RESUME

FOREST IMPACT UPON RUNOFF CONDITIONS AT SMALL CATCHMENT
Vladimír Švihla (pp. 66 - 69)

The analysis of forest impact upon the water in the landscape was performed by: a hydrological balance, regime of M-day water discharge, regime of high water events.

The hydrological balance proved the cumulative discharge from most forests is generally lower than the total runoff from fields and meadows. At early series, about 2/3 - 104 % of agricultural land runoff drains from forests at average. The upper value 104 % is achieved in dry years. The lower cumulative forest land runoff compared to agricultural land is caused namely by substantially higher interception in forest stands compared to meadows or field cultures. Present runoffs from coniferous forest stands are lower than from deciduous ones (Table 1). The quantification of cumulative runoff from forest complexes at the river Svratka catchment down to Dalečín are presented in the Table B.

In the catchment of the river Svratka in Českomoravská vrchovina (Czech-Moravian highlands), minimum runoffs from forests are higher than minimum runoffs from fields and meadows, what means at a long-period average the forest stands increase minima of M-day water runoffs in highland watercourses and decrease maxima of M-day water runoffs. Forest soils in sound forest stands represent an excellent reservoir of underground water which is easy to be filled in for the high infiltration capacity of forest soils and therefore minimisation of surface runoff.

The results of hydrological research prove that there may develop a minimum runoff by 50 % lower in a forested catchment than in a non-forested one. The designed runoff model gives for the non-forested land (fields and meadows) of the river Svratka catchment a high water culmination by 47 % higher than for forested land.

Author’s practical recommendations:

1) Highly positive effects of forests in hydrology of small forest and forest-agricultural catchments with water-management purposes can only be expected in sound forests, corresponding with local site conditions. Forest management should aim at cultivation of forests based on typological principles, environmentally stable.

2) In order to establish environmentally stable forest it is necessary to approach the natural forest composition and to increase spatial and age differentiation of forest stands.

3) Deciduous forests prove themselves hydrologically positive in lowlands, uplands, and highlands. There is requested as wide representation of deciduous species in water management territories in those conditions.

4) Considerable fluctuations in hydrology balance parameters can be prevented by application of fine forms of forest management as are recommended by foremost silviculturists (Poleno, 1999).

5) Larger forest complexes increase the underground and surface water runoff and stabilise minimum runoffs in watercourses. It is a common interest to support the endeavour of central administration to afforest unused agricultural land as much as possible.

6) The quality of water drained from forests represents a special issue. With low runoffs in watercourses the runoff from forests prevails what improves the water quality significantly.

ANALYSES OF STRUCTURED STAND TYPES.
Jaromír Macků (pp. 69 - 71)

Stand typisation, used in designing current management sets is very rough with a very small telling capacity and can be understood as a primary clue for identification of management recommendations. In order to analyse differentiation of forest stand growth conditions representing not only the stand type but also stand mixing so called structured forest types were designed. The structured forest type is determined by enumeration of forest stand types and the character of their mixing.

The forest types are determined by the criteria: the same classification of species, determination of domestic and exotic species, larch, robinia (impact upon ecotope character) and other conifers and/or broadleaves. In this way, 18 forest types were identified. The mixing character is structured by criteria of the type distribution at the forest division unit linked by a key to the structured forest type. This way of forest type distribution linked to a digitised contour map enables creation not only a map of the present species composition of forest stands but also other thematic maps:

• map of stand naturality classes (comparison of present species composition to a natural potential vegetation),
• map of present production potential of stands, and others.

The structured forest type can be related to any forest division unit depending from the requested telling capacity.

Structured stand typysation enables - with the help of analyses of absolute height tree classification of single tree species groups - construction of growth conditions at the level of different stand mixtures. So it characterises the behaviour of species in different mixtures and helps the forest manager to decide on silvicultural interventions.

Designing and analysing of structured forest types is a considerably easy mechanism of differentiation of growth conditions with an excellent telling capacity at the ecosystem level.