Factors controlling shrub encroachment in subtropical montane systems

Abstract

AbstractAimWe aimed to assess the effects of temperature rise and neighbour removal on growth and performance of juvenile individuals of Baccharis uncinella shrubs in a montane grassland. We hypothesized that removal of neighbouring grasses and increased air temperature would enhance B. uncinella growth.LocationHigh‐elevation forest–grassland patches, southern Brazil.MethodsAn experiment with factorial design was carried out from Aug 2014 to Sept 2015 using air temperature and neighbour removal as factors with two levels each. Air temperature was increased using acrylic open‐top chambers (OTC). For the neighbour removal treatment we removed neighbouring grasses from 30 cm around randomly selected B. uncinella juveniles. Survival, growth and plant physiological status were assessed at the end of the experiment.ResultsPlants with OTCs grew more than plants without them. Neighbour removal did not have a significant effect on plant growth. These data suggest that an increase in temperature may enhance encroachment of B. uncinella in the studied grasslands, and that neighbour grasses may act as facilitators for B. uncinella shrubs by improving water balance.ConclusionsConsidering the capacity of B. uncinella to expand from forest edges towards grasslands, it is likely that montane grasslands in southern Brazil will be subject to B. uncinella encroachment within the next decades. The potential synergistic – negative – effects of global warming and habitat loss might jeopardize the high biodiversity of this ecosystem. Specific management actions and conservation public policies are needed to protect this already threatened montane system.