Climate change is predicted to cause widespread declines in biodiversity, but these predictions are derived from coarse-resolution climate models applied at global scales. Such models lack the capacity to incorporate microclimate variability, which is critical to biodiversity microrefugia. In forested montane regions, microclimate is thought to be influenced by combined effects of elevation, microtopography, and vegetation, but their relative effects at fine spatial scales are poorly known. We used boosted regression trees to model the spatial distribution of fine-scale, under-canopy air temperatures in mountainous terrain. Spatial models predicted observed independent test data well (r = 0.87). As expected, elevation strongly predicted temperatures, but vegetation and microtopography also exerted critical effects. Old-growth vegetation characteristics, measured using LiDAR (light detection and ranging), appeared to have an insulating effect; maximum spring monthly temperatures decreased by 2.5°C across the observed gradient in old-growth structure. These cooling effects across a gradient in forest structure are of similar magnitude to 50-year forecasts of the Intergovernmental Panel on Climate Change and therefore have the potential to mitigate climate warming at local scales. Management strategies to conserve old-growth characteristics and to curb current rates of primary forest loss could maintain microrefugia, enhancing biodiversity persistence in mountainous systems under climate warming.

Analyses of long-term records at 35 headwater basins in the United States and Canada indicate that climate change effects on streamflow are not as cl

Baseflow is essential for stream ecosystems and human water uses, particularly in areas with Mediterranean climates. Yet the factors controlling the temporal and spatial variability of baseflow and its sources are poorly understood. Measurements of oxygen and hydrogen isotopic composition (δ¹⁸O and δ²H) were used to evaluate controls on baseflow in the stream network of a 64‐km² catchment in western Oregon. A total of 607 water samples were collected to contrast baseflow in a year of near average precipitation (2016) to a year with low winter snowpack and subsequent summer drought conditions (2015). Spatial autocorrelation structures and relationships between surface water isotopic signatures and geologic and topographic metrics throughout the network were determined using Spatial Stream Network models. Isotope values varied widely in space and between years, indicating disparate baseflow water sources. During average flow conditions, the spatial variation in δ¹⁸O was primarily related to elevation, reflecting the influence of prior precipitation and input of water from snowmelt at higher elevation. In contrast, during drought conditions, the spatial variation in δ¹⁸O was also related to terrain slope and roughness—proxies for local water storage in deep‐seated earthflows and other Quaternary deposits. A prominent spring‐fed tributary with high unit baseflow discharge illustrated the importance of subsurface water storage in porous volcanic bedrock. As drought increases in a warming climate, baseflow in mountain catchments may become more dependent on storage in geologic and geomorphic features.

In this article marking the 40th anniversary of the US National Science Foundation's Long Term Ecological Research (LTER) Network, we describe how a long-term ecological research perspective facilitates insights into an ecosystem's response to climate change. At all 28 LTER sites, from the Arctic to Antarctica, air temperature and moisture variability have increased since 1930, with increased disturbance frequency and severity and unprecedented disturbance types. LTER research documents the responses to these changes, including altered primary production, enhanced cycling of organic and inorganic matter, and changes in populations and communities. Although some responses are shared among diverse ecosystems, most are unique, involving region-specific drivers of change, interactions among multiple climate change drivers, and interactions with other human activities. Ecosystem responses to climate change are just beginning to emerge, and as climate change accelerates, long-term ecological research is crucial to understand, mitigate, and adapt to ecosystem responses to climate change.