For permanent crops, projections show that the amount of cold hours during the winter will keep on decreasing, which may entail a problem for fruit trees and other permanent crops. In most of the wine producing regions, the suitability of vineyards will be compromised (IPCC 2014).
Climate change will alter the geographical distribution of grape varieties, which will reduce the value of wine products and the means of living of local communities in the European Meridional region.
Most of fruit tree species are deciduous. They have this adaptation strategy to survive the winter cold. Fruit trees awaken from their winter rest once they have accumulated enough cold hours. Broadly speaking, cold hours would be the sum of hours in which the tree has been under a certain temperature, that in most of the calculation systems is 7 degrees Celsius.
In the process of adaptation to climate, fruit trees have learned how to predict the arrival of spring by calculating the cold hours. Fruit trees need these cold hours for a good bud breaking and flowering. This characteristic predetermines the geographic areas and microclimates in which certain species can be grown.
DIFFERENT NECESSITIES OF COLD HOURS IN FRUIT TREES
There are species with high, medium and low cold hours needs.
Among the fruit trees with high cold hours needs apple trees, pear trees, plum trees, cherry trees, and walnut trees can be found. These fruit trees can be found in areas with cold winters (continental climate).
Among the fruit trees with medium needs, certain varieties of cherry trees, pear trees, apple trees, hazels, peach trees, olive trees, and other kind of plum trees can be found. These fruit trees grow in intermediate areas.
The fruit trees which require fewer cold hours are almond trees, apricot trees, and fig trees. These can be grown in areas close to the coast.
Among each species there are differences in the cold hours depending on the varieties. Therefore, it is important to know which varieties are better adapted to the area.
COLD HOURS AND CLIMATE CHANGE
If in a year the number of cold hours needed is not reached, the fruit tree reacts with a late and irregular bud bursting, problems with flower buds and/or low fertilization rate, factors that compromise the yields.
Lately, for example during the 2015/2016 season, warmer winters are taking place due to the effect of climate change. Variations of the cold hours in fruit trees areas will affect yields and the economic damages could be catastrophic. It has to be taken into account that the change of species or varieties in permanent crops entail seasons without production and a high investment.
This represents a challenge for the technical management of permanent crop farms, in which “normal” years regarding temperatures will become less frequent.
Source: Baseline Report AgriAdapt and Agrorganics