Agricultural and Food Science, Vol. 19 (2010): 144-159 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 19 (2010): 144–159. 144 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 19 (2010): 144–159. 145 © Agricultural and Food Science Manuscript received October 2008 Climatic potential and risks for apple growing by 2040 Timo Kaukoranta*, Risto Tahvonen and Arto Ylämäki MTT Agrifood Research Finland, Plant Production Research, FI-31600 Jokioinen, Finland, *email: timo.kaukoranta@mtt.fi The impact of climatic change in 1971–2040 on the potential production areas and risks to nine apple cultivars (Malus domestica Borkh.) was studied over continental Finland using agro-climatic indices and gridded daily mean (Tm) and minimum temperatures from the Rossby Centre regional atmospheric climate model (RCA3) with SRES A2. Point data on daily minimum temperatures from 14 weather stations and low and high warming scenarios were also used. From the 1970’s to the present day, the areas of successful maturing of fruits have strongly expanded northwards. It is predicted that in 2011–2040, the warming of climate will allow expansion of commercial production in the south-eastern lake area, and a wider selection of cultivars for home gardens up to latitudes 65–66°N. Risk of extremely low temperatures (Tm< –26 °C) has reduced from 1980’s to the present but may not reduce much more in 2011–2040. Risk to shoots from fluctuating temperatures in winter and spring is likely to increase under the high warming scenario, more in the south-west than in the south-east. Risk to trees from cold days (Tm< –15 °C) with a concurrent thin snow cover is not predicted to increase. In the western inland of the country, below latitude 63°N, and in the south-western coast areas the frost risk during flowering may increase, especially in the early flowering cultivars. In order to adapt to and gain from the climatic change, breeding and testing targets should be modified within five years and they should include reduced sensitivity to temperature fluctuation in winter, late flowering, and frost tolerance of flowers. Key-words: Climate change, regional climate model, climatic index, winter injury, adaptation, acclimation A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 19 (2010): 144–159. 144 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 19 (2010): 144–159. 145 Introduction In Finland, global climate change is expected to cause rise of seasonal mean temperatures in 2010– 2039, relative to the mean values in 1961–1990, in winter by 1.2–5 °C, in spring by 1.1– 4.2 °C, in summer (June-August) by 0.6–1.6 °C, and in fall (September–November) by 0.9–2.3 °C (Jylhä et al. 2004). The temperature change falls slightly outside the 95% interval of natural variation for all seasons. Changes in precipitation are in gen- eral positive, but mostly within the 95% interval of natural variation. In the past since 1960, mean daily temperatures in both spring (March-May) and winter (December-February) have risen by about 1 °C; winter temperatures have risen to even a slightly higher extent, but their inter-annual variation has been much wider than that for spring temperatures (Tuomenvirta 2004). The climatic warming before the mid-century seems is so strong that it is mean- ingful to study its consequences on apple growing in Finland, despite that inherent climatic variability and model uncertainties are very large compared to the magnitude of warming. In relation to the observed warming of the sea- sons in Europe and North America, phenological time series show advancement in the all-leafing, flowering and fruiting of cultivated and natural species, including apple (Malus domestica Borkh) (Wolfe et al. 2005, Menzel et al. 2006, Eccel et al. 2009). Austin and Hall (2001) assessed the impact of climatic warming on future apple production in the mild maritime climate of New Zealand. They concluded that the warming will have no discern- ible effect on growth and development during the next 25 years and only very limited effects before 2050. Eccel et al. (2009) studied risk of frost during flowering over the next 50 years by using statisti- cally downscaled climate data and a thermal model calibrated to two sites at the alpine region of Tren- tino in Italy. They concluded that the risk of frost is more likely to reduce than increase. As regards the cool climate in eastern Canada, the impact on apple production has been found more significant. Rochette et al. (2004) assessed the risks for apple production during fall, winter and spring by computing semi-empirical agro- climatic indices, using climatic data from a Gen- eral Circulation Model with a spatial resolution of 3.75° × 3.75°. The date of the first fall frost, averaged across eastern Canada, is expected to be delayed by 10 days in 2010–2039 and by 16 days in 2040–2069, in comparison to 1961–1990, and correspondingly, the last spring frost (≤–2 °C) would be advanced by 6 days in 2010–2039 and by 15 days in 2040–2069. The delay of the first fall frost was considered to enhance hardening in fall due to the prolongation of the period from the time point of induction of hardening by short daylength until the time of the frost. This conclusion, how- ever, needs to be reconsidered after the finding by Heide and Prestrud (2005) that growth cessation and dormancy induction in apple are not influenced by photoperiod, but they are induced and control- led by low temperatures alone, which is contrary to the results by Howell and Weiser (1970a). The advance of the last spring frost, in connection with faster accumulation of growing degree days with the base temperature 5 °C (DD5), was predicted to reduce the frost risk to flower buds in the Con- tinental North, to have no effect in the Maritimes and Ottawa Valley, and to increase the risk in the milder-climate southern Ontario. An assessment by Winkler et al. (2002) in the Great Lakes region of the USA and Canada for 2025 to 2034 suggests that fruit-growing areas will experience a moderate prolongation of grow- ing season, an increase in seasonal temperature accumulation, and a decrease in the frequency of freezing temperatures. They concluded that the risk of bud injury caused by fluctuating temperatures would increase in mild-climate southern Ontario, based on the accumulating temperature from the first frost in fall to the last frost in spring. Our objective is to predict for Finland changes in suitability of apple cultivar types from the past decades to 2010-2040 and to assess what is needed to adapt to and possibly gain from the change. This study is limited to the first part of the 21st cen- tury because projecting the changes in the apple growing beyond the mid-century would not be very meaningful at this stage. Firstly, by the mid-cen- A G R I C U L T U R A L A N D F O O D S C I E N C E Kaukoranta, T. et al. Climatic potential and risks for apple growing 146 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 19 (2010): 144–159. 147 tury, local fruit growing is likely to be affected at least as much by global economic and technologi- cal developments as by the climatic change. Sec- ondly, the climate projections for Finland (Jylhä et al. 2004), based on the greenhouse gas emissions published in the Special Report on Emission Sce- narios (SRES) by the Intergovernmental Panel on Climate Change (IPCC) (Nakicenovic et al. 2000), do not differ greatly before the year 2050, but thereafter the different emission scenarios result in widely varying estimates of climatic warming, which reduces the practical value of the predictions concerning biological impacts. The CO2 concentra- tions which are expected to be reached after 2050 (IPCC 2007) may also modify cold tolerance in winter and spring (Repo et al. 1996, Wayne et al. 1998) and the onset of hardening in fall (Taylor et al. 2008). There are two parts in the estimation: potential and risks. The potential of an irrigated crop under cool climate is limited by warmness and length of growing seasons, described commonly by tempera- ture accumulation over the season. The risks are caused by inadequate vegetative maturing due to cool summer (Tumanov et al. 1972, Lindén 2001), extreme coldness in winter (Quamme et al. 1976, Lindén et al. 1996, Caprio and Quamme 1999), fluctuating temperatures after dehardening late in winter and spring (Howell and Weiser 1970b, Ketchie and Beeman 1973, Coleman 1992, Caprio and Quamme 1999), and frost during flowering. The temporal patterns of weather leading to win- ter injury are rather well described in qualitative terms, but attempts to detect the causes by statisti- cal analyses have been complicated by the fact that, in addition to large-scale climatic factors, the vul- nerability of orchards to winter injuries is affected by the rootstock and cultivar resistance to cold, the age of trees, and the modification of local climate through the elevation and slope of the orchard, soil type, wind protection, and water bodies. This is well known in practice and established by surveys in Finland (Säkö and Pessala 1967) and in Quebec, Canada (Khanizadeh 2007). Methods Climate data and production of maps Transient daily data on mean temperature (Tm), mini- mum temperature (Tn) and snow water equivalent in Finland during 1971–2040 were extracted from the European climate data for 1961–2100 with a spatial resolution of 0.44° on the rotated coordinate system simulated by the regional atmospheric cli- mate model RCA3 at the Rossby Centre, Sweden (Kjellström et al. 2005). The data were based on SRES A2 (Nakicenovic et al. 2000) and a global climate model (GCM) simulation by ECHAM4/ OPYC3 (Roeckner et al. 1999). It should be pointed out that also the past regional climate data were simulated, not measured. The climate data received from the Rossby Centre were processed with SAS software (SAS Institute Inc., Cary, NC, USA). The maps showing the gridded results under the geodesic coordinate system were drawn up by Mr. H. Ojanen using MapInfo software. The region of Åland Islands, west of south-western continental Finland, was not included in the data despite its be- ing a locally important apple growing area, because the grid point of RCA3 covering the Åland Islands constitutes mainly of sea surface. Point data on Tm and Tn in 1971–2000 from 14 weather stations operated by the Finnish Meteoro- logical Institute (Table 1) were used for estimating the risk of fluctuating temperatures in winter and spring. The lowest and highest seasonal changes of mean temperature by 2010–2039 (SRES A2), given by Jylhä et al. (2004), were interpolated lin- early with respect to day of year and year since 1961–1990 in order to obtain daily changes over the years 2011–2040. By adding the daily changes to the daily Tm and Tn values at the height of 2 m from the period 1971–2000 we obtained data sets for 2011–2040 with the same daily temperature range (DTR) as in 1971–2000, but with the mean and minimum values rising over the years. A G R I C U L T U R A L A N D F O O D S C I E N C E Kaukoranta, T. et al. Climatic potential and risks for apple growing 146 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 19 (2010): 144–159. 147 Agro-climatic indices Frost injury during flowering. The starting point for estimating the risk of frost during flowering is to predict the time of the flowering. In mild climates, the prediction is based on chilling temperatures in winter, which release the dormancy of buds, and on spring temperatures that drive the development of the buds (Richardson et al. 1974, Atkins and Morgan 1990, Legave et al. 2008). In climates with cold winters, the chilling requirement is met during winter under the present climatic conditions (Kronenberg 1979), and will easily be met in winter under the conditions expected by the mid-century in Finland (Jylhä et al. 2004). In the present climate, the timing of flowering in Quebec, Canada (Rochette et al. 2004) and in Finland (Ylämäki, unpublished) is predicted by a linear degree-day model without considering the chilling requirement. The frost risk was first assessed using the point data in 1971–2000 and lowest and highest scenari- os (Jylhä et al. 2004) for the years 2010–2040. For the point data, daily minimum temperature below –2 °C was set as the condition for frost during flow- ering. Under field conditions –2 °C at two metre height is generally a threshold for frost damage. The flowering time was predicted by computing DD5 from the start of a year and using cultivar spe- cific DD5 values for the start and end of flowering (Table 2), as observed at MTT Horticulture, Piik- kiö (60°23’ N, 22°33’ E) (Ylämäki, unpublished). Under the semi-continental climate of Finland, the choice of base temperature above 0 °C affects very little the prediction as the temperatures rise quite rapidly in spring. The vulnerable period was set to start 20 DD5 before the start of flowering. Having Table 1. Weather stations for point data, location and altitude from sea level in metres. Mean annual number of frost days during flowering of cv. Samo during 1971–2000 and 2011–2040. Low and high scenario represent the lowest and high- est seasonal temperature scenarios of temperature change given by Jylhä et al. (2004). LPNN1 WMO2 Station name Location Altitude Frost days 1971–2000 Frost days 2011–40 Low scenario Frost days 2011–40 High scenario 0103 2828 Piikkiö 60°23’N 22°33’E 6 0.7 0.7 0.3 1104 2762 Kokemäki 61°16’N 22°15’E 37 0.0 0.0 0.0 1201 2963 Jokioinen 60°49’N 23°30’E 104 0.7 1.0 0.0 1302 2829 Hyvinkää 60°36’N 24°48’E 86 0.3 0.7 0.0 1306 5274 Pälkäne 61°20’N 24°12’E 103 0.0 0.0 0.0 1701 2958 Lappeenranta 61°03’N 28°09’E 106 0.0 0.0 0.0 2401 2935 Jyväskylä 62°24’N 25°41’E 139 1.0 0.7 1.0 2602 2947 Mikkeli 61°41’N 27°12’E 101 0.0 0.0 0.3 3101 2833 Ylistaro 62°56’N 22°29’E 26 2.3 0.0 0.3 3301 2924 Ähtäri 62°32’N 24°13’E 157 3.7 1.4 0.7 3603 2788 Maaninka 63°09’N 27°19’E 90 0.3 0.3 0.0 3801 2929 Joensuu 62°40’N 29°37’E 121 0.3 0.3 0.7 4601 2897 Kajaani 64°17’N 27°41’E 147 2.0 1.3 1.3 5401 2875 Oulu 64°56’N 25°21’E 14 0.0 0.0 0.0 1LPNN National identification number 2WMO World meteorological organisation identification code A G R I C U L T U R A L A N D F O O D S C I E N C E Kaukoranta, T. et al. Climatic potential and risks for apple growing 148 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 19 (2010): 144–159. 149 estimated, from the point data, the number of frost days during flowering per decade, the Tn threshold for the RCA3 data was adjusted to give a roughly equal number of frost days as that found by means of the point data. Using RCA3 data annual num- bers of frost days during flowering and from these means for periods 1981–2010 and 2011–2040 were computed. Harvesting of fruits. The date of fruit maturing of the cultivars was computed from the RCA3 data based on DD5 accumulated from the start of the year. The number of years in a decade when fruits were predicted to mature successfully was computed to obtain the frequency of fruit maturing by decade. The frequency was scaled to the range from 0 to 1. Temperature accumulation requirements for each cultivar (Table 2) were derived from data collected from trials at MTT Horticulture, Piikkiö (Ylämäki and Tahvonen 1998). In these trials, it has been found that, during hot periods in late July and August when daily maximum temperatures are roughly above 25 °C, the development of the fruits and trees actually slows down. To study the effect of this phenomenon, temperature accumulation was computed also in another way: after 500 DD5 in days when daily maximum temperature (Tm) exceeded 20 °C, the daily accumulation was cut to a low value, which was arbitrarily set at 5 DD5. Requirement of temperature accumulation for vegetative maturity. According to the experiments carried out at MTT Horticulture, Piikkiö, vegetative maturity of trees requires temperature accumulation that is approximately 100–150 DD5 higher than that needed by the harvesting of fruits (Tahvonen, unpublished). We used a rule that 100 DD5 on top of harvesting maturity, as given in Table 2, would provide vegetative maturity that will ensure stable yield year after year in the studied cultivars. The RCA3 data were used. The numbers of years in 1981–2010 and 2011–2040 when vegetative maturity of trees was predicted to be reached were computed to obtain the frequency of vegetative maturing in the respective periods. The frequency was scaled to the range from 0 to 1. Extreme cold and temperature fluctuation in winter. Shoots of apple cultivars grown in cool climate areas can tolerate momentarily very low temperatures, down to –30 to –40 °C (Lindén et al. 1996, Qua- mme et al. 1976) when they are properly hardened. Yet, Caprio and Quamme (1999) concluded from a statistical analysis of apple production data in British Columbia, Canada, that low temperatures during November, December and February (–7 °C to –29 °C) were the main climatic factor limiting the apple production. Similarly, Lindén (2001) found that the variables indicating mid-winter severity, i.e., the monthly mean, minimum, and maximum temperatures from January to March, predicted well winter injuries in historical data in Finland. A precondition for the cold tolerance is that a growing season is warm enough for the termination of apical elongation and the subsequent hardening (Tumanov et al. 1972). There is evidence for Finland derived statistically by Lindén (2001) that low temperature accumulation during growing season has been as- sociated with winter-kill years. In fall the hardening is initiated by low temperatures according to Heide and Prestrud (2005) but a rapid and permanent drop of temperatures from above the hardening level to a winter level will leave apple trees vulnerable to winter injury. Fluctuating temperatures in winter cause bud and shoot damage in dehardened trees (Howell and Weiser 1970b, Ketchie and Beeman 1973). Table 2. Degree-day (base temperature 5 °C) require- ments for flowering (flowers open) and harvest maturity of apple cultivars. Group Cultivar Flowering start Flowering end Fruit maturing Summer Pirja 170 210 970 Summer Petteri 180 220 1120 Early fall Samo 165 205 1160 Late fall Melba 178 218 1190 Late fall Sandra 190 230 1195 Late fall Pekka 190 230 1230 Winter Tobias 195 235 1240 Winter Lobo 200 240 1300 Winter Aroma 200 240 1340 A G R I C U L T U R A L A N D F O O D S C I E N C E Kaukoranta, T. et al. Climatic potential and risks for apple growing 148 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 19 (2010): 144–159. 149 The phenomenon emerged also in the surveys by Caprio and Quamme (1999) in British Columbia, Canada, and by Coleman (1992) in New Bruns- wick, Canada. Ketchie and Beeman (1973) showed that the temporal pattern of cold resistance is dif- ferent from year to year making it difficult to find a single quantitative measure from experimental or survey data to predict the cold injury under vari- able climate. (1) Days with Tm below –27 °C were consid- ered to be extremely cold and potentially damag- ing to shoots or entire trees. The annual number of days with Tm below this threshold in winter was computed from the RCA3 data. When Tm is –27 °C, Tn is below –30 °C which is near the lowest tem- peratures momentarily tolerated by shoots, –30 to –40 °C (Lindén et al. 1996, Quamme et al. 1976). Temperature fluctuation in winter was studied with point data using the lowest and highest warming scenario (Jylhä et al. 2004) and RCA3 data. The fluctuation was expressed as temperature accumu- lation in DD5 units from the start of year until the occurrence of the last daily minimum temperature (Tn) below the set threshold. (2) For the point data, the Tn threshold was –15 °C. Only Tn below this threshold were considered damaging to shoots during the periods when Tm exceeds 5 °C. The threshold represents local prac- tical opinion and is in the range found by Ketchie and Beeman (1973). In their experiment bark from young trees showed increased electrolyte conduct- ance at –10 to –25 °C when Tx was above 5 °C in February in Washington, USA. (3) Using the RCA3 data, 18 different Tn thresh- old values were tried by stepping the Tn threshold from –15 °N to 2 °C by 1 °C increments. Low temperatures with a concurrent thin snow cover. To establish the frequency of conditions injuring roots and rootstock, the number of days in winter with Tm below –15 °C and snow water equivalent below 15 mm were computed from the RCA3 data. Water equivalent above 15 mm was considered to significantly slow down fall of temperature in soil. There is no published data on the exact tolerance of apple roots and rootstock to cumulative cold. Yet, periods with Tm under –15 °C for several days are not common below the latitude 65 °N in Fin- land under the current climate but when such cold spells have occurred, dying of entire trees has been observed (Tahvonen, unpublished). Differences in cold tolerance between the cultivars were not taken into account. Results Due to lack of space graphs and tables for all culti- var and index combinations are not presented. For combinations not shown in graphs the results are described in the text. Frost injury during flowering Result for early fall type cv. Samo (Table 1) shows the trends found for all cultivars using the point data. Generally the risk is expected to stay at current level or decrease. The risk is high under present climatic conditions inland in western Finland (locations Ylistaro, Ähtäri) and in the north-west (Kajaani), but reduces both under the lowest and highest sea- sonal temperature scenarios. The risk will remain lowest at lake areas (Lappeenranta, Mikkeli in the south-east, Pälkäne in the south), by the sea in the north (Oulu) and in the west (Kokemäki). Note that all cultivars do not mature at all sites (see results in chapter 2 below). Based on RCA3 data, the start of flowering will advance from 1971–2000 to 2011–2040 by 6 to 10 days in the south-west, and 5 to 7 days in other areas. Using RCA3 data, the threshold values 4 °C and 5 °C yielded frost risk of the same magnitude as the –2 °C threshold for the point data in central and western Finland. Using the threshold of 5°C with the RCA3 data, the risk increased in 2011– 2040 in the southern inland part of the country for all cultivars, but especially for the early flowering cultivars Pirja, Samo, Petteri, and Melba, while it decreased in the west and remained low in the east. Result for cv. Pirja is shown in Figure 1. A G R I C U L T U R A L A N D F O O D S C I E N C E Kaukoranta, T. et al. Climatic potential and risks for apple growing 150 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 19 (2010): 144–159. 151 70° 66° 68° 60° 64° 62° 26° 30°28° 20° 22° 24° 2011 - 2040 70° 66° 68° 60° 64° 62° 26° 30°28° 20° 22° 24° 1981 - 2010 2.0 - 5.5 1.0 - 1.9 0.6 - 0.9 0.2 - 0.5 0 - 0.1 Fig. 1. Spatial distribution of mean number of potential frost days per year during flower- ing of cv. Pirja in 1981–2010 and 2011–2040. Legend mean number of potential frost days. Maturing of fruits From the 1970’s to the present day, the areas of suc- cessful maturing of fruits have strongly expanded northwards. An example of this is the potential maturing area of cv. Melba shown in Figures 2. Dur- ing the following three decades, the maturing areas are predicted to continue expanding, though not as rapidly as in the past and mainly over central and western Finland where apple is grown only in home gardens. The very early maturing cultivars (cv. Pirja) are predicted to produce fully matured crops every year up to the latitudes 65 to 66°N in 2021–2040 (results not shown). Late maturing cvs Melba (Fig. 2), Sandra, Pekka and Tobias (results not shown) will mature every year up to the latitudes 61 to 62°N in the west and to the latitudes 62 to 63°N in the east, reflecting the effect of lake-richness in the east and hills in central and western Finland. Currently, the latest maturing, commercially grown cultivar on the continental Finland, Lobo, has produced mature fruits since 1991 only along the Baltic Sea in southern Finland and along the shores of large lakes in south-eastern Finland. In 2011–2040, Lobo is expected to mature in the whole southern part of the country up to the latitudes 61°N in the west and 62°N in the south-eastern lake area (results not shown). The cultivar Aroma, currently recommended only for the south-western archipelago, is expected to mature along the southern coast and with high probability also on the southern part of the eastern lake area (Fig. 3). When studying the possible effect of hot days on fruit development by limiting the accumulation of temperature to 5 DD5 in a situation where the Tm exceeded 20 °C, it was found that the limitation did not have any significant effect on the spatial pattern of success of maturation for the majority of cultivars; only the maturing areas of the very late maturing cultivars Lobo and Aroma were lo- cally reduced in southern inland Finland (results not shown). A G R I C U L T U R A L A N D F O O D S C I E N C E Kaukoranta, T. et al. Climatic potential and risks for apple growing 150 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 19 (2010): 144–159. 151 70° 66° 68° 60° 64° 62° 26° 30°28° 20° 22° 24° 2031 - 2040 70° 66° 68° 60° 64° 62° 26° 30°28° 20° 22° 24° 2021 - 2030 70° 66° 68° 60° 64° 62° 26° 30°28° 20° 22° 24° 2011 - 20201 0.9 0.7 - 0.8 0 - 0.6 Fig. 3. Change of spatial distri- bution of frequency of success- ful fruit maturing for cv. Aroma by decade on scale 0–1. Legend frequency. 70° 66° 68° 60° 64° 62° 26° 30°28° 20° 22° 24° 2011 - 2020 70° 66° 68° 60° 64° 62° 26° 30°28° 20° 22° 24° 2021 - 2030 70° 66° 68° 60° 64° 62° 26° 30°28° 20° 22° 24° 1981 - 1990 70° 66° 68° 60° 64° 62° 26° 30°28° 20° 22° 24° 1991 - 2000 70° 66° 68° 60° 64° 62° 26° 30°28° 20° 22° 24° 2001 - 2010 70° 66° 68° 60° 64° 62° 26° 30°28° 20° 22° 24° 2031 - 2040 1 0.9 0.7 - 0.8 0 - 0.6 Fig. 2. Change of spatial distri- bution of frequency of success- ful fruit maturing for cv. Melba by decade on scale 0–1. Legend frequency. A G R I C U L T U R A L A N D F O O D S C I E N C E Kaukoranta, T. et al. Climatic potential and risks for apple growing 152 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 19 (2010): 144–159. 153 Requirement of temperature accumulation for vegetative maturity The areas where temperature accumulation dur- ing growing season is sufficient for successful vegetative maturity are expected to extend 200 to 300 km northwards during the period 2011–2040 in comparison to the period 1981–2010. The very early maturing cultivars (cv. Pirja) are expected to get well ready for winter every year in 2011–2040 up to the latitudes 64 to 65°N and in eight years out of ten up to the latitudes 65 to 66°N (Fig. 4). The slightly later summer cultivars (cv. Petteri, results not shown) and the fall cultivars Samo (Fig. 5), Melba and Sandra (results not shown), will get ready for the winter every year in the whole southern and central Finland. The late fall cv. Pekka (Fig. 6) and early winter cv. Tobias (results not shown) will terminate successfully their development in the Fig. 4. Change of spatial distri- bution of frequency of reaching vegetative maturity for cv. Pirja in 1981–2010 and 2011–2040 on scale 0–1. Legend frequency Fig. 5. Change of spatial distri- bution of frequency of reaching of vegetative maturity for cv. Samo in 1981–2010 and 2011– 2040 on scale 0–1. Legend frequency. 70° 66° 68° 60° 64° 62° 26° 30°28° 20° 22° 24° 1981 - 2010 1 0.8 - 0.9 0.5 - 0.7 0 - 0.4 70° 66° 68° 60° 64° 62° 26° 30°28° 20° 22° 24° 2011 - 2040 70° 66° 68° 60° 64° 62° 26° 30°28° 20° 22° 24° 1981 - 2010 1 0.8 - 0.9 0.5 - 0.7 0 - 0.4 70° 66° 68° 60° 64° 62° 26° 30°28° 20° 22° 24° 2011 - 2040 A G R I C U L T U R A L A N D F O O D S C I E N C E Kaukoranta, T. et al. Climatic potential and risks for apple growing 152 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 19 (2010): 144–159. 153 southern part of the country and in the south-eastern lake area. The latest maturing cultivars Lobo (Fig. 7) and Aroma (results not shown) were not able to prepare themselves for winter in most years in the continental Finland during the period 1981-2010. During the next 30-year period they would be safe choices for orchards and home gardens only in the south-western coastal area and along lake shores in the south-east. 70° 66° 68° 60° 64° 62° 26° 30°28° 20° 22° 24° 1981 - 2010 1 0.8 - 0.9 0.5 - 0.7 0 - 0.4 70° 66° 68° 60° 64° 62° 26° 30°28° 20° 22° 24° 2011 - 2040 70° 66° 68° 60° 64° 62° 26° 30°28° 20° 22° 24° 2011 - 2040 1 0.8 - 0.9 0.5 - 0.7 0 - 0.4 70° 66° 68° 60° 64° 62° 26° 30°28° 20° 22° 24° 1981 - 2010 Fig. 6. Change of spatial distri- bution of frequency of reach- ing vegetative maturity for cv. Pekka in 1981–2010 and 2011– 2040 on scale 0–1. Legend frequency. Fig. 7. Change of spatial distri- bution of frequency of reaching vegetative maturity for cv. Lobo in 1981–2010 and 2011–2040 on scale 0–1. Legend frequency. A G R I C U L T U R A L A N D F O O D S C I E N C E Kaukoranta, T. et al. Climatic potential and risks for apple growing 154 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 19 (2010): 144–159. 155 Extreme cold and temperature fluctuation in winter (1) The frequency of very cold days (Tm be- low –27 °C) has diminished from the 1970s to the 1990s and into the present decade. RCA3 does not predict further reduction of very cold days over the next three decades south of latitudes 65 to 66°N where the coldness is an issue for apple growing in home gardens (results not shown). Above these latitudes the cultivars included in the study cannot be grown. (2) Using the point data, it was found that with the lowest warming scenario, from the start of the year to the last day when Tn was below –15 °C, temperature accumulation did not change appreci- ably at any station point (Table 3). With the high- est scenario, the accumulation increased at all sta- tions, most in the south-west (Piikkiö, Jokioinen, Kokemäki, Hyvinkää) being 14–17 DD5 and least in the east (Joensuu) and south-east (Lappeenran- ta, Mikkeli) in 2011–2040. In terms of days with Tm above 5 °C before the last Tn was –15 °C, the change under the highest scenario was from near zero in 1971-2000 to 5–9 days in 2011–2040. (3) With the RCA3 data, the Tn threshold had to be raised to 2 °C before 10–20 DD5 was accu- mulated in any part of country (results not shown), which means that RCA3 data cannot be used for assessing fluctuation late in winter and spring. Low temperatures with a concurrent thin snow cover According to the RCA3 data, the risk conditions with combined low temperature (Tm below –15 °C) and thin snow cover (snow water equivalent less than 15 mm) would be infrequent during 2011–2040 within the entire area where apple can be grown commercially and in home gardens. The risk varies from decade to decade without any apparent trend (results not shown). Discussion The transient gridded data of RCA3 facilitate the study of the impact of daily and annual variation on the spatial and temporal changes in the adaptation of apple cultivars. Kjellström et al. (2005) reported that, in northern Europe, the inter-annual variation simulated by RCA3 is close to the variation found in the ERA40 reanalysis data (Uppala et al. 2005). RCA3 simulates Tm within ±1 °C of ERA40 values, except in fall and winter in the north-eastern part of their model domain over Russia. Thus, if the per- formance of RCA3 for the past climate in northern Europe is considered to be a sufficient proof for its performance for the next three decades, Tm values from RCA3 SRES A2 are satisfactorily reliable for our study. Table 3. Degree-day (DD5) (base temperature 5 °C) ac- cumulation from January 1 until the last day when dai- ly minimum temperature is –15 °C. Low and high sce- nario represent the lowest and highest seasonal temper- ature scenarios of temperature change given by Jylhä et al. (2004). Location of the stations is given in table 1. Station name 1971–2000 2011–40 Low scenario 2011–40 High scenario Piikkiö 0.2 0.7 15.1 Kokemäki 0.1 0.9 17.3 Jokioinen 0.0 0.5 13.8 Hyvinkää 0.0 0.3 14.8 Pälkäne 0.0 0.1 8.8 Lappeenranta 1.4 1.8 8.8 Jyväskylä 0.0 0.2 10.3 Mikkeli 0.0 0.1 6.4 Ylistaro 0.1 0.4 13.9 Ähtäri 0.0 0.3 12.1 Maaninka 0.0 0.3 10.9 Joensuu 0.0 0.2 6.6 Kajaani 0.1 0.5 10.8 Oulu 0.2 0.7 12.0 A G R I C U L T U R A L A N D F O O D S C I E N C E Kaukoranta, T. et al. Climatic potential and risks for apple growing 154 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 19 (2010): 144–159. 155 However, there are some limitations in the data which are shared by other regional climate models (RCM). According to Kjellström et al. (2005), in the areas covering the central and southern parts of Finland, DTR of RCA3 was in spring and summer about 2 °C smaller than in the ERA40 data (Uppala et al. 2005). RCA3 overestimated Tn throughout a year in the area covering Finland: in southern Finland by 1 to 2 °C, and in northern Finland even more in winter and spring. Switching to another RCM or using averaged data from several RCMs would not offer a much better starting point. Ac- cording to Kjellström et al. (2007) the ten RCMs they investigated, underestimated cold extremes in winter and warm extremes in summer by several degrees Celsius in northern Europe, including Fin- land. They assume that some fraction of the warm bias may be due to an effect of the boundary condi- tions originating from driving GCMs and not due to the RCMs. Examination of the RCA3 data shows that it reflects the effects of the Baltic Sea coasts, large inland water bodies, such as the lake area in south- eastern Finland, and large area altitude differences. Yet, because of the grid cell size it cannot detect the effects of smaller lakes and hill chains which are known to modify significantly local climate, affect- ing the suitability of any site for perennial crops. Furthermore, orchards are generally established in sites which are less prone to low night and winter temperatures than the entire RCA3 grid cell which contains the orchard sites. The limited spatial reso- lution of RCA3 and the bias in Tn mean that the potentials and risks mapped in this study need to be seen only as broadly describing the spatial and temporal trends and not as accurate predictions for any individual site in the mapping area. The data from RCA3 are best suitable for predicting the de- velopment of apple in summer and the risk of cold injuries caused by long lasting cold spells in winter. Short cold spikes in winter and during flowering are not well detected. The frost risk during flowering in 2011–2040 in comparison to 1981–2010, based on RCA3 data, is expected remain at current level in most of the country, reduce in the west, but increase for all cul- tivars in the southern part of the country. The early flowering cultivars will be particularly vulnerable. The geographic differences arise naturally from the gradient of continentality of climate which in- creases from the south-west to the north-east of the Finland, and from the effect of lakes in the south- east. A point to mention for comparison in pest and yield potential studies is that the flowering is predicted to advance 5 to 10 days from 1971–2000 to 2011–2040. The potential growing area where the tempera- ture accumulation during growing season is suffi- cient for successful vegetative maturity and, con- sequently, for successful hardening, is expected to extend 200 to 300 km northwards during the period 2011–2040 in comparison to 1981–2010. Much of the expansion of the potential has already taken place since the 1970’s, which can be partially a result of temporary climatic variation or a result of the global warming trend. If the coming years show that the warming experienced this far is permanent, the expansion of the potential growing area of the cultivars may no longer proceed as rapidly. Rather, the effect of the climatic warming trend would be the stabilization of the expansion experienced since the 1990’s without any occasional retreat south- wards, even despite of climatic variation in the coming decades. The very early cultivars, for example, cv. Pirja, are expected to be able to terminate their vegetative development every year in 2011–2040 up to the latitudes 64 to 65°N and in eight years out of ten up to the latitudes 65 to 66°N. The slightly later summer cultivars, cv. Petteri, and the fall types, cvs Samo, Melba and Sandra, will get ready for the winter every year in the whole southern and central Finland. The late fall cultivars, cv. Pekka, and the early winter types, cv. Tobias, will reach vegetative maturity in the southern part of the country and in the south-eastern lake area. In 1981–2010, the lat- est maturing cultivars Lobo and Aroma could not fully prepare themselves for winter in most years in the continental Finland. During the next 30-year period they are expected to terminate successfully their development along the south-western Baltic Sea coast and along lake shores in the south-east Finland. A G R I C U L T U R A L A N D F O O D S C I E N C E Kaukoranta, T. et al. Climatic potential and risks for apple growing 156 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 19 (2010): 144–159. 157 The very early maturing cultivars are predicted to produce mature fruits up to the latitudes 65 to 66°N in 2011–2040. Correspondingly, the late ma- turing cultivars, Melba, Sandra, Pekka, and Tobias, will mature up to the latitudes 62 to 64°N. In the decade 2031–2040, which in the simulations is as- sumed to be slightly cooler than the preceding dec- ade 2021–2030, the maturing area extends further north in eastern Finland than in western parts of the country, reflecting the warming effect of large lakes in the east and the cooling effect of the hills in central and western inland Finland. Lobo, the latest maturing, commercially grown cultivar in the continental Finland, has since 1991 produced mature yield only on the Baltic Sea coast in south- western Finland and along the shores of the large lakes in south-eastern Finland. In 2011–2040, Lobo is expected to mature in the whole southern part of the country. The cultivar Aroma, currently rec- ommended only for the south-western coast and the archipelago, is expected to mature in western continental Finland up to the latitude 61°N and in the south-eastern lake area up to the latitude 62°N. Even cultivars which require 1400 DD5 for fruit maturing may produce stable yield along the south- western coast and in the south-eastern lake area. With longer and warmer seasons, the prediction of fruit maturity of the currently latest maturing culti- vars, Lobo and Aroma, would need to corrected for nonlinearity of the temperature response inland in southern Finland. The nonlinearity has been shown to be significant by Stanley et al. (2000), though in conditions with much longer growing seasons of New Zealand. The frequency of extremely cold days has been observed to diminish from 1970s to the present (Tuomenvirta et al. 2000), which is caught by RCA3. According to RCA3 (Kjellström et al. 2005), the frequency is not expected to diminish further in the next three decades south of north- ern border of apple growing, latitudes 65 to 66°N. Yet, cold winter weather will not be uncommon in the eastern and northern part of the country. In the south-west and west, extreme coldness will be a lesser risk, but winter injuries may be caused by fluctuating temperatures after reduced dormancy late in winter and spring. Assuming similar distri- bution of temperatures in 2011–2040 as in 1971– 2000 and the highest warming scenario (Jylhä et al. 2004), it is expected that apple trees will be in a clearly more vulnerable state in 2011–2040 when they meet the last very cold days (Tn<–15 °C). The change is larger in the west and south-west reflect- ing stronger expected warming of springs in the west (Jylhä et al. 2004). Under the lowest warming scenario, there would be no change in the risk of very cold days late in winter. It is also possible that the assumed variation of temperature in 2011–2040 is somewhat too large. In the last decades, DTR in winter and spring has reduced in Finland (Tuomen- virta et al. 2000) reflecting the global trend (Kaas and Frich 1995). In the past, in winters when there has been lit- tle protective snow cover, low temperatures have been an occasional problem in central and western Finland. The RCA3 data suggest that the frequency of days with temperature below –15 °C when there is little protective snow cover should not increase. However, the reliability of this prediction may be low as the thickness of snow cover and its insulat- ing value are rather hard to predict with a climate model. High soil moisture and high temperatures in September as well as drought in August are known to interfere with the hardening of apple trees in the present climate (Lindén 2001). Yet, it is not clear whether it has been the soil moisture itself or the rather high temperatures at the time of drought that have affected trees in the past because it has been observed that high temperatures in July and August delay the development of irrigated trees and their fruits in Finland (Ylämäki, unpublished). RCA3 predicts only small changes in temperature and precipitation in October and November in Finland. Earlier, using data from several models, Jylhä et al. (2004) predicted a rise of 0.9 to 2.9 °C in fall tem- peratures during 2010–2039 from/in comparison to 1961–1990, and a slight increase of precipitation, 0 to 15%, over entire Finland. Change of average fall temperature is probably beneficial for the harden- ing of the late cultivars. A potential problem for the hardening lies in a possible sudden drop of tem- perature after a warm fall which will not disappear during 2010–2039 because the alternation of mari- A G R I C U L T U R A L A N D F O O D S C I E N C E Kaukoranta, T. et al. Climatic potential and risks for apple growing 156 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 19 (2010): 144–159. 157 time western and continental north-eastern flows will stay. Perhaps, a more important change in fall is the rising importance of root and shoot canker caused by Phytophtora de Bary and Pythium Pring- sheim species, and Nectria galligena Bres. which benefit from mild and wet conditions. There are already indications from the experimental orchard in Piikkiö that warm falls have aggravated injury from these pathogens. In an ideal model, all the phases of development over a growing season and overwintering should condition the later phases, as they are qualitatively known to do (Howell and Weiser 1970b, Tumanov 1972, Ketchie and Beeman 1973, Coleman 1992, Caprio and Quamme 1999, Lindén 2001, Heide and Prestrud 2005, Khanizadeh 2007). This ap- proach has long been pursued with forest trees but the models are still far from ready to predict the ef- fect of climatic change (Hänninen 2006, Linkosalo et al. 2006, Hänninen and Kramer 2007). With fruit trees this approach would require more quantita- tive, cultivar specific information on response of trees to environment in winter, and a higher spatial resolution of projected climate data and better pre- diction ability of the daily and monthly ranges of temperature than provided by the current genera- tion of RCMs. In conclusion, the projected warming of climate is likely to be mostly beneficial to apple growing in Finland before the mid-century, as found in eastern Canada by Rochette et al. (2004) and for Great Lakes area in USA by Winkler et al. (2002), though exact comparisons between the studied re- gions cannot be made because the regional climates of the regions are different. The warming allows a wider selection of cultivars to home gardens, more productive cultivars in the south for commercial production and expansion of production in the south-eastern lake area. To introduce new cultivars and expand commercial production, winter hardi- ness and yield characteristics need to be tested at potential production sites. To increase the value of commercial production in the south, a programme for breeding and testing cultivars of late winter type should be initiated, with the aim of developing cultivars that produce fruits storable into spring, longer than any of the currently grown cultivars (Kinnanen et al. 2007). Adaption to climate change emphasizes existing general breeding targets which include low sensitivity to temperature fluctuation in winter, late flowering, frost tolerance of flowers, and better resistance to canker. The process from breeding to establishing actual orchards takes 15 to 20 years, and hence, breeding targets should be set within the next five years. Screening of the existing cultivars and rootstocks at sites where they have not been tested could start within 10 to 15 years, because the testing requires, at least, 5 to 10 years, or even more if no cold winters occur within that period. Acknowledgements. We thank Mr. Hannu Ojanen for pro- ducing the figures. References Atkins, T.A. & Morgan, E.R. 1990. Modelling the effects of possible climate change scenarios on the phenolo- gy of New Zealand fruit crops. Acta Horticulturae 276: 201–208. Austin, P.T. & A.J. Hall, A.J. 2001. Temperature Impacts on Development of Apple Fruits. In: Warrick, R.A., Kenny, G.J. & Harman, J.J. (eds.) The Effects of Climate Change and Variation in New Zealand An Assessment Using the CLIMPACTS System. International Global Change Insti- tute (IGCI), The University of Waikato. 127 p. Caprio, J.M. & Quamme, H.A. 1999. Weather conditions associated with apple production in the Okanagan Val- ley of British Columbia. Canadian Journal of Plant Sci- ence 79: 129–137. Coleman, W.K. 1992. A proposed winter-injury classifica- tion for apple trees on the northern fringe of commer- cial production. Canadian Journal of Plant Science 72: 507–516. Eccel, E., Rea, R. & Caffarra, A. 2009. Risk of spring frost to apple production under future climate scenarios: the role of phenological acclimation. International Journal of Biometeorology 53: 273–286. Heide, O.M. & Prestrud, A.K. 2005. Low temperature, but not photoperiod, controls growth cessation and dorman- cy induction and release in apple and pear. Tree Physi- ology 25: 109–114. Howell, G.S. & Weiser, C.J. 1970a. Similarities between the control of flower initiation and cold acclimation in plants. HortScience 5: 18–20. Howell, G.S. & Weiser, C.J. 1970b. Fluctuations in the cold resistance of apple twigs during spring deharden- ing. Journal of American Society for Horticultural Sci- ence 95: 190–192. A G R I C U L T U R A L A N D F O O D S C I E N C E Kaukoranta, T. et al. Climatic potential and risks for apple growing 158 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 19 (2010): 144–159. 159 Hänninen, H. 2006. Climate warming and the risk of frost damage to boreal forest trees: identification of critical ecophysiological traits. Tree Physiology 26:889–898. Hänninen, H. & Kramer, K. 2007. A framework for model- ling the annual cycle of trees in boreal and temperate regions. Silva Fennica 41: 167–205. IPCC. 2007. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth As- sessment Report of the Intergovernmental Panel on Cli- mate Change. Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K.B., Tignor, M. & Miller, H.L. (eds.) Cambridge University Press, Cambridge, UK and New York, NY, USA, 996 p. Jylhä, K., Tuomenvirta, H. & Ruosteenoja, K. 2004. Climate change projections for Finland during the 21st century. Boreal Environmental Research 9: 127–152. Kaas, E. & Frich, P. 1995. Diurnal temperature range and cloud cover in the Nordic countries: observed trends and estimates for the future. Atmospheric Research 37: 211-228 Ketchie, D.O. & Beeman, C.H. 1973. Cold acclimation in ‘Red Delicious’ apple trees under natural conditions dur- ing four winters. Journal of American Society for Horti- cultural Science 98: 257–261. Kinnanen, H., Tahvonen, R. & Ylämäki, A. 2007. Lajikkeis- to. Omenan viljely, Puutarhaliiton julkaisuja nro 345: 180 – 208 (In Finnish). Khanizadeh, S. 2007. Cultural and environmental factors associated with winter injury to apple in Northern East- ern Canada. International Journal of Fruit Science 7: 85–100. Kjellström, E., Bärring, L., Gollvik, S., Hansson, U., Jones, C., Samuelsson, P., Rummukainen, M., Ullerstig, A., Willén, U. & Wyser, K. 2005. A 140-year simulation of Eu- ropean climate with the new version of the Rossby Cen- tre regional atmospheric climate model (RCA3). SMHI Reports Meteorology and Climatology No 108, 54 p. Kjellström, E., Bärring, L., Jacob, D., Jones, R., Lenderink, G. & Schär, C. 2007. Modelling daily temperature ex- tremes: recent climate and future changes over Europe. Climatic Change 81: 249–265. Kronenberg, H.G. 1979. Apple growing potentials in Eu- rope 1. The fulfilment of the cold requirement of the ap- ple tree. Netherlands Journal of Agricultural Science 27: 131-137. Legave, J.M, Farrera, I, Almeras, T., Santamaria, P. & Calle- ja, M. 2008. Selecting models of apple flowering time and understanding how global warming has had an im- pact on this trait. Journal of Horticultural Science and Biotechnology 83: 76–84. Lindén, L., Rita, H. & Suojala, T. 1996. Logit Models for Estimating Lethal Temperatures in Apple. HortScience 31: 91 - 93. Lindén, L. 2001. Re-analyzing historical records of winter injury in Finnish apple orchards. Canadian Journal of Plant Science 81: 479–485. Linkosalo, T., Häkkinen, R. & Hänninen, H. 2006. Mod- els of the spring phenology of boreal and temperate trees: is there something missing? Tree Physiology 26:1165–1172. Menzel, A., Sparks, T.H., Estrella, N., Koch, E., Aasa, A., Ahas, R., Alm-Kubler, K., Bissolli, P., Braslavska, O., Briede, A., Chmielewski, F.M., Crepinsek, Z., Curnel, Y., Dahl, A., Defila, C., Donnelly, A., Filella, Y., Jatczak, K., Mage, F., Mestre, A., Nordli, ., Penuelas, J., Pirinen, P., Remisova, V., Scheifinger, H., Striz, M, Susnik, A.., Van Vliet, A.J.H., Wielgolaski, F..E., Zacht, S. & Zust, A. 2006. European phenological response to climate change matches the warming pattern. Global Change Biology 12: 1969–1976. Nakicenovic, N., Alcamo, J., Davis, G., de Vries, B., Fen- hann, J., Gaffin, S., Gregory, K., Grübler, A., Yong Jung, T., Kram, T., Lebre La Rovere, E., Michaelis, L., Mori, S., Morita, T., Pepper, W., Pitcher, H., Price, L., Riahi, K., Roehrl, A., Rogner, H.–H., Sankovski, A., Schlesin- ger, M., Shukla, P., Smith, S., Swart, R., van Rooijen, S., Victor, N. & Dadi, Z. 2000. Emission scenarios. A special report of working group III of the intergovern- mental panel on climate change. Cambridge Universi- ty Press, 599 p. Repo,T, Hanninen, H, Kellomäki, S. 1996. The effects of long-term elevation of air temperature and CO2 on the frost hardiness of Scots pine. Plant Cell & Environment 19:209–216. Richardson, E.A., Seeley, S. D. & Walker, D. R. 1974. A model for estimating the completion of rest for ‘Red- haven’ and ‘Elberta’ peach trees. HortScience 9: 331– 332. Rochette, P., Bélanger, G., Castonguay, Y., Bootsma, A. & Mongrain, D. 2004. Climate change and winter dam- age to fruit trees in eastern Canada. Canadian Journal of Plant Science 84: 1113–1125. Rosenzweig, C., G. Casassa, D.J. Karoly, A. Imeson, C. Liu, A. Menzel, S. Rawlins, T.L. Root, B. Seguin, P. Try- janowski, 2007. Assessment of observed changes and responses in natural and managed systems. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assess- ment Report of the Intergovernmental Panel on Climate Change, M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden & C.E. Hanson, (eds.), Cambridge Uni- versity Press, Cambridge, UK, 79-131. Roeckner, E., Bengtsson, L., Feicther, J., Lelieveld, J. & Rodhe, H., 1999. Transient climate change simula- tions with a coupled atmosphere-ocean GCM includ- ing the tropospheric sulfur cycle. Journal of Climate 12: 3004-3032. Stanley, C.J., Lupton, G.B, McArtney, S., Cashmore, W.M. & De Silva, H.N. 2000. Towards understanding the role of temperature in apple fruit growth responses in three ge- ographical regions within New Zealand. Journal of Hor- ticultural Science & Biotechnology 75: 413–422. Säkö J. & Pessala, T. 1967. Injuries in Finnish orchards caused by winter 1965–66. Annales Agriculturae Fen- niae 6: 53–62. Taylor, G., Tallis, M.J., Giardina, C.P., Percy, K.E., Migliet- ta, F., Gupta, P.S., Gioli, B., Calfapietra, C., Gielen, B., Kubiske, M.E., Scarascia-Mugnozza, G.E., Kets, K., Long, S.P. & Karnosky, D.F. 2008. Future atmospher- ic CO2 leads to delayed autumnal senescence. Global Change Biology 14: 264–275. Tumanov, I.I., Kuzina, G.V., Karnikova, L.D. & Khvalin, N.N. 1972. Effect of vegetation time on ability of woody plants to increase their frost resistance during the process of hardening. Soviet Plant Physiology 19: 31–39. Tuomenvirta, H. 2004. Reliable estimation of climatic vari- A G R I C U L T U R A L A N D F O O D S C I E N C E Kaukoranta, T. et al. Climatic potential and risks for apple growing 158 A G R I C U L T U R A L A N D F O O D S C I E N C E Vol. 19 (2010): 144–159. 159 ations in Finland. Diss. University of Helsinki. 79 p. Finn- ish Meteorological Institute Contributions No. 43. Tuomenvirta, H., Alexandersson, H., Drebs, A., Frich, P. & Nordli, P.E. 2000. Trends in Nordic and Arctic Tem- perature Extremes and Ranges. Journal of Climate 13: 977–990. Uppala, S. M., Kållberg, P.W., Simmons, A.J., Andrae, U., da Costa Bechtold, V., Fiorino, M., Gibson, J.K., Haseler, J., Hernandez, A., Kelly, G.A., Li, X., Onogi, K., Saarin- en, S., Sokka, N., Allan, R.P., Andersson, E., Arpe, K., Balmaseda, M.A., Beljaars, A.C.M., van de Berg, L., Bid- lot, J., Bormann, N., Caires, S., Chevallier, F., Dethof, A., Dragosavac, M., Fisher, M., Fuentes, M., Hagemann, S., Holm, E., Hoskins, B.J., Isaksen, L., Janssen, P.A.E.M., Jenne, R., McNally, A.P., Mahfouf, J.-F., Morcrette, J.–J., Rayner, N.A, Saunders, R.W., Simon, P., Sterl, A., Tren- berth, K.E., Untch, A., Vasiljevic, D., Viterbo P. & Wool- len, J. 2005. The ERA-40 Re-analysis. Quarterly Journal of Royal Meteorological Society 131: 2961–3012. Wayne, P.M., Reekie, E.G. & Bazzaz, F.A. 1998. Elevated CO2 ameliorates birch response to high temperature and frost stress: implications for modelling climate-induced geographic range shifts. Oecologia. 114: 335–342. Winkler, J.A., Andresen, J.A., Guentchev, G. & Kriegel, R.D. 2002. Possible impacts of projected temperature change on commercial fruit production in the Great Lakes region. Journal of Great Lakes Research 28: 608–625. Wolfe, D.W., Schwartz, M.D., Lakso, A.N., Otsuki, Y., Pool R.M. & Shaulis, N.J., 2005. Climate change and shifts in spring phenology of three horticultural woody peren- nials in north-eastern USA. International Journal of Bi- ometeorology 49: 303–309. Ylämäki, A. & Tahvonen, R. 1998. Omenalajikkeiden sa- don valmistumista voi arvioida lämpösumman avulla. Puutarha & Kauppa 2, 35: 4–5 (In Finnish). Climatic potential and risks for apple growing by 2040 Introduction Methods Climate data and production of maps Agro-climatic indices Results Frost injury during flowering Maturing of fruit Requirement of temperature accumulation for vegetative maturity Extreme cold and temperature fluctuation in winter Low temperatures with a concurrent thin snow cover Discussion References