Efeito individual das variáveis microclimáticas e da competição no crescimento em diâmetro de espécies arbóreas na Amazônia Central

Abstract

Forest dynamics can be conditioned by micrometeorological variation and competition for resources, resulting in physiological changes that interfere with the pattern of species development. In this study, we evaluated the individual effect of micrometeorological variables and levels of competitive status on growth rates in trunk diameter of tree species in terra firme in the Central Brazilian Amazon Forest. For four years (2018-2021), the individual growth in diameter of 33 trees (≥ 20 cm DBH) of seven species was measured with a digital caliper through dendrometric bands attached to the trunk. Five micrometeorological variables were collected, including photosynthetically active radiation, air temperature (minimum, average and maximum), precipitation, vapor pressure deficit (minimum, average and maximum) and evapotranspiration, in addition the soil moisture content. Principal component regression analysis was applied to assess the effect of micro meteorological variability on individual growth. In addition, we tested five widely used distance-dependent competition indices that were correlated with increment rate. Our main findings show that the individual growth pattern varied significantly over time with an average of 0.15 mm month-1 and that precipitation and soil moisture content were the main factors responsible for growth for most species. On the other hand, the atmospheric vapor pressure (VPD) deficit (minimum and average) was the main precursor of the decrease in diameter. The maximum VPD and the minimum and maximum temperature were not significant (p>0.05) for the influence on the mean increment. There are no significant correlations in the relationship between the increment in diameter and the evaluated competition indices that consider only DBH, height and distance between trees (p>0.05), so they were unfeasible to establish the competition-growth relationship in the forest fragment with high density of individuals. These results indicate that changes associated with VPD can limit the photosynthetic capacity, slowing down the growth of trees and, consequently, delaying the rate of carbon dioxide absorption at the site, mainly during the driest periods and at higher temperatures. In addition, competitive relationships seem to be more responsive when Amazonian species are analyzed through the inclusion of more complex breeding variables, such as canopy area. Our study reinforces that the forest is more sensitive to pressure exerted by micrometeorological variables than by competition.