Insufficient winter chilling related to rising temperatures has raised questions about its potential effects on budburst timing (growth initiation) and subsequent tree growth. We quantified budburst timing and growth of seedlings of six Ontario temperate forest tree species after exposure to different levels of winter chilling using controlled forcing experiments. Based on chilling–forcing relationships, chilling requirements for the species tested ranged from 1000 to 1500 weighted chilling hours. Our findings showed that the species’ chilling needs ranked from highest to lowest were yellow birch (Betula alleghaniensis), eastern larch (Larix laricina), eastern white pine (Pinus strobus), red pine (Pinus resinosa), red spruce (Picea rubens), and eastern white cedar (Thuja occidentalis). Species that needed more chilling to release dormancy generally required less cumulative forcing for budburst. The variations in chilling–forcing relationships among species suggest that they would respond differently to temperature changes, resulting in year to year variation in their relative phenology. Insufficient chilling increased cumulative forcing needed for budburst but only extreme chilling deficiency (< 700 weighted chilling hours) caused abnormal budburst and growth, including reduced leaf and shoot expansion, early and erratic budburst in lower branches and stems, and even lack of budburst after 7 months in optimal growing conditions. Overall, our results suggest that based on climate warming projected for this century, insufficient winter chilling is not likely to occur in Ontario temperate forests in the foreseeable future.

与气温升高相关的冬季寒冷不足，引起了人们对其对芽期（生长开始）和随后树木生长的潜在影响的质疑。我们使用受控强迫实验对暴露于不同水平的冬季寒冷后的六种安大略温带森林树种的芽萌发时间和幼苗的生长进行了量化。根据寒冷与强迫的关系，被测物种的寒冷要求为加权的寒冷时间为1000至1500。我们的研究结果表明，该物种的低温需求从高到低依次为黄桦（Betula alleghaniensis），东部落叶松（Larix laricina），东部白松（Pinus strobus），赤松（Pinus resinosa），红云杉（Pus云杉（Picia rubens）和东部白柏（Thuja occidentalis））。需要更多冷却以释放休眠的物种通常需要较少的累积发芽力。物种之间冷强迫关系的变化表明它们对温度变化的反应不同，从而导致其相对物候逐年变化。低温不足会增加芽萌发所需的累积强迫，但只有极端的低温缺乏（<700加权的冷藏时间）会导致异常的萌芽和生长，包括叶片和枝条膨胀减少，下部分支和茎的早期和不稳定芽萌发，甚至在7后芽芽不足在最佳生长条件下可存放几个月。总体而言，我们的结果表明，根据本世纪预计的气候变暖，在可预见的将来，安大略温带森林中不太可能出现冬季寒冷不足的情况。