Nutrient supply and declines in leaf area and production in lodgepoie pine

Abstract

In southeastern Wyoming, stand leaf area and production of lodgepoie pine (Pinuscontorta Dougl.) peak early in stand development and then decline. We tested the hypothesis that these declines followed decreasing nutrient supply and increasing nutrient limitation in older forests. Single-tree fertilization plots in 28 stands were used to test for nutrient limitation with stand age and density. Younger stands (<40 year old) had higher net nitrification and mineralization. These stands showed no significant response to fertilization in either needle fascicle weight or basal area growth. All older age-classes responded strongly in both fascicle weight and basal area growth. Foliar analysis indicated that N, P, and K all limited growth in older stands, but basal area increments indicated maximum responses to N alone. We conclude that increasing nutrient limitation in older stands probably accounts for at least part of the decline in stand leaf area and growth. Such declines may be responsive to a range of management activities that improve or impair stand nutrition.