Abstract:
Tropical montane forests have a large influence on the rate of ongoing climate change, but they
remain relatively understudied. This study investigated physiological and structural traits of
selected tree species aiming to understand plant traits that control shade tolerance in tropical
montane forest tree species and their response to increased temperature. Three climax and three
pioneer species were planted in pots under canopies of three different light transmittance (open,
sparse, and dense) in the Arboretum of Ruhande to study shade tolerance among species from
March 2015 to May 2016 , while other three climax and three pioneer species were planted in
pots at Sigira (high-elevation), Rubona (mid-elevation), and Makera (low-elevation) from
December 2017 to December 2018 to study effects of temperature changes on growth. Results
indicated that climax species had higher fractional biomass in leaves and branches while pioneer
species invested more into stems and these differences were greater under low radiation. The
relative growth rate of the studied species, except Harungana montana increased with
temperature from low- to mid-elevation but dropped at the high-elevation site. Leaf temperatures
in open plots were markedly higher in climax species due to their low transpiration rates and
large leaf sizes. Climax species demonstrated low thermal acclimation capacity with low growth
in the low elevation site, thus confirming that they are less flexible in their responses to rising
temperature. The results of this study confirm that tropical climax species are susceptible to
global warming and suggest that interspecific variation in shade tolerance of tropical trees is
controlled by species differences in whole-plant biomass allocation strateg
