Planting density effects and selective herbivory by kangaroos on species used in restoring forest communities

Abstract

We used exclosures to assess 16 plant species for the effects of planting density and kangaroo herbivory at two recently rehabilitated bauxite mines in eucalypt forests of southwestern Australia. Despite significant climate differences the browsing trends at both mines were similar. By the first harvest (2 months after establishment) there were significant reductions in shoot mass and survival for five species exposed to browsing, while plants at high density were 25% smaller than widely spaced plants. By the second harvest (10 months), this increased to 7 of the 16 species, while spacing effects diminished. We showed the effects of herbivory to be profound, while interactions at the seedling stage were minimal. Species with higher levels of protein were not favoured, while those highest in tannins, salts and sulfur were usually avoided. As with other medium-sized herbivores, plant architecture (leaf shape) was a prominent selective agent: in this case, grasses and grasslike species were most likely to be selected and adversely affected, though some dicots were readily consumed. Browsing optimization (benefiting from herbivory) was identified in three native legumes with high growth rates. In our study, herbivore choice often equated to herbivore impact; however, future planting in rehabilitated areas should allow for resilience and compensation by some species. We offer suggestions aimed at broad silviculture practices: we showed that some species benefit from herbivory and suggest these be identified by land managers as they may serve as diversions for nearby rare or vulnerable species.