Flavonoids ofBignoniaceae from the “cerrado” and their possible taxonomic significance

Flavones and glycosides of flavones and flavonols were obtained from leaves of five species ofBignoniaceae from the cerrado, a savanna ecosystem of Central and Southeast Brazil. A predominance of flavonol glycosides was observed in all samples investigated. Flavones were often found in species of tribeTecomeae and rarely inBignonieae. The species of the former yielded derivatives of 6-hydroxyluteolin. No 6-oxygenated compounds were found in species ofBignonieae. The results point to the flavonoid chemistry evolution ofBignoniaceae following a path of simplification. More complex chemical profiles characterize the more woodyTecomeae rather than the more advancedBignonieae.     

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.     

Revision of the cerrado hemicryptophytic Chamaesyce of Boissier's “Pleiadeniae” (Euphorbiaceae)

The species ofChamaesyce classified by Boissier as the “Pleiadeniae” are revised in light of presently available collections. Six species are accepted and new combinations are proposed forC. nana, C. setosa, C. tamanduana, andC. viscoides. Although these herbaceous perennials of cerrado vegetation of Brazil, northern Argentina, and adjacent countries are distinctive ecologically and geographically, cladistic analysis does not support their recognition as a monophyletic group.     

Are the cerrado and the seasonal forest woody floras assembled by different processes despite their spatial proximity?

Aims The Brazilian cerrado occupies land that could be occupied by seasonal forest, given current climatic conditions and their spatial proximity. Soil has been identified as one of the main determinants of cerrado and forest prevalence. We tested whether cerrado and seasonal forest woody floras were assembled by different processes. We postulated that soil nutrient availability would account for differences in the functional and phylogenetic structure of the cerrado and the seasonal forest.     

Changes in cerrado vegetation after disturbance by frost (São Paulo State,Brazil)

We report changes after frost in cerrado species populations and community structure in Assis, São Paulo State, Brazil and consider the possible impacts of frost on cerrado types and their distribution. Four permanent plots (10 m × 10 m) were established and 736 individuals were marked with enumerated plastic labels and measured one week after the frost. Frost damage for each individual was assessed: 0 - not affected; 1 - slightly affected; 2 - substantially affected; and 3 - strongly affected. The frost impact on vegetation structure was high, reducing tree canopy cover from 88% to 19% in the upper stratum and that of the lower stratum from 48% to 8.5%. Floristic richness did not change, even though a small number (3%) of individuals of some species died. Conversely, the relative dominance of species changed dramatically in the short-term because of varying susceptibility to frost of different species. The largest reductions in crown cover were observed in Xylopia aromatica and Vochysia tucanorum. Of the 57 species recorded, 15% were unaffected, 19% had only their leaves damaged, 25% had some of their leaves and branches damaged, and 41% had all their aerial parts killed. The majority of individuals in the community belonged to frost tolerant species. The regeneration of the stand structure was remarkably rapid; height and canopy cover of the lower stratum recovered completely after five months, and those of the arboreal stratum showed a recovery of about 80% after 11 months. We consider that the frequency and intensity of frosts can maintain more open forms of cerrado vegetation even in sites where both water and nutrient availability could support denser vegetation. It is also probable that some frost-resistant heliophyte species are confined to areas where frosts prevent the development of denser cerrado vegetation. Much of the characteristic floristic composition of the southern region of the cerrado biome may be related to the selection of frost-resistant species. Our study shows, however, that a full complement of cerrado plants is capable of occupying and colonizing frost susceptible sites.     

Protected cerrado fragments grow up and lose even metapopulational birds in central S?o Paulo, Brazil.

Moderately dense woodland (cerrad?o) grew in two isolated patches of bushy savanna (cerrado) in central S?o Paulo over 23 years of bird censuses. Various uncommon birds were lost and some forest species were permanently gained. Fall and winter fruits attract long and short-distance migrants. Woodpeckers and some birds that nest in their holes seem to disappear during tree growth. Some birds in weedy areas nearby disappeared when the pastures replaced these areas, however sugar cane reduced the numbers of birds even more up to the point when some areas became pastures once more. Even travel-prone species disappear with vegetation growth in cerrado protected fragments, and therefore "metapopulations" may not survive over time, only in space.     

Insecticidal activity of cerrado plant extracts on Rhodnius milesi Carcavallo, Rocha, Galvão & Jurberg (Hemiptera: Reduviidae), under laboratory conditions

Chagas' disease is chiefly transmitted by feces of haematophagous bugs (Triatominae) that ingested Trypanosoma cruzi from blood of infected people or animals. Pyrethroids have been the main insecticides used against these insects. However, some populations of insects have shown significant levels of resistance to several pyrethroids, indicating the need of new insecticides for the control of triatomines. Insecticidal activity of 24 Cerrado plant extracts belonging to five species of four families were assayed on fourth instar nymphs of Rhodnius milesi Carcavallo, Rocha, Galv?o & Jurberg (Hemiptera: Reduviidae), under laboratory conditions. For the extract application on triatomines, 50 microg of the extract were topically applied in duplicate on dorsal tergites of ten insects. Insects topically treated with acetone, ethanol, as well as insects with no treatment were used as controls. Triatomines were observed over a 28-day period. Hexanic and ethanolic extracts of Simarouba versicolor, Guarea kunthiana, Guarea guidonia and Talauma ovata caused mortality between 20% and 95% of R. milesi in comparison with the controls, which showed no insect mortality. These preliminary data suggest that the ethanolic extract of the root bark of S. versicolor and the hexanic extract of the root of G. guidonia, responsible for a 95% and 75% insect mortality, respectively, should be chemically investigated and monitored through biological assays in order to determine their insecticidal components, that could be used as a molecular model or as biorational compounds for use in insect control programmes.     

Reproductive phenological patterns of cerrado plant species at the Pé-de-Gigante Reserve (Santa Rita do Passa Quatro, SP, Brazil): a comparison between the herbaceous and woody floras

A natural vegetation area, with 1269 ha, composed mainly by cerrado, located at Santa Rita do Passa Quatro Municipality, S?o Paulo State, southeastern Brazil (21 degrees 36-39'S, 47 degrees 36-38'W), was studied. From September 1995 to February 1997, a floristic survey was carried out, when all vascular plant species at reproductive stage were collected. The flowering and fruiting patterns of the community were studied, comparing the herbaceous and the woody species. In the herbaceous component, 239 species were found and, in the woody one, 108 species. The woody species flowered mainly at the beginning of the rainy season, while the herbaceous ones produced flowers generally at the end of that season. The proportion of anemo and autochorous species was greater in the herbaceous component. The zoochorous ones, on the contrary, were more frequent in the woody component. At the dry season, when their dispersion is more efficient, the proportion of anemo and autochorous species producing fruits was higher. During the rainy season, when their fruits become attractive for longer time, the zoochorous species fruited more intensely.     

Floral visitors of Chamaecrista debilis (Vogel) Irwin & Barneby (Fabaceae - Caesalpinioideae) at cerrado of Estação Ecológica de Jataí, São Paulo State, Brazil

Although Chamaecrista Moench genus is a very important source of pollen to bees in the Cerrado, this relationship is almost unknown. Within flower visitors of Ch. debilis, we found hymenopterans (Apidae) as the most abundants, but Coleoptera (Buprestidae) and Lepidoptera (Noctuidae) were also collected. Bees of great size are pointed out as effective pollinators of Cassiinae. Only five out of seventeen species of floral visitors of Ch. debilis sampled in cerrado, are indicated as possible pollinators, from which four species were not previously indicated in other papers.     

Tree dynamics of a fire-protected <Emphasis Type="Italic">cerrado sensu stricto</Emphasis> surrounded by forest plantations,over a 13-year period (1991–2004) in Bahia,Brazil

Structural and floristic changes of a fire-protected cerrado sensu stricto are described over a 13-year period. The study site is located in a biological reserve (2,800 ha) surrounded by large Pinus spp. and Eucalyptus spp. plantations (36,000 ha), in southwestern Bahia, Brazil. The region occurs in the outer-core of the Cerrado domain, near the Cerrado-Caatinga ecotone, and is mainly occupied by pasture and cropland. Surveys were carried out in 1991 and 2004 in 13 permanent plots (20 × 50 m). Stems with diameter ≥5 cm at 0.30 m above ground level were identified and measured. Floristic changes were significant (Sørensen´s index = 0.45). Species number rose from 62 to 84 (35.48%). Alpha diversity increased significantly (P > 0.001). New species migrated to the area, and there was an expansion of many fire-sensitive species. Woody layer expanded, increasing 19.09% in density and 14.93% in basal area. Diameter distributions followed a “reversed-j” pattern on both occasions, but differed (P > 0.05) due to a significant increase in the first two size-classes, indicating a high recruitment. Community dynamics was high and had a positive balance between recruitment (3.72% yr^?1) and mortality (1.93% yr^?1). Conversely, mean annual increment was very small, 0.096 cm yr^?1 (SD = 0.14; N = 808). Most species, including many dominant ones, had a positive balance in favor of recruitment and low turnover, indicating that although species immigration rate is high (1.42 spp ha^?1), structural changes in species composition happens at a much slower pace. The surrounding forest plantations are permeable and do not limit species immigration; and may be connecting the reserve with the larger neighboring natural fragments, providing an abundant source for diaspores, and possibly neutralizing any fragmentation effects. Succession is also influenced by the ecotonal condition. The structure and floristics of the cerrado sensu stricto at this site (under present climatic conditions) is fire-dependent.