Yann Vitasse
email: yann.vitasse@wsl.ch

Sylvain Ursenbacher

Geoffrey Klein

Yannick Chittaro

Anne Delestrade

Christian Monnerat

Martine Rebetez

Christian Rixen

Nicolas Strebel

Benedikt R Schmidt

Sonja Wipf

Thomas Wohlgemuth

Nigel Gilles Yoccoz

Lenoir

Phenological and elevational shifts of plants, animals and fungi 2 under climate change in the European Alps 3 4

Keywords: biodiversity redistribution, climate change velocity, disequilibrium dynamics, 73 global warming, migration, mountain ecosystems, phenological mismatches, upslope shift

35 Mountain areas are biodiversity hotspots and provide a multitude of ecosystem services of 36 irreplaceable socio-economic value. In the European Alps, air temperature has increased at a 37 rate of about 0.36 °C decade -1 since 1970, leading to glacier retreat and significant snowpack 38 reduction. Due to these rapid environmental changes, this mountainous region is undergoing 39 marked changes in spring phenology and elevational distribution of animals, plants and fungi.

40 Long-term monitoring in the European Alps offers an excellent natural laboratory to 41 synthetize climate-related changes in spring phenology and elevational distribution for a large 42 array of taxonomic groups. This review assesses the climatic changes that have occurred 43 across the European Alps during recent decades, spring phenological changes and upslope 44 shifts of plants, animals and fungi from evidence in published papers and previously 45 unpublished data. Our review provides evidence that spring phenology has been shifting 46 earlier during the past four decades and distribution ranges show an upwards trend for most of 47 the taxonomic groups for which there are sufficient data. The first observed activity of reptiles 48 and terrestrial insects (e.g. butterflies) in spring has shifted significantly earlier, at an average Page 2 of 333 Biological Reviews 49 rate of -5.7 and -6.0 days decade -1 , respectively. By contrast, the first observed spring activity 50 of semi-aquatic insects (e.g. dragonflies and damselflies) and amphibians, as well as the 51 singing activity or laying dates of resident birds, show smaller non-significant trends ranging 52 from -1.0 to +1.3 days decade -1 . Leaf-out and flowering of woody and herbaceous plants 53 showed intermediate trends with mean values of -2.4 and -2.8 days decade -1 , respectively.

54 Regarding species distribution, plants, animals and fungi (N = 2,133 species) shifted the 55 elevation of maximum abundance (optimum elevation) upslope at a similar pace (on average 56 between +18 and +25 m decade -1 ) but with substantial differences among taxa. For example, 57 the optimum elevation shifted upward by +36.2 m decade -1 for terrestrial insects and +32.7 m 58 decade -1 for woody plants, whereas it was estimated to range between -1.0 and +11 m decade - 59 1 for semi-aquatic insects, ferns, birds and wood-decaying fungi. The upper range limit 60 (leading edge) of most species also shifted upslope with a rate clearly higher for animals (from 61 +47 to +91 m decade -1 ) than for plants (from +17 to +40 m decade -1 ), except for semi-aquatic 62 insects (-4.7 m decade -1 ). Although regional land-use changes could partly explain some 63 trends, the consistent upward shift found in almost all taxa all over the Alps is likely reflecting 64 the strong warming and the receding of snow cover that has taken place across the European 65 Alps over recent decades. However, with the possible exception of terrestrial insects, the 66 upward shift of organisms seems currently too slow to track the pace of isotherm shifts 67 induced by climate warming, estimated at about +62 to +71 m decade -1 since 1970. In the light 68 of these results, species interactions are likely to change over multiple trophic levels through 69 phenological and spatial mismatches. This nascent research field deserves greater attention to 70 allow us to anticipate structural and functional changes better at the ecosystem level.

149 eventually leading to local extinction events [START_REF] Wiens | physiology and seasonal activities are also dramatically altered by climate change[END_REF]Giezendanner et al., 2019). The 150 shift of species ranges in response to climate change is also increasingly hampered by human 151 activities such as tourism, urbanization or agriculture, all of which alter species' habitat 152 suitability and distribution by fragmenting natural habitats (Elsen, Monahan & Merenlender, 153 2020). A warmer climate associated with changes in rain regime and snow cover will alter the 154 physiology and phenology of many species, which in turn will affect their fitness and biotic 155 interactions. Numerous studies have shown tight relationships between snow conditions and 156 population dynamics of alpine and arctic plants (e.g. [START_REF] Inouye | The ecological and evolutionary significance of frost in the context of climate 1017 change[END_REF][START_REF] Inouye | Effects of climate change on phenology, frost damage, and floral abundance of 1019 montane wildflowers[END_REF][START_REF] Körner | Alpine plant life[END_REF]Wipf 157 & Rixen, 2010;Berteaux et al., 2016) as well as population dynamics of animal species (e.g.

158 [START_REF] Korslund | Small rodent winter survival: snow conditions limit access to food 1067 resources[END_REF]Helle & Kojola, 2008;[START_REF] Robinson | The influence of snow on the functional response of 1213 grazing ungulates[END_REF]. Hence, any 159 changes in air temperature, precipitation and snow cover patterns in high mountain areas are 160 expected to elicit substantial modifications in plant-animal interactions. In the European Alps, 161 the pace of climate warming is occurring at a faster rate than the average warming in the 162 northern hemisphere [START_REF] Rebetez | [END_REF], generating faster velocities of isotherm 163 shifts. As a result, substantial shifts in spring phenology as well as numerous elevational range 164 shifts have already been observed for plants, animals and even fungi over recent decades (see 165 studies in Tables 1 and2). Long-term monitoring in the European Alps offers an excellent 166 natural laboratory to synthetize climate-related changes in spring phenology and elevational 167 distribution for a large array of taxonomic groups.

168

Here we aim at synthetizing the climatic changes that have occurred across the European 169 Alps during recent decades and gathering the observed biotic responses in terms of both spring 170 phenological changes (the best documented season in terms of phenological observations) and 171 species range shifts, reported for flora, fauna and fungi. We provide a comprehensive 172 synthesis of these changes and discuss the consequences of such phenological and spatial [START_REF] Boé | This was due to models 370 omitting the plant physiological CO 2 response (Schwingshackl et al., 2019) and 371 underestimating both the increase in shortwave radiation and changes in solar radiation 422 term time series of phenological observations show the same consistent trends[END_REF]. For the same reasons, regional 373 models also tended to underestimate the decrease in summer precipitation [START_REF] Boé | This was due to models 370 omitting the plant physiological CO 2 response (Schwingshackl et al., 2019) and 371 underestimating both the increase in shortwave radiation and changes in solar radiation 422 term time series of phenological observations show the same consistent trends[END_REF] as 374 well as the increase in heavy rainfall events (Borodina, Fischer & Knutti, 2017).

375

A strong reduction of snow depth and snow cover is expected to continue at all 376 elevations across the European Alps during the 21st century [START_REF] Jasper | Differential impacts of climate 1032 change on the hydrology of two alpine river basins[END_REF]Rousselot et 377 al., 2012;Schmucki et al., 2015;Marty et al., 2017a), particularly during the spring season 378 [START_REF] Magnusson | Snow cover response to 1102 climate change in a high alpine and half-glacierized basin in Switzerland[END_REF][START_REF] Steger | Alpine snow cover in a changing climate: 1279 a regional climate model perspective[END_REF]. Permanent snow, glaciers and permafrost are 379 expected to decline strongly or disappear, with an overall melt of the snow cover in summer 380 [START_REF] Magnusson | Snow cover response to 1102 climate change in a high alpine and half-glacierized basin in Switzerland[END_REF]. At the end of the 21st century, continuous snow cover in winter may 381 only be present above 2,000 m, while mid-elevations (1,000-1,700 m) should experience 382 random and/or discontinuous snow cover in about one in two winters (Schmucki et al., 2017).

383 These future expected changes in snow cover duration and thickness correspond to an average 384 upward elevation shift of 800 m of the snow cover by the end of the century, while snow cover 385 seasons may be reduced by two or three months, depending on the scenario (Bavay, 386 Grünewald & Lehning, 2013;Marty et al., 2017a;Beniston et al., 2018).

387

Due to these rapid changes in air temperature and snowpack, the European Alps will 388 undergo marked changes in the phenology and distribution of plants, animals and fungi, which 389 are synthetized in the following sections. 392 Our review reveals an advance in spring phenological events for most of the studied taxa, i.e.

393 leaf-out and flowering for plants, singing activity, laying dates, arrival and hatching dates for 394 birds, and the first yearly observation for insects, amphibians and reptiles although these were 395 statistically significant only for reptiles and insects. There were also significant differences 396 among these taxonomic groups (Fig. 2A). Reptiles and terrestrial flying insects such as

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17 397 Lepidoptera and Orthoptera showed the largest advance in their first yearly observation, with a 398 significantly earlier -5.7±3.8 days decade -1 for reptiles (estimated marginal mean±CI; linear 399 mixed-effects model) and -6.0±1.0 days decade -1 for terrestrial insects, whereas a non-400 significant trend towards a slight delay was found for the peak of singing activity, laying dates 401 or hatching dates of resident birds (+1.3±4.5 days decade -1 ) and first yearly observation of 402 amphibians (+0.2±3.6 days decade -1 ; Fig. 2A). Insects with aquatic life stages (Odonata)

403 showed non-significant trends for an earlier first yearly observation of the adult stage (-404 1.0±2.2 days decade -1 , Fig. 2A). Plants also showed non-significant trends for an advance in 405 leaf-out or flowering of -2.8±6.3 and -2.4±2.7 days decade -1 for herbaceous and woody 406 plants, respectively (Fig. 2A). A significant difference was found between semi-aquatic and 407 terrestrial insects (Table 1; Fig. 2A). Whereas resident birds showed a tendency for a slight 408 delay in their singing activity or laying dates (+1.3±4.5 days decade -1 ), an advance was 409 detected for long-and short-distance migrant birds (-1.7±3.1 and -3.2±3.9 days decade -1 , 410 respectively; Fig. 2A), although these differences did not reach statistical significance. When 411 grouped by habitat type, a non-significant trend for a delay in singing activity or laying dates 412 was found for birds inhabiting forest or open land (+0.5±6.9 and +0.6±5.9, respectively),

413 whereas a significantly different advance of about -7.5±7.8 days decade -1 was found for birds 414 living in mixed habitats (Fig. S1).

415

Regarding phenological sensitivity to air temperature, fewer studies were available for 416 some taxa, potentially making it harder to detect statistically significant differences among 417 taxa (Table 1, Fig. 2B). However, we also found significant advances in spring phenology per 418 degree of warming of -5.1±3.9 days °C-1 for woody plants and -4.9±2.8 days °C-1 for 419 terrestrial insects, while non-significant trends for an advance were found in the other taxa.

420

For plants, phenological events are largely mediated by temperature and have the 421 potential to change considerably with climate warming. In alpine environments, the few long- 475 by the haphazard sampling inherent in info fauna data. By contrast, ferns, birds and wood-476 decaying fungi showed small and non-significant changes in optimum elevation, ranging 477 between +4 and +11 m decade -1 (Fig. 3A).

F o r R e v i e w O n l y F o r R e v i e w O n l y F o r R e v i e w O n l y 20 472 decade -1 ,

478

For the leading edge (upper elevational range limit), upward shifts were most 479 pronounced for animals (on average +72.3±17.8 m decade -1 ) than for plants (+28.2±21.8 m 480 decade -1 ; Fig. 3B), with the exception of semi-aquatic insect species that showed a non-481 significant trend for the leading edge to shift downward (-4.7±33.8 m decade -1 ; Fig. 3B and 482 Table 2). Remarkably, only terrestrial insects (+90.5±14.0 m decade -1 ) and reptiles (63.7±57.2 483 m decade -1 ) showed an upward shift of their leading edge within the range or higher than the 484 pace of climate warming (Fig. 3B), estimated at ~62-71 m decade -1 based on a warming rate 485 of 0.36 °C decade -1 (Fig. 1) and a temperature lapse rate of 0.51-0.58 m 100m -1 (Rolland, 486 2003;[START_REF] Kirchner | Altitudinal temperature lapse rates in an Alpine valley: trends and the influence of 1054 season and weather patterns[END_REF].

488 (a) Terrestrial plants and fungi

489 For plants, our review suggests that there may be substantial differences among the studied 490 taxonomic or functional groups, although these did not reach statistical significance, with 491 insignificant shifts in the optimal elevation of +12.0±26.9 and 4.2±33.7 m decade -1 for ferns 492 and alpine plants and significant upward shifts of +23.1±14.4 and 32.7±17.9 m decade -1 for 493 herbaceous and woody species growing below the treeline (Fig. 3A). Notably, this general 494 pattern among the taxonomic groups is the same for changes at the leading edge (Fig. 3B).

495 [START_REF] Lenoir | A significant 1091 upward shift in plant species optimum elevation during the 20th century[END_REF] 3A). This discrepancy may stem from the fact that we did not 509 constrain our review only to forest systems, unlike the above-mentioned studies which 510 specifically focused on range shifts of forest plants [START_REF] Lenoir | A significant 1091 upward shift in plant species optimum elevation during the 20th century[END_REF][START_REF] Küchler | Response of Swiss forests to 1069 management and climate change in the last 60 years[END_REF].

511 Thus, by including data from studies on forest systems with those reporting range shifts for 512 woody plant encroachment beyond the treeline or following land abandonment below the 513 treeline, we have a greater opportunity to detect elevational range shifts for woody plants. By 514 missing the upper part of the elevational gradient beyond the forest limit, studies restricted to 515 forest systems may have underestimated the true rate at which woody plant species are 516 responding to temperature increases or abandonment of land in the Alps. The dynamics of 517 recruitment of forest tree species at the upper elevational limits seems to be changing at a 518 relatively fast rate, with seedlings and saplings currently occurring well beyond the upper 519 elevational limit of adult trees [START_REF] Vitasse | [END_REF]. Similarly, across several mountain areas 520 in western Europe, including the western Alps, [START_REF] Lenoir | Differences 1094 between tree species seedling and adult altitudinal distribution in mountain forests during the 1095 recent warm period (1986-2006)[END_REF]

594

The mean elevation of reptiles has also changed considerably showing a non-significant 595 shift in optimum elevation of +24.2±25.4 m decade -1 (Fig. 3A) and a significant shift in their 596 leading edge elevation of +63.7±22.3 m decade -1 ; Fig. 3B). Nevertheless, more investigation

F o r R e v i e w O n l y 25
597 should be conducted for this group as this result originates from a single network of citizen 598 observations in the Alps. An increase in air temperature will allow reptiles to colonise higher 599 elevations, although the extent to which this is possible may be limited by oxygen availability 600 [START_REF] Jacobsen | The dilemma of altitudinal shifts: caught between high temperature and low 1024 oxygen[END_REF].

601

Interestingly, we found no significant differences in the upwards shift of optimum 602 elevation between plants, fungi and animals (Fig. 3A), whereas animals appear to be 603 responding fastest in terms of the leading edge, especially for terrestrial insects (Fig. 3B). The 604 distribution of mammals and birds is mainly driven by habitat and food availability, and a 605 change in temperature may not affect their distribution directly if features of their habitat 606 remain stable or depend more on the micro-than the macroclimate [START_REF] Jähnig | 1026 Microclimate affects the distribution of grassland birds, but not forest birds, in an Alpine 1027 environment[END_REF] and on 607 plant phenology [START_REF] Peláez | Large scale 1158 variation in birth timing and synchrony of a large herbivore along the latitudinal and altitudinal 1159 gradients[END_REF] (Mouquet et al., 2015). Although citizen science 758 has allowed the collection of a large amount of data from haphazard observations, there is a 759 clear need for more systematic monitoring. Joint analysis of these two sources of data would

773

(3) We suggest that the trend for upward shift likely reflects the strong warming and the 774 receding of snow cover that has occurred across the European Alps over recent decades and 775 reflects the tracking by these taxa of their climatic niche, although regional land-use changes 776 may also provide an explanation in some cases.

777 (4) With the possible exception of some groups of terrestrial insects, such as butterflies, the 778 trend for an upward shift in plants, fungi and animals appears currently too slow to track 779 isotherm shifts induced by climate warming. Indeed, an upward shift of about 330 m would be 780 necessary to match the air temperature rise of close to 1.8°C that has occurred since 1970 in 781 the European Alps region (i.e. 0.36 °C per decade). This roughly corresponds to a mean shift 782 of elevational range of about +62-71 m decade -1 , assuming an annual adiabatic lapse rate of 783 0.51-0.58 °C 100 m -1 as measured across the Alps [START_REF] Rolland | Spatial and seasonal variations of air temperature lapse rates in Alpine regions[END_REF][START_REF] Kirchner | Altitudinal temperature lapse rates in an Alpine valley: trends and the influence of 1054 season and weather patterns[END_REF]. The 784 mean upward shift of most of the species groups observed over the last decades clearly lags 785 behind this value (between -2 and +34 m decade -1 for the optimum elevation and between -5

786 and +64 m decade -1 for the upper elevational limit), except for terrestrial insects (+36.2 and 787 +90.5 m decade -1 for the optimum and upper elevational limits, respectively). Empirical evidence for elevational range shifts of (A) the optimum distribution (i.e elevation of maximum abundance) and (B) the leading edge (i.e. the upper range limit) reported for groups of taxa in the European Alps region. Values correspond to the estimate of the mixed-effect model with study as a random factor; error bars are 95% confidence intervals. The period of time investigated varied among studies but was always more than 10 years within the period 1980-2020, or for diachronic studies comparing historical and modern surveys, the modern survey was conducted within the period 1980-2020, and the median year of the historical survey(s) was after 1950. Only groups with more than five species are shown (all studies are reported in Table 2). Abbreviations: ecm, ectomycorrhizal; sapro., saprophytic; semi-aq., semi-aquatic.

788

760 1 )

 1 allow unbiased inferences(Dorazio, 2014). Developing integrated monitoring programs 761 focusing on different trophic levels, and combining these with underlying conceptual models 762 of the effects of climate and land-use changes on ecosystem structure and functioning should 763 be a priority. In the European Alps, spring phenology has advanced over recent decades for all taxa, 767 except birds and amphibians, with these advances being statistically significant for 768 ectothermic animals such as terrestrial insects and reptiles.769(2) We found a trend for almost all studied taxa to shift their distribution range upslope, with 770 significant changes in optimum elevation found for terrestrial insects, herbaceous and woody in leading edge elevation for terrestrial insects, reptiles, birds and herbaceous 772 plants.

939

  DÉQUÉ, M., ROWELL, D., LÜTHI, D., GIORGI, F., CHRISTENSEN, J., ROCKEL, B., JACOB, D., 940 KJELLSTRÖM, E., DE CASTRO, M. &VAN DEN HURK, B. (2007). An intercomparison of 941 regional climate simulations for Europe: assessing uncertainties in model projections. Climatic 942 Change 81(1), 53-70. 943 DEVICTOR, V., VAN SWAAY, C., BRERETON, T., BROTONS, L., CHAMBERLAIN, D., HELIÖLÄ, J., 944 HERRANDO, S., JULLIARD, R., KUUSSAARI, M. & LINDSTRÖM, Å. (2012). Differences in the 945 climatic debts of birds and butterflies at a continental scale. Nature Climate Change 2(2), 121-946 124. 947 DIEZ, J., KAUSERUD, H., ANDREW, C., HEEGAARD, E., KRISAI-GREILHUBER, I., SENN-IRLET, B., 948 HØILAND, K., EGLI, S. & BÜNTGEN, U. (2020). Altitudinal upwards shifts in fungal fruiting in 949 the Alps. Proceedings of the Royal Society B: Biological Sciences 287(1919), 20192348. 950 DIOLAIUTI, G., BOCCHIOLA, D., VAGLIASINDI, M., D'AGATA, C. & SMIRAGLIA, C. (2012). The 1975-951 2005 glacier changes in Aosta Valley (Italy) and the relations with climate evolution. Progress 952 in Physical Geography 36(6), 764-785. 953 DORAZIO, R. M. (2014). Accounting for imperfect detection and survey bias in statistical analysis of 954 presence-only data. Global Ecology and Biogeography 23(12), 1472-1484. 955 DURAND, Y., GIRAUD, G., LATERNSER, M., ETCHEVERS, P., MÉRINDOL, L. & LESAFFRE, B. (2009). snow cover. Journal of applied meteorology and climatology 48(12), 2487-2512. 958 ELSEN, P. R., MONAHAN, W. B. & MERENLENDER, A. M. (2020). Topography and human pressure in 959 mountain ranges alter expected species responses to climate change. ., BÜNTGEN, U., FRANK, D. C., NIEVERGELT, D. & LIEBHOLD, A. (2007). 1200 years of regular 962 outbreaks in alpine insects. Proceedings of the Royal Society of London B: Biological Sciences 963 274(1610), 671-679.

  time series of snow parameters (snowmelt timing and length of the snow free period) and mean air temperature (spring temperature from March to May and annual temperature) at six sites spread across the Swiss Alps during the period 1970-2019. Data updated from Klein et al. (2016) representing yearly average anomalies over the period 1970-2019 across six sites in Switzerland located between 1,298 and 2,540 m (Arosa, Davos, Grächen, Grimsel Hospiz, Scuol and Weissfluhjoch). Estimated trends from the Theil-Sen estimator method across the six sites are reported with the associated standard errors (grey shading) for each snow and temperature parameter. Significance of the slopes was tested using Mann-Kendell tests, see Klein et al. (2016) for more details. 136x92mm (300 x 300 DPI) Spring phenological change per decade (A) or per degree (B) for different plant and animal groups studied in the European Alps region. Values correspond to the estimated marginal mean of the mixed-effect model with study as a random factor; error bars are 95% confidence intervals. The period of time varied among studies but was always more than 10 years within the period 1980-2020. Only groups with more than five species are shown (all studies are reported in

1 Fig. S1 .

 1S1 Fig. S1. Mean phenological shift of the singing activity or laying dates per decade for birds classified according to their habitat. Values correspond to the estimated marginal mean of the mixed-effect model with study as a random factor; error bars are 95% confidence intervals. The period of time investigated varied among studies but was always more than 10 years within the period 1980-2020. Different letters among groups indicate significant differences (post-hoc Tukey tests at = 0.05).

  that require more investigation in order to be able to predict future structural 175 and functional changes better at the ecosystem level under global warming. database, we believe this data set should provide robust trends of how these species 249 are currently migrating along elevational gradients. Additionally, the data from info fauna do 250 not show identical trends among taxa; if a particular trend was due to observer bias, we would 251 expect to find similar patterns across various taxa, which was not the case.252The PhenoForest database consists of records of visual observations of the leaf-out 253 timing of eight species during the period 1998-2020 from volunteers in different sites in 254 Switzerland (one observer per site, 16 permanent sites in total, 1-5 species per site). At each 255 site, 8-10 trees per species were identified and monitored every year by the same observer.

	F 174 knowledge gaps F F F F F F F 248 into our F 372 connected with cloud cover and aerosols
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173 shifts on species interactions across different trophic levels. Moreover, we point out To 256 estimate trends in the leaf-out dates over this study period, we applied a linear mixed-effect 257 model for each species with leaf-out dates as the response variable, year as the explanatory 258 variable and sites as a random intercept term, and extracted the estimated slope for each 259 species separately.

260

Following collection/calculation of all the species-level biotic responses in days per 261 decade for shifts in spring phenology or meters per decade for elevational range shifts as 262 described above, we compared the estimated rates among taxonomic groups. We ran linear 263 mixed-effects models with species' phenological shift per year or species' elevational range 264 shift per decade as response variables, study/database as a random intercept term and 265 taxonomic group (with as many levels as taxonomic groups for which there were sufficient 266 data, i.e. groups containing at least five species) as the main fixed effect. Based on the model 267 estimates of phenological shift per year or elevational range shift per decade for each 268 taxonomic group separately, we computed the associated 95% confidence intervals. Post-hoc 269 Tukey tests were then applied to test for differences among the different taxonomic groups. In 270 the results, we report the mean shift of the phenology or migration of a given taxonomic group 271 across studies, using the estimated marginal mean value ±CI from the mixed-effect model. We

  Table 2) agrees well with the trend reported in a recent study in Switzerland (+38 m 473 between 2003 and 2010, or 48 m decade -1 ) that systematically monitored butterfly 474 communities (Roth, Plattner & Amrhein, 2014), suggesting that no major bias was introduced

  a mean rate of +29 m decade-1 when comparing vegetation surveys conducted 498 between 1905 and 1985 to surveys conducted between 1986 and 2005. However, when 499 splitting the data between short-lived herbaceous species (e.g. grasses and sedges) and long-500 lived woody species (trees and shrubs),[START_REF] Lenoir | A significant 1091 upward shift in plant species optimum elevation during the 20th century[END_REF] found that only herbaceous plants 501 from the forest understorey have significantly shifted their elevational optimum upslope (mean 502 rate of +38 m decade -1 ). Similarly, by revisiting historical relevés and species indicator values, 503[START_REF] Küchler | Response of Swiss forests to 1069 management and climate change in the last 60 years[END_REF] found an upward shift of forest plant species in the herbaceous layer of 504 Swiss forests at +10 m decade -1 since the 1950s, while the elevational range of species from

	497 elevation at 505	F
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showed for different mountain areas throughout France, including the 496 western Alps, that the optimum elevation of 171 forest plants and trees moved upward in the shrub and tree layers remained rather stable over the same time period. By contrast, our 506 quantitative review across the European Alps suggests that the optimum range of long-lived 507 woody plants is shifting upward at a significant rate, at least at the same rate as non-alpine 508 herbaceous plants (Fig.

  terrestrial insects, especially for pests which receive much more attention. For 573 example, upward shifts in the elevational range of outbreaks of the European spruce bark 574 beetle (I. typographus) were related to the increased frequency of drier summers in the Italian 575 Alps[START_REF] Marini | Climate affects severity and altitudinal 1107 distribution of outbreaks in an eruptive bark beetle[END_REF]. The pine processionary moth (Thaumetopoea pityocampa) shifted 576 its distribution upward between 1975 and 2004 at average rates of +70 m decade -1 and +29 m 577 decade -1 on the southern and northern slopes of the Italian Alps, respectively, with this shift 578 related to the increase in minimum winter air temperature(Battisti et al., 2005). As 579 ectotherms, insects do not regulate their body temperature, and thus climatic variation in 580 temperature will have a direct effect on their physiology. For example, warmer air 581 temperatures in summer generally reduce European bark beetle development time (i.e.

	572 documented for
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reported differences in 521 elevational distribution between seedlings and adult life stages of trees, suggesting an ongoing 582 increased voltinism)

[START_REF] Jakoby | Climate change alters elevational phenology 1029 patterns of the European spruce bark beetle (Ips typographus)[END_REF]

, and therefore are likely to 583 increase infestation pressure

[START_REF] Marini | Climate affects severity and altitudinal 1107 distribution of outbreaks in an eruptive bark beetle[END_REF][START_REF] Jakoby | Climate change alters elevational phenology 1029 patterns of the European spruce bark beetle (Ips typographus)[END_REF]

. The reproductive cycle 584 of insects is expected to be faster under warmer air temperatures, potentially allowing an extra 585 generation per growing season at all elevations by the end of the century for European spruce 586 bark beetle

[START_REF] Jakoby | Climate change alters elevational phenology 1029 patterns of the European spruce bark beetle (Ips typographus)[END_REF]

. Even though molluscs have a relatively low capacity to move 587 over large distances, an upward shift of the land snail Arianta arbustorum of about 164 m has 588 been reported in a comparison of its distribution in 1916-1917 with its distribution in 2011-589 2012 in the eastern Alps, and this upward shift was most pronounced (around 233 m) on 590 south-facing slopes

(Baur & Baur, 2013)

. Both habitat and microclimate are important factors 591 for these organisms and the authors stressed that, on some mountain slopes, snails have 592 already reached natural barriers (vertical rock walls with no soil), that prevent further upward 593 shifts.

  to their strong dependence on freshwater habitats which are heavily fragmented by 648 human activities (e.g. dams) and are also likely to exert strong microclimate buffering on 649 warming rate, especially within mountain ranges where streams are fed by snow and glacier 650 melt[START_REF] Mclaughlin | Hydrologic refugia, plants, and climate change[END_REF]. In addition, most of these organisms are dependent on the 651 vegetation that structures their habitat. Typically, dragonflies inhabiting subalpine and alpine 652 zones live in bogs, fens and their associated small water bodies and runoff. The vegetation of 653 these habitats is very specific and species requirements in terms of vegetation structure are not 654 met in the pioneer water bodies of the upper level. The slower migration rate of these species 655 could therefore partially be explained by their requirement for colonization by vegetation to 656 occur first to offer new potential habitats for them. The formation of new bogs, fens or 657 swamps may take several decades or even centuries. integrate other ecosystem components such as herbivores, granivores and carnivores 748 from groups as diverse as insects, birds and mammals. There is, however, evidence that 749 changes in the abundance and distribution of species may be related to ecological interactions 750 [e.g. the mismatch between larch leaf-out and budmoth emergence(Büntgen et al., 2009; 751 Johnson et al., 2010)], or involve multiple trophic levels(Burgess et al., 2018). The data 752 available for different taxonomic groups often come from different time periods or places. The 753 absence of a common design makes it difficult to build causal models integrating direct and 754 indirect effects [e.g. Grace & Irvine, 2020; but see Thuiller et al. (2018) for a species 755 distribution modelling approach to plant-herbivore interactions]. Our analysis identified a 756 large heterogeneity in species responses to climate change, making it difficult to understand 757 and predict changes at the ecosystem level

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	e v i e e v i e e v i e e v i e e v i e e v i e
	w w w w w w
	O n l O n l O n l O n l O n l O n l
	y y y y y y
	27 31

. For instance, two studies conducted on European roe 608 deer (Capreolus capreolus) identified a strong dependence on the quality of food resources, 609 with individuals performing long-distance seasonal movements upward and downward to 610 locate food resources within their home range and thus tracking plant phenology

(Gaudry et 611 al., 2015;[START_REF] Peláez | Large scale 1158 variation in birth timing and synchrony of a large herbivore along the latitudinal and altitudinal 1159 gradients[END_REF]

. Another study revealed an upward shift of about +37.5±10.3 m 612 decade -1 of four mountain ungulate species in the Swiss Alps based on hunting records, 613 attributing this upward shift to the lengthening of the snow-free period

(Büntgen et al., 2017, 614

Table

2

).

615

The effects of climate warming on animal distribution are likely to be complex, and will 616 include indirect effects. A good example is the Alpine chough (Pyrrhocorax graculus) that 617 nests at high elevations in cavities and fissures on inaccessible rock faces and forages in open 618 alpine meadows (Delestrade & Stoyanov, 1995). Climate and land use are affecting the 619 distribution of plants and forests but obviously not the distribution of the cliffs it uses for 620 nesting. While upward shifts in distribution of birds have been detected in some areas in the 621 Alps such as the central Swiss Alps (Maggini et al., 2011; Knaus, 2018), several other studies 658 659 (4) Plant-animal interactions mediated by species-specific phenological and spatial shifts 660 On the one hand, because plants are the first link of the food web, changes in plant phenology

661 and composition will affect food quantity and quality for higher trophic levels, and may thus 662 affect complex trophic interactions

[START_REF] Plard | Mismatch between birth date and vegetation phenology slows the 1175 demography of roe deer[END_REF] Thackeray et al., 2016; Kharouba et al., 663 2018;[START_REF] Renner | Climate change and phenological mismatch in trophic 1198 interactions among plants, insects, and vertebrates[END_REF] Kharouba & Wolkovich, 2020)

, animal performance

(Sheridan 664 & Bickford, 2011)

and species migration

(Büntgen et al., 2017;[START_REF] Peláez | Large scale 1158 variation in birth timing and synchrony of a large herbivore along the latitudinal and altitudinal 1159 gradients[END_REF] Rehnus et 665 al., 2020)

. Conversely, numerous seed plants are pollinated and dispersed by animals, and are 666 affected by their interactions with herbivores, thus animal range shifts will be intimately 667 involved with plant range shifts. Responses of herbivores to climatic changes are generally 668 mediated through plant quality and quantity

[START_REF] Mysterud | Nonlinear 1139 effects of large-scale climatic variability on wild and domestic herbivores[END_REF][START_REF] Mysterud | 1142 Hierarchical path analysis of deer responses to direct and indirect effects of climate in northern 1143 forest[END_REF][START_REF] Peláez | Large scale 1158 variation in birth timing and synchrony of a large herbivore along the latitudinal and altitudinal 1159 gradients[END_REF] 669 Rehnus et al., 2020)

. In temperate regions, vegetation quantity gradually increases in spring to 670 reach a maximum in the middle of summer, while vegetation quality is generally highest 671 shortly after the beginning of vegetation growth in spring. In mountain ecosystems, mobile

  5) Species interactions mediated by phenological and spatial shifts are likely to be altered by 789 climate warming but very few studies currently focus on biotic interactions across multiple 790 trophic levels. Integrating monitoring programs at ecosystem levels should be fostered to 791 allow better predictions of changes in plant and animal communities in response to climate AUER, I., BÖHM, R., JURKOVIC, A., LIPA, W., ORLIK, A., POTZMANN, R., SCHÖNER, W., UNGERSBÖCK, BODIN, J., BADEAU, V., BRUNO, E., CLUZEAU, C., MOISSELIN, J. M., WALTHER, G. R. & DUPOUEY, J. BURGESS, M. D., SMITH, K. W., EVANS, K. L., LEECH, D., PEARCE-HIGGINS, J. W.,BRANSTON, C. J., DELL, D., SPARKS, T. H. & DENNIS, R. L. (2005). Climate change and the effect of increasing spring 937 temperatures on emergence dates of the butterfly Apatura iris (Lepidoptera: Nymphalidae).

	826 862 898 934	DELESTRADE, A. & STOYANOV, G. (1995). Breeding biology and survival of the Alpine Chough
	935	Pyrrhocorax graculus. Bird Study 42(3), 222-231.
	936
	938	European Journal of Entomology 102(2), 161-167.
		F F F F F
		o r o r o r o r o r
		R R R R R
		e v i e e v i e e v i e e v i e e v i e
		w w w w w
		O n l O n l O n l O n l O n l
		y y y y y
	792 change.
	793 (6) This review provides a valuable synthesis for future research focusing on the responses of
	794 organisms to climate warming in the European Alps.
	795
		34 35 36 37

Table S1 .

 S1 Mean phenological shift of the singing activity or laying dates per decade for birds 1360 classified according to habitat. Spring phenological change per decade or/and per degree for each studied species.

	970 971 972 1006 HOLZINGER, B., HÜLBER, K., CAMENISCH, M. & GRABHERR, G. (2008). Changes in plant species FOSTER, G. & RAHMSTORF, S. (2011). Global temperature evolution 1979-2010. Environmental Research Letters 6(4), 044022. FU, Y. H., GENG, X., HAO, F., VITASSE, Y., ZOHNER, C. M., ZHANG, X., ZHOU, X., YIN, G., PEÑUELAS, 1007 richness over the last century in the eastern Swiss Alps: elevational gradient, bedrock effects 1008 and migration rates. Plant Ecology 195(2), 179-196. 1009 HÖLZINGER, J. (1997). Die Vögel Baden-Württembergs: Muscicapidae (Fliegenschnäpper) und 1359 Fig. S1. 1361 1362
		GALLINAT, A. S., PRIMACK, R. B. & WAGNER, D. L. (2015). Autumn, the neglected season in climate
	976	change research. Trends in Ecology & Evolution 30(3), 169-176.
	977	GAUDRY, W., SAÏD, S., GAILLARD, J.-M., CHEVRIER, T., LOISON, A., MAILLARD, D. & BONENFANT, C.
	978	(2015). Partial migration or just habitat selection? Seasonal movements of roe deer in an
	979	Alpine population. Journal of Mammalogy 96(3), 502-510.
	980	GEHRIG-FASEL, J., GUISAN, A. & ZIMMERMANN, N. E. (2007). Tree line shifts in the Swiss Alps:
	981 982 983	F o r Climate change or land abandonment? Journal of Vegetation Science 18(4), 571-582. F F F F F F F F F F F GELLRICH, M., BAUR, P., KOCH, B. & ZIMMERMANN, N. E. (2007). Agricultural land abandonment and natural forest re-growth in the Swiss mountains: a spatially explicit economic analysis. o r o r o r o r o r o r o r o r o r o r o r
	984 985 986 987 988	R e v i e Agriculture, Ecosystems & Environment 118(1), 93-108. R R R R R R R R R R R GIEZENDANNER, J., BERTUZZO, E., PASETTO, D., GUISAN, A. & RINALDO, A. (2019). A minimalist model of extinction and range dynamics of virtual mountain species driven by warming temperatures. PLoS ONE 14(3), e0213775. GRACE, J. B. & IRVINE, K. M. (2020). Scientist's guide to developing explanatory statistical models e v i e e v i e e v i e e v i e e v i e e v i e e v i e e v i e e v i e e v i e e v i e
	989 990	w using causal analysis principles. Ecology 101(4), e02962. GUO, F., LENOIR, J. & BONEBRAKE, T. C. (2018). Land-use change interacts with climate to determine w w w w w w w w w w w
	991 992 993	O n l elevational species redistribution. Nature communications 9(1), 1-7. GÜSEWELL, S. (2014). Phenological responses to changing temperatures: representativeness and precision of results from the Swiss Phenological Network. Master thesis, ETH Zurich. O n l O n l O n l O n l O n l O n l O n l O n l O n l O n l O n l
	994	y HELLE, T. & KOJOLA, I. (2008). Demographics in an alpine reindeer herd: effects of density and winter y y y y y y y y y y y
	995	weather. Ecography 31(2), 221-230.
	996	HERFINDAL, I., ANDERWALD, P., FILLI, F., ANDRI, S. C. & REMPFLER, T. (2019). Climate, competition
	997	and weather conditions drive vertical displacement and habitat use of an alpine ungulate in a
	998	highly topographic landscape. Landscape Ecology 34(11), 2523-2539.
	999	HERNÁNDEZ-HENRÍQUEZ, M. A., DÉRY, S. J. & DERKSEN, C. (2015). Polar amplification and elevation-
	964 1000	FACCOLI, M. (2009). Effect of Weather on Ips typographus (Coleoptera Curculionidae) Phenology, dependence in trends of Northern Hemisphere snow cover extent, 1971-2014. Environmental
	965 1001	Voltinism, and Associated Spruce Mortality in the Southeastern Alps. Environmental Research Letters 10(4), 044010.
	966 1002 HEWITT, G. (2000). The genetic legacy of the Quaternary ice ages. Nature 405(6789), 907-913. Entomology 38(2), 307-316.
	967	FISCHER, A., KOTLARSKI, S., STRASSMANN, K., SCHÄR, C., CROCI-MASPOLI, M., KNUTTI, R. &
	968	SCHWIERZ, C. (2019). The new Swiss climate change scenarios CH2018. In Geophysical
		38 39 49

1003 HODNEBROG, Ø., MARELLE, L., ALTERSKJAER, K., WOOD, R., LUDWIG, R., FISCHER, E., RICHARDSON, 1004 T., FORSTER, P., SILLMANN, J. & MYHRE, G. (2019). Intensification of summer precipitation 1005 with shorter time-scales in Europe. Environmental Research Letters 14(12), 124050.

Table S2 .

 S2 Elevational range shifts of the optimum distribution (i.e. elevation of maximum 1363 abundance) or/and the leading edge (i.e. the upper range limit) for each studied species.

	1404
	F o r R e v i e F o r R e i v e F o r R e v i e w	O n l y
	w w
	O n l O n l
	y y	52

Table 1 .

 1 Documented spring phenological changes in animals and plants in the European Alps over the recent decades. Mean ± standard errors 1405 are reported where data are available for more than one species. For information on the info fauna and PhenoForest databases, see Section II.1406 The data set used for this table is provided as supporting online information in TableS1. Abbreviations: ldm, long-distance migrants; sdm, short-1407 distance migrants; res., resident.

	Taxa	Study period	Area	Number of species	Phenological variable	Trends (days decade -1 )	Temperature sensitivity (days °C-1 )

Table

  ). Abbreviations: ldm, long-distance migrants; sdm, short-distance migrants; res., resident; semi-aq., semi-aquatic. Different letters among groups indicate significant differences (post-hoc Tukey tests at = 0.05).

	F o
	r
	R
	e
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	O n
	l y
	527x944mm (72 x 72 DPI)

Biological Reviews

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BRIGGS, K., CLARK, J. R., DU FEU, C. R. & LEWTHWAITE, K. (2018). Tritrophic phenological

match-mismatch in space and time. Nature Ecology & Evolution 2(6), 970-975.

Reanalysis of 47 years of climate in the French Alps: climatology and trends for

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PLANTS

Woody