Microtopographic effect on soil temperature during a burn by shifting cultivation in a tropical rain forest.

• Soil temperature was monitored before and during a fire in a tropical rainforest. • Clear cutting the forest increases the amplitude of the daily soil temperature. • Fire only affected soil temperature in the first centimeter of the soil. • Soil moisture depended on hillside position and affected soil temperature behavior. • Nutrient contents were affected in the litter layer, but not in the mineral soil. Fire is an important component of shifting cultivation systems. Although its effects on soil properties depend on its severity and duration, few studies have measured soil temperature during burns at different depths and in relation to topography in tropical forests. Frequent rain keeps the soil moist in these ecosystems, but soil moisture does not only depend on precipitation but also on relief position. Here we monitor soil temperature at 1 and 10 cm depth before the burn along elevation gradients of three logged hillsides to establish the daily temperature variation, and to compare it with the soil temperature under forested sites and during the burn. Additionally, moisture content and physicochemical properties of the soil were measured before and after the burn. Results before the burn indicate a larger daily temperature amplitude in logged versus forested areas, and specially at crests and shoulder positions in comparison to backslopes and toeslopes. The fire increased soil temperature only in 1 cm depth, and for less than 40 degrees at most of the sites. Soil moisture content was negatively correlated with maximum temperature during the burn, however, also fuel loads and litter thickness determined fire intensity, with the spatial distribution of these variables being unrelated to topography. Nutrient contents changed only in the litter layer, in which C and N diminished by 35 % and 24 %, respectively, while total Ca, Mg, K and P increased by 210, 202, 318, 235 % respectively. We conclude that soil moisture contents contributed to maintain fire intensity low at the studied site. [ABSTRACT FROM AUTHOR]