80 FOREST REPORT 2005
4.3 Close to nature
Natural forest
Naturalforests formwhen forests with near-natural tree standsare nolongermanaged.Thisapplies to many Swiss forests today. In 13% of theSwiss forest area there has been no silvicultural inter- vention for the past 50 ormore years and the number of such areas is rising. Thusmore natu- ral forestsare continually form- ing. They contain all the phas- es of naturalforest development and age naturally. So-called old growth forest is found almost ex- clusively in natural forests since trees in forestsused commercial- ly grow to only about half their naturalage.Around aquarter of Swiss stands today are over 120 years old, unlike in most other European countries where the percentage is often not even 5%
andrarely 10%.
How natural a forest is de- pends not only on forest manage- ment but also on howfaraway it is frominhabited areasandhow dense anetwork of forest paths androads it contains.People out walking orjogging frighten sen- sitiveanimalslike thecapercail- lie. Habitats for such animals havebecome rare since only 21%
of the forested areas in Switzer- land are further than500metres from the next road. This is still 1300km2of forest,most ofwhich has not beenusedformore than 50 years. These forestsare con- sideredundisturbed and“left to nature”,and canbe foundin the Alps, in Ticino mostly at high- er altitudes and in the National Parkin theGrisons.
Thecomposition of tree spe- cies in aforest ecosystem is one indicator,among others,of how natural it is. According to the NFIabout 58% of the Swiss for- est hasanear-natural tree species composition.19% is near-natural broadleaf forest and 39% near- natural conifer forest. 41% was, however, previously broadleaf forest that today containsanun- FURTHERINFORMATION
Swiss Federal Research Institute WSL 8903 Birmensdorf
National Forest Inventory Research Dept. LANDSCAPE Section Landscape inventories (0) 44/ 739 23 43
Even intensively used forests can be nearly natu- ral if they consist of native tree species.
In many commercial forests the very young and old forest development phases, which are especial- ly important for species diversity, are often under- represented.
Around 13% less of the Swiss forest is man- aged today than 50 years ago. Unmanaged forests become wild and slowly turn into so-called natural forests.
The percentage of near-natural broadleaf for-
ests in the Central Plateau has increased from 22
to 25%. That of pure spruce forests, which are not
considered natural, is currently 11%.
81 4BIOLOGICAL DIVERSITY
naturally high proportion ofcon- ifers.Fortunately windthrowand more close-to-nature silviculture have helped broadleaf trees to slowly regain territory. Between 1985and1995 the proportion of near-naturalbroadleaf forests on theCentralPlateaurose from22 to25%. But even there conifers still dominate in about 60% of the forest area.Pure spruce for- ests (forests where more than 90% of the treesare spruce)cov- er roughly 11%(25000hectares) of the previously broadleaf for- est area on the Central Plateau.
Theseunnaturalforests harbour ecological and economic risks as they damage the soil and of- ten contain just a few species.
Moreover, they are susceptible to storm damage and bark bee- tleattack.
Virgin forest
Unlike natural forests that were once managed in the past, vir- gin forests have never been in- terfered with. Such pristine ec- osystems are today confined to very smallareas in the whole of Europe. In Switzerland official- ly recognised virgin forestscover only a total of roughly 100hec- tares,i.e.0.01% of the forest area, and are located in Derborence (VS)andScatlé(GR).
Contrary to popular opinion, European virgin forests do not contain more species than man- agedforests.In fact the opposite is true, as human influence on managedforests often increasesa forest’s structuraldiversity,form- ingamosaicofdifferent habitats.
This hasapositive effect on the number of species (> 4.1a Spe- ciesdiversity).Anaturalorclose- to-natural forest ecosystemdoes not necessarily mean highbiodi- versity.Nevertheless, the remain- ing bits of virgin forest are im- portant as their originalstructure andspeciesdiversity are valuable for researchandprovidewonder- ful opportunities for experienc- ing thewild.
A natural or close-to-natural forest ecosys- tem does not necessarily mean high biodi- versity. Nevertheless, the remaining bits of virgin forest are important.
4.3.1
Forest areas without interventions
Percentage of forest areas with nomanagement interventions in thepast 50 years.
Switzerland:13%
■up to 1%
■2–10%
■11–20%
■21–30%
■over 30% 4
0.4 1.1
1 6
5
10 12
20 12
18
26
41 6
4.3.2
Natural forest
TheSihlforest inCantonZurichisdeveloping into anatu- ralforest again.
