CANOPY CLOSURE RATE AND FOREST STRUCTURE

Abstract

Natural disturbances produce openings in forest canopies. Gap opening and closure create a mosaic of regenerating phases in the forest, which are a source of environmental heterogeneity, contributing to the maintenance of community diversity. In this study we measured the rate of canopy closure using hemispherical photographs taken in the same points in August 1992, 1993, and 1994 at three temperate forests in Britain. We analyzed the change in percentage canopy openness in time and found that canopy closure occurred exponentially. These results were used to build a matrix model that incorporated canopy dynamics as a linear Markov-chain process of forest succession by classifying forest patches into types (according to percentage canopy openness) and calculating the probability of each patch type becoming the following patch type in one year’s time. Standard matrix analysis allowed us to project forest structure (i.e., the proportion of patches of each type) at equilibrium, and to explore the effect of different disturbance rates on canopy dynamics. Simulations showed that higher disturbance rates result in a lower proportion of the forest under closed-canopy conditions, and that variation in disturbance rate has a dramatic effect on turnover rate. Forest dynamics studies could be based on a patch characterization system based on a quantitative scale of percentage canopy openness, which would make comparisons between forests possible.