© 2003 Heron Publishing—Victoria, Canada
Sources of variation in ecophysiological parameters in Douglas-fir and grand fir canopies
Jesse B. Nippert (1, 2, 3) and John D. Marshall (1)
1. Department of Forest Resources, University of Idaho, Moscow, ID 83844-1133, USA / 2. Division of Biology, Kansas State University, Manhattan, KS 66506, USA / 3. Author to whom correspondence should be addressed (nippert@ksu.edu) / Received July 2, 2002; accepted November 9, 2002; published online May 15, 2003
Summary
Forest process models predict ecosystem responses from climate variables and physiological parameters. The parameters describe
key ecosystem attributes, often as lumped averages. However, the sources and magnitude of variation in these physiological
parameters are unknown, which complicates sampling if models are to be parameterized with field measurements. We measured
several key parameters, which had been identified by sensitivity analyses of three models, in Abies grandis (Dougl.) Lindl. and Pseudotsuga menziesii var. glauca (Beissn.) Franco trees throughout the growing season. Trees were sampled at eight sites across the interior northwest of
the USA. At each site, fertilized and control plots were sampled. The design provided statistical replication for the analysis
of variance within a site, allowing us to draw inferences about a regional population of stands. Specific leaf area (SLA)
varied by canopy position and treatment (P = 0.0003), by date of sampling (P < 0.0001) and by species (P = 0.0188). Mass-based foliar nitrogen concentration (%N) increased during the summer in both species (P = 0.0019), but at a faster rate in P. menziesii var. glauca than in A. grandis. Sun foliage had a higher mean %N (1.00, SE = 0.02%) than shade foliage (0.92 ± 0.01%). Apparent quantum yield (Φ) varied
among treatments, between species and between canopy positions; each of these variables interacted with date of sampling (P = 0.0207, P < 0.0001 and P = 0.0344, respectively). In A. grandis, mean Φ values (± SE) were 0.048 ± 0.006 mol CO2 (mol incident photon)–1 for sun foliage and 0.067 ± 0.007 mol CO2 (mol incident photon)–1 for shade foliage. In P. menziesii, the corresponding mean Φ values were 0.032 ± 0.003 and 0.047 ± 0.004 mol CO2 (mol incident photon)–1. Parameters SLA, %N and Φ were all influenced by date, fertilizer treatment, species and crown position. We discuss methods
of inferring quantum yields from light response curves and their utility for parameterizing process models. Parameter mean
values are presented for each site; these tables provide a documented data set for the parameterization of models describing
the western interior forests of the USA.
Keywords:
Abies grandis, foliar nitrogen concentration, process models, Pseudotsuga menziesii var. glauca, quantum yield, sensitivity analyses, specific leaf area.
