An analysis of the age-related decline in aboveground net primary production: Potential causes and stand-to global scale implications

We propose to synthesize NPP data for forest age-sequence studies and use three ecosystem process-based models to determine the mechanisms(s) responsible for the age-related NPP decline for natural and plantation forests in contrasting climates. We will emphasize inter-ecosystem comparisons for a broad-range of forest biomes (tropical broad-leaved evergreen, sub-tropical broad-leaved evergreen, warm temperate needle-leaved evergreen, cold-temperate needle-leaved evergreen, broad-leaved evergreen, and broad-leaved deciduous and boreal needle-leaved evergreen forests) to examine the relative importance of three hypothesized mechanisms (an altered balance between photosynthetic and respiring tissue, decreasing soil nutrient availability, and increasing stomatal limitation leading to reduced photosynthetic rates) responsible for NPP decline in aging forests. A second objective is to develop physiology-based algorithms that simulate the mechanisms responsible for age-related NPP decline; these algorithms will be incorporated into ecosystem model (i.e. it simulates carbon, water and energy fluxes) to examine stand-age related effects on carbon dioxide and water vapor exchange between forest biomes and the atmosphere and potential feedbacks.

Full Text of Proposal updated March 1998 to indicate current activity