Migration Lag Research Articles

Climate mismatches with ectomycorrhizal fungi contribute to migration lag in North American tree range shifts

Climate change will likely shift plant and microbial distributions, creating geographic mismatches between plant hosts and essential microbial symbionts (e.g., ectomycorrhizal fungi, EMF). The loss of historical interactions, or the gain of novel associations, can have important consequences for biodiversity, ecosystem processes, and plant migration potential, yet few analyses exist that measure where mycorrhizal symbioses could be lost or gained across landscapes. Here, we examine climate change impacts on tree-EMF codistributions at the continent scale. We built species distribution models for 400 EMF species and 50 tree species, integrating fungal sequencing data from North American forest ecosystems with tree species occurrence records and long-term forest inventory data. Our results show the following: 1) tree and EMF climate suitability to shift toward higher latitudes; 2) climate shifts increase the size of shared tree-EMF habitat overall, but 35% of tree-EMF pairs are at risk of declining habitat overlap; 3) climate mismatches between trees and EMF are projected to be greater at northern vs. southern boundaries; and 4) tree migration lag is correlated with lower richness of climatically suitable EMF partners. This work represents a concentrated effort to quantify the spatial extent and location of tree-EMF climate envelope mismatches. Our findings also support a biotic mechanism partially explaining the failure of northward tree species migrations with climate change: reduced diversity of co-occurring and climate-compatible EMF symbionts at higher latitudes. We highlight the conservation implications for identifying areas where tree and EMF responses to climate change may be highly divergent.

Climate and dispersal limitation drive tree species range shifts in post-glacial Europe: results from dynamic simulations

IntroductionThe ability of species to colonize newly suitable habitats under rapid climate change can be constrained by migration processes, resulting in a shift of the leading edge lagging behind the ameliorating climate, i.e. migration lag. The importance and extent of such migration lags during the forest expansion after the Last Glacial Maximum (LGM) are still debated. Similarly, the relative importance of the main drivers of post-glacial vegetation dynamics (temperature, dispersal limitation, and competition) is still discussed in the literature.MethodsWe used the dynamic global vegetation model LPJ-GM 2.0 to reconstruct the range shifts of 16 competing major European tree species after the LGM (18.5 ka BP) until recent times (0 ka BP). We simulated two dispersal modes by allowing free establishment whenever the climatic conditions suited the species (free dispersal), or by accounting for migration processes in the simulated vegetation dynamics (dispersal limitation). We then calculated thermal and range shift velocities, competition at establishment, thermal and dispersal lags for each species and dispersal mode. Finally, we compared our simulated range shift velocities with pollen-derived migration rates.ResultsThe simulation assuming limited dispersal resulted in more accurate migration rates as compared to pollen-derived migration rates and spreading patterns. We found no marked migration lags in the post-glacial establishment of pioneer species (Pinus sylvestris and Betula pubescens). Under the free dispersal mode, the remaining temperate species expanded rapidly and almost synchronously across central Europe upon climate warming (Bølling-Allerød interstadial). Differently, the northward spread of temperate species simulated under dispersal limitation happened mainly during the Holocene and in successive waves, with late spreaders (e.g. Fraxinus excelsior) experiencing multi-millennial dispersal lags and higher competition.DiscussionOur simulation under dispersal constraints suggests that the post-glacial tree expansion in Europe was mainly driven by species-specific thermal requirements and dispersal capacity, which in turn affected the order of taxa establishment and thus the degree of competition. Namely, taxa with less cold-tolerance and relatively low dispersal ability experienced the highest migration lags, whereas the establishment of pioneer species was mostly in equilibrium with the climate.

Ecological attributes promoting intra-continental range-expansion of a native annual forb triggered by intensified land-use

Intra-continental range-expansion of native species tracking human-induced environmental changes has become an important phenomenon, and recently has been suggested to be recognized as a distinct biogeographic category, namely neonative. However, it remains difficult to analyze how range-expansions are triggered by certain environmental changes and which biological and ecological species attributes are involved. We compared biological and ecological attributes and the performance in different test environments during the entire life cycle of a range-expanding neonative in Romania, Xeranthemum cylindraceum, with a congeneric resident native, X. annuum, through a series of controlled experiments. Both species proved to share several biological and ecological attributes, e.g. high potential for long-distance dispersal by multiple vectors, biochemical defense against herbivores by means of cyanogenic compounds, and surprisingly, they were found to have similar germination and performance niches throughout the range of climatic environments tested by us. Differences between the two species, a broader climatic and habitat niche, higher germination rate and viability of seeds can give explanation to the successful spread beyond the historical range of X. cylindraceum. However, based on shared biological attributes between the two species, which confer the potential to spread, and the considerably higher seed output found in the case of the resident native, X. annuum is equally prepared to expand its range. With changing climate and persisting human-induced disturbance, in this case intensive grazing by sheep, we may expect the spread of this species after passing the presumed migration lag phase.

Assisted Species Migration of Joshua Trees

The Joshua tree evolved in a complex way with its environment, pollinator, and seed dispersers over millions of years. Its survival as a species is now imminently threatened by climate change. Many factors prevent it from migrating to a cooler range quickly enough to keep up with the planet’s current rate of warming. This paper explores the viability of assisted migration for the Joshua tree, where humans help it move to escape extinction. Several studies are examined. One persuasively shows that the Joshua tree had a range contraction when the climate warmed at the end of the Ice Age and that present warming will cause a similar, drastic range reduction. Other studies look at factors such as soil, CO2, pollinator mutualism, and seed longevity to determine if assisted migration would be successful. The ethics of assisted migration is also explored. This paper concludes that humans must try to assist the Joshua tree to migrate but that it will be difficult given the complexities of its evolution, its relationship to its environment, and a migration lag that is not completely understood.

Resurgence of warmth-demanding tree species and a common pending thermophilization in subalpine and northern boreal Sweden-an ecological signal of post-Little Ice Age climate improvement

Largely consistent with general predictions and earlier empirical studies, it appears that post-Little Ice Age climate warming has started to affect large-scale biogeographic patterns in northern Sweden. Long-term monitoring in subalpine and adjacent regions reveals sparse spread of broadleaved thermophilic tree species. Saplings of Quercus robur, Ulmus glabra, Acer platanoides, Alnus glutinosa and Betula pendula have responded to recent climate warming by jump-dispersal in the order of 50-300 km northwards and 500-800 m upwards, relative to their natural range limits. Consistent with treeline rise by boreal tree species, the thermophilies have reinvaded regions where they grew during the warmest phase of the Holocene, 9500-8000 years ago, but were subsequently extirpated by the Neoglacial cooling. Confined to the past 20 years or so, the unique observations of recent termophilies comply with background climate data, i.e. warming of all seasons. These results may contribute to more realistic vegetation models by stressing that the distributions of certain plant species are able to track climate warming without substantial migrational lag. Hitherto, vegetation and climate evolution appear to be well within the frames of natural dynamics during the postglacial era, although mechanisms may differ.

Linking multiple hypotheses to a unifying framework of range‐size variation: A case study with American oaks (Quercus spp.)

AbstractAimClosely related species vary greatly in range size. To understand what drives range‐size variation, we established an integrative framework focusing on two causal pathways: the amount of currently suitable habitat (ASH) and range filling (i.e., the occupancy of ASH). Instead of testing different hypotheses in isolation, we linked four hypotheses to this unifying framework: we tested the niche breadth and niche position hypotheses, which explain range‐size variation via effects on ASH; we also tested the colonization ability and post‐glacial migration lag hypotheses, which explain range‐size variation via range filling.LocationThe Americas.Time periodLast Glacial Maximum (LGM) to present.Major taxa studiedOne hundred and eighty‐three oak species.MethodsWe extracted locality records and measured range size as the area of occupancy (AOO) and extent of occurrence (EOO). We used Maxent models and current environmental layers to quantify ASH, niche breadth and niche position. We used seven phenotypic traits as proxies of colonization ability. We calculated post‐glacial accessibility to currently suitable habitat, in addition to the proportion of currently suitable habitat covered by LGM ice sheets. Using structural equation models and regression models, we tested the four hypotheses. Finally, we examined how ASH and range filling contributed interactively to range‐size variation by quantifying variance and covariance.ResultsOur results supported all four hypotheses. Additionally, we found that variance in ASH and range filling contributed to a similar extent to variance in AOO, with almost zero covariance between ASH and range filling. In contrast, range filling accounted for almost all the variance in EOO, and we detected a significant negative covariance between ASH and range filling.Main conclusionsIn oaks, factors associated with range filling are at least as important as niche properties in determining range size. Our framework is generalizable to other study systems for testing the contributions of two pathways, ASH and range filling, to range‐size variation.

Predicting range shifts of African apes under global change scenarios

AbstractAimModelling African great ape distribution has until now focused on current or past conditions, while future scenarios remain scarcely explored. Using an ensemble forecasting approach, we predicted changes in taxon‐specific distribution under future scenarios of climate, land use and human populations for (1) areas outside protected areas (PAs) only (assuming complete management effectiveness of PAs), (2) the entire study region and (3) interspecies range overlap.LocationTropical Africa.MethodsWe compiled occurrence data (n = 5,203) on African apes from the IUCN A.P.E.S. database and extracted relevant climate‐, habitat‐ and human‐related predictors representing current and future (2050) conditions to predict taxon‐specific range change under a best‐ and a worst‐case scenario, using ensemble forecasting.ResultsThe predictive performance of the models varied across taxa. Synergistic interactions between predictors are shaping African ape distribution, particularly human‐related variables. On average across taxa, a range decline of 50% is expected outside PAs under the best scenario if no dispersal occurs (61% in worst scenario). Otherwise, an 85% range reduction is predicted to occur across study regions (94% worst). However, range gains are predicted outside PAs if dispersal occurs (52% best, 21% worst), with a slight increase in gains expected across study regions (66% best, 24% worst). Moreover, more than half of range losses and gains are predicted to occur outside PAs where interspecific ranges overlap.Main ConclusionsMassive range decline is expected by 2050, but range gain is uncertain as African apes will not be able to occupy these new areas immediately due to their limited dispersal capacity, migration lag and ecological constraints. Given that most future range changes are predicted outside PAs, Africa's current PA network is likely to be insufficient for preserving suitable habitats and maintaining connected ape populations. Thus, conservation planners urgently need to integrate land use planning and climate change mitigation measures at all decision‐making levels both in range countries and abroad.

Hurricanes overcome migration lag and shape intraspecific genetic variation beyond a poleward mangrove range limit.

Expansion of many tree species lags behind climate change projections. Extreme storms can rapidly overcome this lag, especially for coastal species, but how will storm-driven expansion shape intraspecific genetic variation? Do storms provide recruits only from the nearest sources, or from more distant sources? Answers to these questions have ecological and evolutionary implications, but empirical evidence is absent from the literature. In 2017, Hurricane Irma provided an opportunity to address this knowledge gap at the northern range limit of the neotropical black mangrove (Avicennia germinans) on the Atlantic coast of Florida, USA. We observed massive post-hurricane increases in beach-stranded A. germinans propagules at, and past, this species' present day range margin when compared to a previously surveyed nonhurricane year. Yet, propagule dispersal does not guarantee subsequent establishment and reproductive success (i.e., effective dispersal). We also evaluated prior effective dispersal along this coastline with isolated A. germinans trees identified beyond the most northern established population. We used 12 nuclear microsatellite loci to genotype 896 hurricane-driven drift propagules from nine sites and 10 isolated trees from four sites, determined their sources of origin, and estimated dispersal distances. Almost all drift propagules and all isolated trees came from the nearest sources. This research suggests that hurricanes are a prerequisite for poleward range expansion of a coastal tree species and that storms can shape the expanding gene pool by providing almost exclusively range-margin genotypes. These insights and empirical estimates of hurricane-driven dispersal distances should improve our ability to forecast distributional shifts of coastal species.

Extensive mismatches between species distributions and performance and their relationship to functional traits

Mismatches between species distributions and their optimal habitat are predicted by ecological theory and will affect species responses to changing climate. However, empirical tests lack consensus on the prevalence of such mismatches and their underlying mechanisms. Here we present a conceptual framework to quantify the mismatch between optimal conditions for species occurrence and multiple measures of population and individual performance (density, adult growth and survival, and recruitment) and the associated performance reduction, or cost. We quantified these mismatches for 59 tree species in the western US along a soil water balance gradient and found high variability in mismatches among species and among performance measures, often resulting in high costs. We used functional traits to explore how dispersal limitation, migration lags, and competitive exclusion may cause mismatches. Overall, the large variability in mismatches, their costs and the relationship with functional traits highlight the nuanced relationships between species' performance and their distributions.

Arctic shrub colonization lagged peak postglacial warmth: Molecular evidence in lake sediment from Arctic Canada.

Arctic shrubification is an observable consequence of climate change, already resulting in ecological shifts and global-scale climate feedbacks including changes in land surface albedo and enhanced evapotranspiration. However, the rate at which shrubs can colonize previously glaciated terrain in a warming world is largely unknown. Reconstructions of past vegetation dynamics in conjunction with climate records can provide critical insights into shrubification rates and controls on plant migration, but paleoenvironmental reconstructions based on pollen may be biased by the influx of exotic pollen to tundra settings. Here, we reconstruct past plant communities using sedimentary ancient DNA (sedaDNA), which has a more local source area than pollen. We additionally reconstruct past temperature variability using bacterial cell membrane lipids (branched glycerol dialkyl glycerol tetraethers) and an aquatic productivity indicator (biogenic silica) to evaluate the relative timing of postglacial ecological and climate changes at a lake on southern Baffin Island, Arctic Canada. The sedaDNA record tightly constrains the colonization of dwarf birch (Betula, a thermophilous shrub) to 5.9±0.1ka, ~3ka after local deglaciation as determined by cosmogenic 10 Be moraine dating and >2ka later than Betula pollen is recorded in nearby lake sediment. We then assess the paleovegetation history within the context of summer temperature and find that paleotemperatures were highest prior to 6.3ka, followed by cooling in the centuries preceding Betula establishment. Together, these molecular proxies reveal that Betula colonization lagged peak summer temperatures, suggesting that inefficient dispersal, rather than climate, may have limited Arctic shrub migration in this region. In addition, these data suggest that pollen-based climate reconstructions from high latitudes, which rely heavily on the presence and abundance of pollen from thermophilous taxa like Betula, can be compromised by both exotic pollen fluxes and vegetation migration lags.

Experimental test of assisted migration for conservation of locally range-restricted plants in Alberta, Canada

Given projected rates of climate change, species with limited dispersal may be unable to migrate at the pace necessary to maintain their current climate niches. This could lead to increased risk of extirpation or extinction, especially for locally range-restricted species within fragmented landscapes. Assisted migration has been suggested as a proactive conservation tool to mitigate these risks. We tested assisted migration for Liatris ligulistylis and Houstonia longifolia, two perennial forbs considered ‘vulnerable’ and ‘imperilled’, respectively, in Alberta, Canada, where they are at their northern and western range limits. Both mature plants and seeds were translocated to replicate sites at four geographic locations along a north-south gradient representing the current ranges of the species (central) and areas south (warmer) and north (cooler) of their current range. L. ligulistylis adult plants thrived ∼500 km north of the species current range with survival, growth, and flowering similar to or exceeding performance in the current range, the influence of soil was also tested by comparing the performance of transplanted mature plants in soil from the source location versus the translocation (recipient) site. Plants planted into soil from the source location had increased flower bud production at all sites. Seedling establishment was significantly higher at sites north of the current range, but much lower in the southern locations. These results suggest that L. ligulistylis is in climate disequilibrium, potentially due to migration lags, and that it might be vulnerable to near-future climate vulnerability. For H. longifolia, the influence of flower morph type and location were tested. Only 8 out 130 translocated adult plants survived, five with thrum flowers and three with pin flowers; no seedling establishment was observed in the first growing season, which experienced drier than normal conditions. Among the eight adult plants, seven survived in the central location and one in the north demonstrating specific habitat requirements and conditions that may make this species difficult for translocation and establishment. Overall, locally rare and range-restricted plants with limited dispersal demonstrate climate sensitivity to current conditions and potential for assisted migration, yet species-by-species testing is needed to understand vulnerability and efficacy of this approach.

Seed mass predicts migration lag of European trees

We reanalysed a dataset of tree distribution ranges in Europe to identify which plant traits best explain migration potential in woody species. Contrary to our intuition that tree longevity would best explain the ability of trees to migrate, we found that seed biomass was the only good descriptor of migration potential: trees with heavier seeds lag more. To cope with global warming, the majority of plants have either to migrate polewards or risk extinction. This is why conservationists value predictive models that can flag plant species that may not keep pace with global warming. To identify which plant traits best explain migration potential in woody species by reanalysing a dataset of tree distribution ranges in Europe. We used two statistical approaches to quantify migration lag. A direct approach compared frequency of large trees in the two latitudinal extremes and a modelling approach in which we first corrected data for the influence of temperature and then assessed the influence of latitude over the entire distribution of the tree species. Contrary to our intuition that tree longevity would best explain the ability of trees to migrate, we found that seed mass was the only good descriptor of migration potential: trees with heavier seeds lag more. We interpret our results in terms of the well-established trade-off between seed mass and seed production in spermatophytes and discuss the possible functional implications that will result from selectively losing large-seeded trees. In summary, we provide an empirical study on how woody communities will respond to global warming over the next years.

Alpine plant species have limited capacity for long-distance seed dispersal

Seed dispersal will be essential for plants to track future climate space, but dispersal capacity is rarely measured or incorporated into species distribution models. Using the entire alpine flora of the Snowy Mountains, south-eastern Australia, as a case study, we modelled the dispersal capacity of 198 species (93.4% of the flora) using the plant traits dispersal syndrome, seed mass, seed release height and growth form. The modelled maximum dispersal distances were mostly affected by dispersal syndrome of each species. The models reveal that 75% of species disperse up to 10 m, whilst 20% may disperse >100 m. Most species in this flora do not have any specific dispersal strategy, hence their inability to disperse >10 m. However, those species with longer modelled distances were dispersed by animals or wind (>600 and >140 m, respectively). This alpine flora has a low capacity for long-distance seed dispersal and is likely to suffer from migration lag as the local climate undergoes rapid changes.

Tree growth is more sensitive than species distributions to recent changes in climate and acidic deposition in the northeastern United States

Summary Tree‐growth responses to environmental change could provide early detection of shifts in forest composition and help facilitate ecosystem management and conservation. We studied forest tree responses to recent trends in climate and acidic deposition using analyses of tree rings and long‐term climate, deposition and forest plot data along an elevational climatic gradient in the northeastern United States. We analysed how (i) individual growth of dominant species (Picea rubens, Abies balsamea) and (ii) spatial distributions of all species, changed with elevation over time due to changing environment. We observed a mean 220 m upslope shift of temperature envelopes since the 1960s, consistent with regional climate warming, but found no evidence of synchronous upslope shifts in species abundance. Species' ranges were stable although some leaned upslope or downslope, suggesting species‐specific migration lags or controls on species' ranges. Compared to species distributions, the growth of dominant species was more responsive to environmental change. Although the basal area of P. rubens declined within its range since the 1960s, its growth has increased recently with increasing precipitation pH and to a lesser extent with warming climate. Abies balsamea has gradually increased in both basal area and density since the 1960s, with its growth responding to precipitation pH but not climate. Historically, P. rubens grew better at lower and A. balsamea at higher elevations, but these elevation effects appeared to be mediated primarily by moisture, and have disappeared over time. Synthesis and applications. Mean tree‐growth responses to changing climate (temperature, moisture) and precipitation chemistry were more consistent and more clearly detectable than shifts in tree species' ranges, suggesting that monitoring tree growth across climatically controlled species' ranges (e.g. along elevational or latitudinal gradients) may provide a powerful tool for early detection of potential future changes in forest composition in a changing environment.

Patterns and dynamics of European vegetation change over the last 15,000 years

AbstractAimPalaeoecological reconstructions document past vegetation change, with estimates of fast shifts in species distributions. The resulting rates of plant spread are often not matched by model simulations of climate‐driven vegetation dynamics. Genetic surveys of extant plant populations document directions of the post‐glacial spread of trees, challenging traditional interpretations. Our aim is to examine an updated continental pollen data set from Europe in the light of the new ideas about vegetation dynamics emerging from genetic research and vegetation modelling studies.LocationEurope.MethodsWe use pollen data from the European Pollen Database (EPD) to construct interpolated maps of pollen percentages documenting changes in the distribution and abundance of major plant genera and the grass family in Europe over the last 15,000 years.ResultsOur analyses confirm high rates of post‐glacial spread with at least 1000 m year−1 for Corylus, Ulmus and Alnus and average rates of 400 m year−1 for Tilia, Quercus, Fagus and Carpinus. The late Holocene expansions of Picea and Fagus populations in many European regions cannot be explained by migrational lag. Both taxa shift their population centres towards the Atlantic coast suggesting that climate may have played a role in the timing of their expansions. The slowest rates of spread were reconstructed for Abies.Main conclusionsThe calculated rates of post‐glacial plant spread are higher in Europe than those from North America, which may be due to more rapid shifts in climate mediated by the Gulf Stream and westerly winds. Late Holocene anthropogenic land use practices in Europe had major effects on individual taxa, which in combination with climate change contributed to shifts in areas of abundance and dominance. The high rates of spread calculated from the European pollen data are consistent with rapid tracking of early Holocene climate change by common tree species, documenting that plants can spread fast tracing their climate space, regardless of their dispersal strategy.

The 2017 IBS Alfred Russel Wallace Award

Announcements frontiers of biogeography 8.2, e31469, 2016 The 2017 Alfred Russel Wallace Award The IBS Board is pleased to announce that Mar- garet Bryan Davis will be the next to join the distinguished list of recipients of the Alfred Russel Wallace Award. The Wallace Award will be given at the upcoming IBS biennial meeting in Tucson, Arizona, USA (January 9-13, 2017), and was established by the IBS in 2004 to rec- ognize a lifetime of outstanding contributions by an eminent scholar in any subdiscipline of biogeography. Professor Emeritus Margaret Bryan Davis of the University of Minnesota has a long and distinguished career of outstanding contribu- tions to biogeography, and deserves credit for placing paleoecology squarely in the main- stream of biogeography and ecology. Her pa- pers combine magisterial reviews and thought- ful syntheses with a long series of carefully de- signed and elegant empirical studies aimed at addressing specific, focused questions. Professor Davis’ work established many of the current tenets of Quaternary biogeogra- phy: that species shift ranges in response to climate change, these changes are individualis- tic, and that as a consequence communities are transient. Other ideas, such as the role of path- ogens in forest history and the timescale of migrational lags, remain on-going topics of re- search and productive debate. Her ideas opened up new fields of fertile investigation that continue today, including postglacial pat- terns and rates of plant migration, the transi- ence of ecological communities, stand-scale forest history, the mid-Holocene hemlock de- cline in eastern North America, and how pollen data record vegetation. A mark of a truly great scientist is the ability to reconsider, and revise or even reject, strongly held views. Margaret Davis welcomed critiques, and demonstrated that conceptual breakthroughs were not always as effective as hoped. She stood her ground and asked diffi- cult questions, but when others provided com- pelling evidence, she yielded. Professor Davis was rigorous, critical, and set high standards for the field, always with a focus towards doing the best science and getting closer to the truth. She inspired countless young scientists by her professional example, as well as by the quality of her work and thinking. Professor Davis had – and continues to have – few equals in combining rigorous, ana- lytical approaches with broad, discipline- spanning syntheses. The IBS Board notes with thanks, the work of the Wallace Award Committee: Ingolf Kuhn, Mark Lomolino, Jonathan Losos, Susanne Renner, Kathy Willis, and Dov Sax (chair). International Biogeography Society Board frontiers of biogeography, ISSN 1948-6596 — © 2016 the authors; journal compilation © 2016 The International Biogeography Society

Tracking the leading edge of Fagus sylvatica in North-Western Iberia: Holocene migration inertia, forest succession and recent global change

The Iberian Peninsula constitutes the south-western limit of the European distribution of Fagus sylvatica L. However, although the Iberian North-West extreme would appear to be climatically suitable for the species, F. sylvatica is not present there. This fact has led to the suggestion that the species is not yet in equilibrium with the climate and that there is a migration lag in the post-glacial expansion of the species. The objective of this work is to understand the main biotic and abiotic factors driving F. sylvatica distribution and population dynamics in the Iberian Atlantic biogeographical region over recent decades. Furthermore, in the light of other studies which suggest that the expansion of F. sylvatica in North-Western Iberia might be related to the retraction of Q. petraea (Matt.) Leibl. forests, we also study the demographic trends of both F. sylvatica and Q. petraea along with oak-beech interaction processes to infer forest succession dynamics.Using data from the last two cycles of the Spanish National Forest Inventory (1986–2012) for the study area (the Iberian Atlantic biogeographical region); dominance, population structure, recruitment and basal area increment were analyzed in different forest types for the two target species. General linear models and Bayesian structural equation modelling techniques were also applied to study the direct and indirect drivers of recruitment and forest succession.Contrary to what might be expected under the current conditions of climatic change, the population of F. sylvatica in North-Western Iberia is expanding, the basal area increment of F. sylvatica increasing westwards and new recruitment occurring in the lowlands. Accordingly, the Iberian Atlantic biogeographical region may be considered one of the leading edges of F. sylvatica. Our results also identify an inter-specific relationship between Q. petraea and F. sylvatica which negatively affects Q. petraea. The findings demonstrate that Q. petraea forests are being replaced by F. sylvatica forests in North-Western Iberia. These results not only confirm a previous biogeographical hypothesis but also provide new leads for forest management and conservation strategies under current and future climatic conditions.

The regional species richness and genetic diversity ofArctic vegetation reflect both past glaciations and current climate

AbstractAimTheArctic has experienced marked climatic differences between glacial and interglacial periods and is now subject to a rapidly warming climate. Knowledge of the effects of historical processes on current patterns of diversity may aid predictions of the responses of vegetation to future climate change. We aim to test whether plant species and genetic diversity patterns are correlated with time since deglaciation at regional and local scales. We also investigate whether species richness is correlated with genetic diversity in vascular plants.LocationCircumarctic.MethodsWe investigated species richness of the vascular plant flora of 21 floristic provinces and examined local species richness in 6215 vegetation plots distributed across theArctic. We assessed levels of genetic diversity inferred from amplified fragment length polymorphism variation across populations of 23 commonArctic species. Correlations between diversity measures and landscape age (time since deglaciation) as well as variables characterizing current climate were analysed using spatially explicit simultaneous autoregressive models.ResultsRegional species richness of vascular plants and genetic diversity were correlated with each other, and both showed a positive relationship with landscape age. Plot species richness showed differing responses for vascular plants, bryophytes and lichens. At this finer scale, the richness of vascular plants was not significantly related to landscape age, which had a small effect size compared to the models of bryophyte and lichen richness.Main conclusionOur study suggests that imprints of past glaciations inArctic vegetation diversity patterns at the regional scale are still detectable today. SinceArctic vegetation is still limited by post‐glacial migration lag, it will most probably also exhibit lags in response to current and future climate change. Our results also suggest that local species richness at the plot scale is more determined by local habitat factors.

Climate-suitable planting as a strategy for maintaining forest productivity and functional diversity.

Within the time frame of the longevity of tree species, climate change will change faster than the ability of natural tree migration. Migration lags may result in reduced productivity and reduced diversity in forests under current management and climate change. We evaluated the efficacy of planting climate-suitable tree species (CSP), those tree species with current or historic distributions immediately south of a focal landscape, to maintain or increase aboveground biomass productivity, and species and functional diversity. We modeled forest change with the LANDIS-II forest simulation model for 100 years (2000-2100) at a 2-ha cell resolution and five-year time steps within two landscapes in the Great Lakes region (northeastern Minnesota and northern lower Michigan, USA). We compared current climate to low- and high-emission futures. We simulated a low-emission climate future with the Intergovernmental Panel on Climate Change (IPCC) 2007 B1 emission scenario and the Parallel Climate Model Global Circulation Model (GCM). We simulated a high-emission climate future with the IPCC A1FI emission scenario and the Geophysical Fluid Dynamics Laboratory (GFDL) GCM. We compared current forest management practices (business-as-usual) to CSP management. In the CSP scenario, we simulated a target planting of 5.28% and 4.97% of forested area per five-year time step in the Minnesota and Michigan landscapes, respectively. We found that simulated CSP species successfully established in both landscapes under all climate scenarios. The presence of CSP species generally increased simulated aboveground biomass. Species diversity increased due to CSP; however, the effect on functional diversity was variable. Because the planted species were functionally similar to many native species, CSP did not result in a consistent increase nor decrease in functional diversity. These results provide an assessment of the potential efficacy and limitations of CSP management. These results have management implications for sites where diversity and productivity are expected to decline. Future efforts to restore a specific species or forest type may not be possible, but CSP may sustain a more general ecosystem service (e.g., aboveground biomass).

Temporal context affects the observed rate of climate‐driven range shifts in tree species

AbstractAimRange shifts associated with 20th‐century warming have been documented for a wide range of taxa, but many species are not migrating fast enough to keep pace with the rapidly changing climate. Tree species can experience particularly long time lags in their migration response, resulting in altered forest composition and potentially delaying the migration of other obligate species. Here we review potential causes of these time lags and develop a conceptual framework for understanding how migration timing affects the observed rate of change.LocationGlobal forest ecosystems.MethodsWe synthesize evidence from present‐day tree species migrations to determine how different migration constraints can delay tree species range shifts.ResultsThe rate of present‐day tree migrations is frequently slower than expected, and many factors may contribute to observed migration lags. Migration constraints can be overcome given the right combination of circumstances, resulting in episodic range shifts that create temporal variability in migration rates. Given projected increases in forest disturbances and extreme climatic events, episodic range shifts are likely.Main conclusionsRecent efforts to explain the slow rate of tree migration have primarily focused on dispersal limitation and niche‐based constraints such as competition and other biotic interactions. We argue that these constraints cannot be fully understood without considering the temporal context of tree migration. Attempts to forecast and manage future distribution shifts must consequently consider how migration timing may affect observed patterns of change.