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Survival, growth, and allometry of planted Larix occidentalis seedlings in relation to light availability
Forest Ecology and Management 106 Ž1998. 169–179
Survival, growth, and allometry of planted Larix occidentalis seedlings in relation to light availability Han Y.H. Chen ) , Karel Klinka Forest Sciences Department, UniÕersity of British Columbia, 270-2357 Main Mall, VancouÕer, BC, Canada V6T 1Z4 Received 26 June 1997; accepted 16 October 1997
Abstract We conducted a 3-year experiment to determine how survival, growth, allometry, and specific leaf area ŽSLA. of planted, very shade-intolerant, western larch Ž Larix occidentalis. seedlings respond to a wide range of light availability under natural environments. Three study sites were located within a summer-dry, cool-temperate climate near Okanagan Falls, British Columbia. Survival significantly decreased with decreasing light at the end of the third growing season on all study sites Ž P - 0.05.. Relative growth rate in base diameter Ž D . and biomass components increased with increasing light Ž P - 0.05., whereas height Ž H . growth was independent of light availability from 20 to 100% full sun Ž P ) 0.05.. With decreasing light, ratio of height to base diameter significantly increased whereas shoot to root ratio and SLA did not change. Instead, the shoot to root ratio was positively correlated with total biomass. These non-plastic responses in shoot to root ratio and SLA may contribute to the very shade intolerant nature of western larch. q 1998 Elsevier Science B.V. Keywords: Western larch; Field experiment; Morphology; Plasticity; Specific leaf area; Shoot to root ratio
1. Introduction Forest regeneration faces a great challenge as partial cutting systems have been introduced as alternatives to clearcutting in British Columbia ŽKlinka et al., 1990; Klinka et al., 1994; Wang et al., 1994; Mitchell and Arnott, 1995; Chen, 1997.. How regeneration, particularly planted seedlings, of a tree species responds to a variety of light environments created by partial cutting becomes a primary concern for silviculturists to predict the outcome of their regeneration efforts ŽKlinka et al., 1990; Kimmins, 1987; Wang et al., 1994; Chen, 1997.. )
Corresponding author. Tel.: q1-604-822-8993; fax: q1-604822-5744; e-mail: [email protected].
Survival and growth of tree species in relation to light availability have been widely studied in natural environments ŽEmmingham and Waring, 1973; Lorimer, 1981; Lorimer, 1983; Canham, 1988; Carter and Klinka, 1992; Klinka et al., 1992; Pacala et al., 1994; Kobe et al., 1995; Messier and Puttonen, 1995; Sipe and Bazzaz, 1995; Kayahara et al., 1996; Chen et al., 1996; Chen, 1997.. These studies show that survival of shade-intolerant species decreases with decreasing light availability while in shadetolerant species it does not significantly change with light conditions ŽLorimer, 1983; Sipe and Bazzaz, 1995; Kobe et al., 1995; Chen, 1997.. Growth, however, has been mainly measured on the above-ground component of naturally established saplings Že.g., diameter, height, branch, and above-ground biomass
0378-1127r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 3 7 8 - 1 1 2 7 Ž 9 7 . 0 0 3 0 9 - 5
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H.Y.H. Chen, K. Klinkar Forest Ecology and Management 106 (1998) 169–179
ŽAB.. ŽLorimer, 1981; Lorimer, 1983; Carter and Klinka, 1992; Klinka et al., 1992; Pacala et al., 1994; Messier and Puttonen, 1995; Chen et al., 1996.. Only a few studies have been carried out to examine the response of planted seedlings to a wide range of light conditions in natural environments ŽWang et al., 1994; Chen, 1997.. Because of changes in light environments, plants exhibit plastic responses in morphological and physiological properties at the leaf, branch, or whole-plant levels ŽCanham, 1988; Givnish, 1988; Wilson, 1988; Walters et al., 1993; Wang et al., 1994, Gower et al., 1995; Messier and Puttonen, 1995; Tremmel and Bazzaz, 1995; Chen et al., 1996; Chen and Klinka, 1997.. Generally, shade-tolerant species develop thinner leaves and have higher height-to-diameter and shoot-to-root ratios in response to decreasing light availability; however, the pattern of biomass allocation in woody plants, especially in conifers, has been inadequately examined ŽGower et al., 1995.. Furthermore, several studies on the effect of light on biomass allocation in tree species have been confounded by the size of study seedlings ŽGivnish, 1988; Wilson, 1988; Wang et al., 1994.. Western larch Ž Larix occidentalis Nutt.., an important component of the montane forest of western North America, is considered to be a very shade-intolerant species ŽDaniel et al., 1979; Schmidt and Shearer, 1990; Gower and Richards, 1990.. In southeastern British Columbia, it occurs naturally in cool-
temperate and subalpine boreal climate ŽMeidinger and Pojar, 1991.. In this study, our objectives were to address three questions: Ž1. How does survival of western larch seedlings vary with light availability and seedling development stages? Ž2. How do different measures of growth Žbase diameter, height, and biomass components. change in response to light availability? and Ž3. Are there any changes in allometry and SLA with the change in light availability? The ratios of height to base diameter and AB to below-ground biomass ŽBB. were used to quantify the allometric characteristics.
2. Materials and methods 2.1. Study sites and seedlings Three study sites were located near Okanagan Falls, British Columbia Ž50805X N, 119840X W. on gentle slopes ŽTable 1.. Annual total precipitation ranged from 600 to 850 mm and mean annual temperature from 2 to 48C with the precipitation increasing and the temperature decreasing with increasing elevation ŽMeidinger and Pojar, 1991.. Two study sites ŽSites 1 and 2. were within the Interior Douglas-fir zone and one site ŽSite 3. was within the Montane Spruce zone ŽMeidinger and Pojar, 1991.. All study sites had the same soil great group—Dystric Brunisol ŽCanadian Soil Survey Committee, 1987.. The soil moisture and nutrient conditions of
Table 1 General characteristics of study sites and stands
Elevation Žm. Slope Ž%. Aspect BEC subzonea Soil moisture regime Soil nutrient regime Stand age Žyr. Stand composition
a
Site 1
Site 2
Site 3
850 10 NE IDF = h Very dry Medium 35 20% L. occidentalis, 70% Pseudotsuga menziesii, and 10% Pinus ponderosa
1250 7 W IDFdm Moderately dry Medium 55 30% L. occidentalis and 70% Pinus contorta
1525 20 SW MSdm Slightly dry Medium 50 20% L. occidentalis, 20% Populus tremuloides, and 60% P. contorta
IDF = h: very dry hot interior Douglas-fir subzone. IDFdm: dry mild interior Douglas-fir subzone. MSdm: dry mild montane spruce subzone ŽMeidinger and Pojar, 1991..
H.Y.H. Chen, K. Klinkar Forest Ecology and Management 106 (1998) 169–179 Table 2 General characteristics of initially subsampled seedlings prior to planting in April 1993 Ž ns15..
Mean Minimum Maximum
Di Žmm.
Hi Žcm.
AB i Žg.
BB i Žg.
TB i Žg.
3.43 2.33 4.75
30.5 18.5 45.7
1.455 0.540 2.930
0.653 0.350 1.230
2.108 0.890 4.160
Di s base diameter Žmm.. Hi s height Žcm.. AB i sabove-ground biomass Žg.. BB i s below-ground biomass Žg.. TB i s total biomass Žg..
the study sites were identified according to the procedure described by Green and Klinka Ž1994.. Each study site included a portion of a clearcut and an adjacent forest stand. Cutting occurred between 1986 and 1990 and the area of the clearcuts varied from 2 to 10 ha among the study sites. The edges of the adjacent stands were selectively cut resulting in different sizes of gaps providing a variety of light environments in their understories. In April 1993, 1500 1-yr-old, container-grown western larch seedlings of the same local origin were obtained from a nearby nursery ŽPacific Regeneration Technology, Vernon, British Columbia.. Before planting, 15 seedlings were randomly selected to determine initial base diameter Ž D i ., height Ž Hi ., and biomass components ŽTable 2.. At each study site, approximately 500 seedlings were planted at least 1.5 m apart in irregularly spaced transects extending from 60 m inside the clearcut, through the stand edge, to about 60 m inside the adjacent stand. All seedlings were planted on mineral soil, staked, numbered, and measured for height and base diameter. The surrounding herbs and shrubs within 1-m diameter from the planted seedling were removed immediately after planting and twice each year Žin May and June. for 3 years.
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July 25 in 1994 under clear sky conditions, which are common in the summer-dry continental ecosystems. A sunfleck ceptometer ŽModel SF-80, Decagon Devices, Pullman, WA., which had 80 photosynthetically active radiation ŽPAR. sensors placed at 1-cm intervals along a probe, was used to measure instantaneous photon flux density of PAR received by each seedling. The ceptometer was placed at the tip of the terminal shoot of each seedling. Open-sky PAR was measured in 1-min intervals using a point PAR sensor ŽLI-190SA quantum sensor; LI-COR, Lincoln, NE. connected to a LI-1000 datalogger ŽLICOR., which was placed in an open-area adjacent to each study site. With sensors placed side by side, PAR readings from the point sensor and the ceptometer were compared in a range over a 10 to 1500 m mol my2 sy1 . The difference between the two instruments was less than 0.5%. The clocks of the ceptometer and datalogger were synchronized every morning prior to taking measurements. The PAR associated with each seedling was estimated from the average of two measurements taken at a 908 angle. These measurements were taken twice during the day, from 0930 to 1130 and from 1300 to 1500, in an attempt to mitigate variation associated with solar elevation and sunflecks. Absolute PAR values were converted to relative values as a measure of the light availability of the sampled seedlings using the percent of full sun Ž%FS.: %FS s
Qi Qo
= 100
Ž 1.
where Qi is the averaged PAR reading from the ceptometer and Qo is the time-matched PAR reading from the datalogger. The %FS values, one for the morning and one for the afternoon, were averaged to obtain a final %FS value that represented the relative measure of light availability for each seedling.
2.2. Light measurements Light availability for each seedling was determined by the procedure described in the work of Chen et al. Ž1996. during the second growing season; we assumed that canopy transmittance did not change during three growing seasons from 1993 to 1995. Light measurements were taken between July 2 and
2.3. Measurements of surÕiÕal, growth, and allometry Planted seedlings were grown for three growing seasons from May 1993 to August 1995. Every August before leaf fall, all seedlings were examined for survival, dieback, pathological symptoms, foliage
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Table 3 Relationship between initial base diameter Ž Di , mm., height Ž Hi , cm. and biomass components Regression model
R2
SEE Žg.
TB i sy2.208q0.468= Di q0.089= Hi AB i sy0.590q0.148= Di q0.024= Hi BB i sy1.618q0.320= Di q0.065= Hi
0.921 0.866 0.915
0.23 0.09 0.17
50%, 50.1–60%, 60.1–70%, 70.1–80%, 80.1–90% and ) 90%.. To minimize potential confounding factors other than light, which cause mortality, seedlings with signs of previous damage Že.g., dieback, pathological symptoms, foliage chlorosis, and browsing. were not included in calculation of survival. In consequence, totals of 47 and 69
AB i sabove-ground biomass Žg.. BB i s below-ground biomass Žg.. TB i s total biomass Žg. of subsampled seedlings prior to planting Ž ns15.. R 2 is coefficient of determination and SEE is standard error of estimate.
chlorosis, and other symptoms of damage or injury such as browsing. During the third growing season before leaf fall in August 1995, 60 to 90 seedlings were randomly selected from all surviving seedlings without any history of damage. Attention was paid to obtaining a relatively even distribution of samples along a light gradient. After the position of contact with the ground surface was marked on the seedling stem and measured for total height and base diameter, each selected seedling was carefully excavated together with a large volume of soil containing all roots. Much of the soil was separated from the roots by gentle shaking because it was dry. The seedling was then partitioned into above- and below-ground components and leaf samples were taken from uppermost branches, stored in a portable cooler, and maintained at a temperature of about 08C. All samples were placed in paper bags and transported to a laboratory within three days. The reminder of the soil on the roots was washed off and the samples were stored at the temperature of 0 to 28C in the laboratory. The one-sided projected leaf area of fresh foliar samples was averaged from two measurements using a LI-COR 3100 leaf area meter ŽLI-COR.. The leaf, and above- and below-ground samples were then oven-dried at 708C for 48 to 72 h and then weighed. 2.4. Calculations and statistical analysis Survival, the proportion of surviving to all planted seedlings, was calculated for each of 10 %FS classes ŽF 10%, 10.1–20%, 20.1–30%, 30.1–40%, 40.1–
Fig. 1. Survival of study seedlings stratified according to %FS. ŽA. Survival at the end of the first growing season; ŽB. Survival at the end of the second growing season; and ŽC. Survival at the end of the third growing season. Symbols are non-shade for Site 1, diagonal-shade for Site 2, and grid-shaded Site 3. The error bar is one standard error for the mean.
H.Y.H. Chen, K. Klinkar Forest Ecology and Management 106 (1998) 169–179
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sion models ŽTable 3. were used to estimate the initial biomass components for harvested seedlings. For each harvested seedling, relative growth rate ŽRGR. of diameter and height for the period of three growing seasons was calculated using the measured
Fig. 2. RD and RH on %FS. ŽA. RD with fitted regression Žln y sy1.421q0.02= x, ns 223, R 2 s 0.47., and ŽB. RH with fitted regression Ž y s 0.443q0.086=ln x, ns 223, R 2 s 0.014.. Symbols are shaded circles for Site 1, open circles for Site 2, and shaded triangles for Site 3.
seedlings from all three study sites were eliminated from survival calculations at the end of second and the third growing seasons, respectively. Survival, weighted by the number of all seedlings within each group, was tested with likelihood ratio chi-square Ž x 2 . tests following Zar Ž1984. and Neter et al. Ž1996.. The relationship between initial biomass components Žabove-ground biomass, AB i ; below-ground biomass, BB i ; and total biomass, TB i ., base diameter, and height for 15 subsampled seedlings was examined using the ‘all possible combination’ procedure ŽNeter et al., 1996. by adding or eliminating predictors, e.g., height, diameter, diameter squared, height squared, diameter by height, or height by diameter squared ŽTable 3.. The final ‘best’ regres-
Fig. 3. RAB, RBB, RTB on %FS. ŽA. RAB with fitted regression Žln y s 0.894q0.018= x, ns 223, R 2 s 0.37., ŽB. RBB with fitted regression Žln y s 0.161q0.02= x, ns 223, R 2 s 0.402., and ŽC. RTB with fitted regression Ž y s 0.703q0.019= x, ns 223, R 2 s 0.393.. Symbols as in Fig. 2.
H.Y.H. Chen, K. Klinkar Forest Ecology and Management 106 (1998) 169–179
174
values at the end of the third growing against the measured initial diameter and height before planting for relative base diameter growth rate ŽRD, mm mmy1 3 yry1 . and relative height growth rate ŽRH, cm cmy1 3 yry1 . following Hunt Ž1982.. The RGR for each of the biomass components was calculated using the measured value at the end of the third growing against the against the estimated value by the equations in Table 3 for relative above-ground biomass growth rate ŽRAB, g gy1 3 yry1 ., relative below-ground biomass growth rate ŽRBB, g gy1 3 yry1 ., and relative total biomass growth rate ŽRTB, g gy1 3 yry1 ., respectively. The ratios of height to base diameter Ž HrD . and AB to BB ŽABrBB. of the harvested seedlings at the end of the third growing season were calculated to evaluate allometric patterns. To quantify responses of growth ŽRD, RH, RAB, RBB, and RTB., allometric traits Žratios of HrD and ABrBB., and SLA to %FS, the regression with the ‘best’ fit for each characteristic was chosen from linear and non-linear forms through ordinary leastsquare or least mean square of error fit ŽHunt, 1982; Neter et al., 1996.. The ‘best’ fit regression model for a given characteristic was chosen by fitting original values of all observations from the three study sites. To test the response of a given characteristic to %FS, transformation according to the ‘best’ fit regression form was applied to achieve linearity and homoscedasticity if the response was non-linear. The analysis of variance model used to test the effect of
%FS on growth and leaf characteristics ŽRD, RH, RAB, RBB, RTB, and SLA. was: Yi jk s m q L i q S j q L = Si j q SE kŽ i j.
Ž 2.
where Yi jk is an observation for a particular dependent variable; m is the overall mean of the dependent variable; L i is the quantitative variable %FS; S j is the random site effect ŽBenington and Thayne, 1994.; L = Si j is the interaction between %FS and site; and SE kŽ i j. represents the sampling error within %FS and study sites. L = Si j is the experimental error to test the %FS effect. To account for the effect of differences in seedling size, total biomass of each sampled seedling at the end of third growing season ŽTB. was included when testing for effects of %FS on allometry Ž HrD and ABrBB. as: Yi jk s m q L i q S j q L = Si j q TB q SE kŽ i j.
Ž 3.
where Yi jk , m , L i , S j , L = Si j , and SE kŽ i j. are the same as in Eq. Ž2..
3. Results 3.1. SurÕiÕal Survival of planted seedlings varied with %FS and study sites ŽFig. 1.. At the end of the first growing season, survival ranged from 45 to 100% and significantly decreased with decreasing %FS on Site 1 Ž x 2 s 21.6, P s 0.01. and Site 2 Ž x 2 s 95.3,
Table 4 The effect of light availability on growth characteristics and SLA Source c
DF
RD a MS
Li Sj L = Si j SE k Ž i j. a
1 2 2 217
61.0 0.43 0.56 0.33
RH b F 108.9 1.3 1.7
MS ))
0.67 0.05 0.048 0.196
RAB F 13.3ns 0.325 0.244
MS 42.7 1.09 0.855 0.301
RBB F
MS )
50.0 3.61 2.84
47.8 0.513 1.181 0.324
RTB F
MS )
40.5 1.58 3.65
44.4 0.826 0.856 0.284
SLA F )
51.9 2.91 3.02
MS
F
2283 644 307.8 99.2
7.8ns 6.4 3.1
Natural logarithmic transformation was applied on RD Žrelative diameter growth rate, mm mmy1 3 yry1 ., RAB Žg gy1 3 yry1 ., RBB Žg gy1 3 yry1 ., and RTB Žg gy1 3 yry1 .. b L was transformed by natural logarithm when RH Žrelative height growth rate, cm cmy1 3 yry1 . and SLA Žcm2 gy1 . were tested. c Sources are as in Eq. Ž2.. Differences are significant at P - 0.01 Ž ) ) ., P - 0.05 Ž ) .; ns, not significant Ž P G 0.05..
H.Y.H. Chen, K. Klinkar Forest Ecology and Management 106 (1998) 169–179
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P - 0.001., but was unaffected by %FS on the study Site 3 ŽFig. 1A; x 2 s 3.5, P s 0.94.. At the end of the second growing season, survival declined and ranged from 0 to 91% among different %FS classes and study sites ŽFig. 1A and B.. Similar to the first growing season, the survival at low %FS was the highest in the high elevation study site ŽSite 3. ŽFig. 1B.. At the end of the third growing season, survival further declined and ranged from 0 to 83% ŽFig. 1B and C.. On all study sites, survival significantly decreased with decreasing %FS from intermediate to the lowest level ŽFig. 1C; x 2 ) 17.7, P 0.05.. 3.2. Growth RGR in base diameter and biomass components significantly decreased with decreasing %FS ŽFig. 2AFig. 3; Table 4., whereas there was no significant effect of light on RH ŽFig. 2B; Table 4.. Mean RD ranged from 0.2 at the lowest %FS to 1.9 mm mmy1 3 yry1 in full light conditions ŽFig. 2A.. The half of maximum RD was reached at 63% %FS. Mean RGR in biomass components ŽRAB, RBB, and RTB. varied 10-fold among different light conditions ŽFig. 3.. Similar to RD, all three biomass components reached half of their maximum RGR between 60 to 65%FS ŽFig. 3A,B, and C., but mean RAB tended to be higher than RBB in all light conditions ŽFig. 3A and B.. A limited effect of %FS on RH ŽTable 4, 0.1 - P - 0.05. was primarily confined to %FS - 20%, where most samples were taken from only one study site ŽFig. 2B.. Although a great variability in RH
Fig. 4. Ratio of Hr D and SLA Žcm2 gy1 . on %FS. ŽA. Hr D with fitted regression line Ž y s99.267–0.397= x, ns 223, R 2 s 0.282. and ŽB. SLA with fitted regression Ž y s98.4–8.507=ln x, ns 223, R 2 s 0.242.. Symbols as in Fig. 2.
occurred among individual seedlings, a nearly constant mean RH was found when %FS increased from 20 to 100% ŽFig. 2B..
Table 5 The effect of light availability on allometry Ž Hr D; ABrBB ratio at the end of the third growing season. Sourcea
DF
Li Sj L= Si j TB SE k Ž i j.
1 2 2 1 216
Hr D
ABrBB
MS
F
MS
F
17566 1243 651 1.655 244.3
27.0 ) 5.1 2.664 0.007ns
0.006 0.243 2.501 12.03 0.701
0.002ns 0.346 3.571 17.18 ) ) )
a Sources are as in Eq. Ž3.. Difference are significant at P - 0.001 Ž ) ) ) ., P - 0.05 Ž ) .; ns, not significant Ž P G 0.05..
Fig. 5. Correlation ABrBB ratio and TB. The fitted regression is y s 3.456q0.013= x Ž ns 223, r s 0.2, P s 0.002.. Symbols as in Fig. 2.
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H.Y.H. Chen, K. Klinkar Forest Ecology and Management 106 (1998) 169–179
3.3. Allometry and specific leaf area HrD ratio significantly decreased with increasing %FS ŽTable 5.. The mean of this ratio ranged from 100 in low light conditions to 60 in high light conditions ŽFig. 4.. ABrBB ratio did not significantly change with %FS although it varied from 2 to 6.5 among study seedlings ŽTable 5.. A significant positive correlation Ž r s 0.2, P - 0.05., however, existed between ABrBB ratio and total biomass ŽTable 5, Fig. 5.. Similar to ABrBB ratio, SLA did not significantly increase with decreasing FS% ŽTable 4. although the mean SLA ranged from 85 Žcm2 gy1 . at the lowest %FS to 60 Žcm2 gy1 . at full sun ŽFig. 4B..
4. Discussion 4.1. SurÕiÕal In this study, survival of planted western larch seedlings decreased with decreasing light availability. This result agrees with the general relationship between survival and light availability previously reported for shade-intolerant tree species, in which survival decreases with decreasing light ŽLorimer, 1981; Kobe et al., 1995, Walters and Reich, 1996; Chen, 1997.. In natural environments, survival in shade-tolerant species is rather independent of light availability ŽKobe et al., 1995; Sipe and Bazzaz, 1995; Chen, 1997.. With an attempt to make inferences for a large population, we selected study sites that had a wide range in ecological site quality ŽTable 1.. In consequence, survival varied among study sites ŽFig. 1.. The high-elevation, relatively coolest and wettest site ŽSite 3. had higher survival in low light conditions. At the end of the third growing season, most of the seedlings planted in low light conditions Ž- 20% light availability. on the other two sites were all dead or damaged. The differences in survival may be the result of the differences in slope, aspect, elevation, or canopy composition among study sites. In any case, solar radiation, temperature, precipitation, and soil moisture vary diurnally and seasonally ŽChen et al., 1993.. In consequence, carbon balance of seedlings may vary among the study sites. For exam-
ple, on Site 3, the higher components of deciduous tree species in the forest canopy may allow higher penetration of solar radiation to its understory during early spring and late fall. In addition, the low temperature at the high elevation site may slow the consumption of carbohydrate reserves accumulated in the nursery, thus affecting seedling survival. 4.2. Growth Previous studies on more shade-tolerant species indicate that height growth increases with increasing light availability ŽCanham, 1988; Carter and Klinka, 1992; Klinka et al., 1992; Wang et al., 1994; Sipe and Bazzaz, 1995; Chen et al., 1996; Chen, 1997.. In this study, however, height growth of planted western larch seedlings was not significantly affected by light. In fact, Schmidt and Shearer Ž1990. reported that the western larch seedlings growing in partial shade grow taller during the first few years but height growth becomes slower afterwards compared to seedlings growing in full sunlight. It is unclear, however, whether the height growth pattern of western larch can be generalized as characteristic of very shade-intolerant species, although several studies have found that shade-intolerant species tend to allocate photosynthate to height growth in order to penetrate the canopy whereas shade-tolerant species tend to allocate more biomass production to lateral growth ŽCanham, 1988; Oliver and Larson, 1990; Sipe and Bazzaz, 1995; Chen et al., 1996.. There was a pronounced relationship between light availability and growth in base diameter and biomass components of planted western larch seedlings ŽTable 4, Fig. 2BFig. 3.. With decreasing light availability, significant decreases in diameter growth Žat the base or current terminal. and total biomass increment have also been found in planted and naturally regenerated coniferous and broadleaf tree species ŽCanham, 1988; Pacala et al., 1994; Wang et al., 1994; Messier and Puttonen, 1995; Canham et al., 1996; Chen et al., 1996; Kayahara et al., 1996; Chen, 1997.. 4.3. Allometry and specific leaf area Due to the different response trends in height and base diameter growth, the height to diameter ratio in
H.Y.H. Chen, K. Klinkar Forest Ecology and Management 106 (1998) 169–179
western larch increased with decreasing light availability ŽTable 5, Fig. 4A.. This pattern was also found in the planted seedlings of very shade-tolerant western red cedar ŽThuja plicata Donn ex D. Don. and moderately shade-tolerant interior Douglas-fir Ž P. menziesii var. glauca ŽBeissn. Franco. ŽWang et al., 1994; Chen, 1997.. The trade-off by investing more growth into terminal than diameter may imply the strategy of some canopy species to reach a higher level of light resources in a light-limiting environment ŽCanham, 1988; Lei and Lechowicz, 1990; Wang et al., 1994.. Shoot-to-root ratio usually increases with decreasing light ŽGivnish, 1988; Wilson, 1988.. This was not found in our study ŽTable 5.. Instead, the ratio was positively correlated with total biomass ŽTable 5, Fig. 5.. A similar finding was reported for very shade-intolerant ponderosa pine Ž P. ponderosa var. ponderosa Dougl. ex Laws. ŽChen, 1997.. Shoot-toroot ratio increases with increasing seedling size because larger organisms invest a larger proportion of resources into supportive tissues and a smaller proportion into leaves ŽGivnish, 1988; Wilson, 1988; Sims and Pearcy, 1994.. The effect of light on shoot-to-root ratio varies greatly with species ŽGower et al., 1995; Canham et al., 1996; Walters and Reich, 1996., and more shade-tolerant species are more plastic in changing this ratio with light ŽChen, 1997.. Furthermore, seedlings grown in natural environments experience complex interactions between different environmental factors. These factors, such as different degrees of water and nutrient stresses, may override the effect of light on carbon allocation patterns ŽBazzaz and Wayne, 1994; Messier and Puttonen, 1995.. Shade-leaves have a higher SLA and therefore are more efficient in capturing light on a per unit mass basis than sun-leaves in a light-limiting environment ŽSims and Pearcy, 1994; Chen et al., 1996; Chen and Klinka, 1997; Chen, 1997.. More shade-tolerant species have a more plastic SLA in response to light availability ŽAbrams and Kubiske, 1990; Chen et al., 1996; Chen, 1997.. In our study, SLA of planted seedlings did not respond to the changes in light availability. A similar result was found for other very shade-intolerant species such as Pinus banksiana ŽAbrams and Kubiske, 1990. and P. ponderosa ŽChen, 1997.. Although the basis of tolerance to
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shade involves a number of mechanisms at the physiological andror morphological levels and is likely to vary between species ŽCanham, 1988; Lei and Lechowicz, 1990; Chen et al., 1996; Chen, 1997., the non-plastic responses in SLA and ABrBB ratio may be important attributes of the shade intolerance in western larch seedlings.
5. Conclusions Survival of planted western larch seedlings significantly decreased from intermediate to low light availability and varied among study sites. After three growing seasons, growth in diameter and biomass components of surviving seedlings significantly decreased with decreasing light, whereas height growth was independent of light availability. Height to diameter ratio increased with decreasing light, but the ratio of above to below ground biomass and SLA were not plastic to the change in light availability. The low survival and poor growth performance of planted western larch seedlings in low light conditions suggests that, to artificially regenerate this species successfully on the sites which support its productive growth, other regeneration cutting methods than clearcutting or patch-cutting should not be applied.
Acknowledgements We thank D. Brisco, L. Ling, D. New, and Y. Wang for assistance in data collection. Comments from anonymous reviewers and editorial comments from C. Chourmouzis helped greatly in improving the manuscript. Financial support for this study provided by the Natural Sciences and Engineering Research Council of Canada and Forest Practices Branch of British Columbia Ministry of Forests is gratefully acknowledged.
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Wisconsin: influence of light regime and shade-tolerance rank. For. Ecol. Manage. 31, 245–253. Bazzaz, F.A., Wayne, P.M., 1994. Coping with environmental heterogeneity: the physiological ecology of tree seedling regeneration across the gap-understory continuum. In: Caldwell, M.M., Pearcy, R.W. ŽEds.., Exploitation of Environmental Heterogeneity by Plants: Ecophysiological Processes Aboveand Below-ground. Academic Press, New York, pp. 349–390. Benington, C.C., Thayne, W.V., 1994. Use and misuse of mixed model analysis of variance in ecological studies. Ecology 75, 717–722. Canadian Soil Survey Committee, Subcommittee on Soil Classification, 1987. The Canadian System of Soil Classification. Can. Dep. Agric. Publ., 1646. Supply and Services Canada, Ottawa, Ontario. Canham, C.D., 1988. Growth and canopy architecture of shadetolerant trees: response to canopy gaps. Ecology 69, 786–795. Canham, C.D., Berkowitz, A.R., Kelly, V.R., Lovett, G.M., Ollinger, S.V., Schnurr, J., 1996. Biomass allocation and multiple resource limitation in tree seedlings. Can. J. For. Res. 26, 1521–1529. Carter, R.E., Klinka, K., 1992. Variations in shade tolerance of Douglas-fir, western hemlock and western red cedar in coastal British Columbia. For. Ecol. Manage. 55, 87–105. Chen, H.Y.H., 1997. Interspecific responses of planted seedlings to light availability in interior British Columbia, survival, growth, allometric, and specific leaf area. Can. J. For. Res. 27, 1383–1393. Chen, H.Y.H., Klinka, K., 1997. Light availability and photosynthesis of Pseudotsuga menziesii seedlings grown in the open and forest understory. Tree Physiol. 17, 23–29. Chen, H.Y.H., Klinka, K., Kayahara, G.J., 1996. Effects of light on growth, crown architecture, and specific leaf area for naturally established Pinus contorta var. latifolia and Pseudotsuga menziesii var. glauca. saplings. Can. J. For. Res. 26, 1149–1157. Chen, J.M., Black, T.A., Price, D.T., Carter, R.E., 1993. Model for calculating photosynthetic photon flux densities in forest openings on slopes. J. Appl. Meteorol. 32, 1656–1665. Daniel, T.W., Helms, J.A., Baker, F.S., 1979. Principles of Silviculture, 2nd edn., McGraw-Hill, New York. Emmingham, W.H., Waring, R.H., 1973. Conifer growth under different light environments in the Siskiyou mountains of southwestern Oregon. Northwest Sci. 47, 88–99. Givnish, T.J., 1988. Adaptation to sun and shade: a whole-plant perspective. Aust. J. Plant Physiol. 15, 63–92. Gower, S.T., Richards, J.H., 1990. Larches: deciduous conifers in an evergreen world. BioScience 40, 818–826. Gower, S.T., Isebrands, J.G., Sheriff, D.W., 1995. Carbon allocation and accumulation in conifers. In: Smith, W.K., Hinckley, T.M. ŽEds.., Resource Physiology of Conifers: Acquisition, Allocation, and Utilization. Academic Press, New York, pp. 217–254. Green, R.N., Klinka, K., 1994. A field guide to site identification and interpretation for the Vancouver Forest Region. B.C. Min. of For., Victoria, British Columbia, Canada. Land Management Handbook No. 28.
Hunt, R., 1982. Plant Growth Curves. The Functional Approach to Plant Growth Analysis. Edward Arnold, London, United Kingdom. Kayahara, G.J., Chen, H.Y.H., Klinka, K., Coates, K.D., 1996. Relations of terminal growth and specific leaf area to available light in naturally regenerated seedlings of lodgepole pine and interior spruce in central British Columbia. B.C. Ministry of Forests, Victoria, BC, Research Report 09. Kimmins, J.P., 1987. Forest Ecology. Macmillan, New York. Klinka, K., Carter, R.E., Feller, M.C., 1990. Cutting old-growth forests in British Columbia: ecological considerations for forest regeneration. Northwest Environ. J. 6, 221–242. Klinka, K., Wang, Q., Kayahara, G.J., Carter, R.E., Blackwell, B.A., 1992. Light-growth response relationships in Pacific silver fir Ž Abies amabilis . and subalpine fir Ž Abies lasiocarpa.. Can. J. Bot. 70, 1919–1930. Klinka, K., Carter, R.E., Kayahara, G.J., 1994. Forest reproduction methods for British Columbia: principles, criteria, and a stand selection guide. For. Chron. 70, 569–577. Kobe, R.K., Pacala, S.W., Silander, J.A., Canham, C.D., 1995. Juvenile tree survivorship as a component of shade tolerance. Ecol. Appl. 5, 517–532. Lei, T.T., Lechowicz, M.J., 1990. Shade adaptation and shade tolerance in saplings of three Acer species from eastern North America. Oecologia 84, 224–228. Lorimer, C.G., 1981. Survival and growth of understory trees in oak forests of the Hudson Highlands, New York. Can. J. For. Res. 11, 689–695. Lorimer, C.G., 1983. A test of the accuracy of shade-tolerance classifications based on physiognomic and reproductive traits. Can. J. Bot. 61, 1595–1598. Meidinger, D., Pojar, J., 1991. Ecosystems of British Columbia. B.C. Min. of For., Victoria, British Columbia, Canada. Special Report Series No. 6. Messier, C., Puttonen, P., 1995. Growth, allocation, and morphological responses of Betula pubescens and Betula pendula to shade in developing Scots pine stands. Can. J. For. Res. 25, 629–637. Mitchell, A.K., Arnott, J.T., 1995. Effects of shade on the morphology and physiology of amabilis fir and western hemlock seedlings. New For. 10, 79–98. Neter, J., Kutner, M.H., Nachtsheim, C.J., Wasserman, W., 1996. Applied Linear Statistical Models, 4th edn. Richard D. Irwin, Chicago. Oliver, C.D., Larson, B.C., 1990. Forest Stand Dynamics. McGraw-Hill, New York. Pacala, S.W., Canham, C.D., Silander, J.A., Kobe, R.K., 1994. Sapling growth as a function of resources in a north temperate forest. Can. J. For. Res. 24, 2172–2183. Schmidt, W.C., Shearer, R.C., 1990. Larix occidentalis Nutt.— Western larch. In: Burns, R.M., Honkala, H.B. ŽEds.., Silvics of North America, Vol. 1. Conifers. USDA For. Serv., Agri. Hand., Washington, DC, pp. 160–172. Sims, D.A., Pearcy, R.W., 1994. Scaling sun and shade photosynthetic acclimation of Alocasia macrorrhizo to whole-plant performance: I. Carbon balance and allocation at different daily photon flex densities. Plant Cell Environ. 17, 881–887.
H.Y.H. Chen, K. Klinkar Forest Ecology and Management 106 (1998) 169–179 Sipe, T.W., Bazzaz, F.A., 1995. Gap partitioning among maple Ž Acer . in central New England: survival and growth. Ecology 76, 1587–1602. Tremmel, D.C., Bazzaz, F.A., 1995. Plant architecture and allocation in different neighborhoods: implications for competitive success. Ecology 76, 262–271. Walters, M.B., Reich, P.B., 1996. Are shade tolerance, survival, and growth linked? Low light and nitrogen effects on hardwood seedlings. Ecology 77, 841–853. Walters, M.B., Kruger, E.L., Reich, P.B., 1993. Growth, biomass
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distribution and CO 2 exchange of northern hardwood seedlings in high and low light: relationships with successional status and shade tolerance. Oecologia 94, 7–16. Wang, G.G., Qian, H., Klinka, K., 1994. Growth of Thuja plicata seedlings along a light gradient. Can. J. Bot. 72, 1749–1757. Wilson, J.B., 1988. A review of evidence on the control of shoot:root ratio, in relation to models. Ann. Bot. 61, 433–449. Zar, J.H., 1984. Biostatistical Analysis, 2nd edn., Prentice-Hall, Englewood Cliffs, NJ.
Survival, growth, and allometry of planted Larix occidentalis seedlings in relation to light availability Han Y.H. Chen ) , Karel Klinka Forest Sciences Department, UniÕersity of British Columbia, 270-2357 Main Mall, VancouÕer, BC, Canada V6T 1Z4 Received 26 June 1997; accepted 16 October 1997
Abstract We conducted a 3-year experiment to determine how survival, growth, allometry, and specific leaf area ŽSLA. of planted, very shade-intolerant, western larch Ž Larix occidentalis. seedlings respond to a wide range of light availability under natural environments. Three study sites were located within a summer-dry, cool-temperate climate near Okanagan Falls, British Columbia. Survival significantly decreased with decreasing light at the end of the third growing season on all study sites Ž P - 0.05.. Relative growth rate in base diameter Ž D . and biomass components increased with increasing light Ž P - 0.05., whereas height Ž H . growth was independent of light availability from 20 to 100% full sun Ž P ) 0.05.. With decreasing light, ratio of height to base diameter significantly increased whereas shoot to root ratio and SLA did not change. Instead, the shoot to root ratio was positively correlated with total biomass. These non-plastic responses in shoot to root ratio and SLA may contribute to the very shade intolerant nature of western larch. q 1998 Elsevier Science B.V. Keywords: Western larch; Field experiment; Morphology; Plasticity; Specific leaf area; Shoot to root ratio
1. Introduction Forest regeneration faces a great challenge as partial cutting systems have been introduced as alternatives to clearcutting in British Columbia ŽKlinka et al., 1990; Klinka et al., 1994; Wang et al., 1994; Mitchell and Arnott, 1995; Chen, 1997.. How regeneration, particularly planted seedlings, of a tree species responds to a variety of light environments created by partial cutting becomes a primary concern for silviculturists to predict the outcome of their regeneration efforts ŽKlinka et al., 1990; Kimmins, 1987; Wang et al., 1994; Chen, 1997.. )
Corresponding author. Tel.: q1-604-822-8993; fax: q1-604822-5744; e-mail: [email protected].
Survival and growth of tree species in relation to light availability have been widely studied in natural environments ŽEmmingham and Waring, 1973; Lorimer, 1981; Lorimer, 1983; Canham, 1988; Carter and Klinka, 1992; Klinka et al., 1992; Pacala et al., 1994; Kobe et al., 1995; Messier and Puttonen, 1995; Sipe and Bazzaz, 1995; Kayahara et al., 1996; Chen et al., 1996; Chen, 1997.. These studies show that survival of shade-intolerant species decreases with decreasing light availability while in shadetolerant species it does not significantly change with light conditions ŽLorimer, 1983; Sipe and Bazzaz, 1995; Kobe et al., 1995; Chen, 1997.. Growth, however, has been mainly measured on the above-ground component of naturally established saplings Že.g., diameter, height, branch, and above-ground biomass
0378-1127r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 3 7 8 - 1 1 2 7 Ž 9 7 . 0 0 3 0 9 - 5
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ŽAB.. ŽLorimer, 1981; Lorimer, 1983; Carter and Klinka, 1992; Klinka et al., 1992; Pacala et al., 1994; Messier and Puttonen, 1995; Chen et al., 1996.. Only a few studies have been carried out to examine the response of planted seedlings to a wide range of light conditions in natural environments ŽWang et al., 1994; Chen, 1997.. Because of changes in light environments, plants exhibit plastic responses in morphological and physiological properties at the leaf, branch, or whole-plant levels ŽCanham, 1988; Givnish, 1988; Wilson, 1988; Walters et al., 1993; Wang et al., 1994, Gower et al., 1995; Messier and Puttonen, 1995; Tremmel and Bazzaz, 1995; Chen et al., 1996; Chen and Klinka, 1997.. Generally, shade-tolerant species develop thinner leaves and have higher height-to-diameter and shoot-to-root ratios in response to decreasing light availability; however, the pattern of biomass allocation in woody plants, especially in conifers, has been inadequately examined ŽGower et al., 1995.. Furthermore, several studies on the effect of light on biomass allocation in tree species have been confounded by the size of study seedlings ŽGivnish, 1988; Wilson, 1988; Wang et al., 1994.. Western larch Ž Larix occidentalis Nutt.., an important component of the montane forest of western North America, is considered to be a very shade-intolerant species ŽDaniel et al., 1979; Schmidt and Shearer, 1990; Gower and Richards, 1990.. In southeastern British Columbia, it occurs naturally in cool-
temperate and subalpine boreal climate ŽMeidinger and Pojar, 1991.. In this study, our objectives were to address three questions: Ž1. How does survival of western larch seedlings vary with light availability and seedling development stages? Ž2. How do different measures of growth Žbase diameter, height, and biomass components. change in response to light availability? and Ž3. Are there any changes in allometry and SLA with the change in light availability? The ratios of height to base diameter and AB to below-ground biomass ŽBB. were used to quantify the allometric characteristics.
2. Materials and methods 2.1. Study sites and seedlings Three study sites were located near Okanagan Falls, British Columbia Ž50805X N, 119840X W. on gentle slopes ŽTable 1.. Annual total precipitation ranged from 600 to 850 mm and mean annual temperature from 2 to 48C with the precipitation increasing and the temperature decreasing with increasing elevation ŽMeidinger and Pojar, 1991.. Two study sites ŽSites 1 and 2. were within the Interior Douglas-fir zone and one site ŽSite 3. was within the Montane Spruce zone ŽMeidinger and Pojar, 1991.. All study sites had the same soil great group—Dystric Brunisol ŽCanadian Soil Survey Committee, 1987.. The soil moisture and nutrient conditions of
Table 1 General characteristics of study sites and stands
Elevation Žm. Slope Ž%. Aspect BEC subzonea Soil moisture regime Soil nutrient regime Stand age Žyr. Stand composition
a
Site 1
Site 2
Site 3
850 10 NE IDF = h Very dry Medium 35 20% L. occidentalis, 70% Pseudotsuga menziesii, and 10% Pinus ponderosa
1250 7 W IDFdm Moderately dry Medium 55 30% L. occidentalis and 70% Pinus contorta
1525 20 SW MSdm Slightly dry Medium 50 20% L. occidentalis, 20% Populus tremuloides, and 60% P. contorta
IDF = h: very dry hot interior Douglas-fir subzone. IDFdm: dry mild interior Douglas-fir subzone. MSdm: dry mild montane spruce subzone ŽMeidinger and Pojar, 1991..
H.Y.H. Chen, K. Klinkar Forest Ecology and Management 106 (1998) 169–179 Table 2 General characteristics of initially subsampled seedlings prior to planting in April 1993 Ž ns15..
Mean Minimum Maximum
Di Žmm.
Hi Žcm.
AB i Žg.
BB i Žg.
TB i Žg.
3.43 2.33 4.75
30.5 18.5 45.7
1.455 0.540 2.930
0.653 0.350 1.230
2.108 0.890 4.160
Di s base diameter Žmm.. Hi s height Žcm.. AB i sabove-ground biomass Žg.. BB i s below-ground biomass Žg.. TB i s total biomass Žg..
the study sites were identified according to the procedure described by Green and Klinka Ž1994.. Each study site included a portion of a clearcut and an adjacent forest stand. Cutting occurred between 1986 and 1990 and the area of the clearcuts varied from 2 to 10 ha among the study sites. The edges of the adjacent stands were selectively cut resulting in different sizes of gaps providing a variety of light environments in their understories. In April 1993, 1500 1-yr-old, container-grown western larch seedlings of the same local origin were obtained from a nearby nursery ŽPacific Regeneration Technology, Vernon, British Columbia.. Before planting, 15 seedlings were randomly selected to determine initial base diameter Ž D i ., height Ž Hi ., and biomass components ŽTable 2.. At each study site, approximately 500 seedlings were planted at least 1.5 m apart in irregularly spaced transects extending from 60 m inside the clearcut, through the stand edge, to about 60 m inside the adjacent stand. All seedlings were planted on mineral soil, staked, numbered, and measured for height and base diameter. The surrounding herbs and shrubs within 1-m diameter from the planted seedling were removed immediately after planting and twice each year Žin May and June. for 3 years.
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July 25 in 1994 under clear sky conditions, which are common in the summer-dry continental ecosystems. A sunfleck ceptometer ŽModel SF-80, Decagon Devices, Pullman, WA., which had 80 photosynthetically active radiation ŽPAR. sensors placed at 1-cm intervals along a probe, was used to measure instantaneous photon flux density of PAR received by each seedling. The ceptometer was placed at the tip of the terminal shoot of each seedling. Open-sky PAR was measured in 1-min intervals using a point PAR sensor ŽLI-190SA quantum sensor; LI-COR, Lincoln, NE. connected to a LI-1000 datalogger ŽLICOR., which was placed in an open-area adjacent to each study site. With sensors placed side by side, PAR readings from the point sensor and the ceptometer were compared in a range over a 10 to 1500 m mol my2 sy1 . The difference between the two instruments was less than 0.5%. The clocks of the ceptometer and datalogger were synchronized every morning prior to taking measurements. The PAR associated with each seedling was estimated from the average of two measurements taken at a 908 angle. These measurements were taken twice during the day, from 0930 to 1130 and from 1300 to 1500, in an attempt to mitigate variation associated with solar elevation and sunflecks. Absolute PAR values were converted to relative values as a measure of the light availability of the sampled seedlings using the percent of full sun Ž%FS.: %FS s
Qi Qo
= 100
Ž 1.
where Qi is the averaged PAR reading from the ceptometer and Qo is the time-matched PAR reading from the datalogger. The %FS values, one for the morning and one for the afternoon, were averaged to obtain a final %FS value that represented the relative measure of light availability for each seedling.
2.2. Light measurements Light availability for each seedling was determined by the procedure described in the work of Chen et al. Ž1996. during the second growing season; we assumed that canopy transmittance did not change during three growing seasons from 1993 to 1995. Light measurements were taken between July 2 and
2.3. Measurements of surÕiÕal, growth, and allometry Planted seedlings were grown for three growing seasons from May 1993 to August 1995. Every August before leaf fall, all seedlings were examined for survival, dieback, pathological symptoms, foliage
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Table 3 Relationship between initial base diameter Ž Di , mm., height Ž Hi , cm. and biomass components Regression model
R2
SEE Žg.
TB i sy2.208q0.468= Di q0.089= Hi AB i sy0.590q0.148= Di q0.024= Hi BB i sy1.618q0.320= Di q0.065= Hi
0.921 0.866 0.915
0.23 0.09 0.17
50%, 50.1–60%, 60.1–70%, 70.1–80%, 80.1–90% and ) 90%.. To minimize potential confounding factors other than light, which cause mortality, seedlings with signs of previous damage Že.g., dieback, pathological symptoms, foliage chlorosis, and browsing. were not included in calculation of survival. In consequence, totals of 47 and 69
AB i sabove-ground biomass Žg.. BB i s below-ground biomass Žg.. TB i s total biomass Žg. of subsampled seedlings prior to planting Ž ns15.. R 2 is coefficient of determination and SEE is standard error of estimate.
chlorosis, and other symptoms of damage or injury such as browsing. During the third growing season before leaf fall in August 1995, 60 to 90 seedlings were randomly selected from all surviving seedlings without any history of damage. Attention was paid to obtaining a relatively even distribution of samples along a light gradient. After the position of contact with the ground surface was marked on the seedling stem and measured for total height and base diameter, each selected seedling was carefully excavated together with a large volume of soil containing all roots. Much of the soil was separated from the roots by gentle shaking because it was dry. The seedling was then partitioned into above- and below-ground components and leaf samples were taken from uppermost branches, stored in a portable cooler, and maintained at a temperature of about 08C. All samples were placed in paper bags and transported to a laboratory within three days. The reminder of the soil on the roots was washed off and the samples were stored at the temperature of 0 to 28C in the laboratory. The one-sided projected leaf area of fresh foliar samples was averaged from two measurements using a LI-COR 3100 leaf area meter ŽLI-COR.. The leaf, and above- and below-ground samples were then oven-dried at 708C for 48 to 72 h and then weighed. 2.4. Calculations and statistical analysis Survival, the proportion of surviving to all planted seedlings, was calculated for each of 10 %FS classes ŽF 10%, 10.1–20%, 20.1–30%, 30.1–40%, 40.1–
Fig. 1. Survival of study seedlings stratified according to %FS. ŽA. Survival at the end of the first growing season; ŽB. Survival at the end of the second growing season; and ŽC. Survival at the end of the third growing season. Symbols are non-shade for Site 1, diagonal-shade for Site 2, and grid-shaded Site 3. The error bar is one standard error for the mean.
H.Y.H. Chen, K. Klinkar Forest Ecology and Management 106 (1998) 169–179
173
sion models ŽTable 3. were used to estimate the initial biomass components for harvested seedlings. For each harvested seedling, relative growth rate ŽRGR. of diameter and height for the period of three growing seasons was calculated using the measured
Fig. 2. RD and RH on %FS. ŽA. RD with fitted regression Žln y sy1.421q0.02= x, ns 223, R 2 s 0.47., and ŽB. RH with fitted regression Ž y s 0.443q0.086=ln x, ns 223, R 2 s 0.014.. Symbols are shaded circles for Site 1, open circles for Site 2, and shaded triangles for Site 3.
seedlings from all three study sites were eliminated from survival calculations at the end of second and the third growing seasons, respectively. Survival, weighted by the number of all seedlings within each group, was tested with likelihood ratio chi-square Ž x 2 . tests following Zar Ž1984. and Neter et al. Ž1996.. The relationship between initial biomass components Žabove-ground biomass, AB i ; below-ground biomass, BB i ; and total biomass, TB i ., base diameter, and height for 15 subsampled seedlings was examined using the ‘all possible combination’ procedure ŽNeter et al., 1996. by adding or eliminating predictors, e.g., height, diameter, diameter squared, height squared, diameter by height, or height by diameter squared ŽTable 3.. The final ‘best’ regres-
Fig. 3. RAB, RBB, RTB on %FS. ŽA. RAB with fitted regression Žln y s 0.894q0.018= x, ns 223, R 2 s 0.37., ŽB. RBB with fitted regression Žln y s 0.161q0.02= x, ns 223, R 2 s 0.402., and ŽC. RTB with fitted regression Ž y s 0.703q0.019= x, ns 223, R 2 s 0.393.. Symbols as in Fig. 2.
H.Y.H. Chen, K. Klinkar Forest Ecology and Management 106 (1998) 169–179
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values at the end of the third growing against the measured initial diameter and height before planting for relative base diameter growth rate ŽRD, mm mmy1 3 yry1 . and relative height growth rate ŽRH, cm cmy1 3 yry1 . following Hunt Ž1982.. The RGR for each of the biomass components was calculated using the measured value at the end of the third growing against the against the estimated value by the equations in Table 3 for relative above-ground biomass growth rate ŽRAB, g gy1 3 yry1 ., relative below-ground biomass growth rate ŽRBB, g gy1 3 yry1 ., and relative total biomass growth rate ŽRTB, g gy1 3 yry1 ., respectively. The ratios of height to base diameter Ž HrD . and AB to BB ŽABrBB. of the harvested seedlings at the end of the third growing season were calculated to evaluate allometric patterns. To quantify responses of growth ŽRD, RH, RAB, RBB, and RTB., allometric traits Žratios of HrD and ABrBB., and SLA to %FS, the regression with the ‘best’ fit for each characteristic was chosen from linear and non-linear forms through ordinary leastsquare or least mean square of error fit ŽHunt, 1982; Neter et al., 1996.. The ‘best’ fit regression model for a given characteristic was chosen by fitting original values of all observations from the three study sites. To test the response of a given characteristic to %FS, transformation according to the ‘best’ fit regression form was applied to achieve linearity and homoscedasticity if the response was non-linear. The analysis of variance model used to test the effect of
%FS on growth and leaf characteristics ŽRD, RH, RAB, RBB, RTB, and SLA. was: Yi jk s m q L i q S j q L = Si j q SE kŽ i j.
Ž 2.
where Yi jk is an observation for a particular dependent variable; m is the overall mean of the dependent variable; L i is the quantitative variable %FS; S j is the random site effect ŽBenington and Thayne, 1994.; L = Si j is the interaction between %FS and site; and SE kŽ i j. represents the sampling error within %FS and study sites. L = Si j is the experimental error to test the %FS effect. To account for the effect of differences in seedling size, total biomass of each sampled seedling at the end of third growing season ŽTB. was included when testing for effects of %FS on allometry Ž HrD and ABrBB. as: Yi jk s m q L i q S j q L = Si j q TB q SE kŽ i j.
Ž 3.
where Yi jk , m , L i , S j , L = Si j , and SE kŽ i j. are the same as in Eq. Ž2..
3. Results 3.1. SurÕiÕal Survival of planted seedlings varied with %FS and study sites ŽFig. 1.. At the end of the first growing season, survival ranged from 45 to 100% and significantly decreased with decreasing %FS on Site 1 Ž x 2 s 21.6, P s 0.01. and Site 2 Ž x 2 s 95.3,
Table 4 The effect of light availability on growth characteristics and SLA Source c
DF
RD a MS
Li Sj L = Si j SE k Ž i j. a
1 2 2 217
61.0 0.43 0.56 0.33
RH b F 108.9 1.3 1.7
MS ))
0.67 0.05 0.048 0.196
RAB F 13.3ns 0.325 0.244
MS 42.7 1.09 0.855 0.301
RBB F
MS )
50.0 3.61 2.84
47.8 0.513 1.181 0.324
RTB F
MS )
40.5 1.58 3.65
44.4 0.826 0.856 0.284
SLA F )
51.9 2.91 3.02
MS
F
2283 644 307.8 99.2
7.8ns 6.4 3.1
Natural logarithmic transformation was applied on RD Žrelative diameter growth rate, mm mmy1 3 yry1 ., RAB Žg gy1 3 yry1 ., RBB Žg gy1 3 yry1 ., and RTB Žg gy1 3 yry1 .. b L was transformed by natural logarithm when RH Žrelative height growth rate, cm cmy1 3 yry1 . and SLA Žcm2 gy1 . were tested. c Sources are as in Eq. Ž2.. Differences are significant at P - 0.01 Ž ) ) ., P - 0.05 Ž ) .; ns, not significant Ž P G 0.05..
H.Y.H. Chen, K. Klinkar Forest Ecology and Management 106 (1998) 169–179
175
P - 0.001., but was unaffected by %FS on the study Site 3 ŽFig. 1A; x 2 s 3.5, P s 0.94.. At the end of the second growing season, survival declined and ranged from 0 to 91% among different %FS classes and study sites ŽFig. 1A and B.. Similar to the first growing season, the survival at low %FS was the highest in the high elevation study site ŽSite 3. ŽFig. 1B.. At the end of the third growing season, survival further declined and ranged from 0 to 83% ŽFig. 1B and C.. On all study sites, survival significantly decreased with decreasing %FS from intermediate to the lowest level ŽFig. 1C; x 2 ) 17.7, P 0.05.. 3.2. Growth RGR in base diameter and biomass components significantly decreased with decreasing %FS ŽFig. 2AFig. 3; Table 4., whereas there was no significant effect of light on RH ŽFig. 2B; Table 4.. Mean RD ranged from 0.2 at the lowest %FS to 1.9 mm mmy1 3 yry1 in full light conditions ŽFig. 2A.. The half of maximum RD was reached at 63% %FS. Mean RGR in biomass components ŽRAB, RBB, and RTB. varied 10-fold among different light conditions ŽFig. 3.. Similar to RD, all three biomass components reached half of their maximum RGR between 60 to 65%FS ŽFig. 3A,B, and C., but mean RAB tended to be higher than RBB in all light conditions ŽFig. 3A and B.. A limited effect of %FS on RH ŽTable 4, 0.1 - P - 0.05. was primarily confined to %FS - 20%, where most samples were taken from only one study site ŽFig. 2B.. Although a great variability in RH
Fig. 4. Ratio of Hr D and SLA Žcm2 gy1 . on %FS. ŽA. Hr D with fitted regression line Ž y s99.267–0.397= x, ns 223, R 2 s 0.282. and ŽB. SLA with fitted regression Ž y s98.4–8.507=ln x, ns 223, R 2 s 0.242.. Symbols as in Fig. 2.
occurred among individual seedlings, a nearly constant mean RH was found when %FS increased from 20 to 100% ŽFig. 2B..
Table 5 The effect of light availability on allometry Ž Hr D; ABrBB ratio at the end of the third growing season. Sourcea
DF
Li Sj L= Si j TB SE k Ž i j.
1 2 2 1 216
Hr D
ABrBB
MS
F
MS
F
17566 1243 651 1.655 244.3
27.0 ) 5.1 2.664 0.007ns
0.006 0.243 2.501 12.03 0.701
0.002ns 0.346 3.571 17.18 ) ) )
a Sources are as in Eq. Ž3.. Difference are significant at P - 0.001 Ž ) ) ) ., P - 0.05 Ž ) .; ns, not significant Ž P G 0.05..
Fig. 5. Correlation ABrBB ratio and TB. The fitted regression is y s 3.456q0.013= x Ž ns 223, r s 0.2, P s 0.002.. Symbols as in Fig. 2.
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3.3. Allometry and specific leaf area HrD ratio significantly decreased with increasing %FS ŽTable 5.. The mean of this ratio ranged from 100 in low light conditions to 60 in high light conditions ŽFig. 4.. ABrBB ratio did not significantly change with %FS although it varied from 2 to 6.5 among study seedlings ŽTable 5.. A significant positive correlation Ž r s 0.2, P - 0.05., however, existed between ABrBB ratio and total biomass ŽTable 5, Fig. 5.. Similar to ABrBB ratio, SLA did not significantly increase with decreasing FS% ŽTable 4. although the mean SLA ranged from 85 Žcm2 gy1 . at the lowest %FS to 60 Žcm2 gy1 . at full sun ŽFig. 4B..
4. Discussion 4.1. SurÕiÕal In this study, survival of planted western larch seedlings decreased with decreasing light availability. This result agrees with the general relationship between survival and light availability previously reported for shade-intolerant tree species, in which survival decreases with decreasing light ŽLorimer, 1981; Kobe et al., 1995, Walters and Reich, 1996; Chen, 1997.. In natural environments, survival in shade-tolerant species is rather independent of light availability ŽKobe et al., 1995; Sipe and Bazzaz, 1995; Chen, 1997.. With an attempt to make inferences for a large population, we selected study sites that had a wide range in ecological site quality ŽTable 1.. In consequence, survival varied among study sites ŽFig. 1.. The high-elevation, relatively coolest and wettest site ŽSite 3. had higher survival in low light conditions. At the end of the third growing season, most of the seedlings planted in low light conditions Ž- 20% light availability. on the other two sites were all dead or damaged. The differences in survival may be the result of the differences in slope, aspect, elevation, or canopy composition among study sites. In any case, solar radiation, temperature, precipitation, and soil moisture vary diurnally and seasonally ŽChen et al., 1993.. In consequence, carbon balance of seedlings may vary among the study sites. For exam-
ple, on Site 3, the higher components of deciduous tree species in the forest canopy may allow higher penetration of solar radiation to its understory during early spring and late fall. In addition, the low temperature at the high elevation site may slow the consumption of carbohydrate reserves accumulated in the nursery, thus affecting seedling survival. 4.2. Growth Previous studies on more shade-tolerant species indicate that height growth increases with increasing light availability ŽCanham, 1988; Carter and Klinka, 1992; Klinka et al., 1992; Wang et al., 1994; Sipe and Bazzaz, 1995; Chen et al., 1996; Chen, 1997.. In this study, however, height growth of planted western larch seedlings was not significantly affected by light. In fact, Schmidt and Shearer Ž1990. reported that the western larch seedlings growing in partial shade grow taller during the first few years but height growth becomes slower afterwards compared to seedlings growing in full sunlight. It is unclear, however, whether the height growth pattern of western larch can be generalized as characteristic of very shade-intolerant species, although several studies have found that shade-intolerant species tend to allocate photosynthate to height growth in order to penetrate the canopy whereas shade-tolerant species tend to allocate more biomass production to lateral growth ŽCanham, 1988; Oliver and Larson, 1990; Sipe and Bazzaz, 1995; Chen et al., 1996.. There was a pronounced relationship between light availability and growth in base diameter and biomass components of planted western larch seedlings ŽTable 4, Fig. 2BFig. 3.. With decreasing light availability, significant decreases in diameter growth Žat the base or current terminal. and total biomass increment have also been found in planted and naturally regenerated coniferous and broadleaf tree species ŽCanham, 1988; Pacala et al., 1994; Wang et al., 1994; Messier and Puttonen, 1995; Canham et al., 1996; Chen et al., 1996; Kayahara et al., 1996; Chen, 1997.. 4.3. Allometry and specific leaf area Due to the different response trends in height and base diameter growth, the height to diameter ratio in
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western larch increased with decreasing light availability ŽTable 5, Fig. 4A.. This pattern was also found in the planted seedlings of very shade-tolerant western red cedar ŽThuja plicata Donn ex D. Don. and moderately shade-tolerant interior Douglas-fir Ž P. menziesii var. glauca ŽBeissn. Franco. ŽWang et al., 1994; Chen, 1997.. The trade-off by investing more growth into terminal than diameter may imply the strategy of some canopy species to reach a higher level of light resources in a light-limiting environment ŽCanham, 1988; Lei and Lechowicz, 1990; Wang et al., 1994.. Shoot-to-root ratio usually increases with decreasing light ŽGivnish, 1988; Wilson, 1988.. This was not found in our study ŽTable 5.. Instead, the ratio was positively correlated with total biomass ŽTable 5, Fig. 5.. A similar finding was reported for very shade-intolerant ponderosa pine Ž P. ponderosa var. ponderosa Dougl. ex Laws. ŽChen, 1997.. Shoot-toroot ratio increases with increasing seedling size because larger organisms invest a larger proportion of resources into supportive tissues and a smaller proportion into leaves ŽGivnish, 1988; Wilson, 1988; Sims and Pearcy, 1994.. The effect of light on shoot-to-root ratio varies greatly with species ŽGower et al., 1995; Canham et al., 1996; Walters and Reich, 1996., and more shade-tolerant species are more plastic in changing this ratio with light ŽChen, 1997.. Furthermore, seedlings grown in natural environments experience complex interactions between different environmental factors. These factors, such as different degrees of water and nutrient stresses, may override the effect of light on carbon allocation patterns ŽBazzaz and Wayne, 1994; Messier and Puttonen, 1995.. Shade-leaves have a higher SLA and therefore are more efficient in capturing light on a per unit mass basis than sun-leaves in a light-limiting environment ŽSims and Pearcy, 1994; Chen et al., 1996; Chen and Klinka, 1997; Chen, 1997.. More shade-tolerant species have a more plastic SLA in response to light availability ŽAbrams and Kubiske, 1990; Chen et al., 1996; Chen, 1997.. In our study, SLA of planted seedlings did not respond to the changes in light availability. A similar result was found for other very shade-intolerant species such as Pinus banksiana ŽAbrams and Kubiske, 1990. and P. ponderosa ŽChen, 1997.. Although the basis of tolerance to
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shade involves a number of mechanisms at the physiological andror morphological levels and is likely to vary between species ŽCanham, 1988; Lei and Lechowicz, 1990; Chen et al., 1996; Chen, 1997., the non-plastic responses in SLA and ABrBB ratio may be important attributes of the shade intolerance in western larch seedlings.
5. Conclusions Survival of planted western larch seedlings significantly decreased from intermediate to low light availability and varied among study sites. After three growing seasons, growth in diameter and biomass components of surviving seedlings significantly decreased with decreasing light, whereas height growth was independent of light availability. Height to diameter ratio increased with decreasing light, but the ratio of above to below ground biomass and SLA were not plastic to the change in light availability. The low survival and poor growth performance of planted western larch seedlings in low light conditions suggests that, to artificially regenerate this species successfully on the sites which support its productive growth, other regeneration cutting methods than clearcutting or patch-cutting should not be applied.
Acknowledgements We thank D. Brisco, L. Ling, D. New, and Y. Wang for assistance in data collection. Comments from anonymous reviewers and editorial comments from C. Chourmouzis helped greatly in improving the manuscript. Financial support for this study provided by the Natural Sciences and Engineering Research Council of Canada and Forest Practices Branch of British Columbia Ministry of Forests is gratefully acknowledged.
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