Opportunistic farming of road verges reduces plant diversity and promotes weeds in intensively managed farmland mosaics

POGGIO, SANTIAGO L.

Praga

Congreso; 7th International Weed Science Congress; 2016

Agricultural intensification has promoted the loss of semi-natural habitats, which primarily resulted from cropland increase at the expense of rangeland areas, fencerow removal, and the extension of cropped areas closer to road margins. Habitat loss resulting from the rapid inception of herbicide tolerant transgenic crops has not been studied as thoroughly as introgression of engineered genes into wild relatives and development of glyphosate resistant weeds. In the Rolling Pampa, the corn belt of Argentina, semi-natural habitat loss associated with road verges has been promoted by the rapid adoption of no-tillage and soybean varieties genetically modified to tolerate glyphosate. Here, I present preliminary results from surveys of weeds and the spontaneous vegetation along road verges, whether cropped with soybean or uncropped. Surveys of road verges are also compared with others of crop fi elds and along fences in the same region. Results indicate that uncropped road verges retain a substantial share of plant diversity, particularly native species from thepampa grassland. Total richness decreased from 233 species in uncropped road verges to 60 species when these habitats were opportunistically cropped with transgenic soybean. Consequently, many native species reduced their occurrence, or even became locally extinct, especially perennial grasses and subshrubs. Wind-dispersed species, both native and exotic, were notably more frequent along uncropped road verges and fencerows, suggesting that these habitats may function as seed traps. Occurrence of conspicuous weed species in warm-season crops increased when road verges were cropped with soybean (Anoda cristata, Digitaria sanguinalis, Echinochloa crusgalli, Portulaca oleraceae). These fi ndingshighlight the critical role of uncropped road verges and fence row networks for conserving habitat heterogeneity and biodiversity in intensively managed farmland mosaics. Results presented here stress the urgent need for both discontinuing the cultivation of road verges and implementing initiatives to restore and conserve semi-natural vegetation across these patch types.