Dynamics of alien and native understorey plants following variable retention harvesting in Nothofagus temperate forests

SOLER, R; RUMPF, S; MARTÍNEZ PASTUR, G; BARRERA, MD; CELLINI, JM; PÉREZ FLORES, M; SAÁ, M; RABITSCH, W; LENCINAS, MV

Otro; 48th. Annual Meeting of the Ecological Society of Germany, Austria and Switzerland; 2018

Disturbances have frequently been shown to increase invasibility of communities by alien plants. Logging, the most common and severe anthropogenic disturbance in forests, enhances resource availability for alien plants. However, it is unclear whether and to which extant these initial changes are permanent or just temporary. Using annually surveyed permanent plots, we analyzed temporal changes of understorey structure and composition of Patagonian Nothofagus pumilio forests during 12 years under three site conditions created by variable retention harvesting: retained forest patches of 30m radius in a density of 1 patch ha-1 (AR), edges of such retained patches (DRI), retained dispersed single trees (DR); and old-growth primary forests as control (PF). Most interesting trends include that (a) AR supported a high cover of forest species in the top layer that, however, declined along the 12 years and increasing alien species became dominant at 9 years after harvesting (YAH), (b) DR and DRI supported much higher cover of aliens in the top layer and aliens became dominant at 2 to 3 YAH and started to decline, however, after a maximum at 8 YAH; (c) in the bottom layer, the cover of forest species was high at the beginning but aliens surpassed them in DR and DRI after 4 and 7 years, respectively. Tree regeneration had significant relationships with understorey dynamics, i.e. (a) in DR, a negative relationship with alien species cover and a positive relationship with native colonizers from other habitats; (b) in DR and in DRI negative relationships with alien species richness; (c) in DRI, a positive relationship with native colonizers (cover and richness). We conclude that alien plants invade Patagonian forests after logging, but decline with succession and increasing tree regeneration cover. Our results highlight the role of harvesting on facilitating plant invasions in forests, and how this depends on treatments.