Improvement felling, selective sanitary and other types of felling

3.3. Improvement felling, selective sanitary and other types of felling

Improvement felling is a type of forestry activities, annually covering the largest forest area and taking the greatest amount of human and other resources of forestry enterprises. Taking care of undergrowth, forestry specialists ensure an optimal tree species composition of forest plantations. Later, severance felling and advance thinning are carried out to assure the quality of future timber harvest. Besides, they allow to use timber which would otherwise never be used: it would be treated as dropout and, having undergone by rotting and mineralization, would decompose.

Selective sanitary felling is conducted in forest stands, whenever necessary, depending on its condition, in particular, on the presence of a great number of dry, sick or damaged trees.

The improvement felling in the basin forests is fairly large-scale: 650-700 thousand cubic meters of timber are annually cut on 80-100 thousand hectares of the improvement felling sites. Severance felling and advance thinning is annually conducted on about 100 thousand hectares of forests with the cutting of 2.4-3.0 million cubic meters of timber. Selective sanitary felling is also rather extensive: it annually affects 175-200 thousand hectares where 2.5-3.0 million cubic meters of timber are cut.

Over the last years, though, the scale of improvement felling in the Russian and Ukrainian parts of the basin has decreased, remaining relatively stable in the Belorussian one.

Improvement, sanitary and other types of felling inevitably change the forest community composition and environment conditions under the forest canopy. As a result, the forest becomes better lit, ventilated and heated by sunlight, the air humidity decreases, as well as the moisture content of ground litter and surface soil layers. Thus the natural succession processes in forest phytocoenosis are interrupted, part of surface phytomass is removed, other felling-related changes occur.

These types of felling have the following adverse impacts on biological and, to a lesser degree, landscape diversity:

- change in the natural dynamics of forest stand composition resulting from felling;

- frequently observed transformation of mixed and uneven-aged forests into pure (unmixed) and even-aged ones;

- practically complete removal form forest stand of biologically useful trees: snags, den and wolf trees, chatwood, etc serving as habitats for numerous groups of insects, fungi, weeds, den-nestling fauna species and alike;

- created conditions for the penetration of non-forest invasive species into lower layers due to temporary climate change under the forest canopy;

- deteriorating habitats and living conditions for species pertaining to closed forests;

- reduced diversity of species participating in the community dynamics;

- substitution of natural succession with the semi-natural one;

- removal from the forest stand of trees potentially capable of maintaining ecosystem’s sustainability and enhancing its biodiversity;

- random damage caused in the course of felling to the field layer with all its components;

- sporadic burn-down of natural forest vegetation in the course of felling site cleaning, accompanied with the kill of many plant and animal organisms;

- contamination of habitats with oil products, lubricants or their combustion products left by forestry equipment or transport vehicles;

- mechanical damage caused to trees and undergrowth in the cutting area;

- sometimes, weakened forest stand resistance to pests or forest diseases;

- anxiety factor in the period of reproduction, breeding and raining young animals and birds.

On the other hand, these types of cutting can affect the forest positively. Among such positive influences are:

- decreased probability of massive propagation of forest pests and development of forest diseases;

- improvement of habitat conditions for light-demanding and heat-loving species;

- better growing conditions for the most economically valuable biodiversity components due to the weakened competition with other species and forest stand at large;

- formed conditions for micro-successions at the sites of storing and/or burning brushwood;

- emerging micro-mosaic of new biotopes enhancing biological diversity owing to the species requiring burnt or mineralized soils, slash piles or drifts.

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