The importance of monsoon precipitation for foundation tree species across the semiarid Southwestern U.S.
The importance of monsoon precipitation for foundation tree species across the semiarid Southwestern U.S.
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DOI：
10.3389/ffgc.2023.1116786
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发表时间：
2023-03
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通讯作者：
K. Samuels‐Crow;D. Peltier;Yao Liu;Jessica S. Guo;J. Welker;W. Anderegg;G. Koch;C. Schwalm;M. Litvak;J. Shaw;K. Ogle
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作者：
K. Samuels‐Crow;D. Peltier;Yao Liu;Jessica S. Guo;J. Welker;W. Anderegg;G. Koch;C. Schwalm;M. Litvak;J. Shaw;K. Ogle
干旱和半干旱地区的森林动态对水的供应情况很敏感，而随着全球气候变化，水越来越稀缺。自21世纪世纪开始以来，美国西南部半干旱地区（“西南部”）降水的时间和强度发生了变化。随着世纪的推进，该地区预计将变得更加炎热和干燥，这对碳储存、害虫爆发和野火恢复能力都有影响。我们的目标是量化夏季季风降水对该地区森林生态系统的重要性。我们开发了一个同位素混合模型的贝叶斯框架来表征夏季（季风）降水土壤水补给和三个基础树种（山杨[白杨]，紫松[piñon]，和杜松osteosperma [犹他州杜松]）用水。2016年，季风降水和树木对季风水分的依赖所补充的土壤深度在西南部各不相同，物种之间存在明显差异。季风降水补给土壤在皮农杜松（PJ）和白杨网站的深度至少为60厘米。研究中的所有树木在季风爆发之前和之后都主要依赖于中层至深层（10-60厘米）的水分。虽然树木继续主要依赖于中间到深层水分后，季风，所有物种增加依赖浅土壤水分在不同程度上。白杨树增加了13%至20%对浅层土壤水分的依赖。犹他州杜松和共同优势种对浅层土壤水分的依赖增加了约6%至12%。尽管如此，采样的皮农（38-58%）和杜松（47-53%）茎中约有一半的季风后水分可归因于季风。季风贡献了较低的金额白杨干水（24-45%）在整个研究区域的影响最大的网站与最近的降水。因此，季风降水是西南部半干旱森林所依赖的生长季节水分的关键驱动力。这种季风依赖现在比以往任何时候都更加重要，因为全球气温升高导致北美季风越来越不可预测和减弱。
Forest dynamics in arid and semiarid regions are sensitive to water availability, which is becoming increasingly scarce as global climate changes. The timing and magnitude of precipitation in the semiarid southwestern U.S. (“Southwest”) has changed since the 21st century began. The region is projected to become hotter and drier as the century proceeds, with implications for carbon storage, pest outbreaks, and wildfire resilience. Our goal was to quantify the importance of summer monsoon precipitation for forested ecosystems across this region. We developed an isotope mixing model in a Bayesian framework to characterize summer (monsoon) precipitation soil water recharge and water use by three foundation tree species (Populus tremuloides [aspen], Pinus edulis [piñon], and Juniperus osteosperma [Utah juniper]). In 2016, soil depths recharged by monsoon precipitation and tree reliance on monsoon moisture varied across the Southwest with clear differences between species. Monsoon precipitation recharged soil at piñon-juniper (PJ) and aspen sites to depths of at least 60 cm. All trees in the study relied primarily on intermediate to deep (10-60 cm) moisture both before and after the onset of the monsoon. Though trees continued to primarily rely on intermediate to deep moisture after the monsoon, all species increased reliance on shallow soil moisture to varying degrees. Aspens increased reliance on shallow soil moisture by 13% to 20%. Utah junipers and co-dominant ñons increased their reliance on shallow soil moisture by about 6% to 12%. Nonetheless, approximately half of the post-monsoon moisture in sampled piñon (38-58%) and juniper (47-53%) stems could be attributed to the monsoon. The monsoon contributed lower amounts to aspen stem water (24-45%) across the study area with the largest impacts at sites with recent precipitation. Therefore, monsoon precipitation is a key driver of growing season moisture that semiarid forests rely on across the Southwest. This monsoon reliance is of critical importance now more than ever as higher global temperatures lead to an increasingly unpredictable and weaker North American Monsoon.