Towards an optimal management of the invasive plant Rubus niveus in the Galapagos Islands

Abstract

Management actions to mitigate the impacts of invasive plant species require knowledge of the mechanisms influencing invasion success and anticipating interactions with various control options. To meet this need, I examined the impacts of the invasive plant Rubus niveus on the native communities of the Scalesia forest of Santa Cruz Island; its competitive abilities compared to some native, woody, species; and, factors affecting the invasion process. This knowledge was then used to evaluate and understand the failure of a five year eradication attempt of R. niveus on Santiago Island. Increasing densities of R. niveus had a negative effect on plant diversity and abundance also resulting in changes of forest structure. Experimental plots were used to elucidate mechanisms of how it displaced native species. Rubus niveus showed a faster growth rate and biomass production than native woody species; it also had a vastly larger seed bank. Increasing sunlight positively affected the growth, biomass production and reproduction of adult plants whereas germination was optimal at intermediate light conditions. Conversely, water stress affected mainly the performance of R. niveus whereas native species were more resilient. Although increasing native canopy cover negatively affected density of R. niveus, it still survived under low light conditions. The implication is that R. niveus rapidly invades after individual tree-falls or stand dieback but also is capable of invading undisturbed forest. After five years of intensive management of R. niveus in Santiago Island eradication seems unlikely. The invasion area continues to expand because: a failure to find all plants before they fruit, bird dispersal over long distance and the ability to colonize undisturbed areas and outcompete native vegetation. Furthermore, management actions have altered ecosystem processes. A more strategic paradigm in needed for R. niveus in Galapagos.