European larch phenology in the Alps: can we grasp the role of ecological factors by combining field observations and inverse modelling?

Vegetation phenology is strongly influenced by climatic factors. Climate changes may cause phenological variations, especially in the Alps which are considered to be extremely vulnerable to global warming. The main goal of our study is to analyze European larch (Larix decidua Mill.) phenology in alpine environments and the role of the ecological factors involved, using an integrated approach based on accurate field observations and modelling techniques. We present 2 years of field-collected larch phenological data, obtained following a specifically designed observation protocol. We observed that both spring and autumn larch phenology is strongly influenced by altitude. We propose an approach for the optimization of a spring warming model (SW) and the growing season index model (GSI) consisting of a model inversion technique, based on simulated look-up tables (LUTs), that provides robust parameter estimates. The optimized models showed excellent agreement between modelled and observed data: the SW model predicts the beginning of the growing season (BGS) with a mean RMSE of 4 days, while GSI gives a prediction of the growing season length (LGS) with a RMSE of 5 days. Moreover, we showed that the original GSI parameters led to consistent errors, while the optimized ones significantly increased model accuracy. Finally, we used GSI to investigate interactions of ecological factors during springtime development and autumn senescence. We found that temperature is the most effective factor during spring recovery while photoperiod plays an important role during autumn senescence: photoperiod shows a contrasting effect with altitude decreasing its influence with increasing altitude.

[1]  J. Tenhunen,et al.  Severe drought effects on ecosystem CO2 and H2O fluxes at three Mediterranean evergreen sites: revision of current hypotheses? , 2002 .

[2]  Nathaniel A. Brunsell,et al.  Vegetation Phenology in Global Change Studies , 2003 .

[3]  Albert Tarantola,et al.  Inverse problem theory - and methods for model parameter estimation , 2004 .

[4]  P. Hari,et al.  The utilization of old phenological time series of budburst to compare models describing annual cycles of plants. , 1991, Tree physiology.

[5]  Denis-Didier Rousseau,et al.  Fitting models predicting dates of flowering of temperate‐zone trees using simulated annealing , 1998 .

[6]  H. Lieth.  Phenology and Seasonality Modeling , 1974, Ecological Studies.

[7]  Denis-Didier Rousseau,et al.  Selecting models to predict the timing of flowering of temperate trees: implications for tree phenology modelling , 1999 .

[8]  R. Myneni,et al.  Investigation of a model inversion technique to estimate canopy biophysical variables from spectral and directional reflectance data , 2000 .

[9]  Jörg Schaber,et al.  Physiology-based phenology models for forest tree species in Germany , 2003, International journal of biometeorology.

[10]  Richard J. Norby,et al.  Phenological responses in maple to experimental atmospheric warming and CO2 enrichment , 2003 .

[11]  Jiri Nekovar,et al.  Phenology in central Europe – differences and trends of spring phenophases in urban and rural areas , 2000, International journal of biometeorology.

[12]  Heikki Hänninen,et al.  Effects of photoperiod and temperature on the timing of bud burst in Norway spruce (Picea abies). , 1998, Tree physiology.

[13]  P. Hari,et al.  Effects of dormancy and environmental factors on timing of bud burst in Betula pendula. , 1998, Tree physiology.

[14]  T. Vesala,et al.  On the separation of net ecosystem exchange into assimilation and ecosystem respiration: review and improved algorithm , 2005 .

[15]  J. Worrall.  Temperature Effects on Bud-Burst and Leaf-Fall in Subalpine Larch , 1993 .

[16]  J. Privette,et al.  Inversion methods for physically‐based models , 2000 .

[17]  Hans W. Linderholm,et al.  Growing season changes in the last century , 2006 .

[18]  O. M. Heide.  High autumn temperature delays spring bud burst in boreal trees, counterbalancing the effect of climatic warming. , 2003, Tree physiology.

[19]  C. Appenzeller,et al.  Inter-Annual Variability and Decadal Trends in Alpine Spring Phenology: A Multivariate Analysis Approach , 2005 .

[20]  C. Rolland,et al.  Changes in radial tree growth for Picea abies, Larix decidua, Pinus cembra and Pinus uncinata near the alpine timberline since 1750 , 1998, Trees.

[21]  Thuy Le Toan,et al.  Bud‐burst modelling in Siberia and its impact on quantifying the carbon budget , 2005, Global change biology.

[22]  Tiina Markkanen,et al.  Air temperature triggers the recovery of evergreen boreal forest photosynthesis in spring , 2003 .

[23]  R. Snyder,et al.  Phenological stages of natural species and their use as climate indicators , 1999 .

[24]  Josep Peñuelas,et al.  Complex spatiotemporal phenological shifts as a response to rainfall changes. , 2004, The New phytologist.

[25]  I. Leinonen,et al.  The importance of phenology for the evaluation of impact of climate change on growth of boreal, temperate and Mediterranean forests ecosystems: an overview , 2000, International journal of biometeorology.

[26]  L. Finér,et al.  The effect of soil temperature on the bud phenology, chlorophyll fluorescence, carbohydrate content and cold hardiness of Norway spruce seedlings. , 2004, Physiologia plantarum.

[27]  A. Skjelvåg,et al.  Quantification of photoperiodic effects on growth of Phleum pratense. , 2004, Annals of botany.

[28]  R. Colombo,et al.  Inversion of a radiative transfer model with hyperspectral observations for LAI mapping in poplar plantations , 2004 .

[29]  S. I. Rosenthal,et al.  Photosynthetic decline and pigment loss during autumn foliar senescence in western larch (Larix occidentalis). , 1997, Tree physiology.

[30]  P. Kramer,et al.  Responses of Plants to Environmental Stresses , 1973 .

[31]  Annette Menzel,et al.  Growing season extended in Europe , 1999, Nature.

[32]  J. Hadley.  Effect of Daily Minimum Temperature on Photosynthesis in Eastern Hemlock (Tsuga canadensis L.) in Autumn and Winter , 2000 .

[33]  C. Körner,et al.  The Role of Photoperiodism in Alpine Plant Development , 2003 .

[34]  H. Hänninen.  Does climatic warming increase the risk of frost damage in northern trees , 1991 .

[35]  Thomas Rötzer,et al.  Annual and spatial variability of the beginning of growing season in Europe in relation to air temperature changes , 2002 .

[36]  T. Rötzer,et al.  Response of tree phenology to climate change across Europe , 2001 .

[37]  Andrew D. Richardson,et al.  Phenology of a northern hardwood forest canopy , 2006 .

[38]  Pascal Yiou,et al.  Historical phenology: Grape ripening as a past climate indicator , 2004, Nature.

[39]  T. A. Black,et al.  Predicting the onset of net carbon uptake by deciduous forests with soil temperature and climate data: a synthesis of FLUXNET data , 2005, International journal of biometeorology.

[40]  A. Menzel,et al.  Trends in phenological phases in Europe between 1951 and 1996 , 2000, International journal of biometeorology.

[41]  Isabelle Chuine,et al.  Climatic determinants of budburst seasonality in four temperate‐zone tree species , 1999 .

[42]  J. Schaber,et al.  Responses of spring phenology to climate change , 2004 .

[43]  K. E. Moore,et al.  Climatic Consequences of Leaf Presence in the Eastern United States , 2001 .

[44]  M. Dettinger,et al.  Changes in the Onset of Spring in the Western United States , 2001 .

[45]  K. Loague,et al.  Statistical and graphical methods for evaluating solute transport models: Overview and application , 1991 .

[46]  T. Myking.  Effects of constant and fluctuating temperature on time to budburst in Betula pubescens and its relation to bud respiration , 1997, Trees.

[47]  P. Heuberger,et al.  Calibration of process-oriented models , 1995 .

[48]  Robert Tibshirani,et al.  An Introduction to the Bootstrap , 1994 .

[49]  G. Öquist.  Effects of low temperature on photosynthesis , 1983 .

[50]  Jörg Schaber,et al.  Evaluation of methods for the combination of phenological time series and outlier detection. , 2002, Tree physiology.

[51]  Ramakrishna R. Nemani,et al.  A generalized, bioclimatic index to predict foliar phenology in response to climate , 2004 .

[52]  M. Lechowicz,et al.  Predicting the timing of budburst in temperate trees , 1992 .

[53]  Peter E. Thornton,et al.  Generating surfaces of daily meteorological variables over large regions of complex terrain , 1997 .

[54]  O. M. Heide,et al.  Daylength and thermal time responses of budburst during dormancy release in some northern deciduous trees. , 1993, Physiologia plantarum.

[55]  Thomas Rötzer,et al.  Phenological maps of Europe , 2001 .

[56]  M. D. Schwartz.  Phenology: An Integrative Environmental Science , 2003, Tasks for Vegetation Science.

[57]  H. Hänninen,et al.  Models of the spring phenology of boreal and temperate trees: Is there something missing? , 2006, Tree physiology.

[58]  I. Chuine,et al.  A unified model for budburst of trees. , 2000, Journal of theoretical biology.

[59]  Mark D. Schwartz,et al.  Changes in North American spring , 2000 .

[60]  J. Partanen,et al.  Effect of accumulated duration of the light period on bud burst in Norway spruce (Picea abies) of varying ages , 2001 .

[61]  J. Monteith,et al.  Principles of Environmental Physics , 2014 .

[62]  H. Freeland,et al.  Spring phenology trends in Alberta, Canada: links to ocean temperature , 2000, International journal of biometeorology.

[63]  M. D. Schwartz,et al.  Determining the growing season of land vegetation on the basis of plant phenology and satellite data in Northern China , 2000, International journal of biometeorology.

[64]  Alastair H. Fitter,et al.  Environmental physiology of plants , 1982 .

[65]  M. Cannell,et al.  Thermal time, chill days and prediction of budburst in Picea sitchensis , 1983 .

[66]  M. V. van Wijk,et al.  Interannual variability of plant phenology in tussock tundra: modelling interactions of plant productivity, plant phenology, snowmelt and soil thaw , 2003 .