Our woods are of comparatively good ecological quality thanks to nature-friendly forest management. Deficits exist in the open pioneer phases and in the late stages of succession rich in deadwood and old growth. However, future challenges such as climate change, intensified forestry practices as a result of the transition to renewable energy, and excessive recreation pressure could have adverse effects.
Woodland (including shrub forest) covers about one third of the area of Switzerland. The most densely wooded regions are in the southern Alps (52 % of forest cover) and the Jura (41 %), while the Alps (27 %) and the Central Plateau (25 %) have the least forest cover. The Pre-Alps are in the middle range at 35 %.
The larger part of forest area consists of conifer woods at 62 %, compared to deciduous woods at 38 %. The respective proportions of conifer and deciduous forest differ greatly depending on altitude: the lowlands are characterised by naturally occurring deciduous woods dominated by beech, in southern Switzerland also with sweet chestnut. Maple, sycamore, ash and oaks often occur too, and are more dominant than beech in dry or damp locations. Mixed stands with spruce and fir also occur in the lowlands, as well as pure conifer stands that are not well adapted to this type of site. Conifer stands account for about 20 % of the area that would naturally be covered with deciduous trees. The proportion of conifers grows with increasing altitude, and deciduous trees become scarcer. Beech-fir forests are the rule, followed by fir-spruce forests higher up. High altitudes are dominated by naturally occurring pure conifer forests, composed mainly of spruce, with some pine, larch and stone pine, and transitioning to very open woodland or shrub forest close to the tree line, with shrub-like green alder and mountain pine.
Silviculture has become less diverse
Almost 90 % of forest area in Switzerland consists of managed forests. Trees are often harvested in their optimal phase of growth, i.e. no later than when they reach half their biologically possible age. Two thirds of stands contain trees of the same age, or the same diameter at breast height. Another feature of these forests is a vertical structure showing distinct layers. On about 20 % of forest area, in contrast, stands are made up of trees of various ages – from young growth to old trees with thick trunks. Such stands have a highly complex vertical structure.
These two forms of managed forest, created by two different types of cultivation – high forest with area felling and permanent or plenter forest – are generally characterised by a large timber volume of living trees (i.e. growing stock). In fact, at 352 m3/ha, Switzerland has one of the highest average values in Europe.
Other management forms such as coppice forests or coppice with standards (5 %) in the lowlands of the Central Plateau and Jura, wooded pastures in the Jura, Grisons and Valais (7 %) and chestnut orchards in Ticino (0.2 %) only take up small areas. These traditional forms of management that created nutrient-poor and light-flooded forest types and contributed to woodland diversity are becoming less and less important. Remaining patches of old, unmanaged natural and alluvial forests, where natural processes can take place unhindered and all forest phases can be present, are also scarce. Virgin forests have practically vanished in Switzerland (0.01 % of forest area).
Continued increase in forest area and growing stock
Changes in the forest are periodically recorded in the National Forest Inventory (NFI). A comprehensive catalogue of features has been inventoried three times so far since 1983 (1983–1985, 1993–1995 and 2004–2006). Continuous annual surveys have been in progress since 2009 as part of the fourth NFI, of which results are available up to 2013.
The increase in forest area and growing stock has continued uninterrupted ever since the first federal Forest Police Act of 1876 prohibited any reduction in forest area. Overall, forest area increased by 7 % on average between 1993–1995 and 2009–2013 and growing stock by 3 %, although there are large regional differences. Forest area did not increase during this period on the Central Plateau and in the Jura, and growing stock actually decreased (by 11 % on the Central Plateau). In contrast, forest area grew by 8 % in the northern Alps and by as much as 15 % and 12 %, respectively, in the central and southern Alps. Growing stock increased significantly in the central Alps (15 %) and southern Alps (30 %). The increase occurred mainly above 1200 m and is not accounted for by the reforestation of protection forest; rather, it is a result of the abandonment of land that is marginally productive or difficult to access. In addition, climate warming stimulates the growth of trees at higher altitude and on unproductive soil, causing the forest and tree line to shift upwards. Other factors driving the increase in growing stock are declining timber exploitation in areas where access is difficult, high harvesting costs, and sinking wood prices.
Nevertheless, from an ecological point of view, forests in Switzerland are quite young. On the Central Plateau, only 11 % of all forest stands are more than 120 years old and only 0.5 % are older than 180; in the Alps, only 7 % are more than 180 years old. In all of Switzerland, 0.4 % of forests are more than 250 years old. Forest stands with trees older than 120 years that are no longer profitable have been in decline since 1993–1995 both in Switzerland as a whole (−18 %) and in the individual biogeographical regions.
More natural structures through natural regeneration, deadwood and habitat trees
The practice of natural and site-adapted forest regeneration has been implemented throughout the country since the start of the millennium. This practice has reduced stands that are not natural to the site they grow on – stands with a larger proportion of conifer trees than would naturally occur – by one fifth and increased naturally occurring deciduous woods by 19 %, especially in the lowlands. The economically profitable but not naturally occurring spruce stands in the lowlands have decreased by one third in volume or, in terms of area, from 11 % to 6 %. Storms «Vivian» in 1990 and «Lothar» in 1999, the subsequent bark beetle infestations and the dry periods in 2003 contributed to this development. The storms also increased structural diversity in the affected areas of forest.
The concept of biodiversity-friendly management has increasingly been incorporated into forestry practices, with the result that deadwood more than doubled in volume from 11 to 26 m3/ha between 1993–1995 and 2009–2013. In fact, the average volume of deadwood in Switzerland is currently among the highest in Europe, though there are large regional differences. Despite a significant increase in deadwood in the more intensively used forests of the Jura and the Central Plateau (127 % and 256 %, respectively) between 1993–1995 and 2009–2013, the amount of deadwood in these regions is still only half that of the Alps and Pre-Alps. In heavily used forests, deadwood is concentrated in the windthrow sites created by storm «Lothar» and is still largely absent from other areas. Many areas in the Jura and on the Central Plateau have not yet reached the federal target of 20 m3/ha, to be achieved by 2030, and the distribution of deadwood is unsatisfactory.
Promoting biodiversity has also led to an increase in trees with thick trunks (diameter of at least 80 cm, so-called giants) as compared to 1993–1995 (from 1.1 to 1.7 trees/ha). As they age and are exposed to external influences, large old trees often form rot, cracks, crevices, cavities as well as moss and lichen growth; these so-called habitat trees provide shelter and food for a wide range of organisms. However, there is still a large gap between the current number of giants in our managed woods and the number typical for natural forests. In the primeval beech forests of the Ukrainian Carpathians there are about 30 times as many giants.
On the way to becoming an ecological hotspot?
The Forest Act of 1991 requires owners and foresters to use a close-to-nature approach to forest management. Thanks to this practice of nature-friendly silviculture and the fact that the total extent of forest area is protected by law, the ecological quality of woodlands is high compared to other habitats. As promising as the increasing use of biodiversity-friendly methods in forestry is, there have been other changes in recent years that are less encouraging from an ecological point of view.
Most forests are medium-aged with a large growing stock, while only a few small areas of open, light-flooded woodland remain, so there is little suitable habitat for species that need a lot of light and warmth. Similarly, mature forests with lots of old trees and large amounts of deadwood also only take up a fraction of the overall forest area, especially in the lowlands. Although the volume of deadwood continues to increase, the quality and distribution of deadwood are unsatisfactory in terms of biodiversity. More dead trees with a large diameter and in advanced stages of decay would be of benefit in many areas, not only those that have little deadwood. Due to the increased use of wood for fuel, which involves removing not only stemwood but also the crown of the tree as well as ecologically valuable trees of low timber quality, the proportion of deadwood could decline again in the future if no measures are taken to prevent this.
So far, forest reserves, which cover about 6 % of forest area and are protected by contract from commercial timber use, have not been able to alleviate the lack of either open or mature, deadwood-rich forest phases. Moreover, the reserves are unevenly distributed across Switzerland.
Similarly, the increase in forest area is not all positive. In fact, the encroachment of forest into ecologically valuable habitats such as dry grassland and the loss of forest edges as patches of forest grow together are undesirable processes in terms of overall species diversity. Many remaining forest edges are of poor ecological quality. 84 % of forest edges lack a sufficiently broad and well-structured shrub belt bordered by a herb fringe on the outside, especially on the Central Plateau, in the Jura and in the Pre-Alps.
Forests are also becoming more and more popular with leisure seekers. Visitor numbers and the range of activities are growing, especially in woodland areas located near urban centres, and even extending into the night. But even relatively low degrees of human disturbance during the day can reduce the density and richness of breeding bird communities. Finally, trends in forest management that involve ever larger wood-harvesting machinery and interventions at all times of the year – including during the breeding season – affect the quality of the forest as a habitat. For example, the total length of forest roads that are wide enough for lorries has increased significantly since 1993–1995: 969 km of road were newly built or expanded.
Along with greater volumes of deadwood (>20 m3/ha), more habitat trees and more old-growth patches, the federal government's ecological targets propose that forest reserves are to take up 10 % of forest area in Switzerland by 2030. «Natural forest reserves» are to enable natural forest succession without intervention all the way to the decay stage, while the purpose of «special forest reserves» is to promote valuable habitats like open woodland. A further objective is the ecological enhancement of suitable forest edges. The rigorous implementation of measures to achieve these targets is critical for the conservation of organisms that rely on forest habitats.
The forest must satisfy many demands, not only as a habitat, but also as a provider of protection, resources and recreation. As a system with developmental cycles that last hundreds of years – in current commercial forests 80–120, in beech forests up to 350 years – forests are coming under pressure in a changing socio-economic environment that gives rise to diverse and sometimes conflicting needs. The effects of climate change, which will alter the composition of tree species in the long term, and the growing influence of wildfires, storms, hail storms and dry periods will further increase the pressure on the forest and its functions. An additional threat comes from harmful organisms introduced to our forests as a result of global trade (e.g. the Asian longhorn beetle or the fungus that causes ash dieback). Next to suitable native tree species, several non-native trees are present in our forests, such as Douglas fir or red oak. From the point of view of biodiversity, the use of non-native species should be discouraged.
On the whole, the forestry sector faces great challenges. Balancing different interests and demands, defining priority functions and taking advantage of synergies that arise from the forest's various functions will be critical going forward. The targeted promotion and safeguarding of valuable woodland habitats that has begun in recent years must continue in the future. Targeted interventions as well as information and awareness campaigns must strive to reconcile recreation with other forest functions, and forest management should continue to seek alignment with natural processes and sustainability. It remains to be seen whether these measures are sufficient in view of the rapid changes expected in the coming decades, and whether forests will be able to continue fulfilling their many functions.
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