Small gap creation in Belizean mangrove forests by a wood-boring insect

We investigated the role of wood-boring insects in the creation of light ga ps within mangrove forests. We compared the frequency of gaps caused by woo d borers to other gap-forming processes and characterized the physical attr ibutes of light gaps in mangrove forests on small islands in Belize. Method s of quantifying light gaps included aerial photography, ground surveys, an d experimental plots. Small light gaps (less than or equal to 12 m(2)) were very common in Rhizophora mangle fringe, comprising almost: 22 percent of these forests. Rhizophora mangle gaps were smaller than gaps in Avicennia g erminans forests. In R, mangle forests, gaps were caused by branch death, a nd in R germinans forests, gaps were caused primarily by downed trees. More than 91 percent of the gap-forming branches and boles in the R. mangle fri nge were killed by a wood-boring cerambycid beetle, Elaphidion mimeticum, i ndicating that it is the major cause of small-scale disturbances in these f orests. No trees or branches in the A. germinans forest were attacked by th is beetle. In R. mangle forests, small gaps had significantly higher light levels and soil temperatures than areas under the closed canopy; however, s oil conditions for sulfide concentrations, porewater salinity and redox pot entials were similar in small gaps and under the closed canopy. Survival of R. mangle, A. germinans, and Laguncularia racemosa seedlings was also high er inside these small gaps, indicating their importance in regeneration of mangrove forests. Feeding by wood borers is thus an important type of indir ect herbivory in mangrove forests, with a critical role in ecological proce sses such as gap dynamics.