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      A global analysis of the comparability of winter chill models for fruit and nut trees

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          Abstract

          Many fruit and nut trees must fulfill a chilling requirement to break their winter dormancy and resume normal growth in spring. Several models exist for quantifying winter chill, and growers and researchers often tacitly assume that the choice of model is not important and estimates of species chilling requirements are valid across growing regions. To test this assumption, Safe Winter Chill (the amount of winter chill that is exceeded in 90% of years) was calculated for 5,078 weather stations around the world, using the Dynamic Model [in Chill Portions (CP)], the Chilling Hours (CH) Model and the Utah Model [Utah Chill Units (UCU)]. Distributions of the ratios between different winter chill metrics were mapped on a global scale. These ratios should be constant if the models were strictly proportional. Ratios between winter chill metrics varied substantially, with the CH/CP ratio ranging between 0 and 34, the UCU/CP ratio between −155 and +20 and the UCU/CH ratio between −10 and +5. The models are thus not proportional, and chilling requirements determined in a given location may not be valid elsewhere. The Utah Model produced negative winter chill totals in many Subtropical regions, where it does not seem to be useful. Mean annual temperature and daily temperature range influenced all winter chill ratios, but explained only between 12 and 27% of the variation. Data on chilling requirements should always be amended with information on the location and experimental conditions of the study in which they were determined, ideally including site-specific conversion factors between winter chill models. This would greatly facilitate the transfer of such information across growing regions, and help prepare growers for the impact of climate change.

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          Most cited references21

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          Plant science. Phenology under global warming.

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            Response of tree phenology to climate change across Europe

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              A unified model for budburst of trees.

              I Chuine (2000)
              Accurate plant phenology (seasonal plant activity driven by environmental factors) models are vital tools for ecosystem simulation models and for predicting the response of ecosystems to climate change. Since the early 1970s, efforts have concentrated on predicting phenology of the temperate and boreal forests because they represent one-third of the carbon captured in plant ecosystems and they are the principal ecosystems with seasonal patterns of growth on Earth (one-fifth of the plant ecosystems area). Numerous phenological models have been developed to predict the growth timing of temperate or boreal trees. They are in general empirical, nonlinear and non-nested. For these reasons they are particularly difficult to fit, to test and to compare with each other. The methodological difficulties as well as the diversity of models used have greatly slowed down their improvement. The aim of this study was to show that the most widely used models simulating vegetative or reproductive phenology of trees are particular cases of a more general model. This unified model has three main advantages. First, it allows for a direct estimation of (i) the response of bud growth to either chilling or forcing temperatures and (ii) the periods when these temperatures affect the bud growth. Second, it can be simplified according to standard statistical tests for any particular species. Third, it provides a standardized framework for phenological models, which is essential for comparative studies as well as for robust model identification. Copyright 2000 Academic Press.
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                Author and article information

                Contributors
                +254-20-7224120 , +254-20-7224001 , e.luedeling@cgiar.org
                Journal
                Int J Biometeorol
                International Journal of Biometeorology
                Springer-Verlag (Berlin/Heidelberg )
                0020-7128
                1432-1254
                22 August 2010
                22 August 2010
                May 2011
                : 55
                : 3
                : 411-421
                Affiliations
                [1 ]Department of Plant Sciences, University of California Davis, Mail Stop Two, One Shields Ave, Davis, CA 95616 USA
                [2 ]World Agroforestry Centre (ICRAF), United Nations Ave, Gigiri, P.O. Box 30677-00100, Nairobi, Kenya
                Article
                352
                10.1007/s00484-010-0352-y
                3077742
                20730614
                1b1590a2-8431-4589-89cb-b605d4e2483e
                © The Author(s) 2010
                History
                : 9 February 2010
                : 25 July 2010
                : 25 July 2010
                Categories
                Original Paper
                Custom metadata
                © ISB 2011

                Atmospheric science & Climatology
                dynamic model,utah model,chilling hours,chilling requirement,chill portions,winter chill

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