Crescimento e sobrevivência da castanheira do Brasil em três habitats antropogênicos após dez anos de plantação / Growth and survival over ten years of Brazil-nut trees planted in three anthropogenic habitats in northern Amazonia

No presente estudo analisamos o crescimento e a sobrevivência da castanheira, Bertholletia excelsa (Lecythidaceae) em diferentes condições ambientais e níveis de abertura de dossel em plantações experimentais localizadas na bacia do Rio Trombetas, na Amazônia oriental brasileira. Plantamos 144 mudas em habitats antrópicos com diferentes intensidades de luz: roçados recentemente abandonados (100% de abertura de dossel), capoeira de 2-3 anos (20-80% de abertura de dossel) e castanhal maduro (< 10% de abertura de dossel). Anualmente, durante dez anos, medimos a altura e diâmetro das plantas, e registramos mortalidade e rebrotação. A performance de B. excelsa variou significativamente entre os habitats, tendo a taxa de crescimento mais alta sido observada no roçado. A sobrevivência foi mais alta no roçado (85%) e na capoeira (63%) e mais baixa no castanhal (17%). A capacidade de rebrotação das plantas de castanheira foi maior no roçado, onde as plantas de castanheira se recuperaram após episódios de fogo, a maioria com rebrotação de mais de um caule. Algumas plantas do roçado começaram a produzir flores e frutos aos 9-10 anos do plantio. Nós mostramos que plantas jovens de B. excelsa são heliófilas (com alta demanda de luz), com maior crescimento e sobrevivência em condições de alta luminosidade. Sugerimos a utilização da castanheira em programas de reflorestamento, restauração de áreas degradadas e enriquecimento de floresta secundária, sempre que se adotem medidas adequadas de manejo (e.g., manutenção das condições de exposição direta à luz solar e controle de espécies pioneiras competidoras. (AU)

White sand vegetation in an Amazonian lowland under the perspective of a young geological history.

What controls the formation of patchy substrates of white sand vegetation in the Amazonian lowlands is still unclear. This research integrated the geological history and plant inventories of a white sand vegetation patch confined to one large fan-shaped sandy substrate of northern Amazonia, which is related to a megafan environment. We examined floristic patterns to determine whether abundant species are more often generalists than the rarer one, by comparing the megafan environments and older basement rocks. We also investigated the pattern of species accumulation as a function of increasing sampling effort. All plant groups recorded a high proportion of generalist species on the megafan sediments compared to older basement rocks. The vegetation structure is controlled by topographic gradients resulting from the smooth slope of the megafan morphology and microreliefs imposed by various megafan subenvironments. Late Pleistocene-Holocene environmental disturbances caused by megafan sedimentary processes controlled the distribution of white sand vegetation over a large area of the Amazonian lowlands, and may have also been an important factor in species diversification during this period. The integration of geological and biological data may shed new light on the existence of many patches of white sand vegetation from the plains of northern Amazonia.

A new species of Coccoloba P. Browne (Polygonaceae) from the Brazilian Amazon with exceptionally large leaves

We describe and illustrate a new species of Coccoloba (Polygonaceae), named Coccoloba gigantifolia, from the Brazilian Amazon. It resembles Coccoloba mollis Casar, but differs from the latter species by its much larger leaves in the fertile branches. The species has only been recorded in the Madeira River basin, in the states of Amazonas and Rondônia, in the central and southwestern Brazilian Amazon. The description was based on herbarium material, cultivated plants, and individual trees in their natural habitat. We provide illustrations, photographs, and an identification key with morphological characteristics that distinguish the new taxon from the other two related taxa of the Coccoloba sect. Paniculatae, as well as comments on the geographic distribution and conservation status of the species. (AU)

Conservation implications of the mating system of the Pampa Hermosa landrace of peach palm analyzed with microsatellite markers.

Peach palm (Bactris gasipaes) is cultivated by many indigenous and traditional communities from Amazonia to Central America for its edible fruits, and is currently important for its heart-of-palm. The objective of this study was to investigate the mating system of peach palm, as this is important for conservation and breeding. Eight microsatellite loci were used to genotype 24 open-pollinated progenies from three populations of the Pampa Hermosa landrace maintained in a progeny trial for genetic improvement. Both the multi-locus outcrossing rates (0.95 to 0.99) and the progeny level multi-locus outcrossing rates (0.9 to 1.0) were high, indicating that peach palm is predominantly allogamous. The outcrossing rates among relatives were significantly different from zero (0.101 to 0.202), providing evidence for considerable biparental inbreeding within populations, probably due to farmers planting seeds of a small number of open-pollinated progenies in the same plot. The correlations of paternity estimates were low (0.051 to 0.112), suggesting a large number of pollen sources (9 to 20) participating in pollination of individual fruit bunches. Effective population size estimates suggest that current germplasm collections are insufficient for long-term ex situ conservation. As with most underutilized crops, on farm conservation is the most important component of an integrated conservation strategy.

Hyperdominance in the Amazonian tree flora.

The vast extent of the Amazon Basin has historically restricted the study of its tree communities to the local and regional scales. Here, we provide empirical data on the commonness, rarity, and richness of lowland tree species across the entire Amazon Basin and Guiana Shield (Amazonia), collected in 1170 tree plots in all major forest types. Extrapolations suggest that Amazonia harbors roughly 16,000 tree species, of which just 227 (1.4%) account for half of all trees. Most of these are habitat specialists and only dominant in one or two regions of the basin. We discuss some implications of the finding that a small group of species--less diverse than the North American tree flora--accounts for half of the world's most diverse tree community.

Seed germination from lowland tapir (Tapirus terrestris) fecal samples collected during the dry season in the Northern Brazilian Amazon.

This study evaluated the potential of lowland tapirs as seed dispersers in the northern Brazilian Amazon. The study analyzed the viability of seeds after passage through the gut. Fecal samples were collected from 6 different vegetation physiognomies in Viruá National Park during the dry season. The samples were then kept in a greenhouse for 16 months to allow the seeds to germinate. The seedling species were identified and classified according to the type of fruit, plant habit, seed size and type of ingestion. Of the 111 fecal samples, 94 (84.7%) had viable seeds of 75 species. Melastomataceae was the most frequent family with viable seeds in the fecal samples (69.1% of samples, N= 18 species). The data suggest that the importance of the lowland tapirs as dispersers is not restricted to the species consumed actively by frugivory but also extends to species accidentally consumed during browsing. The occurrence of both large and small viable seeds in the fecal samples as well as a number of large drupes, which probably cannot be transported via endozoochory by any other animal species, provide evidence of the ecological importance of lowland tapirs to the dynamics of the forest-campinarana vegetation mosaic in the region.

Low plant density enhances gene dispersal in the Amazonian understory herb Heliconia acuminata.

In theory, conservation genetics predicts that forest fragmentation will reduce gene dispersal, but in practice, genetic and ecological processes are also dependent on other population characteristics. We used Bayesian genetic analyses to characterize parentage and propagule dispersal in Heliconia acuminata L. C. Richard (Heliconiaceae), a common Amazonian understory plant that is pollinated and dispersed by birds. We studied these processes in two continuous forest sites and three 1-ha fragments in Brazil's Biological Dynamics of Forest Fragments Project. These sites showed variation in the density of H. acuminata. Ten microsatellite markers were used to genotype flowering adults and seedling recruits and to quantify realized pollen and seed dispersal distances, immigration of propagules from outside populations, and reproductive dominance among parents. We tested whether gene dispersal is more dependent on fragmentation or density of reproductive plants. Low plant densities were associated with elevated immigration rates and greater propagule dispersal distances. Reproductive dominance among inside-plot parents was higher for low-density than for high-density populations. Elevated local flower and fruit availability is probably leading to spatially more proximal bird foraging and propagule dispersal in areas with high density of reproductive plants. Nevertheless, genetic diversity, inbreeding coefficients and fine-scale spatial genetic structure were similar across populations, despite differences in gene dispersal. This result may indicate that the opposing processes of longer dispersal events in low-density populations vs. higher diversity of contributing parents in high-density populations balance the resulting genetic outcomes and prevent genetic erosion in small populations and fragments.

Genetic structure of traditional varieties of bitter manioc in three soils in Central Amazonia.

Manioc is the most important food crop that originated in Amazonia. Many studies have increased our understanding of its evolutionary dynamics under cultivation. However, most of them focused on manioc cultivation in environments with low soil fertility, generally Oxisols. Recent ethnobotanical observations showed that bitter manioc also performs well in high fertility soils, such as Amazonian dark earths (ADE) and the floodplain. We used 10 microsatellite loci to investigate the genetic diversity and structure of bitter manioc varieties grown in different soil types in communities of smallholder farmers along the middle Madeira River in Central Amazonia. The genetic diversity of some sweet varieties and seedlings was also evaluated. Adult individuals showed higher levels of genetic diversity and smaller inbreeding coefficients (A ( R ) = 5.52, H ( O ) = 0.576, f = 0.086) than seedlings (A ( R ) = 4.39, H ( O ) = 0.421, f = 0.242). Bitter manioc varieties from the floodplain showed higher levels of genetic diversity (A ( R ) = 5.19, H ( O ) = 0.606) than those from ADE (A ( R ) = 4.45, H ( O ) = 0.538) and from Oxisols (A ( R ) = 4.15, H ( O ) = 0.559). The varieties grown in the floodplain were strongly differentiated from the varieties grown in Oxisols (F ( ST ) = 0.093) and ADE (F ( ST ) = 0.108), suggesting important genetic structuring among varieties grown in the floodplain and upland soils (ADE and Oxisols). This is the first time that genetic divergence of bitter manioc varieties in cultivation in different Amazonian soils in a small geographic area is reported.

Development and characterization of microsatellite markers for the Brazil nut tree Bertholletia excelsa Humb. & Bonpl. (Lecythidaceae).

Twelve polymorphic microsatellite markers were developed for the Brazil nut (Bertholletia excelsa), one of the most valuable non-timber forest products from the Amazon, based on enrichment protocol. Six to 18 (mean 10.4) alleles per locus were identified and the expected heterozygosity ranged from 0.663 to 0.923 based on a screen of 40 individuals from one population of B. excelsa. The combined probabilities of genetic identity (8.39 × 10(-17) ) and paternity exclusion (0.999999) indicated that multilocus genotypes are likely to be unique allowing precise analyses of genetic structure, gene flow, and mating system of this economically important species.

Extreme long-distance dispersal of the lowland tropical rainforest tree Ceiba pentandra L. (Malvaceae) in Africa and the Neotropics.

Many tropical tree species occupy continental expanses of rainforest and flank dispersal barriers such as oceans and mountains. The role of long-distance dispersal in establishing the range of such species is poorly understood. In this study, we test vicariance hypotheses for range disjunctions in the rainforest tree Ceiba pentandra, which is naturally widespread across equatorial Africa and the Neotropics. Approximate molecular clocks were applied to nuclear ribosomal [ITS (internal transcribed spacer)] and chloroplast (psbB-psbF) spacer DNA sampled from 12 Neotropical and five West African populations. The ITS (N=5) and psbB-psbF (N=2) haplotypes exhibited few nucleotide differences, and ITS and psbB-psbF haplotypes were shared by populations on both continents. The low levels of nucleotide divergence falsify vicariance explanations for transatlantic and cross-Andean range disjunctions. The study shows how extreme long-distance dispersal, via wind or marine currents, creates taxonomic similarities in the plant communities of Africa and the Neotropics.

Demographic threats to the sustainability of Brazil nut exploitation.

A comparative analysis of 23 populations of the Brazil nut tree (Bertholletia excelsa) across the Brazilian, Peruvian, and Bolivian Amazon shows that the history and intensity of Brazil nut exploitation are major determinants of population size structure. Populations subjected to persistent levels of harvest lack juvenile trees less than 60 centimeters in diameter at breast height; only populations with a history of either light or recent exploitation contain large numbers of juvenile trees. A harvesting model confirms that intensive exploitation levels over the past century are such that juvenile recruitment is insufficient to maintain populations over the long term. Without management, intensively harvested populations will succumb to a process of senescence and demographic collapse, threatening this cornerstone of the Amazonian extractive economy.

Population genetic structure of mahogany (Swietenia macrophylla King, Meliaceae) across the Brazilian Amazon, based on variation at microsatellite loci: implications for conservation.

Mahogany (Swietenia macrophylla, Meliaceae) is the most valuable and intensively exploited Neotropical tree. No information is available regarding the genetic structure of mahogany in South America, yet the region harbours most of the unlogged populations of this prized hardwood. Here we report on the genetic diversity within and the differentiation among seven natural populations separated by up to 2100 km along the southern arc of the Brazilian Amazon basin. We analysed the variation at eight microsatellite loci for 194 adult individuals. All loci were highly variable, with the number of alleles per locus ranging from 13 to 27 (mean = 18.4). High levels of genetic diversity were found for all populations at the eight loci (mean HE = 0.781, range 0.754-0.812). We found moderate but statistically significant genetic differentiation among populations considering both estimators of FST and RST, theta = 0.097 and rho = 0.147, respectively. Estimates of theta and rho were significantly greater than zero for all pairwise population comparisons. Pairwise rho-values were positively and significantly correlated with geographical distance under the isolation-by-distance model. Furthermore, four of the populations exhibited a significant inbreeding coefficient. The finding of local differentiation among Amazonian mahogany populations underscores the need for in situ conservation of multiple populations of S. macrophylla across its distribution in the Brazilian Amazon. In addition, the occurrence of microgeographical genetic differentiation at a local scale indicates the importance of maintaining populations in their diverse habitats, especially in areas with mosaics of topography and soil.