State of the Swiss forest (NFI)

The National Forest Inventory (NFI) examines and records the state of the forest based on a number of variables, three of which (degree of mixedness, tree species, ages) are shown in this map. This depicts the development of the forest over centuries of continuous management. In the forest’s natural state, undisturbed by human activity, both its species composition and its age distribution would be quite different.

Degree of mixedness
The degree of mixedness, which is surveyed terrestrially, refers to the ratio of deciduous trees to conifers at the basal area (sum of the cross-sectional areas of the trunks of all trees in a stand, measured at a height of 1,3 metres). Forests where more than 90% of the trees are conifers are classed as “purely coniferous”, while those with 51% to 90% conifers are “mixed coniferous” and those with 11% to 50% are “mixed deciduous”. Woodland where conifers account for less than 10% is classed as “purely deciduous”. The “Degree of mixedness” graphic presents the proportions of forest types broken down by region and shows how they have changed since records began (scrub forests are not taken into account in this case). There has been a noticeable increase in deciduous forests at the expense of coniferous ones. This is primarily due to changes in forest management, including measures taken to adapt forests to climate change. Spruce, which has also long been cultivated outside of its natural habitat, is disappearing further and further in lower-lying areas.

The proportion of conifers increases with altitude, with purely coniferous forests commanding 65% of high-elevation woodland. At lower levels, where deciduous trees naturally dominate, more than half of the forest is either purely deciduous or mixed deciduous.

Main tree species
The appearance of the Swiss forest is strongly influenced by its main tree species. Coniferous trees make up 59% of the forest overall, with the highest proportions found in the Alpine foothills (67%) and in the Alps themselves (76%). In Jura and the Swiss Plateau, the ratio of conifers to deciduous trees is more or less equal. In addition to spruce, beech and fir – the three most common tree species – which make up 65% of the trees in the forest and 76% of the timber stock, European larch, sycamore, common ash and Scots pine are also prevalent in Switzerland. From an ecological point of view, however, the rarer species are also important. The fourth National Forest Inventory (NFI4) recorded 143 different species of trees and shrubs (22 coniferous varieties and 121 deciduous ones), although 68 of these are only found in young woodland (trees measuring up to 30 cm in diameter).

Without factoring in scrub forest, the number of forest stands where one particular deciduous species predominates rose slightly across Switzerland between the third and fourth inventories (NFI3 and NFI4), especially those dominated by sycamores. There has also been a slight increase in stands where fir is prevalent, whereas spruce-dominated stands have declined: their numbers have dropped by 4% in the Swiss Plateau, falling at virtually the same rate as between the second and third inventories (NFI2 and NFI3). Taking all forest sampling areas into account, including those established between the two inventories, stands with larch, fir or sycamore as the dominant tree species have increased slightly.

Age of stands
The age of the forest has been determined on a stand-by-stand basis. A stand is a contiguous group of trees that is distinguished from its neighbouring sections of forest by its age, composition of species or structure. While many stands are homogeneous, a good 25% of the forest consists of areas where the age distribution is very mixed. These are known as uneven-aged stands.

Old stands and thick trees provide important habitats and are vitally important for many typical woodland species. Many different species are reliant on thick tree trunks, areas of rotten wood or hollows in branches, for example, which young trees do not offer. Compared to other european countries, the proportion of old stands (>120 years old) in Switzerland is very high at just under 19%. Only a fifth of countries can claim an old stand level of more than 10%. Switzerland tops the list by a considerable margin, ahead of Finland and the Russian Federation, although Russia does have a large proportion of intact forest landscapes of global significance. In addition to the old forest stands, the hundred thickest trees in each of around one third of the uneven-aged stands are over 120 years old on average (dominant age).

The distribution of stand ages across the Swiss forest varies significantly depending on region and altitude. This is largely due to the accessibility of the forests and, therefore, how intensively they are managed. However, different forms of management also have an impact. As the altitude becomes higher, for example, young stands decline and older ones become more prevalent. Uneven-aged stands increase significantly with rising altitudes too. Stands more than 160 years old are predominantly made up of spruces, larches and Swiss pines and are most commonly found at higher levels, where these species are naturally mainly distributed.

Clear differences can also be seen between different species of trees. Coniferous stands with an age of 120 years or more are far more common than deciduous ones in that age bracket. This is partly because the coniferous stands grow mostly on poorer land and it therefore takes longer for them to reach their required size, or they are simply not used at all due to problems with accessibility. However, it is also partly because some deciduous species have a shorter life expectancy and grow in places that are intensively managed.