Controlled environment treatments were applied to assess the effects o
f temperature on the seedling mortality and growth rates of Toona aust
ralis and Flindersia brayleyana, two tropical rainforest tree species
from northeast Queensland, Australia. Past workers have assigned these
two species to the same ecological niche in terms of their response t
o canopy disturbance and gap-phase regeneration; however, their geogra
phic ranges are very different. The hypothesis was that the species co
nfined to the warm tropics (F. brayleyana) would have higher seedling
mortality and a slower growth rate at lower temperatures than the spec
ies that occurs over a wide latitudinal range from the warm tropics to
cooler temperate environments (T. australis). Significant differences
were found in the growth rates of these two species in the warm (29/2
2 degrees C) and cool (22/10 degrees C), but not the intermediate (24/
16 degrees C), day/night temperature regimes. Their growth rates both
decreased with decreasing temperature, but the decrease was significan
tly less for F. brayleyana which had the faster growth rate and lower
seedling mortality in the cool regime. These results led to the reject
ion of the hypothesis and a test of the assignment of these two specie
s to the same ecological niche. The test involved monitoring their gro
wth to sapling-size in the intermediate temperature regime together wi
th four other co-occurring tropical rainforest tree species belonging
to different ecological niches. The growth rates and proportions of ab
oveground biomass allocated to woody tissue distinguished T. australis
and a fast-growing pioneer species from F. brayleyana and three prima
ry forest species. The stem heights and aboveground biomass of T. aust
ralis and the pioneer species exceeded the other four species by facto
rs ranging from two to five. It is concluded that T. australis does no
t belong to the same ecological niche as F. brayleyana, and it is reco
mmended that more research be conducted on the ecotypic temperature re
sponses of the taxon T. australis.