Variations in leaf morphometry and in diameter and height growth of plants may occur due to changes in light and temperature conditions of the forest in order to compensate the stress in the habitat. In this study, we examine the relationship of seedling and juvenile size and leaf area of woody species in forests of different ages ([55 and 19 years) in northeastern Brazil. A total of 600 individuals of four species, seedlings and juveniles that survived a rainy season were evaluated. Seedlings and juveniles of Croton blanchetianus Baill, Poincianella pyramidalis (Tul.) L. P. Queiroz, Myracrodruon urundeuva Allemão and Commiphora leptophloeos (Mart.) J.B. Gillett were measured for height and stem diameter in the beginning of the rainy season of 2014. One leaf of each individual was collected in the beginning of the rainy season. Leaves were photographed, and leaf area was measured. Differences in height, diameter and leaf area between forests and the existence of a relationship of diameter and height to leaf area were examined. Leaf area and seedling and juvenile size of C. blanchetianus and C. leptophloeos decreased as succession progressed. However, this was not observed for seedlings of P. pyramidalis and juveniles of M. urundeuva. Leaf area explained 7-26% of the variation in size of individuals in the young forest and 11-39% of the variation in size of individuals in the mature forest. Despite variations in leaf area, significant changes in growth rate were not found with the increase in forest age for most ontogenetic stages and species.

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The Tropical dry forests cover large regions of the world and have been extensively altered by human activities. This study was aimed at characterizing and comparing the density, diversity and structural parameters of a human-altered secondary dry within an interval of five years of regeneration. Two hundred plots were established in the forest and two monitoring surveys were carried out, with interval of five years between them. All individuals in each plot with diameter at the ground level ≥ 3 cm were measured. After five years, no differences were observed in the number of species. Total density and mean basal area decreased, as a result of the maturation of the forest and possibly due to a prolonged drought in 2012. In 2008, the total basal area was 10.59 m².ha-1, increasing to 11.01 m².ha-1 in 2013. The mean height of the community did not increase significantly, from 3.59 m in 2008 to 3.65 min 2013. The number of individuals in the larger diameter classes reduced between 2008 and 2013, while the opposite was observed for smaller classes. Some structural parameters increased or decreased depending on the group of species analyzed and there was still a group that did not present significant changes. Therefore, age since abandonment can affect the regeneration process and the resilience of the forest. We realized, the speed in which these alterations occurred in an interval of five years can be considered slow and changes in the recovery process of a 16-year-old forest may not be detected.

Aims In dry tropical forests, herbaceous species may have dormancy mechanisms and form persistent and transient seed banks in the soil. Evolutionarily acquired, these mechanisms are efficient for the establishment and survival of these herbs, especially in forests with unpredictable climates, such as the Caatinga. Thus, our objective was to verify whether the studied herbaceous species adopt the physical dormancy mechanism and how these natural barriers are overcome, to understand the temporal dynamics existing in the soil seed bank from a Brazilian dry tropical forest. Methods Seeds of five native herbaceous species from the Caatinga forests were selected and submitted to pre-germinative treatments for verifying the presence of physical dormancy. We collected soil samples in the rainy and dry seasons for four consecutive years and monitored the emergence of the selected herbaceous in the greenhouse. We verified the differences in germination and seed bank emergence in the soil by generalized linear models. Important Findings The presence and absence of physical dormancy were observed in seeds from Caatinga herbaceous species. We found intraspecific and interspecific differences in the herbaceous emergence from soil seed banks between years and climatic seasons. In perennial herbs, consecutive lack of emergence between seasons and years was frequent, which suggests a direct relationship with the mechanism of physical dormancy and the environmental conditions necessary to overcome integument barriers. In these species, seed dimorphism and dormancy may confer additional advantages to their survival. Moreover, presenting intermediate levels of physical dormancy in an annual species may be an evolutionary adjustment to rainfall unpredictability. In contrast, we found that the annual herb without dormancy is more sensitive to seasonal and interannual climate changes, as evidenced by the increase and significant reduction of its emergence in the soil seed bank. These differences acquired evolutionarily are advantageous for the establishment of herbaceous populations, mainly in semiarid regions with an unpredictable climate.

No abstract

Leaves present adjustments in response to reducing the availability of environmental resources, which may reflect in the plant development. The study investigated the interannual variation in the morphofunctional foliar attributes of seedlings and juveniles of Myracrodruon urundeuva Allemão and Cenostigma pyramidale (Tul.) Gagnom & G.P. Lewis, besides the survival time and growth rates of individuals from two forests of different ages. We analyzed the relationships of the leaf characteristics with plant growth rate and survival time. In two forests, young (24 years) and mature (> 55 years), from the Brazilian semiarid, data sampling of the specific leaf area, specific leaf mass, leaf water content, and mean number of leaves was conducted for 2 years; the growth rate in diameter and height was evaluated during the rainy season of 2016 and the survival time. Most leaf characteristics, growth, and survival rates presented higher values in the young forest, besides more relationships between the leaf attributes and the survival time, according to the species and ontogenetic stage.

IntroduçãoFlorestas jovens, que voltam a se restabelecer após perturbação, apresentam diferenças em suas condições ambientais quando comparadas as florestas maduras, as quais apresentam a estrutura da copa das árvores mais fechada, proporcionando maiores taxas de umidade e sombreamento no sub-bosque (LOPES et al., 2012;PEREIRA et al., 2001).Tais variações nas condições ambientais das florestas podem influenciar o desenvolvimento das plantas (ARAÚJO et al., 2008a). Além disso, pode atuar sobre as concentrações dos macronutrientes nas folhas, podendo assim alterar alguns processos fisiológicos das plantas, como a fotossíntese e, consequentemente, o crescimento e sobrevivência das mesmas no ambiente (DOLOSO et al., 2009; ZHU et al., 2013). Assim, estudos que investiguem repostas do desenvolvimento e crescimento de plantas sobre diferentes condições ambientais encontradas entre florestas jovem, com histórico de perturbação, e florestas maduras, sem histórico de perturbação, são importantes para compreensão dos diferentes comportamentos das espécies, bem como, da resiliência dessas florestas. Além de, poder auxilia trabalhos de recuperação de florestas tropicais secas que foram degradadas.Nesse contexto, o presente estudo objetivou investidas o tamanho e a taxa de crescimento de regenerantes (juvenil e plântulas) de Commiphora leptophoeos entre florestas de caatinga jovem e madura durante a estação chuvosa.