Vegetation Physiognomy Research Articles

Tropical montane forest ecotones: climate gradients, natural disturbance, and vegetation zonation in the Cordillera Central, Dominican Republic

AbstractAim We examined relationships between climate–disturbance gradients and patterns of vegetation zonation and ecotones on a subtropical mountain range.Location The study was conducted on the windward slopes of the Cordillera Central, Dominican Republic, where cloud forest appears to shift in a narrow ecotone to monodominant forest of Pinus occidentalis.Methods Climate, disturbance and vegetation data were collected over the elevation range 1100–3100 m and in 50 paired plots along the ecotone. Aerial photographs were georeferenced to a high‐resolution digital elevation model in order to enable the analysis of landscape‐scale patterns of the ecotone.Results A Shipley–Keddy test detected discrete compositional ecotones at 2200 and 2500 m; the distributions of tree species at lower elevations were continuous. The elevation of the ecotone determined with aerial photographs was fairly consistent, namely ± 164 m (SD) over its 124‐km length, but it exhibited significant landscape variation, occurring at a lower elevation in a partially leeward, western zone. The ecotone also occurred significantly lower on ridges than it did in drainage gullies. Ecotone forest structure and composition differed markedly between paired plots. In pine paired plots, the canopy height was 1.7 times higher and the basal area of non‐pine species was 6 times lower than in the cloud forest directly below. Fire evidence was ubiquitous in the pine forest but rare in the abutting cloud forest. Mesoclimate changed discontinuously around the elevation of the ecotone: humidity and cloud formation decreased markedly, and frost frequency increased exponentially.Main conclusions The discreteness of the ecotone was produced primarily by fire. The elevational consistency of the ecotone, however, resulted from the overarching influence of mesoclimate on the elevational patterns of fire occurrence. Declining temperature and precipitation combine with the trade‐wind inversion to create a narrow zone where high‐elevation fires extinguish, enabling fire‐sensitive and fire‐tolerant taxa to abut. Once established, mesotopography and contrasting vegetation physiognomy probably reinforce this boundary through feedbacks on microenvironment and fire likelihood. The prominence of the pine in this study – and of temperate and fire‐tolerant taxa in subtropical montane forests in general – highlights the importance of climate‐disturbance–biogeography interactions in ecotone formation, particularly where fire mediates a dynamic between climate and vegetation.

Vertical and horizontal distribution of pollination systems in cerrado fragments of central Brazil

In fragments of the cerrado, we determined the frequency of pollination systems and analyzed their spatial distribution. We placed 38 transects, sampling 2,280 individuals and 121 species. As expected in Neotropical regions, bee-pollination was the most frequent pollination system. We found a decrease in the frequency of plants pollinated by beetles towards the fragment interior. Similarly, we found significant variation in relation to height just for the bats; there was an increase in the frequency of plants pollinated by bats towards the higher heights. In general, we found no horizontal and vertical variation in the pollination systems, probably as consequence of the more open physiognomy of the cerrado vegetation.

Organization of dung beetle communities (Coleoptera, Scarabaeidae) in areas of vegetation re-establishment in Feira de Santana, Bahia, Brazil

The present work refers to the study of colonization of four vegetation physiognomies considered as succession stages by Scarabaeidae beetles in Feira de Santana, Brazil. The four environments present structures of 1) herbs, 2) herbs and bushes, 3) bushes, and 4) bushes and trees. The last one has similar vegetation elements to the original vegetation of the area (Caatinga, in transition with deciduous forest). Beetles’ richness was not statistically different in the three structurally simpler habitats, the composition, as well as the abundance structure of the communities of the four sites were very similar. Guild structure changed in number and proportion of specimens, with an increase in the number of tunnelers as the vegetation grew in complexity. The positive/negatives effects on the composition and beetles’s community structure were related to the interference with the dissemination of odor plumes or maintenance of sources of resources (vertebrates). The organization of the functional structure in the beetles’ community should be related to the time needed for the establishment of complex ecological connections.

Changes of Landscape Structure for the Recent 20 Years in the Wangsuk Stream Basin of the Central Korea

Landscape changes for 20 years between 1981 and 2001 in the Wangsuk stream basin located on the central Korea were investigated on the basis of physiognomic vegetation map made from the aerial photograph interpretation and field check. Changes of landscape structure were noticeable in agricultural field and forest landscape elements. Changes in the agricultural fields due to transformation of agricultural pattern into the institutional agriculture dominated landscape change, although urbanization also contributed to such change. The former change due to change of food production structure originated from socio-economic development during this period and the latter to the overpopulation of Seoul. As energy sources for heating and cooking, fertilizer, and fodder for livestock transform from plant materials to fossil fuel, manufactured one, and grain, succession of forest escaped from direct human disturbance dominated change of landscape structure in forested land. Differently from the positive landscape change in the upper area, change in the lower area deteriorated landscape quality by increasing artificial land. It was estimated that such landscape deterioration in the Wangsuk stream basin would influence water quality of the stream. In order to realize sustainable land-use against such environmental degradation, systematic environmental management based on landscape ecological perspective such as "an eco-plan for creating riparian vegetation belt," which is under preparation by Ministry of Environment, was recommended.

Abundance and diversity of rodents at the human–wildlife interface in Western Serengeti, Tanzania

AbstractRodent species abundance and diversity in Western Serengeti are evaluated and discussed in relation to different levels of conservation status [Unprotected Area (UA), Game Reserve (GR) and National Park (NP)] and broad site differences in human livelihood activities. A total of 2170 individuals, spread over 16 rodent species, were caught in a capture‐mark‐recapture study which covered both the dry and wet seasons. The more humid site (Tabora B) in the northern part of Serengeti had the highest diversity of rodents followed by the Mihale site at the western extension. The driest site at Robanda had the lowest overall species diversity. Diversity also varied between the three levels of conservation status whereby the UA had the least diversity while the NP, which enjoyed the highest level of conservation status, had the highest diversity of rodents. Unprotected Area and NP plots at Tabora B showed a rodent species similarity index of 40%; all the other paired plots scored over 50% similarity indices, suggesting that, within a site, species composition did not vary significantly between the three levels of conservation status. The Robanda site had the highest (56%) overall abundance of rodents; Mihale and Tabora B sites had about the same level of rodent abundance (20 and 24% respectively). For the Mihale site, Mastomys natalensis ranked first followed by Arvicanthis niloticus and Tatera robusta, each of which contained 40, 38 and 16%, respectively, of all individuals caught at the site. For the Robanda site, the figures were 66%A. niloticus, 22%M. natalensis and 9%T. robusta; while for the Tabora B site the scores were 37%M. natalensis, 18%T. robusta and 11%Lemniscomys barbarus. The differences in diversity, species composition and population abundance appear to result largely from physiognomic vegetation types, and habitat perturbations caused by livelihood activities in Western Serengeti.

Spatial heterogeneity, land use and conservation in the cerrado region of Brazil

AbstractAim This paper presents a spatial classification of the environmental and ecological diversity of the cerrado region of Brazil, as well as an appraisal of the levels of conversion to agriculture and of the extent of land protection.Location The cerrado region of Brazil, located in the centre of Brazil, occupies c. 2.5 million square kilometres. Our study area represents roughly 85% of the total. This ecologically heterogeneous region is dominated by savannas, but also contains several types of forests and xerophytic communities that often form mosaics with the savannas. Its high biodiversity is seriously threatened by the accelerated process of conversion to agriculture and a deficiency in the extent and the representativeness of protected areas.Methods We selected 124 land systems from a previous study of the lowlands of South America. The maps were digitized and 41 parameters, where environmental information was available, were used to build a matrix. A cluster analysis was then performed and the results used to classify the land systems into units at two scales. The larger units, characterized by the dominant landform and vegetation, were considered as landscape units. Within each of these, smaller units called ecological units were defined by the physiognomy and phenology of the dominant vegetation, topography and drainage. Using GIS, we mapped the resulting ecological units and incorporated the information on land use from the municipal agricultural census of 1996. In addition, data on the extent of protected land units was used to assess the status of land protection in each ecological unit.Results Five landscape units and 15 ecological units were identified, mapped and explained. These units were not continuous but were represented by disjunct patches located in different parts of the study region. Brief descriptions are given including the geographical locations and dominant ecological features. They also include the extent of land conversion to agriculture (1996 census figures) in each of the various patches as well as the number and area of units of conservation.Main conclusions The high level of land conversion to agriculture is a major threat to the conservation of the remarkable biodiversity of the cerrado region. This, together with the poor status of land protection, represents the major environmental problem facing this region. However, the fact that areas with similar general ecological conditions have a disjunct distribution is important for conservation purposes, even though the details of floristic similarities and biogeographic influences have still to be worked out. Our detailed spatial classification has made this disjunction clearly apparent and has allowed us to map ecologically similar areas accurately. This allows the evaluation of the status of these areas in terms of land use and land protection and may be used in the design of conservation strategies.

Tree–grass coexistence in the Brazilian cerrado: demographic consequences of environmental instability

AbstractAim Tropical savanna ecosystems are uniquely characterized by the co‐dominance of both trees and grasses. An operational understanding of the ecological processes involved in maintaining this condition is essential for understanding both the functioning of savanna systems as well as their potential response to environmental change. A simple model is presented to explore the potential for a demographic mechanism of long‐term tree persistence and temporal physiognomic stability in the Brazilian cerrado.Location The model is developed based on data from the humid cerrado of Brazil.Methods In contrast to many existing models of tree–grass dynamics a model is presented which is based on data from the humid cerrado of Brazil, which is both qualitatively and quantitatively different from many of the more arid savannas of the palaeotropics. The model focuses on the dynamics of a synthetic tree population, with particular attention given to reproduction, seedling establishment and fire effects; with separate sub‐models for grass production, fire and rainfall.Results The model successfully predicts coexistence across the full range of observed vegetation physiognomies, but only under limited conditions. Under coexistence conditions, the dynamics of the tree population are characterized by long periods of gradual decline, punctuated by occasional bursts of growth. However, in agreement with earlier studies, the model consistently over‐predicts domination by the tree component. Fire is identified as an overriding factor in determining model behaviour, and the response of reproduction and sapling recruitment to variance in the frequency of fire ignition is identified to be of potential importance in the functioning of the Brazilian cerrado. The key dynamics of the model which promote tree–grass coexistence are consistent with a number of established determinants of ecological resilience in savanna systems.Main conclusions The model identifies the importance of the effective exploitation of rare opportunities for favourable recruitment (e.g. exclusion from fire) by the tree population, in promoting coexistence within a predominantly adverse environment. Support is provided for an alternative demographic mechanism of tree–grass coexistence in the cerrado (the storage effect), which is not based on the limiting assumption of niche partitioning through differences in rooting depth. The results are consistent with those presented by recent modelling work based on the more arid savannas of southern Africa. The model presented here differs in the emphasis given to particular environmental and life‐history attributes which are critical in determining the tree–grass balance, but provides further general support for the potential role of demographic mechanisms (such as the storage effect) in determining the structure of tropical savannas. Despite having clear limitations, models can serve as valuable heuristic tools to aid the integration and exploration of existing data sets as well as our present understanding of key ecological processes.

The Sensitivity of CLAMP to Taphonomic Loss of Foliar Physiognomic Characters

Abstract CLAMP (Climate Leaf Analysis Multivariate Program) is a powerful paleoclimate proxy with the ability to yield quantitative data on past temperatures, precipitation, growing season length, and humidity, as well as enthalpy (a property of a parcel of air that is useful in studies of paleoaltimetry). Commonly quoted uncertainties in CLAMP predictions relate to the statistical uncertainty inherent in the combined quality of the modern calibration data sets and the relationship of foliar architecture to the various climate parameters. This minimum uncertainty assumes that the fossil assemblage represents faithfully the foliar physiognomy of the source vegetation. Taphonomic processes degrade this physiognomic fidelity. Differential selection for size, shape, and species composition during transport and post-depositional processes biases the physiognomic profile of the fossil assemblage. The sensitivity of CLAMP precision to taphonomic filtering was assessed empirically using a modern data set from the...

Modeling early forest succession following clear-cutting in western Oregon

In the Pacific Northwest, the process of conifer development after stand-replacing disturbance has important implications for many forest processes (e.g., carbon storage, nutrient cycling, and biodiversity). This paper examines conifer development in the Coast Range Province and Western Cascades Province of Oregon using repeat interpretation of historic aerial photographs from 1959 to 1997 to examine the canopy cover change of different life forms: shrubs, hardwood trees, and conifer trees. Ninety-four stands from the Western Cascades Province and 59 stands from the Coast Range Province were photointerpreted in roughly 5-year intervals. A Chapman–Richards growth function was used to model conifer cover development for all sample stands. Based on the photo data and the Chapman–Richards function, these stands were classified into one of seven early forest successional trajectories defined by the vegetation physiognomy. Succession in the Coast Range Province and Western Cascades Province were compared using parameters derived from the Chapman–Richards growth function. Our results echo previous studies in that rates and densities of conifer regeneration varied markedly among sites; however, our results also indicate that early forest succession differs in the two study regions in terms of both trajectories and rates. Conifer regeneration in the Western Cascades Province tends to have longer delays in establishing and slower rates compared with the Coast Range Province.

Diversity and productivity of plant communities across the Inland Northwest, USA

No definitive explanation for the form of the relationship between species diversity and ecosystem productivity exists nor is there agreement on the mechanisms linking diversity and productivity across scales. Here, we examine changes in the form of the diversity-productivity relationship within and across the plant communities at three observational scales: plots, alliances, and physiognomic vegetation types (PVTs). Vascular plant richness data are from 4,760 20 m2 vegetation field plots. Productivity estimates in grams carbon per square meter are from annual net primary productivity (ANPP) models. Analyses with generalized linear models confirm scale dependence in the species diversity-productivity relationship. At the plot focus, the observed diversity-productivity relationship was weak. When plot data were aggregated to a focus of vegetation alliances, a hump-shaped relationship was observed. Species turnover among plots cannot explain the observed hump-shaped relationship at the alliance focus because we used mean plot richness across plots as our index of species richness for alliances and PVTs. The sorting of alliances along the productivity gradient appears to follow regional patterns of moisture availability, with alliances that occupy dry environments occurring within the increasing phase of the hump-shaped pattern, alliances that occupy mesic to hydric environments occurring near the top or in the decreasing phase of the curve, and alliances that occupy the wettest environments having the fewest species and the highest ANPP. This pattern is consistent with the intermediate productivity theory but appears to be inconsistent with the predictions of water-energy theory.

Site‐level evaluation of satellite‐based global terrestrial gross primary production and net primary production monitoring

AbstractOperational monitoring of global terrestrial gross primary production (GPP) and net primary production (NPP) is now underway using imagery from the satellite‐borne Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. Evaluation of MODIS GPP and NPP products will require site‐level studies across a range of biomes, with close attention to numerous scaling issues that must be addressed to link ground measurements to the satellite‐based carbon flux estimates. Here, we report results of a study aimed at evaluating MODIS NPP/GPP products at six sites varying widely in climate, land use, and vegetation physiognomy. Comparisons were made for twenty‐five 1 km2 cells at each site, with 8‐day averages for GPP and an annual value for NPP. The validation data layers were made with a combination of ground measurements, relatively high resolution satellite data (Landsat Enhanced Thematic Mapper Plus at ∼30 m resolution), and process‐based modeling. There was strong seasonality in the MODIS GPP at all sites, and mean NPP ranged from 80 g C m−2 yr−1 at an arctic tundra site to 550 g C m−2 yr−1 at a temperate deciduous forest site. There was not a consistent over‐ or underprediction of NPP across sites relative to the validation estimates. The closest agreements in NPP and GPP were at the temperate deciduous forest, arctic tundra, and boreal forest sites. There was moderate underestimation in the MODIS products at the agricultural field site, and strong overestimation at the desert grassland and at the dry coniferous forest sites. Analyses of specific inputs to the MODIS NPP/GPP algorithm – notably the fraction of photosynthetically active radiation absorbed by the vegetation canopy, the maximum light use efficiency (LUE), and the climate data – revealed the causes of the over‐ and underestimates. Suggestions for algorithm improvement include selectively altering values for maximum LUE (based on observations at eddy covariance flux towers) and parameters regulating autotrophic respiration.

Demography, population dynamics and sustainability of the Patagonian sheep flocks

Sheep production is the main agricultural activity in Patagonia. Since the middle of the 20th century, sheep numbers have declined steadly. We used historical records of stock numbers in four ranches to analyze the importance of regional factors so as to explain the decline of the Patagonian sheep flocks. We found that the stocks of all the four ranches declined with a similar trend but fluctuated independently, thus reflecting a complex interaction between regional and local factors. Aboveground net primary production (ANPP) and vegetation physiognomy explained most of the differences in the flocks declining rates. We estimated demographic parameters for two ranches differing in their average annual growth rates. From these demographic parameters, we constructed deterministic and stochastic matrix models to establish the relative contribution of demographic processes to the observed decline. Matrix models projected a faster decline than that observed in the ranch used to calibrate the model. This suggests that the recorded demographic parameters could drive most stocks to extinction in less than 100 years. We concluded that the observed dynamics would be generated by demographic processes, but extinction is delayed or avoided by a continuous intake of animals. Ewe survival was the most important parameter in controlling the growth rate of the flocks. The environmental stochastic model showed that the growth of the stocks was highly sensitive to increases in the frequency of good years (those that produce a positive growth) and in the transition from normal years to bad years. All these evidences point out the existence of biological constraints to sheep production in Patagonia: ANPP and vegetation structure would control flock population dynamics throughout its effects on key demographic parameters, ewe survival and marking rate (a recruitment measure). Our model results suggest that the decline in sheep numbers, and hence the sustainability of the activity, is driven, to a large extent, by the demographic characteristics of the flocks.

Resposta da comunidade de Histeridae (Coleoptera) a diferentes fisionomias da vegetação de restingas no Espírito Santo

Buscando determinar se a estrutura da vegetação afeta a riqueza e estrutura da comunidade de besouros predadores (Histeridae), quatro ambientes no Espírito Santo, com grau decrescente de complexidade estrutural de vegetação (restinga arbórea preservada, restinga aberta de Clusia spp., restinga queimada e pastagem) foram amostrados com armadilha iscada (fezes humanas e de cavalo). Foram encontradas oito espécies de Histeridae, sendo que a riqueza de espécies foi praticamente igual nos oito ambientes (4 a 5 espécies), e a diferença de diversidade não foi significativa. Apesar da não significância, as comunidades podem ser diferenciadas pela substituição de espécies dominantes e diferenciação de composição. O padrão de substituição de espécies foi relacionado à diferença de fisionomia da vegetação, que ao impor barreiras à dispersão de odores, afeta a localização dos recursos, o que permite que espécies raras (porém mais eficientes na localização de recursos) sejam mantidas na comunidade. A riqueza local nos vários ambientes estudados não foi diferente devido à natureza efêmera (restritos quanto ao tempo em que fica disponível para colonização e terem seu poder de atração reduzido no tempo) dos recursos em decomposição, impondo uma restrição ao número de espécies. Sua distribuição aleatória e imprevisível, por sua vez, é responsável pelo caráter lotérico de sua colonização, onde tanto espécies abundantes quanto raras podem colonizá-lo, seja pela vantagem numérica ou por uma eventual superioridade na capacidade de localização do recurso.

Impact of short‐term rainfall fluctuation on interannual land cover change in sub‐Saharan Africa

ABSTRACTAim Interannual land cover change plays a significant role in food security, ecosystem processes, and regional and global climate modelling. Measuring the magnitude and location and understanding the driving factors of interannual land cover change are therefore of utmost importance to improve our understanding and prediction of these impacts and to better differentiate between natural and human causes of land cover change. Despite advances in quantifying the magnitude of land cover change, the interpretation of the observed land cover change in terms of climatic, ecological and anthropogenic processes still remains a complex issue. In this paper, we map land cover change across sub‐Saharan Africa and examine the influences of rainfall fluctuations on interannual change.Location The analysis was applied to sub‐Saharan Africa.Methods Ten‐day rainfall estimates (RFE) obtained from National Oceanic and Atmospheric Administration's (NOAA) Climate Prediction Center (CPC) were used to extract information on inter and intra‐annual rainfall fluctuations. The magnitude of land cover change was quantified based on the multitemporal change vector method measuring year‐to‐year differences in bidirectional reflectance distribution function (BRDF) corrected 16‐day enhanced vegetation index (EVI) data from the Moderate Resolution Imaging Spectro‐radiometer (MODIS). Statistical models were used to estimate the relationship between short‐term rainfall variability and the magnitude of land cover change. The analysis was stratified first by physiognomic vegetation type and second by chorological data on species distribution to gain insights into spatial variations in response to short‐term rainfall fluctuations.Results The magnitude of land cover change was significantly related to rainfall variability at the 5% level. Stratification considerably strengthened the relationship between the magnitude of change and rainfall variability. Explanatory power of the models ranged from R2 = 0.22 for the unstratified model to 0.40–0.96 for the individual models stratified by patterns of species distribution. The total variability explained by the combined models including the influence of rainfall and differences in vegetation response ranged from 22% for the model not stratified by vegetation to 76% when stratified by chorological data.Main conclusions Using this methodology, we were able to measure the contribution of natural variation in precipitation to land cover change. Several ecosystems across sub‐Saharan Africa are highly sensitive to short‐term rainfall variability.

Significance of temporal changes when designing a reservoir for conservation of dragonfly diversity

While there has been much focus in biodiversity conservation that transcends place, few studies transcend time. Yet an appreciation of vegetational and hydrological succession is essential for maintaining a habitat that has been created with the aim of conserving a particular group of organisms. This is a study of changes in a dragonfly assemblage over a period of 13 years at a biodiversity-rich, southern hemisphere reservoir. A total of 30 dragonfly species were recorded in this study, compared to 12 species before the reservoir was constructed in 1988, and 26 species in 1993, with 25 species resident in both 1993 and 2001. Two of these are local endemics. One other endemic was lost to succession in 1993 but reappeared in 2001. Three other species never reappeared after succession in 1993, yet six other species appeared after this date. Multivariate analyses identified structural and compositional vegetation, especially marginal forest, percentage vegetation cover, percentage shade, as the most important environmental variables determining dragonfly species composition. Other important environmental variables were grasses of tall, medium and short height categories, submerged vegetation, water flow and amount of open water. Not surprisingly, successional changes in vegetation physiognomy and in water conditions significantly increased Odonata species richness and diversity over the years. More importantly, the study shows that to maintain both high species richness, including endemics, it is essential to maintain a variety of biotopes using selective management of the marginal vegetation without allowing succession to proceed to a point where overgrowth of the bank and silting of the bottom begin to impoverish the fauna.

Relação entre índice de área foliar e frações de componentes puros do modelo linear de mistura espectral, usando imagens ETM+/Landsat

O índice de área foliar (IAF) é uma das mais importantes variáveis biofísicas da vegetação, estando relacionado diretamente com a evapotranspiração, com a produtividade da vegetação e com a interceptação da chuva pelo dossel. O objetivo deste trabalho foi analisar a relação do IAF de diversos tipos de cobertura do solo com Frações de Componentes Puros (FCPs) do Modelo Linear de Mistura Espectral (MLME). A área de estudo foi a microbacia hidrográfica do Ribeirão dos Marins, localizada no município de Piracicaba - SP. O IAF foi medido, no campo, com o equipamento LAI-2000, em 32 áreas com diferentes coberturas vegetais. A imagem utilizada foi do sensor ETM+ a bordo do satélite Landsat-7. No MLME, foram considerados três componentes puros (vegetação, solo e sombra), selecionados com o auxílio dos componentes principais. Como resultado, tem-se que o IAF variou de 0,47 a 4,48, quando consideradas todas as áreas. As relações do IAF com a fração do componente puro vegetação F VEG e com a fração do componente puro solo (F SOL) foram significativas, embora fracas. Ao considerar apenas dados de IAF de cana-de-açúcar, houve aumento da variação explicada tanto para F VEG como para F SOL, sugerindo que a estratificação da vegetação pelo tipo pode melhorar a estimativa do IAF.

Holocene vegetation change and the mammal faunas of South America and Africa

AbstractAim Although sharing many similarities in their vegetation types, South America and Africa harbour very dissimilar recent mammal faunas, not only taxonomically but also in terms of several faunistic patterns. However late Pleistocene and mid‐Holocene faunas, albeit taxonomically distinct, presented many convergent attributes. Here we propose that the effects of the Holocene climatic change on vegetation physiognomy has played a crucial role in shaping the extant mammalian faunistic patterns.Location South America and Africa from the late Pleistocene to the present.Methods Data presented here have been compiled from many distinct sources, including palaeontological and neontological mammalian studies, palaeoclimatology, palynology, and publications on vegetation ecology. Data on Pleistocene, Holocene and extant mammal faunas of South America and Africa allowed us to establish a number of similar and dissimilar faunistic patterns between the two continents across time. We then considered what changes in vegetation physiognomy would have occurred under the late Pleistocene last glacial maximum (LGM) and the Holocene climatic optimum (HCO) climatic regimes. We have ordained these proposed vegetation changes along rough physiognomic seral stages according to assumptions based on current botanical research. Finally, we have associated our hypothesized vegetation changes in South America and Africa with mammalian faunistic patterns, establishing a putative causal relationship between them.Results The extant mammal faunas of South America and Africa differ widely in taxonomical composition; the number of medium and large species they possess; behavioural and ecological characteristics related to herbivore herding, migration and predation; and biogeographical patterns. All such distinctions are mostly related to the open formation faunas, and have been completely established around the mid‐Holocene. Considering that the mid‐Holocene was a time of greater humidity than the late Pleistocene, vegetation cover in South America and Africa would have been dominated by forest or closed vegetation landscapes, at least for most of their lower altitude tropical regions. We attribute the loss of larger‐sized mammal lineages in South America to the decrease of open vegetation area, and their survival in Africa to the existence of vast savannas in formerly steppic or desertic areas in subtropical Africa, north and south of the equator. Alternative explanations, mostly dealing with the disappearance of South American megamammals, are then reviewed and criticized.Main conclusions The reduction of open formation areas during the HCO in South America and Africa explains most of the present distinct faunistic patterns between the two continents. While South America would have lost most of its open formations within the 30° latitudinal belt, Africa would have kept large areas suitable to the open formation mammalian fauna in areas presently occupied by desert and semi‐arid vegetation. Thus, the same general climatic events that affected South America in the late Pleistocene and Holocene also affected Africa, leading to our present day faunistic dissimilarities by maintaining the African mammalian communities almost unchanged while dramatically altering those of South America.

Phenological description of natural vegetation in southern Africa using remotely‐sensed vegetation data

Abstract. Various attempts have been made to describe and map the vegetation of southern Africa with recent efforts having an increasingly ecologi cal context. Vegetation classification is usually based on vegetation physiognomy and floristic composition, but phenology is useful source of information which is rarely used, although it can contribute functional information on ecosystems. The objectives of this study were to identify a suite of variables derived from time‐series NDVI data that best describe the phenological phenomena of vegetation in southern Africa and, secondly, to assess a classification of pixels of the study area based on NDVI variables using a preexisting map of the biomes that was delimited on the basis of life forms and climate. A number of variables were derived from the satellite data for describing phenological phenomena, which were analysed by multivariate techniques to determine which variables best explained the variation in the satellite data. This set of variables was used to produce a phenological classification of the vegetation of southern Africa, the results of which are discussed in relation to their concordance with the existing biome boundaries.

Flora y Vegetación de las zonas núcleo de la Reserva de la Biosfera Mariposa Monarca, México

Se realizó un estudio florístico y fisonómico de la vegetación en las zonas núcleo de la Reserva de la Biosfera Mariposa Monarca en los estados de México y Michoacán. Se efectuaron colectas botánicas durante un ciclo anual y se realizó una revisión de material previamente recolectado en la zona, depositado en los herbarios mexicanos IEB, EBUM y MEXU. El listado florístico incluye 423 especies que incluyen 32 taxa infraespecificos de plantas vasculares, agrupadas en 87 familias y 244 géneros. Las familias con mayor riqueza de especies fueron Asteraceae (103), Lamiaceae (21 ), Fabaceae ( 17) y Scrophulariaceae (17), en tanto que a nivel de género sobresalen Salvia ( 13), Stevia (8) y Ageratina (7). Un total de 135 especies (31.9%), que incluyen 13 taxa infraespecificos, son endémicas de México; 40 de estas especies pertenecen a Asteraceae. Las hierbas fueron la forma de crecimiento más frecuente (326 especies), seguidas por los arbustos (51) y los árboles (33). Se reconocen principalmente los siguientes tipos de vegetación: bosque de coniferas, bosque de Quercus, bosque mesófilo de montaña y pastizal antropogénico.

Vegetation patterns, regeneration rates and divergence in an old-field succession of the high tropical Andes

Vegetation restoration during old-field succession was studied in an alpine Andean ecosystem (paramo). 123 plots with different fallow times (1 to 12 years) and 8 plots under natural vegetation were sampled. The results indicate that secondary succession in the paramo, like in other extreme environments, can be interpreted as an autosuccession: there are mainly changes in species relative abundance and little floristic relay (i.e. species turnover). Only a few herbaceous species, mostly introduced (e.g. Rumex acetosella), act as strict pioneers and strongly dominate the early stages. Then, they undergo a progressive decline, while native forbs (e.g. Lupinus meridanus) and grasses (e.g. Vulpia myuros) have their peak abundance in intermediate stages. The characteristic paramo life forms, sclerophilous shrubs (e.g. Baccharis prunifolia, Hypericum laricifolium) and giant rosettes (e.g. Espeletia schultzii), appear very early and gradually increase in abundance during succession, becoming dominant in the late stages and showing a dual behaviour, both as ruderal and stress tolerant species. The 1st axis of a Detrended Correspondence Analysis arranges the sites according to their fallow time. The 2nd and 3rd axes, associated with diverging pathways of regeneration, are correlated with topographic factors and physio-chemical soil characteristics. Hence, structural divergence between plots increases along succession as community composition starts to reflect the conditions of each site. We found evidence of a constant rate of succession during the first 12 years, contradicting the generally accepted hypothesis in the succession literature of a continous slow down up to the climax. Regeneration of vegetation physiognomy is relatively fast, questioning the prevailing idea of slow restoration in alpine ecosystems. However, 12 years of fallow are insufficient to attain the species richness of the natural paramo. Under the current trend of fallow length reduction observed in traditional potato cultivation in the Andes, our results raise doubts about the conservationist value of this management strategy.