Assistant Professor University of Alberta Edmonton, Alberta, Canada
Tropical alpine páramo ecosystems play important supporting and regulating roles for lower elevation ecosystems, yet little is known about the drivers of ecosystem process rates in páramos, such as organic matter decomposition. Decomposition rates are known to decrease as altitude increases, but arthropod effects on decomposition vary depending on the context and the trophic level of the arthropods under consideration. Under climate change, the different abiotic and biotic drivers of decomposition rates may shift semi-independently. Thus, disentangling the relative importance of the separate drivers of decomposition rates will be important to predicting changes to organic matter accumulation in páramos going forward. I used litter bags with two mesh sizes (1 x 2 mm and 3 x 4 mm openings), placed at replicated sites at three elevations (3370, 3570, and 3770 m.a.s.l.) on the mountain Cerro Ventisqueros, Chirripó National Park, Costa Rica, to test the separate and interactive effects of altitude and presence of macroarthropods on the amount of litter mass loss after four years. Upon collection of the litter bags, I extracted and identified the invertebrates, measured soil and leaf litter chemistry, and documented plant community composition at each site. I found that litter mass loss decreased as altitude increased, and that mass loss was higher in litter bags with the smaller mesh size, which excluded arthropods with a body width greater than 2 mm. The effect of mesh size increased with altitude, suggesting that predatory arthropods inhibit decomposition rates more at higher altitudes.
