Seasonally Dry Tropical Forests Research Articles

Holocene southward expansion in seasonally dry tropical forests in South America: phylogeography ofFicus 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) (FCT = 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.

LEAF AND STEM TRAIT VARIATION AND PLANT FUNCTIONAL TYPES IN 113 WOODY SPECIES OF A SEASONALLY DRY TROPICAL FOREST

In seasonally dry tropical forest (SDTF) plant trait variation has been associated with adaptation to light and water availability and a coordinated tolerance of plants to shortage of both resources has been proposed. We tested this hypothesis in a set of 113 species by analyzing the relationships amongst eleven leaf and stem traits that have been related to shade and drought tolerance. In addition, the usefulness of different types of functional classifications describing community plant trait variation was evaluated. Strong relationships were observed between leaf and stem traits, potentially conferring coordinated tolerance to shade and drought, and three axes of variation were identified by means of a principal component analysis. The first axis described leaf and stem economy, the second was related to leaf thickness and organization and the third was related to the trade-offs between leaf size, stem density and bark thickness. Stem density was correlated strongly with several plant traits, emphasizing its key role in explaining variation in life history strategies of SDTF species. Significant differences were found between functional groups categorized by phylogeny and leaf phenology, whereas for life forms differences were only observed for palms and bamboos.

The establishment of Central American migratory corridors and the biogeographic origins of seasonally dry tropical forests in Mexico

Biogeography and community ecology can mutually illuminate the formation of a regional species pool or biome. Here, we apply phylogenetic methods to a large and diverse plant clade, Malpighiaceae, to characterize the formation of its species pool in Mexico, and its occupancy of the seasonally dry tropical forest (SDTF) biome that occurs there. We find that the ~162 species of Mexican Malpighiaceae represent ~33 dispersals from South America beginning in the Eocene and continuing until the Pliocene (~46.4–3.8 Myr). Furthermore, dispersal rates between South America and Mexico show a significant six-fold increase during the mid-Miocene (~23.9 Myr). We hypothesize that this increase marked the availability of Central America as an important corridor for Neotropical plant migration. We additionally demonstrate that this high rate of dispersal contributed substantially more to the phylogenetic diversity of Malpighiaceae in Mexico than in situ diversification. Finally, we show that most lineages arrived in Mexico pre-adapted with regard to one key SDTF trait, total annual precipitation. In contrast, these lineages adapted to a second key trait, precipitation seasonality, in situ as mountain building in the region gave rise to the abiotic parameters of extant SDTF. The timing of this in situ adaptation to seasonal precipitation suggests that SDTF likely originated its modern characteristics by the late Oligocene, but was geographically more restricted until its expansion in the mid-Miocene. These results highlight the complex interplay of dispersal, adaptation, and in situ diversification in the formation of tropical biomes. Our results additionally demonstrate that these processes are not static, and their relevance can change markedly over evolutionary time. This has important implications for understanding the origin of SDTF in Mexico, but also for understanding the temporal and spatial origin of biomes and regional species pools more broadly.

THE DISTRIBUTION OF WOODY LEGUMES IN NEOTROPICAL DRY FORESTS: THE PLEISTOCENE ARC THEORY 20 YEARS ON*

The Pleistocene Arc Theory (PAT) suggests that present-day disjunct fragments of dry forests in central tropical South America give evidence of a previously more continuous distribution during the Pleistocene that has been disrupted by dry-cold vs. humid-warm climatic cycles. This Arc extends from NE Brazil to NE Argentina and eastern Paraguay, through the Chiquitanía to NW Argentina and SW Bolivia and into the dry inter-Andean valleys in Peru and Ecuador, with intrusions into the Great Chaco. Seasonally Dry Tropical Forests (SDTFs) are floristically and physiognomically dominated by woody legumes, mostly deciduous in the dry season. In the last two decades field collection and research on legume taxa has greatly increased, with a significant number of taxonomic revisions and molecular phylogenetic studies, together with some paleoclimatic modelling studies. The evidence accumulated in the last 23 years has confirmed the integrity of the Chaco and Caatingas phytogeographical provinces, with an impressive and increasing level of botanical endemism discovered. The PAT pattern has also been supported, specifically through the mapping of five selected woody Leguminosae species (Anadenanthera colubrina, Enterolobium contortisiliquum, Pterogyne nitens, Amburana cearensis and Piptadenia viridiflora). The pre-existing nuclei of South American SDTF (Caatingas, Misiones and Piedmont) are now increased to four with the postulation of the Chiquitanía Nucleus in south-eastern Bolivia and bordering Paraguay. Some new endemisms are compiled from recent literature and mapped for the Misiones and Chiquitanía nuclei. The need for more botanical collections and further taxonomic, phylogenetic and demographic studies of South American legumes is emphasised.

Spatial genetic structure of Cavanillesia arborea K. Schum. (Malvaceae) in seasonally dry Tropical forest: Implications for conservation

Worldwide, Seasonally Dry Tropical Forests (SDTF) are among the least known and most degraded vegetation types. Cavanillesia arborea (Malvaceae) is an endemic dry forest tree that is bat-pollinated and the seeds are wind-dispersed. The present study sought to characterize the spatial genetic structure (SGS) in natural populations of C. arborea growing in SDTF fragments in Minas Gerais State, Brazil, using ISSR molecular markers. Seven ISSR primers generated 81 polymorphic loci in 175 individuals. In three populations (FU, MO and PC), we found random distributions of genotypes, while two populations (JAN and MV) showed SGS in their first distances classes (171 m and 17 m, respectively), with significant kinship (Sp) values (0.0189 and 0.0005 respectively; P < 0.05). Sp values for these populations indicate that the effects of kinship can be minimized by collecting seeds from distance classes beyond the species' first distance class. The continuous anthropogenic impacts on remnant tree populations, low species densities, and the observed genetic structure, all indicate the need to preserve large areas of dry forest vegetation for conservation purposes.

Genetic diversity and structure of the tree Enterolobium contortisiliquum (Fabaceae) associated with remnants of a seasonally dry tropical forest

Fragmentation of tropical forests is one of the major threats to biodiversity and viable natural populations. Brazilian seasonally dry tropical forests (SDTF) are endangered because of human occupation, conversion of lands to agriculture and high deforestation rates in these fertile soils. Enterolobium contortisiliquum has been removed from SDTF natural areas due to the advance of cattle grazing and agriculture in Brazilian SDTFs. To aid conservation efforts of this species we used molecular markers to study the genetic diversity and population structure of E. contortisiliquum in Brazilian SDTF remnants. A total of 263 individuals in 13 forest patches were analyzed with 103 ISSR fragments. In spite of being found scattered among the SDTF patches, E. contortisiliquum populations exhibited high genetic diversity (mean Shannon's index of diversity=0.384; mean genetic diversity=0.280) and genetic divergence between populations was detected (ΦST=0.155, p<0.0001). UPGMA dendrogram, principal coordinate analysis and Bayesian analysis showed that E. contortisiliquum populations were clustered into three groups that were not related to geographic distance (r=0.119, p=0.197). However, these populations are spatially structured into groups distributed in the West, Central and East of the study area. This genetic structure may be related with landscape and both the Espinhaço Range and São Francisco River may act as a partial geographic barrier limiting the gene flow. Because the highest rates of genetic diversity were found outside of conservation units, we propose the creation of protected areas in different geographic regions that include E. contortisiliquum populations from different genetic clusters.

Identifying deforestation attractors and patterns of fragmentation for seasonally dry tropical forest in central Veracruz, Mexico

Seasonally dry tropical forests (SDTF) are exposed to numerous threats stemming from human activity and are considered a high conservation priority globally. Nevertheless, planning the conservation, management, and restoration of forests requires a detailed regional understanding of current forest distribution, and patterns and attractors of deforestation. We explored SDTF cover in the state of Veracruz, Mexico, where little is known about this type of forest since it was erroneously considered to have been eliminated and thus has not be included in recent conservation planning in Mexico. A time-series of land use and land cover (LULC) maps, based on Landsat imagery from 1973 (MSS), 1990 (TM), and 2000 (ETM+), was used to analyze historical patterns of deforestation and fragmentation of SDTF in a priority watershed in central Veracruz. Stepwise logistic regression was used to identify the main attractors of forest loss. Maps based on higher resolution SPOT imagery (2007–2008) were used to determine the current extent of SDTF. Results from our LULC analysis revealed landscapes that were consistently dominated (>50%) by some combination of intensified land use including cattle pastures, rain-fed and irrigated agricultural lands, with closed SDTF cover fluctuating from 11.3 to 9.26% during the study period (1973–2007). Annualized rates of forest loss between Landsat images (1973 vs. 2000; −2.02%) and between Landsat and SPOT images (1973 vs. 2007; −0.59), were moderate to low, with historical records suggesting that most deforestation occurred more than a century ago before the Mexican revolution. Nevertheless, rates of forest loss varied considerable between different time periods, with slight reforestation initially (1.55%; 1973–1990), followed by a marked decline (−8.08%; 1990–2000), and finally a noticeable increases in forest cover (4.92%; 2000–2007) that corresponds with changes in public policy and trends in population migration. The number of forest patches tripled between 1973 and 2000 and the mean forest patch area decreased almost 80% over the same time period. Logistic regression analysis (1973–2000) indicated that the main attractors of closed forest transformation were proximity to gentle slopes, cattle pastures, and the hydraulic infrastructure needed for crop irrigation. Although SDTF is highly fragmented and perturbed, important remnants of this diverse native forest still persists in the region. Our findings are discussed in the context of future conservation and restoration efforts.

Tree community structure in a seasonally dry tropical forest remnant, Brazil

Most studies on Seasonally Dry Tropical Forests (SDTFs) investigate phytogeographic patterns and floristic connections of this disjunct biome. However, little is known about the structural characteristics of SDTFs. We aimed to describe the structure of a SDTF in an ecotonal area between the Cerrado and Caatinga domains. In total, 79 tree species were recorded, and high values of Shannon diversity index (3.6 nats/individual) and equability (0.83) were observed. The diameter distribution for the species with higher cover values and for the entire community did not exhibit a reverse-J shaped distribution, which indicates the occurrence of different growth strategies and ecological adaptations to water stress. The results did not indicate the formation of floristic groups, as the high soil fertility in the study area results in a homogeneous environment. The structural characteristics of the study area associated with the soil composition highlight its importance for conservation and emphasize the need for community structure studies in SDTFs.

Árvores e variáveis ambientais influenciam a regeneração natural de uma floresta estacional decidual no Brasil Central

Seasonally dry tropical forests (SDTFs) have high tree species richness and endemism, whose dynamics and succession depend on natural regeneration (NR). To test whether NR is influenced by the mature stratum and environmental variables, we compared structural and floristic patterns of mature trees [Mt (DBH ? 5 cm)] with the NR of a SDTF on limestone outcrops in Central Brazil. Additionally, we tested for effects of environmental variables on species abundance in these different strata. Within NR categories [JuvA (total height &lt; 100 cm) and JuvB (total height ? 100 cm and DBH &lt; 5 cm)], we recorded 597 individuals in 69 angiosperm species. Within NR and Mt we recorded 110 species distributed in 33 families, and 54 were common to both (~50% of total richness). Shannon diversity was 3.83, 3.13 and 3.33 for Mt, JuvA and JuvB, respectively. Besides the high number of exclusive species recorded in Mt (23), JuvA (18) and JuvB (24), comparisons indicated high floristic similarity (51%) between strata. Mt, JuvA and JuvB were influenced by different environmental variables, indicating that species requirements change along the establishment process. This highlights the importance of environmental variability for maintaining tree species diversity in SDTFs, and the importance of this remnant for the conservation of SDTFs in Central Brazil.Keywords: Cafuringa, Cerrado, dry forest, forest succession, limestone outcrops, sapling.

Soil seed bank, seed removal, and germination in a seasonally dry tropical forest in Veracruz, Mexico

The soil seed bank has a limited role in the seasonal dry tropical forest regeneration process, but seed removal and germination can also be limiting factors during the early forest recovery. In central Veracruz, Mexico, the soil seed bank was determined en five fallows and two forests. Seed bank decreased from fallow to forest (1303 to 101 seeds m-2); herbs and grasses predominated thus the similarity between species composition of seed bank and vegetation was low. Seed removal and germination were evaluated for Acacia cochliacantha, Caesalpinia cacalaco, Ipomoea wolcottiana and Senna atomaria in contrasting habitats represented by pasture, fallow and forest. Seed removal was determined under treatments of total access, rodent exclosure, and insect exclosure. Caesalpinia (largest seeds) displayed the lowest seed removal (5%), whereas Senna (63%) and Ipomoea (29%) displayed the highest. Rodent exclosure reduced seed removal for Ipomoea (medium-sized seeds); and insect exclosure reduced removal for Senna and Acacia (small seeds). With the exception of Senna (18% germination), the scarified seeds displayed the highest germination percentage (53-99%). For all species, germination was higher in forest than in open habitats, only Senna seeds displayed the lowest germination percentage in the forest habitat. Results suggested that in the dry forest of Veracruz, seed removal may not limit forest regeneration; however seeds must be scarified for use in restoration activities.

Changes in tree phenology along natural regeneration in a seasonally dry tropical forest

The applicability of succession models from temperate and tropical wet forests to threatened seasonally dry tropical forests (SDTFs) is questioned. Plant phenology affects ecosystem functions and changes along forest regeneration gradient. To investigate the recovery of ecological functions after disturbances in a SDTF, we recorded the vegetative and reproductive phenologies for trees (DBH >5 cm) for 17 months in southeast Brazil in three successional stages: early (10–15 years after clearing), intermediate (25–30) and late (>50). The vegetative phenology of the 523 individuals was strongly seasonal, with 3% of individuals presenting green leaves in a deciduous dry season. Besides structural and floristic differences, phenological trends were similar between the later stages. Reproduction occurred with higher intensities in the early stage and in the advanced stages only in the dry season, providing key resources to local fauna. The studied SDTF is resilient to ecological functions, rapidly recovering functional processes. The integration of structural and functional knowledge of succession of STDFs may lead to better management of its secondary remnants. Our study suggests that classical forest succession theory developed for other ecosystems may not fully reflect the pattern of SDTF succession, an ecosystem that originally covered 42% of the earth's tropical and subtropical landmass.

The dichotomy between protection and logging of the Endangered and valuable timber speciesAmburana cearensisin north-west Argentina

AbstractAmburana cearensisis a commercially valuable timber species, categorized as Endangered on the IUCN Red List. It is distributed throughout the seasonal dry tropical forests of Brazil, Paraguay, Bolivia, Peru and Argentina. In Argentina it is restricted to the provinces of Salta, where legislation sets a minimum cutting diameter of 60 cm, and Jujuy, where logging of this species has been banned since 1972. The effect of these laws on the species’ conservation status has not been assessed. We estimated species density, using distance sampling methodology, and measured the diameter at breast height of each individual encountered at 13 sites in north-west Argentina. Across both provinces we found a density of 1.12 individuals ha−1(95% CI 0.48–2.63) and there was no significant difference between the density in Salta (5.15 ha−1;; 95% CI 3.14–8.45) and that in Jujuy (3.67 ha−1;; 95% CI 2.59–5.17), although 84% of the individuals encountered in Salta were found at one site. Diameter at breast height was significantly lower in Salta than in Jujuy (23 ± 12 vs 41 ± 18 cm; P &lt; 0.05). These differences in the demography of the species between the provinces may be attributable to the application of different legislation. Our results indicate that it would be prudent to halt logging of this species in Salta until further information is gathered and a sustainable management plan developed.

Genetic structure of disjunct Argentinean populations of the subtropical tree Anadenanthera colubrina var. cebil (Fabaceae)

Anadenanthera colubrina var. cebil is a native South American tree species inhabiting seasonally dry tropical forests (SDTFs). Its current disjunct distribution presumably represents fragments of a historical much larger area of this forest type, which has also been highly impacted by human activities. In this way the hypothesis of this study is that the natural populations of A. colubrina var. cebil from Northern Argentina represent vestiges of ancient fragmentation, but they are additionally influenced by a certain degree of gene flow among them. We aimed to analyze the genetic structure of both nuclear and chloroplast DNA to evaluate the relative role of ancient and recent fragmentation on intraspecific diversity patterns. Sixty-nine individuals of four natural populations were analyzed using eight nuclear microsatellites (ncSSR) and four chloroplast microsatellite loci (cpSSR). The level and distribution of genetic variation were estimated by standard population genetic parameters and Neighbor Joining as well as Bayesian analyses. The eight ncSSR loci were highly polymorphic, while genetic diversity of cpSSRs was low. Nuclear SSRs displayed lower genetic differentiation among populations than cpSSR haplotypes (FST 0.11 and 0.95, respectively). However, high differentiation between phytogeographic provinces was observed in both genomes. The high genetic differentiation detected emphasizes the role of ancient fragmentation. However, the Paranaense province also shows the effects of recent fragmentation on genetic structure, whereas gene flow by pollen preserves the effects of genetic drift in the Yungas province. © 2014 Springer-Verlag Wien.

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.

A STUDY IN AN AREA OF TRANSITION BETWEEN SEASONALLY DRY TROPICAL FOREST AND MESOTROPHIC CERRADÃO, IN MATO GROSSO DO SUL, SOUTHWESTERN BRAZIL

This study describes the tree vegetation and soils occurring in a seasonally dry tropical forest (SDTF) and mesotrophic cerradão transition in southwestern Brazil. All trees ≥ 5 cm diameter were measured in 20 plots of 20 × 25 m, 10 in SDTF, and 10 in mesotrophic cerradão. Ten soil samples of 0−20 cm depth were made per plot and mixed in plot groups to produce two composite samples. A total of 71 species was recorded. Anadenanthera colubrina had the highest importance values in both formations. Differences in soil fertility were found between SDTFs (eutrophic soils) and mesotrophic cerradão (mesotrophic soils). A non-metric multidimensional scaling and cluster analysis confirmed the soil fertility segregation, and also showed an agreement between soil fertility and variance in species composition gradients. The mesotrophic cerradão showed higher species richness since it also includes many species typical of more dystrophic and open forms of Cerrado.

Disturbance History of a Seasonal Tropical Forest in Western Thailand: A Spatial Dendroecological Analysis

AbstractDisturbances play an important role in forest dynamics across the globe. Researchers have mainly focused on the temporal context of disturbances, but have largely ignored the spatial patterns of tree recruitment they create. Geostatistical tools enable the analysis of spatial patterns and variability in tropical forest disturbance histories. Here, we examine the potential of combining dendroecological analysis and spatial statistics to reconstruct the disturbance history of a seasonal dry evergreen tropical forest plot at the Huai Kha Khaeng Wildlife Sanctuary (HKK), western Thailand. We used tree‐ring‐derived age estimates for 70 individuals of the shade‐intolerant pioneer speciesMelia azederach(Meliaceae) and tree locations across a 316‐ha study plot to identify the timing and spatial extent of past disturbances. Although the age distribution forMeliasuggested that regeneration had been continuous over the past 60 yr, spatial analyses (mark correlation function and kriging) demonstrated the presence of three spatially discrete age cohorts. Two of these cohorts suggested a severe disturbance ~20 yr before present. A third cohort appears to have established ~50 years ago. Using historical records, we conclude that fire disturbance is the most likely disturbance factor affectingHKK. Nevertheless, we do not rule out other disturbance factors. The combined application of tree‐ring analysis and spatial statistics as applied in this study could be readily applied to reconstruct disturbance histories in other tropical regions where tree species with annual growth rings are present.

Competition Among Surface Roots in a Selectively-Logged, Semi-Deciduous Forest in Southeastern Mexico — Effects on Seedlings of Two Species of Contrasting Shade Tolerance

Experimental manipulations of root competition on naturally established seedlings were conducted across canopy openness and soil depth gradients in a selectively-logged, semideciduous forest on limestone-derived soils in southeastern Mexico. We studied the relatively shade intolerant mahogany (Swietenia macrophylla, Meliaceae) and shade tolerant ramon (Brosimum alicastrum, Moraceae). Both species are ecologically and economically important canopy trees that respond differently to selective logging, hurricanes, and fires on the Yucatan Peninsula. The canopy openness gradient used in the experiment was created by low-intensity selective logging operations. The responses of naturally occurring seedlings of both species growing within 20–30 cm deep circular trenches were examined over a 19-month experimental period. Trenching resulted in increased relative growth in diameter, stem length, and number of leaves of Swietenia compared with controls, but had no effect on Brosimum relative growth or on seedling survival of either species. There was no significant interaction between increased light availability and trenching on Swietenia seedlings, perhaps because of their larger size in gaps. Trenching effects on Swietenia were not greater during the dry season, suggesting that surface trenching affected growth during transitions between seasons. Contrasting responses of Swietenia and Brosimum seedlings to changes in soil and light environments point to the need for diversity in silvicultural practices in seasonally-dry tropical forests such as the community-managed forest examined in this study.

Reinterpretation of the nomenclatural type of Pseudobombax heteromorphum (Malvaceae, Bombacoideae) reveals an overlooked new species from Bolivia

In the course of a taxonomic revision of Pseudobombax Dugand, one of us (JGCS) frequently has observed herbarium specimens of Bombacoideae that comprise a mixture of different Angiosperm families. In particular, Pseudobombax heteromorphum (Kuntze) A. Robyns, a frequent name in checklists of the Bolivian flora, is based on type material of Bombax heteromorphum Kuntze that is clearly a mixture of Pseudobombax flowers and Tabebuia Gomes ex DC. (Bignoniaceae) leaves. We herein designate as the lectotype of Bombax heteromorphum the flowers of an herbarium sheet deposited in NY and as epitype a complete specimen (leaves, flowers, and fruit) in HUEFS. We consider Bombax heteromorphum to be a synonym of Pseudobombax longiflorum (Mart.) A. Robyns, a species widespread in Neotropical seasonally dry forest of Bolivia, Brazil, Paraguay, and Peru. Furthermore, we describe a new species, Pseudobombax pulchellum Carv.-Sobr., apparently endemic to seasonally dry tropical forest (SDTF) in Bolivia (Chiquitano dry forest), based on specimens commonly but incorrectly identified as Pseudobombax heteromorphum.We also comment on the morphology, distribution, and conservation status of this new species.

Sensitivity of Bolivian seasonally-dry tropical forest to precipitation and temperature changes over glacial–interglacial timescales

We used fossil pollen to investigate the response of the eastern Chiquitano seasonally-dry tropical forest (SDTF), lowland Bolivia, to high-amplitude climate change associated with glacial–interglacial cycles. Changes in the structure, composition and diversity of the past vegetation are compared with palaeoclimate data previously reconstructed from the same record, and these results shed light on the biogeographic history of today’s highly disjunct blocks of SDTF across South America. We demonstrate that lower glacial temperatures limited tropical forest in the Chiquitania region, and suggest that SDTF was absent or restricted at latitudes below 17°S, the proposed location of the majority of the hypothesized ‘Pleistocene dry forest arc’ (PDFA). At 19500 yrs b.p., warming supported the establishment of a floristically-distinct SDTF, which showed little change throughout the glacial–Holocene transition, despite a shift to significantly wetter conditions beginning ca. 12500–12200 yrs b.p. Anadenanthera colubrina, a key SDTF taxon, arrived at 10000 yrs b.p., which coincides with the onset of drought associated with an extended dry season. Lasting until 3000 yrs b.p., Holocene drought caused a floristic shift to more drought-tolerant taxa and a reduction in α-diversity (shown by declining palynological richness), but closed-canopy forest was maintained throughout. In contrast to the PDFA, the modern distribution of SDTF most likely represents the greatest spatial coverage of these forests in southern South America since glacial times. We find that temperature is a key climatic control upon the distribution of lowland South American SDTF over glacial-interglacial timescales, and seasonality of rainfall exerts a strong control on their floristic composition.

Spatio‐temporal evolution of Fosterella (Bromeliaceae) in the Central Andean biodiversity hotspot

AbstractAimTo reconstruct the spatio‐temporal evolution of Fosterella (Bromeliaceae), a genus characterized by a high degree of endemism in the Central Andes, and to account for contemporary patterns of diversity and distribution within the genus.LocationFosterella has its centre of diversity in the Central Andes (24 species), where it occurs in two major biomes: the Yungas and seasonally dry tropical forests (SDTF). The genus displays three major disjunctions: Amazonia (one species), Central America (one species), and the Brazilian Shield (five species).MethodsPhylogenetic relationships within Fosterella were inferred based on six plastid DNA regions. Parsimony and likelihood methods, a Bayesian relaxed molecular clock, ancestral area reconstructions, and diversification rate analyses were used to infer the spatio‐temporal evolution of Fosterella.ResultsThe origin of extant lineages of Fosterella was placed in the late Miocene (c. 9.6 Ma) during the last rapid Andean uplift. SDTF and azonal lowland sites were inferred as the most likely ancestral habitats. The Yungas were colonized several times independently from c. 4.7 Ma onwards. Only one clade diversified in the Yungas, indicative of an ecological shift to moister and cooler conditions. Two recent long‐distance dispersals to Central America and to Amazonia were inferred. Diversification rates within Fosterella were found to be constant through time and comparatively low (0.4 species Myr−1).Main conclusionsAllopatric speciation is the main mode of diversification in Fosterella. The isolated distribution of suitable habitats fostered the evolution of a high degree of endemism. The low speciation rates in Fosterella contrast with high diversification rates of Andean high‐elevation taxa but are similar to other Andean low‐ to mid‐elevation taxa. The last rapid Andean uplift did not leave a detectable signature in the diversification rates of Fosterella.