Compreendendo o estabelecimento inicial de seis espécies florestais sob gradiente de irradiância em sistema silvicultural de enriquecimento de floresta secundária

Abstract

Silvicultural treatments are critical for the suitable initial establishment of the planted tree species in secondary forest enrichment planting. However, the optimum irradiance level – obtained with silvicultural interventions that promote canopy openness (e.g. thinning) – rely on the introduced species. Besides silvicultural treatments at the canopy level, understory treatment (e.g. slashing) reduce the competition between natural and planted species and can improve canopy openness effect. The phenotypic plasticity is crucial to understand the interspecific responses to canopy openness during the early years following the planting. The principal objective in this doctoral study is to understand the initial establishment of six commercial tree species under a gradient of canopy openness in a secondary forest enrichment planting. Therefore, in March 2017, a secondary forest enrichment planting was implemented at Experimental Farm of Amazonas Federal University (FAEXP-UFAM). The experiment was conducted in a full factorial design in split-plots (canopy refinement x understory treatments). Between September and December 2016, were applied six levels of basal area reduction by canopy refinement (0, 20, 40, 60, 80 and 100%) in main plots of 2318 m2 replicated in five blocks. Each main plot was divided into two sub-plots (with and without understory slashing) where were planted six tree species of recognized economic value (Cedrela fissilis, Tabebuia rosea, Swietenia macrophylla, Hymenaea courbaril, Carapa guianensis and Bertholletia excelsa). Silvicultural treatments affected the secondary forest microclimate, mainly light environment (Chapter 1), and, consequently, the growth, survival and pest attack susceptibility of the six species (Chapter 2). The variation in species growth had a good relationship with the plasticity of leaf photosynthetic characteristics (morphological and physiological) and, therefore can to help our understanding about the main mechanisms responsible to growth responses of tropical tree seedlings to silvicultural treatments in secondary forest enrichment planting (Chapter 3).