Print PageCompetition is a major determinant of plant growth and is often used in studies of tree growth and species coexistence. However, these approaches are usually temporally static, i.e., assessed at a single point or period in time. While constantly changing forest conditions due to natural and human-induced disturbances potentially alter competition among individuals, static approaches cannot qualify the temporal variability of competitive interactions. Here we present a longitudinal analysis of competitive interactions among trees and discuss the implication of our results for ecological interpretation. Spatially-explicit tree growth data were obtained from 18 study plots (0.4 ha each) in sugar maple (Acer saccharum Marsh.) stands in Quebec, Canada. During the studied period (1980 – 2003), these stands had been disturbed by insect outbreaks (forest tent caterpillar, Malacosoma disstria Hubner) and by commercial partial harvest. We analyzed radial growth rates (outcome of competition) on an annual basis and as a function of tree biology (bole diameter, crown position), competition (above- and belowground competition from neighbors) and environmental conditions (light availability, harvest disturbance).
Results/Conclusions
Competitive interactions changed throughout the studied period. Canopy disturbance from partial harvest interacted with defoliators and influenced competition symmetry by favoring smaller trees. Competitive interactions seemed to have switched from below- to above-ground following canopy recovery after harvest. Release from competition due to partial harvest increase neighborhood size (radius of effective competition) and enhanced the competitive pressure from larger individuals. Our results also show that temporal variability in competitive interactions could contribute to the maintenance of high tree species diversity and structural complexity in some ecosystems by temporally altering species-specific responses to environmental change and disturbance.
