Effects of Land Use History on Soil Carbon Dioxide Flux in Ecuadorian Páramo Grasslands

Abstract:

Soil carbon dioxide (CO₂) respiration is a primary mechanism for soil carbon (C) loss and is intricately linked to processes that affect soil C storage. As a result, land-use changes that affect soil CO₂ flux (Flux) rates can significantly influence regional C budgets. The páramo grasslands of the high altitude Ecuadorian Andes are important in regional C budgets due to large soil C stocks. Though some forms of land use history have been shown to reduce soil C and affect known drivers of Flux, such as soil moisture (M_S) and soil temperature (T_S), the effect of land use history on Flux and its role in páramo soil C budgets remains poorly understood. This study investigated Flux differences among sites representing four land-use histories (PA-páramo; PAB-páramo recently burned; NA-native forest; PI-planted pine forest) and assessed the role of M_S and T_S on Flux rates within and across sites. Flux, M_S, and T_S were measured over a 3-week period at the Mazar Wildlife Reserve in southern Ecuador. Flux varied significantly among site pairs, except PI and NA. Flux rates were highest in the PI (5.79 g CO₂-C m^-2 d^-1) and NA sites (5.59 g CO₂-C m^-2 d^-1), with Flux rates at PA and PAB of 4.84 g CO₂-C m^-2 d^-1 and 3.76 g CO₂-C m^-2 d^-1, respectively. M_S ranged from 29% at PI to 55% at PA, with grass sites having higher M_S than forested sites. On average, páramo soils were ~3°C warmer than forested soil, with PI warmer than NA. Across all sites, Flux was weakly, negatively correlated with M_S. Flux and T_S were positively correlated within each site except PAB; the strongest correlation (p<0.0001) was observed at PI. Our results show that in the Ecuadorian Andes, Flux is significantly affected by land use history with higher Flux rates observed in forested areas than in páramo grasslands. To our knowledge, these are the first Flux rates reported for the Ecuadorian páramo region.