(1) Background: Global climate change is expected to significantly alter growing conditions along mountain gradients. Landscape ecological patterns are likely to shift significantly as species attempt to adapt to these changes. We evaluated the extent to which spatial (elevation and canopy cover) and temporal (decadal trend and El Niño–Southern Oscillation/Pacific Decadal Oscillation) factors impact seasonal snowmelt and forest community dynamics in the Western Hemlock–True Fir ecotone region of the Oregon Western Cascades, USA. (2) Methods: Tsuga heterophylla and Abies amabilis seedling locations were mapped three times over 20 years (2002–2022) on five sample transects strategically placed to cross the ecotone. Additionally, daily ground temperature readings were collected over 10 years for the five transects using 123 data loggers to estimate below-canopy snow metrics. (3) Results: Based on validation using time-lapse cameras, the data loggers proved highly reliable for estimating snow cover. The method reported fewer days of snow cover as compared to meteorological station-based snow products for the region, emphasizing the importance of direct under-canopy field observations of snow. Snow season variability was most significantly impacted temporally by cyclical ENSO/PDO climate patterns and spatially by differences in canopy cover within the ecotone. The associated seedling analysis identified clear sorting of species by elevation within the ecotone but reflected a lack of a long-term trend, as species dominance in the seedling strata did not significantly shift along the elevation gradient over the 20-year study. (4) Conclusions: The data logger-based approach provided estimates of snow cover at ecologically significant locations and fine enough spatial resolutions to allow for the study of forest regeneration dynamics. The results highlight the importance of long-term, understory snow measurements and the influence of climatic oscillations in understanding the vulnerability of mountain areas to the changing climate.

中文翻译：

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太平洋西北山区森林对雪况变化脆弱性的 20 年生态交错带研究

(1) 背景：全球气候变化预计将显着改变山区梯度的生长条件。随着物种试图适应这些变化，景观生态模式可能会发生显着变化。我们评估了俄勒冈州西部铁杉-真冷杉生态交错带地区空间（海拔和冠层覆盖）和时间（年代际趋势和厄尔尼诺-南方涛动/太平洋年代际涛动）因素对季节性融雪和森林群落动态的影响程度美国喀斯喀特。 (2) 方法：在 20 年间（2002 年至 2022 年），在策略性地穿越生态交错带的 5 个样带上绘制了 3 次铁杉和冷杉幼苗位置图。此外，使用 123 个数据记录仪收集了 10 年来五个样带的每日地面温度读数，以估计树冠下的积雪指标。 (3) 结果：基于使用延时摄像机的验证，数据记录仪在估计积雪方面具有高度可靠性。与该地区基于气象站的积雪产品相比，该方法报告的积雪天数较少，强调了直接在树冠下实地观测积雪的重要性。雪季变化在时间上受周期性 ENSO/PDO 气候模式的影响最为显着，在空间上受生态交错带内冠层覆盖差异的影响最为显着。相关的幼苗分析确定了生态交错带内按海拔对物种进行了清晰的排序，但反映出缺乏长期趋势，因为在 20 年的研究中，幼苗地层中的物种优势并没有沿着海拔梯度发生显着变化。 (4) 结论：基于数据记录器的方法提供了对具有重要生态意义的地点的积雪的估计，并提供了足够精细的空间分辨率，以便研究森林再生动态。结果强调了长期林下积雪测量的重要性以及气候波动对了解山区对气候变化的脆弱性的影响。