Friday, August 7, 2009: 10:10 AM
Dona Ana, Albuquerque Convention Center
Dan Binkley, Forest, Range and Watershed Stewardship, COlorado State University, Fort Collins, CO, Jose Luiz Stape, Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC, William L. Bauerle, Horticulture and Landscape Architecture, Colorado State University, Fort Collins, CO and Michael G. Ryan, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO
Background/Question/Methods The rates of resource supply (light, water and nutrients) available to individual trees typically change through time, as a result of changing competition with other plants and changes in environmental conditions (such as soil nutrient availability). Entire stands may experience changes in resource supplies as a result of active forest management, climate trends, and changes in soils. These changes contribute changes in growth of individual trees and stands, but explanations based only on resource supplies and rates of use may be incomplete. We tested three fundamental hypotheses about how light interception and efficiency of light use would differ among trees within stands as a function of tree sizes: 1) dominant trees have higher growth rates not only because of higher rates of light interception, but also because of greater growth rate per unit of light intercepted (light use efficiency); 2) stands with lower variation in tree sizes should show greater growth as a result of higher efficiency of light use by non-dominant trees; increasing variation and dominance in a stand would suppress the efficiency of light use by non-dominant trees, without increasing the efficiency of dominant trees; and 3) greater uniformity in stand structure would lead to less age-related decline, as subordinate trees would lose less efficiency of light use in uniform plots.
Results/Conclusions
Across sites, treatments and whole-rotation stand development, dominant trees showed higher rates of stem growth, light interception, and light use efficiency than subordinate trees. For example, the 80th percentile trees at the Aracruz site showed more than twice the growth of the 40th percentile trees, and the extra growth resulted from a 30% increase in light interception a doubling in wood growth per unit of light intercepted. In some cases, greater variety among tree sizes with plots (developed by staggering the day of planting over a 3-month period) led to lower efficiency of light use by average-size trees.
