Abstract:

This study took adjacent deciduous natural broadleaf forest (BF) watershed and evergreen artificial coniferous forest (CF) watershed in the Kuraiyama Experimental Forest of Gifu Prefecture in Japan as research objects. Through comparative analysis of stream temperature, forest air temperature, and soil temperature (at 5cm and 50cm depths) during the deciduous season (November−May of next year) and non−deciduous season (June−October) in 2013−2014 and 2017−2018, effects of different forest types on stream temperature were systematically investigated. The findings could provide a scientific basis for adaptive watershed management and ecological restoration of plantation forests. The results showed that: (1) the annual stream temperature range in the BF watershed (2.76–15.56°C) was approximately 4.56°C narrower than that in the CF watershed (0.07−17.43°C), indicating greater thermal stability. (2) A critical thermal threshold of 10.38℃ was identified in the daily average stream temperatures between the two watersheds. When average stream temperatures in both watersheds were below this threshold, the CF watershed exhibited significantly lower temperatures than the BF watershed by 1.49°C (P<0.05), with the inter−watershed temperature difference increasing as stream temperature decreased. Above the threshold, stream temperatures in the CF watershed became significantly higher than those in the BF watershed by 0.79°C (P<0.05). (3) Soil temperatures at both 5cm and 50cm depths were consistently higher in the BF watershed than in the CF watershed, with the maximum inter−watershed temperature difference reaching 1.00°C in the 5cm soil layer during the deciduous season. (4) Soil temperature showed significantly stronger effects on stream temperature than forest air temperature, with the highest correlations observed between shallow soil temperature (5−15cm) and stream temperature (r=0.907−0.944, P<0.001). The study demonstrated that forest canopy phenology served as the fundamental driver of inter−watershed temperature differences, primarily through its regulation of solar radiation penetration and snow cover dynamics. Based on the research results, authors recommend establishing a stream temperature threshold response system in watershed management, optimizing riparian vegetation composition (e.g., prioritizing deciduous species), and implementing adaptive measures like mixed coniferous−broadleaf forestation to enhance the climate resilience of watershed ecosystems.

Key words: Deciduous broadleaf forest, Evergreen coniferous forest, Deciduous season, Non?deciduous season, Stream temperature, Soil temperature