Effect of grazing and harvesting on diversity, recruitment and carbon accumulation of juvenile trees in tropical dry forests

Abstract

We investigated the effect of grazing and harvesting on diversity, mortality, recruitment and carbon accumulation of juvenile trees at five sites in a tropical dry forest (TDF) to address the questions: (i) How is the TDF structured in terms of juvenile trees and their carbon densities? (ii) What is the level of biotic disturbances in the TDF which affect juvenile tree population? And (iii) what is the relationship between species mortality and recruitment in the sites having different disturbance intensities? Across the sites, we recorded juvenile individuals in 41 species belonging to 22 families. Wood specific gravity (WSG) among species varied between 0.36 and 0.66 g cm⁻³. Carbon density in the juvenile tree populations ranged from 271 to 966 kg-C ha⁻¹ and carbon accumulation from 10 to 210 g-C cm⁻² yr⁻¹. Mortality due to browsing, harvesting, and drought was respectively, 41%, 47% and 12%. Significant differences across sites were observed for species richness, carbon density, carbon accumulation, numbers of dung pellets and damaged juveniles, annual mortality index (AMI) and annual recruitment index (ARI). Species also differed significantly for AMI and ARI. Species richness, carbon density and carbon accumulation were negatively related with AMI and positively with ARI. Soil moisture content, total N and total P across study sites also favored juvenile recruitment. The findings suggest that mortality of juvenile trees in TDF is mainly due to browsing and harvesting. The future floristic composition and carbon accumulation of TDF will depend upon the status of juvenile trees. Therefore, it is important to restrict the livestock grazing in the forest and to particularly protect the juveniles of the dominant canopy trees and those with high carbon accumulation potential.