Document: AND-3-93-5

The effects of spatial pattern on diversity-productivity relationships in a northern mixed grass prairie.

DAVIDSON, A.* ¹, F.CSILLAG ¹ and M.KERTÉSZ ²

University of Toronto, Toronto, ON, Canada. ¹
Hungarian Academy of Sciences, Vácrátót, Hungary. ²

Abstract:
We present an operationally feasible measurement scheme relying on the spatial organization of vegetation for the investigation of grassland diversity-productivity relationships. We hypothesized that stronger fine-scale organization of species within a moderately varying community is associated with (a) higher production, and (b) lower patchiness of production. The assessment of species composition and ecosystem functioning requires finding the appropriate scale for comparison under natural field conditions. Using a geographical information system, we identified three 1ha sites along a resource gradient in the strongly moisture-limited northern mixed-grass prairie (Grasslands National Park, Saskatchewan, Canada). These sites were located in representative undisturbed Stipa-Bouteloua-Agropyron upland communities (primarily above 900m a.s.l. and 50-100m above the floodplain of the Frenchman River). Two sampling transects were positioned within each site. Productivity was characterized by spectral radiometer observations (0.5m resolution) of the normalized difference vegetation index (NDVI) and estimates of leaf-area index (LAI) arranged in a scalable sampling scheme between 0.4m and 50m. Species occurrences were recorded along semi-circular transects allowing scaling between 0.05m and 25m. A wide range of correlations were found between diversity and productivity measures as a function of spatial resolution (e.g. LAI vs. species richness; R²=0 (0.05m) to R²=0.5 (2m)). We demonstrated possible inferences about spatial and temporal characteristics of production based on the number of local species combinations (NRSC). NRSC, as a function of sampling resolution, had a characteristic maximum predicted by patch-level productivity pattern with significantly better confidence than species richness. These observations suggest that single-scale measures are potentially insufficient for the long-term monitoring and prediction of ecosystem structure and functioning. To characterize diversity-productivity relationships under natural conditions scalable observations should be applied with diagnostic statistical models.

Keywords: diversity, productivity, scaling, sampling resolution, remote sensing

This abstract is being presented at: 9:15 AM in session:
Oral Session #58: Landscape Ecology.