DISCUSSION
Studies of local adaptation are severely lacking for rainforest tree
species that are key to restoration efforts. While meta-analyses are
useful to discern drivers of local adaptation in studies across multiple
species (Leimu & Fischer 2008, Hereford 2009, Matesanz &
Ramirez-Valiente 2019), these studies often vary in methodology, site
maintenance and conditions that are not easily accounted for. In this
study, we used three common garden sites to investigate the effects of
site, provenance, and their interaction on the growth and survival of 16
tree species commonly used in restoration plantings in the Australian
Wet Tropics. Site effects were observed in 50% of species for survival,
93% for height increment, and 79% for inherent growth rate. Provenance
effects were noted in 38% of species for survival, 36% for height
increment, and 57% for inherent growth rate. Interestingly, the lowland
provenance generally outperformed the upland provenance regardless of
site. We found a negative correlation between species wood density and
the magnitude and direction of provenance differentiation (mean
sympatric/allopatric comparisons of local adaptation) in both survival
and height increment (but not inherent growth rate). This suggests that
local adaptation may be more evident in faster-growing species, with no
differences or potential maladaptation for slower-growing species, but
further monitoring is needed to determine if these preliminary patterns
hold. These results challenge the usefulness of a ‘local is best’
provenancing strategy for upland restoration plantings in the Australian
Wet Tropics and help to fill the gap in our understanding of the extent
of local adaptation in tropical rainforest trees globally.