J. A. Ratter

Analysis of the floristic composition of the Brazilian cerrado vegetation II: Comparison of the woody vegetation of 98 areas

An analysis was made of the floristic composition of 98 areas of cerrado and Amazonian savanna, encompassing most of the area of such vegetation in Brazil. A total of 534 species of trees and large shrubs were recorded for these areas, of which 158 (30%) occurred at a single site only. Such unicates and taxa without determinations to specific level were excluded from the study since they provide no basis for comparison. The data were analysed by three techniques of multivariate analysis: (a) a divisive hierarchical classification by Two-way Indicator Species Analysis (TWINSPAN). (b) an agglomerative hierarchical classification by UPGMA (Unweighted Pair-Groups Method using Arithmetic Averages) using the Sorensen Coefficient of Community (CC) as a measure of similarity, and (c) an ordination by Detrended Correspondence Analysis (DCA). The results from all three methods showed great similarity, demonstrating a strong geographic pattern in the distribution of the flora of the cerrado biome and allowing the recognition of southern (Sâo Paulo and S Minas Gerais), southeastern (largely Minas Gerais), central (Federal District, Goias and parts of Minas Gerais), central-western (largely Mato Grosso, Goias and Mato Grosso do Sul) and northern groups (principally Maranhao, Tocantins and Para), as well as a disjunct group of Amazonian savannas. Soil type (mesotrophic or dystrophic) is an important factor in determining floristic composition. The study demonstrated that cerrado vegetation is extremely heterogeneous: none of the 534 species occurred at all sites and only 28 species were present at 50% or more.

A study of the origin of central Brazilian forests by the analysis of plant species distribution patterns

The floristic nature of central Brazilian forests, as well as their links to other main forest formations of eastern tropical South America, is assessed by means of multivariate analyses of 106 existing floristic checklists and by the analysis of a series of dot-maps showing the distribution of 55 woody species. Most species of central Brazilian forests seem to conform to two main distribution patterns: (1) species of deciduous and semideciduous forests are dependent essentially on the occurrence of patches of soils of intermediate to high fertility within the cerrado domain and tend to be distributed mostly along a northeast-southwest arch connecting the caatingas to the chaco boundaries; (2) considerable numbers of gallery forest species are dependent on high soil moisture and many appear to link the Amazonian and Atlantic rainforests by crossing the cerrado region in a northwest-southeast route via the dendritic net of gallery forests. Many gallery forest species are habitat generalists, some even occurring in the cerrado vegetation. Nevertheless, significant numbers of gallery endemics are also present. Galleries of the west and north of the Cerrado Province show stronger floristic links to the Amazonian rainforests, while those of the centre and south show stronger affinity with the montane semideciduous forests of southeastern Brazil. Present-day distribution patterns are discussed in the light of the current knowledge of palaeoenvironmental changes in the Neotropics.

Soil resources and plant communities of the central Brazilian cerrado and their development

Cerrado is the natural vegetation of the poorer soils in central Brazil and covers approximately 23% of the land area of the country. It has a marked seasonal climate and possesses a large characteris- tic flora of fire-resistant plants including about 800 species of trees and large shrubs. The soils are acidic with low CEC and high levels of Al saturation. They are well drained and the majority are Oxisols (ferrallitic soils). The vegetation ranges from treeless grasslands to closed xeromorphic forests. Attempts have been made to correlate increased density of the woody vegetation with gradients in soil nutrients but the relationship is complex. Two floristically different types of cerradao (closed savanna woodland) are associated with mesotrophic and dystrophic soils respectively. Fire is also an important factor in influencing the density of woody vegetation. A distinct community of cerrado trees and shrubs occurs in areas where the water table is periodically high. Aluminium is an important factor in cerrado soils and frequently occurs at levels toxic to cultivated plants. On the other hand, the native species are adapted to high Al levels and a number are Al accumulators. Much of the cerrado area is now cultivated. The strategy has been to

SUCCESSIONAL CHANGES IN CERRADO AND CERRADO/FOREST ECOTONAL VEGETATION IN WESTERN SÃO PAULO STATE, BRAZIL, 1962-2000

Surveys over a period of 38 years have shown a rapid successional change in the remaining areas of cerrado vegetation in western Sao Paulo State. Cerradao (the dense, tall, forest form of cerrado (sensu lato)) and cerrado/Atlantic forest ecotonal vegetation have replaced more open forms (such as campo cerrado) during this period. An aerial photographic survey in 1962 showed 75% cerrado (sensu stricto), 16% campo cerrado, and only 9% cerradao, while a survey combining Landsat imaging of 1992 with aerial photography of 1984 gave 69%, 0.6%, and 30.5% respectively for the same physiognomies. Visiting 10% of the sites of the latter survey in 2000 showed that cerradao had become the dominant vegetation of 68% of them. In a particular 180 ha site in Assis municipality, cerradao increased from 12.0 to 41.4% of the area in 22 years. Reduction of anthropic pressures, such as fire and cattle-grazing, is considered responsible for these rapid changes. Conservation issues and research priorities related to these changes are discussed and proposed.

Biogeographic patterns, β-diversity and dominance in the cerrado biome of Brazil

From a total woody flora of ca. 1000 species, a suite of 121 species forms an oligarchy dominating the cerrado biome. This mirrors patterns of dominance described in western Amazonian rain forests. Widespread sampling shows that across the biome this suite of species contributes on average 66% of the total species composition, and 75% of the total Importance Value Index in cerrado communities. An analysis of the floristic similarity between six cerrado phytogeographic provinces (southern, central and south-eastern, central-western, far-western, north-eastern, disjunct Amazonian) reveals great heterogeneity within the biome, principally of the less common species. Of the 951 species recorded from 375 floristic surveys across the biome, 494 species (more than half of the total) are found in only one of the provinces, with very few species (37, i.e., 3.9%) found in all six provinces. Each of the provinces contains a significant number of species which are apparently confined to it, ranging from 15 species (1.6% of the total woody cerrado flora) in the far-western province (primarily in the state of Rondônia) to 162 species (17%) in the central-western province. At the local level, floristic similarity can be very high. An analysis of the floristic composition of 13 sites within the Federal District shows a woody flora of 236 species, indicating that 25% of the total woody flora of the cerrado biome is represented in 0.3% of its area, illustrating the great conservation importance of this region. Floristic similarity between sites within the Federal District is high, although much of this similarity is accounted for by ‘oligarch’ species which account for between 59 and 89% of total species recorded per site. Informed conservation judgements within the cerrado need to take account of regional floristic patterns to ensure maximum protection of biodiversity, as the majority of species are not geographically widespread within the biome.

Floristic Composition and Community Structure of a Central Brazilian Gallery Forest

Summary An intensive study was made of a gallery forest near Cuiaba, State of Mato Grosso. Analysis of the vegetation on 67 plots of 30 m 2 demonstrated a great deal of heterogeneity related principally to differences in topography and drainage. Four distinct communities were recognized: dry cerradao, wet cerradao, wet forest and swampy forest. Comparison of an informal site classification based on field observations, showed a very high degree of coincidence with ordination and a hierarchical classification based on analysis of floristic, topographic and soil data from plots. A total of 89 species with individuals ≥3 cm basal diameter were recorded. Soil data for the plots are also presented.

OBSERVATIONS ON THE VEGETATION OF NORTHEASTERN MATO GROSSO, BRAZIL. IV. AN ANALYSIS OF THE CERRADO–AMAZONIAN FOREST ECOTONE

A study was made of the transition between the cerrado and Amazonian forest biomes on the Serra do Roncador in the northeast of Mato Grosso State, Brazil. The transition was sampled by recording the species and circumference at breast height (cbh) of all woody species ≥ 15 cm cbh on five 20 × 10 m plots in each of the following four communities: ecotonal vegetation (Cerradao areas 1 and 2), and forest (Forest areas 1 and 2); while in the Cerrado sensu stricto a more rapid method had to be used because of time constraints. A total of 138 species was recorded and the results were analysed using Sorensen and Morisita Indices, TWINSPAN and DCA. In addition, comparisons were made with data from studies undertaken in 1968 in the same area by the Xavantina-Cachimbo Expedition. No species was common to all communities sampled but a seral succession of important species occurs along the transition. The Sorensen and Morisita Indices demonstrate this, with the Cerrado s.s . and Forest 2 at the two extremes showing no species in common (zero similarity) and Cerradao 1 and 2 giving the very high figures of Sorensen 0.64 and Morisita 0.84. The ecotonal cerradao is a very characteristic Dystrophic facies cerradao with Hirtella glandulosa, Emmotum nitens, Sclerolobium paniculatum and Vochysia haenkeana as its typical indicator species. The ecotone studied in the present work represents the comparatively abrupt transition from cerrado to the peripheral form of Amazonian forest (dry forest, mata seca ) on flat terrain with a uniform very dystrophic soil. Other workers have suggested that this type of transition may be restricted to the headwaters of the Xingu basin, but one of the present authors has seen similar vegetation at localities in Maranhao, Rondonia, and on the Mato Grosso–Rondonia border. Comparison of the present vegetation with the survey made in 1968 shows that in this area the advancing face of the Amazonian forest has extended about 7 km southwards into the cerrado. However, in the majority of places this process has been obscured by forest clearing for agriculture. The study draws attention to the urgent need for the establishment of conservation areas in this extremely threatened and very little studied ecotone.

THE VEGETATION OF PRIORITY AREAS FOR CERRADO CONSERVATION IN SÃO PAULO STATE, BRAZIL

Natural cerrado vegetation in Sao Paulo State now covers less than 7% of its original area and exists only as isolated fragments. Eighty-six sites in these priority cerrado conservation areas were surveyed using a rapid assessment technique. A total of 554 species of vascular plants, belonging to 77 families, was recorded. The vegetation types encountered comprised: campo sujo, campo cerrado, cerrado sensu stricto , cerradao, wet campo, riparian forest, swamp forest, ecotone cerrado/forest and seasonal semi-deciduous forest. Two-Way Indicator Species Analysis (TWINSPAN), Detrended Correspondence Analysis (DCA) and Unweighted Pair-Groups Method using Arithmetic Averages (UPGMA) revealed a weak similarity pattern based on geography, but divided the sites into two main structural groups: (a) areas where more open forms of cerrado occur (cerrado sensu stricto , campo cerrado); (b) areas where only forest physiognomies occur (cerradao, ecotone cerradao/seasonal semi-deciduous forest, or riparian forest). The first group tends to be located in the east and the second in the west of Sao Paulo State. Cerradao was the most frequent vegetation type, observed in 70% of the sites. Cerrado sensu stricto was recorded in only 31% of the sites. Casearia sylvestris and Byrsonima intermedia were the most widespread species, recorded in 90% and 88% of the sites, respectively. Only 10% of the species were found in 50% or more of the sites, while 19% of species were recorded at a single site only. There was a considerable difference in species number between sites, from a minimum of 29 at Taubate to a maximum of 185 in one of those at Campos Novos Paulista. As shown in other studies, species richness is directly correlated with diversity of vegetation types occurring at a site (beta diversity). As expected, the seven richest fragments contain ecotonal vegetation, which combines both forest and cerrado elements.

Effect of forest clearance and burning on soil properties in northern Roraima, Brazil

Abstract Clearance of evergreen seasonal forest for cattle pasture is examined in an area of northern Roraima. Coloniao (Panicum maximum Jacq.) and kikuyu grass (Brachiaria humidicola (Rendle) Schweik.) are commonly established on cleared forest land. Current rates of clearance are rather low as also is grazing intensity (1–2 animals ha−1), but soil physical and chemical changes are occurring. Thus, topsoil bulk density increases over time in new pastures. Also, available nutrients decline from the enhanced levels that prevail after initial clearance and burning. In particular, available P is low in the acid soils and, as elsewhere in Amaonia, probably limiting to pasture growth. For local ranchers, the best source of nutrients is the standing forest, so every incentive exists to continue forest destruction for new pasture.

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.