Abstract To characterize the floristic composition and horizontal structure of the National Forest of Açú from 2015 to 2019, 20 permanent plots of 400 m² were allocated, and all woody individuals with a diameter at breast height (CBH) ≥ 2 cm were measured on both occasions. Between 2015 and 2019, there was an increase in floristic richness from 23 to 34 species, especially Cenostigma pyramidale and Handroanthus impetiginosus due to their high phytosociological values. Although an 8.7% reduction in the number of individuals in the 4.4 cm class center was observed between the respective years, there was a volumetric increase of 4.85 m³ ha-1, that is 1.21 m³ ha-1 year-1. Changes in floristic composition, diameter distribution, and volumetry reflect the development of vegetation and part of its dynamics; indicating its state of conservation and, consequently, the achievement of the conservation objectives proposed by the Unit.

Resumo A serapilheira é a camada mais superficial do piso florestal e analisar sua deposição é fundamental para avaliar a estabilidade de uma das principais rotas da ciclagem de nutrientes em fragmentos florestais. O objetivo do trabalho foi avaliar o aporte de serapilheira na borda de três fragmentos florestais de Mata Atlântica, em diferentes estágios de sucessão (transitório e maduro), localizados na Floresta Nacional de Nísia Floresta (Rio Grande do Norte, Brasil). Foram instalados 54 coletores, 18 em cada fragmento, distanciados de 0 m a 100 m em relação à borda e, mensalmente, durante 12 meses, foram coletados todo o material aportado. O material foi seco em estufa a 65 °C por 48 h e pesado em balança de precisão. A deposição anual total no gradiente borda interior foi de 3227,90 kg ha-1 (fragmento I), 3315,60 kg ha-1 (fragmento II) e 1775,90 kg ha-1 (fragmento III). Somente para o fragmento III foi verificado diferenças estatísticas no aporte de serapilheira da borda para o interior com valores variando entre 93,87 kg ha-1 ano-1 (borda) a 261,7 kg ha-1 ano-1 (100 m). O maior aporte no fragmento II se deu, a princípio, em razão da diversidade de espécies e maior porte dos indivíduos adultos. O aporte de serapilheira teve comportamento sazonal apresentando maior deposição no período seco, indicando que a pluviosidade atua como agente regulador desse material. Além disso, a borda de fragmentos florestais em estágio inicial de sucessão tende a depositar menor quantidade de serapilheira no piso florestal.

Abstract Litter is the most superficial layer of the forest floor, and analyzing its deposition is essential to assess the stability of one of the main routes of nutrient cycling in forest fragments. The objective of this work was to evaluate the litter input on the edge of three forest fragments in different succession stages (transitional and mature) located in the Floresta Nacional de Nísia Floresta (Rio Grande do Norte, Brasil). 54 collectors were installed, 18 in each fragment, spaced from 0 m to 100 m in relation to the edge and, monthly, for 12 months, all the litterfall was collected. The material was oven-dried at 65 °C for 48 hours and weighed on a precision scale. The estimated annual deposition in the internal edge gradient was 3227,90 kg ha-1 (fragment I), 3315,60 kg ha-1 (fragment II) and 1775,90 kg ha-1 (fragment III). Only for fragment III, there were statistical differences in the total input of dead organic matter from the edge to the interior, with values ranging from 93,87 kg ha-1 year-1 (edge) to 261,7 kg ha-1 year-1 (100 m). The largest amount of organic material in fragment II was, at first, due to the diversity of species and the larger size of adult individuals. The litter input had a seasonal behavior, showing greater deposition in the adverse period, indicating that rainfall acts as a regulating agent for such material. In addition, the edge of forest fragments at an early stage of succession tends to deposit less litter on the forest floor.