Print PageStrategies for conserving plant diversity in agroecosystems generally focus on either expanding land area in non-crop habitat or enhancing diversity within crop fields through changes in within-field management practices. In this study, we compare effects on landscape scale species richness from such land sharing or land sparing strategies. We collected data in arable field, grassland, pasture, and forest habitat types (1.6 ha sampled per habitat type) across a 100 km2 region of farmland in Lancaster County, PA, U.S. We fitted species area curves (SACs) for each habitat type and then combined extrapolations from the curves with estimates of community overlap to estimate landscape scale richness. We then modified these baseline estimates by adjusting parameters in the SACs to compare potential effects of land sharing and land sparing conservation practices on landscape richness.
Results/Conclusions
We found that the richness of the habitat types showed a strong inverse relationship to the relative land area of each type in the region, with 89 species in arable fields (66.5% of total land area), 153 in pastures (6.7%), 196 in woodlots (5.2%), and 213 in grasslands (2.9%). For a hypothetical landscape 1km in radius (314.5 ha), our model estimates 529 plants species in the baseline scenario. Major changes in the richness of arable fields increased landscape scale richness to 545 species, while a modest conversion of cropland into grassland habitat increased richness to 542 species. Sensitivity analysis of our model indicated that relative gains from land sparing would be greatest in landscapes with a low amount of non-crop habitat (<~10%) in the baseline scenario. These results indicate that the majority of plant species in agroecosystems are found in small fragments of non-crop habitat and suggest that especially in landscapes with little non-crop habitat, richness can be more readily conserved through land sparing approaches.
