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Environmental information systems
Forest biodiversity is the (genetic) diversity in plant and animal species in forests. Biodiversity can be measured by counting species and their uniqueness. Since it is difficult to monitor all species, biodiversity often is characterised according to its composition, structure and function. Based on these characteristics, forest biodiversity currently shows a trend of improvement, e.g. the number of tree species per stand, stand age and the amount of deadwood is increasing. On a European level, there are very few assessments that directly monitor forest biodiversity indicators, e.g. forest birds, threatened plant and animal species. Assessment of the conservation status of protected forest habitats show that 85% of these habitats have unfavourable to inadequate conditions. According to the IUCN Red list of tree species, it is estimated the about 40 percent of the native tree species in Europe are threatened.
Tree species composition
Europe’s forests are home to 454 native tree and other woody species. Almost 50% of European forests comprise only two to three species. Around 30% of all forests in Europe have only one tree species, mostly coniferous species such as pine or spruce, but also broadleaved species such as eucalyptus or poplar. The area with two to three tree species gradually increased since 2005.
The species composition has changed through the past centuries, tuned to industrial requirements. For example, pine has been in high demand in mining and construction, spruce and eucalypt have been an important staple for paper production. Monocultures are more vulnerable to climate change, invasive alien species, and pest and disease outbreaks. There are large regional differences in species composition, also in terms of diversity in natural forest types, which typically increases from North to South. Tree species composition is slowly getting more diverse with a larger share of broadleaved species, which has a positive effect on biodiversity and resilience.
Most European forests consist of 2 to 3 tree species
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Introduced tree species
Introduced tree species covered about 5.2 million ha in 2020 which is about 3.1% of the total forest area in Europe. Introduced tree species are valued for their species-specific properties, such as yield potential, industrial requirements, carbon sequestration and erosion prevention. However, introduced species may impact forest ecosystems and negatively affect forest biodiversity. Non-native species may also hybridize with native relatives which may impact native populations.
The genera that represent the largest number of introduced species are Eucalyptus, Pinus, Acacia and Abies. Introduced species growing in the largest areas are Black locust (Robinia pseudoacacia) with 2.44 million ha, Tasmanian blue gum (Eucalyptus globulus) with 1.46 million ha, Sitka spruce (Picea sitchensis) with 1.16 million ha and Douglas fir (Pseudotsuga menziesii) with 0.83 million ha.
Legal frameworks across Europe take a variety of approaches to regulating non-native tree species, ranging from very few restrictions on species choice and plantation surface area to the complete banning of such species from forests.
Threatened trees
According to the IUCN European Red List of trees, about 37% of all tree species in Europe have been assessed as threatened (i.e. Critically Endangered, Endangered or Vulnerable) and therefore have high risk of extinction.
Almost 40% of the natuve tree species in Europe are threatened.
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Structure
The structure of a forest is made up of both horizontal and vertical layers. It not only includes different sizes of trees, but also the various vegetation layers such as trees, shrubs and ground vegetation, as well as open spaces. A structured forest plays a crucial role in supporting biodiversity, as it provides habitats for a diverse range of species.
Naturalness
Naturalness refers to the extent that a forest resembles its undisturbed ‘natural’ state, in terms of structure, composition and processes. Forests that are undisturbed by humans are considered natural. In Europe only a small part of forests are undisturbed by humans and these are very valuable for biodiversity.
Only 2% of Europe's forests are undisturbed by man and mostly located in Northern Europe.
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Only around 2% of forests in the EU are undisturbed by humans. These ecosystems have a natural tree composition, age structure, regeneration processes and substantial amounts of deadwood. Forests like this provide habitats for forest plants, animals and flora. Most undisturbed forests are found in North Europe where they make up almost 4% of the forest area. In other regions the share of undisturbed forests is much lower at about 0.3%.
Most forest habitats in the EU are semi-natural (~93%), and the remaining share is covered by plantations (~4%).
Regeneration
Natural regeneration may have a more positive impact on the naturalness of a forest than active reforestation (planting), as the root systems develop on site and the trees are more adapted to the local conditions, like climate and soil. Natural regeneration also maintains the genetic diversity of the native plant species. When the genetic diversity of a site is limited, it may be beneficial to reforest actively.
Most forests in Europe regenerate and expand naturally.
Age structure
Forest biodiversity is positively affected by an uneven structure of tree age and stem diameter. In the past, even-aged, single species forests were preferred because of pragmatic management benefits. Even-aged forests are more susceptible to storm damage, pests and diseases than uneven-aged forests. Due to more intensive management, even-aged forests also are less favourable for biodiversity. Since the beginning of this century, there has been an increase in uneven-aged forests, but even-aged forests still cover 75% of the forest area.
Only 25% of Europe’s forests are uneven-aged, which is more favourable structure for biodiversity than even-aged forests.
Function
In relation to forest biodiversity, function refers to the specific roles and interactions species have within a forest ecosystem, and their contribution to the ecosystem. Species may have symbiotic and thus enabling or reinforcing relationships, which may vary at different stages of the life cycle. Deadwood is an example of this, and it has an important role as a host for many endangered species, for example fungi and saproxylic insects such as beetles.
Deadwood
Deadwood in forests provides an important habitat, shelter and food source for many rare and threatened species, such as insects (especially beetles), fungi, lichens, birds and bats. For biodiversity, it is important to have both standing and lying deadwood, preferably in a mix of diameters and species. In commercially managed forests, deadwood is often removed to reduce the risk of forest fires and insect outbreaks. This may also take place in protected areas if deadwood is the result of pests that are potentially harmful to local flora and fauna.
Harvesting trees before they can come to a natural end lowers the amount of deadwood. The average amounts of total deadwood (combining both lying and standing deadwood) vary considerably between EU countries, ranging from about 5 m3/ha in Denmark to over 40 m3/ha in Slovakia (Forest Europe, 2020). The amounts also differ a lot between forest types, with the lowest amounts in floodplain forests (about 4 m3/ha) and the highest amounts in Alpine forests (about 22 m3/ha) (Forest Europe, 2020).
Deadwood makes up 7% of the total growing stock (living trees).
Over recent decades, the amount of deadwood has increased in all European regions, but the amount varies strongly per region.
The amount of dead wood in Europe's forests increased significantly over the last decades.
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1 Source of the statistics on this page (except when specifically indicated): FOREST EUROPE pan-European dataset provided by FAO, UNECE and FOREST EUROPE, Food and Agriculture Organization of the United Nations