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.