Exotic vs. native species dominance in modern successions: 20 years of vegetation recovery in pampean farmland

TOGNETTI, P.M.; CHANETON, E.J.; OMACINI, M.; LEÓN, R.J.C.

S.C de Bariloche, RN, Argentina

Congreso; VI Southern Connection Congress; 2010

Invasive exotic plants are major constituents of species pools in modern landscapes. Thus, managing succession requires an understanding of novel trajectories in mixed, native/exotic plant assemblages. We examined trends in native and exotic species abundance over 20 years of spontaneous succession on set-aside farmland in the Inland Pampa, Argentina. Changes in plant cover and species richness were monitored annually on eight permanent plots established in different years (1978?1989). Both native and exotic species occupied early, mid and late successional niches, and exhibited similar life-form replacement patterns, from annual forbs, through annual to perennial grasses. Exotic plant richness declined with plot age, and a few exotic grasses remained dominant through succession. While native perennial grasses slowly increased in richness, only underwent transient abundance peaks. Cluster analysis allowed us to identify alternative community states connected by a network of successional pathways. The system?s dynamics comprised directional trajectories, non-directional loops, and arrested community states dominated by exotic grasses. Our results illustrate the overwhelming role of exotic species in modern succession, and their potential to hinder restoration of native communities on agricultural land. Meeting conservation goals through restoration may require large subsidies, including exotic plant removals and native grass seeding under prescribed disturbance regimes