Forest ecosystems, their management by man and floods in the Orlicke hory Mts in summer 1997

Based on long-term hydrological and hydropedological studies conducted on r esearch areas in the Orlicke hory Mts and their foothills in the Czech Repu blic, water retention in the land with forest ecosystems was evaluated in h eadwaters in the period of high summer precipitation. The retention was ass essed with respect to methods of forest management. The theory of variable source areas was used for the genesis of flow waves. Probable retention cap acity of forest soils in the mountains and foothills ranged between 80 and 100 mm. On a steep southern slope in tile foothills, probable retention cap acity of forest soil increased in relation to increasing field moisture cap acity and decreasing soil moisture from a clearcut area to a spruce mature stand of 0.5 stocking up to a spruce mature stand of full stocking. The stu dy of total retention of forest ecosystems on slopes showed negligible surf ace runoff even in the period of high precipitation and on the contrary, ma ssive subsurface runoff. On a steep southern slope in the foothills, total retention of a spruce thicket was higher than that of a spruce mature stand with respect to the Larger needle biomass and higher total evapotranspirat ion. The total retention of the forest watershed in a mountain region range d between 40 and 50 mm with respect to its considerable avenge saturation, in case of higher desuction of the watershed the retention could reach up t o 100 mm. Thus, forests can reduce smaller floods but generally not extreme flood events. Differentiation of variable source areas, obtaining evaluati ng and synthesis of findings and the proposal of differentiated management of forest ecosystems with the aim to reduce floods and their effects will r equire still much research work.