Eddie Lenza

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.

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.

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.

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.

Carvão pirogênico como condicionante para substrato de mudas de Tachigali vulgaris L.G. Silva & H.C. Lima

The objective of the present study was to investigate the efficiency of charcoal as amendment to the substrate used for high vigor of growing seedlings, testing Tachigali vulgaris as representative species of the ‘Cerrado’ Biome. Amazonian dark earth soil (Terra Preta de Indio), enriched by pyrogenic carbon and available nutrients were taken as model example. The experiment was carried out in the nursery of the State

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.

Impactos do agrupamento do bambu Actinocladum verticillatum (Nees) McClure ex Soderstr. (POACEAE) sobre a vegetação lenhosa de duas fitofisionomias de Cerrado na transição Cerrado-Floresta Amazônica

This study evaluated the effects of a Cerrado native bamboo species (Actinocladum verticillatum) clumps on the floristic composition, diversity and structure of the woody vegetation in two adjacent areas of “cerradao” and typical “cerrado” in the Bacaba Municipal Park, Nova Xavantina, state of Mato Grosso, Brazil. Sixty plots of 10 x 10 m were established, 30 in each forest physiognomy. In each physiognomy, 15 plots were placed in a bamboo-free site (SB) and 15 in a site with an estimated bamboo leaf cover of over 90% (CB). All individuals (shrubs and trees) with a diameter at soil height (DSH = 30 cm aboveground) ≥ 3 cm were sampled. Species richness and diversity, floristic similarity, diameter and height distribution, and the species importance value index (IVI) were evaluated. In general, CB sites of both physiognomies had lower values of number of individuals, species, genera, families, density and basal area compared to SB sites, with marked decrease in these parameters in the cerrado in relation to cerradao. Results suggest that the space occupation and reduction of light incidence caused by bamboo clumping affect seed germination and seedling establishment of Cerrado shrubs and trees, selecting more shade-tolerant species and changing the floristic composition and vegetation structure.

Diversity, floristic composition, and structure of the woody vegetation of the Cerrado in the Cerrado-Amazon transition zone in Mato Grosso, Brazil

We compared the diversity and species composition and the structure of the vegetation of three distinct Cerrado phytophysiognomies (Cerradão, Dense Cerrado, and Typical Cerrado) in the Cerrado–Amazon transition, Mato Grosso (Brazil). Species richness (observed and estimated) in the Cerradão and Dense Cerrado was higher than that recorded in the Typical Cerrado. Species diversity, based on a Rényi profile, was highest in the Dense Cerrado, in comparison with the other phytophysiognomies. We recorded a higher number of exclusive species in the Cerradão and a greater similarity (Morisita and Sørensen indices) between this vegetation type and the Dense Cerrado. While individuals were tallest in the Cerradão and Dense Cerrado and lowest in the Typical Cerrado, there was no difference among phytophysiognomies in mean diameter. A gradient in decreasing species richness and diversity (hypothesis 1) and vegetation vertical structure (hypothesis 3) was expected for the Cerradão–Dense Cerrado–Typical Cerrado; however, neither hypothesis was supported by the results. The Cerradão and Dense Cerrado were most similar in species composition not confirming hypothesis 2, which predicted that the two savanna vegetation types (Dense Cerrado and Typical Cerrado) were more similar to one another than either is to the woodland (Cerradão). Overall, the similarities among the three study communities depended on the type of parameter analyzed. While the species richness and the vertical and structure of the vegetation of the Cerradão and Dense Cerrado are closely similar, the Cerradão and Typical Cerrado are more similar in their species diversity. With regard to the floristic composition, Dense Cerrado occupies an intermediate position between Cerradão and Typical Cerrado.

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.