Applying plant–plant interaction theory to advance tropical dry forest restoration

Key message

Species interactions should be considered during the design of restoration plans for tropical dry forests.

Abstract

Legume trees dominate old-growth and regenerating tropical dry forests with some pioneers becoming temporarily monodominant during secondary succession. Yet, the mechanisms promoting legume coexistence in this ecosystem are poorly understood but essential to develop restoration strategies for degraded forests. We studied plant–plant interactions in the regeneration niche of an early and a late successional legume tree species, increasingly co-occurring in northwestern Mexico due to persistent climatic and anthropogenic disturbance that is altering forest dynamics. Our experiment comprised two species (Acacia cochliacantha, typical early successional and monodominant, and Lysiloma watsonii, typical late successional) × two habitats (direct light and shade) × three plant interaction treatments (control, intraspecific and interspecific). Each of the 12 experimental units contained 20 pots, totaling 240 replicates. We examined germination, seedling survival, and growth dynamics and determined seedling dry mass (total and root: shoot) at the end of the experiment. Our results suggest that legume monodominance in regenerating tropical dry forests starts early during germination and may be temporarily maintained through the interplay between interspecific facilitation and intraspecific competition. In contrast, late successional species may avoid negative heterospecific interactions by recruiting later (benefiting from neighbors’ shade) and maintaining neutral associations with conspecifics since early ontogenetic stages. Therefore, a cautious selection of early and late successional species and their spatial arrangement should be considered during the planning stage of restoration programs for tropical dry forests. Advancing our understanding of plant interactions in tropical dry forests should lead us to develop better tools for restoring this highly degraded ecosystem.