Tree seedling regeneration in a degraded tropical landscape: Barriers to tropical pasture restoration in Los Tuxtlas, Mexico

Background/Question/Methods

The current scale of deforestation and continuing decline of tropical forests underscores an important need to restore degraded tropical landscapes. Research here focuses on highly degraded habitats, such as pastures, where forest regeneration may be impeded or no longer possible. The study site, a former cattle-ranching pasture, borders the tropical rainforest of Los Tuxtlas (Veracruz, Mexico). Approximately 16% of the Los Tuxtlas original rainforest cover remains today, with 5% remaining as continuous forest. To determine tree recruitment success within pasture habitat, seed-seedling experimental exclosures were built to mitigate herbaceous vegetation and abundant pasture fauna. Experimental exclosures tested 1) the degree that pasture herbaceous vegetation inhibits or facilitates recruitment of tree species, 2) the intensity of seed and seedling removal by pasture fauna, and 3) the prevalence of life-history traits that correlate with seedling establishment success. 

Results/Conclusions

Preliminary analyses reveal that herbaceous vegetation and exposure to rodent fauna significantly limit tree seedling recruitment in degraded tropical pastures. After 12 months, seven out of sixteen tree species recruited of which six were categorized as being large seeded with weights ranging from 6.5 to 0.117 grams. Overall, these results are consistent with earlier studies suggesting grass provides a recruitment barrier for tropical tres yet, rodents represent an even larger barrier to recruitment. Furthermore, grass and rodents interact as a recruitment barrier, perhaps reflecting other ecological processes, such as predation risk on rodents and safety of grass cover.