Effects of canopy composition on snow depth and below-the-snow temperature regimes in the temperate secondary forest ecosystem, Northeast China

Abstract

Seasonal snow cover provides a thermally stable and humid refuge for overwintering plants in temperate forests. Canopy composition changes snow processes and shapes the thermal regime. To explore canopy effects on snow depth (SD) and below-the-snow temperature, ultrasonic sensors and time-lapse infrared cameras were used to monitor SD over two winters. Three forest types with different canopy compositions [the ratio of Korean pine (Pinus koraiensis Sieb. et Zucc.) basal area, RKp] on adret (sunny) and ubac (shady) slopes, including broadleaved secondary forests, Korean pine-broadleaved mixed forests, and Korean pine plantations, were selected as sample sites. Results showed time-lapse cameras were more accurate for monitoring SD in studied forests. Increasing RKp increased the snow interception rate and reduced the peak SD, snow melting rate, and snow cover duration. 21–69% of the snowfall was intercepted by the forests, with the RKp explaining 89% of the variance in interception rates. All forest stands had the lowest interception rate for severe snow events. For each forest type, plots on ubac slopes had a lower interception rate and thicker snow cover due to the positive effects of prevailing northerly wind on snow accumulation. Inter-annual variation of snowfall affected SD, snow melting rate, and below-the-snow temperature, with smaller differences among forest stands during the below-normal snow winter (2018/2019). The subnivium established in all plots during the normal snow winter (2019/2020) with the longest maintenance in secondary forest on ubac slopes and the shortest maintenance in Korean pine forests. The temperature increment under snowpack was positively correlated with SD while negatively correlated with air temperature. Overall, the forest with fewer evergreen canopy compositions was covered with thicker snowpack for a longer duration and had a more stable and warmer temperature regime, and fewer freeze-thaw events beneath the snow, which were essential for safe overwintering of regenerated individuals.