Agricultural mosaics: Novel ecosystems in the Rolling Pampas of Argentina

Background/Question/Methods

The Pampas plains, originally covered by grasslands communities organized by small topographic differences, and rainfall and temperature gradients, were developed into an agricultural mosaic.  Human activities altered the natural heterogeneity and introduced new organisms assembling novel ecosystems. Our aim is to highlight the contribution of anthropic elements in farmland mosaics to retain biodiversity and its associated ecological functions and services.  We describe the different elements (land use, cropping activities, field size, road and fence networks, rural homesteads and woodlots).   We also analyze the proportion of the area occupied by each element type and its contribution to the overall diversity. We performed physiographic and physiognomic studies together with plant surveys over the different landscapes in the Rolling Pampas and during a series of years. We also used surveys and trapping to study bird, arthropods and small rodents.  Species richness and abundance were determined for the different taxa and landscape elements. Fauna was also classified according to functional characteristics. Elements´ area was determined, and they were further classified in a hierarchy according to area and species contribution to the agricultural mosaic biodiversity.

Results/Conclusions

Cropland occupy between 85 and 95 % of the mosaic area, whereas the remaining surface is occupied by linear or patch elements such as fence-sides, road sides, woodlots, homesteads, water bodies and abandoned land, each one covering less than 1%. These small area elements contribute the most to sustain the plant diversity of farmland mosaics, since the overall arable plant communities represent c. 30 % of the regional flora. Water bodies and trees, which are novel elements in the Pampas, are important drivers of bird richness and abundance. Similar patterns are observed for arthropods. Predator, parasitoid, and pollinator richness and abundances are also greater in the small surface elements. Interestingly, exotic flowering plants are providing flower resources to native bees. There is evidence that spill-over (the increase of species richness in local communities through seed dispersal from nearby habitats) account for the assembly of biotic communities in the large area cropland occupies. Human activities, on one hand, have increased the abundance and frequency of small area elements in the mosaic, which retain most of the farmland biodiversity and sustain ecosystem function and services. On the other hand, agricultural intensification is changing this trend by both reducing their frequency and impoverishing the habitat quality of these small landscape features.