Forest fragmentation alters the population dynamics of a late-successional tropical tree

Background/Question/Methods

Tropical late-successional tree species are at high risk of local extinction due to habitat loss and fragmentation. Population growth rates in fragmented populations are predicted to decline as a result of reduced fecundity, survival and growth. We examined the demographic effects of habitat fragmentation by comparing the population dynamics of the late-successional tree Poulsenia armata (Moraceae) in southern Mexico between a continuous forest and several forest fragments using integral projection models (IPMs) during 2010–12.

Results/Conclusions

Forest fragmentation did not lead to differences in population density and, even resulted in a higher population growth rate (λ) in fragments compared to continuous forests. Habitat fragmentation had drastic effects on the dynamics of P. armata, causing the population structure to shift towards smaller sizes. Fragmented populations experienced a significant decrease in juvenile survival and growth compared to unaltered populations. Adult survival and growth made the greatest relative contributions to λ in both habitat types during 2011–12. However, the relative importance of juvenile survival and growth to λ was highest in the fragmented forest in 2010–11. Our Life Table Response Experiment analysis revealed that positive contributions of adult fecundity explained most of the variation of λ between both habitats and annual periods. Finally, P. armata has a relatively slow speed of recovery after disturbances, compromising persistence of fragmented populations. Developing a mechanistic understanding of how forest fragmentation affects plant population dynamics, as done here, will prove essential for the preservation of natural areas.