Viewpoint: Implications of spatial variability for estimating forage use

Estimates of forage use are often the basis for important management decisions (e.g., determining carrying capacity and setting stocking rates). Using both hypothetical and field data, we examine the impacts of rangeland spatial heterogeneity and various analysis protocols on estimates of forage use. When using the paired-subplot method, we recommend that the size of caged and uncaged subplots accomodate local heterogeneity to ensure accurate forage use estimates. We further recommend that the type of analysis procedure be determined by the context of the question; phytomass differences when an investigation is herbivore-focused, and relative utilization for plant community studies. All investigations of forage use should employ (field original, or untransformed) data to assess natural variability in forage production and to minimize the degree of confoundment between forage use and spatial heterogeneity. When analyzing these data, non-directional, 2-tailed statistical tests are recommended, particularly in arid (and thus, spatially variable) environments, to avoid bias in the estimate and to facilitate reliable interpretation of the data.