Scaling hierarchy of factors controlling riparian vegetation patterns of the Fynbos Biome at the Western Cape,South Africa

Question: How can vegetation gradients be described in riparian zones located in a species‐rich mountain range and how do these gradients explain the variation found in the vegetation? Location: Hottentots Holland Mountains, Western Cape, South Africa. Methods: Three gradients (geographic, longitudinal, lateral) were defined to describe the complex vegetation patterns found here. The gradients are related as follows: (1) the geographic gradient: related to the climatic and topographical changes across the entire mountain range; (2) the longitudinal gradient related to the changes along the different river reaches; (3) the lateral gradient related to the processes along the profile of the riverbed. These three gradients operated on three different hierarchical levels. Partial Canonical Correspondence Analysis (pCCA) was used to determine the amount of variation that is explained on each of the hierarchical levels. Results: The geographical gradient explained the highest fraction (more than 50%) of the total variation explained. This can be ascribed to the high species turnover across landscapes in the Fynbos Biome; this is most likely an outcome that is specific for this region. The second most important gradient was the lateral gradient, which reflects stream power and inundation frequencies of the river. This gradient is represented by ca. 48% of the explained variation and this gradient explains the major disturbances occurring in a riverine ecosystem. The longitudinal gradient was the least important of the gradients and shows overlap with the geographical gradient. Conclusions: In the species‐rich environment of the Fynbos Biome geographical factors do not only account for variation in zonal vegetation but also for variation within azonal vegetation, like riparian corridors.     

Community composition and soil properties in northern Bolivian savanna vegetation

Abstract. Direct gradient analysis (Canonical Correspondence Analysis) of northern Bolivian savanna vegetation revealed correlations between the composition of plant communities and physical and chemical soil properties. Cover/abundance values for 193 species from 27 sites were related to data on eight soil factors. A water-regime variable and the percentage of sand and silt were correlated with the first axis of the species-environment biplot and explained most of the variation in community composition. Along this axis, species and sites of flood-plain vegetation were separated from sites not affected by flooding rivers. The second axis of the biplot was correlated with soil-chemical variables, namely extract-able phosphate, base saturation, organic carbon, pH, and effective cation exchange capacity. Part of the variation in community composition can be explained by these soil nutrient variables. Grassland communities were separated from woody vegetation along the soil nutrient gradient, and floodplain communities of white-water rivers from those of clear-water rivers. The results of the gradient analysis indicate that the soil texture-moisture gradient is the prime factor determining the variation in the floristic composition of the savanna communities examined, and that, in addition, the soil nutrient gradient accounts for some of the variation.     

Tropical rain forest types and soil factors in a watershed area in Guyana

Abstract. An inventory was made of the vegetation and soils of a watershed area of 480 ha in the tropical rain forest of Guyana. 252 plots of 0.05 ha were sampled. In total 111 tree species > 20 cm were recorded. A TWINSPAN analysis resulted in seven groupings. Correspondence Analysis revealed that the major environmental differentiation underlying the floristic variation is according to soil type. Finally, five main forest communities were described. Most sites in the watershed area are characterized by the dominance of one or a few species. Species distribution patterns are strongly determined by soil type and drainage class.     

Variation in Greek phrygana vegetation in relation to soil and climate

Abstract. Variation in species composition and community structure in nine Greek phrygana (dwarf-shrub) sites was related to soil and climate variables by using Canonical Correspondence Analysis. The distribution of the Greek phrygana communities appeared to be related to soil rather than to climate. It is postulated that human action has eliminated the original variability related to climate factors in western Greek ecosystems; as a result, phrygana communities in this part of Greece are the result of human impact.     

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.     

Determinants of bird species richness: role of climate and vegetation structure at a regional scale

We examined the respective roles of climate and vegetation structure on geographical variation in bird species richness. The Province of Buenos Aires (central-eastern Argentina) was divided into 146 squares of 50 km on a side. For each square we evaluated the number of bird species, the value of thirteen climatic variables, and the value of a vegetation strata index. The climatic matrix was analyzed by Principal Component Analysis (PCA), and the first factors resulting from PCA were considered as multifactorial climatic gradients. Simple and Partial Correlation Analysis among bird species richness, vegetation strata, and the first two factors derived from PCA (65% of total variation) indicated that bird richness distribution was determined by the availability of vegetation strata, associated with different vegetation types that, at the same time, were influenced by the climatic conditions summarized in the first climatic factor (a gradient of precipitation, relative humidity, annual termical amplitude, and frost occurrence). This relationships reflect the complexity of factors that can act directly as well as indirectly on the geographical patterns in species richness. Also, we evaluated the importance of study scale comparing our results with previous studies at macrogeographic and local scales, found out that the vegetation structure was the principal determinant of bird species richness at this three geographical scales.     

阳际峰自然保护区地面生苔藓植物分布与环境因子关系研究

在江西阳际峰自然保护区调查的25个样地中,共采集到地面生苔藓植物34科56属106种（包括1变种）。应用CCA排序法,首次定量分析了该区38种主要地面生苔藓植物与环境因子的关系。结果表明,苔藓植物的分布和生物多样性受环境因子的影响较大,湿度、基质是影响地面生苔藓植物分布的主要环境因子,其他影响因子依次为乔木郁闭度、灌木盖度、海拔高度、人为干扰和坡度。     

Plasticity in Dendroclimatic Response across the Distribution Range of Aleppo Pine (Pinus halepensis)

We investigated the variability of the climate-growth relationship of Aleppo pine across its distribution range in the Mediterranean Basin. We constructed a network of tree-ring index chronologies from 63 sites across the region. Correlation function analysis identified the relationships of tree-ring index to climate factors for each site. We also estimated the dominant climatic gradients of the region using principal component analysis of monthly, seasonal, and annual mean temperature and total precipitation from 1,068 climatic gridpoints. Variation in ring width index was primarily related to precipitation and secondarily to temperature. However, we found that the dendroclimatic relationship depended on the position of the site along the climatic gradient. In the southern part of the distribution range, where temperature was generally higher and precipitation lower than the regional average, reduced growth was also associated with warm and dry conditions. In the northern part, where the average temperature was lower and the precipitation more abundant than the regional average, reduced growth was associated with cool conditions. Thus, our study highlights the substantial plasticity of Aleppo pine in response to different climatic conditions. These results do not resolve the source of response variability as being due to either genetic variation in provenance, to phenotypic plasticity, or a combination of factors. However, as current growth responses to inter-annual climate variability vary spatially across existing climate gradients, future climate-growth relationships will also likely be determined by differential adaptation and/or acclimation responses to spatial climatic variation. The contribution of local adaptation and/or phenotypic plasticity across populations to the persistence of species under global warming could be decisive for prediction of climate change impacts across populations. In this sense, a more complex forest dynamics modeling approach that includes the contribution of genetic variation and phenotypic plasticity can improve the reliability of the ecological inferences derived from the climate-growth relationships.     

Vegetation in Danish beech forests: the importance of soil,microclimate and management factors,evaluated by variation partitioning

The importance of management regime on floristic variation (mosses and vascular plants) in four Danish beech forests was investigated. Sixty-four blocks were sampled, representing beech stands of different age and management types. Nineteen potential explanatory variables were recorded and tested with Monte-Carlo tests and Canonical Correspondence Analysis. In addition results were evaluated by use of Detrended Correspondence Analysis. Explanatory variables were divided into three groups; soil, microclimatic and management parameters. The amount of variation explained by each group of variables was calculated by use of variation partitioning. The group consisting of management variables explained most variation, on local as well as regional scale. Management related variables explained more variation in vegetation than any other variables together. This indicates the importance of management as determining species composition in Danish beech forests. Management related variables explained most variation on local scale. On a regional scale, soil parameters explained the major part of the variation. The results suggest that thirty years without management are sufficient to change species composition significantly, as compared to managed forests.     

Evolution, origin and age of lineages in the Californian and Mediterranean floras

This paper addresses some of the conceptual issues involved in the analysis of the age and origin of mediterranean‐climate plant taxa, paying particular attention to three topics: (1) the importance of an explicit time frame in the definition of biogeographical origins, (2) the distinction between the age of traits and the age of taxa, and (3) the idea of mediterranean‐type ecosystems as environmental islands. (1) In California, recent analyses demonstrate that the diversity of species derived from different biogeographical origins is significantly correlated with temperature and precipitation gradients. These patterns support the hypothesis that niche conservatism is an important factor structuring modern diversity gradients. However, depending on how far back in time one looks, a species may be assigned to different origins; future discussions of biogeographical origins need to address the appropriate time frame for analysis. (2) Past research has demonstrated distinctive trait syndromes among woody plants of the Mediterranean, Chile, California and Mexico, and proposed that the syndromes are associated with lineages of different age in these floras. Reanalysis of individual traits demonstrates greater variability among regions than previously reported. The classification of plants into ‘old’ and ‘new’ genera is re‐evaluated, and it is suggested that greater attention be paid to the age of traits, rather than to the age of taxa, especially at an arbitrary rank such as genus. (3) The idea of mediterranean‐climate regions as ‘climatic islands’ is examined. Space–time diagrams of climate enable one to view the emergence of distinctive climatic regions in a continental context. The terms ‘synclimatic’ and ‘anticlimatic’ are proposed, referring to migration routes that parallel climate contours in space and time versus those that cross contours (including the case of geographic stasis in the face of climate change), respectively. Mediterranean‐climate regions have served as important case studies in plant ecology and evolution, and merit continued close examination in the light of continued advances in phylogenetics and palaeoecology.     

Vegetation‐environment relationships in Atlantic European calcareous grasslands

Abstract. The relationship between vegetation and environment was investigated for calcareous grasslands in a region in the west of Spain, France, Britain and Ireland defined by climatic criteria. Vegetation was sampled using objective methods and data collected on soils, land cover, location and management. Climate data were obtained from an available database. Examination of the first axis of vegetation variation as defined by Detrended Correspondence Analysis (DCA) showed a gradient from the Irish and British samples to those from France. The Spanish samples formed a separate group on the second axis. The species composition along the gradients is discussed. Correlations between the vegetation gradients and environmental variables were determined. The strongest correlations with the first DCA axis were for temperature, latitude, soil organic matter, grazing and land cover. The second DCA axis was highly correlated with rainfall, altitude and land cover. The third and fourth DCA axes were more difficult to interpret but appeared to be related to land cover. The results indicate that climate factors are important at this scale, but should not be considered in isolation and that factors relating to land cover and management should also be taken into account.     

Explaining disparities in species richness between Mediterranean floristic regions: a case study in Gladiolus (Iridaceae)

Aim The causes of geographical variation in species richness in clades that do not follow the latitudinal diversity gradient have rarely been investigated. Here, we examine spatial asymmetries of diversity in Gladiolus (Iridaceae), a large genus (> 260 species) that is present in two mediterranean climate biomes: the Cape of southern Africa (106 species) and the Mediterranean Basin (7 species). Despite convergence of climatic conditions between the two regions, the species density of Gladiolus is over one order of magnitude higher in the Cape than in the Mediterranean Basin. We investigate whether the diversity disparities observed in the genus are better explained by recent colonization of species‐poor areas (temporal hypothesis) or by differential rates of diversification (evolutionary hypothesis). Location Africa, Madagascar and Eurasia Methods We employ a recently developed Bayesian method for the estimation of diversification rates and a biogeographical optimization approach within a phylogenetic framework. Results In Gladiolus, the ‘diversity anomaly’ between the two Mediterranean climate regions cannot be explained solely by the time available for speciation in the Cape, but is also due to locally reduced rates of diversification in the Mediterranean Basin. Furthermore, high overall diversity in southern Africa stems from an ancient origin in the Cape allied with high rates of diversification in the summer‐rainfall region of the subcontinent. Main conclusions Both evolutionary and temporal hypotheses must be taken into account in order to explain the diversity anomaly between the Mediterranean Basin and the Cape. Our results suggest that regions at comparable latitudes and/or with similar climate may not converge in diversity levels due to heterogeneity of diversification rates and contrasting biogeographical histories.     

Fuel shapes the fire–climate relationship: evidence from Mediterranean ecosystems

Aim To understand how vegetation mediates the interplay between fire and climate. Specifically, we predict that neither the switching of climatic conditions to high flammability nor the sensitivity of fire to such conditions are universal, but rather depend on fuel (vegetation) structure, which in turn changes with productivity. Location An aridity/productivity gradient on the Iberian Peninsula (Mediterranean Basin). Methods We defined 13 regions distributed along an aridity gradient, which thus differ in productivity and fuel structure. We then assessed the changes in the temporal fire–climate relationship across regions. Specifically, for each region we estimated three variables: the aridity level for switching to flammable conditions (i.e. climatic conditions conducive to fire), the frequency of these flammable conditions and the area burnt under such conditions. These variables were then related to regional aridity and fuel structure indicators. Results In mediterranean ecosystems, the aridity level for switching to flammable conditions increased along the aridity gradient. Differences in fire activity between regions were not explained by the frequency of flammable conditions but by the sensitivity of fire to such conditions, which was higher in wetter and more productive regions. Main conclusions Under mediterranean climatic conditions, fuel structure is more relevant in driving fire activity than the frequency of climatic conditions conducive to fire. At a global scale, fuel also drives the fire–climate relationship because it determines the climatic (aridity) threshold for switching to flammable conditions. Our results emphasize the role of landscape structure in shaping current and future fire–climate relationships at a regional scale, and suggest that future changes in the fire regime (i.e. under global warming) might be different from what it is predicted by climate alone.     

长白山北坡草本植物分布与环境关系的典范对应分析

在长白山北坡海拔700～2600m的坡面上,海拔每上升100m设立一块样地,共计20个样地,计测样地中草本层植物的生态重要值和包括气候、土壤、林冠郁闭度等在内的13个环境因子,对获得的数据进行典范对应分析,作出了种类、样地分布与环境因子关系的二维排序图,排序图直观地反映了主要草本植物分布与环境因子间的关系。排序图中环境因子与前两个排序轴的相关系数大小表明,海拔高度作为诸多环境因子的综合反映,是影响长白山北坡草本植物分布的主导因素,除此之外,其它环境因子如林冠郁闭度、土壤有机质及有效N、P、K等因素,也对草本植物的分布有较大的影响。高山冻原与2000m以下森林群落内的草本植物明显不同,反映出二种不同类型植被间草本植物组成格局间质的差异。     

Microtopographic control of vascular plant, bryophyte and lichen communities on cliff faces

Cliff faces worldwide have recently been recognized as sites that harbour ancient forests, endangered biota and high levels of biodiversity, but knowledge is limited of the physical factors organizing cliff-face vegetation communities. Two large scale (geographic), five local, and eight fine scale (microtopographic) physical factors were examined using regression and Canonical Correspondence Analysis (CCA) to determine what scale of physical factors best explains variation in cliff-face vegetation on the 785 km long Niagara Escarpment in southern Ontario, Canada. The richness, frequency and community composition of vascular plants, bryophytes and lichens were determined for 72 cliff-face quadrats to discern whether these vegetation groups followed different patterns in their responses to the measured physical factors. A total of 124 different taxa (consisting of 50 vascular plant species, 21 bryophyte species, and 53 lichen taxa) were found on the cliff faces sampled in this study, though only 28 of these taxa were present in more than 10% of the sampled quadrats. Vascular plant and bryophyte species richness and frequency, and lichen frequency were only significantly correlated with microtopographic factors, while lichen species richness was correlated with a variety of fine and local scale physical factors. The fine scale factor ‘volume of soil’, in particular, was highly correlated with variation in richness or frequency for all vegetation groups, with increasing volume of soil correlated with increasing vascular plant richness and frequency and decreasing bryophyte richness and lichen frequency. A suite of local and fine scale physical factors also explained large proportions of variation in cliff-face vegetation community composition. A large scale gradient in the vegetation community was detected, though it resulted from fine scale physical differences between sites rather than from a latitudinal gradient. These results suggest that distinct subcommunities of vegetation exist on cliff faces and correlate with fine scale differences in microtopography.     

The role of bioclimatic origin,residence time and habitat context in shaping non-native plant distributions along an altitudinal gradient

An important factor influencing whether or not a non-native plant species becomes invasive is the climate in the area of introduction. To become naturalised in the new range, a species must either be climatically pre-adapted (climate matching), have a high phenotypic plasticity, or be able to adapt genetically, which in the latter case may take many generations. Furthermore, patterns of successful establishment across species might vary with habitat context. To address the interaction of these factors on non-native species richness, we recorded the presence of non-native annual plant species along an altitudinal gradient on Tenerife (Canary Islands, Spain). We compared the distributions of species differing in bioclimatic origin (Mediterranean and temperate) and time since introduction (old and recent introductions), and compared richness patterns of these groups in anthropogenic and natural habitats. Non-native species richness increased strongly from lowlands to mid-altitudes, but dropped sharply at the transition from anthropogenic to natural habitats, and thereafter declined with altitude in the natural habitat. This pattern indicates that the altitude effects reflected changes in both climate and habitat context. Mediterranean and temperate species were distributed similarly along the altitudinal gradient, and we found no effect of bioclimatic origin on species distributions. As almost all species present at the highest sites also occurred in the lowlands, we conclude that most species were introduced to lowland sites and were therefore pre-adapted to those climatic conditions (lowland introduction filter). The altitudinal ranges of species tended to increase with time since introduction, and the species reaching the highest altitudes were mostly old introductions. This effect of time was more pronounced among Mediterranean than temperate species. Thus, while climatic pre-adaptation is important for establishment along this altitudinal gradient, species tend to extend their altitudinal range with time.     

Diversity patterns in grasslands along a landscape gradient in northwestern France

Abstract. Several measures of biodiversity were calculated (species richness SR, species diversity H', species evenness J', mean similarity, mosaic diversity and factorial diversity) in vascular plant communities along a landscape gradient in the Seine valley, Normandy, France. For these communities, we also recorded environmental and management data. Species and environmental data were analysed simultaneously by Canonical Correspondence Analysis (CCA) in order to study their relationships. CCA identifies one main landscape gradient linked to a set of highly linked ecological factors. Three community types were identified along this gradient: calcicolous communities on chalk slopes, mesophilous communities on colluvium and hydrophilous communities on alluviums. The measures of biodiversity between these groups and their variations along the landscape gradient indicate similar patterns for H', J' and SR. Between‐community biodiversity measures allow consideration of the distribution of species among communities in the landscape. Factorial diversity accounts for the organisation of the communities with reference to the basic mechanisms of species coexistence. Affinity analysis (similarity and mosaic diversity) measures the compositional pattern diversity, which is the function of the variation in species richness. We discuss the indicative versus the predictive value of these measures of biodiversity as regards ecological factors and processes and their application for conservation purposes.     

Models of climate associations and distributions of amphibians in Italy

Analyzing the relationships between the distribution of animal species and climatic variables is not only important for understanding which factors govern species distribution but also for improving our ability to predict future ecological responses to climate change. In the context of global climate change, amphibians are of particular interest because of their extreme sensitivity to the variation of temperature and precipitation regimes. We analyzed species–climate relationships for 17 amphibian species occurring in Italy using species distribution data at the 10 × 10 km resolution. A machine learning method, Random Forests, was used to model the distribution of amphibians in relation to a set of 18 climatic variables. The results showed that the variables which had the highest importance were those related to precipitation, indicating that precipitation is an important factor in determining amphibian distribution. Future projections showed a complex response of species distributions, emphasizing the potential severity of climate change on the distributions of amphibians in Italy. The species that will decrease the most are those occurring in mountainous and Mediterranean areas. Our results provide some preliminary information that could be useful for amphibian conservation, indicating if future conservation priorities for some species should be enhanced.     

Equilibrium of vegetation and climate at the European rear edge. A reference for climate change planning in mountainous Mediterranean regions

Mediterranean mountains harbour some of Europe’s highest floristic richness. This is accounted for largely by the mesoclimatic variety in these areas, along with the co-occurrence of a small area of Eurosiberian, Boreal and Mediterranean species, and those of Tertiary Subtropical origin. Throughout the twenty-first century, we are likely to witness a climate change-related modification of the biogeographic scenario in these mountains, and there is therefore a need for accurate climate regionalisations to serve as a reference of the abundance and distribution of species and communities, particularly those of a relictic nature. This paper presents an objective mapping method focussing on climate regions in a mountain range. The procedure was tested in the Cordillera Central Mountains of the Iberian Peninsula, in the western Mediterranean, one of the ranges occupying the largest area of the Mediterranean Basin. This regionalisation is based upon multivariate analyses and upon detailed cartography employing 27 climatic variables. We used spatial interpolation of data based on geographic information. We detected high climatic diversity in the mountain range studied. We identified 13 climatic regions, all of which form a varying mosaic throughout the annual temperature and rainfall cycle. This heterogeneity results from two geographically opposed gradients. The first one is the Mediterranean-Euro-Siberian variation of the mountain range. The second gradient involves the degree of oceanicity, which is negatively related to distance from the Atlantic Ocean. The existing correlation between the climatic regions detected and the flora existing therein enables the results to be situated within the projected trends of global warming, and their biogeographic and ecological consequences to be analysed.     

Among-population variation and plasticity to drought of Atlantic,Mediterranean, and interprovenance hybrid populations of maritime pine

Maritime pine grows naturally under a wide range of climatic conditions, from strongly Atlantic to strongly Mediterranean. Aiming to improve our understanding of the genetic structure and inheritance of drought resistance strategies in the species, we conducted an environmentally controlled experiment to assess the genetic variation and plasticity to drought of Atlantic and Mediterranean populations, and the interprovenance hybrids between them. Hybridization could also help to provide new genetic material for use in transitional areas between the two regions, for which reproductive materials of good quality are generally lacking. Plastic responses to water stress appeared to be highly conserved among populations, with a common conservative isohydric strategy based on promoting growth when water was abundant, and stopping it when water became limiting. We found, however, a strong intraspecific variation in biomass allocation patterns. The Atlantic populations showed a risky growth-based strategy with a larger amount of juvenile needles, whereas Mediterranean populations showed a more conservative strategy, minimizing aerial growth and increasing the proportion of adult needles that is more resistant to water loss. Hybrid populations performed more similarly to the Mediterranean parent, suggesting a dominance of the Mediterranean-like characteristics. Some of the tested hybrid populations, however, combined high growth with traits of drought adaptation, and thus represent potentially interesting materials for use in transitional regions between the two climate zones.