A digital land cover map of South America has been produced using remotely sensed satellite data acquired between 1995 and the year 2000. The mapping scale is defined by the 1 km spatial resolution of the map grid‐cell. In order to realize the product, different sources of satellite data were used, each source providing either a particular parameter of land cover characteristic required by the legend, or mapping a particular land cover class. The map legend is designed both to fit requirements for regional climate modelling and for studies on land cover change. The legend is also compatible with a wider, global, land cover mapping exercise, which seeks to characterize the world's land surface for the year 2000. As a first step, the humid forest domain has been validated using a sample of high‐resolution satellite images. The map demonstrates both the major incursions of agriculture into the remaining forest domains and the extensive areas of agriculture, which now dominate South America's grasslands.

Summary During the last 40 years, an impressive amount of biological, especially botanical, information concerning the Venezuelan Guayana region has been accumulated. Both the lowlands, as well as the distinctive highland mountains (‘tepuis’), evidence an outstandingly rich and diversified flora and vegetation. It has been postulated that this biological richness and the high degree of endemism are the result of long‐term and highly effective isolation suffered by the flat summit areas during extremely long geologic epochs. This static view is being challenged presently by the results of recent intensive fieldwork made in the Venezuelan Guayana. A detailed analysis of two highly evolved Guayana taxa, Stegolepis (Rapateaceae) and Bonnetia (Theaceae s.l.) shows a rather uniform distribution not only in summit habitats, but also in intermediate and lowland habitats. As a whole, both genera and several related taxa prove to have occupied successfully not only the ancient summit regions of the tepuis, but also the surrounding lowlands of much more recent geomorphological origin. Palaeoecological research also supports the hypothesis that the entire Guayana Shield area has been affected by climatic oscillations during the recent past as have the nearby Andes. This implies significant past fluctuations of the altitudinal vegetation belts in the tepui area and could well explain the wide altitudinal gradient of most of the Guayana Highland taxa. Also, the presence of convergent ‘paramoid’ vegetation types on the summits of the Chimantá Massif, indicates active speciation not only at the systematic level, but especially at the ecologic level. Thus, it is proposed that the Guayana highland and lowland biota have been and still are dynamically and genetically interdependent, not only within the Guayana region itself, but also with the adjacent complex of lowland and mountain biota.

Aims Ecosystems dominated by herbaceous plant communities are amongst the most diversified landscape units in the Guayana (Guiana) Shield region. This paper aims to present a synthetic overview of the wide array of herbaceous ecosystems found in the region in an attempt to furnish a more concrete baseline for a better understanding of the pattern of variation, and to clarify some of the differences that occur in the vegetation of the area.Location The Guayana Shield region, and the area of north-eastern South America extending between the Orinoco River to the North and the Amazon River to the South (c. 8°N to 1°S).Methods Floristic and ecological field data gathered from over 300 study sites located at different altitudinal levels in the Venezuelan Guayana and the northern Brazilian Amazon are evaluated and interpreted in the light of personal observations and existing literature. ResultsThe diversification pattern includes physiognomic as well as floristic variation and shows two opposing tendencies in relation to their altitudinal location: grass-dominated meadows (savannas) predominate in the macrothermic lowlands, whereas non-gramineous, broadleaved herbaceous communities are dominant in the mesothermic highlands of the Guayanan mountains. In detail, the biogeographic region of Guayana (Guiana) consists of three easily recognized altitudinal levels, each of which contains a highly characteristic set of landscape types with their associated ecosystems and endemic plant communities. Between 0 and c. 500 m a.s.l. the extensive macrothermic (mean annual temperature, MAT > 24°C) lowlands are found, where an enormous -still largely unexplored -diversity of forest types represents the main plant cover of the plains, peneplains, glacis and piedmont slopes. Sparsely distributed within this forest cover are numerous herbaceous ecosystems, ranging from true grass savannas to unusual and poorly understood meadows developed on extremely oligotrophic white sandy soils dominated by non-gramineous genera of Rapateaceae and Xyridaceae. In the intermediate submesothermic (MAT 24-18°C) Guayana uplands, extending roughly between 500 and 1500 m a.s.l., the grasslands of the Gran Sabana in south-eastern Venezuela reach their upper altitudinal limit. At the same altitudinal level, however, several distinct herbaceous communities are found, in which other genera of Rapateaceae, together with Bromeliaceae and Xyridaceae, are predominant. Finally, at the uppermost altitudinal level, i.e. in Pantepui (which includes the characteristically flat topped mountain summits (tepuis) of the Guayana highlands) between 1500 and 3000 m a.s.l., encompassing a range of meso-to submicrothermic temperature regimes (MAT 18-8°C), the extensive herbaceous ecosystems are developed either on deep organic soils (peat) or on open sandstone surfaces. These high-tepui meadows present a considerable

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-(Rock outcrop habitats in the Venezuelan Guayana lowlands: their main vegetation types and floristic components). The Guayana Shield, located in north-eastern South America, consists of a highly complex and composite mosaic of landscape elements. Amongst these, inselbergs are very conspicuous, because of their peculiar shape and their unusual associated vegetation. Geologically, these rock outcrops are part of the underlying ancient igneous-metamorphic basement and occur mainly in the lowlands of the periphery of the shield. As azonal habitats, inselbergs harbour a highly specialized flora. The characteristic vegetation is composed of lithophytic and savanna-like plant communities, as well as low dry forests. As a whole, the vegetation of an inselberg may be interpreted as a mosaic of marginal habitats. Therefore a large number of taxa find suitable niches in a quite condensed space. Gradients of soil depth and water availability are the main factors determining the floristic composition. A preliminary floristic inventory of the Venezuelan inselberg flora comprises 614 vascular plant species. 24% of them are endemic to the Guayana region, 15% are endemic to inselbergs of the Guayana region. The distribution patterns of these latter, eco-endemic species allows to distinguish a northern and a southern inselberg district. The two districts overlap in the Átures area, in the surroundings of Puerto Ayacucho, where a true centre of endemism is located. The distinction into two districts is emphasised by different phytogeographic relations. The southern inselberg district shows connections to the "tepui" flora, whereas the northern district reveals phytogeographic relations to the Caribbean region as well as to the Brazilian Shield. Possible explanations for the floristic interchange across the equator are discussed.Key words -endemism, flora, Guayana Shield, inselberg, phytogeography, Venezuela RESUMO -(Hábitats em afloramentos rochosos nas terras baixas da Guiana Venezuelana: os principais tipos vegetacionais e componentes florísticos). O Escudo das Guianas, situado no nordeste da América do Sul, consiste de um mosaico altamente complexo de elementos de paisagem. Dentre estes, os "inselbergs" são particularmente conspícuos, pelo seu formato peculiar e a incomum vegetação associada. Geologicamente, estes afloramentos rochosos são parte de um antigo substrato ígneo-metamórfico e ocorrem principalmente nas terras baixas da periferia do escudo. Como hábitats azonais, os "inselbergs" abrigam uma flora altamente especializada. A vegetação característica é composta de comunidades litofíticas, semelhantes a savanas, bem como de florestas secas baixas. Como um todo, a vegetação de um "inselberg" pode ser vista como um mosaico de hábitats marginais. Assim, um grande número de táxons encontra nichos adequados em um espaço extremamente condensado. Gradientes de profundidade de solo e disponibilidade de água são os principais fatores determinando a composição florística. Um inventário florístico preliminar da flora de "...

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The summits of the tepuis (sandstone table mountains of the Neotropical Guayana region-Guayana Highlands, GH) have been considered valuable for palaeoecological studies due to their pristine nature, which emphasizes the role of natural (i.e. nonhuman) factors on ecological change. Anthropogenic fires, very frequent in the surrounding Gran Sabana (GS) uplands, have been documented in the GH very rarely, and are therefore not considered an important ecological factor in the high-tepui biome. This paper reports the palynological and charcoal results of a late Holocene sequence from the summit of Uei-tepui (2104 m elevation), where extensive signs of fire were recently observed. Since ~2000 cal yr BP the landscape of the study site has been dominated by meadows with occasional shrubs and cloud forests, which underwent expansions and contractions driven by climate changes and fire. A major vegetation shift occurred in the mid-18th century, when a sustained increase in local fires favoured the expansion of the low and spreading Cyrilla racemiflora shrublands at the expense of meadows and forests. Uei-tepui fires most probably were the result of human activities and reached the summit under study from the GS uplands through the vegetated slopes that characterize this tepui. The mostly anthropogenic nature of these fires, especially the more recent ones, is supported by the initial occurrence of wetter conditions, and by its coincidence with significant social changes in the GS indigenous populations, mainly the European contact. The emergence of fire as a disturbing agent of the GH biome highlights the need for an effective management plan in the GS uplands, where the vast majority of present-day fires originate, and designed in collaboration with the indigenous communities. Proactive conservation measures are considered even more important under future warming projections in the area.