The lizard assemblage from Seasonally Dry Tropical Forest enclaves in the Cerrado biome, Brazil, and its association with the Pleistocenic Arc

Aim  To determine if the distributions of lizard species from Seasonally Dry Tropical Forest (SDTF) enclaves within the Cerrado biome in central Brazil are associated with the Tropical Seasonal Forests Region, a recently proposed phytogeographic unit of South America, corroborating the existence of a Pleistocenic Arc of SDTFs.
Location  SDTF remnants in the Paranã River valley, municipality of São Domingos, Goiás, Brazil.
Methods  Lizards were extensively sampled using haphazard sampling, funnel traps, and pitfall traps with drift fences during four expeditions. The composition of the SDTF lizard assemblage was compared with those from other South American phytogeographic regions (Caatinga, Cerrado, Chaco, Llanos, and the dry forests of Colombia and Bolivia), based on the literature and our own unpublished data.
Results  The SDTF lizard assemblage contained 20 species, including 11 species with extensive distributions among the regions considered, seven species shared exclusively with Cerrado localities, a single species shared exclusively with other SDTFs, and one endemic species. The presence of Lygodactylus klugei (Smith, Martin & Swain, 1977), presumably endemic to the Pleistocenic Arc formed by the Tropical Seasonal Forests Region, considerably extends the known distribution of this species, suggesting historical connections between Caatinga and Cerrado SDTF enclaves.
Main conclusions  The composition of the lizard assemblage in Cerrado SDTF enclaves seems to corroborate the recent proposal that the SDTF should be recognized as a phytogeographic unit (or dominium). The presence of disjunct populations and endemic species highlights the urgency of considering the uniqueness of the Paranã River valley SDTFs and the importance of its conservation.     

Climatic stability in the Brazilian Cerrado: implications for biogeographical connections of South American savannas,species richness and conservation in a biodiversity hotspot

Aim To investigate the historical distribution of the Cerrado across Quaternary climatic fluctuations and to generate historical stability maps to test: (1) whether the ‘historical climate’ stability hypothesis explains squamate reptile richness in the Cerrado; and (2) the hypothesis of Pleistocene connections between savannas located north and south of Amazonia. Location The Cerrado, a savanna biome and a global biodiversity hotspot distributed mainly in central Brazil. Methods We generated occurrence datasets from 1000 presence points randomly selected from the entire distribution of the Cerrado, as determined by two spatial definitions. We modelled the potential Cerrado distribution by implementing a maximum‐entropy machine‐learning algorithm across four time projections: current, mid‐Holocene (6 ka), Last Glacial Maximum (LGM, 21 ka) and Last Interglacial (LIG, 120 ka). We generated historical stability maps (refugial areas) by overlapping presence/absence projections of all scenarios, and checked consistencies with qualitative comparisons with available fossil pollen records. We built a spatially explicit simultaneous autoregressive model to explore the relationship between current climate, climatic stability, and squamate species richness. Results Models predicted the LGM and LIG as the periods of narrowest and widest Cerrado distributions, respectively, and were largely corroborated by palynological evidence. We found evidence for two savanna corridors (eastern coastal during the LIG, and Andean during the LGM) and predicted a large refugial area in the north‐eastern Cerrado (Serra Geral de Goiás refugium). Variables related to climatic stability predicted squamate richness better than present climatic variables did. Main conclusions Our results indicate that Bolivian savannas should be included within the Cerrado range and that the Cerrado’s biogeographical counterparts are not Chaco and Caatinga but rather the disjunct savannas of the Guyana shield plateaus. Climatic stability is a good predictor of Cerrado squamate richness, and our stability maps could be used in future studies to test diversity patterns and genetic signatures of different taxonomic groups and as a higher‐order landscape biodiversity surrogate for conservation planning.     

Beta-diversity in seasonally dry tropical forests (SDTF) in the Caatinga Biogeographic Domain, Brazil, and its implications for conservation

Tropical biomes are species rich, but some biomes such as seasonally dry tropical forests (SDTFs) are still inadequately studied compared to their co-occurring rain forest and savanna. SDTFs occur in areas of high environmental heterogeneity, resulting in high beta (β)-diversity or species turnover, but this has so far only been accessed using a single β-diversity measure, and at a spatial scale that is of limited applicability for reserve planning. The Caatinga Biogeographic Domain in Brazil contains the largest known extent of SDTF which are poorly studied and inadequately reserved. We therefore studied the variation in species richness and species turnover among SDTF between localities and between known floristic communities. From six localities within the Caatinga Biogeographic Domain we recorded all tree species with a circumference at breast height equaling or exceeding 10 cm within 106 400 m² survey plots. From the species presence/absence data we calculated three measures of β-diversity between pairs of study localities and between different floristic communities representing: (i) species similarity, (ii) differences between species richness, and (iii) species gain and loss. Our results confirm the high β-diversity of SDTFs and species turnover between localities and also between floristic communities. The three indices were also complementary to each other and can be used to maximize accuracy in β-diversity studies. The implications of our study for conservation and reserve planning of SDTFs are discussed.     

Identity and relationships of the Arboreal Caatinga among other floristic units of seasonally dry tropical forests (SDTFs) of north-eastern and Central Brazil

The tree species composition of seasonally dry tropical forests (SDTF) in north-eastern and central Brazil is analyzed to address the following hypotheses: (1) variations in species composition are related to both environment (climate and substrate) and spatial proximity; (2) SDTF floristic units may be recognized based on peculiar composition and environment; and (3) the Arboreal Caatinga, a deciduous forest occurring along the hinterland borders of the Caatinga Domain, is one of these units and its flora is more strongly related to the caatinga vegetation than to outlying forests. The study region is framed by the Brazilian coastline, 50th meridian west and 21st parallel south, including the Caatinga Domain and extensions into the Atlantic Forest and Cerrado Domains. Multivariate and geostatistic analyses were performed on a database containing 16,226 occurrence records of 1332 tree species in 187 georeferenced SDTF areas and respective environmental variables. Tree species composition varied significantly with both environmental variables and spatial proximity. Eight SDTF floristic units were recognized in the region, including the Arboreal Caatinga. In terms of species composition, its tree flora showed a stronger link with that of the Cerrado Dry Forest Enclaves. On the other hand, in terms of species frequency across sample areas, the links were stronger with two other units: Rock Outcrops Caatinga and Agreste and Brejo Dry Forests. There is a role for niche-based control of tree species composition across the SDTFs of the region determined primarily by the availability of ground water across time and secondarily by the amount of soil mineral nutrients. Spatial proximity also contributes significantly to the floristic cohesion of SDTF units suggesting a highly dispersal-limited tree flora. These units should be given the status of eco-regions to help driving the conservation policy regarding the protection of their biodiversity.     

Holocene southward expansion in seasonally dry tropical forests in South America: phylogeography of Ficus bonijesulapensis (Moraceae)

We conducted a phylogeographical and niche modelling study of the tree Ficus bonijesulapensis, endemic to Brazilian seasonally dry tropical forests (SDTFs), in order to evaluate the effects of Quaternary climatic fluctuations on population dynamics. The trnQ–5′rps16 region of plastid DNA was sequenced from 15 populations. Three phylogeographical groups were identified by the median‐joining algorithm network and spatial analysis of molecular variance (SAMOVA) (F_CT = 0.591): a central‐west, a central‐east and a scattered group. The central groups had higher total haplotype and nucleotide diversities than the scattered group. Ecological niche modelling suggested that, since the Last Interglacial (130 kyr bp ), the central and north regions have been relatively stable, whereas the southern region of the species distribution has been less stable. The phylogeographical groups showed concordance with the floristic units described for SDTFs. The low genetic diversity, unimodal mismatch distribution and unfavourable climatic conditions in the southern region suggest a recent southward expansion of the range of the species during the Holocene, supporting the hypothesis of the southward expansion of SDTFs during this period. The central and northern regions of the current distribution of F. bonijesulapensis, which are consistent with arboreal caatinga and rock outcrop floristic units, were potential refugia during Quaternary climatic fluctuations. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 189–201.     

Vegetation structure determines insect herbivore diversity in seasonally dry tropical forests

Vegetation structure can often determine insect herbivore fauna in forests, but this mechanism has been demonstrated in seasonally dry tropical forests (SDTFs) only at small spatial scales. In this study we evaluated the effects of the geographical location of SDTFs and vegetation structure on insect herbivore communities (leaf-chewing and sap-sucking guilds) in three Brazilian ecoregions (Cerrado, Cerrado/Caatinga transition, and Caatinga). We tested the following predictions: (1) insect herbivore species composition, richness, abundance and beta diversity differ among forests in different ecoregions; (2) insect richness, abundance and beta diversity are positively related to tree richness and density; (3) spatial turnover of species is the primary mechanism that generates herbivorous insect β-diversity in different ecoregions, and is positively influenced by tree richness. The composition, richness, and abundance of herbivorous insects differed over SDFs along the gradient of Cerrado and Caatinga. Both herbivore guilds responded positively to tree richness. Tree density only determined the richness and abundance of sap-sucking herbivores. Insect β-diversity was similar among Cerrado and transition areas, but lower in Caatinga itself; β-diversity was also positively affected by tree richness. Species turnover, as opposed to nestedness, was the main mechanism generating β-diversity, but itself was not related to tree richness. We demonstrate in this study the importance of landscape diversity and availability of local resources for herbivorous insect communities, and we emphasize the importance of SDTF conservation in different ecoregions as a result of species turnover.     

Evolutionary islands in the Andes: persistence and isolation explain high endemism in Andean dry tropical forests

Aim The tropical Andes are a world biodiversity hotspot. With diverse biomes and dramatic, geologically recent mountain uplift, they offer a system to study the relative contributions of geological and biome history to species richness. There are preliminary indications that historical species assembly in the Andes has been influenced by physiographical heterogeneity and that distinct biomes have evolved in relative isolation despite physical proximity. Here we test this ‘Andean biotic separation hypothesis’ by focusing on the low‐elevation, seasonally dry tropical forest (SDTF) biome to determine whether patterns of plant diversification within the SDTF differ from those in mid‐ and high‐elevation biomes. Location Tropical Andes, South America. Methods Densely sampled time‐calibrated phylogenies for five legume genera (Amicia, Coursetia, Cyathostegia, Mimosa and Poissonia) containing species endemic to the Andean SDTF biome were used to investigate divergence times and levels of geographical structure. Geographical structure was measured using isolation‐by‐distance methods. Meta‐analysis of time‐calibrated phylogenies of Andean plant groups was used to compare the pattern and tempo of endemic species diversification between the major Andean biomes. Results Long‐term persistence of SDTF in the Andes is suggested by old stem ages (5–27 Ma) of endemic genera/clades within genera, and deep divergences coupled with strong geographical structure among and within species. Comparison of species diversification patterns among different biomes shows that the relatively old, geographically confined pattern of species diversification in SDTF contrasts with the high‐elevation grasslands that show rapid and recent radiations driven by ecological opportunities. Main conclusions The SDTF biome has a long history in the Andes. We suggest that the diverse SDTF flora has been assembled gradually over the past c. 19 Ma from lineages exhibiting strong phylogenetic niche conservatism. These patterns suggest that Andean SDTFs have formed stable and strongly isolated ‘islands’ despite the upheavals of Andean uplift. Indeed, the Andean SDTFs may represent some of the most isolated and evolutionarily persistent continental plant communities, similar in many respects to floras of remote oceanic islands.     

Genetic diversity of the rain tree (Albizia saman) in Colombian seasonally dry tropical forest for informing conservation and restoration interventions

Albizia saman is a multipurpose tree species of seasonally dry tropical forests (SDTFs) of Mesoamerica and northern South America typically cultivated in silvopastoral and other agroforestry systems around the world, a trend that is bound to increase in light of multimillion hectare commitments for forest and landscape restoration. The effective conservation and sustainable use of A. saman requires detailed knowledge of its genetic diversity across its native distribution range of which surprisingly little is known to date. We assessed the genetic diversity and structure of A.saman across twelve representative locations of SDTF in Colombia, and how they may have been shaped by past climatic changes and human influence. We found four different genetic groups which may be the result of differentiation due to isolation of populations in preglacial times. The current distribution and mixture of genetic groups across STDF fragments we observed might be the result of range expansion of SDTFs during the last glacial period followed by range contraction during the Holocene and human‐influenced movement of germplasm associated with cattle ranching. Despite the fragmented state of the presumed natural A. saman stands we sampled, we did not find any signs of inbreeding, suggesting that gene flow is not jeopardized in humanized landscapes. However, further research is needed to assess potential deleterious effects of fragmentation on progeny. Climate change is not expected to seriously threaten the in situ persistence of A. saman populations and might present opportunities for future range expansion. However, the sourcing of germplasm for tree planting activities needs to be aligned with the genetic affinity of reference populations across the distribution of Colombian SDTFs. We identify priority source populations for in situ conservation based on their high genetic diversity, lack or limited signs of admixture, and/or genetic uniqueness.     

From ice age to modern: a record of landscape change in an Andean cloud forest

Aim To investigate the palaeoecological changes associated with the last ice age, subsequent deglaciation and human occupation of the central Andes. Location Lake Pacucha, Peruvian Andes (13°36′26″ S, 73°19′42″ W; 3095 m elevation). Methods Vegetation assemblages were reconstructed for the last 24 cal. kyr bp (thousand calibrated ¹⁴C years before present), based on pollen analysis of sediments from Lake Pacucha. An age model was established using ¹⁴C accelerator mass spectrometry dates on bulk sediment. Fossil pollen and sedimentological analyses followed standard methodologies. Results Puna brava replaced the Andean forest at the elevation of Lake Pacucha at the Last Glacial Maximum (LGM). Deglaciation proceeded rapidly after 16 cal. kyr bp , and near‐modern vegetation was established by c. 14 cal. kyr bp . The deglacial was marked by the range expansion of forest taxa as grassland taxa receded in importance. The mid‐Holocene was marked by a lowered lake level but relatively unchanged vegetation. Quinoa and maize pollen were found in the latter half of the Holocene. Main conclusions Temperatures were about 7–8 °C colder than present at this site during the LGM. The pattern of vegetation change was suggestive of microrefugial expansion rather than simple upslope migration. The mid‐Holocene droughts were interrupted by rainfall events sufficiently frequent to allow vegetation to survive largely unchanged, despite lowering of the lake level. Human activity at the lake included a 5500‐year history of quinoa cultivation and 3000 years of maize cultivation.     

Regional climate oscillations and local topography shape genetic polymorphisms and distribution of the giant columnar cactus Echinopsis terscheckii in drylands of the tropical Andes

Aim

We sought to determine if the present fragmentary distribution of the giant columnar cactus Echinopsis terscheckii in tropical drylands is a relict of a previously more widespread range during cold and dry phases of the Last Glacial Maximum (LGM).

Location

Tropical and subtropical dry ecotonal areas of northern and central Andes of Argentina.

Methods

We combined ecological niche models (ENM) with molecular polymorphisms of isozymes and DNA sequences. We collected samples from 30 individuals at 24 locations for genetic analysis covering a wide range of environmental conditions. We sequenced the nuclear ITS and three non‐coding regions of the chloroplast DNA and we resolved 15 isozyme loci. Potential distribution was modelled using 88 E. terscheckii presence training records and a reduced set of 10 modern bioclimatic variables. LGM and the Mid‐Holocene distributions were derived by projecting bioclimatic data under present to past environmental conditions according to CCSM4 and MIROC‐ESM Global Climate Models.

Results

We detected high isozyme diversity towards the south. The multivariate cluster analysis yielded two groups of populations that were geographically concordant with the DNA haplotypes located north and south of a divide at 27°S. Distribution models show range expansion during the LGM in two north and south areas separated by a gap of low suitability at 27°S. Suitable areas in the south were close to current populations, while in the north, populations survived in more disjunct locations that probably suffered from founder effects. In contrast, Mid‐Holocene bioclimatic conditions were relatively unsuitable in the south.

Main conclusions

Our results suggest that the divergence of north and south groups of E. terscheckii populations reflect long‐lasting persistence through climatic cycles that were reinforced by the presence of an orogenic divide at mid‐latitudes. Latitudinally divergent groups of populations should be treated as distinct evolutionary significant units that deserve independent conservation actions. Increased genetic diversity and inbreeding towards the south may guide setting up priorities for the long‐term protection of a dominant element of drylands as E. terscheckii.     

The Late Glacial–Holocene record from Central Adriatic Sea: Paleoenvironmental reconstruction based on benthic foraminiferal assemblages

New micropaleontological data coming from three cores collected on the meso-Adriatic continental shelf (Vasto area) are studied. Comparisons to foraminiferal assemblages and radiocarbon dates previously collected from cores in the San Benedetto del Tronto and Tremiti areas allow the correlation of patterns observed in shallow water areas with those in deeper parts of the basin. We focused on the response of benthic foraminifera during the Holocene high-stand, corresponding to the installation of the recent sedimentary and trophic system. An influence of anthropogenic impacts cannot be ruled out; its effects consist of a depletion of oxygen level with a consequent modification of the structure of benthic foraminiferal assemblages. During the glacial/post glacial cycle, three phases, characterized by a total of six foraminiferal biofacies including different species assemblages were recognized. The first phase, from 14 kyr BP to 11 kyr BP, corresponds to the Bölling/Alleröd and Younger Dryas cold event, before the Holocene sea-level rise. During this phase, the continental shelf was characterized by an infralittoral environment with productive waters owing to the proximity of the Po river delta at the edge of the Mid-Adriatic Deep. The second phase, from 11 kyr BP to 4 kyr BP, represents the Holocene sea-level rise and is characterized by a condensed sedimentation spread over the entire basin. The third phase corresponds to the Holocene high-stand, during which time the modern current system became established. During this phase, the eastern portion of the shelf underwent to the central part of the mud-belt, corresponding to the sub-recent conditions. Recent eutrophication resulting from human activities over the last few centuries is evidenced by frequency fluctuations of typically opportunistic taxa such as Nonionella turgida and Epistominella vitrea.     

Formation of disjunct plant distributions in Northeast Asia: a case study of <Emphasis Type="Italic">Betula davurica</Emphasis> using a species distribution model

Repeated climate change during glacial and interglacial periods of the Quaternary led to mass migrations that resulted in disjunct distributions for many species. However, few studies have examined the processes that form disjunct distributions in Northeast Asia (NEA). In this study, we examined the disjunct distribution of Betula davurica Pall. in the Japanese archipelago. This species is a dominant canopy tree found in cool-temperate deciduous broad-leaved forests of continental NEA. We hypothesized that Quaternary climate change caused the present disjunct distribution pattern of this species. To test this hypothesis, we adopted a species distribution model and examined a series of potential habitats in the Last Glacial Maximum (LGM), the mid-Holocene, and the present. We generated models in MaxEnt with B. davurica presence as the response variable and six bioclimatic variables as predictor variables. During the LGM, projected potential habitats were distributed around the Korean Peninsula, East China, and the Japanese archipelago, excluding Hokkaido. In the mid-Holocene, habitats retreated both from East China and western Japan, remained unchanged in the Korean Peninsula and central Honshu mountains, and expanded to northern China, the Russian Far East, as well as northern Japan (Hokkaido). Thus, post-LGM global warming led to an expansion of B. davurica distribution to northern parts of continental NEA, along with a retreat in the Japanese archipelago. This shift in populations formed the present disjunct distribution.     

Genetic turnovers and northern survival during the last glacial maximum in European brown bears

The current phylogeographic pattern of European brown bears (Ursus arctos) has commonly been explained by postglacial recolonization out of geographically distinct refugia in southern Europe, a pattern well in accordance with the expansion/contraction model. Studies of ancient DNA from brown bear remains have questioned this pattern, but have failed to explain the glacial distribution of mitochondrial brown bear clades and their subsequent expansion across the European continent. We here present 136 new mitochondrial sequences generated from 346 remains from Europe, ranging in age between the Late Pleistocene and historical times. The genetic data show a high Late Pleistocene diversity across the continent and challenge the strict confinement of bears to traditional southern refugia during the last glacial maximum (LGM). The mitochondrial data further suggest a genetic turnover just before this time, as well as a steep demographic decline starting in the mid‐Holocene. Levels of stable nitrogen isotopes from the remains confirm a previously proposed shift toward increasing herbivory around the LGM in Europe. Overall, these results suggest that in addition to climate, anthropogenic impact and inter‐specific competition may have had more important effects on the brown bear's ecology, demography, and genetic structure than previously thought.     

The Role of Edaphic Environment and Climate in Structuring Phylogenetic Pattern in Seasonally Dry Tropical Plant Communities

Seasonally dry tropical plant formations (SDTF) are likely to exhibit phylogenetic clustering owing to niche conservatism driven by a strong environmental filter (water stress), but heterogeneous edaphic environments and life histories may result in heterogeneity in degree of phylogenetic clustering. We investigated phylogenetic patterns across ecological gradients related to water availability (edaphic environment and climate) in the Caatinga, a SDTF in Brazil. Caatinga is characterized by semiarid climate and three distinct edaphic environments – sedimentary, crystalline, and inselberg –representing a decreasing gradient in soil water availability. We used two measures of phylogenetic diversity: Net Relatedness Index based on the entire phylogeny among species present in a site, reflecting long-term diversification; and Nearest Taxon Index based on the tips of the phylogeny, reflecting more recent diversification. We also evaluated woody species in contrast to herbaceous species. The main climatic variable influencing phylogenetic pattern was precipitation in the driest quarter, particularly for herbaceous species, suggesting that environmental filtering related to minimal periods of precipitation is an important driver of Caatinga biodiversity, as one might expect for a SDTF. Woody species tended to show phylogenetic clustering whereas herbaceous species tended towards phylogenetic overdispersion. We also found phylogenetic clustering in two edaphic environments (sedimentary and crystalline) in contrast to phylogenetic overdispersion in the third (inselberg). We conclude that while niche conservatism is evident in phylogenetic clustering in the Caatinga, this is not a universal pattern likely due to heterogeneity in the degree of realized environmental filtering across edaphic environments. Thus, SDTF, in spite of a strong shared environmental filter, are potentially heterogeneous in phylogenetic structuring. Our results support the need for scientifically informed conservation strategies in the Caatinga and other SDTF regions that have not previously been prioritized for conservation in order to take into account this heterogeneity.     

The history of Seasonally Dry Tropical Forests in eastern South America: inferences from the genetic structure of the tree Astronium urundeuva (Anacardiaceae)

Today, the Seasonally Dry Tropical Forests (SDTF) of eastern South America occur as large, well-defined nuclei (e.g. Caatinga in the northeast) and as smaller enclaves within other vegetations (e.g. Cerrado and Chaco). In order to infer the way the present SDTF distribution was attained, the genetic structure of Astronium urundeuva, a tree confined to SDTF, was assessed using two chloroplast spacers and nine microsatellite loci. Five haplotypes were identified, whose distribution was spatially structured. The distribution of the two most common and divergent haplotypes suggested former vicariance and progressive divergence due to isolation. More recent range expansions of these two lineages subsequently occurred, leading to a secondary contact at the southern limit of the Caatinga SDTF nucleus. The multilocus-Bayesian approach using microsatellites consistently identified three groups of populations (Northeast, Central and Southwest). Isolation by distance was found in Northeast and Southwest groups whereas admixture was detected in the Central group, located at the transition between Caatinga and Cerrado domains. All together, the results support the existence of range expansions and secondary contact in the Central group. This study provides arguments that favour the existence of a previously more continuous formation of SDTF in eastern South America.     

Insights into the historical construction of species-rich Mesoamerican seasonally dry tropical forests: the diversification of Bursera (Burseraceae, Sapindales)

? Mesoamerican arid biomes epitomize neotropical rich and complex biodiversity. To document some of the macroevolutionary processes underlying the vast species richness of Mesoamerican seasonally dry tropical forests (SDTFs), and to evaluate specific predictions about the age, geographical structure and niche conservatism of SDTF-centered woody plant lineages, the diversification of Bursera is reconstructed. ? Using a nearly complete Bursera species-level phylogeny from nuclear and plastid genomic markers, we estimate divergence times, test for phylogenetic and temporal diversification heterogeneity, test for geographical structure, and reconstruct habitat shifts. ? Bursera became differentiated in the earliest Eocene, but diversified during independent early Miocene consecutive radiations that took place in SDTFs. The late Miocene average age of Bursera species, the presence of phylogenetic geographical structure, and its strong conservatism to SDTFs conform to expectations derived from South American SDTF-centered lineages. ? The diversification of Bursera suggests that Mesoamerican SDTF richness derives from high speciation from the Miocene onwards uncoupled from habitat shifts, during a period of enhanced aridity resulting mainly from global cooling and regional rain shadows.     

Post-Hypsithermal plant disjunctions in western Alberta, Canada

Aim Evaluate the hypothesis that nine disjunct vascular plant species along the eastern slopes of the Rocky Mountains and in the Peace River District of west‐central Alberta represent remnants of more southerly vegetation that occupied these areas during the Holocene Hypsithermal (9000–6000 yr bp ). Alternatively, these plants represent populations that became established because of independent chance dispersal events. Location This study focuses on the area east of the Rocky Mountain Continental Divide in the Province of Alberta and the State of Montana in western Canada and USA, respectively. Methods Disjunct species were identified and their distributions mapped based on a review of occurrence maps and records, botanical floras and checklists, herbaria specimens, ecological and botanical studies, and field surveys of selected species. A disjunct species was defined as a plant population separated from its next nearest occurrence by a distance of > 300 km. Evaluation of the hypothesis was based on a review of published and unpublished pollen stratigraphy and palaeoecological studies. The potential geographical distribution of Hypsithermal vegetation was based on modern regional‐based ecosystem mapping and associated monthly temperature summaries as well as future climatic warming models. Results The hypothesis was compatible with Holocene pollen stratigraphy, Hypsithermal permafrost and fen occurrence, and palaeosol phytolith analyses; and future global climatic warming models. Modelled regional Hypsithermal vegetation based on a 1 °C increase in July temperatures relative to current conditions, indicated that much of the boreal forest zone in Alberta could have been grassland, which would explain the occurrence of Prairie species in the Peace River District. This amount of latitudinal vegetation shift (6.5°) was similar to an earlier Hypsithermal permafrost zone location study. An equivalent shift in vegetation along the eastern Cordillera would have placed south‐western Montana‐like vegetation and species such as Boykinia heucheriformis (Rydb.) Rosend. and Saxifraga odontoloma Piper within the northern half of the Rocky Mountains and foothills in Alberta, which represents the location of modern‐day disjunct populations of these species. Main conclusions Warmer and drier climatic conditions during the Holocene Hypsithermal resulted in the northward displacement of vegetation zones relative to their current distribution patterns. Most of Alberta was probably dominated by grasslands during this period, except the Rocky Mountains and northern highlands. Modern‐day species disjunctions within the Rocky Mountains and Peace River District as well as more northerly areas such as the Yukon Territory occurred when the vegetation receded southward in response to climatic cooling after the Hypsithermal. Wind dispersal was considered an unlikely possibility to explain the occurrence of the disjunct species, as most of the plants lack morphological adaptations for long distance transport and the prevailing winds were from west to east rather than south to north. However, consumption and transport of seeds by northward migrating birds could not be excluded as a possibility.     

Effects of El Niño drought on seedling dynamics in a seasonally dry tropical forest in Northern Thailand

As El Niño is predicted to become stronger and more frequent in the future, it is crucial to understand how El Niño-induced droughts will affect tropical forests. Although many studies have focused on tropical rainforests, there is a paucity of studies on seasonally dry tropical forests (SDTFs), particularly in Asia, and few studies have focused on seedling dynamics, which are expected to be strongly affected by drought. Seedlings in SDTFs are generally more drought-tolerant than those in the rainforests, and the effects of El Niño-induced droughts may differ between SDTF and tropical rainforests. In this study, we explored the impact of El Niño-induced drought at an SDTF in northern Thailand by monitoring the seedling dynamics at monthly intervals for 7 years, including a period of strong El Niño. The effects were compared between two forest types in an SDTF: a deciduous dipterocarp forest (DDF), dominated by deciduous species, and an adjacent lower montane forest (LMF) with more evergreen species. El Niño-induced drought increased seedling mortality in both the forest types. The effect of drought was stronger in evergreen than in the deciduous species, resulting in higher mortality in the LMF during El Niño. However, El Niño increased seedling recruitment only in the DDF, mainly because of the massive recruitment of the deciduous oak, Quercus brandisiana (Fagaceae), which compensated for the mortality of seedlings in the DDF. As a result, El Niño increased seedling density in the DDF and decreased it in the LMF. This is the first long-term study to identify the differences in the impacts of El Niño on seedlings between the two forest types, and two leaf habits, evergreen and deciduous, in Southeast Asia. Our findings suggest that future climate change may alter the species composition and spatial distribution of seedlings in Asian SDTFs.     

Strong paleoclimatic legacies in current plant functional diversity patterns across Europe

Numerous studies indicate that environmental changes during the late Quaternary have elicited long‐term disequilibria between species diversity and environment. Despite its importance for ecosystem functioning, the importance of historical environmental conditions as determinants of FD (functional diversity) remains largely unstudied. We quantified the geographic distributions of plant FD (richness and dispersion) across Europe using distribution and functional trait information for 2702 plant species. We then compared the importance of historical and contemporary factors to determine the relevance of past conditions as predictors of current plant FD in Europe. For this, we compared the strength of the relationships between FD with temperature and precipitation stability since the LGM (Last Glacial Maximum), accessibility to LGM refugia, and contemporary environmental conditions (climate, productivity, soil, topography, and land use). Functional richness and dispersion exhibited geographic patterns with strong associations to the environmental history of the region. The effect size of accessibility to LGM refugia and climate stability since the LGM was comparable to that of the contemporary predictors. Both functional richness and dispersion increased with temperature stability since the LGM and accessibility to LGM refugia. Functional richness' geographic pattern was primarily associated with accessibility to LGM refugia growing degree‐days, land use heterogeneity, diversity of soil types, and absolute minimum winter temperature. Functional dispersion's geographic pattern was primarily associated with accessibility to LGM refugia growing degree‐days and absolute minimum winter temperature. The high explained variance and model support of historical predictors are consistent with the idea that long‐term variability in environmental conditions supplements contemporary factors in shaping FD patterns at continental scales. Given the importance of FD for ecosystem functioning, future climate change may elicit not just short‐term shifts in ecosystem functioning, but also long‐term functional disequilibria.     

Mid-Holocene and glacial-maximum vegetation geography of the northern continents and Africa

BIOME 6000 is an international project to map vegetation globally at mid‐Holocene (6000 ¹⁴C yr bp ) and last glacial maximum (LGM, 18,000 ¹⁴C yr bp ), with a view to evaluating coupled climate‐biosphere model results. Primary palaeoecological data are assigned to biomes using an explicit algorithm based on plant functional types. This paper introduces the second Special Feature on BIOME 6000. Site‐based global biome maps are shown with data from North America, Eurasia (except South and Southeast Asia) and Africa at both time periods. A map based on surface samples shows the method’s skill in reconstructing present‐day biomes. Cold and dry conditions at LGM favoured extensive tundra and steppe. These biomes intergraded in northern Eurasia. Northern hemisphere forest biomes were displaced southward. Boreal evergreen forests (taiga) and temperate deciduous forests were fragmented, while European and East Asian steppes were greatly extended. Tropical moist forests (i.e. tropical rain forest and tropical seasonal forest) in Africa were reduced. In south‐western North America, desert and steppe were replaced by open conifer woodland, opposite to the general arid trend but consistent with modelled southward displacement of the jet stream. The Arctic forest limit was shifted slighly north at 6000 ¹⁴C yr bp in some sectors, but not in all. Northern temperate forest zones were generally shifted greater distances north. Warmer winters as well as summers in several regions are required to explain these shifts. Temperate deciduous forests in Europe were greatly extended, into the Mediterranean region as well as to the north. Steppe encroached on forest biomes in interior North America, but not in central Asia. Enhanced monsoons extended forest biomes in China inland and Sahelian vegetation into the Sahara while the African tropical rain forest was also reduced, consistent with a modelled northward shift of the ITCZ and a more seasonal climate in the equatorial zone. Palaeobiome maps show the outcome of separate, independent migrations of plant taxa in response to climate change. The average composition of biomes at LGM was often markedly different from today. Refugia for the temperate deciduous and tropical rain forest biomes may have existed offshore at LGM, but their characteristic taxa also persisted as components of other biomes. Examples include temperate deciduous trees that survived in cool mixed forest in eastern Europe, and tropical evergreen trees that survived in tropical seasonal forest in Africa. The sequence of biome shifts during a glacial‐interglacial cycle may help account for some disjunct distributions of plant taxa. For example, the now‐arid Saharan mountains may have linked Mediterranean and African tropical montane floras during enhanced monsoon regimes. Major changes in physical land‐surface conditions, shown by the palaeobiome data, have implications for the global climate. The data can be used directly to evaluate the output of coupled atmosphere‐biosphere models. The data could also be objectively generalized to yield realistic gridded land‐surface maps, for use in sensitivity experiments with atmospheric models. Recent analyses of vegetation‐climate feedbacks have focused on the hypothesized positive feedback effects of climate‐induced vegetation changes in the Sahara/Sahel region and the Arctic during the mid‐Holocene. However, a far wider spectrum of interactions potentially exists and could be investigated, using these data, both for 6000 ¹⁴C yr bp and for the LGM.