© 2001 Heron Publishing—Victoria, Canada
Changes in physiological attributes of ponderosa pine from seedling to mature tree
Nancy E. Grulke (1) and William A. Retzlaff (2)
1. USDA Forest Service, Pacific Southwest Research Station, 4955 Canyon Crest Drive, Riverside, CA 92507, USA / 2. Environmental Science Program, Southern Illinois University Edwardsville, Edwardsville, IL 62026, USA / Received August 30, 2000
Summary
Plant physiological models are generally parameterized from many difference sources of data, including chamber experiments
and plantations, from seedlings to mature trees. We obtained a comprehensive data set for a natural stand of ponderosa pine
(Pinus ponderosa Laws.) and used these data to parameterize the physiologically based model, TREGRO. Representative trees of each of five
tree age classes were selected based on population means of morphological, physiological, and nearest neighbor attributes.
Differences in key physiological attributes (gas exchange, needle chemistry, elongation growth, needle retention) among the
tree age classes were tested. Whole-tree biomass and allocation were determined for seedlings, saplings, and pole-sized trees.
Seasonal maxima and minima of gas exchange were similar across all tree age classes. Seasonal minima and a shift to more efficient
water use were reached one month earlier in seedlings than in older trees because of decreased soil water availability in
the rooting zone of the seedlings. However, carbon isotopic discrimination of needle cellulose indicated increased water-use
efficiency with increasing tree age. Seedlings had the lowest needle and branch elongation biomass growth. The amount of needle
elongation growth was highest for mature trees and amount of branch elongation growth was highest for saplings. Seedlings
had the highest biomass allocation to roots, saplings had the highest allocation to foliage, and pole-sized trees had the
highest allocation to woody tissues. Seedlings differed significantly from pole-sized and older trees in most of the physiological
traits tested. Predicted changes in biomass with tree age, simulated with the model TREGRO, closely matched those of trees
in a natural stand to 30 years of age.
Keywords:
gas exchange, growth rates, mature trees, ontogenetic changes, TREGRO, whole tree biomass.
