Data from: Forest fragmentation alters winter microclimates and microrefugia in human-modified landscapes

With over half of earth’s terrestrial biota living beneath forest canopies, our ability to accurately capture organism-climate relationships in forested ecosystems is imperative for predicting species’ vulnerability to future climate change. Assessing the vulnerability of forest dependent species, however, hinges on quantifying microclimates that exist below the forest canopy and might be influenced by varying levels of disturbance in human-modified landscapes. The goal of our study was to examine the multi-scaled predictors of subcanopy microclimate variability across a heterogeneous landscape in Midwestern USA during winter, and to further evaluate whether a widely available interpolated climate model accurately captures this variability. By deploying a network of temperature sensors along a fragmentation gradient, we found that forests in more fragmented landscapes experienced colder minimum and average daily temperatures throughout the winter than forests in less fragmented landscapes. We found that greater tree densities and higher elevations led to warmer microclimates while increasing distances from urban centers led to colder microclimates. The negative effect of forest edge on minimum temperatures was lessened by the effect of increasing basal area, highlighting the importance of local- and landscape-scale features on microclimate heterogeneity. Temperature discrepancies between subcanopy microclimates and climate interpolations were influenced by many of the same features, and could be of a similar magnitude as those predicted by future climate change scenarios. Using a biological threshold based on metabolic and demographic constraints for winter birds, we found that the variability in microclimates along our forest fragmentation gradient (50 km) was comparable to the magnitude captured by weather stations across a latitudinal gradient spanning more than 650 km. Our results suggest that biophysical properties of landscapes can alter spatial gradients of microclimates and should be considered when assessing species’ vulnerabilities to future climate change.地球上超过一半的陆地生物群系（terrestrial biota）栖息于林冠之下，因此精准刻画森林生态系统中生物与气候的关联，对于预测物种应对未来气候变化的脆弱性至关重要。然而，评估依赖森林的物种的脆弱性，需要量化林冠下微气候（subcanopy microclimate）——这类微气候可能受到人为改造景观中不同程度干扰的影响。本研究的目标是，在美国中西部的异质景观中，探究冬季林冠下微气候变异的多尺度预测因子，并进一步评估一款广泛可用的插值气候模型（interpolated climate model）能否精准捕捉这类变异。我们沿着森林破碎化梯度（forest fragmentation gradient）布设温度传感器网络，结果发现，相较于破碎化程度较低的森林，破碎化程度更高的景观中的森林在整个冬季的日均最低气温和平均气温均更低。我们还发现，更高的树木密度与海拔会带来更温暖的微气候，而距城市中心的距离越远，微气候则越寒冷。森林边缘对最低气温的负面影响，会随着断面积（basal area）的增加而减弱，这凸显了局地和景观尺度特征对微气候异质性的重要性。林冠下微气候与气候插值结果之间的温差，受到诸多同类因素的影响，其温差幅度甚至可与未来气候变化情景下的预测幅度相媲美。基于冬季鸟类代谢和种群限制的生物学阈值，我们发现，在本研究的50公里森林破碎化梯度上的微气候变异幅度，与横跨650多公里纬度梯度的气象站所捕捉到的幅度相当。我们的研究结果表明，景观的生物物理属性能够改变微气候的空间梯度，因此在评估物种应对未来气候变化的脆弱性时，应当将这类属性纳入考量。