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ABSTRACT: The phenotypic responses of functional traits in natural populations are driven by genetic diversity and phenotypic plasticity. These two mechanisms enable trees to cope with rapid climate change. We studied two European temperate tree species (sessile oak and European beech), focusing on (i) in situ variations of leaf functional traits (morphological and physiological) along two altitudinal gradients and (ii) the extent to which these variations were under environmental and/or genetic control using a common garden experiment. For all traits, altitudinal trends tended to be highly consistent between species and transects. For both species, leaf mass per area displayed a positive linear correlation with altitude, whereas leaf size was negatively correlated with altitude. We also observed a significant increase in leaf physiological performance with increasing altitude: populations at high altitudes had higher maximum rates of assimilation, stomatal conductance and leaf nitrogen content than those at low altitudes. In the common garden experiment, genetic differentiation between populations accounted for 0-28% of total phenotypic variation. However, only two traits (leaf mass per area and nitrogen content) exhibited a significant cline. The combination of in situ and common garden experiments used here made it possible to demonstrate, for both species, a weaker effect of genetic variation than of variations in natural conditions, suggesting a strong effect of the environment on leaf functional traits. Finally, we demonstrated that intrapopulation variability was systematically higher than interpopulation variability, whatever the functional trait considered, indicating a high potential capacity to adapt to climate change.
Tree Physiology 09/2011; 31(11):1164-74. · 2.88 Impact Factor
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ABSTRACT: Summary1. Phenotypic plasticity allows large shifts in the timing of phenology within one single generation and drives phenotypic variability under environmental changes, thus it will enhance the inherent adaptive capacities of plants against future changes of climate.2. Using five common gardens set along an altitudinal gradient (100–1600 m asl.), we experimentally examined the phenotypic plasticity of leaf phenology in response to temperature increase for two temperate tree species (Fagus sylvatica and Quercus petraea). We used seedlings from three populations of each species inhabiting different altitudes (400, 800 and 1200 m asl.). Leaf unfolding in spring and leaf senescence in autumn were monitored on seedlings for 2 years.3. Overall, a high phenological plasticity was found for both species. The reaction norms of leaf unfolding date to temperature linearly accelerated for both species with an average shift of −5·7 days per degree increase. Timing of leaf senescence exhibited hyperbolic trends for beech due to earlier senescence at the lowest elevation garden and no or slight trends for oak. There was no difference in the magnitude of phenological plasticity among populations from different elevations. For both species, the growing season length increased to reach maximum values at about 10–13 °C of annual temperature according to the population.4. Since the magnitude of phenological plasticity is high for all the tested populations, they are likely to respond immediately to temperature variations in terms of leaf phenology. Consequently the mid- to high-elevation populations are likely to experience a longer growing season with climate warming. The results suggest that climate warming could lengthen the growing season of all populations over the altitudinal gradient, although the low-elevation populations, especially of beech, may experience accelerated senescence and shorter growing season due to drought and other climate changes associated with warming.
Functional Ecology 11/2010; 24(6):1211 - 1218. · 4.57 Impact Factor
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ABSTRACT: The aim of the study was to determine whether there are genetic variations in growth and leaf phenology (flushing and senescence) among populations of six woody species (Abies alba Mill., Acer pseudoplatanus L., Fagus sylvatica L., Fraxinus excelsior L., Ilex aquifolium L., and Quercus petraea (Matt.) Liebl.) along altitudinal gradients, using a common-garden experiment. We found (i) significant differences in phenology and growth among provenances for most species and (ii) evidence that these among-population differences in phenology were related to the annual temperature at the provenance sites for ash, beech, and oak. It is noteworthy that along the same climatic gradient, species can exhibit opposing genetic clines: beech populations from high elevations flushed earlier than those from low elevations, whereas we observed the opposite trend for ash and oak. For most species, significant altitudinal clines for growth were also revealed. Finally, we highlighted the fact that both phenology timing and growth rate were highly consistent from year to year. The results demonstrated that despite the proximity of the populations in their natural area, differences in altitude led to genetic differentiation in their phenology and growth. These adaptive capacities acting along a natural climatic gradient could allow populations to cope with current climate change.L'objectif de cette étude était de déterminer à l'aide d'un test de provenances, s'il existe des variations génétiques de la croissance et de la phénologie foliaire (feuillaison et sénescence) entre des populations issues de gradients altitudinaux, chez six espèces ligneuses (Abies alba Mill., Acer pseudoplatanus L., Fagus sylvatica L., Fraxinus excelsior L., Ilex aquifolium L. et Quercus petraea (Matt.) Liebl.). Pour la plupart de ces espèces, des différences significatives ont été observées entre les provenances pour la phénologie et la croissance. Ces différences phénologiques sont corrélées avec la température annuelle des sites de provenances chez le frêne, le hêtre et le chêne. Il est important de noter que les espèces présentent des clines opposés alors que les populations étudiées proviennent d'un même gradient climatique : les populations de hêtre provenant de hautes altitudes présentaient une feuillaison plus précoce que celles issues de basses altitudes, alors que le frêne et de chêne montraient des clines opposés. Des clines altitudinaux significatifs ont également été trouvés pour la croissance de la plupart des espèces. Nous avons également mis en évidence que la phénologie et le taux de croissance étaient stables d'une année sur l'autre. Les résultats de notre étude montrent que le gradient altitudinal a induit une différenciation génétique de ces populations pour leur croissance et leur phénologie, malgré la proximité des populations étudiées dans leur milieu naturel. Ces mécanismes adaptatifs, qui ont eu lieu le long d'un gradient climatique naturel, pourraient permettre aux populations de faire face au changement climatique actuel.
Canadian Journal of Forest Research 07/2009; 39(7):1259-1269. · 1.68 Impact Factor
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ABSTRACT: While changes in spring phenological events due to global warming have been widely documented, changes in autumn phenology, and therefore in growing season length, are less studied and poorly understood. However, it may be helpful to assess the potential lengthening of the growing season under climate warming in order to determine its further impact on forest productivity and C balance. The present study aimed to: (1) characterise the sensitivity of leaf phenological events to temperature, and (2) quantify the relative contributions of leaf unfolding and senescence to the extension of canopy duration with increasing temperature, in four deciduous tree species (Acer pseudoplatanus, Fagus sylvatica, Fraxinus excelsior and Quercus petraea). For 3 consecutive years, we monitored the spring and autumn phenology of 41 populations at elevations ranging from 100 to 1,600 m. Overall, we found significant altitudinal trends in leaf phenology and species-specific differences in temperature sensitivity. With increasing temperature, we recorded an advance in flushing from 1.9 +/- 0.3 to 6.6 +/- 0.4 days degrees C(-1) (mean +/- SD) and a 0 to 5.6 +/- 0.6 days degrees C(-1) delay in leaf senescence. Together both changes resulted in a 6.9 +/- 1.0 to 13.0 +/- 0.7 days degrees C(-1) lengthening of canopy duration depending on species. For three of the four studied species, advances in flushing were the main factor responsible for lengthening canopy duration with increasing temperature, leading to a potentially larger gain in solar radiation than delays in leaf senescence. In contrast, for beech, we found a higher sensitivity to temperature in leaf senescence than in flushing, resulting in an equivalent contribution in solar radiation gain. These results suggest that climate warming will alter the C uptake period and forest productivity by lengthening canopy duration. Moreover, the between-species differences in phenological responses to temperature evidenced here could affect biotic interactions under climate warming.
Oecologia 06/2009; 161(1):187-98. · 3.41 Impact Factor
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ABSTRACT: Questions: 1. Is there a primary role of disturbance at local scale and of environmental stress at regional scale? 2. Does disturbance increase or decrease environmental stress at local scale?Location: The Atlantic coastal dune system of the Aquitaine Region (France).Methods: Species biomass and 16 environmental variables were sampled in 128 quadrats along a local beach-inland gradient and a regional North-South gradient. Environmental data were analysed with ANOVAs and vegetation-environment relationships with Canonical Correspondence Analysis.Results: At the local scale community composition was primarily driven by disturbance due to sand burial, whereas water and nutrient stress better explained regional differences. However, random biogeographical events are very likely to also affect community composition at the largest scale. The main interaction between environmental stress and disturbance was the mitigation of nutrient stress induced by disturbance at a local scale. This was due to a positive direct effect of sand burial and a positive indirect effect of wind (decrease in VPD by ocean spray). Although wind had also a significant effect on soil conductivity and pH, there was no evidence that these factors had any role in community composition.Conclusions: Our results support the hypothesis that disturbance had a primary role at local scale and environmental stress at regional scale but further research is needed to separate the effect of stress from that of dispersal at regional scale. We also demonstrated that environmental stress in primary succession may not always decline with decreasing disturbance.
Journal of Vegetation Science 01/2009; 19(4):493 - 502. · 2.77 Impact Factor
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ABSTRACT: In mountain forest ecosystems where elevation gradients are prominent, temperature gradient-based phenological variability can be high. However, there are few studies that assess the capability of remote sensing observations to monitor ecosystem phenology along elevation gradients, despite their relevance under climate change. We investigated the potential of medium resolution remotely sensed data to monitor the elevation variations in the seasonal dynamics of a temperate deciduous broadleaf forested ecosystem. Further, we explored the impact of elevation on the onset of spring leafing. This study was based on the analysis of multi-annual time-series of VEGETATION data acquired over the French Pyrenees Mountain Region (FPMR), in conjunction with simultaneous ground-based observations of leaf phenology made for two dominant tree species in the region (oak and beech). The seasonal variations in the perpendicular vegetation index (PVI) were analyzed during a five-year period (2002 to 2006). The five years of data were averaged into a one sole year in order to fill the numerous large spatio-temporal gaps due to cloud and snow presence – frequent in mountains – without altering the temporal resolution. Since a VEGETATION pixel (1 km²) includes several types of land cover, the broadleaf forest-specific seasonal dynamics of PVI was reconstructed pixel-by-pixel using a temporal unmixing method based on a non-parametric statistical approach. The spatial pattern of the seasonal response of PVI was clearly consistent with the relief. Nevertheless the elevational or geographic range of tree species, which differ in their phenology sensitivity to temperature, also has a significant impact on this pattern. The reduction in the growing season length with elevation was clearly observable from the delay in the increase of PVI in spring and from the advance of its decrease in the fall. The elevation variations in leaf flushing timing were estimated from the temporal change in PVI in spring over the study area. They were found to be consistent with those measured in situ (R2 N 0.95). It was deduced that, over FPMR, the mean delay of leaf flushing timing for every 100 m increase in elevation was estimated be approximately 2.3 days. The expected estimation error of satellite-based leaf unfolding date for a given elevation was approximately 2 days. This accuracy can be considered as satisfactory since it would allow us to detect changes in leafing timing of deciduous broadleaf forests with a magnitude equivalent to that due to an elevation variation of 100 m (2.3 days on average), or in other words, to that caused by a variation in the mean annual air temperature of 0.5 °C. Although averaging the VEGETATION data over five years led to a loss of interannual information, it was found to be a robust approach to characterise the elevation variations in spring leafing and its long-term trends.
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ABSTRACT: Modelling phenology is crucial to assess the impact of climate change on the length of the canopy duration and the productivity of terrestrial ecosystems. Focusing on six dominant European tree species, the aims of this study were (i) to examine the accuracy of different leaf phenology models to simulate the onset and ending of the leafy season, with particular emphasis on the putative role of chilling to release winter bud dormancy and (ii) to predict seasonal shifts for the 21st century in response to climate warming.Models testing and validation were done for each species considering 2 or 3 years of phenological observations acquired over a large elevational gradient (1500 m range, 57 populations). Flushing models were either based solely on forcing temperatures (1-phase models) or both on chilling and forcing temperatures (2-phases models). Leaf senescence models were based on both temperature and photoperiod.We show that most flushing models are able to predict accurately the observed flushing dates. The 1-phase models are as efficient as 2-phases models for most species suggesting that chilling temperatures are currently sufficient to fully release bud dormancy. However, our predictions for the 21st century highlight that chilling temperature could be insufficient for some species at low elevation. Overall, flushing is expected to advance in the next decades but this trend substantially differed between species (from 0 to 2.4 days per decade). The prediction of leaf senescence appears more challenging, as the proposed models work properly for only two out of four deciduous species, for which senescence is expected to be delayed in the future (from 1.4 to 2.3 days per decade). These trends to earlier spring leafing and later autumn senescence are likely to affect the competitive balance between species. For instance, simulations over the 21st century predict a stronger lengthening of the canopy duration for Quercus petraea than for Fagus sylvatica, suggesting that shifts in the elevational distributions of these species might occur.Highlights► Provided a temperature range of about 7 °C, the altitudinal gradient used here is particularly relevant to calibrate phenological models. ► Most of the phenological models used were able to explain and predict accurately the leaf unfolding date for all the tree species considered, whereas they failed to predict senescence date for two out of four deciduous species. ► Overall, dates of leaf unfolding are expected to be advanced in the coming decades and dates of senescence to be delayed. ► The results suggest that chilling temperature could be insufficient for some species at low elevation with winter temperatures rising in the next decades. ► The simulations showed species differences in lengthening of canopy duration and consequently suggested changes in the competitive balance between species over the current century.
Agricultural and Forest Meteorology 151(7):969-980. · 3.39 Impact Factor
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ABSTRACT: Consequences of climate warming on tree phenology are readily observable, but little is known about the differences in phenological sensitivity to temperature between species and between populations within a species. The aim of the present study is to compare phenological sensitivities to temperature of seven woody species between each other and within-species between two geographical areas using both altitudinal and temporal gradients (Abies alba, Acer pseudoplatanus, Carpinus betulus, Fagus sylvatica, Fraxinus excelsior, Ilex aquifolium and Quercus petraea). The timing of leaf unfolding was monitored (i) over 2 years along two altitudinal gradients in the Pyrénées mountains (six species), and (ii) over 22 years in Fontainebleau forest (four species). Three species were present in both areas which allowed us to compare their phenological sensitivity to temperature over altitudinal and temporal gradients. Along altitudinal gradients, we observed for all species an advance in leaf unfolding with decreasing elevation, ranging from 11 to 34 days 1000 m−1 for beech and oak, respectively. Across the temporal gradient, we found significant advances in leaf unfolding for oak (−0.42 days year−1) and ash (−0.78 days year−1) since 1976, whereas no significant advance was observed for beech and hornbeam. For both gradients and for all species, significant correlations were found between leaf unfolding dates and temperature, except for beech in the temporal study. Moreover, we highlighted that phenological sensitivity to temperature was very similar between the two geographically separated populations (Pyrénées and Fontainebleau forests). Thus, oak had the strongest sensitivity (−7.48 and −7.26 days °C−1 in altitudinal and temporal gradient, respectively) and beech had the lowest (−2.09 and −2.03 days °C−1). Our results suggest that population sensitivity to global warming might be stable for a given species, in spite of its possible local adaptation.
Agricultural and Forest Meteorology.
