The alien weed flora of the Argentine Pampas: disentangling the ecological and historical patterns involved in its formation

SANTIAGO POGGIO; FEDERICO MOLLARD

Kapsovar

Simposio; XV European Weed Research Society Simposium; 2010

European Weed Research Society

Naturalisation of plant species introduced into a region is limited by several geographic, biotic, and abiotic barriers regulating species dispersion and perpetuation. In agroecosystems, these ecological filters define the regional species pool of alien weeds. We studied how alien weed richness increased in the Pampas from early agriculture expansion to the present (1877-2007). Our study is based on a comprehensive biographical revision including floras, manuals, and scientific and technical publications. Species number was accumulated according to the year of first report of an alien weed species in the region. Total species richness was 260. Most species were annuals (53%) native from Eurasia (78%). We identified three periods of richness accumulation of alien weeds. Richness first sigmoidally increased (1877-1935). These periods coincides with the notable increase of rural population, railroad network and row-crop area in the Pampas, suggesting high propagule pressure, dispersal, and open site availability. Richness linearly increased during the second phase (1937-69 1.6 spp/yr), while there were not significant change during the third stage (1970-99 0.3 spp/yr, P = 0.06). No new alien weeds were recorded after 1999. The turning point (1969 CI95% = 4.9) coincide with the start of agriculture intensification, which implied the increase of herbicide use and the implementation of phytosanitary measures to prevent the presence of weed seed contaminants in crop seeds entering the country. These practices hence constrained propagule pressure and receptivity of cropped areas. Our results highlight the importance of anthropic factors in modulating alien plant introduction and naturalisation into agricultural regions.