Regeneration

Tree species selection 

Tree species selection is an important step in the regeneration of a forest stand, as this will determine the composition and structure of the stand, directly impacting functions and services such as biodiversity and the quantity and quality of wood. The main aspects considered when selecting tree species are the management goals, the site conditions, and the availability and cost of regeneration materials.

Economically important trees in Europe

Forest managers have long favoured relatively few tree species which are economically important for timber and fuelwood production. These are Scots pine, Norway spruce, Pedunculate and Sessile oak, and European beech.

Although pure coniferous stands were recurrent in Europe, a shift towards an increased share of broadleaved species can be observed, especially in Central Europe since the 1990s. That can be attributed to the realization that pure coniferous forests are more susceptible to disturbances such as storms, wildfires, and insect outbreaks (see Forest Health). 

Besides native species, at least 150 non-native tree species have been introduced in Europe, intentionally or accidentally. The area covered by introduced tree species increased steadily in Europe between 1990 and 2015 but decreased slightly in Central-West Europe between 2005 and 2015. Eucalyptus, Pinus, Acacia and Abies are the most common introduced genera in Europe. 

The most common non-native species are Douglas fir, Sitka spruce, Tasmanian blue gum and black locust. The species mainly originate from North America and to a lesser extent from Asia and Australia. They are generally not invasive and grow in European forests and provenance trials, covering an area of approximately 8.5 M ha (Total forest area EU27: 159.2 Mha).  

Types of regeneration

Over 60% of forests in the EU originate from natural regeneration

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Main regeneration types 

Natural regeneration

Natural regeneration is the establishment of forest stands through natural seeding. Seeds can be dispersed by gravity. animals, wind and water.

Natural seeding is largely determined by the availability of seeds from nearby stands. This method relies to a large extent on the existing composition of tree species and genotypes.

Artificial regeneration

Artificial regeneration encompasses planting and artificial seeding activities, allowing the selection of tree species. It is guided by the environmental site conditions that ultimately determine whether a species will survive and remain healthy. as well as its growth rate. Artificial regeneration provides more direct control over the tree species. genotypes and placement of trees in the new stand.

Combination of natural and artificial regeneration

A combination of natural and artificial regeneration is also possible. The choice of a regeneration method is guided by the management goal (e.g., timber production. biodiversity protection), the preferred tree species and the availability and cost of reproductive material (such as seeds and seedlings). The choice of a regeneration method is also closely linked to the harvest regimes that are applied.

Coppice

Coppice is the stimulation of the development of new shoots from the stumps and roots of cut trees. The feasibility of this method relies mainly on the capability of trees species to sprout from the base, which is far more common on broadleaves.

Overall, planting is the most common artificial regeneration method in Europe. Regeneration by sowing is limited to regenerating stands of light-demanding conifers on sites that have been clear-felled in North and Central-East Europe.

The main regeneration practice varies between EU countries

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Forest reproductive material 

The forest manager chooses the forest reproductive and breeding material to be used during the regeneration stage, such as seeds or seedlings produced from seeds, cuttings, or other propagating parts of a tree. This depends on the tree species composition and regeneration method. 

When applying artificial regeneration, a forest manager can choose whether to use seeds (or seedlings produced from seeds) that have been collected in registered seed stands, or to use improved forest reproductive material developed from seed orchards. Improved forest reproductive material relates to material that has been selected and/or tested to obtain benefits, such as increased productivity, improved timber quality, or better resilience to climatic conditions, pests and diseases. 

Use of forest reproductive material

Information on the use of tree breeding material in forest management is limited and can only be inferred from statistics on the production and trade of seedlings and seeds, and information on tree breeding programmes. In the period 2004–2014, on average, 30 million plants and 400,000 kg seeds were traded annually. Coniferous reproductive material trade is dominated by Scandinavian and Baltic countries, while about 15% of traded seedlings were of hardwood tree species, especially in Central Europe.

Norway spruce seedlings were the most traded species in Europe over the period 2004-2014

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Annual trade of seedlings within the European Union, including data on Spain, France, Belgium, Austria, Czech Republic, Slovakia, Poland, U.K, Netherlands, Germany, Denmark, Latvia, Lithuania, Estonia, Finland, and Sweden [7].

Common practices for forest regeneration management

Regardless of the type of regeneration selected, there are common practices which can be applied before or after the regeneration technique, encouraging the process.

Soil preparation

Enhancing seed germination and seedling establishment can be improved by manipulating the growing conditions through soil preparation.

Techniques like scarification or tilling are used to break up the soil and expose mineral layers, improving conditions for seedling establishment. 

Ungulate management

Controlling herbivore populations can prevent overgrazing and damage to young trees. 

Installing deer exclosures or implementing controlled hunting programmes can reduce browsing pressure on regenerating forests. 

Reduce species competition

Limiting competing vegetation ensures resources are available for a desired tree species. 

Removing fast-growing shrubs helps ensure that the target tree species receives sufficient light and nutrients. 

Disturbance  mitigation

Mitigating harmful disturbances like fire, drought and pests can maintain stable regeneration conditions. 

Prescribed burns or limiting combustible matter in the regeneration area can reduce fire risks. Species or genotypic selections can be tailored for improved drought or pest resilience.