The role of canopy gaps in the regeneration of coastal dune forest

Abstract

In regenerating coastal dune forest, the canopy consists almost exclusively of a single species, Acacia karroo. When these trees die they create large canopy gaps. If this promotes the persistence of pioneer species to the detriment of other forest species then the end-goal of a restored coastal dune forest may be unobtainable. We wished to ascertain if tree species composition and richness differed significantly between canopy gaps and intact canopy, and across a gradient of gap sizes. In three known-age regenerating coastal dune forest sites, we measured 146 gaps, the species responsible for gap creation, the species most likely to reach the canopy and the composition of adults, seedlings and saplings. We paired each gap with an adjacent plot of the same area that was entirely under intact canopy and sampled in the same way. Most species (15 out of 23) had higher abundance in canopy gaps. The probability of self-replacement was low for A. karroo even in the largest gaps. Despite this predominance of shade intolerant species, regenerating dune forest appears to be in the first phase of succession with “forest pioneers” replacing the dominant canopy species. The nature of these species should lead to successful regeneration of dune forest.