High Arctic vegetation lowers soil temperatures on sunny days despite low stature

The impact of vegetation on soil temperatures in low Arctic and boreal regions is well documented, where dense vegetation reduces soil temperatures. However, equivalent empirical evidence for influence of sparse, low-stature high Arctic vegetation and its interaction with cloud cover is limited. Improved understanding of this relationship is vital, because soil temperatures drive important ecosystem processes, such as nutrient cycling and carbon fluxes. We investigated whether effects on soil temperature are found under smaller high Arctic vegetation in Svalbard, Norway, by modeling soil temperatures in relation to vegetation cover and height across forty plots, using July temperature recordings from 2020 to 2023. We found reduced minimum temperatures under thicker moss layers and taller forb and shrub vegetation, whereas organic layers reduced maximum temperatures. These effects were strongest under sunny conditions, whereas shrub cover showed weak interactions with cloud cover. This contrasts with lower latitudes, where shrubs exert strong shading effects and vegetation reduces maximum and raises minimum soil temperatures. This discrepancy might stem from smaller diurnal temperature fluctuations, lower vegetation height, and lower solar radiation in the high Arctic. Our results indicate that predicted vegetation shifts resulting from climate change may lead to complex soil temperature responses in the future.