Quaternary and pre‐Quaternary historical legacies in the global distribution of a major tropical plant lineage

Aim The relative importance of current climate and past historical legacies is hotly debated. Here, we assess their role in determining the global distribution and diversity patterns of palms (Arecaceae), a widespread, species‐rich group of keystone ecological importance in tropical ecosystems. Location Global. Methods We assembled country‐level species lists world‐wide and compiled associated data on potential contemporary environmental drivers (current climate, habitat heterogeneity, area, and insularity), Quaternary glacial–interglacial climate change and major biogeographic regions to evaluate to what extent the global distribution and species richness patterns in palms reflect Quaternary climatic oscillations or regional effects reflecting pre‐Quaternary legacies. We also assessed for the first time if historical legacies differ between continents and islands, providing novel insights into determinants of insular species richness. Results Palm species richness was significantly affected by Quaternary climate changes and further differed between biogeographic regions even when both current environmental conditions and Quaternary climate changes were accounted for. In contrast, global limits to the distribution of the palm family were best explained by current temperature while biogeographic regional differences were unimportant and Quaternary climate change caused only a small constraint. Historical legacies were weak on islands, with only a small regional effect and no effect of Quaternary climate changes. Main conclusions Strong historical legacies supplement current environment as determinants of palm species richness. These primarily comprise pre‐Quaternary historical effects, reflected in low African species richness (possibly linked to pre‐Quaternary extinctions) and outstandingly high Neotropical and Indomalayan palm species richness (possibly linked to these regions' long‐term climatic suitability for palms). In contrast to species richness, the global distribution of the family range is largely in equilibrium with current climate. The small historical effects on islands are consistent with climatic buffering from their oceanic environment.     

Effects of two centuries of global environmental variation on phenology and physiology of Arabidopsis thaliana

Intraspecific trait variation is caused by genetic and plastic responses to environment. This intraspecific diversity is captured in immense natural history collections, giving us a window into trait variation across continents and through centuries of environmental shifts. Here we tested if hypotheses based on life history and the leaf economics spectrum explain intraspecific trait changes across global spatiotemporal environmental gradients. We measured phenotypes on a 216‐year time series of Arabidopsis thaliana accessions from across its native range and applied spatially varying coefficient models to quantify region‐specific trends in trait coordination and trait responses to climate gradients. All traits exhibited significant change across space or through time. For example, δ¹⁵N decreased over time across much of the range and leaf C:N increased, consistent with predictions based on anthropogenic changes in land use and atmosphere. Plants were collected later in the growing season in more recent years in many regions, possibly because populations shifted toward more spring germination and summer flowering as opposed to fall germination and spring flowering. When climate variables were considered, collection dates were earlier in warmer years, while summer rainfall had opposing associations with collection date depending on regions. There was only a modest correlation among traits, indicating a lack of a single life history/physiology axis. Nevertheless, leaf C:N was low for summer‐ versus spring‐collected plants, consistent with a life history–physiology axis from slow‐growing winter annuals to fast‐growing spring/summer annuals. Regional heterogeneity in phenotype trends indicates complex responses to spatiotemporal environmental gradients potentially due to geographic genetic variation and climate interactions with other aspects of environment. Our study demonstrates how natural history collections can be used to broadly characterize trait responses to environment, revealing heterogeneity in response to anthropogenic change.     

Will climate change affect ectoparasite species ranges?

Aim  Over the next 100 years, human-driven climate change and resulting changes in species occurrences will have global impacts on biodiversity, ecosystem function, and human health. Here we examine how climate change may affect the occurrences of tick species in Africa and alter the suitability of habitat outside Africa for African ticks.
Location  Africa and the world.
Methods  We predicted continental and global changes in habitat suitability for each of 73 African tick species, using multiple regression models in different climate change scenarios that cover a wide range of uncertainty.
Results  Global habitat suitability improves for nearly all tick species under each of a representative range of eight climate change scenarios. Depending on the scenario, African tick species experience an average increase in global habitat suitability of between 1 million and 9 million square kilometres between 1990 and 2100.
Main conclusions  The potential for successful translocations of ticks and their pathogens from Africa to the rest of the world is likely to increase over the next 100 years. Although the general trend is one of range expansion, there are winners and losers among tick species in each scenario, suggesting that tick community composition will be disrupted substantially by climate change. If this is also typical of other invertebrates, then climate change will disrupt not only the geographic location of communities but also their structure. Changes in tick communities are also likely to influence tick-borne pathogens.     

Cold truths: how winter drives responses of terrestrial organisms to climate change

Winter is a key driver of individual performance, community composition, and ecological interactions in terrestrial habitats. Although climate change research tends to focus on performance in the growing season, climate change is also modifying winter conditions rapidly. Changes to winter temperatures, the variability of winter conditions, and winter snow cover can interact to induce cold injury, alter energy and water balance, advance or retard phenology, and modify community interactions. Species vary in their susceptibility to these winter drivers, hampering efforts to predict biological responses to climate change. Existing frameworks for predicting the impacts of climate change do not incorporate the complexity of organismal responses to winter. Here, we synthesise organismal responses to winter climate change, and use this synthesis to build a framework to predict exposure and sensitivity to negative impacts. This framework can be used to estimate the vulnerability of species to winter climate change. We describe the importance of relationships between winter conditions and performance during the growing season in determining fitness, and demonstrate how summer and winter processes are linked. Incorporating winter into current models will require concerted effort from theoreticians and empiricists, and the expansion of current growing‐season studies to incorporate winter.     

Antagonistic effects of growing season and autumn temperatures on the timing of leaf coloration in winter deciduous trees

Autumn phenology remains a relatively neglected aspect in climate change research, which hinders an accurate assessment of the global carbon cycle and its sensitivity to climate change. Leaf coloration, a key indicator of the growing season end, is thought to be triggered mainly by high or low temperature and drought. However, how the control of leaf coloration is split between temperature and drought is not known for many species. Moreover, whether growing season and autumn temperatures interact in influencing the timing of leaf coloration is not clear. Here, we revealed major climate drivers of leaf coloration dates and their interactions using 154 phenological datasets for four winter deciduous tree species at 89 stations, and the corresponding daily mean/minimum air temperature and precipitation data across China's temperate zone from 1981 to 2012. Results show that temperature is more decisive than drought in causing leaf coloration, and the growing season mean temperature plays a more important role than the autumn mean minimum temperature. Higher growing season temperature and lower autumn minimum temperature would induce earlier leaf coloration date. Moreover, the mean temperature over the growing season correlates positively with the autumn minimum temperature. This implies that growing season mean temperature may offset the requirement of autumn minimum temperature in triggering leaf coloration. Our findings deepen the understanding of leaf coloration mechanisms in winter deciduous trees and suggest that leaf life‐span control depended on growing season mean temperature and autumn low temperature control and their interaction are major environmental cues. In the context of climate change, whether leaf coloration date advances or is delayed may depend on intensity of the offset effect of growing season temperature on autumn low temperature.     

Microhabitat specialization in a species-rich palm community in Amazonian Ecuador

1 Relationships between microhabitat variables (altitude, inclination, topographic position, drainage, canopy height) and the distribution and abundance of palms and palm-like plants in 50 ha of old-growth terra firme rain forest in the Yasuní National Park, lowland Amazonian Ecuador, were examined using 118 20 × 20 m plots laid out in a stratified random design.
2 If microhabitat niche differentiation is important for maintaining the species richness of the community, then (i) the distribution of the palms will be strongly influenced by microhabitat heterogeneity and (ii) palms of similar growth form will show antagonistic microhabitat relationships.
3 Mantel and cluster analyses showed that palm species distributions were strongly structured by topography. The main difference in species composition was between plots in the bottomland and plots on the upper slopes and hill tops.
4 Logistic and logit analyses showed that 20 of the 31 palm and palm-like taxa analysed had distributions that were significantly related to the microhabitat variables measured, mainly to topography but also to drainage and canopy height.
5 Spatial autocorrelation in the overall community structure was not explained by the microhabitat variables. Analyses of distributions or abundances of single species showed neighbourhood effects for seven taxa.
6 Antagonistic patterns of microhabitat preferences were recognizable among some species pairs of small palms, medium-sized palms and palm-like plants, but not among canopy palms.
7 It is concluded that microhabitat specialization is an important factor in maintaining the diversity of this palm community, while mass effects might also be important.     

Climate change increases the risk of malaria in birds

Malaria caused by Plasmodium parasites is one of the worst scourges of mankind and threatens wild animal populations. Therefore, identifying mechanisms that mediate the spread of the disease is crucial for both human health and conservation. Human‐induced climate change has been hypothesized to alter the geographic distribution of malaria pathogens. As the earth warms, arthropod vectors may display a general range expansion or may enjoy longer breeding season, both of which can enhance parasite transmission. Moreover, Plasmodium species may directly benefit for elevating temperatures, which provide stimulating conditions for parasite reproduction. To test for the link between climate change and malaria prevalence on a global scale for the first time, I used long‐term records on avian malaria, which is a key model for studying the dynamics of naturally occurring malarial infections. Following the variation in parasite prevalence in more than 3000 bird species over seven decades, I show that the infection rate by Plasmodium is strongly associated with temperature anomalies and has been augmented with accelerating tendency during the last 20 years. The impact of climate change on malaria prevalence varies across continents, with the strongest effects found for Europe and Africa. Migration habit did not predict susceptibility to the escalating parasite pressure by Plasmodium. Consequently, wild birds are at an increasing risk of malaria infection due to recent climate change, which can endanger both naïve bird populations and domesticated animals. The prevailing avian example may provide useful lessons for understanding the effect of climate change on malaria in humans.     

Impacts of climate change on the seasonal distribution of migratory caribou

Arctic ecosystems are especially vulnerable to global climate change as temperature and precipitation regimes are altered. An ecologically and socially highly important northern terrestrial species that may be impacted by climate change is the caribou, Rangifer tarandus . We predicted the current and potential future occurrence of two migratory herds of caribou [Rivière George herd (RG) and Rivière-aux-Feuilles (RAF) herd] under a Canadian General Circulation Model climate change scenario, across all seasons in the Québec–Labrador peninsula, using climatic and habitat predictor variables. Argos satellite-tracking collars have been deployed on 213 caribou between 1988 and 2003 with locations recorded every 4–5 days. In addition, we assembled a database of climate (temperature, precipitation, snowfall, timing and length of growing season) and habitat data obtained from the SPOT VEGETATION satellite sensor. Logistic regression models indicated that both climatic and physical habitat variables were significant predictors of current migratory caribou occurrence. Migratory caribou appeared to prefer regions with higher snowfall and lichen availability in the fall and winter. In the summer, caribou preferred cooler areas likely corresponding to a lower prevalence of insects, and they avoided disturbed and recently burnt areas. Climate change projections using climate data predicted an increased range for the RAF herd and decreased range for the RG herd during 2040–2069, limiting the herds to northeastern regions of the Québec–Labrador peninsula. Direct and indirect consequences of climate change on these migratory caribou herds possibly include alteration in habitat use, migration patterns, foraging behaviour, and demography, in addition to social and economic stress to arctic and subarctic native human populations.     

Convergent Evolution towards High Net Carbon Gain Efficiency Contributes to the Shade Tolerance of Palms (Arecaceae)

Most palm species occur in the shaded lower strata of tropical rain forests, but how their traits relate to shade adaptation is poorly understood. We hypothesized that palms are adapted to the shade of their native habitats by convergent evolution towards high net carbon gain efficiency (CGE_n), which is given by the maximum photosynthetic rate to dark respiration rate ratio. Leaf mass per area, maximum photosynthetic rate, dark respiration and N and P concentrations were measured in 80 palm species grown in a common garden, and combined with data of 30 palm species growing in their native habitats. Compared to other species from the global leaf economics data, dicotyledonous broad-leaved trees in tropical rainforest or other monocots in the global leaf economics data, palms possessed consistently higher CGE_n, achieved by lowered dark respiration and fairly high foliar P concentration. Combined phylogenetic analyses of evolutionary signal and trait evolution revealed convergent evolution towards high CGE_n in palms. We conclude that high CGE_n is an evolutionary strategy that enables palms to better adapt to shady environments than coexisting dicot tree species, and may convey advantages in competing with them in the tropical forest understory. These findings provide important insights for understanding the evolution and ecology of palms, and for understanding plant shade adaptations of lower rainforest strata. Moreover, given the dominant role of palms in tropical forests, these findings are important for modelling carbon and nutrient cycling in tropical forest ecosystems.     

黄淮海地区干旱变化特征及其对气候变化的响应

为了探究气候变化背景下黄淮海地区的干旱特征,基于黄淮海平原34个气象站点的1961—2012年气象数据,使用相对湿润指数探讨分析了近50年黄淮海地区冬小麦生长季及4个季节干旱的时空变化及其对气候变化的响应。结果表明:(1)在整个分析期内(1961—2011)冬小麦生长季干旱减轻,但是在近20年干旱有了加重的趋势,且干旱加重的趋势是一种突变现象。(2)黄淮海地区1961年以来,春季、冬季以及冬小麦生长季内均表现为不同程度的干旱,干旱频率都达到90%以上,其中春、冬两季最为干旱,3个时段整个黄淮海中北部地区都为高频干旱区域,且4个季节及冬小麦生长季干旱程度与干旱频率的区域分布均表现为由南向北递增的趋势。(3)黄淮海地区的干旱特征对降水、太阳辐射和相对湿度这3个气候要素的变化最为敏感。     

Determinants of palm species distributions across Africa: the relative roles of climate,non‐climatic environmental factors,and spatial constraints

Most of the Earth's biodiversity resides in the tropics. However, a comprehensive understanding of which factors control range limits of tropical species is still lacking. Climate is often thought to be the predominant range‐determining mechanism at large spatial scales. Alternatively, species’ ranges may be controlled by soil or other environmental factors, or by non‐environmental factors such as biotic interactions, dispersal barriers, intrinsic population dynamics, or time‐limited expansion from place of origin or past refugia. How species ranges are controlled is of key importance for predicting their responses to future global change. Here, we use a novel implementation of species distribution modelling (SDM) to assess the degree to which African continental‐scale species distributions in a keystone tropical group, the palms (Arecaceae), are controlled by climate, non‐climatic environmental factors, or non‐environmental spatial constraints. A comprehensive data set on African palm species occurrences was assembled and analysed using the SDM algorithm Maxent in combination with climatic and non‐climatic environmental predictors (habitat, human impact), as well as spatial eigenvector mapping (spatial filters). The best performing models always included spatial filters, suggesting that palm species distributions are always to some extent limited by non‐environmental constraints. Models which included climate provided significantly better predictions than models that included only non‐climatic environmental predictors, the latter having no discernible effect beyond the climatic control. Hence, at the continental scale, climate constitutes the only strong environmental control of palm species distributions in Africa. With regard to the most important climatic predictors of African palm distributions, water‐related factors were most important for 25 of the 29 species analysed. The strong response of palm distributions to climate in combination with the importance of non‐environmental spatial constraints suggests that African palms will be sensitive to future climate changes, but that their ability to track suitable climatic conditions will be spatially constrained.     

The Many Uses ofTrachycarpus fortunei (Arecaceae) in China

One of the most useful and widely grown palms in China is the windmill palm, Trachycarpus fortunei. It provides food for man and beast, fiber, structural materials, medicinal drugs, and a high grade of wax. The windmill palm, one of the hardiest of all palms, can be grown widely in subtropical and warm-temperate regions. It thus has the potential for production of unique palm products in regions where other palms will not grow.     

Winter climate change affects growing‐season soil microbial biomass and activity in northern hardwood forests

Understanding the responses of terrestrial ecosystems to global change remains a major challenge of ecological research. We exploited a natural elevation gradient in a northern hardwood forest to determine how reductions in snow accumulation, expected with climate change, directly affect dynamics of soil winter frost, and indirectly soil microbial biomass and activity during the growing season. Soils from lower elevation plots, which accumulated less snow and experienced more soil temperature variability during the winter (and likely more freeze/thaw events), had less extractable inorganic nitrogen (N), lower rates of microbial N production via potential net N mineralization and nitrification, and higher potential microbial respiration during the growing season. Potential nitrate production rates during the growing season were particularly sensitive to changes in winter snow pack accumulation and winter soil temperature variability, especially in spring. Effects of elevation and winter conditions on N transformation rates differed from those on potential microbial respiration, suggesting that N‐related processes might respond differently to winter climate change in northern hardwood forests than C‐related processes.     

Plant invasions differentially affected by diversity and dominant species in native‐ and exotic‐dominated grasslands

Plant invasions are an increasingly serious global concern, especially as the climate changes. Here, we explored how plant invasions differed between native‐ and novel exotic‐dominated grasslands with experimental addition of summer precipitation in Texas in 2009. Exotic species greened up earlier than natives by an average of 18 days. This was associated with a lower invasion rate early in the growing season compared to native communities. However, invasion rate did not differ significantly between native and exotic communities across all sampling times. The predictors of invasion rate differed between native and exotic communities, with invasion being negatively influenced by species richness in natives and by dominant species in exotics. Interestingly, plant invasions matched the bimodal pattern of precipitation in Temple, Texas, and did not respond to the pulse of precipitation during the summer. Our results suggest that we will need to take different approaches in understanding of invasion between native and exotic grasslands. Moreover, with anticipated increasing variability in precipitation under global climate change, plant invasions may be constrained in their response if the precipitation pulses fall outside the normal growing period of invaders.     

No adaptation to altitude in the invasive plant Erigeron annuus in the Swiss Alps

The altitudinal distribution of plants is restricted by various environmental factors, with climatic conditions being one of the primary constraints. Here, we investigate what limits the altitudinal range of the introduced species Erigeron annuus in the Swiss Alps. We planted offspring of E. annuus plants originating from different altitudes into two common gardens, one located at an altitude representing the main area of distribution (400 m) and the other close to the current altitudinal limit of E. annuus in Switzerland (1000 m). In both common gardens all established plants survived and grew vigorously during the growing season. However, there was high winter mortality of seedlings at 1000 m. Furthermore, plant phenology was delayed and reproductive output was reduced at 1000 m, although the seeds produced were larger. The general lack of adaptation to altitude and only moderate levels of plasticity suggest that there is little potential for E. annuus to persist beyond its current altitudinal limit in the Swiss Alps. However, climate warming might promote the upward range expansion of E. annuus by reducing winter mortality and by increasing the chance of producing seeds within the growing season.     

Winter climate change effects on soil C and N cycles in urban grasslands

Despite growing recognition of the role that cities have in global biogeochemical cycles, urban systems are among the least understood of all ecosystems. Urban grasslands are expanding rapidly along with urbanization, which is expected to increase at unprecedented rates in upcoming decades. The large and increasing area of urban grasslands and their impact on water and air quality justify the need for a better understanding of their biogeochemical cycles. There is also great uncertainty about the effect that climate change, especially changes in winter snow cover, will have on nutrient cycles in urban grasslands. We aimed to evaluate how reduced snow accumulation directly affects winter soil frost dynamics, and indirectly greenhouse gas fluxes and the processing of carbon (C) and nitrogen (N) during the subsequent growing season in northern urban grasslands. Both artificial and natural snow reduction increased winter soil frost, affecting winter microbial C and N processing, accelerating C and N cycles and increasing soil : atmosphere greenhouse gas exchange during the subsequent growing season. With lower snow accumulations that are predicted with climate change, we found decreases in N retention in these ecosystems, and increases in N₂O and CO₂ flux to the atmosphere, significantly increasing the global warming potential of urban grasslands. Our results suggest that the environmental impacts of these rapidly expanding ecosystems are likely to increase as climate change brings milder winters and more extensive soil frost.     

Divergent carbon cycle response of forest and grass‐dominated northern temperate ecosystems to record winter warming

Northern temperate ecosystems are experiencing warmer and more variable winters, trends that are expected to continue into the foreseeable future. Despite this, most studies have focused on climate change impacts during the growing season, particularly when comparing responses across different vegetation cover types. Here we examined how a perennial grassland and adjacent mixed forest ecosystem in New Hampshire, United States, responded to a period of highly variable winters from 2014 through 2017 that included the warmest winter on record to date. In the grassland, record‐breaking temperatures in the winter of 2015/2016 led to a February onset of plant growth and the ecosystem became a sustained carbon sink well before winter ended, taking up roughly 90 g/m² more carbon during the winter to spring transition than in other recorded years. The forest was an unusually large carbon source during the same period. While forest photosynthesis was restricted by leaf‐out phenology, warm winter temperatures caused large pulses of ecosystem respiration that released nearly 230 g C/m² from February through April, more than double the carbon losses during that period in cooler years. These findings suggest that, as winters continue to warm, increases in ecosystem respiration outside the growing season could outpace increases in carbon uptake during a longer growing season, particularly in forests that depend on leaf‐out timing to initiate carbon uptake. In ecosystems with a perennial leaf habit, warming winter temperatures are more likely to increase ecosystem carbon uptake through extension of the active growing season. Our results highlight the importance of understanding relationships among antecedent winter conditions and carbon exchange across land‐cover types to understand how landscape carbon exchange will change under projected climate warming.     

Climate response of Picea schrenkiana based on tree-ring width and maximum density

The effect of global warming on alpine forests is complex. It is crucial, therefore, to investigate the effects of climate change on the radial growth of trees at different altitudes. The tree growth–climate relationship remains poorly understood at large spatial scales in the Tianshan Mountains, China. Schrenk spruce (P. schrenkiana) is a unique tree species to this area. In this study, we collected tree-ring width and maximum density data from nine plots along an altitudinal gradient. Results showed that altitude affected both tree-ring width and maximum density. At high altitudes, tree-ring width was positively correlated with temperature in February of the current year. Tree-ring width was also positively correlated with precipitation in July of the previous year, and January and July of the current year, and negatively correlated with the monthly diurnal temperature range (DTR). At low altitudes, tree-ring width was negatively correlated with temperature in the early growing season and the growing season. Tree-ring width was positively correlated with precipitation in June and September of the previous year, and May of the current year. The tree-ring maximum density was positively correlated with temperature and the DTR of the growing season, and negatively correlated with precipitation in winter and growing season. Moving correlation analysis showed that the positive response of tree-ring width to precipitation in the growing season was enhanced over time at high altitudes. In the low-altitude trees, the negative response of tree-ring width to temperature in the growing season was reduced, while the positive response to precipitation in the growing season was enhanced. The positive response relationship between tree-ring maximum density and the temperature in July weakened over time. At low altitudes, the negative response of tree-ring maximum density to winter precipitation was strengthened, and a stable negative response to July precipitation was observed. As the climate becomes wetter and warmer in the Tianshan Mountains, our results suggest that the radial growth of trees may benefit at elevations above 2400 m a.s.l. There was no obvious elevation limit for the increase in tree-ring maximum density. These findings provide a basis for sustainable forest management under global climate change.     

Comparative dendroecological characterisation of Ailanthus altissima (Mill.) Swingle in its native and introduced range

Knowledge on the ecology of tree species in both their native and introduced range can increase the understanding of their successful establishment and spread outside the native range. Here, we analysed radial growth patterns of Ailanthus altissima (Mill.) Swingle in two sites in its native range in eastern China and in two sites in the introduced range in southern Switzerland, where it started to disperse into forests in the 1950s. Growth rates were similar despite lower amounts of growing season precipitation in China. Furthermore, we found negative correlations between annual radial growth and average temperatures in the growing season at the warmest of the four sites, which suggest that radial growth of A. altissima starts to be limited by average growing season temperatures above 21 °C. Regarding wood anatomy, we did not find clear correlations between vessel lumen area and monthly temperature or precipitation at the time of tissue formation in spring. Overall, our results demonstrate that A. altissima has the potential to grow in drier conditions than currently found in Switzerland, which is in line with previous studies.     

The timing of autumn senescence is affected by the timing of spring phenology: implications for predictive models

Autumn senescence regulates multiple aspects of ecosystem function, along with associated feedbacks to the climate system. Despite its importance, current understanding of the drivers of senescence is limited, leading to a large spread in predictions of how the timing of senescence, and thus the length of the growing season, will change under future climate conditions. The most commonly held paradigm is that temperature and photoperiod are the primary controls, which suggests a future extension of the autumnal growing season as global temperatures rise. Here, using two decades of ground‐ and satellite‐based observations of temperate deciduous forest phenology, we show that the timing of autumn senescence is correlated with the timing of spring budburst across the entire eastern United States. On a year‐to‐year basis, an earlier/later spring was associated with an earlier/later autumn senescence, both for individual species and at a regional scale. We use the observed relationship to develop a novel model of autumn phenology. In contrast to current phenology models, this model predicts that the potential response of autumn phenology to future climate change is strongly limited by the impact of climate change on spring phenology. Current models of autumn phenology therefore may overpredict future increases in the length of the growing season, with subsequent impacts for modeling future CO₂ uptake and evapotranspiration.