Applications of a hydro-biogeochemical model and long-term simulations of the effects of logging in forested watersheds

We simulated hydrological and biogeochemical responses to logging in a forested watershed to determine the vulnerability and/or resiliency of the forest ecosystems in the Lake Shumarinai Basin in northern Hokkaido, Japan. We used a biogeochemical model (PnET-CN) and a rainfall–runoff model (HYCYMODEL) to predict ecosystem responses. The PnET-CN model simulated well the observed NO₃ ⁻ concentrations in streamwater, particularly at high concentrations during snowmelt; however, the model could not simulate small increases in NO₃ ⁻ during the summer. By considering hydrological processes within the watershed and combining the model with the HYCYMODEL (PnET + HYCYMODEL), the seasonality of streamwater NO₃ ⁻ concentrations was better simulated. Using these models, the long-term effects of logging were simulated for coniferous, deciduous, and mixed forests. NO₃ ⁻ concentrations in streamwater increased in response to the logging disturbance in both coniferous and deciduous forests. In the coniferous forest, NO₃ ⁻ concentrations reached a maximum 10 years after logging, and high concentrations persisted for 30 years. In contrast, NO₃ ⁻ concentrations in the deciduous forest reached a maximum within 3–4 years and recovered to pre-disturbance levels after 15 years. We also used the models to determine the effects of different sizes and types (coniferous, deciduous, and mixed forest) of logging areas on Lake Shumarinai. The model results indicated that large areas of cutting require more than 100 years for complete lake recovery. Whereas the annual discharge to the lake minimally increased, the annual NO₃ ⁻ load greatly increased. Our simulation results elucidate the vulnerability and resiliency of forest ecosystems and provide valuable information for ecosystem management.     

Separate estimation of N export into baseline N leakage without disturbance and N loss due to insect defoliation in a pine forest watershed in central Japan

Pine wilt disease (PWD) is caused by a non-native pest that has spread extensively throughout Japan. Previous research has indicated that most infected trees have died and the litter deposited has resulted in changes to stream-water chemistry, particularly increased nitrate (NO ₃ ^? ) concentrations. In this study, we divided stream nitrogen (N) export into N loss due to PWD and baseline N leakage without disturbance based on long-term monitoring. The annual N export was 110.0 mol N ha^?1 year^?1 in 1990 and 749.8 mol N ha^?1 year^?1 in 1997, and had decreased to 37.0 mol N ha^?1 year^?1 in 2005. N export under PWD influence was estimated to be 3697 mol N ha^?1, and N loss due to PWD was 2810 mol N ha^?1. N loss due to PWD was three times larger than baseline N leakage for the disturbed period. These changes in plant–herbivore relationships could affect N status in a forest ecosystem. So-called “semi-natural” disturbances related to non-native species invasion and increases of atmospheric N deposition caused by human activity will increase. Long-term monitoring studies of various aspects are necessary to offer insight into this ecosystem.     

Organic acids and aldehydes in throughfall and dew in a Japanese pine forest

We analyzed low molecular weight organic acids and aldehydes in throughfall under pine forest, and organic acids in dew on chemically inert surfaces and pine needle surfaces at urban- and mountain-facing sites of pine forest in western Japan. Low molecular weight organic acids and aldehydes accounted for less than 5% of the dissolved organic carbon in throughfall at both sites. Formaldehyde at both sites and formate at the mountain-facing site were found at significantly lower concentrations in throughfall than in rainfall, which may be explained by the degradation and/or retention of these components by the pine canopy as the incident precipitation passed through it. The oxalate concentration in throughfall was significantly higher than those in rainfall at both sites, suggesting that oxalate was derived from leaching from the pine foliage. At both sites, organic acid concentrations were higher in dew on the pine needles than in throughfall or dew on chemically inert surfaces. This could be due to the long contact time of dew on pine needles, during which leached substances from pine needles and dry deposits accumulated on their surfaces can dissolve into the small volume of dew. The role of enhanced concentrations of oxalate in an aqueous phase on the plant surfaces (e.g., dew) is discussed in relation to hydroxyl radical formation via the photo-Fenton reaction.