A Comparison of Moisture Scalars and Water Budget Methods to Assess Vegetation-site Relationships

Quantification of vegetation-site relationships is often required in biogeographic research. Methods linking species to particular sites typically assess evaporative demand and soil moisture availability at the site, though methods differ in how these factors are assessed. This study compares three approaches—a water-budget approach, and field-based and map-based moisture scalars—in their ability to predict the occurrence of a single species, American beech (Fagus grandifolia), observed in 102, 0.04 ha plots in SE Ohio. Actual evapotranspiration and deficit provided results superior to field-based and map-based scalars. Map-based techniques are potentially limited at fine spatial scales, due to the large discrepancy between observed topographic variables, and those modeled with 7.5-minute elevation grids. The study concludes that a water budget approach is applicable to a wide range of studies exploring vegetation-site linkages. It has advantages of being objective in its computation, and applicable at a wide range of spatial scales. Perhaps most importantly with regard to global change research is the dynamic nature of the method: a site's classification will change concurrently with changes in climate. [