The Maturation of Pinus sylvestris Seeds in Relation to Temperature Climate in Northern Finland

The probability of achieving an anatomically mature seed crop of Scots pine (Pinus sylvestris L.) in Northern Finland has been studied on the basis of earlier data and meteorological observations. The meteorological data over the period of 1951-1980 was used to calculate the probability of having a mature seed crop in various parts of Northern Finland. The climatic variables used were: (a) June-August mean temperature (b) June-September mean temperature, and (c) annual temperature sum (+5 degrees C base temperature). A non-linear relationship between the percentage of mature seeds in a seed crop and the annual temperature sum was detected, indicating that 50% mature seed crop was achieved at appr. 890 degree days. The results suggest that the probability of having 50% mature seed crop is approximately 0.02-0.03 near the polar timber line. The probability of the occurrence of such years is, however, considerably higher in lowlands and lake districts even near the timber line.