Forest Structure and Productivity along the Oregon Transect

Abstract

The Oregon Transect Ecosystem Research (OTTER) Project, conducted from 1990 to 1992, was an investigation of regional and seasonal variations in forest ecosystem processes involving carbon (C), nitrogen (N) and water. Methods of field ecology, surface meteorology, computer simulation and remote sensing were applied to the study of six primary coniferous forest sites and three fertilizer-treatment sites along an environmental gradient across west central Oregon, USA. The objective of the OTTER Project was to address two main questions: (i) can generalized ecosystem models, designed to use mainly variables to be derived from remote sensing data, explain the variation in ecosystem functioning found across the environmentally variable landscape of Oregon, and (ii) do good relationships exist between the regional variation in these driving variables and remotely sensed data? A large team of scientists supported by airborne remote sensing efforts collected a very wide range of ecological, climatological, biophysical and biochemical variables relating to net primary production (NPP), photosynthesis, evapotranspiration and nutrient cycling in these forests. The team used both a light-use efficiency model and a mechanistic ecosystem process model to predict NPP across the transect. The driving variables of each model formed the basis for the remote sensing studies. Correlative analyses and radiative transfer models were used to study the relationships between LAI (leaf area index), specific leaf area, standing biomass, foliar biomass, foliar chemistry, canopy temperature, relative humidity, vapour pressure deficit, incident and fraction of absorbed photosynthetically active radiation (PAR) and spectral reflectance from a wide variety of remotely sensed data.