Abstract:

Based on case studies from nearly 20 forest ecological stations in different bioregions of China, the characteristics of eco-hydrological functions of forest ecosystems were studied in terms of canopy interception, soil-water storage and holding capacity. Annual canopy rainfall interception ranged from 134 to 626 mm, and was ranked in the descending order as follows : tropical mountain rain forest, subtropical western mountain evergreen coniferous forest, tropical semi-deciduous monsoon forest, temperate mountain deciduous/evergreen coniferous forest, cold-temperate/temperate mountain evergreen coniferous forest, subtropical bamboo forest, subtropical/tropical eastern mountain evergreen coniferous forest, cold-temperate temperate mountain deciduous coniferous forest, temperate subtropical deciduous broadleaf forest, subtropical mountain evergreen broadleaf forest, subtropical tropical south-west mountain evergreen coniferous forest, south subtropical evergreen broadleaf forest, and subtropical mountain evergreen broadleaf forest. The moisture holding capacity of litter was about two-to-five times its dry-weight, but varied with forest type. The soil non-capillary moisture capacity of forests ranged from 36 to 142 mm with an average of 89 mm. Non-capillary capacity of evergreen broadleaf forests was more than 100 mm, but was less than 100 mm in the cold-temperate temperate deciduous broadleaf and evergreen coniferous forests. From an ecosystem point of view, the soil non-capillary holding capacity counted for more than 90% of the total, followed by forest litter, which ranged from 3 to 10 mm, and canopy interception only occupied a small proportion (less than 2 mm). This indicates that forest soils play a significant role in regulating rainfall interception. The hydrological role of forest soil depends on its structure and porosity, which is further affected by litter-fall and forest vegetation on sites. There was no consistent result with respect to the relationship between forest cover and annual runoff based on paired comparison of forest watersheds or direct measurements of the same forest watershed with a change of forest cover over time. Soil surface runoff was found to increase remarkably after forest logging, in particular, after clear-cut on a large scale irrespective of forest types or regions. An appropriate thinning or tending practices, however, could reduce soil surface runoff to a certain degree in forest watersheds. With increasing precipitation, forest evapo-transpiration increased slightly, while the Relative Evapo-transpiration Ratio (RER) decreased with the RER variation ranging from 40% to 90%.