Long-term monitoring of talus microclimates portrays crevices as critical thermal refuge for vulnerable alpine species

Broken rock land cover, such as talus, provides a critical microhabitat for small vertebrates in alpine environments, yet the specific thermal benefits of crevice use are understudied. We studied twelve talus patches in the North Cascades National Park in Washington, USA, over ten years (2015–2024) to quantify seasonal, annual, and diurnal patterns in crevice and surface temperatures. We also measured rock size and shape, vegetation and moss cover, and solar radiation at a high spatial resolution (Ground sampling distance (GSD) <1.05 mm) using handheld photogrammetry to evaluate their influence on thermal conditions. Summer surface temperatures increased an average of 0.37°C/year, whereas winter surface temperatures remained stable. Crevices buffered high midday and evening temperatures in summer and retained warmth during winter and at night, averaging 5°C cooler than the surface in summer and 0.45°C warmer in winter. Surface and crevice temperatures were affected by solar radiation, area of southwest-facing rocks, vegetation and moss cover, rock circularity, and elevation. These results emphasize the value of precise rock measurements for understanding the thermal benefits of rocky habitats. Crevices play a crucial role in moderating temperature extremes, highlighting their importance as microhabitat refuge, which is likely important for the survival of alpine species as climate change accelerates warming.