Livestock reduces juvenile tree growth of alien invasive species with a minimal effect on natives: a field experiment using exclosures.

CAPÓ, E. A.; AGUILAR, R.; RENISON, D.

BIOLOGICAL INVASIONS

SPRINGER

Lugar: Berlin; Año: 2016 vol. 18 p. 2650 - 2943

1387-3547

Manyalien invasive tree species were originallyintroduced to their non-native ranges for use in forestry and as urban trees.These alien species were selected for their fast growth and not necessarily forpossessing mechanisms which deter browsing. Instead, many tree species native to semiarid areas of the worldevolved mechanisms which deter browsing, presumably at the cost of slowergrowth. In a semiarid rangeland we observed that livestock exclusion greatly promotedthe growth of juveniles of several alien species but not of native species, and we hypothesized that this increase ingrowth of aliens was due to livestock preference for alien and not native trees.With the objective of quantifying our observations and understanding themechanism underlying the increased growth rates of alien juvenile trees underlivestock exclusion, we assessed growthand browsing levels in juveniles of two alien invasive and four abundant nativetree species within three parcels where livestock was excluded and threeparcels with livestock at 0.20 cattle equivalents.ha-1. Alienspecies grew around four-fold faster under livestock exclusion than withlivestock and, as predicted, received five times more browsing than natives.Instead, native species did not significantly increase their growth rate withlivestock exclusion. The results support our hypothesis and the implicationsfor management would be that stocking paddocks with livestock to browseexisting alien juveniles and re-growth of felled adults should be effective indelaying invasions of trees used for forestry without significantly affectingthe growth of the most abundant native trees.