ABSTRACT

Restoring tropical rainforests is vital for mitigating climate change and conserving biodiversity. Appropriate seed-sourcing strategies are important for ensuring the success of restoration efforts, but require species-specific and context-dependent information, such as the strength of local adaptation. With studies of local adaptation severely lacking for tropical rainforest tree species, the current industry default is to source seed locally, which may not be beneficial in a rapidly changing climate. We therefore sought to identify the effects of provenance, site, and their interaction on the growth and survival of 16 tropical tree species commonly used for rainforest restoration in the Australian Wet Tropics. Saplings from lowland and upland populations were planted in common gardens across three field sites with contrasting climatic and edaphic conditions. We observed consistent site effects on growth, with all species performing better at the lowland, high-nutrient site compared to the lowland, low-nutrient and upland sites. Provenance effects were observed for both growth and survival, but evidence for local adaptation was mixed, with the lowland provenance often outperforming the upland provenance across most sites. Interestingly, species-variation in the effects of provenance was related to species wood density, with provenance effects more pronounced in faster-growing species. Together, these findings highlight the complexity of local adaptation in tropical tree species, which brings a note of caution to the current practice of sourcing seed locally.