Apple tree phenology in relation to temperature in Sauherad (Norway)

Abstract

Temperature plays a crucial role for the phenological development of plants and since past few decades Earth’s temperature is increasing. Plants are responding to this rise in temperature, through variations in their phenology. The temperature related changes in phenology have been studied for various fruit trees, including apple. Therefore, our study presents the relationship of phenology of three apple cultivars i.e. Red Aroma, Summerred and Discovery with the temperature in Sauherad, Norway. Moreover, the study looks for variation in phenological development and temperature between two years i.e. 2015 and 2016. This study makes use of multiple statistical tests (Spearman’s rank correlation test, Wilcoxon signed ranks test and paired t-test). It shows that the phenological development of all the considered three apple cultivars have a strong positive correlation with cumulative growing degree days while moving from the green top stage to the fruit diameter (10 mm) stage in the year 2016. Phenological development of 2015 does not differ statistically from the phenological development of 2016 while looking at all cultivars together. However, in the individual case of Discovery, phenological development of the year 2015 varies from 2016. Another finding is the interannual variation of cumulative growing degree days during the period of January to mid-July. In the year 2015 cumulative growing degree days were reduced by 30.89 0C compared to the year 2016. Apple cultivation is economically important in Norway and the findings of the study can be useful to the local apple farmers in Sauherad as well as researchers interested in this field.