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Forest canopies are the functional interface between ecosystem and the atmospheric nitrogen (N) deposition. However, the sources of spatio‐temporal variability and intra‐event variation of N deposition via throughfall (TF) remain ambiguous. Here, we analysed TF samples for concentrations and fluxes of ammonium (NH4+) and nitrate (NO3−) using an array of 20 fixed‐position collectors on an event and within event basis throughout the 2019 growing season in a Chinese pine plantation, Northern China. Results showed that the volume weighted mean concentrations of NH4+ and NO3− in TF were significantly higher than those in bulk precipitation (BP) during the study period. A canopy budget model indicated that canopy uptake was more dominant than dry deposition for NH4+, while the reverse was true for NO3−. This caused a comparable TF NH4+ flux but an enhanced TF NO3− fluxes compared to BP. The intra‐event trend and magnitude of TF NH4+ and NO3− concentrations were influenced by the antecedent dry period and rainfall intensity, and indicated that biological nitrification may occur in the canopies. In addition, due to the larger of canopy NH4+ uptake that counteracted the amplifying effect of dry deposition, the spatial variability of TF NH4+ concentration was significantly lower than that of TF NO3− concentration, and exhibited more temporal persistence. No relationship was found between the spatial distribution of TF NH4+ concentration and the TF amount, the distance to the nearest trunk, nor the canopy cover, whereas the TF NO3− concentration was significantly related to the TF amount and the canopy cover. These findings can enhance our understanding of N processes within canopies, and have important implications for evaluating the impacts of N deposition in forest ecosystems. [ABSTRACT FROM AUTHOR]

Thinning results in more open-stand canopies and then immediately modifies the environmental factors that influence forest floor evaporation ( E f ). Thus, the changes in E f induced by thinning would play an important role in the forest water cycle, whereas few studies have reported this topic. This study analyzes the effect of strip thinning on E f , its spatial variation and identifies the factors influencing it in a Japanese cypress ( Chamaecyparis obtusa Endl.) plantation in Tochigi Prefecture, Japan. Strip thinning, which removed 50% of the stems, was conducted in a headwater basin during the period of October 11–November 5, 2011. The E f was monitored by weighing lysimeters before and after thinning. The daily E f was strongly correlated with the daily solar radiation ( R 2 = 0.62) followed by vapor pressure deficit ( R 2 = 0.41) below the canopy, whereas the soil water content had a poor effect on it in post-thinning. After thinning, the daily E f among the measuring points had no significant difference, indicating that the daily E f had a small spatial variation. This responded to the small spatial variability in the daily solar radiation under the canopy. Additionally, on an annual scale, thinning resulted in the daily mean E f increasing from 0.34 ± 0.23 to 0.68 ± 0.47 mm d −1 . The total E f increased by 97.6% from 124.0 to 245.0 mm. These findings indicate that E f composes a significant part of the forest water budget after thinning and emphasize the importance of E f measurements for management practices. This study also provides useful information for modeling the changes in hydrological processes at the forest floor and for evaluating the E f response to different management practices. [ABSTRACT FROM AUTHOR]

Summary We examined the effect of strip thinning on rainfall interception ( E i ) in a 32-year-old Japanese cypress plantation in central Japan. Strip thinning was conducted in the catchment in October 2011; that removed 50% of the stems. The gross precipitation ( P g ), throughfall ( TF ) and stemflow ( SF ) were monitored in a 12-m × 13-m plot before and after thinning. E i was calculated as the difference between P g and the sum of TF and SF . The interception processes were illustrated using the revised Gash model with quantifying interception parameters. The results showed that the Gash model successfully predicted E i on a rainy-season basis in both pre- and post-thinning periods. Thinning altered the interception components whereas the largest part during and after rainfall accounted for similar proportion in both periods. Additionally, after thinning, the annual TF rate was increased from 61.4% to 73.0%, whereas the annual SF rate was decreased from 9.8% to 6.1%, and the annual E i rate was decreased from 28.7% to 20.8%. The summarized findings of previous studies indicate that the degree of decline in the E i caused by thinning is related to P g and the thinning ratio. These results provide useful information for understanding the changes in interception processes induced by thinning, and for acquiring a more accurate forecast of the effects of forest management practices on water resources in the watershed. The response in rainfall partitioning to strip thinning can also help us to acquire an integrated understanding of the changes in canopy water balance under different forest practices. [ABSTRACT FROM AUTHOR]

Interception loss ( E) in forests has been studied widely. However, E parameters and modeling as well as spatial patterns of throughfall ( TF) in abandoned Japanese cypress ( Chamaecyparis obtusa) plantations remain poorly documented. In this study, gross precipitation ( P), stemflow ( SF), and TF were monitored in an unmanaged 32-year-old Japanese cypress stand throughout the 2011 rainy season. Results indicate that P partitioning into TF, SF, and E were, respectively, 64.2 ± 3.6, 10.6 ± 0.6, and 25.2 ± 1.1 % of the 880.8 mm cumulative P from 29 rainfall events. Direct throughfall proportion ( p) and drainage from the canopy contributed about 14 ± 7 and 50 ± 21 % of the total TF for the events, respectively. The mean canopy storage capacity ( S) was 2.4 ± 0.7 mm. The coefficient of variability (CV) of TF rate decreased asymptotically with increasing P amount, ranging from 16 to 56 % with median 26 %. The CV of TF rate was not significantly correlated with canopy cover ( r = 0.152, P = 0.521, n = 20) and distance from the nearest trunk ( r = 0.196, P = 0.408, n = 20). Based on the revised Gash analytical model, the total simulated E was close to the observed, with a general underestimation magnitude of 5.7 %. The E components were quantified, and most of the interception loss (62.9 %) evaporated during rainfall, while 26.8 % evaporated after rainfall ceased. Climatic and forest structural parameters required by the model were identified and analyzed by sensitivity analysis, implying that the revised Gash analytical model is robust and reliable enough for abandoned Japanese cypress plantations in a maritime climate. [ABSTRACT FROM AUTHOR]