Arctic plant diversity in the Early Eocene greenhouse

For the majority of the Early Caenozoic, a remarkable expanse of humid, mesothermal to temperate forests spread across Northern Polar regions that now contain specialized plant and animal communities adapted to life in extreme environments. Little is known on the taxonomic diversity of Arctic floras during greenhouse periods of the Caenozoic. We show for the first time that plant richness in the globally warm Early Eocene (approx. 55-52 Myr) in the Canadian High Arctic (76° N) is comparable with that approximately 3500 km further south at mid-latitudes in the US western interior (44-47° N). Arctic Eocene pollen floras are most comparable in richness with today's forests in the southeastern United States, some 5000 km further south of the Arctic. Nearly half of the Eocene, Arctic plant taxa are endemic and the richness of pollen floras implies significant patchiness to the vegetation type and clear regional richness of angiosperms. The reduced latitudinal diversity gradient in Early Eocene North American plant species demonstrates that extreme photoperiod in the Arctic did not limit taxonomic diversity of plants.     

Development and regional differentiation of the European vegetation during the Tertiary

The Tertiary vegetation of Europe evolved from paratropical to warm-temperate and temperate forms in response to a progressive, non-linear, climatic cooling. Its vegetational forms are composed mainly of two separate ecological units: the evergreen, laurophyll paleotropical geoflora and the deciduous, broad-leaved Arctotertiary geoflora. The development of the Tertiary climate and its interaction with the vegetation are convincingly indicated by the geoflora's migration; the changes in its composition; and the development of the Tertiary forest, swamp, and aquatic plant communities. The paleotropical geoflora is characterized in the upper Cretaceous to the upper Miocene by paratropical rain forest, subtropical rain and laurel forests, temperate laurel forests and edaphically-mediated formation of laurel-conifer forests. The Arctotertiary geoflora advanced into Europe in waves since the Paleocene and formed the basis for the Tertiary mixed mesophytic forests. These can be divided into warm-temperate rain forests, oak-hornbeamchestnut or mixed beech-oak-hornbeam forests, and edaphic formations such as bottomland and swamp forests. Beginning in the lower Cretaceous, the hydrophytic vegetation developed independently of the forest vegetation and formed very diverse herbaceous fresh water, swamp, salt water, and coastal formations. Considerable differences in composition allow to separate floral regions and provinces in Eurosiberia. Instead of three ill-defined floral regions in the Paleocene, there are four well-defined floral regions in the Pliocene. A Mediterranean region cannot be recognized, although Mediterranean (eumesogeic) floral elements appear in the Eocene/Oligocene and thereafter. The Mediterranean sclerophyll forests probably arose after the destruction of the laurophyll forests during the Pleistocene.     

Phylogeny of Acridocarpus-Brachylophon (Malpighiaceae): implications for tertiary tropical floras and Afroasian biogeography

Abstract.— A major tenet of African Tertiary biogeography posits that lowland rainforest dominated much of Africa in the late Cretaceous and was replaced by xeric vegetation as a response to continental uplift and consequent widespread aridification beginning in the late Paleogene. The aridification of Africa is thought to have been a major factor in the extinction of many African humid-tropical lineages, and in the present-day disparity of species diversity between Africa and other tropical regions. This primarily geologically based model can be tested with independent phylogenetic evidence from widespread African plant groups containing both humid- and xeric-adapted species. We estimated the phylogeny and lineage divergence times within one such angiosperm group, the acridocarpoid clade (Malpighiaceae), with combined ITS, ndhF , and trnL-F data from 15 species that encompass the range of morphological and geographic variation within the group. Dispersal-vicariance analysis and divergence-time estimates suggest that the basal acridocarpoid divergence occurred between African and Southeast Asian lineages approximately 50 million years ago (mya), perhaps after a southward ancestral retreat from high-latitude tropical forests in response to intermittent Eocene cooling. Dispersion of Acridocarpus from Africa to Madagascar is inferred between approximately 50 and 35 mya, when lowland humid tropical forest was nearly continuous between these landmasses. A single dispersal event within Acridocarpus is inferred from western Africa to eastern Africa between approximately 23 and 17 mya, coincident with the widespread replacement of humid forests by savannas in eastern Africa. Although the spread of xeric environments resulted in the extinction of many African plant groups, our data suggest that for others it provided an opportunity for further diversification.     

Floristic and vegetational changes in the Iberian Peninsula during Jurassic and Cretaceous

The successive vegetations inhabiting the Iberian Peninsula from the Triassic/Jurassic boundary to the Cretaceous/Tertiary Boundary is reviewed based on published palynological and macrofloral data, and the vegetational changes set in a palaeogeographical and climate context. Xerophytic microphyllous coniferous forests and pteridophyte communities of arid environments dominated the Jurassic and earliest Cretaceous vegetation. This vegetation was replaced in the mid Early Cretaceous by mixed forests of pteridophytes, gymnosperms and angiosperms. The composition of the successive plant assemblages suggests that a subtropical arid climate generally prevailed in the Iberian Peninsula during Jurassic-Cretaceous, although palaeobotanical and sedimentological evidences suggest that the climate was not uniform through the whole interval and that were two episodes in the Tithonian-Berriasian and Aptian-Albian periods of pronounced dry and/or arid environmental conditions. The composition and structure of the vegetation was not only affected by evolutionary changes but also by successive global geographical and climate changes. Hence, significant changes in the distribution of continental areas during the Mesozoic resulted in the latitudinal or sublatitudinal extensions of the climatic belts.     

太白山表土花粉和气孔器与植物类型的关系研究

通过陕西太白山13个样点表土花粉组合特征和气孔器及其与植物类型之间关系的分析,结果发现:针阔混交林花粉组合能很好地反映植物类型特征,落叶阔叶林和针叶林花粉组合能较好地与植物类型相对应,高山灌丛草甸花粉组合未能反映植物类型数量特征;主要花粉类型松属、铁杉属和桦属花粉具超代表性,胡桃属和榆属花粉具适宜代表性,落叶松属、冷杉属、杜鹃花科和槭属花粉具低代表性;DCA(Detrended Correspondence Analysis)分析表明,通过花粉数据能够较好区分不同植被类型,结合气孔器特征能够准确反映植被特征。     

Zur Taxonomie und Chorologie der Gattung Scopolia Jacq.

At the present time 5 species of the genus Scopolia Jacq. are demonstrating the close relations between the distribution patterns, situations and ecology of plants. They are growing recently in broadleaved deciduous forests and mixed forests with a different part of evergreen trees, shrubs and perennial herbs. Hyoscyamus L., a genus of Hyoscyaminae has become adapted to increasing aridity and shows now a center of distribution in the mountains of the eastern Mediterranean area and Near East within a semiarid climate on the western side of Eurasia. Scopolia Jacq. may be judged as relictic genus of mixed Tertiary broadleaved forest with a special evolution center on the eastside of the Eurasian continent under humid monsoon conditions. The recent scattered and disjunct distribution with gaps in arid-semiarid areas indicates the result of a long way of plantevolution, plant dispersal and changable history of the vegetation. The important, climatical conditions for the growth of Scopolia species are sufficient rainfall and moisture in summertime. Chill and frost in winter were forcing these herbs in temperate and northern regions to survive in superficial strata of the soils.     

The environmental implications of upper Paleozoic plant-fossil assemblages with mixtures of wetland and drought-tolerant taxa in tropical Pangea

We evaluate the influences of elevation and climate on the spatio-temporal distribution of wetland and dryland biomes during the Pennsylvanian and early Permian in tropical Pangea. The longstanding “upland model” places drought-tolerant vegetation in elevated habitats, where slope and drainage created moisture-limited substrates under a humid climate that simultaneously promoted peat accumulation in contemporaneous lowlands. Upland plants were periodically transported to, and buried in, lowlands. Rare preservation of dryland vegetation thus reflects its general absence in basins, and taphonomic vagaries of long-distance transport. The alternative “climate model” proposes that drought-tolerant plants dominated tropical habitats when climate was seasonally dry, with wetland vegetation reduced to scattered refugia. Environmental changes attending glacial-interglacial cycles caused alternating wetter-drier conditions, and the relative abundance of wetland versus dryland biomes in basinal lowlands thus varied with climatic oscillations. The paucity of drought-tolerant plants reflects a preservational megabias against habitats with seasonal moisture deficits.The environmental signal of “mixed” plant-fossil assemblages, comprising taxa characteristic of both wetland and dryland biomes, may help resolve these debates. We review key Pennsylvanian and lower Permian mixed assemblages from tropical Euramerican Pangea, and interpret their original habitats and climatic contexts based on multidisciplinary lines of evidence, including sedimentology, taphonomy, physiology, and paleoecology. Evaluations also consider patterns of vegetational distribution and taphonomy in modern tropical environments. We suggest that even a cursory view of current tropical plant distribution exposes flaws in the upland model. Where tropical climate is sufficiently humid to support peat swamps, slopes and elevated habitats do not host drought-tolerant vegetation, but are occupied by plants similar to those in lowland settings. This occurs because equable, high precipitation strongly dampens water-table variation across entire landscapes. Furthermore, taphonomic studies indicate that most plant-fossil assemblages record vegetation living near the burial site. Fossil floras thus reflect environmental conditions near their growth site, excluding an upland origin for most occurrences of drought-tolerant taxa. Conversely, the climate model is consistent with modern tropical vegetational distribution and soundly explains late Paleozoic floristic patterns. When Pangean tropical lowlands experienced seasonally dry conditions, plants tolerant of moisture deficits dominated most habitats, whereas wetland vegetation was restricted to wetter sites with greater preservation potential. This occurred because topographic variations are magnified under seasonal precipitation regimes, creating a complex habitat mosaic with wetland patches in a landscape subject to seasonal drought. Accordingly, we propose that a macrofloral assemblage with even rare drought-tolerant taxa indicates seasonality in the broader landscape.At larger spatio-temporal scales, disagreement also persists about whether tectonic uplift or long-term climatic drying was the primary driver of changes in late Paleozoic floristic patterns and areal extent of tropical peat swamps. We argue that tectonic activity alone cannot explain the drastic reduction in peat swamps or coincident changes in dominance-diversity of wetland vegetation. Rates of plant dispersal and evolution far outpace that of mountain building, and peat-forming wetlands persisted in elevated habitats well into the Late Pennsylvanian. Therefore, progressive late Paleozoic aridification was the most probable driver of changing floral patterns and the distribution of wetland and dryland biomes in tropical Pangea.     

Early Cretaceous angiosperm invasion of Western Europe and major environmental changes

BACKGROUND AND AIMS: At the beginning of the Late Cretaceous, angiosperms already inhabited all the environments and overtopped previously gymnosperm-dominated floras, especially in disturbed freshwater-related environments. The aim of this paper is to define what fossil plant ecology occurred during the early Cretaceous in order to follow the early spread of angiosperm taxa. METHODS: Floristic lists and localities from the Barremian to the Albian of Europe are analysed with the Wagner's Parsimony Method. KEY RESULTS: The Wagner's Parsimony Method indicates that (a) during the Barremian, matoniaceous ferns formed a savannah-like vegetation, while angiosperms composed freshwater aquatic vegetation; (b) during the Late Aptian humid phase, conifers increased, while matoniaceous ferns decreased, reflecting the closure of the vegetation; and (c) from the Albian, warmer and drier conditions induced the recovery of the matoniaceous ferns, while core angiosperms first developed in floodplains. CONCLUSIONS: During the late Early Cretaceous (Barremian-Albian), angiosperms showed a stepwise widening of their ecological range, being recorded first during the Barremian as aquatic plant mega-remains and at the Cenomanian onwards occurred in all the environments.     

Trade-off between light availability and soil fertility determine refugial conditions for the relict light-demanding species in lowland forests

Identifying potential refugial habitats in the face of rapid environmental change is a challenge faced by scientists and nature conservation managers. Relict populations and refugial habitats are the model objects in those studies. Based on the example of Actaea europaea from Central Poland, we analyse the habitat factors influencing relict populations of continental, light-demanding species in lowland forests and examine which habitats of studied species corresponding most closely to ancient vegetation. Our results indicate that the current refugial habitats of Actaea europaea include not only communities which are very similar to ancient open forest but also forests with a closed canopy. Although the populations are influenced by nitrogen and light availability, the co-occurrence of these two factors in forest communities is limited by dense canopy formation by hornbeam and beech trees on fertile soils and in more humid conditions. Our findings indicate that the future survival of relict, light-demanding communities in lowland forests requires low-intensity disturbances to be performed in tree-stands, according to techniques, which imitate traditional forests management.     

Seed dispersal mechanisms and the vegetation of forest islands in a West African forest-savanna mosaic (Comoé National Park,Ivory Coast)

The transition zone between forest and savanna is typically characterized by a dynamic patchwork of forest and savanna. We studied the woody plant species composition of 49 forest islands, 18 savanna, and 3 gallery forest plots in the Comoé National Park (Ivory Coast), West Africa's largest savanna reserve. TWINSPAN makes a clear distinction in vegetational composition between these three major habitat types but, nevertheless, more than 50% of the 292 species occur in at least 2 of them. The gallery forest is dominated by Cynometra megalophylla (Caesalpiniaceae), a genus known to dominate humid forests in other afrotropical regions. Ordination reveals four distinct categories of forest islands, (1) humid forests comparable to the gallery forest in their species composition, (2) dry disturbed and (3) dry undisturbed forests and (4) forests formerly inhabited by humans. Disturbed forests harbor more savanna species but also a distinct group of disturbance-tolerant forest species. Compared to other forest species, in this latter group we found an exceptionally high fraction of animal dispersed species (80% vs. 58%), while wind dispersed species or species lacking long distance seed dispersal mechanisms were correspondingly rare. This pattern occurs in spite of the fact that the frequency of wind dispersed species in general increases from dense humid forests to open dry forests and savanna. Species lacking long distance dispersal mechanisms are most abundant among those specialized on humid forests. These observations suggest that the species composition of forest islands is to some extent determined by the seed dispersal abilities of the different species.     

Effects of altitude and climate in determining elevational plant species richness patterns: A case study from Los Tuxtlas,Mexico

Altitudinal changes of composition and richness of montane plant assemblages are complex, depending on the taxonomic group and gradient conditions, with different factors involved that are directly altitude-dependent (e.g., temperatures, air pressure) and altitude-independent (e.g., precipitation, cloud cover, area). In order to assess the relative impacts of temperature, precipitation, air humidity, and area of altitudinal belts on plant diversity, we analyzed diversity patterns of five species-rich groups, mostly herbaceous plants, in 74 forest plots along three climatically contrasting elevational transects from humid tropical lowland vegetation up to cloud forests at Los Tuxtlas, Mexico. We recorded 278 plant species, with ferns being the most species-rich group followed by orchids, bromeliads, aroids, and piperoids. The most striking results were the contrasting patterns and model results for terrestrial and epiphytic taxa. Whereas the richness of all terrestrial species taken together did not change significantly with elevation, vascular epiphytes showed increasing species numbers with altitude. However, a number of individual terrestrial taxa showed also significant elevation-related changes: aroids showed a marked decline with hight, orchids and piperoids increased, and ferns displayed a hump-shaped pattern with highest richness in mid-altitudes. Among the epiphytes, aroids declined while most other groups increased with altitude. This distinction is relevant for projections of responses of plant communities to climate change, which will lead to increased temperatures and to changing precipitation and cloud condensation regimes and thus will likely affect terrestrial and epiphytic species in different ways.     

Zelkova carpinifolia (Pallas) K. Koch in Holocene sediments of Georgia—an indicator of climatic optima

Zelkova pollen has been found in Oligocene- to Pleistocene-aged deposits from many parts of Europe and northern Africa, but became extinct in mainland Europe prior to the last glacial maximum. This paper presents some observations on the ecology, pollen productivity and Holocene history of Zelkova carpinifolia to further understanding of Quaternary climatic trends. Georgia is one of the last refuges of this Tertiary relict tree.Based on palynological data from 20 Holocene sediment profiles in Georgia, we have established that Zelkova pollen is almost always accompanied by elevated proportions of thermophilous taxa (Castanea sativa, Quercus hartwissiana, Quercus iberica, and Pterocarya pterocarpa) in pollen spectra. These spectra are associated with phases of climatic amelioration and humidification. Zelkova carpinifolia is characterised by low pollen productivity and is underrepresented in pollen spectra by four-to-five orders of magnitude. Because of this, even single grains of Zelkova pollen may play a significant role in pollen-based climatic reconstructions.Six major climatic optima occurred in Georgia through the course of the Holocene, the longest and warmest of which occurred in the mid-Holocene and reached its maximum between 6000 and 5500 Cal. yr BP. During that period, Zelkova and Castanea forests were widespread. In Western Georgia, the upper tree line was elevated by as much as 300 m above its present-day level. In semiarid Eastern Georgia, the tree line may have been 500–600 m higher. Other climatic optima are seen in late-Holocene pollen spectra dating to 3800–2500 Cal. yr BP and 1350–800 Cal. yr BP.     

Reduced community diversity in semi-natural meadows in southern Sweden, 1965–1990

Two data sets, one from the 1960s and one from 1990, from continuously managed semi-natural meadows (semi-natural grasslands used for hay-cutting) in Småland, southern Sweden, were analysed to describe the vegetation and in an attempt to characterise changes that have occurred in the vegetation. Based on a classification of the data set, nine plant communities were recognised. The main vegetational differences, as revealed by an ordination, were due to variation in soil moisture, which ranged from wet to dry.During the investigation period, the amount of hay meadow area decreased, particularly the area of wet-moist meadows. In addition, the total variation in the vegetation diminished, and three plant communities more or less disappeared. The turnover index of species in the data set was 36%, and most of the species that were lost had initially been uncommon. Lost species included rare taxa, such as Gentianella campestris and Linum catharticum, while the new species tended to be common in the region. Annual and biennial species accounted for a greater proportion of the lost taxa than did perennial species. The mean cover of species per plot and the relative abundance of graminoids per plot increased.The recorded changes in the vegetation may be related to the increased loads of nitrogen pollutants as well as to a decrease in management intensity. The diminished area is related to changes in land-use. The meadow sites in Småland have been part of a landscape rich in grasslands, but today they have a more or less relict status. They differ from grasslands found elsewhere in Sweden and Scandinavia. In Sweden, the majority (68%) of endangered vascular plants belong to the agricultural landscape. To ensure the survival of individual species it is important to preserve all types of meadows, not only a few selected ones, since no two meadows are alike.     

Neotropical seasonally dry forests and Quaternary vegetation changes

Seasonally dry tropical forests have been largely ignored in discussions of vegetation changes during the Quaternary. We distinguish dry forests, which are essentially tree‐dominated ecosystems, from open savannas that have a xeromorphic fire‐tolerant, grass layer and grow on dystrophic, acid soils. Seasonally dry tropical forests grow on fertile soils, usually have a closed canopy, have woody floras dominated by the Leguminosae and Bignoniaceae and a sparse ground flora with few grasses. They occur in disjunct areas throughout the Neotropics. The Chaco forests of central South America experience regular annual frosts, and are considered a subtropical extension of temperate vegetation formations. At least 104 plant species from a wide range of families are each found in two or more of the isolated areas of seasonally dry tropical forest scattered across the Neotropics, and these repeated patterns of distribution suggest a more widespread expanse of this vegetation, presumably in drier and cooler periods of the Pleistocene. We propose a new vegetation model for some areas of the Ice‐Age Amazon: a type of seasonally dry tropical forest, with rain forest and montane taxa largely confined to gallery forest. This model is consistent with the distributions of contemporary seasonally dry tropical forest species in Amazonia and existing palynological data. The hypothesis of vicariance of a wider historical area of seasonally dry tropical forests could be tested using a cladistic biogeographic approach focusing on plant genera that have species showing high levels of endemicity in the different areas of these forests.     

A floristic framework of Australian rainforests

In the first comprehensive floristic classification of Australian rainforests and monsoon forests, fresh insights made possible by the use of floristic as distinct from structural data are outlined. A set of 561 individual communities, on sites ranging from North Queensland westwards to the Kimberley region and southwards to Tasmania, is defined by the presence or absence of 1316 tree species, or 406 genera. The data have been subjected to numerical classification, first with respect to species, then to genera. The species classification first divides into three ‘ecofloristic regions’: A, temperate (microtherm) and subtropical (mesotherm) humid evergreen rainforests; B, tropical (megatherm) humid evergreen grading into highly seasonal raingreen (monsoon) forests; and C, subtropical (mesotherm) moderately seasonal humid/subhumid raingreen forests. The sites are further divided into eight ‘ecofloristic provinces’, for each of which a core area is identified and the ten most common diagnostic tree species listed for selected floristic elements, whose ecological relationships are briefly described. Gradients of quantitative thermal-moisture indices are added to standard climatic typology to provide a more flexible identification of local climates that characterize community-types of each province across a wide latitudinal/altitudinal range. Community disjuncts and outliers of a particular province are interpreted as the results of past environmental sifting (in which ecological factors are not entirely determinate), of previously more continuous rainforest vegetation. The genera classification first divides into humid eastern coastal and subhumid western and subcoastal sites, then four thermal types, and finally nine groups of floristic ‘paleo-provinces’. Where the species and genera classifications are not in substantial agreement, a wide-ranging generic element across the provinces in northern and northeastern Australia is interpreted in paleogeographic terms. The relict distribution of existing community types, as the result of climatic sifting of ancient floral stocks, is discussed in support of emerging ideas about the autochthony of Australian rainforests, especially those tropical types that are not intrusive. It is argued that the unique ecological relationships of Australian rainforests justify the most conservative uses of the relatively small remaining areas.     

Variation in modern pollen from tropical evergreen forests and the monsoon seasonality gradient in SW India

Abstract. This study analyses the pollen signature of tropical lowland forests (< 1000 m a.s.l.) in the Asian monsoon climate. Its aim is to investigate how well the pollen data can reproduce the vegetation patterns in tropical India, and how the variations in the pollen composition are related to the gradient of decreasing plant moisture availability (measured by the ratio of actual over equilibrium evapotranspiration) that is associated with the strong seasonality of precipitation that characterizes the monsoon climate regime. We used canonical correspondence analysis (CCA) to relate the variations in the pollen composition of 71 surface soil samples from evergreen and semi‐evergreen forests distributed along the western coast of south India (8° 48’ N‐15° 08’ N), with the climate characteristics of the sampling sites. We show that variations in plant moisture availability strongly determine variations in the pollen composition; for example evergreen and semi‐evergreen forests can be distinguished on the basis of their pollen assemblages. Variations in the mean temperature of the coldest month associated with elevation also determine distinct pollen assemblages; for example evergreen forests above 800 m a.s.l. present different pollen signatures than those below this altitude/temperature limit. Variations in the relative abundance of some pollen taxa are strongly related to plant moisture availability and taxa indicators of climate can be identified. Hence, modern pollen assemblages from tropical forests in south India carry considerable information about vegetation patterns and climate. Paleoclimatic changes, notably in the monsoon season, could be quantified.     

History meets ecology: a geographical analysis of ecological restriction in the Neotropical humid montane forests avifaunas

Aim To analyse the ecological patterns of distribution of the avifaunas of the Neotropical humid montane forests, by assessing the degree of habitat restriction among species through the calculation of a numerical index, analysing their relationships with adjacent habitat, and exploring the relative contribution of both higher and lower habitats in shaping the avian assemblages. Location The Neotropical humid montane forests, from Mexico to north‐western Argentina. Methods The degree of species’ restriction to the habitat was calculated through a restriction index based on published endemicity indexes. The index scores range from 0 to 1: a score of 1 indicates a totally endemic species (i.e. fully restricted to the habitat); values tending to 0 indicate a widespread species. Results In Mesoamerica, completely restricted species represent a lower proportion of the total avifauna than in South American humid montane forests; whereas species shared to other habitats showed a higher proportion of the avifauna with affinities to higher altitude forests (e.g. pine and pine‐oak forests). South America, on the other hand, holds assemblages with a high proportion of completely restricted species; species shared to other habitats showed a high proportion of taxa with affinities to lowland forests. Main conclusions The ecological distribution of the HMF's avifauna could be partitioned in three main components: the ecologically restricted avifauna, the high altitude species and, the lower altitude species, which are tightly associated to the floristic composition along the gradient. The history of formation of the HMF flora and the ecological distribution of different avian taxa suggest a common history. Finally, the restriction index allowed a detailed evaluation of the composition of avian assemblages, their degree of restriction to the habitat and of the affinities regarding adjacent habitats, as well as an accurate distinction between species richness and restricted species richness, which should be a fundamental step towards the establishment of conservation priorities.     

Vegetation patterns and their dependency on site conditions in the pre-industrial landscape of north-eastern Japan

We reconstructed the vegetational landscape of the pre-industrial era (the beginning of the twentieth century) in north-eastern Japan, and estimated the distribution patterns of traditional land-uses, as suggested from the vegetation. We found significant correspondence between the spatial patterns of vegetational landscape and site attributes, and hypothesized the underlying mechanisms. The study area was classified into three vegetation types: grasslands, secondary forests and old-growth forests. It was determined that the grasslands were formed and maintained by burning; secondary forests were derived from either charcoal woods or forests recovered on abandoned grasslands; and old-growth forests had suffered the least anthropogenic disturbance. Each past vegetation type showed significant dependency on site attributes such as altitude, slope angle, slope aspect, hydrological topography and distance from the nearest human habitation. The relative importance of these site attributes varied depending on the vegetation type. Grasslands and old-growth forests, which were the most and the least disturbed sites in the study area, respectively, showed clear contrasts in their dependencies especially on the slope aspect and on elevation. These site attributes were thought to have had influences on each vegetation type by determining the inflammability of the site. Satellite photographs indicated that north-facing valleys had been relatively wet throughout the fire-prone spring season. Hence, these areas would have been free from frequent fire, and more likely to preserve old-growth forests. Ground wetness in spring was thought to be the underlying factor determining the contrasts in past vegetation and land-use patterns in the area.An erratum to this article can be found at     

Fire and resprouting in Mediterranean ecosystems: insights from an external biogeographical region, the mexical shrubland

We investigated modes of regeneration of dominant species of the mexical vegetation after fire. The mexical shrubland shows a remarkable structural, morphological, and floristic similarity to Mediterranean-type vegetation and is considered a relict of the Madro-Tertiary Geoflora under a non-Mediterranean climate. This vegetation provides an ideal scenario to test the role of fire in Mediterranean ecosystems because historical fire occurrence is absent and the species assembly is constituted mostly by Madro-Tertiary elements and Neotropical species (some of them, endemic species from Mexico). The existence of congeneric species of the California chaparral allows us to determine the regeneration ability of these communities after fire in relation to resprouting and seeding strategies, which are widespread modes reported in the Mediterranean-type vegetation. By the experimental application of fire in the two biogeographical groups of species, we tested the hypothesis that low resprouting ability of California congeneric species (Madro-Tertiary species) after fire would indicate that fire has played an important selective force in the resprouting habit. A low resprouting ability in the Neotropical group of species would suggest that fire has molded the set of species dominating fire-prone environments.Our results indicated that resprouting is a widespread trait in the mexical species characterized by the presence of lignotubers and burls. Resprouting can be considered an ancient trait, probably linked to losses of aboveground biomass, that became a pre-adaptation in Mediterranean fire-prone communities. The Neotropical group of species showed less ability to regenerate after fire, and small plants were more likely to die after disturbance in this group than in the Madro-Tertiary group. The resprouting feature and the seeder strategy of other species after a fire in the mexical shrubland are similar to Mediterranean-type ecosystems, emphasizing their common origin and the relevance of phylogenetic and biogeographical studies to explain current patterns of vegetation.     

Climate and vegetational regime shifts in the late Paleozoic ice age earth

The late Paleozoic earth experienced alternation between glacial and non-glacial climates at multiple temporal scales, accompanied by atmospheric CO₂ fluctuations and global warming intervals, often attended by significant vegetational changes in equatorial latitudes of Pangaea. We assess the nature of climate–vegetation interaction during two time intervals: middle–late Pennsylvanian transition and Pennsylvanian–Permian transition, each marked by tropical warming and drying. In case study 1, there is a catastrophic intra-biomic reorganization of dominance and diversity in wetland, evergreen vegetation growing under humid climates. This represents a threshold-type change, possibly a regime shift to an alternative stable state. Case study 2 is an inter-biome dominance change in western and central Pangaea from humid wetland and seasonally dry to semi-arid vegetation. Shifts between these vegetation types had been occurring in Euramerican portions of the equatorial region throughout the late middle and late Pennsylvanian, the drier vegetation reaching persistent dominance by Early Permian. The oscillatory transition between humid and seasonally dry vegetation appears to demonstrate a threshold-like behavior but probably not repeated transitions between alternative stable states. Rather, changes in dominance in lowland equatorial regions were driven by long-term, repetitive climatic oscillations, occurring with increasing intensity, within overall shift to seasonal dryness through time. In neither case study are there clear biotic or abiotic warning signs of looming changes in vegetational composition or geographic distribution, nor is it clear that there are specific, absolute values or rates of environmental change in temperature, rainfall distribution and amount, or atmospheric composition, approach to which might indicate proximity to a terrestrial biotic-change threshold.