Conservação da diversidade de plantas tolerantes à sombra em mosaicos agrícolas da Amazônia Oriental.

Abstract

Under the increase of deforestation and the need to meet conservation and food production, agricultural mosaics have great importance for maintaining diversity, but with conservation values still not recognized. A promising approach to understanding species distribution patterns in agricultural mosaics is to understand the factors that work in each of its components: local species richness (alpha diversity), variation in species composition between locations (beta diversity) and total regional richness (gamma diversity). This approach also considers the vegetation stratification, as the strata establish different niches for plant species, consequently influencing the independence of the diversity found in vertical strata. In this sense, this work aimed to evaluate the response of each component of the diversity of shade-tolerant species in agricultural mosaics in Eastern Amazon, considering three strata of the vegetation cover separately. The study was carried out in six agricultural mosaics located in different regions of the State of Pará, Brazil. The vegetation cover inventory was carried out within each mosaic in the main types of land use, in the upper, middle and lower strata. After identification and classification into ecological groups, only shade-tolerant species were selected, since these are the most important species in the analyzes for plant species conservation. The diversity of each mosaic and each stratum was partitioned into alpha diversity (or plots), beta 1 diversity (β1, within the land use types) and beta 2 diversity (β2, between the land use types), using the additive model and species richness as a measure of diversity. A generalized linear model (GLM) analysis was performed to assess the influence of geographic factors, stratum, rainfall, number of dry months, forest cover and number of land use types. The contribution of land use types to the alpha and total beta diversity, the contribution of each plot in the gamma diversity and the conservation value of the types of uses were also assessed. The diversity partition showed observed values of alpha and β1 lower than expected and observed values of β2 higher than expected. Overall, the evaluation of alpha, β1 and β2 richness components of shade-tolerant plants analyzed here showed clear patterns in alpha and β2, and that β1 is more dependent on the land use types found in agricultural mosaics. Among the factors tested, alpha richness responded only to strata, β1 responded to mosaics and strata, and β2 responded only to the amount of annual precipitation. The contributions of plots and land use types differed between components of diversity, and these between mosaics and strata, hence the conservation value also differs. The conservation value of mature forests is influenced by the percentage of forest cover in the mosaics, but the conservation value of secondary forests does not depend on this cover.