Geographic variation in cold hardiness among eastern white pine (Pinus strobus L.) provenances in Ontario

Needle and shoot samples of eastern white pine provenances in Ontario were subjected to a series of artificial freezing tests to determine provenance differentiation in fall and winter cold hardiness. Results indicated that under the natural processes of cold acclimation in the fall, above ground tissues of eastern white pine could withstand low freezing temperatures in September – October that exceeded the local long-term minimum climate extremes of the same periods. The severity of cold damage increased at a faster rate in September than in October and November when temperature was further decreased below the thresholds that started to cause cold damage. Under the selected freezing temperatures that inflicted between 15 and 85% average needle or/and cambium damage, consistent results were observed among freezing tests that were conducted using samples of different ages and cold acclimation stages. A clinal pattern of geographic variation in the severity of cold damage was detected with a trend parallel to that of growth potential. As thermal conditions improve from the north to south in Ontario, the growth potential of a provenance increases but the degree of cold hardiness decreases. Based on risk assessments using a spatial regression approach, it was, however, believed that northward seed transfer within a distance of 2–2.58 in latitude could be acceptable to promote stand growth while incurring no statistically significant increase in cold damage.