| Water cycle is one of important functions of forest ecosystem. In this paper, we choose a typical catchment as research object, this catchment consists of six forest communities—broad leaf Korean pine hag, birch forest, trembling aspen forest, Shaw, larch-birch swamp forest, larch plantation. By using the method of field research and combing collected research results, the water balance was studied quantificationally on ecosystem level and landscape level in order to provide some reference data for forest ecosystem management. The conclusion as followed:Crown canopy interception, throughfall and stemflow in different communities were different in the forest catchment. The relationship between crown canopy interception volume and rainfall volume was logarithm relation, and relationship between rate of crown canopy interception and rainfall volume was negative power exponent relation in the communities. On crown canopy interception volume, larch plantation was better than nature secondary forest and broad leaf Korean pine forest. Throughfall volume and rainfall volume had significantly linear relationship. In growth season, the critical rainfall volume which induced stemflow was 1.76-3.38 mm. The throughfall volume and rate of throughfall of nature secondary forest were bigger than that of larch plantation. Stemflow volume and rainfall volume had significantly linear relationship. In total stemflow volume and average rate of stemflow, all communities had little difference. The total stemflow volume accounted for 2%-4% in rainfall volume.In all communities, the relationship between litter interception volume and rainfall volume was sigmoid. When rainfall volume was above 21.5 mm, litter interception volume was approximate equality (2.46-3.58 mm).Transpiration volumes among different communities were different. The transpiration of trembling aspen, Shaw, swamp forests were higher (162.6-165.9 mm); hag, birch, larch plantation were lower (150-153.2 mm).Soil runoff volume and rainfall volume had linear relationship in all communities. Soil runoff volume of four secondary forest communities were 135.58 mm-160.48 mm. Soil runoff volume of artificial forest was 123.13 mm, and was less than natural secondary forest communities.Ability of adjusting rainfall was different among different communities. In field status, the abilities were 362.54 mm, 426.72 mm, 418.83 mm, 425.47 mm, 659.15 mm, and 479.65 mm, respectively. In saturation status, the abilities were 498.8 mm, 552.7 mm, 549.7 mm, 562.3 mm, 702.1 mm, and 597.5 mm, respectively.The runoff processes of soil-thaw period and growth season were different. Soil thaw began from April thirteen; soil-thaw period in catchment's level was seventeen days. soil thaw period in hag and birch is seventeen days. In Shaw, swamp forest and larch plantation, the soil- thaw period all was seven days. During soil-thaw period, the total runoff volume of riverwas 1156896 m3, the runoff volume in former seven days accounted for 64.9%. The total runoff volume of river in growth season was 129.67 mm. The total runoff volume of river was 2453590 m3 in growth season and soil thaw period, the runoff volume of river during soil-thaw period accounted for 47.15%, the runoff volume of river in growth season accounted for 52.85%.The storing water capacity of the forest catchment was great, and appeared water distribution pattem.The storing water capacity of litter layer and soil layer in summer was great: the nature water rate and saturation water rate in litter layer was 38.8%-48.5% and 200.13%-269.36%, respectively; the nature water rate and saturation water rate in A, AB, B layer of soil wasllO%-181%, 43%-58%, 30%-46% and 202-253%, 84-97%, 40-70%, respectively.The field storing water capacity of litter layer and soil layer in summer was 163.18 mm (accounted for 38. 77% of rainfall volume), and was highest in swamp larch-birch forest (accounted for 38.08% of the nature water capacity). In larch plantation, the field storing water capacity of litter layer and soil layer in summer was lowest (accounted for 8.69% of the nature water capacity), the other communities were 10. 16%-16. 86%.The saturation storing water capacity of litter layer and soil layer in summer was 279.57 mm (accounted for 66.42% of rainfall volume), and was highest in swamp larch-birch forest (accounted for 24.5% of the saturation water capacity). In larch plantation, the saturation storing water capacity of litter layer and soil layer in summer was lowest (accounted for 9.52% of the saturation water capacity), the other communities were 14.7%-19. 94%.The function of water balance component in the forest catchment was different, and changes with season. Crown interception and throughfall were important in water balance: the proportions of throughfall volume, crown interception volume, and stemfiow volume in rainfall volume were 68.92%, 27.73%, 3.35%, respectively. The main component of water balance in the forest catchment was obviously different in different month: in May, runoff and evapotranspiration proportions in rainfall were 41.46% and 50.99%, respectively; in other months, monthly evapotranspiration amount was as 1.7-2.4 times as monthly runoff. In growth season, the proportions of soil runoff amount and evaportranspiration amount in rainfall amount were 32.4% and 65.25%, respectively.
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