Evaluation of vegetative phenological stages in a spruce monoculture depending on parameters of the environment

Vegetative phenological stages were evaluated in a spruce monoculture of the third age class in the region of the Drahanská vrchovina Upland. Methods of the ČHMÚ (Czech Hydro-Meteorological Office) were used. Temperature requirements of Norway spruce for the onset of particular phenological stages were evaluated on the basis of sums of air effective temperatures higher than 5 oC and at soil temperatures, values exceeding 1 oC were taken into account. In the paper, years 2005 to 2007 were evaluated. Results obtained were compared with long-term monitoring for the period 1991–2004. The onset and duration of phenological stages differed in particular years depending on the course of weather. Evaluation of the 17-year period shows that onsets of phenological stages in particular years differed markedly. An interval for the “onset of budbreak stage” was 13 days, at the “stage of 50% foliation” 14 days, the “stage of 100% foliation” 17 days. At the stage “full foliation”, the interval amounts to 33 days in the period 1991 to 2007. The start of budbreak and foliation is affected by air and soil temperatures, which was also proved by statistical evaluations. High dependence between the onset of budbreak and air temperatures is confirmed by statistically significant correlation coefficients R2 = 0.854 (2005–2007) and R2 = 0.754 (1991–2004). Dependence of the onset of budbreak and foliation on the soil temperature is proved by a correlation coefficient R2 = 0.658 (2005 to 2007) and R2 = 0.687 in the period 1991 to 2004. Results show that in recent years, the earlier onset of spring phenological stages occurs at the higher sum of effective temperatures. The length of their duration shortens.