The effect of treefall gaps on the understorey structure and composition of the tropical dry forest of Nizanda Oaxaca Mexico: implications for forest regeneration
Dechnik-Vázquez Y.A; Meave J.A; Pérez-García E.A; Gallardo-Cruz J.A; Romero-Romero M.A
Journal of Tropical Ecology
The role of canopy gaps in tropical dry forest (TDF) dynamics remains unclear. Here 75 canopy gaps mostly formed by the fall of Bursera spp. and Pachycereus pecten-aboriginum individuals are described and their potential consequences for forest regeneration are analysed in a Mexican TDF. In 50 randomly selected gaps understorey vegetation was sampled with a paired design (inside and outside gaps) and by distinguishing two plant height categories. In total 1940 plants were recorded (63% in gaps and 37% in non-gap plots). Community attributes (density community cover taxonomic richness and Shannon diversity) were significantly higher for both height categories in gap plots. Conversely neither an NMDS ordination nor a multinomial classification of 187 species by habitat affinities revealed floristic segregation between gaps and non-gaps; almost all species were classified as habitat generalists with only a few opportunistic forbs (but no single tree species) being classified as gap specialists. The most important effects of gap formation are significant increases in plant abundance and species richness but not a different species composition. Against earlier views that gap-phase dynamics is inconsequential for TDF dynamics these results suggest a more active albeit modest role of treefall gaps in TDF through promoting an abundant establishment.