A mechanistic understanding of invader success is essential for the effective prevention and control of invasive species under global environmental change. Indeed, global change phenomena are expected to increase the spread of invasive species, with rising temperatures predicted to have stronger positive effects on performance of invasive rather than of native plant species. Achieving this understanding is difficult, given that the effects of most drivers, including management actions, vary according to wider environmental conditions; and this context dependency is typically poorly understood. Here we achieve this understanding with an approach that integrates physiological insight, biotic interactions and biogeography, which although inherent to the concept of the ecological niche, are rarely integrated. We use a national vegetation database from Japan to understand the drivers of secondary forest invasion by giant bamboo (Phyllostachys sp.).
Results/Conclusions
A three-way interaction between temperature, solar radiation and canopy cover was important in explaining bamboo occupancy, which manifested, under high light conditions, as a shift in the thermal niche of bamboo with increasing canopy cover. At relatively low levels of solar radiation, canopy cover had little effect on the thermal niche of bamboo in secondary forests. In regions with high light intensity, canopy cover became an important facilitator of bamboo occupancy, with bamboo able to establish in secondary forests at lower temperatures when under dense canopies. However, at higher temperatures, dense canopies become more limiting than open canopies, with bamboo occupancy more likely under open than closed canopies. The additive and interactive effects of regional climate with local biotic effects translated to high spatial heterogeneity in the effect of canopy cover on bamboo occupancy. Our results suggest that reducing secondary forest canopy cover by thinning in cooler regions of Japan receiving relatively high levels of solar radiation will reduce the forest’s susceptibility to invasion by bamboo, while forest susceptibility to invasion will increase with thinning in relatively warm regions receiving high solar radiation. We mapped the effect of forest thinning on invasion probability to inform the spatial targeting of this management action.