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The direction and magnitude of long-term changes in local plant species richness are highly variable among studies, while species turnover is ubiquitous. However, it is unknown whether the nature of species turnover is idiosyncratic or whether certain types of species are consistently gained or lost across different habitats. To address this question, we analyzed the trajectories of 1,827 vascular plant species over time intervals of up to 78 years at 141 sites in three habitats in Europe – mountain summits, forests, and lowland grasslands. Consistent across all habitats, we found that plant species with small geographic ranges tended to be replaced by species with large ranges, despite habitat-specific trends in species richness. Our results point to a predictable component of species turnover, likely explained by aspects of species’ niches correlated with geographic range size. Species with larger ranges tend to be associated with nutrient-rich sites and we found community composition shifts towards more nutrient-demanding species in all three habitats. Global changes involving increased resource availability are thus likely to favor large-ranged, nutrient-demanding species, which are typically strong competitors. Declines of small-ranged species could reflect not only abiotic drivers of global change, but also biotic pressure from increased competition. Our study highlights the need to consider the traits of species such as the geographic range size when predicting how ecological communities will respond to global change.

Paru sous le titre :"Response to Comment on “Forest microclimate dynamics drive plant responses to warming”; International audience; Schall and Heinrichs question our interpretation that the climatic debt in understory plant communities is locally modulated by canopy buffering. However, our results clearly show that the discrepancy between microclimate warming rates and thermophilization rates is highest in forests where canopy cover was reduced, which suggests that the need for communities to respond to warming is highest in those forests.

International audience; Bertrand et al . question our interpretation about warming effects on the thermophilization in forest plant communities and propose an alternative way to analyze climatic debt. We show that microclimate warming is a better predictor than macroclimate warming for studying forest plant community responses to warming. Their additional analyses do not affect or change our interpretations and conclusions.

Kutatasunk sokretű megkozelitest tukroz. Honos fafajaink becsult reakcioi alapjan elemeztuk őshonos fafaju erdőtarsulasaink varhato atrendeződeset. Az elmeleti becsleseket osszedolgoztuk az ujulatra es mortalitasra vonatkozo terepi vizsgalatok eredmenyeivel. Potencialis, invaziobiologiai szempontbol alacsony kockazatu cserefafajokat kerestunk a varhatoan visszaszorulo fafajaink esetleges helyettesitesere. A honos es invazios fafafajok eseteben orszagos adatokon nyugvo, cserefafajok eseteben europai leptekű modellezessel is becsultuk a fajok potencialis es prognosztikus elterjedeset. Potencialis termeszetes erdőtarsulas (PTE) adatbazist epitettunk fel az orszag erdőteruleteire az Orszagos Erdőallomany Adattar alapjan, a jelenre es jovőre vonatkozoan egyarant. Eredmenyeink alapjan az erdő- es erdőssztyep-tarsulasok eseteben egyarant a magas osszeteteli (elegyesseg) es szerkezeti diverzitas (gyepekkel, cserjesekkel mozaikolo allomanyok) jelenthet nagyobb alkalmazkodokepesseget. A kivalasztott tajidegen fafajok alkalmazasara csak az uj korulmenyek kozott is vitalis, őshonos taxonok es az altaluk alkotott (akar ujszerű) tarsulasok altal nyujtott lehetősegek kimeruleset kovetően kerulhet sor.

The aim of this study is to provide quantitative information on the effect of climaticchange on the growth and vitality of European beech: although the species is considered in itsoptimum highly plastic and adaptable, it becomes climate-sensitive closer to its xeric (lower)distribution limits. The future of beech in Southeast Europe requires special attention because thisregion harbours significant populations living at or near their xeric distribution boundary. Even thoughthe low elevation occurrences are uniquely vulnerable to climatic shifts, observations and modellingstudies pertaining to this region are particularly scarce.Out of climatic factors determining the xeric distributional limits for beech, Ellenberg’s droughtindex (EQ) appeared as the most influential. Growth response analyses in comparative tests haveconfirmed the existence of macroclimatic adaptation of beech and have proven that warming and morearid conditions lead to decline of growth and vitality, while no decline was observed if EQ changed inthe opposite direction. The response to weather extremes was investigated in field plots. Recurrentsummer droughts of 3 to 4 consecutive years, above mean EQ value 40-42 resulted in pest and diseaseattacks and mass mortality.The discussed approaches indicate consistently a high level of uncertainty regarding the future ofbeech at the xeric limit in Southeast Europe. According to field observations and bioclimatic data inHungary, a large part of low-elevation beech forests presently in the zone of EQ index 20 might bethreatened by the warming in the second half of the century, while higher-elevation occurrences mayremain stable.The interpretation of the results bears some stipulations, such as the consequence of ecologicaland human interactions in influencing present distribution patterns, the unclear role of persistence,natural selection and plasticity and uncertainties of climate projections. Grim projections mayprobably be partly overwritten by the mentioned stipulations and by careful and prudent humansupport.

Climate warming is causing a shift in biological communities in favor of warm-affinity species (i.e., thermophilization). Species responses often lag behind climate warming, but the reasons for such lags remain largely unknown. Here, we analyzed multidecadal understory microclimate dynamics in European forests and show that thermophilization and the climatic lag in forest plant communities are primarily controlled by microclimate. Increasing tree canopy cover reduces warming rates inside forests, but loss of canopy cover leads to increased local heat that exacerbates the disequilibrium between community responses and climate change. Reciprocal effects between plants and microclimates are key to understanding the response of forest biodiversity and functioning to climate and land-use changes.

Local factors restrain forest warming Microclimates are key to understanding how organisms and ecosystems respond to macroclimate change, yet they are frequently neglected when studying biotic responses to global change. Zellweger et al. provide a long-term, continental-scale assessment of the effects of micro- and macroclimate on the community composition of European forests (see the Perspective by Lembrechts and Nijs). They show that changes in forest canopy cover are fundamentally important for driving community responses to climate change. Closed canopies buffer against the effects of macroclimatic change through their cooling effect, slowing shifts in community composition, whereas open canopies tend to accelerate community change through local heating effects. Science , this issue p. 772 ; see also p. 711