Henrique Augusto Mews

Disequilibrium and hyperdynamic tree turnover at the forest-cerrado transition zone in southern Amazonia

Background: The zone of transition (ZOT) between the Cerrado and the Amazon forest in southern Amazonia represents a unique and rapidly shrinking area due to land-use change. Aims: To compare the dynamics and above-ground biomass of vegetation located in the ZOT with core Amazon forest and to determine how ZOT dynamics differ within vegetation types for different tree diameter classes. Methods: Censuses of trees were conducted in seven plots in monodominant forest, semi-deciduous seasonal forest, gallery forest, cerrado sensu stricto and cerradão, in north-eastern Mato Grosso, Brazil from 1996 to 2010, including data for the 2005 drought year. Separate analyses of stem dynamics and biomass were carried out for two different diameter (d) classes: 5 ≤ d < 10 cm and d ≥ 10 cm. Results: For trees with d ≥ 10 cm the average mortality rate was 2.8% year−1, with an estimated above-ground dry biomass of 210 Mg ha−1. Trees with 5 ≤ d < 10 cm constituted only a small fraction of the total biomass store (ca. 10 Mg ha−1) and had a mortality rate of 7.4% year−1 and recruitment of 6.5% year−1. Overall, mortality and recruitment in the ZOT were greater than in core Amazonian forests (1–2% year−1). Conclusions: The distinct vegetation formations of the southern Amazon ZOT are markedly more dynamic than core Amazonian forest. Continued long-term monitoring throughout the region is required to assess whether they also respond differently to climate change.

Does size matter? Conservation implications of differing woody population sizes with equivalent occurrence and diversity of species for threatened savanna habitats

The Cerrado stands out from other savannas of the world for hosting the highest biodiversity and for its ongoing massive destruction. Savannas on plain relief and with deep soils (DS) in Central Brazil have been widely converted into agropastoral ecosystems. In contrast, savannas on steep relief with shallow and rocky soils (RS) have been considered as future biodiversity refuges in Central Brazil. In this study, we show that adjacent DS and RS savanna sites (each with ten 1-ha plots) differ based on their woody species population sizes, but not based on species occurrence or diversity. In addition, we discuss the implications of these results for species conservation. Our research indicates that the DS and RS savannas are complementary, but not equivalent, regarding their representation of savanna vegetation in Central Brazil. We hypothesize that if RS savannas become the only refuges for savannic vegetation, widespread biodiversity losses will occur in the short term (through loss of exclusive and habitat-specialist species) and long term (due to fragmentation, reductions in population size and loss of genetic variability). Thus, we suggest that the consideration of savannas on distinct substrates should be considered for improving conservation decision-making and initiatives and can be beneficial when expanding or creating new conservation units.

Mudanças na estrutura de um cerradão em um período de seis anos, na transição Cerrado-Floresta Amazônica, Mato Grosso, Brasil

Vegetation changes in transition zones are still poorly studied. Changes in the vegetation structure of a savanna forest (cerradao) were assessed in the Amazon-Cerrado transition (14o42’2.3”S; 52o21’2.6”W), eastern Mato Grosso, within a period of six years (2002, 2005 and 2008). In 2002, fifty plots of 10 × 10 m were set up, where all trees with DSH 30 ³ 5 cm were measured; in 2005 and 2008 the plots were re-inventoried. In 2008, 84 species from 70 genera and 37 families were sampled; absolute density was 1,998 individuals/ha and basal area was 25.95 m2.ha-1. On the one hand, the absolute density of live individuals decreased from 2005 to 2008 (2,066 individuals/ha); on the other hand, the basal area increased in 2008 compared to 2005 (23.56 m2.ha-1) and 2002 (1,884 individuals/ha and 21.38 m2.ha-1). The species with the highest importance value in the period were Hirtella glandulosa, Tachigali vulgaris and Xylopia aromatica. Except for these three species, all other species underwent hierarchic changes in the importance value, indicating that most species frequently alternate. Community structure exhibited changes throughout the period; hence, we suggest investigations on the role of T. vulgaris in these changes, since environmental conditions caused by gap opening from the fall of senile individuals of this pioneer species with a short life cycle may contribute to community dynamics.

Dinâmica estrutural da comunidade lenhosa em Floresta Estacional Semidecidual na transição Cerrado-Floresta Amazônica, Mato Grosso, Brasil

Understanding ecological processes, especially the structural and floristic changes in natural ecosystems, is essential before conserving and/or restoring these areas. The aim of this study was to assess the changes that occurred in the woody plant community from 2003 to 2008. Sixty permanent plots of 10 x 10 m were established, in which all individuals with diameter at breast height > 5 cm were sampled. A total of 1,140 ind. ha-1 were recorded in 2003 (basal area 24.35 m2 ha-1) and 1,071 ind. ha-1 in 2008 (basal area of 22.04 m2 ha-1). The recruitment (2.76% year-1) did not compensate mortality (3.95% year-1) and the basal area gain (0.54% year-1) did not exceed the loss (3.77% year-1). Because of this unbalance, the half-life (17.3 years) was lower than the doubling time (29.9 years), resulting in low stability (12.6 yrs) and replacement (23.6 yrs) in relation to other seasonal forests. The parameters of community and species dynamics suggest that the forest is undergoing changes characterized mainly by the density and biomass reduction of trees, which may be related to an increase in lianas, an early rebuilding phase of the forest silvigenetic cycle or even the severe drought that occurred in the region in 2005.

The tree-shrub vegetation in rocky outcrop cerrado areas in Goiás State, Brazil

We describe the floristic composition of the tree-shrub vegetation in 10 areas of rocky outcrop cerrado in Goias State, Brazil. Ten 20×50m plots (totaling 1ha) were established and all of the individuals with diameters at 30cm above soil level (DB30) ³5cm were included in the sampling. Comparative analyses of the flora were realized using similarity indices (Sorensen and Czekanowski), classification analysis (TWINSPAN), and the Mantel test. A total of 13,041 tree-shrub individuals were sampled, distributed among 219 species, 129 genera and 55 families. Fabaceae was the most well-represented family, followed by Myrtaceae, Melastomataceae, Vochysiaceae, Malphigiaceae, and Rubiaceae. Fully 42.3% of the comparisons evaluated by the Sorensen index were >0.50, while all the values were <0.50 for the Czekanowski index, with the exception of Jaragua and Mara Rosa areas. The TWINSPAN classification generated four divisions and, in general, only the differences in the size of the population were responsible for the groupings. The Mantel test indicated that there was no relationship between floristic similarity and the distances between the areas (r=0.32, P=0.05). It therefore appears that the areas of rocky outcrop cerrado in Goias State are relatively floristically homogeneous and that they are principally distinguished by the differences in the sizes of the populations of their dominant species, and the presence of exclusive species in certain areas.

Surface fire drives short-term changes in the vegetative phenology of woody species in a Brazilian savanna

We evaluated the effects of fire on the vegetative phenological behavior (crown foliage cover, sprouting, mature and young leaves) of woody species at two sites in the Brazilian savanna, one of which had been accidentally burned. We used generalized additive mixed models to test the hypothesis that: 1) fire damages total foliage cover, thus leading to changes in vegetative phenological patterns. As this hypothesis was corroborated, we also tested whether 2) the damage caused by fire to the total crown foliage cover and mature leaves is greater in evergreen than in deciduous species, and 3) the negative effects of fire on vegetative phenology persist after the first fire-free year. The first two hypotheses were corroborated, but the third was not. Fire effects on total crown foliage cover and mature leaves were greatest during the first three months following the fire, and were significantly greater in evergreen species. For shoots and young leaves, the greatest differences found between three and seven months post-fire. On the other hand, no differences were observed in phenological events between burned and unburned sites in the second year post-fire, indicating that marked effects of the fire were only observed over a short period. Our results showed immediate negative effects on the vegetative phenophases, but also that these effects are transient, and cannot be discerned after the first fire-free year.

Ecology of Floodplain Campos de Murundus Savanna in Southern Amazonia

Premise of research. This represents one of the first studies of the ecology, diversity, and structure of campos de murundus termite savannas in the vast seasonal wetlands of southern Amazonia. We aimed to improve understanding of this threatened system by assessing species richness, abundance, and co-occurrence among trees and herbs of murundus (earth mounds), investigating the environmental and biological mechanisms underlying these patterns, and discussing implications for biodiversity conservation. Methodology. We identified every tree, shrub, subshrub, and herb on 373 murundus across 11 ha at Araguaia State Park, southern Amazonia. We constructed species abundance distributions of trees and herbs, assessed best-fit models, and tested for nonrandom patterns of species co-occurrence using checkerboard scores. Using detrended correspondence analysis (DCA), we assessed the affinities among tree species and their positions in murundus. Pivotal results. A total of 166 species, 123 genera, and 49 families occupied the murundus. The species abundance distribution of trees followed a lognormal distribution, whereas that of herbs was best described by a Mandelbrot distribution. Observed C-score indices for trees and herbs were significantly larger than expected by chance, indicating nonrandom distributions and species segregation among murundus. DCA revealed a strong gradient in species occurrence within murundus, suggesting that internal structuring may be hydrologically based (e.g., variation in mound microrelief). Conclusions. Environmental (e.g., flooding) and biological (e.g., competition between plants) factors are important for controlling the occurrence of tree and herb species on the murundus. The murundus function as critical bases for the maintenance of species diversity in this extensive floodplain, thereby deserving recognition among ecosystems with high conservation priorities.

Structure and floristic relationships between Cerrado sensu stricto sites on two types of substrate in northern Cerrado, Brazil

We described and compared the floristic composition, richness, species diversity and structure of the tree-shrub component in pairs of Typical Cerrado (Cerrado Tipico) and rocky outcrop Cerrado (Cerrado Rupestre) in two localities in Tocantins State. In each locality, we set up 10 plots of 20 × 50 m at a site, the Cerrado Tipico and other Cerrado Rupestre, and sampled the individuals with Db30cm ≥ 5 cm. The rocky outcrop Cerrado did not present any trend towards lower richness and basal area compared to the Cerrado on deep soil. Few species occurred across the four sites and only two important species (Anacardium occidentale and Qualea parviflora) in the four vegetation structure were common to both environments assessed. Furthermore, the occurrence of habitat-specialist species of rocky outcrops and high altitudes (Mimosa claussenii, Tibouchina papyrus, Schwartzia adamantium and Wunderlichia cruelsiana) and the high dissimilarity among sites suggest that altitude is the main responsible for the floristic dissimilarity, followed by the influence of substrate type. Therefore, the information with respect to phytophysiognomy type as a parameter to select areas for conservation, by itself, does not effectively ensure biodiversity preservation, owing to the existing flora heterogeneity not only at local but also at regional scale, revealed by the floristic and structural particularity of each site.

Variações na riqueza e na diversidade de espécies arbustivas e arbóreas no período de 14 anos em uma Floresta de Vale, Mato Grosso, Brasil

The goal of this study was evaluate changes in richness, diversity and the contribution of successional groups to tree species composition of a Valley Forest in the Chapada dos Guimaraes National Park, Mato Grosso State, Brazil, over 14 years (1996 - 2010) from five surveys intervals (1996-1999, 1999-2003, 2003-2006, 2006-2010, 1996-2010). All tree species (dbh > 5 cm) were sampled systematically in a total of 18 plots (600 m2) established into three transects in valley. Whereas the changes in species richness were positive, but barely noticeable when analyzed in shorter intervals, the range considering the whole interval (1996-2010) was significant (comparisons of Poisson counts) with a net increase of 20 species. Despite the observed species turnover, maintaining evenness seems to have given the absence of significant changes in diversity over the period studied (Hutcheson t test). The contribution of successional groups to the tree species composition of tree community also did not show significant changes during 14 years of monitoring. These results suggest that tree community dynamics of a Valley forest is accelerated in tree species composition, although maintaining temporal diversity and distribution of species among successional groups.