Consequences of fragmentation and forest conversion on leaf litter decomposition in tropical forests

Background/Question/Methods

Forest conversion and fragmentation are major causes of diminished ecosystem function and biodiversity loss at a global scale. Understanding landscape effects on leaf litter decomposition and recycling of available nutrients is critical for conservation, especially in diverse tropical rainforests. Here, we studied the effects of land conversion and forest fragmentation on these two processes in a tropical ecosystem. We examined decomposition and nutrient cycling during the wet season in 22 sites across four habitat types: continuous forests, large fragmented forest patches, small fragmented forest patches, and orange plantations, in the tropical moist forest zone of NW Guanacaste, Costa Rica. The study employed a two-by-two factorial design to explore the effects of leaf litter type (site-specific litter vs. control litter) and mesh size (9 mm vs. 1 mm) on decomposition rate across land cover types. Litter bags with different mesh sizes either included (9 mm) or excluded (1 mm) macroinvertebrates. We removed litter bags from the field after 3 and 8 weeks, and cleaned and weighed the contents. Additionally, we utilized Plant Root Simulator (PRS™) Probes to examine nutrient cycling of 14 cations and anions including N, P, K, Ca, and Mg in all site specific litter types and both mesh treatments.

Results/Conclusions

We found that the rate of decomposition differed depending on leaf litter type, mesh size and habitat type. Leaf litter decomposition rates differed among habitat types when examining site-specific litter but not control litter. Leaf litter decomposition rates were slower in site-specific litter than in control litter, except in orange plantations. Leaf litter decomposition was faster in 9 mm litter bags, which included macroinvertebrates, than in 1 mm litter bags. Finally, mineralization of organic nutrients differed across the four habitat types. For example, nitrogen, which is an important compound for plant cell structure and function, mineralized more quickly in orange plantations and small fragmented patches than in continuous forests or large fragmented patches. Thus, this study demonstrates that leaf litter decomposition and nutrient recycling are altered after forest conversion and tropical forest fragmentation.