Physiological Processes during Winter Dormancy and Their Ecological Significance

Pseudothecia of Swiss needle cast fungus, Phaeocryptopus gaeumannii, physically block stomata of Douglas fir, reducing CO2 assimilation

“…However, no difference between infected and noninfected branches was noted until there were obvious pseudothecia present in infected needles. Depressions of needle physiology during the winter are a typical phenomenon in conifers, particularly at higher elevations (Havranek & Tranquillini, 1995). In our work, winter depressions of Douglas-fir needle physiology have been detected in seedlings (present study) and saplings, c. 15-yr-old (K. Kavanagh, unpublished).…”

“…Similarly to the disease mechanism to be presented, the reduced supply of CO # from the low stomatal conductance might cause a down-regulation in the activation of Rubisco. However, ' normal seasonal changes in cell physiology ' (Havranek & Tranquillini, 1995) such as membrane permeability should not be overlooked.…”

Climatic Sensitivity of a Mixed Forest Association of White Spruce and Trembling Aspen at Their Southern Range Limit

“…Furthermore, aspen growth showed a consistent relationship with the month of January (−, t) for all of the temperature variables. This indicates that mild winters can negatively affect growth, as it increases the incidence of thaw-freeze events [54,55]. In other words, Tranquillini [54] and Havranek and Tranquillini [55] reported that while the cold hardiness of trees is elevated during mid-winter, the occurrence of extreme climate anomalies such as warm temperatures in December and January followed by the rapid return to cold temperature results in substantial bud damage.…”

“…This indicates that mild winters can negatively affect growth, as it increases the incidence of thaw-freeze events [54,55]. In other words, Tranquillini [54] and Havranek and Tranquillini [55] reported that while the cold hardiness of trees is elevated during mid-winter, the occurrence of extreme climate anomalies such as warm temperatures in December and January followed by the rapid return to cold temperature results in substantial bud damage. Furthermore, warm temperatures during mid-winter may increase the rate of desiccation and thus deplete water reserves [54,55].…”

“…In other words, Tranquillini [54] and Havranek and Tranquillini [55] reported that while the cold hardiness of trees is elevated during mid-winter, the occurrence of extreme climate anomalies such as warm temperatures in December and January followed by the rapid return to cold temperature results in substantial bud damage. Furthermore, warm temperatures during mid-winter may increase the rate of desiccation and thus deplete water reserves [54,55]. Thaw-freeze events have also been implicated as having a negative impact on the growth of trembling aspen within the aspen parkland zone of Alberta and Saskatchewan [52].…”