Relationship between plant species diversity and grassland condition

Although the maintenance of biodiversity has become one of the goals in eco system management, the relationships of diversity to ecosystem characterist ics such as level of herbivory, productivity, and vegetation structure are still poorly understood, We examined these relationships in 8 native grassl and sites differing in grazing histories and range condition in the Mixed G rassland (6), Moist Mixed Grassland (1) and Aspen Parkland (1) ecoregions o f southern Saskatchewan. Range condition, assessed using standard methods, ranged from fair to excellent. The Shannon's diversity index followed a cur vi-linear relationship with range condition, increasing from fair to good, but decreasing from good to excellent condition, within a range between 0.6 6 and 2.58. Species evenness was affected by range condition in a similar m anner ranging from 0.44 to 0.86, Species richness varied among sites and pl ots between 4 and 28 plants 0.25 m(-2), but changed little with range condi tion. Most structural parameters, such as the cover, height, or thickness o f standing plants (live or dead) and litter, increased with range condition especially from good to excellent. The Shannon's diversity index was posit ively correlated with forb biomass, but not with biomass of any other group or their combination. Grazing regimes that maintain good range condition a lso maintain species and structural diversity of grasslands.