Vignette d'image

Vitasse, Yann

Nom
Vitasse, Yann
Affiliation principale
Identifiants
https://libra.unine.ch/handle/123456789/1023

Résultat de la recherche

Filtres

2
2
2
Réinitialiser les filtres

Paramètres

Voici les éléments 1 - 2 sur 2
  • Publication
    Métadonnées seulement
    Declining global warming effects on the phenology of spring leaf unfolding
    (2015-10-1)
    Fu, Yongshuo
    ;
    Zhao, Hongfang
    ;
    Piao, Shilong
    ;
    Peaucelle, Marc
    ;
    Peng, Shushi
    ;
    Zhou, Guiyun
    ;
    Ciais, Philippe
    ;
    Huang, Mengtian
    ;
    Menzel, Annette
    ;
    Peñuelas, Josep
    ;
    Song, Yang
    ;
    Vitasse, Yann 
    ;
    Zeng, Zhenzhong
    ;
    Janssens, Ivan A.
    Earlier spring leaf unfolding is a frequently observed response of plants to climate warming1–4. Many deciduous tree species require chilling for dormancy release, and warming-related reductions in chilling may counteract the advance of leaf unfolding in response to warming5,6. Empirical evidence for this, however, is limited to sap- lings or twigs in climate-controlled chambers7,8. Using long-term in situ observations of leaf unfolding for seven dominant European tree species at 1,245 sites, here we show that the apparent response of leaf unfolding to climate warming (ST, expressed in days advance of leaf unfolding per 6C warming) has significantly decreased from 1980 to 2013 in all monitored tree species. Averaged across all spe- cies and sites, ST decreased by 40% from 4.0 6 1.8 days 6C21 during 1980–1994 to 2.3 6 1.6 days 6C21 during 1999–2013. The declining ST was also simulated by chilling-based phenology models, albeit with a weaker decline (24–30%) than observed in situ. The reduction in ST is likely to be partly attributable to reduced chilling. Nonetheless, other mechanisms may also have a role, such as ‘photo- period limitation’ mechanisms that may become ultimately limiting when leaf unfolding dates occur too early in the season. Our results provide empirical evidence for a declining ST, but also suggest that the predicted strong winter warming in the future may further reduce ST and therefore result in a slowdown in the advance of tree spring phenology
  • Publication
    Métadonnées seulement
    Increased heat requirement for leaf flushing in temperate woody species over 1980-2012: effects of chilling, precipitation and insolation
    (2015-7-1)
    Fu, Yongshuo
    ;
    Piao, Shilong
    ;
    Vitasse, Yann 
    ;
    Zhao, Hongfang
    ;
    De Boeck, Hans
    ;
    Liu, Qiang
    ;
    Yang, Hui
    ;
    Weber, Ulrich
    ;
    Hänninen, Heikki
    ;
    Ivan A., Janssens
    Recent studies have revealed large unexplained variation in heat requirement-based phenology models, resulting in large uncertainty when predicting ecosystem carbon and water balance responses to climate variability. Improving our understanding of the heat requirement for spring phenology is thus urgently needed. In this study, we estimated the species-specific heat requirement for leaf flushing of 13 temperate woody species using long-term phenological observations from Europe and North America. The species were defined as early and late flushing species according to the mean date of leaf flushing across all sites. Partial correlation analyses were applied to determine the temporal correlations between heat requirement and chilling accumulation, precipitation and insolation sum during dormancy. We found that the heat requirement for leaf flushing increased by almost 50% over the study period 1980–2012, with an average of 30 heat units per decade. This temporal increase in heat requirement was observed in all species, but was much larger for late than for early flushing species. Consistent with previous studies, we found that the heat requirement negatively correlates with chilling accumulation. Interestingly, after removing the variation induced by chilling accumulation, a predominantly positive partial correlation exists between heat requirement and precipitation sum, and a predominantly negative correlation between heat requirement and insolation sum. This suggests that besides the well-known effect of chilling, the heat requirement for leaf flushing is also influenced by precipitation and insolation sum during dormancy. However, we hypothesize that the observed precipitation and insolation effects might be artefacts attributable to the inappropriate use of air temperature in the heat requirement quantification. Rather than air temperature, meristem temperature is probably the prominent driver of the leaf flushing process, but these data are not available. Further experimental research is thus needed to verify whether insolation and precipita- tion sums directly affect the heat requirement for leaf flushing.