LAUSR

Abstract Anthropogenic fires have strong impacts in tropical rainforests that are not necessarily restricted to the burnt areas, as edge influence from the burnt patch may significantly alter the unburnt vegetation. Conversely, the remaining forest patches may mitigate changes in microclimate in the adjacent burnt areas. We studied variation in air and soil temperature in burnt and unburnt areas in the Atlantic forest of southern Bahia, Brazil. In November-December 2017, approx. two years after a series of wildfires, we sampled six transects at three burnt-unburnt edges, placing soil and temperature data loggers at the edge and at 20, 60, and 120 m into the burnt and unburnt areas and keeping them there for seven days. One data logger of each pair was buried at a depth of 3 cm and the other was kept at a height of 1 m above ground in a protective case. Air in the burnt area was cooler than in the forest at night and warmer in the morning, whereas soil was cooler than in the forest at night and early morning and warmer in the afternoon. We did not observe gradients in air or soil temperature, but soil temperature was more variable in the burnt area than in the unburnt forest. Conversely, notwithstanding the differences between diurnal and noctural temperatures, daily average, minimum and maximum air temperature varied little between the environments, possibly due to shading by bracken fern in the burnt areas. The variation in soil temperature is likely due to changes in vegetation structure, as the bracken fern does not provide as much shade and temperature control as the native forest canopy. Thus, even in the absence of strong effects on air temperature, changes in the temporal and spatial variability of soil temperature may be observed, with possible consequences for plant recruitment and soil organisms.