Vegetation Physiognomy Research Articles

Physiognomy and structure of vegetation along an altitudinal gradient in the semi-arid region of northeastern Brazil

Physiognomy and structure of vegetation along an altitudinal gradient in the semi-arid region of northeastern Brazil

Combined effects of environment and grazing on vegetation structure in Argentine granite grasslands

Abstract. Effects of grazing and environment on vegetation structure have been widely acknowledged, but few studies have related both factors. We made 57 floristic samples in a highly variable landscape of mountain grasslands in central Argentina; 26 sample were in fence‐lines with contrasting vegetation. For each sample, we recorded topographic and edaphic parameters, as well as grazing intensity indicators. Floristic gradients were analysed with DCA and relations with abiotic and grazing‐related variables were detected with DCCA. Floristic axis 1 was explained by edaphic parameters associated to topography, ranging from communities in well drained soils on upper topographic positions to hydromorphic vegetation in poorly drained soils on lower topographic positions. Species richness decreased as soil moisture increased. Floristic axis 2 was associated with present and long‐term grazing indicators, and reflected shifts in vegetation physiognomy and species evenness. Tall tussock grasslands, with low species evenness and evidences of low or null grazing intensity were located at one extreme. Tussocks were gradually replaced by short graminoids and forbs towards the centre of the gradient, as grazing increased, and evenness reached a maximum. In degraded sites with heavy long‐term grazing intensities, short perennial species were replaced by an annual species, and evenness decreased. The magnitude of changes in floristic composition produced by grazing decreased with increasing soil moisture, and vegetation‐environment relationships were stronger in moderate to highly grazed situations than in lightly or non grazed situations.

Assessing the quality of native vegetation: The ‘habitat hectares’ approach

Summary Assessments of the ‘quality’, condition or status of stands of native vegetation or habitat are now commonplace and are often an essential component of ecological studies and planning processes. Even when soundly based upon ecological principles, these assessments are usually highly subjective and involve implicit value judgements. The present paper describes a novel approach to vegetation or habitat quality assessment (habitat hectares approach) that can be used in almost all types of terrestrial vegetation. It is based on explicit comparisons between existing vegetation features and those of ‘benchmarks’ representing the average characteristics of mature stands of native vegetation of the same community type in a ‘natural’ or ‘undisturbed’ condition. Components of the index incorporate vegetation physiognomy and critical aspects of viability (e.g. degree of regeneration, impact of weeds) and spatial considerations (e.g. area, distribution and connectivity of remnant vegetation in the broader landscape). The approach has been developed to assist in making more objective and explicit decisions about where scarce conservation resources are allocated. Although the approach does not require an intimate botanical knowledge, it is believed to be ecologically valid and useful in many contexts. Importantly, the index does not provide a definitive statement on conservation status nor habitat suitability for individual species. It purposefully takes a ‘broad‐brush’ approach and is primarily intended for use by people involved with making environmentally sensitive planning and management decisions, but may be useful within environmental research programmes. The ‘habitat hectares’ approach is subject to further research and ongoing refinement and constructive feedback is sought from practitioners.

Combined effects of environment and grazing on vegetation structure in Argentine granite grasslands

Abstract. Effects of grazing and environment on vegetation structure have been widely acknowledged, but few studies have related both factors. We made 57 floristic samples in a highly variable landscape of mountain grasslands in central Argentina; 26 sample were in fence-lines with contrasting vegetation. For each sample, we recorded topographic and edaphic parameters, as well as grazing intensity indicators. Floristic gradients were analysed with DCA and relations with abiotic and grazing-related variables were detected with DCCA. Floristic axis 1 was explained by edaphic parameters associated to topography, ranging from communities in well drained soils on upper topographic positions to hydromorphic vegetation in poorly drained soils on lower topographic positions. Species richness decreased as soil moisture increased. Floristic axis 2 was associated with present and long-term grazing indicators, and reflected shifts in vegetation physiognomy and species evenness. Tall tussock grasslands, with low species evenness and evidences of low or null grazing intensity were located at one extreme. Tussocks were gradually replaced by short graminoids and forbs towards the centre of the gradient, as grazing increased, and evenness reached a maximum. In degraded sites with heavy long-term grazing intensities, short perennial species were replaced by an annual species, and evenness decreased. The magnitude of changes in floristic composition produced by grazing decreased with increasing soil moisture, and vegetation-environment relationships were stronger in moderate to highly grazed situations than in lightly or non grazed situations.

Evaluation of environmental degradation in northern Ethiopia using GIS to integrate vegetation, geomorphological, erosion and socio-economic factors

The scale of human induced land degradation is very high in northern Ethiopia. However, there are only a few studies of land degradation in Ethiopia which provide an integrated assessment of the driving forces and consequences. A pilot study was made in Adwa district (Tigray) with the objective of evaluating the factors related to environmental degradation and assessing the effects of agricultural activities on the natural resources. Environmental data, a digital terrain model, vegetation, geomorphological, and erosion maps of the study area were integrated with socio-economic variables using a geographical information system (GIS). The classification of the data used in the integration, and the information extracted using the GIS gave three main groups of Tabias and four main groups of variables. The relationship among the Tabias (smallest administrative units), groups of Tabias and environmental variables were quantified using various statistical, multivariate numerical methods and fuzzy set analysis. The application of fuzzy set theory showed that each group of Tabia, recognized as a rural subsystem (RS) was associated with a group of variables. Analysis of variance showed that the three RSs were significantly different in most of the environmental variables considered. Human and livestock population densities, geomorphology, altitude and some natural and anthropogenic vegetation types were highly discriminatory. Percentage cover of evergreen scrub, bushlands and severe badlands are considered key indicators of the scale of environmental degradation. Results of the canonical correlation analysis (CCA) indicated that human pressure had more impact on the physiognomy of the vegetation than on its floristic composition. The Evergreen scrub vegetation type appeared to be expanding with increasing human influence signifying a decrease in biomass of vegetation as a result of collecting wood for fuel and other domestic uses. Bushland appeared to be expanding with the same trend. Woodland, which was abundant in one of the RSs, is considered to be the natural physiognomic vegetation type in the area and efforts to maintain it and/or recover it elsewhere in the study area are recommended. Food production in the area did not match population growth. The expected crop yield under good soil and rainfall conditions was low by any standard. The per capita energy obtained from the grain harvested in the farm plots ranged from 428 to 4347 cal per person per day (the average is far below the basic minimum required for mere subsistence) suggesting that there is a need for substantial supplementary income from off-farm activities and/or other sources. This study indicated that regional and site specific approaches and interaction with the people at all stages of the research, program development and implementation are required for sustainable rehabilitation.

Composition Patterns of Caribbean Limestone Forests: Are Parsimony, Classification, and Ordination Analyses Congruent?1

This study presents an analysis of floristic composition patterns for limestone vegetation from three Caribbean islands: Hispaniola, Mona, and Puerto Rico. The physical setting of these communities varies from very dry to wet climates, and from ridgetops, slopes, to plateaus. Consequently, vegetation communities have variable species composition. The questions addressed were: (1) What are the patterns of species composition among limestone vegetation types based on a parsimony analysis of species assemblages (PASA) and how congruent are they with geography, climate, topography, and vegetation physiognomy? and (2) How do PASA patterns compare to floristic patterns obtained with a classification (UPGMA) and an ordination (NMS)? The main distinction of floristic categories was between communities of humid and dry climates, followed by a finer separation of communities congruent with topography; vegetation physiognomy corresponded with both. PASA, UPGMA, and NMS produced highly coincident floristic groups; however, affinities among groups were different. Advantages of PASA over UPGMA and NMS are that PASA produces groupings strictly based on the shared species and provides different measures of support for floristic groups. The three techniques indicated that the humid and dry limestone areas of Puerto Rico had floristically divergent dry-type vegetation, even when they were structurally and physiognomically convergent. Also, floristic affinities of dry communities in Puerto Rico were stronger with dry communities on other islands than to more humid communities on the same island; thus, humidity regime is stronger than geography in promoting floristic links among limestone vegetation communities of the Caribbean. Almost every conclusion obtained from UPGMA and NMS was also taken from PASA, and so all three techniques are compatible. The methodological, theoretical, and interpretive simplicity of PASA is what makes it an attractive procedure for studies that examine composition patterns.

La vegetación de la Reserva Ecológica Lomas del Seminario, Ajusco, México

El presente trabajo fue realizado en la Reserva Ecológica Lomas del Seminario, Ajusco Medio, México, Distrito Federal, con la finalidad de conocer el estado actual de la vegetación. Se reconocieron 2 tipos de vegetación primaria: matorral xerófilo y bosque de Quercus, además de 2 tipos de vegetación secundaria: matorral de Quercus asociado a Sedum y matorral xerófilo asociado a Sedum. Se elaboró un mapa de vegetación de la zona y se determinó la composición florística y la estructura de la vegetación.

Distribution, abundance, and habitat preferences of Ixodes ricinus (Acari: Ixodidae) in northern Spain.

Ixodes ricinus (L.) was collected by standard dragging in 2,082 different sites in 18 broad vegetation categories in northern Spain to explore the influence of vegetation on its abundance. Of these, 785 sites were surveyed in 1995, 636 in 1996, and 661 in 1997. The impact of habitat features on differences in tick numbers is addressed. The tick was present in low numbers in areas of old, heterogeneous coniferous forests. Ticks appeared to prefer sites that had substantial secondary plant growth such as river canopies, heterogeneous Pinus uncinata forests, mixed forests, and deciduous heterogeneous woods. Highest tick abundance was recorded for sites that contained Quercus spp., as well as for mixed old forests that had many ecotones. I. ricinus was absent in open habitats, homogeneous young coniferous forests, and open hillsides. These differences were attributed to greater shrub cover and litter depth, which created more favorable microclimatic conditions for tick survival. The abundance of I. ricinus nymphs was not homogeneous in sites within the same habitat category and vegetation physiognomy at these sites did not appear to cause differences in tick abundance. Analysis of variance (ANOVA) indicated that variation in tick abundance could be explained by the exposure of the sampled site, at least for some zones within deciduous forest categories. However, this factor did not explain the variation observed in other habitats. Temperature and vegetation (normalized derived vegetation index) features were recorded daily by remotely sensed imagery throughout the study period and the data were used to obtain long-term mean and maximum values of the physical parameters considered. Multiple regression analysis performed between these long-term abiotic factors and nymphal abundance in positive sites showed high relationship (R2 coefficients) for every habitat category and explained >50% of the variation in tick abundance.

Elevational gradients in species richness and endemism of selected plant groups in the central Bolivian Andes

I analyzed the distribution of Acanthaceae, Araceae, Bromeliaceae, Cactaceae, Melastomataceae, and Pteridophyta in 62 vegetation plots of 400 m2 along an elevational transect between 500 m and 2450 m, and at a nearby lowland site in western Santa Cruz department, Bolivia. These groups were selected because they are physiognomically distinctive, have high species numbers, are comparatively easy to identify, adequately reflect overall floristic relationships, include a wide range of life forms, and are small. The transect was located in the Tucumano-Boliviano biogeographic zone and included drought-deciduous ( 1800 m) forests. Elevational patterns of species richness were group-specific and probably related to the ecophysiological properties of each group. Species richness in Pteridophyta and Melastomataceae was correlated with moss cover (i.e., humidity), with elevation (i.e., temperatures) in Acanthaceae and epiphytic Bromeliaceae, with potential evapotranspiration (i.e., ecosystem productivity) in Araceae, and with light availability at ground level in terrestrial Bromeliaceae and Cactaceae. Community endemism generally increased with elevation, but showed a maximum at 1700 m for terrestrial Pteridophyta, and a nonsignificant decline for epiphytic Bromeliaceae and Cactaceae. Endemism was higher for terrestrial than for epiphytic taxa, and was lower among Pteridophyta compared to all other groups, reflecting different dispersal ability among taxonomic and ecological groups. Elevational zonation, tested against a null-model of random distribution of elevational limits, revealed a significant accumulation of upper and lower elevational range boundaries at 900–1050 m and at 1500–1850 m, corresponding to the elevational limits of the main physiognomic vegetation types.

Ecohydrological perspective of phytogenic organic and inorganic components in Greek lignites: a quantitative reinterpretation

A consensus about the development of freshwater wetlands in relation to time and space is urgently required. Our study aims to address this issue by providing additional data for a fine-scaled comparison of local depositional settings of Greek mires during the Pliocene and Pleistocene. Lignite profiles exhibit phytogenic organic components (macerals) that have been used to investigate the past peat-forming vegetation structure and their succession series. The organic petrology of lignite samples from the opencast mines of Komanos (Ptolemais) and Choremi (Megalopolis) was achieved to assess the water supply, wetland type, nutrient status and vegetation physiognomy. A holistic approach (a study of ecosystems as complete entities) was carried out for a paleoecological reconstruction of the mires. Huminite, liptinite and inertinite were traced by means of their chemical and morphological differences together with the morphogenic and taphonomic affinities. The problem of combining independent information from different approaches in a multivariate calibration setup has been considered. Linear regression, non-metric multidimensional scaling and one-way analysis of variance tested the occurrence of palynological and petrological proxies. Although the lignite formation and deposition are less related to humid periods than expected, the resulting differences occurring in the reconstructed development stages appear to be related to astronomically forced climate fluctuations.

Fuzzy set analysis of the Ethiopian rift valley vegetation in relation to anthropogenic influences

Vegetation data of the Rift Valley have been revisited using fuzzy set theory to give quantitative measures of the links between species and vegetation states. Vegetation is considered as a global indicator of both land use and natural conditions. Human activities in the area have influenced the physiognomy of vegetation so much that an apparently uniform state has developed over most of the Rift Valley floor. Fuzzy set theory has made it possible to interpret the pattern of variation in vegetation on the basis of some reference states corresponding to protected and cultivated sites. The concept of stratocoena is applied to analyse the anthropogenic influences on the tree-shrub and herb layers in order to investigate how they respond to human interference individually.

The Role of Soil Seed Banks in the Rehabilitation of Degraded Hillslopes in Southern Wello, Ethiopia1

ABSTRACTThe species composition in the soil seed bank of degraded hillslopes in southern Wello, Ethiopia, was assessed using the seedling emergence method and compared with that of the standing vegetation. Surface soils were sampled at 0‐to 5‐cm depth from 49 plots of four physiognomic vegetation classes (hereafter vegetation classes): forests, shrublands, grasslands, and degraded sites. Soils were spread on sterile sand in a glasshouse and watered. Emerging seedlings were recorded for five months until no new seedlings emerged. A total of 3969 seedlings belonging to 71 species and 30 families germinated. The species composition of the seed bank was dominated by 53 herb species (75%) compared to 2 tree species which accounted for only 3 percent of the total number of species. Seedling density differed significantly among vegetation classes and ranged from 391 to 7807 seeds/m2. Mean species richness also differed significantly among the vegetation classes. Forty‐two species were found to be common to the seed banks and the standing vegetation; however, correspondence between species numbers and composition of the seed banks and the standing vegetation was poor. Although most of the species that germinated in the seed banks were herbs and grasses, they can develop a vegetative cover and contribute to reduction of soil erosion. Regeneration of the tree species (some of which have seed viability up to four years) however, requires both time and the presence of mature individuals. Together with hillside closure and soil conservation measures (e.g., terracing), planting of native woody seedlings might help to expedite rehabilitation of degraded hillslopes devoid of trees and shrubs.

Relationships between Leaf Area Index and Landsat TM Spectral Vegetation Indices across Three Temperate Zone Sites

Mapping and monitoring of leaf area index (LAI) is important for spatially distributed modeling of vegetation productivity, evapotranspiration, and surface energy balance. Global LAI surfaces will be an early product of the MODIS Land Science Team, and the requirements for LAI validation at selected sites have prompted interest in accurate LAI mapping at a more local scale. While spectral vegetation indices (SVIs) derived from satellite remote sensing have been used to map LAI, vegetation type, and related optical properties, and effects of Sun–surface–sensor geometry, background reflectance, and atmospheric quality can limit the strength and generality of empirical LAI–SVI relationships. In the interest of a preliminary assessment of the variability in LAI–SVI relationships across vegetation types, we compared Landsat 5 Thematic Mapper imagery from three temperate zone sites with on-site LAI measurements. The sites differed widely in location, vegetation physiognomy (grass, shrubs, hardwood forest, and conifer forest), and topographic complexity. Comparisons were made using three different red and near-infrared-based SVIs (NDVI, SR, SAVI). Several derivations of the SVIs were examined, including those based on raw digital numbers (DN), radiance, top of the atmosphere reflectance, and atmospherically corrected reflectance. For one of the sites, which had extreme topographic complexity, additional corrections were made for Sun–surface–sensor geometry. Across all sites, a strong general relationship was preserved, with SVIs increasing up to LAI values of 3 to 5. For all but the coniferous forest site, sensitivity of the SVIs was low at LAI values above 5. In coniferous forests, the SVIs decreased at the highest LAI values because of decreasing near-infrared reflectance associated with the complex canopy in these mature to old-growth stands. The cross-site LAI–SVI relationships based on atmospherically corrected imagery were stronger than those based on DN, radiance, or top of atmosphere reflectance. Topographic corrections at the conifer site altered the SVIs in some cases but had little effect on the LAI–SVI relationships. Significant effects of vegetation properties on SVIs, which were independent of LAI, were evident. The variability between and around the best fit LAI–SVI relationships for this dataset suggests that for local accuracy in development of LAI surfaces it will be desirable to stratify by land cover classes (e.g., physiognomic type and successional stage) and to vary the SVI.

SPACE IMAGERY IN THE STUDY OF INDUSTRIAL IMPACTS ON NORTHERN VEGETATION: DIFFICULTIES AND UNRESOLVED PROBLEMS

A comparative analysis is made of materials from four groups of researchers—Russian, British, Norwegian, and Finnish—who have used space imagery to study industrial impacts on northern vegetation in the vicinity of Monchegorsk. The problems encountered by the groups included variable survey weather conditions, the strong influence of seasonal changes, differences in the physiognomy of the vegetation, and the inapplicability of impact indicators used in one region to another.

Estrutura de duas formações vegetais do cordão externo da restinga de Marambaia, RJ

Foram caracterizadas duas formações vegetais, psamófila-reptante e arbustiva de Palmae, no cordão arenoso externo da restinga de Marambaia (RJ) com base na posição topográfica, na fisionomia e na estrutura, utilizando-se o método de parcelas. Embora as duas formações sejam visualmente distintas, há uma zona de transição entre elas. Das 23 espécies amostradas na formação psamófila-reptante, Ipomoea pes-caprae, Ipomoea imperati, Allagoptera arenaria, Sporobolus virginicus, Remirea marítima e Panicum racemosum despontaram com maiores valores de importância (VI). A formação halófila dominada por Blutaparon portulacoides, típica de outras restingas no litoral brasileiro, não foi identificada devido ao intenso dinamismo da faixa entre o mar e a primeira linha de cristas praiais estabilizadas. A formação arbustiva de Palmae é dominada por Allagoptera arenaria, com 56% do VI total, dentre as 64 espécies amostradas. As duas formações são dominadas por geófitas rizomatosas.

Four decades of old field vegetation development and the role of Celastrus orbiculatus in the northeastern United States

Abstract. This paper describes four decades of in situ vegetation change in a post‐agricultural site in southern New England where the role of the introduced vine, Celastrus orbiculatus, has drastically modified the course of vegetation development. An initial perennial forb‐grassland community was replaced by two strikingly different physiognomic vegetation types‐an early hardwood forest and a vine community occupying the same site 40 yr later. This ecological phenomenon was unpredictable since Celastrus was not recorded at the site until the 1970s. Within the young hardwood forest dominated by Prunus serotina and Acer rubrum, a few old field species (five) persist, whereas 17 forest herbs have become established. Typical forest shrubs are rare or absent. The Celastrus‐dominated vine community has suppressed or eliminated pre‐existing growth to form a relatively stable community where a forest vegetation is the regional vegetation type. Celastrus also appears to be facilitating a native vine (Vitis labrusca) by forming a ‘ladder’ for its advance. Although A. rubrum and Quercus spp. could ultimately dominate the forest community, the contiguous and aggressive nature of Celastrus makes predictions questionable. This long‐term study highlights the unpredictable nature of old field succession and the role of an exotic species in threatening the natural vegetation development.

Brazilian Páramos I. An introduction to the physical environment and vegetation of the campos de altitude

Summary Aim The campos de altitude are a series of cool‐humid, grass‐dominated formations restricted to the highest summits of the southeastern Brazilian Highlands. Relatively little is known of the ecology, biogeography, or developmental history of this archipelago of mountaintop formations. This contribution presents an overview of our present state of knowledge with respect to the past and present physical environment and vegetation of the campos de altitude. The aim is (1) to introduce an international audience to the natural history of these diminutive yet important ecosystems, and (2) to provide the background for a series of forthcoming contributions that will treat the ecology of the campos de altitude and explore physical and biotic relationships between these ‘Brazilian páramos’ and similar formations in the high mountains of equatorial South and Central America. Location Beginning at altitudes of 1800–2000 m, the campos de altitude are found atop the highest summits of the main ranges of the southeastern Brazilian Highlands, between the states of Santa Catarina and Minas Gerais/Espírito Santo. Methods Drawing upon both original data and previously published results, this contribution reviews what we presently know about the physical environment and vegetation of the campos de altitude, in the context of geographic setting, geology, palaeoclimatology and palaeobotany, modern climate, modern vegetation, and conservation. Results and main conclusions Uplift of the southeastern Brazilian ranges to altitudes high enough to support orographic grasslands may have occurred as early as the middle‐ to late‐Tertiary; pollen records show that campos de altitude have been extant on southeastern summits at least since the Late Pleistocene. The present‐day climate of the campos de altitude is cool and (per)humid, but patterns of rainfall, temperature, and frost are distinctly seasonal. Although the flora of the campos de altitude is highly diverse and characterized by a high degree of endemism, the campos de altitude maintain strong floristic similarities to equatorial alpine formations of the Andean and Central American Cordillera; these similarities also extend to climate, soils, and vegetation physiognomy. Anthropogenic fires and grazing are widespread in the campos de altitude and probably contribute significantly to the modern structure of vegetation communities.

Mesoscale Disturbance and Ecological Response to Decadal Climatic Variability in the American Southwest

Climatic variables such as radiation, temperature and precipitation determine rates of ecosystem processes from net primary productivity to soil development. They predict a wide array of biogeographic phenomena, including soil carbon pools, vegetation physiognomy, species range, and plant and animal diversity. Climate also influences ecosystems indirectly by modulating the frequency, magnitude, and spatial scales of natural disturbances (Clark 1988; Overpeck et al. 1990; Swetnam 1993).

Fitossociologia do componente lenhoso de um refúgio vegetacional no município de Buíque, Pernambuco

Com o objetivo de contribuir para o conhecimento da vegetação lenhosa das chapadas sedimentares do sertão de Pernambuco, foi realizada a caracterização fisionômica e a análise da estrutura da vegetação arbustiva perenifólia localizada em uma vertente a barlavento da serra do Catimbau, na propriedade sítio Cigano, Buíque (8°67'LS e 37°1' LW) a 800 m de altitude. Em cem pontos quadrantes, distribuídos em 10 linhas paralelas, interdistantes 30 m, cada uma com 10 pontos quadrantes distanciados 10 m, foram amostrados todos os indivíduos com diâmetro do caule > ou = 3 cm no nível do solo e altura total > ou = 1 m. Densidade total, área basal total, alturas e diâmetros médios e máximos foram de 2.207,7 ind./ha, 6,07 m²/ha, 2,3 m e 7,0 m, 5,1 cm e 21,96 cm, respectivamente, revelando um padrão fisionômico distinto das vegetações de caatinga e carrasco estudadas no nordeste do Brasil. Das 35 espécies amostradas, Eremanthus capitatus, Piptadenia obliqua, Gochnatia oligocephala, Senna cana var. cana e Eugenia punicifolia foram responsáveis por 63,3% do índice do valor de importância total. O índice de diversidade de Shannon para espécies foi de 2,73 nats/ind.

Contribution to the study of the Greek flora: Flora and vegetation of the E Aegean islands Agathonisi and Pharmakonisi

Panitsa, M. & Tzanoudakis, D.: Contribution to the study of the Greek flora: Flora and vegetation of the E Aegean islands Agathonisi and Pharmakonisi. — Willdenowia 28: 95–116. 1998. — ISSN 0511-9618.The flora and vegetation of the north-easternmost islands of the prefecture of Dodekanisos, Agathonisi and Pharmakonisi, which remained floristically almost unexplored until recently, have been investigated. Included are also the flora and vegetation of the seven islets around Agathonisi. Altogether, 402 species and infraspecific taxa of higher plants belonging to 131 genera and 52 families have been found. The analysis of the flora and the classification of the taxa into three main chorological units and five life form types shows that the Mediterranean elements and the therophytes predominate. A comparison of the individual floras of the two islands and seven islets revealed very low values of Sørensen's similarity coefficient, indicating a remarkable floristic independence. This floristic independence is also expressed by the fact that the nine islands and islets have not one taxon in common, whereas 130 taxa occur only on one island or islet each. Three vegetation zones (littoral, epilittoral and interior) are distinguished and described. The vegetation physiognomy differs from islet to islet due to different dominant species. Human activities such as agriculture, grazing, fires, etc. likewise affect the local floristic composition and vegetation physiognomy.