The impact of two continuous cover forestry methods on the forest microclimate

Sammanfattning

Forestry is globally recognized for its effects on biodiversity and climate change, yet the microclimatic consequences of different management strategies have received limited attention. Forest canopies regulate understory climates by modulating radiation, thereby buffering macroclimatic extremes. While research of clear-cutting impacts is increasing, continuous cover forestry (CCF) methods remain comparatively understudied. Therefore, this study evaluated short-term microclimate responses to two CCF practices, shelterwood and gap-cutting, in comparison with clear-cutting and unharvested reference forest stands in southeast Sweden. Microclimate was monitored before and one year after harvest at high temporal resolution for soil, surface, and air temperatures, and for soil moisture. The openness of forest canopy was also quantified to investigate to what extent canopy changes impact microclimate variables. To separate management effects from annual variations in reference forests, pre- and post-harvest changes were calculated using a Before-After-Control-Impact (BACI) framework and then harvest-induced changes in canopy were associated with the observed microclimate shifts. As expected, clear-cutting produced the greatest deviation from reference conditions and were characterized by warmer days and cooler nights. In turn, CCF treatments buffered these extremes. Shelterwood generally produced intermediate responses, and contrary to expectations, the gap-cut revealed contrasting gap dynamics with open gaps tending to cool more at night and closed patches warming more during the day, especially in autumn. Soil temperature changed the least across the treatments, consistent with strong thermal buffering in the soil layer. Meanwhile, soil moisture exhibited clear seasonal increases in the more open conditions but showed no diurnal variations. Changes in canopy openness were closely aligned with changes in surface and air temperatures with the most explained variation in summer daytime (R2 = 0.412; R2 = 0.552). However, the explained power depended on season for soil temperature and soil moisture, suggesting that hydrology, topography, and soil layer structure also have strong impacts. In summary, these results show that CCF treatments can enhance above-ground temperature stability, using canopy openness as a reliable predictor of boreal forest thermal conditions, while soil processes are more dependent on site-specific and hydrological implications.