Functional Resilience against Climate-Driven Extinctions – Comparing the Functional Diversity of European and North American Tree Floras

Future global change scenarios predict a dramatic loss of biodiversity for many regions in the world, potentially reducing the resistance and resilience of ecosystem functions. Once before, during Plio-Pleistocene glaciations, harsher climatic conditions in Europe as compared to North America led to a more depauperate tree flora. Here we hypothesize that this climate driven species loss has also reduced functional diversity in Europe as compared to North America. We used variation in 26 traits for 154 North American and 66 European tree species and grid-based co-occurrences derived from distribution maps to compare functional diversity patterns of the two continents. First, we identified similar regions with respect to contemporary climate in the temperate zone of North America and Europe. Second, we compared the functional diversity of both continents and for the climatically similar sub-regions using the functional dispersion-index (FDis) and the functional richness index (FRic). Third, we accounted in these comparisons for grid-scale differences in species richness, and, fourth, investigated the associated trait spaces using dimensionality reduction. For gymnosperms we find similar functional diversity on both continents, whereas for angiosperms functional diversity is significantly greater in Europe than in North America. These results are consistent across different scales, for climatically similar regions and considering species richness patterns. We decomposed these differences in trait space occupation into differences in functional diversity vs. differences in functional identity. We show that climate-driven species loss on a continental scale might be decoupled from or at least not linearly related to changes in functional diversity. This might be important when analyzing the effects of climate-driven biodiversity change on ecosystem functioning.     

Tree diversity,tree height and environmental harshness in eastern and western North America

Does variation in environmental harshness explain local and regional species diversity gradients? We hypothesise that for a given life form like trees, greater harshness leads to a smaller range of traits that are viable and thereby also to lower species diversity. On the basis of a strong dependence of maximum tree height on site productivity and other measures of site quality, we propose maximum tree height as an inverse measure of environmental harshness for trees. Our results show that tree species richness is strongly positively correlated with maximum tree height across multiple spatial scales in forests of both eastern and western North America. Maximum tree height co‐varied with species richness along gradients from benign to harsh environmental conditions, which supports the hypothesis that harshness may be a general mechanism limiting local diversity and explaining diversity gradients within a biogeographic region.     

Relative influences of current and historical factors on mammal and bird diversity patterns in deglaciated North America

Aim To investigate the relative contributions of current vs. historical factors in explaining broad‐scale diversity gradients using a combination of contemporary factors and a quantitative estimate of the temporal accessibility of areas for recolonization created by glacial retreat following the most recent Ice Age. Location The part of the Nearctic region of North America that was covered by ice sheets during the glacial maximum 20 000 BP. Methods We used range maps to estimate the species richness of mammals and terrestrial birds in 48 400 km² cells. Current conditions in each cell were quantified using seven climatic and topographical variables. Historical conditions were estimated using the number of years before present when an area became exposed as the ice sheets retreated during the post‐Pleistocene climate warming. We attempted to tease apart contemporary and historical effects using multiple regression, partial regression and spatial autocorrelation analysis. Results A measure of current energy inputs, potential evapotranspiration, explained 76–82% of the variance in species richness, but time since deglaciation explained an additional 8–13% of the variance, primarily due to effects operating at large spatial scales. Because of spatial covariation between the historical climates influencing the melting of the ice sheet and current climates, it was not possible to partition their effects fully, but of the independent effects that could be identified, current climate explained two to seven times more variance in richness patterns than age. Main Conclusions Factors acting in the present appear to have the strongest influence on the diversity gradient, but an historical signal persisting at least 13 000 years is still detectable. This has implications for modelling changes in diversity patterns in response to future global warming.     

Evolutionary and ecological causes of species richness patterns in North American angiosperm trees

Climate and evolutionary factors (e.g. diversification, time‐for‐speciation, niche conservatism) are both thought to be major drivers of species richness in regional assemblages. However, few studies have simultaneously investigated the relative effects of climate and evolutionary factors on species richness across a broad geographical extent. Here, we assess their relative effects on species richness of angiosperm trees across North America. Species richness of angiosperm trees in 1175 regional assemblages were related to climate and phylogenetic structure using a structural equation modeling (SEM) approach. Climate was quantified based on the mean temperature of the coldest month and mean annual precipitation. Evolutionary factors (time‐for‐speciation vs diversification) were inferred from phylogeny‐based measures of mean root distance, phylogenetic species variability, and net relatedness index. We found that at the continental scale, species richness is correlated with temperature and precipitation with approximately similar strength. In the SEM with net relatedness index and phylogenetic species variability and with all the 1175 quadrats, the total direct effect size of phylogenetic structure on species richness is greater than the total direct effect size of climate on species richness by a factor of 3.7. The specific patterns of phylogenetic structure (i.e. greater phylogenetic distances in more species rich regions) are consistent with the idea that time and niche conservatism drive richness patterns in North American angiosperm trees. We conclude that angiosperm tree species richness in regional assemblages in North America is more strongly related to patterns of phylogenetic relatedness than to climatic variation. The results of the present study support the idea that climatic and evolutionary explanations for richness patterns are not in conflict, and that evolutionary processes explain both the relationship between climate and richness and substantial variation in richness that is independent of climate.     

Global angiosperm family richness revisited: linking ecology and evolution to climate

Aim The global richness gradient of angiosperm families is correlated with current climate, and it has been claimed that historical processes are not necessary to understand patterns of plant family richness. This claim has drawn criticism, and there have been doubts about the quality of the data used to quantify the pattern. We revisit this issue using the Angiosperm Phylogeny Group (APG) III classification and revised range maps, and we incorporate an evolutionary variable, family age, to explore covariation between evolution and ecology and their links to climate via the tropical conservatism hypothesis (TCH). Location Global. Methods The richness pattern for 408 families was derived from range maps, and family ages were derived from a dated angiosperm phylogeny. Patterns were generated for all families, 143 families composed of trees, and 149 families composed of herbs. We also examined family range size patterns to test the extent to which extratropical floras are nested subsets of tropical floras. Ordinary least squares (OLS) multiple and partial regressions were used to generate climate models for richness, mean range size and mean age for each plant dataset and to evaluate the covariation between contemporary climate and clade age as correlates of family richness. Results We confirmed the strong association between contemporary climate and family richness. Age patterns predicted by TCH were also found for families comprising trees. The richness of herbaceous families, in contrast, was correlated with climate but the age pattern was not as predicted by TCH. Floras in cold and dry areas are strongly nested within richer tropical floras. Main conclusions Phylogenetic niche conservatism at the family level offers a likely explanation for the global diversity gradient of trees, but not for non‐desert herbs, probably because of the faster evolutionary rates for herbs and less constrained evolutionary responses to climate change. Thus, it appears that multiple processes account for the overall angiosperm family gradient. Our analysis also demonstrates that even very strong associations of taxon richness and climate do not preclude evolutionary processes, as has been widely argued, and that climatic and evolutionary hypotheses for richness gradients are not mutually exclusive.     

Disturbances in deciduous temperate forest ecosystems of the northern hemisphere: their effects on both recent and future forest development

Disturbances in forests can kill mature trees, but also create the conditions necessary for the establishment of new tree cohorts and create micro-habitats for new plant and animal species, thereby increasing the species diversity compared to undisturbed stands. We review the types and intensities of disturbances on forests in three regions of the temperate zone of the northern hemisphere: northeastern North America, Central Europe, and East Asia. We focus on (1) the ways in which disturbances affect forest stand development; (2) the differences among the three areas in this regard; (3) the consequences for future forest management. In both northeastern North America and East Asia, hurricanes and typhoons represent the major mode of natural disturbance, while in Central Europe winter windstorms occur after deciduous trees have lost their leaves. Tornadoes can have even greater destructive power (but affect relatively narrow strips of land), and the more severe of these mainly occur in North America. The general disturbance patch system therefore is relatively large in northeastern North America, small in Central Europe, and of intermediate size in temperate East Asia. In addition to wholly natural disturbance factors, human commerce and globalization have enabled new disturbance types by introducing pests and diseases from one region to another. In North America especially, several of the most important foundation species in temperate forests are strongly affected, so that not just the species composition but also the whole forest structure is changing fundamentally. In all three areas in the past the change in land use by growing human populations strongly affected the structure as well as the species composition of forests. Nearly all the recent forest stands of the temperate zone had been used in the past in a particular way, and many of today’s forests had previously been converted into agricultural land. Finally climate change is superimposing itself on forest development worldwide. Nevertheless, climate change is not a new phenomenon, so forest ecosystems in all time periods have been exposed to changing climatic conditions and have had to adapt. Each forest stand therefore represents a unique recent expression of the interaction of environmental conditions and plant species, a “snapshot” of the relevant abiotic and biotic factors, including human impact.     

Comparative biogeography of New Zealand trees: species richness, height, leaf traits and range sizes

New Zealand forests grow under highly oceanic climates on an isolated southern archipelago. They experience a combination of historical and environmental factors matched nowhere else. This paper explores whether the New Zealand tree flora also differs systematically from those found in other temperate and island areas. A compilation of traits and distributions from standard floras is used to compare the New Zealand tree flora with those of Europe, North America, Chile, southern Australia, Fiji and Hawaii. New Zealand has a large number of trees (215 species ≥6 m in height). It is more tree-rich than temperate North America and Europe having up to 50% more species at a quadrat scale of 2.5? latitude x 2.5? longitude. However, this richness is due to a greater abundance of small trees (≤15 m in height) and we argue that it is a legacy of allopatric speciation and radiation during the late Neogene (2.5?10 million yrs ago) when the New Zealand landmass was repeatedly split into smaller island groups and mountain building occurred. The leaves of New Zealand trees, along with those of southeast Australia, are smaller and narrower than those of the temperate northern hemisphere. Dominance of the canopy by small-leaved evergreen conifers and angiosperms may have facilitated the persistence of small tree species in the lower canopy. The proportion of tree species with a deciduous or divaricating habit, and toothed-margin leaves, increases with latitude, suggesting a link with lower winter temperatures in the south. Tree species richness decreases with increasing latitude and, in conformity with Rapoport?s Rule, latitudinal range width increases. Wide-range trees are mainly bird-dispersed, fast-growing seral small trees, or long-lived, tall podocarps. Wide-range trees appear to have no greater tolerance of climate extremes than narrow-range trees, and their persistence at high latitudes derives from their enhanced colonization ability.     

Spatial Pattern of Vascular Plant Diversity in North America North of Mexico and its Floristic Relationship with Eurasia

This paper reports: (1) patterns of taxonomic richness of vascularplants in North America (north of Mexico), an area accountingfor 16.6% of the total world land, in relation to latitudinaland longitudinal gradients; (2) floristic relationships betweendifferent latitudinal zones, longitudinal zones, and geographicregions of North America; and (3) floristic relationships betweenNorth America and Eurasia at various geographic scales. NorthAmerica was geographically divided into twelve regions, whichwere latitudinally grouped into four zones, each with threeregions, and longitudinally grouped into three zones, each withfour regions. The native vascular flora of North America consistsof 162 orders, 280 families, 1904 genera and 15352 species.Along the latitudinal gradient, species richness shows a strikingincrease with decreasing latitude (e.g. the northernmost latitudinalzone has only 11.7% of the number of species in the southernmostlatitudinal zone). However, about 63% of the species of thenorthernmost latitudinal zone are also present in the southernmostlatitudinal zone of North America. Among the three longitudinalzones, the zone on the Pacific coast has 1.48 and 1.64-timesas many species as the zones in the interior and on the Atlanticcoast, respectively. About 36% of the species in the zone ofthe Atlantic coast also occur in the Pacific coast zone. However,each of over 40% of the species in North America occupies lessthan 10% of the total land area of North America. Some 48% ofthe genera and 6.5% of the species of North America are alsonative to Eurasia. In general, the number of genera common toNorth America and Eurasia increased from the north to the southand from the west to the east of North America, whereas thenumber of species common to the two continents decreased alongthe same two geographic gradients.Copyright 1999 Annals of BotanyCompany Asia, biodiversity, Europe, floristic similarity, latitudinal and longitudinal gradients, North America, taxonomic richness.     

Douglas‐fir plantations in Europe: a retrospective test of assisted migration to address climate change

We evaluate genetic test plantations of North American Douglas‐fir provenances in Europe to quantify how tree populations respond when subjected to climate regime shifts, and we examined whether bioclimate envelope models developed for North America to guide assisted migration under climate change can retrospectively predict the success of these provenance transfers to Europe. The meta‐analysis is based on long‐term growth data of 2800 provenances transferred to 120 European test sites. The model was generally well suited to predict the best performing provenances along north–south gradients in Western Europe, but failed to predict superior performance of coastal North American populations under continental climate conditions in Eastern Europe. However, model projections appear appropriate when considering additional information regarding adaptation of Douglas‐fir provenances to withstand frost and drought, even though the model partially fails in a validation against growth traits alone. We conclude by applying the partially validated model to climate change scenarios for Europe, demonstrating that climate trends observed over the last three decades warrant changes to current use of Douglas‐fir provenances in plantation forestry throughout Western and Central Europe.     

Tracing the patterns of non-marine turtle richness from the Triassic to the Palaeogene: from origin to global spread

Turtles are key components of modern vertebrate faunas and their diversity and distributions are likely to be affected by anthropogenic climate change. However, there is limited baseline data on turtle taxonomic richness through time or assessment of their past responses to global environmental change. We used the extensive Triassic–Palaeogene (252–223 Ma) fossil record of terrestrial and freshwater turtles to investigate diversity patterns, finding substantial variation in richness through time and between continents. Globally, turtle richness was low from their Triassic origin until the Late Jurassic. There is strong evidence for high richness in the earliest Cretaceous of Europe, becoming especially high following the Cretaceous Thermal Maximum and declining in all continents by the end-Cretaceous. At the K–Pg boundary, South American richness levels changed little while North American richness increased, becoming very high during the earliest Palaeogene (Danian). Informative data are lacking elsewhere for this time period. However, the Selandian–Thanetian interval, approximately 5 myr after the K–Pg mass extinction, shows low turtle richness in Asia, Europe and South America, suggesting that the occurrence of exceptional turtle richness in the post-extinction Paleocene fauna of North America is not globally representative. Richness decreased over the Eocene–Oligocene boundary in North America but increased to its greatest known level for Europe, implying very different responses to dramatic climatic shifts. Time series regressions suggest number of formations sampled and palaeotemperature are the primary influencers of face-value richness counts, but additional factors not tested here may also be involved.     

Tropical niche conservatism and the species richness gradient of North American butterflies

Aim We explore the potential role of the ‘tropical conservatism hypothesis’ in explaining the butterfly species richness gradient in North America. Its applicability can be derived from the tropical origin of butterflies and the presumed difficulties in evolving the cold tolerance required to permit the colonization and permanent occupation of the temperate zone. Location North America. Methods Digitized range maps for butterfly species north of Mexico were used to map richness for all species, species with distributions north of the Tropic of Capricorn (Extratropicals), and species that also occupy the tropics (Tropicals). A phylogeny resolved to subfamily was used to map the geographical pattern of mean root distance, a metric of the evolutionary development of assemblages. Regression models and general linear models examined environmental correlates of overall richness and for Extratropicals vs. Tropicals, patterns in summer vs. winter, and patterns in northern vs. southern North America. Results Species in more basal subfamilies dominate the south, whereas more derived clades occupy the north. There is also a ‘latitudinal’ richness gradient in Canada/Alaska, whereas in the conterminous USA richness primarily varies longitudinally. Overall richness is associated with broad‐ and mesoscale temperature gradients. The richness of Tropicals is strongly associated with temperature and distance from winter population sources. The richness of Extratropicals in the north is most strongly correlated with the pattern of glacial retreat since the more recent Ice Age, whereas in the south, richness is positively associated with the range of temperatures in mountains and the presence of forests but is negatively correlated with the broad‐scale temperature gradient. Main conclusions The tropical conservatism hypothesis provides a possible explanation for the complex structure of the species richness gradient. The Canada/Alaska fauna comprises temperate, boreal and tundra species that are nevertheless constrained by cold climates and limited vegetation, coupled with possible post‐Pleistocene recolonization lags. In the USA tropical species are constrained by temperature in winter as well as recolonization distances in summer, whereas temperate‐zone groups are richer in cooler climates in mountains and forests, where winter conditions are more suitable for diapause. The evolution of cold tolerance is key to both the evolutionary and ecological patterns.     

High migration rates shape the postglacial history of amphi‐Atlantic bryophytes

Paleontological evidence and current patterns of angiosperm species richness suggest that European biota experienced more severe bottlenecks than North American ones during the last glacial maximum. How well this pattern fits other plant species is less clear. Bryophytes offer a unique opportunity to contrast the impact of the last glacial maximum in North America and Europe because about 60% of the European bryoflora is shared with North America. Here, we use population genetic analyses based on approximate Bayesian computation on eight amphi‐Atlantic species to test the hypothesis that North American populations were less impacted by the last glacial maximum, exhibiting higher levels of genetic diversity than European ones and ultimately serving as a refugium for the postglacial recolonization of Europe. In contrast with this hypothesis, the best‐fit demographic model involved similar patterns of population size contractions, comparable levels of genetic diversity and balanced migration rates between European and North American populations. Our results thus suggest that bryophytes have experienced comparable demographic glacial histories on both sides of the Atlantic. Although a weak, but significant genetic structure was systematically recovered between European and North American populations, evidence for migration from and towards both continents suggests that amphi‐Atlantic bryophyte population may function as a metapopulation network. Reconstructing the biogeographic history of either North American or European bryophyte populations therefore requires a large, trans‐Atlantic geographic framework.     

The environmental basis of North American species richness patterns among Epicauta (Coleoptera: Meloidae)

Understanding regional variability in species richness is necessary for conservation efforts to succeed in the face of large-scale environmental deterioration. Several analyses of North American vertebrates have shown that climatic energy provides the best explanation of contemporary species richness patterns. The paucity of analyses of insect diversity patterns, however, remains a serious obstacle to a general hypothesis of spatial variation in diversity. We collected species distribution data on a North American beetle genus, Epicauta (Coleoptera: Meloidae) and tested several major diversity hypotheses. These beetles are generally grasshopper egg predators as larvae, and angiosperm herbivores as adults. Epicauta richness is highest in the hot, dry American southwest, and decreases north and east, consistent with the species richness-energy hypothesis. Potential evapotranspiration, which is also the best predictor of richness patterns among North American vertebrates, explains 80.2% of the variability in Epicauta species richness. Net primary productivity and variables measuring climatic heat energy only (such as PET) are not generally comparable, though they are sometimes treated as if they were equivalent. We conclude that the species richness-energy hypothesis currently provides a better overall explanation for Epicauta species richness patterns in North America than other major diversity hypotheses. The observed relationship between climatic energy and regional species richness may provide significant insight into the response of ecological communities to climate change.     

Increasing temperature sensitivity caused by climate warming,evidence from Northeastern China

The “Divergence Problem” in northern forests has been confirmed in a large number of empirical studies, especially in North America and Europe, climate warming having been identified as a cause for reduced sensitivity of recent tree-growth and increased tree mortality. However, according to other studies, tree growth patterns are keeping pace with climate warming. Covariation between rising temperatures and tree growth varies regionally. Therefore, extensive evidence is still needed across more geographic areas around the world. In the present study, we examined the sensitivity of Manchurian ash forest growth, which is one of the dominant species in the mixed coniferous and broad-leaved forests in the area around Changbai Mountain in Northeastern China. Five Manchurian ash tree-ring width chronologies were constructed from sites ranging along the elevational gradients of 750 m, 800 m, 900 m, 1000 m and 1100 m. We analyzed climate-growth relationships using Pearson correlation coefficients between ring-width indices and climate variables in two separate periods (before 1984 and after 1984), because instrumental temperature data have increased sharply after 1984. Along all of the elevational gradients, the sampled Manchurian ash forests show a higher growth rate and more sensitivity to climatic factors due to climate warming since the beginning of the 1984s. Comparatively, the forest growth at low elevation sites has increased faster than that at high elevation sites. If climate warming continues in northeastern China, further continuous and substantial increase in tree growth would substantially raise forest productivity in mixed coniferous and broad-leaved forests.     

Phylogenetic assemblage structure of North American trees is more strongly shaped by glacial–interglacial climate variability in gymnosperms than in angiosperms

How fast does biodiversity respond to climate change? The relationship of past and current climate with phylogenetic assemblage structure helps us to understand this question. Studies of angiosperm tree diversity in North America have already suggested effects of current water–energy balance and tropical niche conservatism. However, the role of glacial–interglacial climate variability remains to be determined, and little is known about any of these relationships for gymnosperms. Moreover, phylogenetic endemism, the concentration of unique lineages in restricted ranges, may also be related to glacial–interglacial climate variability and needs more attention. We used a refined phylogeny of both angiosperms and gymnosperms to map phylogenetic diversity, clustering and endemism of North American trees in 100‐km grid cells, and climate change velocity since Last Glacial Maximum together with postglacial accessibility to recolonization to quantify glacial–interglacial climate variability. We found: (1) Current climate is the dominant factor explaining the overall patterns, with more clustered angiosperm assemblages toward lower temperature, consistent with tropical niche conservatism. (2) Long‐term climate stability is associated with higher angiosperm endemism, while higher postglacial accessibility is linked to to more phylogenetic clustering and endemism in gymnosperms. (3) Factors linked to glacial–interglacial climate change have stronger effects on gymnosperms than on angiosperms. These results suggest that paleoclimate legacies supplement current climate in shaping phylogenetic patterns in North American trees, and especially so for gymnosperms.     

Shifts in trait means and variances in North American tree assemblages: species richness patterns are loosely related to the functional space

One of the key hypothesized drivers of gradients in species richness is environmental filtering, where environmental stress limits which species from a larger species pool gain membership in a local community owing to their traits. Whereas most studies focus on small‐scale variation in functional traits along environmental gradient, the effect of large‐scale environmental filtering is less well understood. Furthermore, it has been rarely tested whether the factors that constrain the niche space limit the total number of coexisting species. We assessed the role of environmental filtering in shaping tree assemblages across North America north of Mexico by testing the hypothesis that colder, drier, or seasonal environments (stressful conditions for most plants) constrain tree trait diversity and thereby limit species richness. We assessed geographic patterns in trait filtering and their relationships to species richness pattern using a comprehensive set of tree range maps. We focused on four key plant functional traits reflecting major life history axes (maximum height, specific leaf area, seed mass, and wood density) and four climatic variables (annual mean and seasonality of temperature and precipitation). We tested for significant spatial shifts in trait means and variances using a null model approach. While we found significant shifts in mean species’ trait values at most grid cells, trait variances at most grid cells did not deviate from the null expectation. Measures of environmental harshness (cold, dry, seasonal climates) and lower species richness were weakly associated with a reduction in variance of seed mass and specific leaf area. The pattern in variance of height and wood density was, however, opposite. These findings do not support the hypothesis that more stressful conditions universally limit species and trait diversity in North America. Environmental filtering does, however, structure assemblage composition, by selecting for certain optimum trait values under a given set of conditions.     

Species distribution modelling as a macroecological tool: a case study using New World amphibians

Although species distribution modelling (SDM) is widely accepted among the scientific community and is increasingly used in ecology, conservation biology and biogeography, methodological limitations generate potential problems for its application in macroecology. Using amphibian species richness in North and South America, we compare species richness patterns derived from SDM maps and ‘expert’ maps to evaluate if: 1) richness patterns derived from SDM are biased toward climate‐based explanations for diversity when compared to expert maps, since SDM methods are typically based on climatic variables; and 2) SDM is a reliable tool for generating richness maps in hyperrich regions where point occurrence data are limited for many species. We found that although three widely used SDM methods overestimated amphibian species richness in grid cells when compared to expert richness maps in both North and South America due to systematic overestimation of range sizes, diversity gradients were reasonably robust at broad scales. Further, climatic variables statistically explained patterns of richness at similar levels among the different richness sources, although climatic relationships were stronger in the much better known North America than in South America. We conclude that in the face of the high deforestation rates coupled with incomplete data on species distributions, especially in the tropics, SDM represents a useful macroecological tool for investigating broad‐scale richness patterns and the dynamics between species richness and climate.     

Phylogenetic structure of angiosperm trees in local forest communities along latitudinal and elevational gradients in eastern North America

Latitudinal and elevational gradients both represent thermal gradients. Assessing the consistency of the relationships between phylogenetic structure and climate between latitudinal and elevational gradients can provide insight into the mechanisms driving assembly of species from regional pools into local assemblages. The aim of this study is to compare patterns of phylogenetic structure measures for angiosperm tree species between latitudinal and elevational gradients, using a dataset of angiosperm tree species in 14 092 forest plots in eastern North America. We assessed whether these two gradients produce similar relationships between climate and phylogenetic structure, hypothesizing that they should differ in magnitude but not direction. We used correlation and regression analyses to assess the relation of measures of phylogenetic structure to elevation, latitude and climatic variables, which included minimum temperature, temperature seasonality, annual precipitation and precipitation seasonality. We found that 1) phylogenetic relatedness of angiosperm trees increases with decreasing temperature along both latitudinal and elevational gradients but the relationship between phylogenetic relatedness and temperature is steeper for elevational gradients than for latitudinal gradients; 2) the tip-weighted metric of phylogenetic relatedness (nearest taxon index) is more strongly correlated with climatic variables than the basal-weighted metric of phylogenetic relatedness (net relatedness index); 3) winter cold temperature exerts a stronger effect on community assembly of angiosperm trees than does temperature seasonality. These results suggest that winter cold temperature, rather than temperature seasonality, drives phylogenetic structure of plants in local forest communities, and that species distributions along elevational gradients are more in equilibrium with temperature, compared with those along latitudinal gradients.     

The phylogeographic architecture of the fucoid seaweed Ascophyllum nodosum: an intertidal ‘marine tree’ and survivor of more than one glacial–interglacial cycle

Aim Ascophyllum nodosum (L.) Le Jolis is a dominant fucoid seaweed occurring along sheltered, rocky shores throughout the North Atlantic (but not in the Pacific), where it is a foundational species of the intertidal community. Its large size and vulnerability to ice‐scour have led to the hypothesis that contemporary populations in the north‐west Atlantic may be the result of de novo recolonization from the north‐east Atlantic since the Last Glacial Maximum (LGM) (c. 20 ka). We tested this hypothesis. Location Temperate North Atlantic rocky intertidal between c. 42 and 65° N latitude. Methods More than 1300 individuals from 28 populations were sampled from across the entire range of A. nodosum and genotyped for six microsatellite loci, and > 500 individuals were genotyped for two mitochondrial loci, an intergenic spacer (IGS) and the tRNA (W) gene (trnW). Population structure and historical demography were analysed in a standard population genetics and coalescence framework. Results Based on the presence of private alleles and haplotypes, we found that A. nodosum has survived on both sides of the Atlantic (since before the LGM, dating back to at least the penultimate Eemian interglacial) with similar effective population sizes and divergence times (1.2 and 0.8 Ma). Dispersal has been predominantly from Europe to North America, and there is very weak present‐day population differentiation across the North Atlantic. Diversity measures provided additional support for determining the location of refugia. Main conclusions Ascophyllum nodosum was apparently little affected by the LGM, although contemporary climate change is likely to have major effects on its latitudinal distribution on both sides of the North Atlantic. It is a very long‐lived species, analogous in virtually all demographic aspects to a tree – resistant to extinction but vulnerable to catastrophic events. The Brittany peninsula is a hotspot of genetic diversity worthy of conservation.     

Native tree regeneration in native tree plantations: understanding the contribution of Araucaria angustifolia to biodiversity conservation in the threatened Atlantic Forest in Argentina

Deforestation is a global process that has strongly affected the Atlantic Forest in South America, which has been recognised as a threatened biodiversity hotspot. An important proportion of deforested areas were converted to forest plantations. Araucaria angustifolia is a native tree to the Atlantic Forest, which has been largely exploited for wood production and is currently cultivated in commercial plantations. An important question is to what extent such native tree plantations can be managed to reduce biodiversity loss in a highly diverse and vulnerable forest region . We evaluated the effect of stand age, stand basal area, as a measure of stand density, and time since last logging on the density and richness of native tree regeneration in planted araucaria stands that were successively logged over 60 years, as well as the differences between successional groups in the response of plant density to stand variables. We also compared native tree species richness in planted araucaria stands to neighbouring native forest. Species richness was 71 in the planted stands (27 ha sampled) and 82 in native forest (18 ha sampled) which approximate the range of variation in species richness found in the native forests of the study area. The total abundance and species richness of native trees increased with stand age and time since last logging, but ecological groups differed in their response to such variables. Early secondary trees increased in abundance with stand age 3–8 times faster than climax or late secondary trees. Thus, the change in species composition is expected to continue for a long term. The difference in species richness between native forest and planted stands might be mainly explained by the difference in plant density. Therefore, species richness in plantations can contribute to local native tree diversity if practices that increase native tree density are implemented.