Institute for Resources, Environment and Sustainability, University of British Columbia, Vancouver, British Columbia, Canada.
School of International and Public Affairs, Columbia University, New York, New York, USA.
Glob Chang Biol. 2022 Oct;28(20):6002-6020. doi: 10.1111/gcb.16313. Epub 2022 Jul 16.
Temperature is a key climate indicator, whose distribution is expected to shift right in a warming world. However, the high-temperature tolerance of trees is less widely understood than their drought tolerance, especially when it comes to sub-lethal impacts of temperature on tree growth. I use a large data set of annual tree ring widths, combined with a flexible degree day model, to estimate the relationship between temperature and tree radial growth. I find that tree radial growth responds non-linearly to temperature across many ecoregions of the United States: across temperate and/or dry ecoregions, spring-summer temperature increases are beneficial or mostly neutral for tree growth up to around 25-30°C in humid climates and 10-15°C in dry climates, beyond which temperature increases suppress growth. Thirty additional degree days above the optimal temperature breakpoint lead to an average decrease in tree ring width of around 1%-5%, depending on ecoregions, seasons, and inclusion or exclusion of temperature-mediated drought impacts. High temperatures have legacy effects across a 5-year horizon in dry ecoregions, but none in the temperate-humid South-East or among temperature-sensitive trees. I find limited evidence that trees acclimatize to high temperatures within their lifetime: local variation in early exposure to high temperatures, which stems from local variation in the timing of tree birth, does not significantly impact the response to high temperatures, although temperature-sensitive trees acquire some heightened sensitivity from early exposure. I also find some evidence that trees adapt to high temperatures in the long run: across humid ecoregions of the United States, high temperatures are 40% less harmful to tree growth, where their average incidence is one standard deviation above average. Overall, these results highlight the strength of a new methodology which, applied to representative tree ring data, could contribute to predicting forest carbon uptake potential and composition under global change.
温度是一个关键的气候指标，预计在变暖的世界中，其分布将向右移动。然而，树木的高温耐受性不如其耐旱性广为人知，尤其是在涉及温度对树木生长的亚致死影响时。我使用了一个大型的年度树木年轮宽度数据集，并结合了一个灵活的度日模型，来估计温度与树木径向生长之间的关系。我发现，在美国的许多生态区，树木的径向生长与温度呈非线性关系：在温带和/或干旱生态区，春夏季温度升高对树木生长有益或基本中性，在潮湿气候下可达 25-30°C，在干旱气候下可达 10-15°C，超过这个温度，温度升高会抑制生长。在最佳温度断点之上再增加 30 个度日，平均会导致树木年轮宽度减少 1%-5%，具体取决于生态区、季节以及是否考虑温度介导的干旱影响。在干旱生态区，高温具有 5 年的滞后效应，但在温带湿润的东南地区或对温度敏感的树木中则没有。我发现的证据有限，表明树木在其一生中可以适应高温：早期暴露于高温的局部变化，这源于树木出生时间的局部变化，并不会显著影响对高温的响应，尽管对温度敏感的树木会因早期暴露而获得一些更高的敏感性。我还发现了一些证据表明，树木可以从长远来看适应高温：在美国潮湿的生态区，高温对树木生长的危害减少了 40%，因为它们的平均发生率比平均值高出一个标准差。总的来说，这些结果突出了一种新方法的优势，该方法应用于代表性的树木年轮数据，可以有助于预测全球变化下森林碳吸收潜力和组成。
