Rodman Kyle C, Bradford John B, Formanack Alicia M, Fulé Peter Z, Huffman David W, Kolb Thomas E, Miller-Ter Kuile Ana T, Normandin Donald P, Ogle Kiona, Pedersen Rory J, Schlaepfer Daniel R, Stoddard Michael T, Waltz Amy E M
Ecological Restoration Institute, Northern Arizona University, Flagstaff, Arizona, USA.
US Geological Survey, Northwest Climate Adaptation Science Center, Seattle, Washington, USA.
Ecol Appl. 2025 Jan;35(1):e3072. doi: 10.1002/eap.3072. Epub 2024 Dec 3.
The frequency and severity of drought events are predicted to increase due to anthropogenic climate change, with cascading effects across forested ecosystems. Management activities such as forest thinning and prescribed burning, which are often intended to mitigate fire hazard and restore ecosystem processes, may also help promote tree resistance to drought. However, it is unclear whether these treatments remain effective during the most severe drought conditions or whether their impacts differ across environmental gradients. We used tree-ring data from a system of replicated, long-term (>20 years) experiments in the southwestern United States to evaluate the effects of forest restoration treatments (i.e., evidence-based thinning and burning) on annual growth rates (i.e., basal area increment; BAI) of ponderosa pine (Pinus ponderosa), a broadly distributed and heavily managed species in western North America. The study sites were established at the onset of the most extreme drought event in at least 1200 years and span much of the climatic niche of Rocky Mountain ponderosa pine. Across sites, tree-level BAI increased due to treatment, where trees in treated units grew 133.1% faster than trees in paired, untreated units. Likewise, trees in treated units grew an average of 85.6% faster than their pre-treatment baseline levels (1985 to ca. 2000), despite warm, dry conditions in the post-treatment period (ca. 2000-2018). Variation in the local competitive environment promoted variation in BAI, and larger trees were the fastest-growing individuals, irrespective of treatment. Tree thinning and prescribed fire altered the climatic constraints on growth, decreasing the effects of belowground moisture availability and increasing the effects of atmospheric evaporative demand over multi-year timescales. Our results illustrate that restoration treatments can enhance tree-level growth across sites spanning ponderosa pine's climatic niche, even during recent, extreme drought events. However, shifting climatic constraints, combined with predicted increases in evaporative demand in the southwestern United States, suggest that the beneficial effects of such treatments on tree growth may wane over the upcoming decades.
预计由于人为气候变化，干旱事件的频率和严重程度将会增加，并对森林生态系统产生连锁反应。诸如森林疏伐和计划火烧等管理活动，通常旨在减轻火灾隐患并恢复生态系统过程，也可能有助于提高树木的抗旱能力。然而，尚不清楚这些处理措施在最严重的干旱条件下是否仍然有效，或者它们的影响在不同环境梯度下是否存在差异。我们利用美国西南部一个重复的长期（>20年）实验系统中的树木年轮数据，来评估森林恢复处理（即基于证据的疏伐和火烧）对黄松（Pinus ponderosa）年生长率（即断面积生长量；BAI）的影响，黄松是北美西部分布广泛且管理密集的一个树种。研究地点是在至少1200年来最极端的干旱事件开始时设立的，涵盖了落基山黄松的大部分气候生态位。在各个地点，处理使树木水平的BAI增加，处理单元中的树木生长速度比配对的未处理单元中的树木快133.1%。同样，尽管处理后时期（约2000 - 2018年）气候温暖干燥，但处理单元中的树木平均生长速度比处理前基线水平（1985年至约2000年）快85.6%。当地竞争环境的变化促进了BAI的变化，无论处理如何，较大的树木都是生长最快的个体。树木疏伐和计划火烧改变了生长的气候限制，在多年时间尺度上降低了地下水分可利用性的影响，并增加了大气蒸发需求的影响。我们的结果表明，恢复处理可以提高跨越黄松气候生态位的各个地点的树木水平生长，即使在近期的极端干旱事件期间也是如此。然而，不断变化的气候限制，加上预计美国西南部蒸发需求的增加，表明此类处理对树木生长的有益影响在未来几十年可能会减弱。
