Abstract. The climate-change-induced poleward shift of agriculture could lead to
enforced deforestation of subarctic forest. Deforestation alters the
microclimate and, thus, soil temperature, which is an important driver of
decomposition. The consequences of land-use change on soil temperature and
decomposition in temperature-limited ecosystems are not well understood. In
this study, we buried tea bags together with soil temperature loggers at two
depths (10 and 50 cm) in native subarctic forest soils and adjacent
agricultural land in the Yukon Territory, Canada. A total of 37 plots was
established on a wide range of different soils and resampled after 2 years
to quantify the land-use effect on soil temperature and decomposition of
fresh organic matter. Average soil temperature over the whole soil profile
was 2.1 ± 1.0 and 2.0 ± 0.8 ∘C higher in
cropland and grassland soils compared to forest soils. Cumulative degree
days (the annual sum of daily mean temperatures > 0 ∘C)
increased significantly by 773 ± 243 (cropland) and 670 ± 285
(grassland). Litter decomposition was enhanced by 2.0 ± 10.4 % and
7.5 ± 8.6 % in cropland topsoil and subsoil compared to forest
soils, but no significant difference in decomposition was found between
grassland and forest soils. Increased litter decomposition may be attributed not only
to increased temperature but also to management effects,
such as irrigation of croplands. The results suggest that
deforestation-driven temperature changes exceed the soil temperature
increase that has already been observed in Canada due to climate change. Deforestation
thus amplifies the climate–carbon feedback by increasing soil warming and
organic matter decomposition.