RESUME

J. Bělský, M. Jařabáč, B. Tureček (pp. 414-415)

Retention and retarding capacity of the forest is irreplaceable however always limited in the nature. Rehabilitation of flood damage is always time demanding, tiresome, and expensive, therefore flood prevention has to be more and more effective.

Average total annual wood harvest has been about 13 - 14 millions of cubic metres in the last years and an adequate volume of logging residues remained at logging areas. Its burning after application of inconsiderate technologies during thinning and regeneration resulting in forming stripes, rills, and minor streams, increases hazard of culverts and bridges clogging and random barriers in water beds with consequent damage.

Torrent streams make 26 % of total water streams in Czechia. Stream banks are aligned by streamside stands even outside forestland and they affect flow capacity and course stability of stream beds during floods. There are important relations between tree species stability and their resistance to scouring, falls, and washing away by water stream. This depends from the length, thickness, strength, and deepness of the root system. Spruce belonging the less resistant tree species is abundant in higher altitudes and it is usually often hurt by floods. Even adult trees may be scoured and washed away and may then endanger the profile flow capacity. Solution to this issue is a long run matter and consists namely in the change of species composition and application of tender management operations.

One measure able to help immediately is represented by removing trees threatened by scouring, sliding, falling, and washing away. Movement of driftwood, where whole trees and logging residues are the most dangerous, is a social hazard. One example of an active protection from driftwood has been used in torrent protection in southern Bavaria - steel nets. There experience in avalanche protection was applied to driftwood protection. According to Italian avalanche model there was erected a steel net 1 m over a torrent bottom, 3 m7,2 m and top length 10,7m. It was anchored with 4 anchors into each bank. The net was spliced from 8 mm steel cables carried by 18 mm cables. The joins are mechanic without welds and all construction parts were double zinced. The construction was tested statically and its function was assessed by a model. 

The maintenance consists in mechanic removal of driftwood, which is consequently chipped and composted. The construction of nets is easy and they are easy to maintain. They are permeable to fauna. Trapped wood has to be removed according to real needs. However it is obvious the torrent protection will not consist only in those nets in future.

ENERGY FROM WOOD - BENEFIT TO GLOBAL ECOLOGY - I.
Alois Švenda (pp. 405-407)

The importance of wood as a technical raw material and renewable energy source will increase in seeking solution to the global environmental problem consisting in stabilisation of carbon cycle in the nature, therefore to mitigation of greenhouse effect on climate. The energy from wood opens the chance to solve effectively the wood overproduction and abundance of agricultural land. Major benefits of energy from biomass include decrease of greenhouse gasses and other pollutants (like SO2, NOx) emissions, use of own energy sources immediately in the regions

Renewable energy sources made 5,44 % of total energy consumption in EU in 1995 (biomass out of it 60 %) and and solution to regional policy problems.it shall achieve 12 % in 2010 (biomass out of it 74 %). This target was already achieved by Sweden, Austria, abd Finland in 1995.

Using renewable energy sources is at its initial phase in Czechia. Its share in total use of primary sources represents just 1,5 %. Use of renewable energy sources is included in national Energy Policy (however the share shall only increase to 3-6 % by 2010). Therefore these sources cannot become a crucial energy source and national energy policy will be based on fossil fuels and nuclear energy. That is, the goals of national energy policy regarding renewable sources do not correspond with real possibilities of our forestry and agriculture.