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Late or spring frost damage is a significant risk to grape production in frost-prone viticulture regions all over the world, such as parts of North America (Johnson and Howell 1981, Poling 2008), Australia (Cashman 2000), New Zealand (Trought et al. 1999), France (Brun and Cellier 1992), Italy (Orlandini et al. 2003), Germany (Hill et al. 2011) or Poland (Lisek 2008). In the Luxembourgish winegrowing region, official records (1948‒2011) reported spring frost damage in the vineyards in 11 out of 64 seasons (Anonymous 2011). In other winegrowing regions, the frequency of severe frost damage is even higher. In Champagne, for example, such events occurred every fourth year from 1875 to 1975 (Brun and Cellier 1992) and in Michigan 11 times from 1957 to 1977 (Johnson and Howell 1981). Spring frost can result in severe crop losses, threatening the financial existence of winegrowers. Molitor and Junk (2011) showed that the average yield in the Luxembourgish winegrowing region was reduced by 39% in years with spring frost damage.
The temperature conditions necessary for freeze damage of plant tissue are dependent on the phenological growth stage reached (Trought et al. 1999). Young grape tissues with a high water content are killed as soon as ice crystals are formed (Poling 2008). Such crystal formation on young leaves and shoots is possible at an air temperature around or slightly below 0°C, depending on the type of the freeze event (radiation freeze or advection freeze) (Trought et al. 1999). Damaged tissues rapidly lose their turgor, darken completely and become water soaked (Poling 2008). Even though freeze damage can happen on closed grape buds, budburst can be seen as the onset of the most susceptible period.
Consequently, for an estimation of the risk of late frost under future climate conditions two pieces of information need to be known: (i) the budburst period; and (ii) the air temperature conditions during and after budburst.
Different approaches for the prediction of the day of budburst are presented in the literature (Amerine and Winkler 1944, Garcia de Cortazar-Atauri et al. 2009, Nendel 2010, Urhausen et al. 2011). An overview of phenological models for grapevine budburst simulation is given in Table 1. Models of Amerine and Winkler (1944), Nendel (2010), and Urhausen et al. (2011) are only of local or regional validity. This is probably due to the models not adequately describing the underlying physiology of dormancy and release from dormancy. Factors not considered by the models may change between sites, so that site-specific estimation of model parameters is required. For example, despite the fact that the early literature described the grapevine as relatively insensitive to photoperiod (Alleweldt 1964), recent literature shows that this factor indeed influences the physiology and phenology of Vitis species (Schnabel and Wample 1987, Fennell and Hoover 1991, Perez et al. 2009, 2011) as with the majority of plant species (Kobayashi and Weigel 2007). To overcome these shortcomings, Caffarra et al. (2011) developed the phenological model DORMPHOT that considers photoperiod and makes an attempt at describing the physiological processes taking place during dormancy. The inclusion of dormancy induction, of the interaction between photoperiod and temperature and the use of an experimentally established relationship for quantifying the action of a warm temperature on growth, ensures that the DORMPHOT model is more process based than phenological models based on degree-days or bioclimatic indices. While the DORMPHOT model was originally calibrated and validated on birch, it can be adapted to different plant species provided an adequately large and varied data set is available (Caffarra et al. 2011).
Table 1. A comparison of different published phenological models to forecast budburst
|Model reference||Method employed||Model type||Dormancy effects considered||Starting point for temperature sum accumulation (northern hemisphere)|
|Urhausen et al. (2011)||Relationship between temperature drivers and phenology, obtained by multiple regression methods||Statistical||No||–|
|Amerine and Winkler (1944)||Heat summation||Process-based||No||1 April|
|Nendel (2010)||Heat summation||Process-based||No||1 March|
|Garcia de Cortazar-Atauri et al. (2009) (BRIN Model)||Chill and heat summation||Process-based||Yes||1 January|
|Riou and Pouget (1992)||Cumulative thermal daily actions||Process-based||Yes||1 January|
|Caffarra et al. (2011) (DORMPHOT)||Relationship between rate of development, temperature and photoperiod during the subphases of dormancy||Process-based||Yes||1 September|
Climate change projections indicate that the date of the last spring frost as well as the date of budburst will advance in response to a higher temperature (Caffarra and Eccel 2011). So far, it is unclear if one of these trends will be more pronounced than the other and, therefore, whether the risk of frost damage will increase or decrease. Molitor and Junk (2011) showed that in Luxembourg, the average time span between the last frost and budburst had tended to increase in the last decades, decreasing spring frost risk. In contrast, under the climatic conditions of Tuscany (Orlandini et al. 2009), earlier budburst is expected to increase the late frost risk in the future. Similarly, Poling (2008) suggests that earlier budburst could result in an elevated risk of damaging frost events in the eastern and mid-west regions of the USA. Further complicating the picture is the prediction by White et al. (2006) that frost risks will be reduced overall. If the estimations in the literature are that contrasting, a precise simulation of the late frost risk under future climate conditions in Luxembourg (as an example for a cool climate viticultural region in central Europe) is justified.
The Vitis vinifera cultivar Müller-Thurgau (synonym Rivaner) is the most common grape cultivar in Luxembourg. Because of its frost vulnerability and its economic importance for Luxembourg's viticulture, this study focused on Müller-Thurgau. Based on lengthy phenological observation, all important cultivars grown in Luxembourg (Müller-Thurgau, Riesling, Pinot Blanc, Pinot Gris, Pinot Noir, Elbling and Auxerrois) show almost identical precocity (Urhausen et al. 2011). Hence, with regard to budburst period, Müller-Thurgau can be considered representative of the majority of V. vinifera cultivars grown in Luxembourg.
This study aimed to: (i) develop and validate a model to predict the date of grape budburst; and (ii) estimate the risk of late frost damage in the vineyards of the Luxembourgish winegrowing region under future climate conditions.
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We thank the Institut Viti-Vinicole in Remich (Luxembourg) for financial support. Parts of this study were carried out in the framework of the CLIMPACT (FNR C09/SR/16) and REMOD projects. The authors gratefully acknowledge Serge Fischer and Robert Mannes (Institut Viti-Vinicole, Remich, Luxembourg), Ottmar Baus (Geisenheim University, Germany), Bernd Ziegler (DLR Rheinpfalz, Neustadt an der Weinstrasse, Germany), Ulrike Maaß and Heinrich Hofmann (LWG Veitshöchsheim, Germany), Barbara Schildberger (HBLA Klosterneuburg, Austria), and Dr Horst Caspari (Colorado State University, Grand Junction, CO, USA) for providing the historical meteorological and phenological data sets as well as Vanessa Peardon for language support.