Intervenciones para rehabilitar sistemas silvopastoriles degradados: Una oportunidad para las especies vegetales exóticas

Abstract

Interventions needed for degraded natural ecosystems rehabilitation create an opportunity for the establishment of exotic species. In caldén woodland areas in the semi-arid Pampas region, proven techniques for grassland recovery generate disturbances of varying intensity, ranging from soil removal with the total elimination of plant cover to partial aerial phytomass reduction. The objective was to evaluate the exotic plants species entry in communities subjected to different interventions and their permanence at different times from the last intervention. Treatments included bulldozer with rake, roller, and a prescribed burn. For the bulldozer intervention, the control and disturbed treatments were defined. For the rest, the following were established: control, burned, rolled and rolled + burned. In each of them, a gradient from the edge to the interior of the community was considered. For the capped areas, evaluations were carried out after one year, at five for the rolled ones and at three for the burned and rolled + burned ones. Coverage of species in the grassy-herbaceous stratum, total cover of vegetation and brush, and proportion of soil without cover were determined. A total of 79 species were recorded, 23% were exotic. In the bulldozer intervened areas, its proportion reached 33% (23% in the control). In the other interventions, their contribution was 26% in rolling, 21% in burning, and 28% in rolled+burned (18% in the control). Regarding the intensity of the disturbance, in those rolled areas or intervened with a bulldozer, the exotic species proportion was higher. The areas towards inside community and without disturbance (or with low intensity disturbances [e.g., prescribed burns]) showed a lower invasion level. After five years the communities recovered the coverage of the perennial grasses of the grassland, but a high proportion of exotics that exceeds that registered in the control one.