02084nas a2200121   4500008004100000245008700041210006900128300001200197490000700209520161700216100002301833856010601856       2001                        eng d00aThe influence of species diversity on ecosystem productivity: how, where, and why?0 ainfluence of species diversity on ecosystem productivity how whe  a514-5260 v933 aThe effect of species diversity on ecosystem productivity is controversial, in large part because field experiments investigat- ing this relationship have been fraught with difficulties. Unfortu- nately, there are few guidelines to aid researchers who must overcome these difficulties and determine whether global species losses seriously threaten the ecological and economic bases of terrestrial ecosystems. In response, I offer a set of hypotheses that describe how diversity might influence productivity in plant communities based on three well-known mechanisms: comple- mentarity, facilitation, and the sampling effect. Emphasis on these mechanisms reveals the sensitivity of any diversity-produc- tivity relationship to ecological context (i.e., where this relation- ship should be found); ecological context includes characteristics of the surrounding environment, temporal and spatial scales of observation, and the intensity of human management. In particu- lar, the legitimacy of the sampling effect as a mechanism of productivity enhancement is dependent upon the degree to which stochastic events influence immigration and extinction processes in a given ecosystem. A mechanistic approach also requires that the three mechanisms be separated and quantified in diversity experiments, and I examine the most appropriate analyses for doing so, focusing on the overyielding technique. Finally, I question why productivity per se is a relevant management concern in non-agricultural systems once relationships among diversity, productivity, and the qualities of the surrounding environment are considered. 1 aFridley, Jason, D.  uhttps://scarabnet.myspecies.info/influence-species-diversity-ecosystem-productivity-how-where-and-why