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> Forest Report 2015 Condition and Use of Swiss Forests FOEN / WSL 2015
4.2 Regeneration
Urs-Beat Brändli, Nicole Imesch
> Unstocked regeneration areas are created through timber felling or through natural disturbances such as storms or forest fires and provide a habitat for species requiring light and warmth. Between 1995 and 2006 these areas doubled in size, partly as a result of the windstorm ‘Lothar’.
> Natural regeneration has economic and ecological advantages over planting. In Switzerland it has increased markedly. Today, 90 per cent of forest stands in the regeneration and young forest phases developed from natural seeding. In this respect Switzerland is in first place among West European countries.
> Planting has continued to decrease considerably since 1995. Today planting is only done to reinforce pro- tection forests, promote species diversity or produce timber from native tree species.
> The regeneration of some tree species has been severely affected by wild ungulates. Browsing of the sensitive silver fir has increased since 1995, and hardly any young growth of the rare yew has occurred for decades.
Regeneration sites
Young forest stands form part of the diversity of habitats in the forest. They develop naturally in places where old trees have died, growing on small areas when single trees die, or on a larger scale when storms, forest fires and other disturbances produce large clearings. Forest managers imitate these natural processes and rejuvenate forests either through felling single trees (in mountain plenter, plenter and permanent forests) or felling trees on small areas up to half a hectare in area (in high forests with group selection).
Regeneration areas, i.e. temporarily unstocked areas where the young forest should grow, provide very good pre- requisites for a varied forest sucession (Priewasser 2013).
They not only enable a change in tree generation, but also provide habitats for animal and plant species requiring light and warmth, regardless of whether the unstocked areas have developed naturally or through small-scale felling. The regen- eration areas in the Swiss forest doubled in area between 1995 and 2006, according to the National Forest Inventory NFI.
The majority of them were created by the windstorm ‘Lothar’
in 1999. Large regeneration areas favour tree species requiring light, like willows, poplars, birches, rowans or oaks.
Natural regeneration or planting?
In principle, forests regenerate by themselves. Natural regen- eration has many ecological advantages. Forests that regener- ate naturally are more diverse because they consist of more tree species and have a higher genetic diversity. Moreover, the tree species in such forests are well adapted to the site.
Both these factors reduce the risk of failure, particularly in the
light of climate change. Even non-native (section 4.4) or tree species badly adapted to the site can regenerate themselves, which is often not desirable from the points of view of for- estry management and ecology. Natural regeneration is there- fore not necessarily better than planting, which often cannot be avoided if the aim is to transform pure spruce stands into near-natural forests. On windthrow and cleared sites, artificial regeneration may also be better if, for example, suitable ‘seed trees’ are lacking or competition from herbaceous vegetation is strong, or if a rare or economically interesting species needs to be promoted or a protection forest to be made effective quickly. Nevertheless, less planting than previously is done today for three main reasons: planting is costly; it may go against the principles of near-natural silviculture if applied to large areas; and wild ungulates are particularly fond of eating planted saplings (cf. Browsing).
Overall, more and more of the regeneration in the Swiss forest is natural. In forest stands that are in a regeneration or young forest phase, the proportion of natural regeneration rose from 81 per cent in 1995 to 90 per cent in 2013 according to the NFI. In the mountain forests of the subalpine zone, the proportion is as high as 98 per cent. If larger areas are regen- erated – mostly in forests at lower altitudes – so-called young growth and thickets are formed. The proportion of purely nat- ural regeneration in such areas rose from 64 to 79 per cent between 1995 and 2013 (Fig. 4.2.1). During the same period, the number of trees planted per year dropped from 4.4 to 1.2 million (FOEN 2013a).
> 4 Biodiversity 4.2 Regeneration 75
Browsing by game
Only a few young plants manage to grow into adult trees. Many of them die due to competition between young trees, lack of light or water, frost, insects or diseases. Lack of light can be dealt with by felling trees. Where old stands are sufficiently thinned, enough saplings belonging to site-adapted species develop, as a rule, from the natural regeneration. In places with overly large populations of wild ungulates (especially of roe deer, red deer and chamois), regeneration is, however, endangered. The animals then eat many more of the saplings than normal and thereby impede or even prevent their growth.
They prefer silver fir (Fig. 4.2.2), maple, ash, oak and yew, but are less keen on spruce and beech. For tree species that reproduce in large numbers, like maple or ash, the number of young saplings is usually high enough despite browsing. With the silver fir, which is an important tree species for protec- tion forests, the ecologically interesting oak and the rare yew and wild service tree, browsing is often so severe that natu- ral regeneration can no longer be guaranteed. Thus there has been practically no young yew growth in the Swiss forest for decades (Brändli et al. 2009). Browsing intensity is measured by counting the number of apical shoots browsed, and then dividing it by the total number of saplings and young trees.
Overall, browsing intensity slightly decreased between 1995 and 2013 in the Jura, the Swiss Plateau and the Pre-Alps, but increased in the Alps, especially on the Southern slopes of the Alps. The increase in the Alps is due mainly to the heav- ier browsing of silver fir and, on the Southern slopes of the Alps, to more browsing of broadleaf species like maple and ash (Brändli et al. 2015). Even though the Forest Act requires
natural regeneration of these species, it is, in many places, no longer possible without expensive protection measures, such as fences and individual safeguards. One important reason for the increase in browsing is the growth in red deer populations (section 4.1). Damage from fraying and bark stripping – mainly by red deer – has been found on 3 per cent of the saplings with a diameter of 1 to 11 centimetres (Brändli et al. 2015). A key factor in solving the problem is the regulation of the wild ungulate population through hunting. Moreover, measures to increase habitat quality that improve the food supply for game and reduce disturbances are important. Such measures involve not only the forestry services but also other ‘actors’ like tour- ism or agriculture. A prerequisite for solving the problem is a cooperative partnership between the hunting and forestry authorities, which the development of forest-game schemes is intended to promote (FOEN 2010).
Fig. 4.2.1 Proportional area of natural regeneration in young growth and thickets in the whole of Switzerland and in the 5 production regions. Source: NFI
0 % 20 % 40 % 60 % 80 % 100 %
2009/13 1993/95 2009/13 1993/95 2009/13 1993/95 2009/13 1993/95 2009/13 1993/95 2009/13 1993/95
Switzerland Southern slopes of the Alps Alps Pre-Alps Swiss Plateau Jura
Natural regeneration Mixed Planted 79 64
100 96
98 75
85 62 60 30
76 54
14 21
4 16
6 26 31 33
15 29
7 15
2 9 9 13 9 37
9 17
Fig. 4.2.2 Browsing by roe deer of the apical and side shoots of a silver fir. Photo: Urs-Beat Brändli
