Journal of Sustainable Forestry Paper Birch ...

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Journal of Sustainable Forestry

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Paper Birch Genecology and Physiology

David G. Simpsona; Wolfgang D. Binderb; Sylvia L'hirondelleb a The BC Ministry of Forests, Kalamalka Research Station, Vernon, BC, Canada b The BC Ministry of Forests, Glyn Road Research Station, Victoria, BC, Canada

To cite this Article Simpson, David G. , Binder, Wolfgang D. and L'hirondelle, Sylvia(1999) 'Paper Birch Genecology and

Physiology', Journal of Sustainable Forestry, 10: 1, 191 — 198 To link to this Article: DOI: 10.1300/J091v10n01_22 URL: http://dx.doi.org/10.1300/J091v10n01_22

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Paper Birch Genecology and Physiology: Spring Dormancy Release and Fall Cold Acclimation David G. Simpson Wolfgang D. Binder Sylvia L’Hirondelle

INTRODUCTION Forest managers in British Columbia increasingly manage some forests as mixed species stands that include paper birch (Betula papyrifera Marsh.), which regenerates naturally or can be planted. This genecology study, in association with ongoing tree improvement field studies, is aimed at developing seed transfer guidelines and identifying faster growing sources of paper birch for use in BC forests. Two of the objectives discussed here are to examine the effects of seed origin on (1) dormancy release (bud flushing), and (2) growth cessation and cold acclimation. David G. Simpson is affiliated with the BC Ministry of Forests, Kalamalka Research Station, Vernon, BC V1B 2C7, Canada. Wolfgang D. Binder and Sylvia L’Hirondelle are affiliated with the BC Ministry of Forests, Glyn Road Research Station, Victoria, BC V8W 9C4, Canada. [Haworth co-indexing entry note]: ‘‘Paper Birch Genecology and Physiology: Spring Dormancy Release and Fall Cold Acclimation.’’ Simpson, David G., Wolfgang D. Binder, and Sylvia L’Hirondelle. Co-published simultaneously in Journal of Sustainable Forestry (Food Products Press, an imprint of The Haworth Press, Inc.) Vol. 10, No. 1/2, 2000, pp. 191-198; and: Frontiers of Forest Biology: Proceedings of the 1998 Joint Meeting of the North American Forest Biology Workshop and the Western Forest Genetics Association (ed: Alan K. Mitchell et al.) Food Products Press, an imprint of The Haworth Press, Inc., 2000, pp. 191-198. Single or multiple copies of this article are available for a fee from The Haworth Document Delivery Service [1-800-342-9678, 9:00 a.m. - 5:00 p.m. (EST). E-mail address: getinfo@ haworthpressinc.com].

191

192

FRONTIERS OF FOREST BIOLOGY

METHODS


Dormancy Release (Bud Flushing) Seed collected from about 10 paper birch trees at each of 18 locations throughout the species’ natural range in BC was used to produce one-year-old seedlings that were overwinter stored at *2_C. Spring bud flushing was determined in six forcing environments in a factorial of photoperiod (8 and 16 h) and temperature (7, 15, 25_C). The growing degree hours > 0_C for 50% bud flushing were estimated for each seed source and averaged for all forcing environments. Growth Cessation and Fall Cold Acclimation Seedlings of the 18 seed sources were located out-of-doors where they were exposed to natural photoperiod and temperature conditions at Prince George (54_N), Vernon (50.3_N) and Victoria (48.6_N). From late September through the end of October, chlorophyll fluorescence was measured weekly on the sixth leaf from the apex using either the PK Morgan CF-1000 (Vernon) or the Opti-Sciences OS-500 (Victoria) fluorometer (Binder et al., 1997; Mohammed et al., 1995). The fluorometers both measure dark-adapted Fv/Fm, but had different maximum values (Binder et al., 1997). Stem samples were freeze tested by freezing to a specific temperature at a cooling rate of 4 to 6_C h*1. Damage from freezing was assessed with electrolyte leakage (L’Hirondelle et al., 1992; Simpson 1994). RESULTS Dormancy Release (Bud Flushing) There was no effect of forcing environment photoperiod or temperature on the degree days above 0_C for bud flushing. The average heat sum required for 50% bud flush ranged from 487 to 1963 degree hours. The physiographic variables, seed source latitude and elevation, explained more than 63% of the variability among the seed sources (Figure 1). The seed sources from 49-51_N flushed in less than 1000 degree hours whereas the more northerly seed sources required more

Part Two: Frontiers of Plant Physiology

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FIGURE 1. Heat sum for 50% bud flushing versus seed source elevation and latitude.


2200 2000 1800 1600 1400 1200 1000 800 600 400

1000

800

600

400

200

49 0

50

52 51

56 55 54 53

48

than 1000 degree hours. One low elevation (70 m) northern (54.5_N 128.57_W) collection was an exception to this trend, perhaps reflecting a maritime influence. An environmental variable, seed origin degree days above 0_C (from January to the end of March), was estimated from long-term weather station data nearest to the origin of each seed source. This single variable explained more than 52% of the bud flushing variation among the seed sources (Figure 2). Bud flushing evaluated at several field sites (not shown) in most cases reflected the results from controlled environment tests. Growth Cessation and Fall Cold Acclimation At Vernon from late September until mid-October (Julian day 270-285), the chlorophyll fluorescence variable Fv/Fm was between 0.60 and 0.75 indicating unimpaired photosynthetic potential (Figure 3a). Although differences existed among seed sources, these do not appear to be related to seed source latitude, longitude or elevation.


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FIGURE 2. Heat sum for 50% bud flushing versus growing degree days between January 1 and March 31 at seed source origin (r2 = 0.52, n = 18). 2,000

Degree Hours (>0_C) for 50% Bud Flush


1,800 1,600 1,400 1,200 1,000 800 600 400 200 0

0

20

40 60 80 100 120 Weather Stn. Degree Days (Jan 1ĆMarch 31)

140

After Julian day 292, Fv/Fm of seedlings decreased indicating onset of foliage senescence, and variation among seed sources increased. Fv/Fm declined first in central seed sources followed by southeast then northwest. The difference between central and southeast sources was not significant. At Victoria, quantum yield (QY of dark-adapted foliage = Fv/Fm) remained optimum (near 0.80) from the first measurement date, Julian day 255, until about day 285 (Figure 3b). The QY values of all seed sources began to decline between Julian days 286 and 300 and decreased quickly after the latter date. The QY decline after Julian day 280 was first for central sources followed by northwest then southeast. Frost hardiness of stems from seedlings at Victoria and Prince George increased through the fall sampling period. For both locations, seed sources from higher latitudes and elevations had less damage after freezing and thus were more hardy. At Victoria, normalized seed source latitude plus elevation accounted for 79% of the variation in frost hardiness after freezing to *15_C at the end of October (Figure 4). Furthermore, electrolyte leakage (normalized relative conductivity) results from Victoria correlated strongly with freezing damage averaged for five field sites (Figure 5). This suggests that cold hardiness


195

FIGURE 3. Mean Fv/Fm (Vernon) or quantum yield (Victoria) for paper birch seed sources. Critical threshold for Fv/Fm 0.5 and 60% for quantum yield are indicated. 1

Vernon

Fv/Fmax

0.6 0.4 0.2 0

100

SouthEast Central NorthWest

270

280

290

Julian Date (1996)

300

310

Victoria

80 Quantum Yield (%)


0.8

60 40 20 SouthEast Central NorthWest

0 250

260

270

280

290

Julian Date (1996)

300

310

rankings based on laboratory measurements of seedlings from a common garden plot reflect actual field results. Growing Season Length Bud flushing and foliage senescence data can be used to estimate growing season length as follows. To a nominal average growing season length (L) of 100 frost-free days, a bud flushing value (b) and a leaf senescence value (s) are added (or subtracted). L (days) = 100 + b + s


196

Relative Conductivity After *15_C


FIGURE 4. Frost hardiness (October 28, 1996) of birch stem sections from Victoria versus seed source latitude and elevation (r2 = 0.79, n = 16).

70 60 50 40 30 14

SouthEast Central NorthWest

16

18 20 22 Seed Source Latitude/1.1 + Elevation

24

26

where: b = (1121.67 * d)/h s = (e * 295.56) d = seed source degree hours > 0_C for 50% bud flush e = day of year when Fv/Fm falls below 0.5 using the Morgan CF1000 fluorometer or a QY of 60% using the Opti Sciences OS 500 h = 100 degree hours > 0_C (nominal degree hours accumulated on an early spring day) 1121.67 = average d for all 18 seed sources 295.56 = average e for all 18 seed sources Estimated growing season length for the 18 seed sources ranged from 89 (a central source) to 109 (a northwest source). This range of growing season lengths resulted from various combinations of days being added or subtracted at both ends of the growing season (Figure 6). When the estimated growing season lengths are compared with the seed source origin frost-free days, estimated from weather station data, a significant (r = 0.71) correlation was found. DISCUSSION AND CONCLUSIONS For the 18 seed sources tested, the heat sum above 0_C required for 50% bud flush ranged from 487 to 1963 growing degree hours. As a


197

FIGURE 5. Linear relationship between normalized percent damage (fall 1997) at all field plantings and normalized electrolyte leakage after *15_C at Victoria on October 28, 1996 (r = 0.71, n = 16).

Normalized % Damage (all plantations)


2

1

0

(1)

(2)

(2)

(1)

0

1

2

3

Normalized RC After *15_C at Victoria

general rule, seed sources from 49-51_N latitude flushed in less than 1000 degree hours while more northerly sources took longer. We found that the seed source physiographic parameters latitude and elevation explained 63% of the bud flushing variation among the seed sources. In the two geographically different (Vernon and Victoria, BC) common garden leaf senescence began about mid-October. Seed sources from the center of the province began leaf senescence before either southeast or northwest sources. We did not determine if the primary trigger for this event is day length or temperature (or a combination of both). Leaf senescence can easily be measured in the field with a fluorometer as loss of photosynthetic capacity. Freezing tolerance was highest in the central (Prince George area) seed sources. Normalized seed source latitude plus elevation accounted for 79% of the variation among sources after freezing to *15_C at the


198

Seed Source


FIGURE 6. Days added (subtracted) for early bud flush and later leaf senescence. 101 103 105 107 109 111 113 115 117 119 121 123 125 127 129 131 133 135 (15)

(10)

(5) 0 5 Days Greater or Less Than A bud flushing

10

15

loss of Fvar

end of October. The timing and intensity of freezing will affect this value. Laboratory freeze injury tests from common garden plot samples correlated (r = 0.71) with actual freeze injury data collected from the field plantation sites. From the phenological data collected, we estimated the growing season length of the 18 seed sources tested ranges from 89 to 109 days. This information, along with frost hardiness results, will be useful in developing seed transfer guidelines. REFERENCES Binder, W.D. and Fielder, P. 1996. Chlorophyll fluorescence as an indicator of frost hardiness in white spruce from different latitudes. New Forests 11: 233-253. Binder, W.D., Fielder, P., Mohammed, G.H. and L’Hirondelle, S.J. 1997. Applications of chlorophyll fluorescence for stock quality assessments with different types of fluorometers. New Forests 13: 63-89. L’Hirondelle, S.J., Jacobson, J.S. and Lassoie, J.P. 1992. Acid mist and nitrogen fertilization effects on growth, nitrate reductase activity, gas exchange, and frost hardiness of red spruce seedlings. New Phytologist 121: 611-622. Mohammed, G.H., Binder, W.D. and Gilles, S. 1995. Chlorophyll fluorescence: A review of its practical forestry applications and instrumentation. Scand. J. For. Res. 10: 383-410. Simpson, D.G. 1994. Seasonal and geographic origin effects on cold hardiness of white spruce buds, foliage and stems. Can. J. For. Res. 24: 1066-1070.