How tree communities respond to distance to edges and canopy openness

Tropical forests frequently experience the opening and closing of canopy gaps as part of their natural dynamics. When an edge is created, and the area outside the boundary is a disturbed or unnatural system, forests can be seriously affected even at some distance from the fragmented edge, since sunlight and wind penetrate to a much greater extent. This increases tree mortality and, consequently, canopy openness close to the edge. Thus, canopy openness can be both part of a natural gap-dynamics cycle and the direct manifestation of human edge effects.

A new study, published in Tropical Conservation Science, investigates how tree communities respond to both distance to edges and canopy openness in a tropical montane forest at Las Cruces Biological Station, SW Costa Rica. Luis Cayuela of the Universidad de Granada in Spain and colleagues found that proximity to the forest edge does not increase the rate of canopy openness. When looking closely at the separate effects of edges and natural canopy gaps, a small or even negligible effect of edges on tree structure, diversity and composition was found, whereas natural canopy gaps exerted a stronger influence on these variables. The study concluded that edge effects may be minimized — or even suppressed — in older fragments through the sealing of edges by a thick growth of thin stems and through lateral growth of tree crowns; whereas canopy gap formation remains an active force that can create micro-environmental conditions that have significant effects on plant communities.