Re-defining Aboveground Net Primary Productivity (ANPP) for Complex Terrain: A Case Study from the H.J. Andrews Experimental Forest

Many environmental factors, such as temperature, precipitation, and nutrient balances, have been associated with the rate of aboveground net primary productivity (ANPP) in forest ecosystems, and in turn ANPP has been used to predict the growth and yield of forest stands. When quantifying ANPP, a particular “slice” in time is selected for measurement (usually calculating an average rate of radial growth over a re-measurement interval) and often this single measurement is extrapolated to a much larger scale based on the assumption of homogeneity across a site. However, in complex terrain, such as the Western Cascades Range in Oregon, not all microsites in a forest stand develop along the same successional trajectory, both in terms of species and rate of growth, so that maximum ANPP is not achieved at the same “slice” in time. As a result, extrapolations made and conclusions drawn about one “slice” in time may not be representative of actual stand behaviors and site characteristics. Our objective is to qualify the multiple trajectories of stand development that occur in one watershed (WS01) in the H.J. Andrews Experimental Forest (HJA) following clear-cutting and determine if an estimations of maximum productivity (predicted from maximum likelihood estimators) differ from and may better represent temporal and spatial heterogenity when relating ANPP to site characteristics, environmental conditions, and forest history.