Biomassa abaixo do solo em áreas de agricultura familiar no arco do desmatamento da Amazônia, Pará.

Abstract

This study aims to bring a holistic approach, investigating the interaction of many factors and determining their importance to fine roots with the objective to create knowledge about estimation of biomass and carbon belowground that can contribute to establish methods of payments for environmental service in rural settlements. The study was conducted in three agricultural areas located in the arc of deforestation region in the Brazilian Amazon, in Pará state: Praia Alta Piranheiras agroextractivist settlement (Maçaranduba), Palmares II settlement and Travessão 338-S. In each area nine proprieties were chosen (n = 27), which five plots of 10x50 m were established (n = 135). The plots represented nine types of land cover: conserved forest, exploited forest, burned forest, old secondary forest, young secondary forest, invaded pasture, clean pasture, annual crop, and perennial crop. The biomass was evaluated in the 135 plots (R1 ≤ 1 mm; R2 > 1 mm e ≤ 2 mm; R3 > 2 mm e ≤ 5 mm; RM = dead roots ≤ 5 mm) and total carbon biomass (R1 + R2 + R3 + RM) of fine roots. In the same sites of root sampling was done the classification of the soils, determination of the physical and chemical proprieties of the soil and the structure of the vegetation. Socioeconomic surveys were completed and calculated metric structure and occupation of landscape of the 27 proprieties. The analyses were done considering two scales of observation: plot scale (n = 135) where it was considered nine types of land cover; and settlement scale where it was considered the three agricultural areas. The socioeconomic and landscape variables were used only in the analyses of the settlement scale. The type of land cover influenced the biomass of fine roots that decreased with the increase of the disturbance of the land cover, varying from 516.3 g m-2 to 189.1 g m-2 in the conserved forest and annual crop, respectively. In the plot scale, the vegetation structure was more determinant to the fine roots biomass than the soil characteristics. In the settlement scale the total biomass varied from 2.69 Mg ha-1 to 4.73 Mg ha-1 and carbon varied from 1.01 Mg ha-1 to 2.06 Mg ha-1 . In this scale the socioeconomic context influenced the roots’ carbon and the distribution of biomass among the diameter classes that were associated with the dominant production of activities in the areas. In order of importance in the landscape scale, the socioeconomic variables were most determinant for fine roots, followed by soil variables, vegetation and finally, by landscape variables. Independently of the observation scale, the biomass of R1 class showed the highest proportion of total biomass, highlighting the importance of many fine roots to quantify the root biomass. In the landscape scale the factors that influenced the biomass and the carbon storage of fine roots occupied different positions of those seen in the plot scale.