Black Carbon in Seasonally Dry Tropical Forests of Costa Rica.

Seasonally dry tropical forests (DTF) in Costa Rica burn frequently. The amount and dynamics of fire-derived black carbon (BC) in DTF soils is, however, not known. Thus, for credible C budgets a better understanding of the role of BC in DTF soils is needed. We compared total organic C (TOC), BC and chemically oxidized C fractions in 0- to 10-cm depth at repeatedly burnt 60-yr old Quercus oleoides (Qu) and >100 yr old mature (Mf) forests at Santa Rosa National Park, Costa Rica. BC was determined by chemical oxidation followed by solid-state ¹³C nuclear magnetic resonance spectroscopy. The TOC concentrations at Mf were higher than at Qu (61.3 g C kg^-1 vs. 45.8 g C kg^-1). Preliminary results indicated that 15.2 % of TOC at Mf were in the form of BC whereas 11.6 % of TOC at Qu were BC. However, only 6.3 % of TOC at Mf was non-oxidizable by treatment with Na₂S₂O₈ but 12.0 % of TOC at Qu. Yet, BC may contribute less to SOC stabilization in DTF soils compared to biological, chemical and physical stabilization mechanisms. BC plays probably are more dynamic role in soils than previously thought. As the likelihood of tropical forest burning may increase by climate change, studies on the effects of increased fire frequency on BC dynamics in DTF in relation to soil type, climate, biota (e.g., microbial community, ants, termites), and land use are therefore needed.