a moist boundary layer. The decrease in minimum relative humidity with elevation is a clear phenomenon, insufficiently recorded in the literature. Its biological significance, tied to leaf temperature and boundary layer conditions through VPD, is uncertain at the community scale, due to the difficulty in extrapolating valid figures from macro-scale data. Bean et al. (1994) proposed a simple regression model to estimate evaporation at high elevations based on VPD. Despite the slight increase in maximum VPD with elevation, the low values of osmotic water potential in high altitude plants in general, together with their hygrophilous adaptations (Heilborn 1925; Baruch 1979; Gonzalez 1985; Halloy 1989) suggest that the definitive VPD sensed by the plant is low rather than high. Morphological and physiological evidence attributed to drought stress in high mountain plants (Webster 1961; Hedberg 1964; Ruthsatz 1978) should be seen within this relative context. Indeed hygrophilous plants can suffer drought stress in their native environment when moisture conditions are lower than their tolerance. The rapidly fluctuating VPD, along with air relative humidity, at high elevations may be important in producing adaptations such as leaf rolling and pubescence (Halloy 1985). Species numbers The number of species for full floras at different sites was reasonably similar (130—200, Table 3), suggesting that parameters derived from these groups can be validly compared. Most of the areas are in effect biogeographical "islands", but their surface areas are not the same (Table 1). The islands of New Zealand have an undersaturated flora, with total species numbers well below those expected for similar size areas (Halloy, unpublished data). Despite this general poverty at the regional level, New Zealand sites showed as much local diversity ("a" diversity, Whittaker 1972) as did continental sites, meaning that each species can be found in a wider range of associations. Because whole florulas were measured, there should be no

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Log Leaf Area (mm2) Fig. 8 Distribution of leaf sizes by species abundance. Each cross represents one species. Abundance is expressed as the frequency of occurrence of each species in 29 vegetation samples of the Mt Burns alpine florula. Species not recorded in vegetation samples but found in the area are accumulated below I %. The mean ±1 SD show how common species tend to have larger leaves.

discrepancy between regional floras and our sampling (e.g. as there may be in smaller samples, Dolph 1978). Morphological trends Summarizing trends between low- and high- alpine areas (Fig. 9 and 10), one can say that leaves become smaller and rounder (reduced LAV), considerably softer (less coriaceous), tend to be more often folded into crypts or similar structures, and have a higher proportion of pubescence with increasing elevation. Leaves may be proportionately less crowded in relation to their lengths, but more crowded in relation to width. Number of leaves per group will increase and the length of stem on which they are inserted will decrease, leading to greater absolute crowding. Finally, the leaf groups will tend to be slightly more distant in relation to leaf length, although in absolute terms they are closer together. These trends at the community level may differ from those observed between populations of the same species, or species in the same genus, or small samples of species. For example, in a sample of 8 species from 1220 and 1390 m on Rock and Pillar Range, group distance tips (GDT) increased on average by 5.6%, with three decreasing (calculated from Bliss & Mark 1974). The following changes with increased elevation may be more uncertain: fewer species may have petioles, but those that have tend to be longer, both absolutely and relative to leaf length. Leaf margins and division do not seem to show consistent trends between these lowalpine and high-alpine environments. Entire margins increase remarkably with decreasing temperature (from 49% at Calilegua to 93% at Huaca Huasi) but with no consistent trend between low- and high-alpine pairs. Relation of character trends to environmental factors Environment-morphology studies usually presume that there are causal relationships to be



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Fig. 9 Schematic phyllograms of average leaf parameters for floras of specified sites. • (with sawtoothed edge) = dentate to serrate margins. • = coriaceous; • = pubescent. All lengths, widths and areas are to scale with the average antilog for that site. The area covered by shading or the proportion of the margin represent the percentage ofthat flora with the given characteristic. There are no data for margin, L and W for Colombia. The proportions in that case are simply estimated but the area is correct. Note the Calilegua sites are reduced to half scale and there are no data for pubescence and consistence.

found. However, when multiple environmental factors are related, at least within a certain range, the question of which factor may be causally correlated to a morphological character may be difficult to answer (or impossible if the correlation is over the full study range, Box et al. 1978). In this paper, this is the case with temperature (only within the New Zealand group of mountains) and mean minimum relative humidity (over the whole range). It is possible to obtain insights into the relations between these variables by obtaining other sites in which altitude is the same but these variables change (e.g. Halloy 1983), building the data into a factorial design. As temperature does not correlate with altitude outside of New Zealand, we can confidently distinguish the temperature effect on leaf area from that of altitude. With variables such as mean minimum relative humidity, correlated with altitude throughout the range of this study, it may be impossible to determine causality. Even without certainty as regards causality, the relationships found are of use for the following reasons: • they have predictive value, providing other conditions are maintained (e.g. Box et al. 1978) • they act as "replacements" or "indicators" for some variable(s) which may be discovered by further research Table 4 shows the correlations and p values of regressions between environment and plant characters. Significant matches are included that show both obvious causal relations (e.g.


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altitude and pressure) and "nonsense" relations (e.g. latitude and altitude). The latter highlight the well known difficulty of deducing causality from a correlation alone. The close correlation between some environmental factors may also produce misleading conclusions. Altitude is correlated with the percentage of entire leaves (across all sites) or with leaf area (for New Zealand). Since altitude by itself means nothing biologically, this is probably only a stand-in for an environmental factor correlated in turn with altitude (which could be pressure, CO2 partial pressure, mean minimum relative humidity or temperature). In the same way the correlation between mean air temperature and LAV ratio may be only very indirectly related to temperature itself. The following discussion attempts to clarify the biological meaning of the correlations observed. Leaf area has often been recognised as being closely correlated with temperature and precipitation, to the point of being a eing a a Morphological spectra of New Zealand lowuseful paleoclimatic predictor a]pBjne (5 sites) ^ hig5h.alp4 (4 sites) floras defmed by (Bailey & Sinnot 1915; 1916;Dolpnth the mean logarithms of the characters recorded for all species. 1978; Wing & Greenwood 1993). D..D iow-alpine sites; •—• high-alpine sites, b. Proportional Such predictive attributes could help change in characters between low-alpine and high-alpine in the development of global climate New Zealand floras, expressed as mean (hap-lap)/lap (•) +1 change models (Kerr 1993). In the SD (o) Where hap = high -alpine and lap = low-alpine. absence of significant water stress, the leaf area information in this paper clearly confirms a correlation with temperature. Korner et al. (1983) found a decrease of leaf area with elevation for a sample of 41 species in New Guinea, but found no significance between species of the same genus. They also found a change of L/W ratio of—36% between 1,100 and 3,480 m. The within-genus variation there was —3 8% for Rhododendron but not significant for Ranunculus. Several of the character states found to be common in the alpine sites (e.g. coriaceous leaves, pubescence, folded leaves) have often been related to dry environments. Alternatively, they have been attributed to nutrient-poor soils (Loveless 1971 ; Schulze 1982). All three characters are prevalent for example in the nutrient-poor Fynbos of South Africa (Campbell & Werger 1988) with mean pH of 4.0 and total exchangeable bases of only 2.0 meq/100 g soil. It has been widely stated that leaf folding and pubescence increase with elevation due to cold- induced drought stress (e.g. Hedberg 1964; Hedberg & Hedberg 1979). However, Halloy (1985, 1989) described crypts as an adaptation related to the efficiency of gas exchange, with their frequency increasing at lower atmospheric pressures. The trend observed here, more related to elevation than to latitude, total exchangeable bases or temperature,



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seems to confirm this hypothesis. Halloy (1985) suggested mechanisms whereby hair cover, in combination with crypts, could have value for improving gas exchange (mainly water use efficiency) at high elevation. In addition, he proposed that an increase in hairs in wetter climates (at least in alpine zones) could be one strategy to protect against excessive wetting. Maintaining a dry leaf surface is essential for gas exchange and may also inhibit fungal attack. The data in this paper show a clear increase in leaf folding with elevation, and of pubescence with both elevation and precipitation (the latter being an indication of the duration of leaf wetting). The increase in pubescence with elevation and precipitation found in this study is consistent with a gas exchange function and wetness-evading mechanism. It has also been explained as a herbivore defence mechanism Fig. 11 Ideal normal character frequency distribution, a, b: means of 2 curves. An when productivity is reduced, or as a radiation environmental change tending to displace the mean filter. Leaf pubescence varies considerably as from a to b could produce character shifts in in its capacity to attenuate UV-B (Robberecht existing populations or produce some combination et al. 1980) and is thus not necessarily related of extinction, evolution, and immigration of species to radiation. The lack of a clear trend in the to restore the environmentally optimum shape of New Guinea mountains (Körner et al., 1983) the curve (arrows). may be an artifact of small sample size (18 species below tree line to 23 above) such as in the data from the Remarkables pair presented here, or may be related to the decreasing radiation in the New Guinea transect. In this study, decrease in sclerophylly shows no relation to an increase in soil fertility (as shown by Campbell and Werger (1988) for the Fynbos) but does coincide with increasing precipitation. It is also contrary to expectations of cold-induced drought stress in high mountains (e.g. Hedberg & Hedberg 1979) or cold induced peinomorphosis (Loveless 1971; Walter 1977) or plain increase with elevation for whatever reason (Körner et al. 1983). Sclerophylly is often believed to be coupled with folded leaves and pubescence as either a water-stress or low-nutrient syndrome. The present data show that these characters can become uncoupled in certain situations. Contrary to the reduction of coriaceousness observed here, Körner et al. (1983) observed remarkable increases in thickness of cuticle and epidermal cell walls (from 19 to 580% in ranges of elevation between 1100 to 3480 or 2700 to 4420 m) in the mountains of New Guinea. It is doubtful whether these data are comparable. Körner et al. (1983) worked with anatomical characters on a transect characterised by diminishing light intensity due to cloud cover. In this paper coriaceousness was evaluated as a qualitative character of "hardness to touch". Despite apparent subjectivity, the values obtained are consistent in as much as various authors obtain similar values for the same floras. The altitudinal gradients studied here were also more typical in that light intensity increased with altitude. Cuticle and epidermal thickness, on the other hand, may or may not relate consistently to "hardness". In fact Körner et al. (1983) explain that the mountain cuticles have a very different structure (reticulate or dendritic) from that of typical xerophytes (lamellate). The New Guinea trend is based on within-genus comparisons, and this has repeatedly proven to diverge from the whole-community trend (as was the case with leaf area in New Guinea). In


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a comparison of three species at 3000 and 4250 or 4600 m, Gonzalez (1986) found that the total thickness of epidermis (upper and lower) in relation to the leaf thickness decreased in two of the species with a small increase in one. The average reduction was -7.8% and included a reduction of cell wall thickness. Cuticle thickness may relate to a series of factors other than water stress, including herbivore and fungal protection, radiation, mechanical damage and non-adaptive factors (Korner et al. 1983). One could expect hardness to decrease overall in relation to a higher proportion of plants needing less mechanical support by having leaves closer to the ground. Such leaves are in a micro environment with reduced winds. The Mt Burns low- alpine flora has 58.6% of species with coriaceous leaves, but only 48% of species with apices near the surface (0-4 cm) have coriaceous leaves, whereas species above 4 cm have 81.6%. Plants with underground apices often have large erect leaves requiring strong mechanical support, and the percentage for these is 56.9%. Thus the reduction of coriaceous species in the flora with elevation seems a logical result of the reduction in plant height. Community coriaceousness may thus decrease with elevation, even while within given life forms, coriaceousness may increase. Korner (1989) observed that greater leaf rigidity may be associated with a clear trend for increased leaf weight per area, carbon content and percent nitrogen thought to be related to a reduction of sink size for carbon investment (Korner & Larcher 1988). Although the percentage of species with entire leaves has been positively correlated with mean annual temperature in forest vegetation (e.g. Bailey & Sinnott 1915; Wolfe 1971; Kerr 1993) the general trend found here is either in the opposite direction or is too variable to be meaningful. This was also found to be the case by Dolph (1978). Nevertheless, the Calilegua subtropical montane forest value of 49% agrees closely with Wolfe's data for that type of vegetation. Clearly there is a case for correlation within given ranges and depending on the behaviour of other parameters. Bailey and Sinnott (1915) found that in cold temperate zones, entire margins predominated in arid and other physiologically dry (sic) habitats including, according to them, alpine regions. Their value for entire leaves from the New Zealand mountains is 77%, well within the range of values in this paper and an independent confirmation of the robustness of this kind of information. New Zealand - tropical similarities Biogeographers have long been aware of the similarities between types of New Zealand broadleaved forest structure and plant morphology, and both tropical montane forests (e.g. Troll 1960; Dawson & Sneddon 1969; Dawson 1988) and cloud forests (Henning 1978). Similarities between tropical paramos, the New Zealand alpine grasslands, and the subantarctic vegetation have also been reported (Troll 1960; Bliss 1971 ; Troll & Lauer 1978). This study provides measurable morphological evidence of such similarities. Wet alpine sites in New Zealand (Blue Mountains, and Mt Burns, both low-alpine and high-alpine) were more similar to equatorial paramo than to either New Zealand drier sites at similar altitudes or Tierra del Fuego, both in terms of leaf area frequency distribution and environmental measurements (summer values), despite large differences in latitude. In contrast, higher latitude alpine sites (Tierra del Fuego and Obergurgl out groups) differed from New Zealand alpine sites and paramo sites as a whole by having less crowded leaves and less coriaceous leaves. The crowded leaves of New Zealand and tropical alpine sites corresponds to the common observation of a high frequency of cushions and tussocks in these environments (Heilborn 1925; Wade & McVean 1969; Bliss 1971; Halloy 1990b). Mt Burns also had the mean leaf area closest to the paramos and super-paramos both in low-alpine and high-alpine. The Colombian paramo leaf-area frequency distribution was significantly different from all other sites measured. But the super-paramo showed no significant difference to either Mt Burns high-alpine or Remarkables low-alpine. In terms of mean leaf area the paramo showed similarity to Waituna, Mt Burns subalpine, Mt Burns low-alpine and Old Man low-alpine, while the super-paramo showed similarity to Blue Mts, Mt Burns, Old Man and Tierra del Fuego low-alpine and Mt Burns and Tierra del Fuego high-alpine. Further site comparisons


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would be needed to reach definitive conclusions, but the available data confirm previous reports that, from an eco-morphological perspective, New Zealand alpine sites are akin to tropical and subtropical alpine sites, whereas Tierra del Fuego, at latitudes closer to those of New Zealand, is more similar to sites in the European Alps. This apparent anomaly may relate to New Zealand's oceanic climate, with low temperature amplitudes and relatively high moisture availability (i.e. humidity/precipitation) throughout the year. Tropical mountains in South America (as well as in Africa and Hawaii) have oceanic climates with similar characteristics. Tierra del Fuego, despite its oceanic position, has larger amplitudes, with long winter snow cover and short summers, more akin to continental climates. The equable oceanic climates could favour year-round activity, leading to leaf and whole plant longevity and to characters such as sclerophylly and larger plant biomass (cushions, tussocks, giant rosettes). The short summer continental climates may favour shorter leaf and life cycles, with corresponding consequences for the whole syndrome of adaptations. CONCLUSIONS Previous work in environment-vegetation research has suggested strong correlations between variables of both. In particular, leaf area and other leaf characters such as margin, are claimed to be predictable to a certain degree of accuracy given such factors as temperature and/or precipitation (Wolfe 1971, 1978, 1979; Wing & Greenwood 1993). Conversely, vegetation characters should allow us to predict at least some aspects of the environment (e.g. Richter 1992). Our information indicates that leaf morphology characteristics at the community level may, in combination, predict the key environmental factors for alpine vegetation and vice versa. The evidence in this paper tends to confirm the relation between leaf area and temperature and between leaf area and precipitation. The leaf area/temperature relationship did not vary significantly between New Zealand sites. Leaf margin was correlated with both temperature and altitude: however the correlation was opposite in the global compared with the New Zealand sets of sites. This suggests a limiting level of correlation or a curvilinear relation. Additional relations have appeared which may be worth examining in future studies. Mean minimum relative humidity was positively correlated with leaf area. Altitude, independently of temperature, was inversely correlated with leaf area in the New Zealand set, but did not show significant correlation in the global set. Altitude may act as a replacement for pressure, radiation or mean minimum relative humidity. Significance of frequency distributions We found that both the mean and the frequency distribution (including multimodal distributions) of various parameters of leaf size and shape were characteristic of each locality, and localities with similar environments had similar values for these parameters (i.e. were not significantly different, hypothesis 1). The non-falsification of difference between communities in similar environments supports the convergence between their vegetations in at least some important morphological characters (see Wilson et al. 1994 for a different approach). With strictly random sampling, 20 species were enough to represent the mean leaf area (hypothesis 2). In our example, this was 12% of the local flora. With sampling weighed by abundance, significant differences appeared 10% of the time with 20 species measured. This discrepancy is due to the ten most common species differing more in mean leaf area, length and width than did ten randomly selected rare species (hypothesis 5b). Wolfe (1978) argued on empirical evidence that a sample of 30 or more species provided reliable data for leaf margin estimates of whole floras. Other parameters (NL for example) show a sensitivity to sample size which is different from that of leaf area and margins (i.e. a different number of species may be required). Sampling weighed by abundance (e.g. as in Campbell & Werger 1988) has the practical advantage of being less labour intensive but, as shown here, will tend to bias the estimates.


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Full floras have the significant advantage of eliminating the bias caused by skewed frequency of species morphological characters (Fig. 8) and by recent perturbation. In most cases, degradation may alter the abundance of major species, but not result in immediate extinction. The data were thought to be robust, given the consistency of different combinations of lowalpine or high- alpine sites and their fit with published data. The use of data from the literature (such as for Colombia and Tierra del Fuego here) may be questioned but it has generally produced results consistent with directly measured data. Logarithmic transformation of character values was found to be an appropriate mechanism to analyse character state distribution and trends in means. The frequency distribution of character classes produced similarities to normal curves (leaf area, hypotheses 3 and 4), or more surprisingly, multimodal curves (Fig. 3, 5, 7). In both cases, close parallelism between curves for different sites but with similar environments strongly suggests selective pressures acting to shape these curves. The normal distribution of life form characters is not mathematically unexpected. It implies that, in effect, the community of plants is acting as a mathematical population, i.e. it is distributed randomly around a mean that is characteristic of that "population" (Fig. 11). In a real ecological population (i.e. one species), the normal distribution is a result of random effects around a genetically determined mean. The genetic mechanism is in turn the result of environmental selection and developmental-phylogenetic constraints. This mechanism may itself maintain variability. One would not expect this effect in an assemblage of randomly collected populations from different species and various biogeographic origins. In contrast to simple normal distributions, however, lognormal distributions usually require an interdependence between values (Koch 1966). The frequency curves could thus express a functionally constrained emergent property of the assemblage of species (e.g. emergent in the sense of a system property not present in the individual species, Kauffman 1993; hypothesis 6). As the genetic and historical background of each species varies, this constraint can be assumed to represent environmental selection combined with competitive and adaptive shifts (e.g. Hutchinson 1959; Futuyma 1986). Several peaks in the multi-modal distribution suggest a "polymorphic" population, with several selective optima rather than one. The adaptive space suggested by the data in this paper is not a continuum but rather an uneven area with species clustering towards one or several peaks or centres of attraction. This is reminiscent of a mathematical landscape with several stable hollows for niches (e.g. Maynard-Smith 1974: 8). The case of peak repetition in very different environments, as in LAV, suggests some basic, uneven architectural constraints of a more universal nature or some form of emergent pattern. From a theoretical viewpoint, a morphological frequency distribution is a reflection of functional characteristics. As such it identifies functional groups or guilds. Species at the centre of the curve would have a high level of redundancy (e.g. Chapin et al. 1992) whereas species at the outer fringes could not be easily replaced. Implications The broad coverage of this study (and hence the large sources of variation) does not allow a lot of depth and precision. However, it allows the exploration of a wider range of factors and morphological characters, thus suggesting promising directions for future research. A certain degree of confirmation is supplied by the consistency of parallel lines of evidence in three different experimental designs, and by a comparison with the literature. Future research directions could include working on the following testable hypotheses: 1. Similar shaped curves involving different sites imply that, to maintain that pattern, a newly introduced species should result in another one possessing the same character state being displaced. The present information implies that we can predict the probable morphological character class of an outgoing species, or predict that character displacement will shift the pressure onto another species in another character class. 2. Sustaining biological diversity may be helped by trying to manage systems so as to obtain assemblages with character distributions close to natural. In impoverished agro-ecosystems,



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one would expect a natural tendency to revert to the typical curve for the given environment, hence the prediction of this paper is that a number of "weeds" will continuously invade until the natural curve (or environmentally optimum curve) is achieved. Raunkiaer (1934) maintained that biological spectra of exotic plants should be similar to those of native plants. Semi-natural and managed systems might also be expected to benefit from managing species diversity so as to obtain character frequency distributions in harmony with the environmental optimum, thus reducing the need for inputs in pest and weed control (e.g. Altieri 1991). 3. In environments changing in response to climate change or human impact, new frequency curves could be predicted (see Fig. 11) with consequences for the extinction or immigration of affected species. Floret et al. (1987) have presented results of human-induced changes in character frequency curves. In 2 and 3, modifying soil fertility would have a major effect in localised areas. For example, in the alps, small leaved (