Sincronismo de produção e degradação da serapilheira em caatinga preservada no Semiárido da Paraíba.

Abstract

Synchronism of litter production and degradation in caatinga preserved in the semiarid region of Paraíba. In the Caatinga, most of the plants exhibit the caducifolia mechanism during the dry season, with the vegetal material deposited on the surface of the forest floor and, later, the nutrients are cycled. The nutrient cycling will aid in the development of the vegetation present in the ecosystems, providing the necessary nutrients for its equilibrium. The study aimed to estimate the spatial and temporal variation of deposition, accumulation and decomposition of the litter present in a preserved caatinga area and the interference of climatic variables in the dynamics of these events. The research was conducted at RPPN Fazenda Tamanduá, in Santa Terezinha-PB. A randomized complete block design with 20 replicates in a 24 x 2 factorial arrangement was used, and the Tukey test at 5% was used to compare the means. The litter deposition was estimated in two periods: period I (August/2015 to July/2016) and period II (August/2016 to July/2017), with monthly collections in 20 collectors of 1,0m x 1,0m. The litter collected monthly was separated into the fractions leaves, branches + bark, reproductive material and miscellaneous, these fractions being dried in a greenhouse and later weighed. The quantification of litter accumulated in the forest floor was carried out with the aid of a metallic frame of dimensions of 0.5m x 0.5m, randomly launched in the experimental area. The litter decomposition rate was estimated by the annual and average annual production of accumulated litter, and the average renewal time and the time required to decompose 50% and 95% were then calculated. The deposition of the total litter in periods I and II was 2,356.83 kg ha-1 and 1,163.67 kg ha-1, respectively. The leaf fraction was the one that contributed the most during the two collection periods. The accumulation of litter on the forest floor was 33,145.24 kg ha-1 for period I and 21,990.48 kg ha-1 for period II. The decomposition coefficient for period I was 0.85 and 0.64 for period II. Data analysis allowed to conclude that the total deposition of litter in the two periods is in line with the average production for the Caatinga. The increase in precipitation provided higher deposition of litter after the rainy season. Climatic variables such as temperature, sunshine and wind speed presented negative correlation with all constituents of litter. Due to several factors, the decomposition of litter in the caatinga is slower than in other biomes.