Vegetation and soil recovery in wilderness campsites ... - Springer Link

Vegetation and Soil Recovery in Wilderness Campsites Closed to Visitor Use THOMAS J. STOHLGREN DAVID J. PARSONS National Park Service Sequoia and Kings Canyon National Parks Three Rivers, California 93271, USA ABSTRACT / Recreational use of wilderness results in impacts to vegetation and soil in trails and campsites. Traditionally, campsite impact studies have compared campsites receiving various levels of use with unused control areas. Field studies in Sequoia National Park, California, indicate that the degree of impact to vegetation and soils also varies

Recreational use of backcountry or wilderness areas results in disturbance of vegetation and soils associated with trails and campsites (Bratton and others 1978, Cole 1982 and 1983). For campsites, the degree of impact is a function of such variables as vegetation type, soil characteristics, and microclimate, as well as the type and history of visitor use (for example, number and behavior of visitors, seasonality, duration of visits). Likewise, the degree of impact within a given campsite may vary for similar reasons. Concentrated trampling in the center of many campsites has resulted in the creation of a core area devoid of vegetation and with highly compacted soil (Holmes and Dobson 1976). An intermediate area of trampled vegetation and less compacted soil commonly surrounds the barren core. Beyond this is an untrampled or lightly trampled periphery of unimpacted soil and vegetation (Easterbrook 1968, Holmes and Dobson 1976). The degree and extent of such impacts have been the basis for a number of systems for classifying or inventorying campsite impacts (Frissel and Duncan 1965, Parsons and MacLeod 1980, Cole 1983). Much of the campsite development in the southern Sierra Nevada of California is concentrated in the high-elevation subalpine zone. Such areas are characterized by cool temperatures and a relatively short dry summer growing season. Precipitation is predominately in the form of winter snow. Vegetation typically consists of an overstory of widely spaced conifers and a sparse shrub and herb understory (Rundel and others 1977). Little is known about the natural resiliency of these high-elevation ecosystems following disturbance. In other areas, studies have consistently documented such impacts to campsites as the loss of vegetaKEY WORDS: Vegetation recovery; Soil recovery; Wilderness campsites; Sequoia National Park; Recreational impacts

EnvironmentalManagementVol. 10, No. 3, pp. 375-380

within campsites. The central areas of campsites, where trampling is concentrated, show lower plant species diversity, differences in relative species cover, more highly compacted soils, and lower soil nutrient concentrations than do peripheral, moderately trampled, and untrampled areas within the same campsite. Three years afte( closure to visitor use, the central areas show less increase in mean foliar plant cover, and soils remain more highly compacted than in previously moderately trampled areas of the same sites. Changes in relative species cover over time are used to assess both resiliency to trampling and species composition recovery within campsites closed to visitor use.

tive cover and decreased plant species diversity (LaPage 1967, Hartley 1976, Cole 1977 and 1982, Fichtler 1980) as well as increased soil compaction (Dotzenko and others 1967, Easterbrook 1968, Settergren and Cole 1970, Young and Gilmore 1976, Dawson and others 1978, Monti and Mackintosh 1979, Cole 1982). Soil chemistry in campsites can be highly variable. In Illinois, Young and Gilmore (1976) found increases in soil Ca, K, P, N, and pH in campsites relative to control areas, but no change in Mg. Other studies have shown variable responses of N as well as major cations (Rutherford and Scott 1979, Cole 1982). Several investigators have reported decreased levels of soil organic matter in campsites (Dotzenko and others 1967, Settergren and Cole 1970, Dawson and others 1978), while others have reported increased levels (Young and Gilmore 1976, Monti and Mackintosh 1979, Cole 1982). In many of these studies, data were lumped from transects or quadrats spread over the entire campsite, ignoring within-site variation of vegetation and soils (Dykema 1971, Cole 1977 and 1982, Sim6n 1978, Stohlgren 1982). Problems with data comparison can also occur when control sites are not truly similar to original conditions (Cole 1982). The objectives of this study were to determine the variation of vegetation and soil properties within three heavily used subalpine campsites, and to document the relative recovery rates of core, intermediate, and periphery areas during the first three years after cessation of visitor use.

Study Area and Methods

Emerald Lake and Pear Lake are located at elevations of 2804 m (9197 ft) and 2899 m (9510 ft), respectively, in adjacent granitic subalpine basins in Sequoia 9 1986 Springer-VerlagNew York lnc.

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T.J. Stohlgren and D. J, Parsons

National Park, in the southern Sierra Nevada of California. Only 8 km and 10 km (5 and 6 miles) from the popular Lakes Trail trailhead, the two areas have received heavy recreational use for decades. The vegetation surrounding the lakes is characterized by lodgepole pine (Pinus contorta spp. murrayana), willow (Salix sp.), and a sparse understory of graminoids and herbs. The long-term average precipitation at Giant Forest, located 8 km away at an elevation of 1952 m (6404 ft), is 1128 mm (44.4 in.) per year. This falls primarily as winter snow. Two campsites at Emerald Lake and one at Pear Lake were closed to visitor use in October 1978. These were roped off, signed, and protected by a park ranger stationed in the area. Within each campsite, a 10 x 10-m study area was selected along compass directions. This area was divided into a grid of 1-m2 sections. The outer boundaries of the grid were permanently marked with metal stakes. Together with detailed base maps of each study area (Figure 1), this marking allowed the exact reconstruction of the grids each year prior to sampling. Within the study area, each 1-m 2 section was further subdivided into 0.25-m 2 plots. These plots were subjectively stratified as core, intermediate, or periphery on the basis of visual criteria. Core plots were generally in the center of the site and showed nearly complete elimination of above-ground vegetation, removal or pulverization of litter and duff layers, and continuous disturbance of surface soil. Periphery plots appeared as unimpacted or apparently unimpacted areas that bordered the campsites. Intermediate plots were located along the impact gradient between core and periphery plots. These plots showed notable, but less substantial impact compared to core areas. They generally showed more vegetation cover, less litter and duff pulverization, and contained pockets of intact surface sod. All 0.25-m 2 plots were numbered and pooled by impact stratum and by campsite. Plots incorporating more than one impact stratum were excluded from future sampling. A subsample of five to ten 0.25-m 2 plots were randomly selected to characterize vegetation in each impact stratum at each site. Foliar cover by plant species was visually estimated to the nearest 5% (to the nearest 1% where cover was less than 5%). Soil bulk density was determined for the top 5 cm of soil from additional sets of five to ten 0.25-m z plots randomly drawn each year from each stratum at each site. Bulk density sampling involved pounding a 5.08-cm-diameter pipe into the soil approximately 5 cm. Each soil sample was placed in an airtight container and dry weight was determined at the lab. The volume of the hole was de-

R

L--

C*

C I

INTERMEDIATE

p

I.p |

~ i! R

A

N

NON HOMOGENEOUS AREA

Figure 1. Example of a detailed base map of one of the campsites closed to visitor use.

termined by pouring water into a thin plastic liner placed in the hole, and then measuring the volume of the water in a graduated cylinder. All other bulk density methods were as outlined by Blake (1965). These vegetation and soil plots were mapped and sampled immediately following closure in 1978 and then again in late September or early October (to standardize climatic and phenological conditions) each year through 1981. These data were used to quantify both withinsite variation and recovery over time. A total of 45 bulk density samples (five in each stratum at each of the three campsites) collected in 1978 were used for analysis of soil particle size and texture as outlined by Bouyoucos (1926). Ten approximately 20-g scoops (0-5 cm depth) of soil were collected from each stratum at each campsite and pooled by strata in the summer of 1979 for baseline chemical analysis. A Technicon Auto-Analyzer and an Atomic Absorption Spectrometer were used for analysis of N, P, K, Ca, and Mg (Schuman and others 1973, PerkinElmer Company 1976, Isaac and Johnson 1976). Percentage of loss on ignition (percentage of organic matter) and pH were also analyzed. Percentage of soil moisture of a typical midsummer day was sampled between 12:00 and 14:00 on 20 August 1979. A total of 18 (two in each stratum at each campsite) airtight, cylindrical soil cans were filled from holes 5 cm deep by 5 cm diameter, and were analyzed according to Peters (1965). These data provide both a spatial comparison between strata and a baseline measurement against which future changes might be compared. Analysis of variance and Newman-Keuls multiple range tests were used to evaluate significant differences between campsites and strata for foliar cover, mean number of species per plot, soil bulk density,

377

Vegetation and Soil Recovery in Closed Campsites

Table 1.

Preclosure variation of selected vegetation and soil characteristics between campsite impact strata,

Macronutrients,pH, and percentlosson ignitionwerepooledsamples. Core

Impact strata Intermediate

Periphery

1.19 _ 0.39 a,b (32)

15.39 + 1.98a (24)

25.26 + 3.39 b (19)

4 - 0.14a.b (32)

2.38 4- 0.22 a (24)

3.47 --+ 0.40 b (19)

1.33 _ 0.02~,b (16)

0.68 4- 0.082 (16)

0.47 -+ 0.05 b (17)

85.2 + 1.5 12.3 + 1.4 2.5 4- 0.3

83.6 + 0.9 13.8 + 0.8 2.7 _+ 0.3

84.8 _ 1.7 11.9 + 1.6 3.2 4- 0.3

Characteristic Vegetation Foliar cover (%) x + 1 SE (n) No. of species per plot x -4- 1 SE (n) Soil Bulk density (g/cc) x _+ 1 SE (n) Texture (x 4- SE, n = 15) Sand % Silt % Clay % Macronutrients N (ppm) P (ppm) K (ppm) Mg (ppm) Ca (ppm)

0.56

28.6 47.9 50.3 7.2 108.8

40.4 28.1 65.2 11.4 181.0

74.8 56.4 107.2 37.6 967.3

pH

3.70

3.55

3.52

% Loss on ignition

6.36

15.43

29.62

28.2 _+ 2.1

33.8 + 1.9

% Moisture (x + 1 SE, n = 6)

13.8 _+ 4.7 c

a.bSignificantlydifferent at p < 0.001. c Significantlydifferent at p < 0.05. and soil moisture. No tests for significance were possible for pooled soil chemical samples.

Results and Discussion Preclosure Vegetation and Soil Conditions Barren core plots showed significantly lower foliar cover and fewer plant species, significantly higher soil compaction, lower soil N, K, Mg, and Ca concentrations, and lower soil organic matter than did intermediate and periphery plots o f the same campsites (Table 1). Soil moisture, t h o u g h measured for only one point in time, was also significantly lower in the core stratum. N o difference in soil texture between strata was evident, and p H was only slightly higher in the core than in the intermediate and periphery strata. T h e intermediate impact stratum, assumed to have received moderate levels o f trampling over many years, showed moderately high foliar cover and

n u m b e r o f plant species while not having significantly higher soil compaction than periphery areas o f the same campsites. T h e y were most like the heavily trampled core stratum in concentration o f soil macronutrients, percentage o f organic matter, and soil moisture content. We speculate that while moderately trampled areas retain tufts o f vegetation and surface sod necessary to significantly buffer soil compaction, increased leaching o f macronutrients and loss o f soil organic matter may still occur. Once the tufts o f vegetation are r e m o v e d and barren core areas are created, soil compaction significantly increases while soil macronutrient concentrations, percentage o f organic matter, and moisture decrease even further. T h e variability in vegetation and soil characteristics f o u n d within campsites emphasizes the shortcomings in utilizing l u m p e d data for campsite impact studies. Had we combined the core and intermediate data for the various vegetation and soil characteristics shown in Table 1, many o f the significant impacts to the core

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T.J. Stohlgren and D. J. Parsons

Table 2. Mean foliar cover, mean number of species, and mean soil bulk density per plot by stratum.

Table 3. Percentage of relative foliar cover of selected dominant species by strata and by year.

ANOVA was analyzed separately for each year. All f-test ratios were significant (p < 0.005). Within each year, means with different letter superscripts are significantly different at p < 0.05.

Year

Characteristic/ stratum Mean foliar cover (%) Core (n = 32) Intermediate (n = 24) Periphery (n = 19) f-test ratio Mean number of species per 0.25-m 2 plot Core (n = 32) Intermediate (n = 24) Periphery (n = 19) f-test ratio Mean bulk density (g" cc- l) Core (n = 16) Intermediate (n = 16) Periphery (n = 17) f-test ratio

Year 1978

1979

1980

1981

1.2a 15.4 b 25.3 c

1.7a 15.6 b 26.0 c

3.1 a 24.8 b 28.7 b

2.9 a 23.4 b 27.2 b

42.9

44.1

41.0

41.1

Core

Intermediate

Periphery

77.1 8.3 0 14.6

75.9 2.6 12.6 8.9

58.6 0.6 18.5 22.3

67.9 20.4 1.0 11.7

71.4 3.6 6.7 18.3

57.5 3.1 18.8 20.6

50.6 29.1 1.3 19.0

64.3 5.3 13.2 17.2

56.4 3.3 18.0 22.3

52.5 29.5 1.3 16.7

65.7 4.6 13.5 16.2

56.9 4.1 18.4 20.6

1978

Juncus parryi Agrostis lepida Carex rossii All others 1979

Juncus Parryi Agrostis lepida Carex rossii All others 1980

0.6 a 2.4 b 3.5 c 38.6

1.33a 0.68 b 0.47 c 73.6

1.2a 2.6 b 3.2 b 18.6

1.31 a 0.68 b 0.49 b 88.8

2.2 a 3.8 b 3.9b 10.3

2.0 ~ 3.9 b 3.8 b 14.7

1.30 ~ 0.64 b 0.49 c 113.7

1.26a 0.638 0.51 b 45.2

areas would have b e e n masked. Stratifying impact areas within campsites p r i o r to s a m p l i n g should help decrease sampling variability a n d provide a m o r e realistic evaluation o f recreational impacts.

Vegetation and Soil Recovery after Three Years of Closure Vegetation recovery following three years o f closure was slower in core strata than in the i n t e r m e d i a t e strata (Table 2). Core strata were significantly lower in m e a n foliar cover than i n t e r m e d i a t e a n d p e r i p h e r y strata for each y e a r following closure. I n t e r m e d i a t e strata were significantly d i f f e r e n t f r o m p e r i p h e r y strata for only the first year following closure. T h e percentage o f recovery o f foliar cover after campsite closure was greatest in the i n t e r m e d i a t e stratum. This may have been d u e to vegetation growth o f previously established individuals (Easterbrook 1968) as well as some seeding in o f new individuals. T h e m e a n n u m b e r o f species p e r plot (Table 2) in the core s t r a t u m was significantly less than for intermediate a n d p e r i p h e r y strata in all years. A f t e r one recovery year, i n t e r m e d i a t e strata were not significantly d i f f e r e n t f r o m p e r i p h e r y strata. Estabfishment o f both new individuals a n d species d u r i n g the threeyear recovery period, however, also o c c u r r e d in the

Juncus parryi Agrostis lepida Carex rossii All others 1981

Juncus parryi Agrostis lepida Carex rossii All others

core plots. T h e n u m b e r o f core plots totally b a r r e n o f vegetation d r o p p e d f r o m 20 o f 32 in 1978 to only f o u r o f 32 by 1981. Nevertheless, while several species a n d individuals b e c a m e established in the core plots, increases in m e a n foliar cover were slight. Climatic influences on vegetation were evident t h r o u g h o u t the study. T h e winter o f 1980 was particularly wet a n d was followed by a w a r m summer. This combination optimizes growing conditions. All the impact strata r e s p o n d e d with g r e a t e r increases in m e a n foliar cover a n d n u m b e r o f species than o c c u r r e d in the d r i e r years o f 1979 a n d 1981. T h e resistence o f g r a m i n o i d s to t r a m p l i n g d e m o n strated in o t h e r studies (LaPage 1967, P a l m e r 1972, Dale a n d W e a v e r 1974, Cole 1977 a n d 1978, Fichtler 1980) was evident h e r e (Table 3). Juncus parryi, the d o m i n a n t u n d e r s t o r y species, was h i g h e r in cover in the core a n d i n t e r m e d i a t e strata than in the p e r i p h e r y strata in 1978 (preclosure). Following t h r e e years o f recovery, Juncus parryi h a d decreased in relative cover in the core a n d i n t e r m e d i a t e strata while Agrostis lepida h a d increased greatly in the core strata. T h e changes d o c u m e n t e d in relative foliar cover provide a means for assessing species resiliency a n d vegetation composition recovery. Juncus parryi maintained its d o m i n a n c e u n d e r both core a n d p e r i p h e r y conditions indicating its resilience to trampling. Agrostis lepida showed its i m p o r t a n c e as an early successional species by increasing in heavily t r a m p l e d core areas following closure. W e speculate that in time its

Vegetation and Soil Recovery in Closed Campsites

379

relative cover may decrease as Carex ~vssii increases to levels proportional to those found in the periphery strata. T h e absence of Carex rossii in the 1978 core strata, and its slow establishment in core areas (relative to levels in the periphery strata), indicate that it is less resistant to trampling and is probably a later successional species. Core strata bulk density was significantly different each year from intermediate and periphery strata. There was little change in soil bulk density values in any of the strata following closure (Table 2). Some studies suggest harmful effects of soil compaction on forest understory plants when bulk densities exceed 1.3 g/cc (Bratton and others 1966, Minore and others 1969). Core strata bulk density values in this study were near this threshold. This, in combination with low soil macronutrient concentrations, may be limiting vegetation recovery in core areas. The stratification of use areas in campsite impact studies appears to be an important first step in assessing recovery. Reporting mean foliar cover or soil compaction changes of an entire campsite can severely mask possible long-term impacts to portions of that campsite. For example, in this study, mean foliar cover recovers much slower in core areas than in intermediate areas (Table 2). Ranz (1979) showed ground cover on closed campsites in the Selway-Bitterroot Wilderness increased significantly after five years. Pooled data of mean foliar cover from core and intermediate plots in our study could have been analyzed to show increase, but it would have failed to show severely retarded recovery of major portions of the campsites.

growth), soil compaction release (due to freezing and thawing action), nutrient recycling (through litter fall and soil organisms), and microclimate may hasten recovery rates in future years. We hypothesize that if these closed campsites were to be reopened for visitor use, one season of trampling would revert the vegetation and soil characteristics to levels found in 1978. In Sequoia and Kings Canyon National Parks, decades of wilderness use have resulted in numerous campsites with barren core areas. Since these barren core areas can be expected to be maintained by intermittent use, we advise wilderness travelers to use existing campsites rather than create new barren core areas in pristine areas. In this way, the total area of severely impacted vegetation and soils can be kept from increasing. Because of the slow recovery periods for vegetation and soils in campsites like those studied at Emerald and Pear Lakes, a "rest/rotation" campsite management option is impractical for this vegetation type. Frissell and Stankey (1972) suggest that the role of management in a national park or wilderness area is to define what "limits of acceptable change" will be allowed. Managers of such areas must ultimately decide what degree of campsite impact is acceptable as well as whether campsite impacts are to be concentrated or dispersed (Cole and Dalle-Molle 1982). Comparisons of relative recovery rates of heavily, moderately, or lightly trampled areas provide part of the necessary framework for a quantitative assessment of the longterm impacts associated with various use levels in different vegetation types.

Management Implications

Acknowledgments

T h e different recovery rates of the core and intermediate strata after three years suggest that a "resiliency threshold" exists between moderately and heavily trampled areas of vegetation. In this study, a resiliency threshold is defined as the point at which given vegetation and soil types withstand trampling while maintaining enough surface sod and tufts of vegetation so that "barren core" areas are not created. In this case, areas that received low to moderate levels of long-term trampling maintained enough vegetation and surface sod to recover quickly once the trampling stress was removed. O u r denuded core areas, having lost their ability to buffer trampling because of longterm concentrated use, have exceeded this resiliency threshold and will recover only very slowly. Projecting full recovery of the core strata of such campsites would be speculative at this time. Interaction between vegetation recovery (establishment and

T h e authors gratefully acknowledge S. H. DeBenedetti for assistance early in the study and David Cole and David Graber for helpful review of the manuscript. This research was supported by the US Department of the Interior, National Park Service, Sequoia and Kings Canyon National Parks.

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