Geological control of floristic composition in Amazonian forests

AIM: Conservation and land-use planning require accurate maps of patterns in species composition and an understanding of the factors that control them. Substantial doubt exists, however, about the existence and determinants of large-area floristic divisions in Amazonia. Here we ask whether Amazonian forests are partitioned into broad-scale floristic units on the basis of geological formations and their edaphic properties. LOCATION: Western and central Amazonia. METHODS: We used Landsat imagery and Shuttle Radar Topography Mission (SRTM) digital elevation data to identify a possible floristic and geological discontinuity of over 300 km in northern Peru. We then used plant inventories and soil sampling to document changes in species composition and soil properties across this boundary. Data were obtained from 138 sites distributed along more than 450 km of road and river. On the basis of our findings, we used broad-scale Landsat and SRTM mosaics to identify similar patterns across western and central Amazonia. RESULTS: The discontinuity identified in Landsat and SRTM data corresponded to a 15-fold change in soil cation concentrations and an almost total change in plant species composition. This discontinuity appears to be caused by the widespread removal of cation-poor surface sediments by river incision to expose cation-rich sediments beneath. Examination of broad-scale Landsat and SRTM mosaics indicated that equivalent processes have generated a north-south discontinuity of over 1500 km in western Brazil. Due to similarities with our study area, we suggest that this discontinuity represents a chemical and ecological limit between western and central Amazonia. MAIN CONCLUSIONS: Our findings suggest that Amazonian forests are partitioned into large-area units on the basis of geological formations and their edaphic properties. The evolution of these units through geological time may provide a general mechanism for biotic diversification in Amazonia. These compositional units, moreover, may correspond to broad-scale functional units. The existence of large-area compositional and functional units would suggest that protected-area, carbon sequestration, and other land-use strategies in Amazonia be implemented on a region-by-region basis. The methods described here can be used to map these patterns, and thus enable effective conservation and management of Amazonian forests.     

Altitudinal zonation of Andean cryptogam communities

To test whether cryptogamic plant communities in tropical Andean rain forests are distributed in floristically discrete communities corresponding to altitudinal belts, I subjected the elevational distribution of pteridophytes along two elevational gradients in Bolivia, and of bryophytes and lichens along two transects in Peru and Colombia (data from Gradstein & Frahm, 1987 ; Wolf, 1993 ) to an analysis of deviance. All well‐defined elevational boundaries in floristic composition were related to marked ecological changes: the transition from the steep mountains to the hilly lowland zone coupled with a change in geological substrate at 400 m along the Bolivian Carrasco transect, a strong humidity gradient at 1000 m at the Bolivian Masicurí transect and at 1250–1980 m along the Colombian transect, and the transition from mixed cloud forests to forests dominated by Polylepis or Podocarpus at 3400–3600 m in Carrasco, at 1650–1800 m in Masicurí, and at 3670 m in Colombia. Consequently, floristic elevational belts appear to be well‐defined at strong environmental boundaries and in fairly species‐poor forest communities where the presence or absence of one or a few tree species influences the whole ecosystem while they are ill‐defined in species‐rich communities such as tropical forests at low to mid‐elevations.     

Notes on the Burseraceae in central Amazonia,including four new taxa. Studies in neotropical Burseraceae XXVI

The Burseraceae are known to comprise one of the most important tree families in Amazonia, but examination of Burseraceae diversity indicates that this importance is achieved differently in different parts of the Amazon, generally showing greater relative density compared to relative diversity in the east and greater relative diversity compared to relative density in the west, but both high relative density and diversity in central Amazonia. The patterns of relative density may be explained by current climates and by soils, but those of diversity are more likely a function of historical events. Revision of the Burseraceae for two projects near Manaus, Brazil revealed four new taxa. Protium hebetatum is widespread in western Amazonia, but it is one of the most common trees in central and west-central Amazonia; it resembles P. grandifolium. Protium tonyanum is a distinctive new species in poorly resolved sect. Sarcoprotium. Protium paniculatum var. modestum is known thus far only from the vicinity of Manaus plus several localities in the state of Amazonas, Venezuela; a key to the varieties is provided. Dacryodes hopkinsii is one of a group of four species in that genus from Amazonia and the Venezuelan Guayana with relatively large and fleshy flowers that are functionally bisexual. The discovery of these new taxa underscores the biological importance of Manaus and vicinity as a center of diversity for many taxa and exemplifies the synergy between well-designed floristic projects and systematics.     

Tree species composition and diversity gradients in white-water forests across the Amazon Basin

Aim Attention has increasingly been focused on the floristic variation within forests of the Amazon Basin. Variations in species composition and diversity are poorly understood, especially in Amazonian floodplain forests. We investigated tree species composition, richness and α diversity in the Amazonian white‐water (várzea) forest, looking particularly at: (1) the flood‐level gradient, (2) the successional stage (stand age), and (3) the geographical location of the forests. Location Eastern Amazonia, central Amazonia, equatorial western Amazonia and the southern part of western Amazonia. Methods The data originate from 16 permanent várzea forest plots in the central and western Brazilian Amazon and in the northern Bolivian Amazon. In addition, revised species lists of 28 várzea forest inventories from across the Amazon Basin were used. Most important families and species were determined using importance values. Floristic similarity between plots was calculated to detect similarity variations between forest types and over geographical distances. To check for spatial diversity gradients, α diversity (Fisher) of the plots was correlated with stand age, longitudinal and latitudinal plot location, and flood‐level gradient. Results More than 900 flood‐tolerant tree species were recorded, which indicates that Amazonian várzea forests are the most species‐rich floodplain forests worldwide. The most important plant families recorded also dominate most Neotropical upland forests, and c. 31% of the tree species listed also occur in the uplands. Species distribution and diversity varied: (1) on the flood‐level gradient, with a distinct separation between low‐várzea forests and high‐várzea forests, (2) in relation to natural forest succession, with species‐poor forests in early stages of succession and species‐rich forests in later stages, and (3) as a function of geographical distance between sites, indicating an increasing α diversity from eastern to western Amazonia, and simultaneously from the southern part of western Amazonia to equatorial western Amazonia. Main conclusions The east‐to‐west gradient of increasing species diversity in várzea forests reflects the diversity patterns also described for Amazonian terra firme. Despite the fine‐scale geomorphological heterogeneity of the floodplains, and despite high disturbance of the different forest types by sedimentation and erosion, várzea forests are dominated by a high proportion of generalistic, widely distributed tree species. In contrast to high‐várzea forests, where floristic dissimilarity increases significantly with increasing distance between the sites, low‐várzea forests can exhibit high floristic similarity over large geographical distances. The high várzea may be an important transitional zone for lateral immigration of terra firme species to the floodplains, thus contributing to comparatively high species richness. However, long‐distance dispersal of many low‐várzea trees contributes to comparatively low species richness in highly flooded low várzea.     

High-Andean vegetation and environmental gradients in northwestern Patagonia,Argentina

Abstract. We analysed the heterogeneity of high-elevation vegetation on three mountains along a west-east transect at 41 °S lat. in the Andes of northwestern Patagonia, Argentina. In this area, high-Andean vegetation occurs as islands on mountain tops above Nothofagus pumilio forests ? with the timberline at ca. 1700 m a.s.l. We recorded floristic, topographic and substrate data in 166 sites stratified according to longitude, altitude, slope and aspect. Vegetation data were classified with TWINSPAN and ordinated with Detrended Correspondence Analysis. The relationship between environmental and floristic variation was analysed using Canonical Correspondence Analysis. In order of importance, geographical longitude, altitude and aspect were the major determinants of vegetation variation, whereas substrate texture and slope appeared less important. The combination of these factors resulted in two main vegetation gradients. The first gradient is related to a moisture availability gradient, primarily determined by longitude and secondarily to variation in wind exposure (east vs. west aspect). The second vegetation gradient is related to variation in temperature, primarily determined by altitude, and secondarily by variation in insolation related to the contrast between north and south aspects. The four communities obtained with TWINSPAN are therefore associated with four characteristic habitat types: moist-cold, moist-warm, dry-cold and dry-warm. The community of warm and dry environments is the richest and has elements in common with dry steppe communities situated at lower elevations to the east, while the vegetation of the cold-moist habitat type has unique elements that are typical of the southern Andes. Although current climatic factors appear to be the major determinants of high-Andean vegetation gradients, historical events of Pleistocene times probably also affected the vegetation patterns we see today.     

Secondary forests on anthropogenic soils in Brazilian Amazonia conserve agrobiodiversity

Throughout Brazilian Amazonia anthropogenic soils that are the product of pre-Columbian settlements are called Terra Preta de índio (Indian Dark Earths, TPI). These soils are dramatically different from surrounding soils due to long-term human activity, but there is little information about how secondary forest succession is affected by these differences. We tested if community structure (density, richness and basal area), floristic composition and domesticated species’ richness and density were similar between TPI and non-anthropogenic soils (NAS) in 52 25 × 10 m secondary forest plots in different successional stages near three traditional communities along the middle Madeira River, Central Amazonia. We sampled 858 woody individuals on TPI (77 domesticated) and 1095 on NAS (27 domesticated); 550 understory palms on TPI (169 domesticated) and 778 on NAS (123 domesticated). We found 179 species on TPI (10 domesticated), 190 on NAS (8 domesticated), and 74 (25%) in both environments. Although community structure on TPI and NAS was fairly similar, they showed significantly distinctive floristic compositions, both for woody individuals and understory palms. The density and richness of domesticated species was significantly higher on TPI than on NAS for woody individuals, but not for palms. The intimate long-term association of TPI with human activity has lead to the formation of distinct secondary forests and has favored the concentration of domesticated populations of crop species. Hence, secondary forests on anthropogenic soils concentrate agrobiodiversity, offering advantages for in situ conservation of genetic resources, and are unique ecosystems that should be considered in conservation efforts.     

Distance Decay of Tree Species Similarity in Protected Areas on Terra Firme Forests in Colombian Amazonia

In this study, we investigated the pattern of floristic similarity as a function of geographical distances and environmental variability in well-drained uplands (terra firme) in Colombian Amazonia. The study site comprised three National Natural Parks, Tinigua, Chiribiquete, and Amacayacu, located in different geological units that represent a soil fertility gradient linked to parental materials. Differences in species richness between sites were compared using rarefaction analysis. A clear floristic transition appeared in the east–west direction following a soil fertility gradient along the first PCoA axis. In multiple regression analyses based on distance matrices, both geographical distances and geology explained 64 percent of the total floristic variation. Geographical distances alone accounted for 12 percent of variation in floristic similarities among plots, while geology alone accounted for 1 percent, and the joint effect of both explained 51 percent of the floristic variation. The species richness trend supports the existence of a latitudinal corridor southward of the geographical Equator in the Amazon basin, where tree diversity reaches the maximum expected values. A coupled effect of stochastic dispersal limitation and habitat specialization would certainly appear to be an appropriate explanation for tree species turnover in terra firme forests in Colombian Amazonia, strongly emphasizing that competition and neutrality must be supplementary rather than mutually exclusive processes. This result pinpoints the effect of dispersal on floral mixing as an ongoing active process for structuring tree communities in NW Amazonia, and the size of the reserves as a relevant issue to protect rare species from extinction by chance.
     

Variation in species composition, abundance and microhabitat preferences among western Amazonian terra firme palm communities

Western Amazonia harbours one of the richest palm floras of the Neotropics. About 121 palm species and 33 genera occur in this region. Approximately 40% of these species and three monotypic genera ( Aphandra , Itaya and Wendlandiella ) are restricted to western Amazonia. Bactris (23 spp.), Geonoma (20 spp.), Attalea (17 spp.), Astrocaryum (11 spp.) and Oenocarpus (7 spp.) are the most well-represented genera in the region. Palms, however, are not homogeneously distributed across western Amazonia. A major change in palm composition occurs between Yasuní (eastern Ecuador) and Iquitos (eastern Peru). Species that are very abundant on the unflooded forest of Yasuní, such as Iriartea deltoidea or Prestoea shultzeana , are replaced by Socratea exorrhiza , Lepidocaryum tenue var. tenue or Iriartella stenocarpa in the Iquitos–Pebas region. Moreover, the distribution ranges of the majority of eastern Ecuadorean palms reach the Iquitos region, but the converse is not observed. Censuses of palm communities along transects, studies of microhabitat preferences of Oenocarpus bataua and documentation of the distribution limit of Astrocaryum species in the intermediate zone provide new insights on the floristic change that is occurring. Modern ecological constraints and geological history during the Cenozoic may explain the observed variations.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 151 , 127–140.     

Peatland forests are the least diverse tree communities documented in Amazonia,but contribute to high regional beta‐diversity

Western Amazonia is known to harbour some of Earth's most diverse forests, but previous floristic analyses have excluded peatland forests which are extensive in northern Peru and are among the most environmentally extreme ecosystems in the lowland tropics. Understanding patterns of tree species diversity in these ecosystems is important both for quantifying beta‐diversity in this region, and for understanding determinants of diversity more generally in tropical forests. Here we explore patterns of tree diversity and composition in two peatland forest types – palm swamps and peatland pole forests – using 26 forest plots distributed over a large area of northern Peru. We place our results in a regional context by making comparisons with three other major forest types: terra firme forests (29 plots), white‐sand forests (23 plots) and seasonally‐flooded forests (11 plots). Peatland forests had extremely low (within‐plot) alpha‐diversity compared with the other forest types that were sampled. In particular, peatland pole forests had the lowest levels of tree diversity yet recorded in Amazonia (20 species per 500 stems, Fisher's alpha 4.57). However, peatland pole forests and palm swamps were compositionally different from each other as well as from other forest types in the region. Few species appeared to be peatland endemics. Instead, peatland forests were largely characterised by a distinctive combination of generalist species and species previously thought to be specialists of other habitats, especially white‐sand forests. We suggest that the transient nature and extreme environmental conditions of Amazonian peatland ecosystems have shaped their current patterns of tree composition and diversity. Despite their low alpha‐diversity, the unique combination of species found in tree communities in Amazonian peatlands augment regional beta‐diversity. This contribution, alongside their extremely high carbon storage capacity and lack of protection at national level, strengthens their status as a conservation priority.     

Modelling distribution patterns in a species-rich plant genus, Anthurium (Araceae), in Ecuador

Modelling potential species distributions has become a powerful tool for botanists in recent years. Using herbarium specimen data and GIS desktop software, we modelled the potential distribution of 36 endemic and 47 non‐endemic species of Anthurium (Araceae) in Ecuador based on mean annual temperature and humidity. Our results indicate the most important region for endemics in western Ecuador lies between the Andes and Coastal mountain ranges between 200 and 700 m, while for eastern Ecuador a belt of potential high diversity occurs directly along the foothills of the Andes under 1000 m. A very interesting result of this study highlights a site of predicted high species diversity at the borders of Guyas, Cañar, Bolivar, and Chimborazo, as well as sites within the Cordillera del Condor along the border with Peru. Potential richness for non‐endemic Anthurium species was similar to that of endemics with the inclusion of a large area of Amazonian lowlands in the east of the country. Over 40% of the protected areas in Ecuador occur in the eastern Amazonian lowlands, an area of low diversity for Anthurium endemics. Overall, for areas with potential high concentrations of endemic species identified in this study, only 3.1% are within Ecuador's protected areas.     

Phytogeographical relations of the Andean dry valleys of Bolivia

Aim The objective of this study is to examine the phytogeographical affinities of the Andean dry valleys of Bolivia in order to contribute to a better understanding of the Andean dry flora's distribution, origin and diversity. Particular emphasis is given to the analysis of the floristic connections of this flora with more austral parts of South America. Location The dry valleys of Bolivia are located in the Andes of the southern half of the country, at elevations between 1300 and 3200 m. Methods An extensive floristic list compiled by the author to evaluate plant diversity in these Andean regions was used as the base for this study. To accomplish this, all recorded genera and species were assigned, respectively, to 11 and 12 phytogeographical elements established previously by the author. Two phytogeographical spectra were thus obtained and analysed. Results At the genus level, the Andean dry valleys of Bolivia are clearly dominated by genera that have widespread distributions (cosmoplitan and subtropical genera). Many of these reached the Andes from the lowland region of the Chaco. At species level, Andean elements constitute more than 60% of the species total, most of which are restricted to the central‐southern Andes. This suggests that Chaco‐related and Andean genera had considerable levels of speciation in these valleys. Many genera and more than half the species have their northernmost distribution in the dry valleys of Bolivia, thereby underlining strong relationships with central‐southern South America (mainly Argentina, Paraguay and southern Brazil). The data supports the belief of the existence, in central‐southern Peru, of a floristic disjunction in dry to arid environments that separates a tropical dry flora north of this limit from a dry subtropical/warm temperate flora south of it. Main conclusions The Andean dry valleys of Bolivia are diverse plant communities with high levels of endemism (c. 18% of the species). The species of this region are more related to those present in central‐southern South America than to the flora of northern South America that ranges southwards to Peru. Many of the species have restricted distributions in the dry Andes of Bolivia and Argentina, and many genera of these dry valleys have their northernmost distribution in Bolivia/southern Peru, too. The data point to high levels of speciation also in the central Andes.     

South Patagonian ombrotrophic bog vegetation reflects biogeochemical gradients at the landscape level

Question: Which environmental variables affect the floristic composition of south Patagonian bog vegetation along a gradient of climate and biogeochemical changes with increasing distance from the Pacific ocean? Location: Trans‐Andean transect (53° S), southern Patagonia Material and Methods: Floristic composition, peat characteristics (water level, decomposition, pH, total nitrogen, total carbon, ash content and plant available P, K, Na, Ca, Mg, Fe, Mn, Zn, and Al) and climatic constraints of ombrotrophic peat‐lands were measured at 82 plots along a gradient of increasing distance from the Pacific Ocean. Results: Climatic constraints and biogeochemical peat characteristics significantly change with increasing distance from the Pacific. Peatland vegetation shifted from hyperoceanic blanket bogs dominated by cushion forming vascular plants to the west to Sphagnum bogs to the east. Climatic and biogeochemical variables explained a large proportion of the floristic variation along the first DCA axis. The second axis represented a water level gradient. When ‘distance to the Pacific’ was defined as a covariable in partial CCA, the proportion of variance explained declined for most other variables, especially in the case of annual precipitation and exchangeable base cations and related traits. The differences in biogeochemical characteristics related to peat were mainly attributed to the input of sea‐borne cations. Conclusions: While variation in vegetation composition along a longitudinal gradient crossing the southern Andes was attributed to climatic constraints as expected, vegetation composition was also strongly affected by the biogeochemical characteristics of peat. Sea spray was of high ecological importance to peat chemistry and, consequently, to floristic composition. Presumably, south Patagonian peat bogs represent a glimpse of pre‐industrial environments, so that these peat bogs may act as reference systems with respect to atmospheric inputs in mire ecology research.     

Tree species distribution in<Emphasis Type="Italic">Várzea</Emphasis> forests of Brazilian Amazonia

Amazonian várzea forests are floodplains inundated by nutrient-rich white-water rivers occurring along the Amazon River. They are regularly flooded for up to 210 days per year by water columns of 10–15 m. Topographic variation results in different flooding amplitudes and durations along the flooding gradient, where the different tolerance to flooding of different plant species results in a vegetation zonation. We made a review of literature about the vegetation composition ofvárzea floodplain forests of Brazilian Amazonia along the Amazon River. Twenty-two studies were selected. Basing on the distribution of inventories which are concentrated in three main areas around the three larger cities Belém, Manaus and Tefé, we classified the inventories into three regions: (A) Estuary region with flooding regime influenced by daily inundations linked to the tides; (B) Central Amazonia near Manaus; (C) Western part of Brazilian Amazonia bordering Peru and Colombia, including Tefé and the “Reserva de Desenvolvimento Sustentável Mamirauá”. Summarizing the analyzed species lists, 36 tree species were registered in all sampled regions including the estuary. The regions A +C have 63 species in common, region B+C 143, and A+B 50. In the inventories analyzed here, an increase in species numbers from East to West can be confirmed, but it is difficult to state whether this is not an artefact due to local sampling. Vertical zonation patterns are difficult to discuss due to the lack of comparable data. The inventoried areas are small, and there is an urgent need for comparable floristic inventories throughout the basin. Destruction is spreading rapidly and the traditional use of forests and its resources is changing to a destructive exploitation that already has changed much of the physiognomy and diversity of this unique ecosystem.     

A subtidal transect in Jervis Bay,New South Wales

Long-term variations in the intertidal algal flora of the entire rock platform at Plantation Point, Jervis Bay, are described by May (1981). The study now reported presents similar long-term changes in the flora of a subtidal region of the same headland, observed within the same period of time. This first detailed report of subtidal macroalgal communities in New South Wales describes a several-year study of the benthic communities along a transect in the upper sublittoral region of a rocky headland at Plantation Point, Jervis Bay. Eighty-nine species of algae were recorded, five of which were previously unrecorded for New South Wales. The area studied is dominated by the large brown algae Ecklonia radiata and Phyllospora comosa, large areas of which were cleared periodically by storms. Turf, shade and crustose coralline algal communities also were present. Storms, seasonal variation and longer term changes all affected the abundance and distribution of the algal species growing along the transect and hence the floristic composition of the area.     

Patterns of plant species endemism in Ecuador

Distribution patterns of plant species endemic to Ecuador and adjacent parts of southern Colombia and northern Peru are analysed on the basis of information in the Flora of Ecuador. A total of 827 restricted-range species were found, many of which are known from extremely small areas, often only one or a few localities. A total of 27% of the species treated in the Flora of Ecuador are endemic to that country. The overall proportion of endemic and restricted-range species is greater in the Andes than in the lowland areas on either side of these mountains; particularly the southern Andes appears to be very rich in endemic species. Spatial analysis of distribution data results in the recognition of 15 floristic elements and 18 geographical endemism regions in Ecuador, the characteristics of which are discussed. Comparison with distribution patterns of restricted-range bird species show a general correspondence, with the main difference that birds tend to be more widely distributed than plants along the Andes. Comparison of the results with the location of national parks and other protected areas shows that the endemic floras in the northern and eastern parts of the country are much better protected than those of the southern and western parts.     

Vegetation changes along a precipitation gradient in Central Argentina

Changes in vegetation along a precipitation gradient in Central Argentina were studied. Floristic samples were taken along an east-west transect of about 300 km. Correlation analysis between precipitation and ordination axes was used to provide an environmental interpretation of vegetation variability.Floristic analysis produced an ordination of plant communities from evergreen forests (precipitation >500 mm) to desert shrublands and therophyte communities (precipitation <200 mm). Results showed a trend of floristic and structural impoverishment towards the west. There is a replacement of species along the transect and a shift in dominant growth forms. The first ordination axis is significantly, negatively correlated with annual precipitation.     

Diversity and biogeography of vascular epiphytes in Western Amazonia, Yasuní, Ecuador

Aim Although vascular epiphytes are important components of species richness and complexity of Neotropical forests, vascular epiphytes are under‐represented in large scale biogeographical analyses. We studied the diversity, biogeography and floristic relationships of the epiphytic flora of the Yasuní region (Western Amazonia) in a Neotropical context, with special emphasis on the influence of the Andean flora on floristic composition and diversity of surrounding lowland forests. Location Western Amazonian lowland rainforest, Tiputini Biodiversity Station (0°38′ S 76°09′ W, 230 m a.s.l., 650 ha), Yasuní National Park, Ecuador. Methods We compared the vascular epiphyte flora of Yasuní with 16 published Neotropical epiphyte inventories. Secondly, based on a floristic database with records of more than 70,000 specimens of vascular epiphytes from the Neotropics the elevational composition of eight selected inventories was analysed in detail. Results The vascular epiphyte flora of Yasuní is characterized by a very high species richness (313 spp.). A moderate portion of species is endemic to the Upper Napo region (c. 10%). However, this figure is much higher than previous analyses primarily based on woody species suggested. Geographical ranges of these species match with a proposed Pleistocene forest refuge. Compared with Northern and Central Amazonian sites, Western Amazonian epiphyte communities are characterized by a higher portion of montane and submontane species. Species richness of vascular epiphytes at the sites was correlated with the amount of rainfall, which is negatively correlated with the number of dry months. Main conclusion Recent and historic patterns of rainfall are the driving forces behind diversity and floristic composition of vascular epiphytes in Western Amazonia: high annual rainfall in combination with low seasonality provides suitable conditions to harbour high species richness. The proximity to the Andes, the most important centre of speciation for most Neotropical epiphytic taxa, in combination with the climatic setting has allowed a continuous supply of species richness to the region. At least for epiphytes, the borderline between the Andean and Amazonian flora is much hazier than previously thought. Moreover, the comparatively moist climate in Western Amazonia during the Pleistocene has probably led to fewer extinctions and/or more speciation than in more affected surrounding lowlands.     

Relationships between cluster root-bearing taxa and laterite across landscapes in southwest Western Australia: an approach using airborne radiometric and digital elevation models

As part of a general soil and regolith mapping exercise across cleared and remnant bush land, radiometric data for distribution of potassium (K), uranium (U) and thorium (Th) were examined alongside relief models and floristic and soil surveys in test catchments at Elashgin and Toolibin in the Western Australian wheat-belt. The Elashgin survey showed that highly weathered low K soils co-concentrated U and Th and were vegetated mainly by cluster root-bearing Proteaceae and Casuarinaceae. In granitic soils ratios of U to Th were higher and cluster root bearing taxa much less prominent, except where ferricrete gravels were concentrated. Draping of radiometric imagery over a digital elevation model showed spiral waveforms of high and low U and Th signal which were largely independent of topography but demarcated different oligotrophic communities. General observations and a detailed 900-m transect along an aeolian sand plume at Toolibin showed very high U and Th in ferricrete gravels where Proteaceae were dominant, but failed to separate proteaceous versus myrtaceous shrublands on deep sands due to truncation of signal. Augering along the transect and examination of floristic, soil and signal composition of 32 sites in the Lake Toolibin catchment confirmed presence and degree of development of ferricretes in the rhizosphere of Proteaceae-dominated communities and showed high reactivity scores for Al in `Bs' horizons in profiles carrying such vegetation. Highly specific associations between Proteaceae and very high U and Th were generally evident on exposed ferricrete gravels. The data are discussed in relation to the effects of root exudates on ferricrete formation and destruction and how the broader spatial pattern of such processes might relate to competition for soil phosphorous.     

Distribution of Pteridophyta and Melastomataceae along an edaphic gradient in an Amazonian rain forest

Abstract. Pteridophyta and Melastomataceae were studied in an area of non-flooded (tierra firme) rain forest in Peruvian Amazonia, close to the village of Mishana (River Nanay, in the vicinity of Iquitos City). The general objective of the study was to establish a method for rapidly documenting changes in the floristic composition among and within rain forests in geologically different areas. More specifically, the changes in the plant communities were documented along an edaphic and topographic gradient from clay soil on level ground to quartzitic sand on a hill top. Two 5-m-wide, parallel transects were established 50 m apart. A total of 40 species of pteridophytes were found; 18 of these were confined to clayey soil and 11 to sandy soil. The total number of Melastomataceae on the transects was 22, and 14 of these were confined to clayey soil while only two were confined to sandy soil. Further differences in the abundance of many species correlated with drainage conditions and the accumulation of organic matter on the soil surface. Cluster analyses were made using both edaphic and floristic criteria, and in all cases the transects could be divided into distinct sections. Both transects gave rather similar results, and therefore it was concluded that the chosen transect width was sufficient to document the prevalent floristic patterns.     

Population analysis using the nuclear white gene detects Pliocene/Pleistocene lineage divergence within Anopheles nuneztovari in South America

Anopheles (Nyssorhynchus) nuneztovari Gabaldón (Diptera: Culicidae), a locally important malaria vector in some regions of South America, has been hypothesized to consist of at least two cryptic incipient species. We investigated its phylogeographic structure in several South American localities to determine the number of lineages and levels of divergence using the nuclear white gene, a marker that detected two recently diverged genotypes in the primary Neotropical malaria vector Anopheles darlingi Root. In An. nuneztovari, five distinct lineages (1-5) were elucidated: (1) populations from northeastern and central Amazonia; (2) populations from Venezuela east and west of the Andes; (3) populations from Colombia and Venezuela west of the Andes; (4) southeastern and western Amazonian Brazil populations, and (5) southeastern and western Amazonian Brazil and Bolivian populations. There was a large amount of genetic differentiation among these lineages. The deepest and earliest divergence was found between lineage 3 and lineages 1, 2 and 4, which probably accounts for the detection of lineage 3 in some earlier studies. The multiple lineages within Amazonia are partially congruent with previous mtDNA and ITS2 data, but were undetected in many earlier studies, probably because of their recent (Pleistocene) divergence and the differential mutation rates of the markers. The estimates for the five lineages, interpreted as recently evolved or incipient species, date to the Pleistocene and Pliocene. We hypothesize that the diversification in An. nuneztovari is the result of an interaction between the Miocene/Pliocene marine incursion and Pleistocene climatic changes leading to refugial isolation. The identification of cryptic lineages in An. nuneztovari could have a significant impact on local vector control measures.