Leandro Maracahipes

On the delineation of tropical vegetation types with an emphasis on forest/savanna transitions

Background: There is no generally agreed classification scheme for the many different vegetation formation types occurring in the tropics. This hinders cross-continental comparisons and causes confusion as words such as ‘forest’ and ‘savanna’ have different meanings to different people. Tropical vegetation formations are therefore usually imprecisely and/or ambiguously defined in modelling, remote sensing and ecological studies. Aims: To integrate observed variations in tropical vegetation structure and floristic composition into a single classification scheme. Methods: Using structural and floristic measurements made on three continents, discrete tropical vegetation groupings were defined on the basis of overstorey and understorey structure and species compositions by using clustering techniques. Results: Twelve structural groupings were identified based on height and canopy cover of the dominant upper stratum and the extent of lower-strata woody shrub cover and grass cover. Structural classifications did not, however, always agree with those based on floristic composition, especially for plots located in the forest–savanna transition zone. This duality is incorporated into a new tropical vegetation classification scheme. Conclusions: Both floristics and stand structure are important criteria for the meaningful delineation of tropical vegetation formations, especially in the forest/savanna transition zone. A new tropical vegetation classification scheme incorporating this information has been developed.

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.

Annual variation in soil respiration and its component parts in two structurally contrasting woody savannas in Central Brazil

Background and aimsDue to the high spatial and temporal variation in soil CO2 efflux, terrestrial carbon budgets rely on a detailed understanding of the drivers of soil respiration from a diverse range of ecosystems and climate zones. In this study we aim to evaluate the independent influence of vegetation structure and climate on soil CO2 efflux within cerrado ecosystems.MethodsWe examine the seasonal and diel variation of soil CO2 efflux, including its autotrophic and heterotrophic components, within two adjacent and structurally contrasting woody savannas in central Brazil.Principle resultsWe found no significant difference in the annual soil CO2 efflux between the two stands (p = 0.53) despite a clear disparity in both LAI (p < 0.01) and leaf litterfall (p < 0.01). The mean annual loss of carbon from the soil was 17.32(±1.48) Mg C ha−1 of which approximately 63% was accounted for by autotrophic respiration. The relative contribution of autotrophic respiration varied seasonally between 55% in the wet season to 79% of the total soil CO2 efflux in the dry season. Furthermore, seasonal fluctuations of all the soil respiration components were strongly correlated with soil moisture (R2 = 0.79–0.90, p < 0.01).ConclusionsAcross these two structurally distinct cerrado stands, seasonal variations in rainfall, was the main driver of soil CO2 efflux and its components. Consequently, soil respiration within these ecosystems is likely to be highly sensitive to any changes in seasonal precipitation patterns.

Influence of edaphic variables on the floristic composition and structure of the tree-shrub vegetation in typical and rocky outcrop cerrado areas in Serra Negra, Goiás State, Brazil

The present study analyzed the influence of edaphic variables on the floristic compositions and structures of the arboreal and shrub vegetation of typical cerrado (TC) and rocky outcrop cerrado (RC) communities in the Serra Negra mountain range in Piranhas Municipality, Goias State, Brazil. Ten 20×50m plots were established in each community, and all individuals with minimum diameters ³5cm measured at 30cm above soil level were sampled. Composite soil samples were collected at 0-20cm depths in each plot for physical and chemical analyses. The proportions of above-ground rock cover work also estimated in each RC plot. A total of 2,009 individuals (83 species, 69 genera, and 34 families) were recorded. Qualea parviflora was the only species consistently among the 10 most structurally important taxa in both communities, and was considered a generalist species. The observed and estimated species richnesses were greater in RC than in TC, although plant basal areas and heights did not differ between them. There were positive correlations between rock cover×plant density and rock cover×basal areas. TWINSPAN and PCA analysis separated the TC and RC plots, and three RC habitat specialist species (Wunderlichia mirabilis, Norantea guianensis, and Tibouchina papyrus) were identified. Soil variables were found to have greater effects on the species compositions of the TC and RC sites than the geographic distances between sampling plots. According to CCA analysis, the exclusive (or more abundant species) of each community were correlated with soil variables, and these variables therefore determined the selection of some species and influenced the differentiation of the vegetation structures of the communities studied.

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.

Evolutionary heritage influences Amazon tree ecology

Lineages tend to retain ecological characteristics of their ancestors through time. However, for some traits, selection during evolutionary history may have also played a role in determining trait values. To address the relative importance of these processes requires large-scale quantification of traits and evolutionary relationships among species. The Amazonian tree flora comprises a high diversity of angiosperm lineages and species with widely differing life-history characteristics, providing an excellent system to investigate the combined influences of evolutionary heritage and selection in determining trait variation. We used trait data related to the major axes of life-history variation among tropical trees (e.g. growth and mortality rates) from 577 inventory plots in closed-canopy forest, mapped onto a phylogenetic hypothesis spanning more than 300 genera including all major angiosperm clades to test for evolutionary constraints on traits. We found significant phylogenetic signal (PS) for all traits, consistent with evolutionarily related genera having more similar characteristics than expected by chance. Although there is also evidence for repeated evolution of pioneer and shade tolerant life-history strategies within independent lineages, the existence of significant PS allows clearer predictions of the links between evolutionary diversity, ecosystem function and the response of tropical forests to global change.

Insect galls of the Parque Nacional das Emas (Mineiros, GO, Brazil)

In this study we perform an inventory of the insect leaf galls of the Parque Nacional das Emas, Goias State, Brazil. We found 97 gall morphotypes, distributed on 24 botanical families comprising 37 genera and 55 species. The plant taxa that showed the greatest richness of galls were the families Myrtaceae, with 17 morphotypes and Fabaceae with 14, and the genera Myrcia (Myrtaceae) and Qualea (Vochysiaceae) with 10 and eight morphotypes, respectively. The plant species Andira cujabensis Benth. (Fabaceae) and Myrcia guianensis (Aubl.) DC., with four morphotypes each, were the most diverse. We found galling insects belonging to Diptera, Hemiptera and Lepidoptera. The galling insects of family Cecidomyiidae (Diptera) were the most common inducing 38.1% of the gall morphotypes. All recorded gall morphotypes are first records to Parque Nacional das Emas. Among the 55 host plant species listed in the survey, 16 species (20%) have the first report of hosting galls.

Diversity, abundance and distribution of lianas of the Cerrado–Amazonian forest transition, Brazil

Background: Lianas strongly influence tropical forest dynamics and diversity. Aims: To determine the relationship among richness, diversity, abundance and distribution of liana species in different vegetation formation types along a gradient within a savanna–forest transition zone in central Brazil. Methods: All liana species were identified and their girth measurements (≥5 cm) taken in one 1 ha plot at each of 15 sites that encompassed a range of vegetation types: dystrophic cerradão (tall closed woodland cerrado), gallery forest, flooded forest, semi-deciduous seasonal forest (one monodominant) and evergreen forest. We evaluated and compared the communities in terms of richness, community diversity (Shannons H’), equitability (Hurlberts, PIE), and the distribution of liana abundance. Results: In total, 1467 individual lianas belonging to 65 species, 41 genera and 17 families were recorded in the 15 ha sampled. The value of H’ varied from 0–2.47, and that of PIE ranged from 0–0.90. While flooded forests had remarkably high liana densities, their liana community was dominated by just one species, Combretum laxum (64% of stems); the most abundant liana in non-flooded forests was Heteropterys eglandulosa (13%). The different liana species showed varying affiliations with vegetation type, with distinct species groupings associated with the different vegetation types. Conclusions: Variations in species composition and distribution of lianas in this savanna–forest transition were found to be driven by environmental gradients that cause distinct species associations with discrete vegetation formation types.

Dynamics of the woody vegetation of two areas of Cerrado sensu stricto located on different substrates

Differences in substrates can provoke distinct responses in the dynamics of a plant community. We compared changes the floristic, structural and dynamic parameters of the woody vegetation between burned sites dominated by cerrado tipico (CT) and cerrado rupestre (CR), which is characterized by the presence of rocky outcrops, over time. We set up 10 plots (20 m × 50 m) at each site. All individuals (diameter of ≥ 3 cm at 30 cm height above the ground) were identified in the two censuses (2009 and 2012) and measured (stem diameter), after an accidental fire in 2008. Changes in floristic parameters between the CT and CR were not significant. However, we found significant differences (p < 0.05) in structural and dynamic parameters, such as density (CT = 1,523; CR = 2,171 ind.ha-1), basal area (CT = 8.70; CR = 13.00 m2.ha-1), recruitment rates (CT = 24.35; CR = 15.14% year-1; p = 0.01), gain (CT = 8.58; CR= 3.58% year-1), and the loss rates of basal area (CT = 3.88; CR= 2.45% year-1). These differences emphasize the need for a differential evaluation of these sites for the development of effective conservation strategies.

Trait data from: "Evolutionary heritage influences Amazon tree ecology"

Lineages tend to retain ecological characteristics of their ancestors through time. However, for some traits, selection during evolutionary history may have also played a role in determining trait values. To address the relative importance of these processes requires large-scale quantification of traits and evolutionary relationships amongst species. The Amazonian tree flora comprises a high diversity of angiosperm lineages and species with widely differing life history characteristics, providing an excellent system to investigate the combined influences of evolutionary heritage and selection in determining trait variation. We used trait data related to the major axes of life history variation among tropical trees (e.g. growth and mortality rates) from 577 inventory plots in closed-canopy forest, mapped onto a phylogenetic hypothesis spanning >300 genera including all major angiosperm clades to test for evolutionary constraints on traits. We found significant phylogenetic signal for all traits, consistent with evolutionarily related genera having more similar characteristics than expected by chance. Although there is also evidence for repeated evolution of similar, pioneer and shade tolerant life history strategies within independent lineages, the existence of significant phylogenetic signal allowsLineages tend to retain ecological characteristics of their ancestors through time. However, for some traits, selection during evolutionary history may have also played a role in determining trait values. To address the relative importance of these processes requires large-scale quantification of traits and evolutionary relationships amongst species. The Amazonian tree flora comprises a high diversity of angiosperm lineages and species with widely differing life history characteristics, providing an excellent system to investigate the combined influences of evolutionary heritage and selection in determining trait variation. We used trait data related to the major axes of life history variation among tropical trees (e.g. growth and mortality rates) from 577 inventory plots in closed-canopy forest, mapped onto a phylogenetic hypothesis spanning >300 genera including all major angiosperm clades to test for evolutionary constraints on traits. We found significant phylogenetic signal for all traits, consistent with evolutionarily related genera having more similar characteristics than expected by chance. Although there is also evidence for repeated evolution of similar, pioneer and shade tolerant life history strategies within independent lineages, the existence of significant phylogenetic signal allows clearer predictions of the links between evolutionary diversity, ecosystem function and the response of tropical forests to global change. clearer predictions of the links between evolutionary diversity, ecosystem function and the response of tropical forests to global change.