1 We hypothesized that the survival of shade-tolerant juvenile trees in the
understorey depends on allocation strategies that slow their growth but en
hance recovery from herbivore damage. In contrast, allocation patterns shou
ld maximize height growth in gaps where competitors grow rapidly. We tested
the interactive effects of canopy gaps and simulated herbivory (by removin
g the apical meristem, or 10%, 50% or 90% of tissue from all leaves) on juv
enile (<1 cm diameter at breast height) Shorea quadrinervis Sloot (Dipteroc
arpaceae), a dominant canopy tree in Borneo.
2 Damage did not diminish survival over 8 months, except for 90% foliage re
moval from understorey plants. Height growth in the understorey was negligi
ble in both control and damaged plants. In gaps, height growth was stimulat
ed by removal of either the apical meristem or 10% of leaf tissue; growth w
as reduced only after 90% foliage removal.
3 Higher damage levels increased subsequent net leaf loss. Leaf production
was much greater, but leaf retention much lower, in gaps than in the unders
torey. Ninety per cent foliage removal drastically reduced production in ga
ps and retention in the understorey. After 10% defoliation, height growth w
as enhanced in gaps despite approximately 30% net leaf loss.
4 In a separate experiment. juveniles were moved from a shade house to gaps
. After 8 months, gap plants had more leaves and more total biomass, but on
ly half the root : shoot ratio of plants left in the shade.
5 Allocation patterns, together with the survival of understorey plants aft
er all but the highest levels of damage, indicate that root : shoot allocat
ion there tends to reduce the risk of mortality following herbivore or mech
anical damage at the expense of growth. In contrast, in gaps, where interfe
rence competition for light is high, resource allocation apparently maximiz
es height growth.
The interaction between resource availability and herbivore damage provides
the basis for a more synthetic theory of resource allocation and growth st
rategies than one based on resource availability alone.