USDA Forest Service, Pacific Northwest Research Station, Olympia, WA, USA.
USDA Forest Service, Pacific Northwest Research Station, Corvallis, OR, USA.
Glob Chang Biol. 2017 Aug;23(8):3348-3362. doi: 10.1111/gcb.13690. Epub 2017 Apr 11.
The phenology of diameter-growth cessation in trees will likely play a key role in mediating species and ecosystem responses to climate change. A common expectation is that warming will delay cessation, but the environmental and genetic influences on this process are poorly understood. We modeled the effects of temperature, photoperiod, and seed-source climate on diameter-growth-cessation timing in coast Douglas-fir (an ecologically and economically vital tree) using high-frequency growth measurements across broad environmental gradients for a range of genotypes from different seed sources. Our model suggests that cool temperatures or short photoperiods can induce cessation in autumn. At cool locations (high latitude and elevation), cessation seems to be induced primarily by low temperatures in early autumn (under relatively long photoperiods), so warming will likely delay cessation and extend the growing season. But at warm locations (low latitude or elevation), cessation seems to be induced primarily by short photoperiods later in autumn, so warming will likely lead to only slight extensions of the growing season, reflecting photoperiod limitations on phenological shifts. Trees from seed sources experiencing frequent frosts in autumn or early winter tended to cease growth earlier in the autumn, potentially as an adaptation to avoid frost. Thus, gene flow into populations in warm locations with little frost will likely have limited potential to delay mean cessation dates because these populations already cease growth relatively late. In addition, data from an abnormal heat wave suggested that very high temperatures during long photoperiods in early summer might also induce cessation. Climate change could make these conditions more common in warm locations, leading to much earlier cessation. Thus, photoperiod cues, patterns of genetic variation, and summer heat waves could limit the capacity of coast Douglas-fir to extend its growing season in response to climate change in the warm parts of its range.
树木直径生长停止的物候学可能在调节物种和生态系统对气候变化的响应方面发挥关键作用。一个普遍的预期是，气候变暖将延迟停止，但这个过程的环境和遗传影响还知之甚少。我们使用来自不同种子来源的一系列基因型在广泛的环境梯度上进行高频生长测量，模拟了温度、光周期和种子源气候对海岸道格拉斯冷杉（一种具有生态和经济重要性的树木）直径生长停止时间的影响。我们的模型表明，凉爽的温度或短的光周期可以在秋季诱导停止。在凉爽的地方（高纬度和高海拔），停止似乎主要是由初秋的低温（在相对较长的光周期下）引起的，因此气候变暖可能会延迟停止并延长生长季节。但在温暖的地方（低纬度或低海拔），停止似乎主要是由秋季后期的短光周期引起的，因此气候变暖只会导致生长季节略有延长，反映出光周期对物候变化的限制。来自秋季或初冬频繁有霜的种子源的树木往往会在秋季早些时候停止生长，这可能是一种适应，以避免霜冻。因此，在温暖地区，很少有霜的基因流可能会对延迟平均停止日期的潜力有限，因为这些地区的树木已经相对较晚地停止生长。此外，来自异常热浪的数据表明，初夏长光照下的极高温度也可能导致停止。气候变化可能会使这些条件在温暖地区更为普遍，导致更早的停止。因此，光周期线索、遗传变异模式和夏季热浪可能会限制海岸道格拉斯冷杉在其分布范围内的温暖地区适应气候变化而延长生长季节的能力。
