Throughfall and stemflow chemical dynamics of Satoyama, a traditional secondary forest system under threat in Japan

The term 'Satoyama' refers to traditional and unique secondary forests in Japan that occupy intermediate zones between villages ('sato') and hills or mountains ('yama'). Satoyama landscapes help sustain ecosystem services and the diversity of secondary natural environments. As Japan relies more heavily on foreign timber imports, the traditional role of Satoyama in providing forest products has diminished, and this has led to their abandonment and poor management. The chemical behavior of cations, anions, and dissolved organic matter in throughfall and stemflow from one such threatened Satoyama system in central Japan was investigated. From autumn to winter, the atmospheric deposition of sulfates and nitrates was 2.5–6.0 times higher compared to the amounts in summer due to the intrusion of air masses from the Asian continent. The dissolved organic matter in the throughfall and stemflow was composed mainly of humic substances and protein derivatives. The deposition fluxes of dissolved organic carbon from throughfall (7.31–10.1 g m⁻² a⁻¹) and stemflow (1.79–3.84 g m⁻² a⁻¹) in this study were within ranges seen in temperate forests in previous studies. The deposition flux of sulfates was low compared to that in other forest types because canopy interaction was lower, suggesting higher canopy openness than in primary forests. If a shift from a mixed species Satoyama forest to a conifer-dominated forest occurs after the mass mortality of oak, the deposition flux of dissolved organic carbon and K⁺ might decrease by 33% and 62%, respectively, while NO₃⁻ might increase by 20%. In the near future, the degradation of Satoyama landscapes might change the levels of dissolved organic carbon and nitrogen loads, resulting in imbalances in river-ocean linkages affecting forested catchments and aquatic ecosystems in Japan.