ABSTRACT Fragmentation is one of the main causes of biodiversity loss in tropical forests through consequences on their different components. Beta diversity patterns across fragments have been studied across multiple spatial scales, but comparisons with intact landscapes and in a variety of vegetation types are scarce. In order to address this issue of anthropogenic landscape disturbance, we tested two hypotheses relating to fragmentation and beta diversity: 1. Floristic homogenization at patch-level scale and 2. Floristic differentiation at landscape-level scale. The study was conducted in the Espinhaço Range biosphere reserve, Brazil. Three landscapes encompassing a broad range of vegetation types were sampled in 115 plots. Two landscapes were fragmented due to mining activities (Sabará and Brumadinho) and one is protected (Parque Estadual Serra do Rola-Moça). Results showed high overall beta diversity both between landscapes (conserved and fragmented) and vegetation types (forest, Brazilian savanna “campos rupestres”, ecotone and ironstone “canga”) with high turnover and species losses, even in highly disturbed vegetation types. The conserved landscape was most diverse in terms of richness. Thus, fragmentation effects differed from the expected with a main role of differentiation processes, and we argue that high beta diversity is not always a good predictor of ecosystem health.

ABSTRACT Background: Seasonally Dry Tropical Forests (SDTF) are recognized by their great biological diversity, but little is known about their temporal patterns, which may be crucial in a changing world. Here we aimed to characterize the SDTF dynamic patterns in floristic and structural changes, and also to evaluate shifts in dynamic rates and structural attributes such as richness, number of trees and biomass. Our hypothesis is that SDTF tree communities have their dynamic characterized by temporal fluctuations related to an instability pattern, in according to the already found for others tropical forests. For this we used a data of 42 400 m² plots in three fragments in the Brazilian Arboreal Caatinga, measured in 2005, 2010 and 2015. We evaluated temporal changes in richness, species composition, trees density, biomass and rates of tree mortality and recruitment; and also rates of biomass gain and loss. Results: We found a pattern of floristic composition stability, but with changes in structure and dynamics. There was a tree density decrease driven by constant mortality and by recruitment decrease, and biomass increase due to decrease in biomass loss and to increase in biomass gain. The biomass increase was main related to a small set of dominant species that are the most representative in the community dynamics. Conclusion: SDTF dynamics are related to stability in species composition, but with structural changes towards higher biomass stocks. The results are main related to community dynamics and to SDTF attributes such as climatic seasonality that drives the local ecological processes.

RESUMO Este trabalho teve como objetivo analisar a ocorrência de processo sucessional em uma floresta madura, utilizando para isto a distribuição das árvores em fases de desenvolvimento. O fragmento estudado consiste em uma floresta estacional semidecidual em estágio avançado de recuperação com cerca de 11 ha, localizado as margens do Rio Capivari no município de Lavras, estado de Minas Gerais, Brasil. A coleta de dados ocorreu nos anos de 1998, 2003, 2009 e 2014, nos quais foram mensurados e identificados em nível de espécie todos os indivíduos arbóreos que atingiram o critério de inclusão preestabelecido (circunferência a 1,3 m do solo - CAP≥15,7 cm). A partir destes dados foram obtidos os valores de riqueza para cada uma das quatro fases estabelecidas com base em critérios de circunferência (Juvenis, Preestabelecidos, Estabelecidos e Emergentes), bem como informações sobre rotatividade de espécies, estrutura, composição florística e compartilhamento entre essas fases. Os resultados indicaram a inexistência de diferenças temporais quanto à estrutura e distribuição da riqueza em fases de desenvolvimento. Foram observadas movimentações temporais de espécies principalmente entre as fases menores. Com relação à similaridade entre fases, ocorreu a divisão em um grupo contendo as duas menores e outro composto pelas duas maiores, nos quais a composição florística e espécies mais representativas foram mais semelhantes. Ademais, observou-se uma substituição não direcional das espécies mais representativas de cada fase, provavelmente relacionado a não correspondência entre ciclos de vida das populações. Assim, a ocorrência de modificações temporais nos padrões de riqueza na floresta indica a existência de processos sucessionais dinâmicos em uma comunidade em estágio clímax.

ABSTRACT This study aimed to test the occurrence of the successional process in a mature forest using the distribution of the trees in phases of development. The study forest remnant, a 11-ha old-growth seasonal forest, is located in the margins of Rio Capivari in Lavras, Minas Gerais state, Brazil. The data collection was carried out in 1998, 2003, 2009 and 2014, when we measured and identified to species level all trees that have reached the pre-established inclusion criteria (circumference at 1.3 above the ground level - CBH ≥15,7 cm). From these data, we obtained the species richness for each of the four development phases established on the basis of circumference criteria (Juvenile, Pre-established, Established and Emerging), as well as information on the species turnover, structure, floristic composition and the sharing between these phases The results indicated that there are no significant temporal differences in the structure and the distribution of species richness in development phases. Besides, we found a subtle movement of species mainly among the small phases. Concerning to the similarity among phases, we observed a clustering of the two smallest development phases and the clustering of the two largest ones, in which the floristic composition and most representative species were more similar. In addition, there was a non-directional turnover of the most representative species of each phase, probably related to a mismatch among the population life cycles. Thus, the occurrence of temporal changes in richness’ patterns can indicate the existence of dynamic succession processes in a climax stage community.

RESUMO Galhas são resultantes da interação específica entre um indutor e a planta hospedeira. A espécie Heteropterys byrsonimifolia A. Juss. ocorre em abundância em ecótones de floresta estacional semidecidual e formações abertas adjacentes. No Parque Ecológico Quedas do Rio Bonito no estado de Minas Gerais, Brasil, essa espécie é afetada por um único morfotipo de galhas. O presente estudo objetivou avaliar se a complexidade estrutural do hospedeiro (teste da Hipótese da Complexidade Estrutural) e a distância entre hospedeiros (teste da Hipótese da Concentração de Recursos) têm influência sobre a densidade de galhas em H. byrsonimifolia, além de caracterizar a espacialização da infestação. Os resultados corroboram as duas Hipóteses testadas, sugerindo um comportamento metapopulacional das galhas em H. byrsonimifolia. Encontrou-se também um maior sucesso dos galhadores em ambientes de transição abrupta entre floresta-cerrado, o que pode estar associado à maior vulnerabilidade dos hospedeiros ocasionados por estresse que as plantas usualmente sofrem em ambientes ecotonais.

ABSTRACT Galls are the result of a specific interaction between an inducer and a host plant. The species Heteropterys byrsonimifolia A. Juss. occurs in abundance in semideciduous seasonal forest ecotones and adjacent open formations. In the ecological reserve Quedas do Rio Bonito, located in the state of Minas Gerais, Brazil, this species is affected by a single gall morphotype. The present study aimed to evaluate whether the structural complexity of the host (test of the structural complexity hypothesis) and the distance between hosts (test of the resource concentration hypothesis) affect gall density in H. byrsonimifolia and to characterize the spatial distribution of the infestation. The results corroborate the two hypotheses tested, suggesting a metapopulation pattern of gall infestation in H. byrsonimifolia. Gallers were more successful in abrupt forest-savannah transition environments, which may be associated with greater stress-induced host vulnerability that plants usually experience in ecotones.

A maior parte dos estudos envolvendo as Florestas Tropicais Sazonalmente Secas aborda questões fitogeográficas e conexões florísticas deste bioma disjunto. Porém, pouco se conhece a respeito das características estruturais da FTSS. Devido a esta lacuna existente na literatura, buscamos descrever a estrutura de um fragmento remanescente de FTSS em uma área ecotonal entre domínio do Cerrado e da Caatinga. Ocorreram no estudo grande número de espécies arbóreas, 79, e altos valores para os índices de diversidade e equabilidade (3,6 nats/indivíduos e 0,83, respectivamente). A distribuição diamétrica para os indivíduos que apresentaram maiores valores de cobertura e para a comunidade não resultou em padrão de J-reverso, o que indica adaptações ecológicas ao stress hídrico adotadas em diferentes estratégias de crescimento. Não houve formação de grupos florísticos, já que a alta fertilidade do solo da área de estudo configura um ambiente homogêneo. A característica da área de estudo detectada através da estrutura, associada a dados edáficos, nos permitiu vislumbrar sua importância em termos de conservação e reforçar a importância de estudos com este enfoque nas FTSS.

Most studies on Seasonally Dry Tropical Forests (SDTFs) investigate phytogeographic patterns and floristic connections of this disjunct biome. However, little is known about the structural characteristics of SDTFs. We aimed to describe the structure of a SDTF in an ecotonal area between the Cerrado and Caatinga domains. In total, 79 tree species were recorded, and high values of Shannon diversity index (3.6 nats/individual) and equability (0.83) were observed. The diameter distribution for the species with higher cover values and for the entire community did not exhibit a reverse-J shaped distribution, which indicates the occurrence of different growth strategies and ecological adaptations to water stress. The results did not indicate the formation of floristic groups, as the high soil fertility in the study area results in a homogeneous environment. The structural characteristics of the study area associated with the soil composition highlight its importance for conservation and emphasize the need for community structure studies in SDTFs.