Simulação do comportamento do fogo em material combustível de caatinga no Estado da Paraíba.

Abstract

Forest fire is a phenomenon of natural or anthropic origin that occurs frequently in almost the entire planet. In the Caatinga biome, this phenomenon has been occurring due to the indiscriminate use of fire to clean the land and burn for pasture regrowth. Thus, the present study aimed to evaluate the behavior of fire in experimental burns in a closed environment of combustible material collected in areas of preserved caatinga in different Immediate Geographic Regions of Paraíba. The collection of fuel material was carried out in different Immediate Geographic Regions of the Sertão da Paraíba, namely: Patos, Pombal, Catolé do Rocha São Bento, Sousa, Itaporanga, Cajazeiras and Princesa Isabel. In each area, seven samples were collected with the aid of a template (1.0 m x 1.0 m) that was randomly launched, where all the combustible material was removed and placed in plastic bags. After collection in the areas, the combustible material was sent to the laboratory, weighed on a scale, quantifying the available material in 1m² and, subsequently, estimated at t ha ¹, in addition to determining the moisture content in each sample. To evaluate the fire behavior, 21 fires were performed with the combustion table at 0º (flat) and 21 fires with the combustion table at 25º, whose design was in a 7x2 factorial arrangement (collection regions x types of inclination), with three repetitions, totaling 42 burns. In the evaluation of the fire behavior, during the burning the variables, speed of propagation, fire intensity, duration of the burning, height of the flames, and heat released per unit area were measured. To determine the calorific value, ash content, organic matter and chemical analysis (N, P, K, Mg and Ca), a completely randomized design was used, with three repetitions, totaling 21 repetitions. Regarding the average weight of the fuel material, a difference was found, with the preserved areas of the Pombal (23 t ha ¹), Itaporanga (22.3 t ha1) and Catolé do Rocha (20.42 t ha1) as those with the highest amount of combustible material on the forest floor. The moisture content of combustible materials in the evaluated areas did not differ, varying from 6.94 to 4.43%. Regarding the speed of propagation, fire intensity and heat released per unit area, it was found that there was no interaction between the degree of slope and the geographical regions, only the geographical regions exerted an influence on these variables. For organic matter, ash content and calorific value, there was no significant difference between the combustible materials of the evaluated regions. The variations between the concentrations of each nutrient, determined before and after burning, were not very evident for the levels of N and Mg and marked for those of P, K and Ca. The areas of preserved caatinga in the different regions, responded in a different way the behavior of the fire, due to the different types and amount of available combustible material. It is essential to develop new studies that seek to understand the behavior of fire to better outline measures to prevent and combat forest fires in caatinga areas.