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Aim Determine if differences in species richness between currently climatically similar regions correlate to dissimilarities in functional diversity. Location Time period Europe and eastern North America. Neogene and Quaternary. Major taxa studied Methods Temperate trees of Europe and eastern North America. Using classic functional traits defining distinct ecological strategies, we described the trait spaces of European and eastern North American tree floras. The trait space of each region was described based on the occupied area, species accumulation pattern, and the trait-space size, dispersion and clustering. We then evaluated if the species richness differences between these two climatically similar regions correlate to dissimilarities in both occupied areas and species accumulation patterns; as well as differences in the trait-space size, dispersion and clustering. Results Main conclusions Differences in species richness between climatically similar regions do not necessarily result in functional dissimilarities. Regardless of eastern North American species having a larger trait-space, occupied areas and species accumulation patterns converged. Although in both regions species clumped towards the trait-space centroid, we observed statistically significant differences between Europe and eastern North America in the dispersion and clustering but not in size of the trait space. Moreover, traits from species in genera still present in eastern North America but lost from Europe during the Neogene and Quaternary were fully contained within the currently occupied European trait space. Positional convergence between European and eastern North American trait spaces suggests that this species richness anomaly does fully translate to the functional space. Our results suggest that species accumulation within a region occurs within a climatically restricted trait space, and not via trait-space expansion. Moreover, the consistent aggregation of species towards the trait-space centre aligns with the idea of a directional section towards a generalized morphology, which might provide the best way to interact with a broad array of environmental conditions.

The functional composition of plant communities is commonly thought to be determined by contemporary climate. However, if rates of climate‐driven immigration and/or exclusion of species are slow, then contemporary functional composition may be explained by paleoclimate as well as by contemporary climate. We tested this idea by coupling contemporary maps of plant functional trait composition across North and South America to paleoclimate means and temporal variation in temperature and precipitation from the Last Interglacial (120 ka) to the present. Paleoclimate predictors strongly improved prediction of contemporary functional composition compared to contemporary climate predictors, with a stronger influence of temperature in North America (especially during periods of ice melting) and of precipitation in South America (across all times). Thus, climate from tens of thousands of years ago influences contemporary functional composition via slow assemblage dynamics.

Tree range shifts during geohistorical global change events provide a useful real‐world model for how future changes in forest biomes may proceed. In North America, during the last deglaciation, the distributions of tree taxa varied significantly as regards the rate and direction of their responses for reasons that remain unclear. Local‐scale processes such as establishment, growth, and resilience to environmental stress ultimately influence range dynamics. Despite the fact that interactions between trees and soil biota are known to influence local‐scale processes profoundly, evidence linking below‐ground interactions to distribution dynamics remains scarce. We evaluated climate velocity and plant traits related to dispersal, environmental tolerance and below‐ground symbioses, as potential predictors of the geohistorical rates of expansion and contraction of the core distributions of tree genera between 16 and 7 ka bp. The receptivity of host genera towards ectomycorrhizal fungi was strongly supported as a positive predictor of poleward rates of distribution expansion, and seed mass was supported as a negative predictor. Climate velocity gained support as a positive predictor of rates of distribution contraction, but not expansion. Our findings indicate that understanding how tree distributions, and thus forest ecosystems, respond to climate change requires the simultaneous consideration of traits, biotic interactions and abiotic forcing.

As the earth system moves to a novel state, model systems (experimental, observational, paleoecological) are needed to assess and improve the predictive accuracy of ecological models under environments with no contemporary analog. In recent years, we have intensively studied the no-analog plant associations and climates in eastern North America during the last deglaciation to better constrain their spatiotemporal distribution, test hypotheses about climatic and megaherbivory controls, and assess the accuracy of species- and community-level models. The formation of no-analog plant associations was asynchronous, beginning first in the south-central United States; at sites in the north-central United States, it is linked to declining megafaunal abundances. Insolation and temperature were more seasonal than present, creating climates currently nonexistent in North America, and shifting species-climate relationships for some taxa. These shifts pose a common challenge to empirical paleoclimatic reconstructions, species distribution models (SDMs), and conservation-optimization models based on SDMs. Steps forward include combining recent and paleoecological data to more fully describe species' fundamental niches, employing community-level models to model shifts in species interactions under no-analog climates, and assimilating paleoecological data with mechanistic ecosystem models. Accurately modeling species interactions under novel environments remains a fundamental challenge for all forms of ecological models.

Observing a constant fraction of the population over time, locations, or species is virtually impossible. Hence, quantifying this proportion (i.e. detection probability) is an important task in quantitative population ecology. In this study we determined, via computer simulations, the ef- fect of population characteristics on estimates of detection probability. Simulation results showed a consistent and significant over-prediction of detection probability across sampling methodologies and estimators. Comparisons between estimators and sampling methods showed sig- nificant differences amongst them (estimators accounting for hetero- geneity are the most accurate). Population size was the most important factor influencing the uncertainty and accuracy of the estimates. Our results show the need to include population characteristics (either as a correction function or as factors in the observation model) when estim- ating detection probabilities. The study concludes by suggesting two methods for using population characteristics to estimate detection probabilities.

1. A prevalent question in the study of plant invasions has been whether or not invasions can be explained on the basis of traits. Despite many attempts, a synthetic view of multi-trait differences between alien and native species is not yet available.2. We compiled a database of three ecologically important traits (specific leaf area, typical maximum canopy height, individual seed mass) for 4473 species sampled over 95 communities (3784 species measured in their native range, 689 species in their introduced range, 207 in both ranges).3. Considering each trait separately, co-occurring native and alien species significantly differed in their traits. These differences, although modest, were expressed in a combined 15% higher specific leaf area, 16% lower canopy height and 26% smaller seeds.4. Using three novel multi-trait metrics of functional diversity, aliens showed significantly smaller trait ranges, larger divergences and a consistent differentiation from the median trait combination of co-occurring natives.5. We conclude that the simultaneous evaluation of multiple traits is an important novel direction in understanding invasion success. Our results support the phenotypic divergence hypothesis that predicts functional trait differences contribute to the success of alien species.