Evaluation of thermal comfort in a silvipastoral system in a tropical environment
The use of trees in silvipastoral systems can improve quality of the microclimate and thermal comfort of animals. The object of this research was to compare differences in microclimatic conditions in three environments (under the canopy of trees of the species Acacia holosericea, in the space between rows of trees and in full sunlight in monoculture grass) of a sylvopastoral system, at three hours of the day (9:00, 12:00, and 15:00), in two seasons of the year (dry = winter and wet = summer), in the municipality of Seropédica, RJ. The statistical design was randomized complete blocks in which environment represented the main plots and hour of day and season of year were split plots, with four replications. The nine microclimatic variables studied were: black globe temperature (bgt), dry bulb temperature (dbt), humid bulb temperature (hbt), maximum daily temperature (MaxT), minimum temperature (MinT), air velocity (av), temperature humidity index (THI), black globe humidity index (BGHI), and radiant thermal load (RTL). Results showed that the values of bgt, hbt, THI, and BGHI were lower in the dry than the wet season. BGHI was lower in the morning and afternoon than at noon, correlated with THI (r = 0.85) and was shown to be more precise than the latter as an indicator of thermal comfort. The tree canopy reduced the heat load that the animal would feel by 26% compared with the full sunlight environment.