Abstract
A modified Loomis-William model was originally developed to estimate the theoretical maximum yields of crops. That model was adapted in this paper to measure how much of the theoretical maximum potential productivity (tNpp(tmax)) is reached in any forest due to edaphic and climatic limits to growth, i.e., its "Ecosystem fit" (eFit). The procedure to calculate eFit has not been published except as a concept. Our goal is to describe the methodology in sufficient detail to facilitate its use by the scientific community and forest managers. To calculate eFit you need: 1) to convert all photosynthetically active radiation to a photosynthetic product for each forest plot or stand to calculate its tNpp(tmax), and 2) use field-collected data of total observed net primary productivity (tNpp(obs)). Theoretical maximum potential tNpp is calculated with a simple light-use efficiency model as the product of the efficiency at which forest canopies absorb solar radiation, the photosynthetic conversion efficiency into biomass, and remotely sensed solar radiation with temperature data extracted to the geographic coordinates for the site. Ecosystem fit represents a forest's realized percent productive capacity and is the ratio of field-collected tNpp (i.e., tNpp(obs)) to the theoretical maximum potential tNpp (i.e., tNpp(tmax)).•Available indices to assess forest productivity and adaptive capacity to land-use disturbance and climate change are sensitive at the small-to-meso spatio-ecophysiological scales.•A more holistic index (such as eFit) will provide an informative picture of forest conditions where management practices are undertaken and the ecosystem's capacity to adapt to environmental change.•A comparison of eFit across similar forests within a climatic zone is an indication of the stressors or constraints that are being imposed locally and that limit tNpp(obs.)