SPECIES-AREA CURVES AND DIVERSITY-PRODUCTIVITY RELATIONSHIPS IN BEAVER MEADOWS OF VOYAGEURS NATIONAL-PARK, MINNESOTA, USA

Species richness (S) increases with area (A) as shown in the well-know n power function proposed by Arrhenius: S=cA(z). We show that the expo nent of the species area curves, z, was negatively correlated with abo veground annual production (biomass) but the coefficient of the curves , c, was positively correlated with production in two communities domi nated by grasses and sedges in beaver meadows in northern Minnesota. T he parameters of the species-area power function were not correlated w ith water table depth nor with soil nutrient availabilities. We then s how that the often-reported unimodal relationship between richness and productivity can be derived from the negative correlation of z and th e positive correlation of c with productivity. We also show that the p roductivity corresponding to maximum richness declines with increasing area sampled. All other correlations of c and z with productivity yie ld either monotonically increasing or decreasing richness with increas ing productivity. The relationships between richness and productivity depend on the area censused and the correlations of the coefficient an d exponent of the species-area curve with productivity. Interpretation s of diversity-productivity relationships are sensitive to plot size a nd require specification of the species-area relationship for the comm unity in question.