CANOPY CLOSURE RATE AND FOREST STRUCTURE

Natural disturbances produce openings in forest canopies. Gap opening and closure create a mosaic of regenerating phases in the forest, whic h are a source of environmental heterogeneity, contributing to the mai ntenance of community diversity. In this study we measured the rate of canopy closure using hemispherical photographs taken in the same poin ts in August 1992, 1993, and 1994 at three temperate forests in Britai n. We analyzed the change in percentage canopy openness in time and fo und that canopy closure occurred exponentially. These results were use d to build a matrix model that incorporated canopy dynamics as a linea r Markov-chain process of forest succession by classifying forest patc hes into types (according to percentage canopy openness) and calculati ng the probability of each patch type becoming the following patch typ e in one year's time. Standard matrix analysis allowed us to project f orest structure (i.e., the proportion of patches of each type) at equi librium, and to explore the effect of different disturbance rates on c anopy dynamics. Simulations showed that higher disturbance rates resul t in a lower proportion of the forest under closed-canopy conditions, and that variation in disturbance rate has a dramatic effect on turnov er rate. Forest dynamics studies could be based on a patch characteriz ation system based on a quantitative scale of percentage canopy openne ss, which would make comparisons between forests possible.