The effect of spatial scale on evenness

The effect of spatial scale on species evenness has not previously been inv estigated. As the area of each sample of vegetation (i.e. the spatial grain ) increases, evenness could in theory increase, decrease, or stay the same, though the simplest model predicts an increase. We use biomass data from f our dune slack sites and two semi-arid grasslands, sampled to allow calcula tion of evenness at a range of spatial grains. In all six sites, evenness d ecreases as grain size increases, almost monotonically. It is hypothesized that such a pattern is a result of a general feature of plant species abund ance distributions and of vegetation response to environmental microheterog eneity.