Jeanine Maria Felfili

Savanna vegetation-fire-climate relationships differ among continents.

Surveying Savannas Savannas are structurally similar across the three major continents where they occur, leading to the assumption that the factors controlling vegetation structure and function are broadly similar, too. Lehmann et al. (p. 548) report the results of an extensive analysis of ground-based tree abundance in savannas, sampled at more than 2000 sites in Africa, Australia, and South America. All savannas, independent of region, shared a common functional property in the way that moisture and fire regulated tree abundance. However, despite qualitative similarity in the moisture–fire–tree-biomass relationships among continents, key quantitative differences exist among the three regions, presumably as a result of unique evolutionary histories and climatic domains. Evolution cannot be overlooked when aiming to predict the potential global impacts on savanna dynamics in a warming world. Ecologists have long sought to understand the factors controlling the structure of savanna vegetation. Using data from 2154 sites in savannas across Africa, Australia, and South America, we found that increasing moisture availability drives increases in fire and tree basal area, whereas fire reduces tree basal area. However, among continents, the magnitude of these effects varied substantially, so that a single model cannot adequately represent savanna woody biomass across these regions. Historical and environmental differences drive the regional variation in the functional relationships between woody vegetation, fire, and climate. These same differences will determine the regional responses of vegetation to future climates, with implications for global carbon stocks.

A comparative study of cerrado ( sensu stricto ) vegetation in Central Brazil

Floristic and structural comparisons and a numerical classification were performed to identify the priority areas for conservation of genetic resources in central Brazil. The main type of woody vegetation, cerrado sensu stricto (savanna woodland with 10–60% tree cover), was sampled under a uniform methodology in six selected sites (total sample of 6 ha) scattered in a physiographic unit called the Pratinha Plateau located between 15–20° S and 46–49° W. A total of 6971 trees belonging to 139 species and 42 families was measured. Each site had a combination of 50–80 species and approximately 30 families but only 22 species from 14 families were common to all sites. Similarity decreased with distance, indicating the existence of geographical gradients as the physical characteristics were relatively uniform and the soils were dystrophic at all sites. The most dissimilar sites, in the localities of Patrocinio-MG and Paracatu-MG were recommended for the establishment of conservation units. The already existent conservation units arc all clumped in the Federal District and are not enough to protect the genetic heritage of the plateau. Floristics and phytosociological surveys based on land system zoning were recommended as useful tools in planning conservation areas at a regional level to preserve the maximum biodiversity.

DIVERSITY, STRUCTURE AND DYNAMICS OF A GALLERY FOREST IN CENTRAL BRAZIL

The structure and dynamics of approximately 64 ha of undisturbed gallery forest were studied over six years. Trees from 31 cm gbh (c. 10 cm dbh) were measured every three years from 1985. They were in 151 (10×20 m) permanent plots in the Gama forest in the Federal District of Brazil. Natural regeneration (individuals under 31 cm gbh) was measured in subplots (of 2×2 m, 5×5 m and 10×10 m) within the 200 m2 plots. The total tree flora (gbh≥31 cm) consisted of 93 species, 81 genera and 44 families in 1985. The Leguminosae, Myrtaceae and Rubiaceae were the families richest in number of species. Most individuals and species were under 45 cm diameter and 20 m high while the maximum diameter per species ranged from 30 to 95 cm. The density structure of trees and natural regeneration was similar, in which the densities of c. 80% of the species represented less than 1% of the total density. The periodic mean annual diameter increment for trees from 10 cm dbh, was c. 0.25 cm/year. Variability was high with coefficients of variation c. 100% or more. The Gama community may maintain tree diversity and structure in undisturbed conditions. Regeneration of c. 80% of the species was found in the establishing phase (poles); the diameter structure was typical of native forests with the number of individuals decreasing with increasing size classes and showing little change over the six years; recruitment compensated for the mortality of most of the abundant species. The soils in Gama gallery forest were dystrophic with high aluminium content. Multivariate analysis suggested the stream, natural gaps and edges as the main causes of floristic differentiation at the community level.

Diversity, floristic and structural patterns of cerrado vegetation in Central Brazil

The cerrado has been identified as one of the richest and most threatened biomes of the world, but few phytogeographical studies have been undertaken in the region. A total of 70 land systems based on climate, landscape and soils have been identified in the region, but it remains to be seen if the distribution and structure of the plant communities support these divisions. The aim of this work was to compare the floristic and structural similarity of cerrado sensu stricto within and between three physiographic units, named Pratinha, Veadeiros and São Francisco, which contain six land systems in central Brazil and cover 10 degrees of latitude and five degrees of longitude. The woody vegetation of 15 selected sites of the cerrado sensu stricto physiognomy was surveyed under a standardized methodology. The number of species per site varied from 55 to 97, with most sites having around 60 to 70 species, and Shannon´s diversity indices ranged from 3.44 to 3.73, with most sites around 3.5 suggesting high alpha diversity. Sørensen´s floristic similarity index was high, with all Figures above 0.5 between the sites in the same land system in each physiographic unit but low between sites in different land systems in the Veadeiros. Czekanowski similarity indices were lower than Sørensen’s in the comparisons due to a high structural differentiation between the sites. There is a large overlap in species occurrence in the sites but the size of their populations is very different at each site. Therefore, the high beta diversity is mostly due to differences in abundance of species between sites. The sites were separated by physiographic units, considering the first three divisions of TWINSPAN classification. The first axis of DCA ordination showed a gradient going from the cerrado on deep soils in Pratinha, through to those on sandy soils in São Francisco and ending on the shallower soils of the Veadeiros. Land systems conformed well with the floristic and structural variations of the vegetation, indicating their potential use in designing a network of conservation areas in the cerrado region and as a basis for decision-making on management.

Changes in the floristic composition of cerrado sensu stricto in Brazil over a nine-year period.

Changes in floristic composition and structure in a cerrado sensu stricto area were studied over a 9-y period. A sample of 19 (20-m x 50-m) permanent plots was assessed at 3-y intervals from 1985 to 1994, when all stems ≥ 5 cm at 0.30 m above the ground level were measured. There was little change in species composition over the period. Changes in density and basal area of the whole community were in the range of 5% over the 9 y. These parameters fluctuated over the years with the greatest differences found in the comparisons of 1991, 2 y after an accidental fire reached the site, with other years. The changes in density and basal area were greater than in several tropical forests, probably due to disturbances such as fire occurring at 3 to 5-y intervals, The nearly constant density and basal area suggested a highly resilient community.

Growth, recruitment and mortality in the Gama gallery forest in central Brazil over a six-year period (1985–1991)

Diameter increments, recruitment and mortality were studied over a six-year period in a 3.02 ha sample in an area of 64 ha of undisturbed gallery forest alongside the Gama stream. The study site is located in Fazenda Agua Limpa in Brasilia, Federal District, Brazil. Trees ≥ 31 cm gbh (10 cm dbh) were measured every three years from 1985 in 151 (10 m × 20 m) permanent plots in Gama forest. The mean annual diameter increment for trees ≥ 10 cm dbh was 0.25 cm y -1 . Variability was high with coefficients of variation c. 100% or more. Light-demanding and large upper storey species tended to grow faster than shade-tolerant and lower storey species. Mean increments for the community increased with increasing diameter classes. The mean annual mortality rate for the community was 3.5% y −1 while the recruitment was 2.7%. The community was dynamic with 86% of all species either suffering mortality or gaining recruits or both during the six years. The net difference between recruitment and mortality was zero for 55 species. The recruitment compensated for the mortality of most of the abundant species.

Comportamento de plântulas de Sclerolobium paniculatum Vog. var. rubiginosum (Tul.) Benth. sob diferentes níveis de sombreamento, em viveiro

The gallery forests of Central Brazil are very diverse, but over the last two decades, recurrent fires, deforestation and mining activities have become increasingly threatening to their maintenance. Impoverishment of the fauna, erosion and other consequences followed their disappearance. Therefore, the establishment of some criteria to restore the gallery forest is urgent. The objective of this study was to analyse the responses of Sclerolobium paniculatum to four shading levels, which simulated gallery forest conditions. The experimental design was randomised with four treatments containing 15 replicates each. The treatments were: full sunlight (0% shading), representing a fully degraded site; a gap condition (average 50% shading); a closing canopy condition (70% shading) and, closed canopy condition (90% shading). Base stem diameter, height, number of leaves and leaflets were measured every two months during twelve months. Dry weight was determined at the end of the experiment. The highest values of biomass and base steam diameter were attained in gaps and full sunlight conditions, suggesting that it is a pioneer species. Therefore, Sclerolobium paniculatum should be planted at the initial stage of succession in degraded forests.

Dynamics of the natural regeneration in the Gama gallery forest in central Brazil

Abstract Permanent plots were studied over 6 years in approximately 64 ha of undisturbed gallery forest alongside the Gama stream in the Federal District, Brazil. Trees from 31 cm girth at breast height (gbh) (ca. 10 cm diameter at breast height (dbh)) were measured every 3 years from 1985 in 151 (10 m × 20 m) permanent plots. Natural regeneration (individuals under 31 cm gbh) was measured in 1986, 1989 and 1991 in subplots within the 200 m2 plots. The total tree flora (gbh ≥ 31 cm) consisted of 93 species, 81 genera and 44 families in 1985. Almost all species, present as trees, had seedlings and saplings at some time during the measurement period, but for most species one of these phases was missing on some occasions. Regeneration of about 80% of the species occurred in the establishment phase (poles). The density structure of trees and natural regeneration was similar to each other with more than 80% of the species occurring at low densities. The rate of decrease between successive height classes was around 50%, indicating the typical low level of establishment for juveniles in tropical forests. The species most abundant as trees also had abundant regeneration, apart from few exceptions. Therefore, the Gama community seems to be robust enough to maintain a diversity of species and structure in undisturbed conditions.

Diversidade alfa e beta no cerrado sensu strictu da Chapada Pratinha, Brasil

The cerrado flora is one of the richest among the worlds savannas with more than 6000 species. The cerrado covers a large territory, contains the three most important hydrographycal basins in South America and a high diversity. The objective of this work, that is part of the project Biogeography of the Cerrado Biome, was to analyse alfa and beta diversity in the cerrado sensu stricto. The sampled places were: Brasilia National Park ¾ DF, Aguas Emendadas Ecological Station ¾ DF, Environmentally protected Area of Gama-Cabeca de Veado ¾ DF, Silvânia ¾ GO, Paracatu ¾ MG and Patrocinio ¾ MG. The sampling was randomized with 10 plots of 20x50m in each study-site. Woody plants from 5cm dbh, excluding lianas were sampled. Shannon & Wienners and Simpsons diversity index were used to calculate alfa diversity and Whittakers index for beta diversity. The latter measures the rate of replacement in species composition from one place to another. A species-area curve was also drawn for the sixty plots sampled. A classification by the TWINSPAN method was also carried out. The cerrado sensu stricto in Chapada Pratinha can be separated in two phytogeographic zones: Distrito Federal ¾ Silvânia and Paracatu ¾ Patrocinio. Those coincide with a land system classification which places the first zone in the highlands and the second in the lowlands.

Mudanças temporais na composição florística e na diversidade de um cerrado sensu stricto do Brasil Central em um período de 18 anos (1985-2003)

Inventories were conducted at three-year intervals in 19 permanent plots of 1000 m2 located at Fazenda Agua Limpa (FAL) - DF. Three events of disturbance by fire occurred in the area. A total of 69 species, 54 genera and 35 families were registered. Floristic composition was compared using the modified Morisita-Horn index, a quantitative similarity index, and Sorensen, a qualitative index. Both indices showed high similarity between inventories with little change in species composition over time. Changes in richness caused differences in the values of Simpsons index, and Shannons index according to Hutchesons t-test (P < 0.05). Floristic composition has not changed over time under the current fire regime. But diversity increased after a longer interval without fire. In this nine-year period free from fire, new species appeared and others returned to the plots, increasing diversity, but not up to its initial values.