The effects of partial defoliation on photosynthesis, whole-seedling carbon allocation, partitioning and growth
were studied for two species with contrasting foliar traits. Field-grown seedlings of deciduous Japanese larch
(Larix leptolepis) and evergreen red pine (Pinus resinosa) were defoliated by hand in early summer for 2 consecutive
years. In the first year (1990), seedlings were defoliated by removing the distal 0, 25, 50 or 75% of each needle.
In the second year (1991), seedlings were defoliated either 0 or 50%, regardless of previous defoliation treatments.
Defoliation had little effect on photosynthesis and starch concentration in whole seedlings of either species in the
first year. In the second year, photosynthesis increased in both species in response to the 1991 defoliation
treatment, and in red pine also increased in response to the 1990 defoliation treatment. Further, in 1991 both larch
and pine had decreased whole-seedling total non-structural carbohydrate concentrations in all seedlings that were
defoliated at least once over the 2-yr period. This decrease was noted mostly in the starch component of the non-structural carbohydrates, and was similar in both species. In 1991, biomass was similarly decreased in both species
in response to 1991 defoliation. Both species showed overcompensation in total and component biomass in
seedlings defoliated by 25% in 1990. Overall, the results do not support the widely held belief that evergreen trees
are substantially more affected than deciduous trees by defoliation.