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Use of natural succession and pioneer tree species for the restoration of forests after large-scale bark beetle outbreaks

Good practices

Nov 06, 2025
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Forest restoration efforts following large-scale bark beetle outbreaks aim to replace degraded spruce monocultures with more diverse, resilient stands that are better adapted to changing climate conditions. The use of natural succession and pioneer tree species represents a key tool for restoring areas affected by extensive disturbances. Successful implementation requires assessment of the natural regeneration potential, taking into account both the local site conditions and long-term management objectives. This good practice methodology presents solutions to address specific challenges associated with large-scale calamity clearings. These include microclimatic harshness that limits the use of certain tree species, potential shortages of planting material and constraints in establishing structurally complex forests.

Context:

Forests in the Czech Republic have undergone profound changes driven by climate change and related disturbance regimes. Dominated by Norway spruce (Picea abies) monocultures, these ecosystems have become increasingly susceptible to drought, wind damage and large-scale bark beetle outbreaks. The resulting extensive forest decline highlights the urgent need for coordinated and effective restoration approaches. Current restoration strategies, therefore, focus on establishing more resilient, mixed-species stands that are better suited to projected climate conditions. A key component of this shift is the utilisation of natural succession processes, where pioneer tree species - including Betula, Populus, Alnus, Sorbus and Salix - play a crucial role during the early phases of forest recovery on large clearings. This approach not only accelerates the re-establishment of forest cover but also improves conditions for the regeneration of late-successional species, helps address potential shortages of planting material, and reduces costs associated with artificial regeneration. It also supports the development of diverse and structurally complex forests from the outset.

Problem Description:

Although restoration objectives are generally well-defined, implementing forest recovery measures in the Czech Republic remains challenging. The extent and intensity of disturbances caused by bark beetle outbreaks, windthrow events, and prolonged drought have led to large tracts of severely affected forest. Many of these areas now exhibit reduced site quality and limited natural regeneration capacity. A further obstacle is the restricted availability of suitable planting stock, particularly for less common native species. Seasonal shortages frequently disrupt planting schedules, complicating efforts to establish species-rich and resilient forest stands. High populations of browsing ungulates pose an additional problem, as intensive browsing can prevent the successful establishment of both naturally regenerating and planted target species. In many regions, achieving stable, mixed-species forests is unrealistic without first reducing game pressure. A viable way to help address these constraints is to make systematic use of natural regeneration with pioneer tree species, incorporating them intentionally into restoration planning and stand formation on large disturbance areas.

Implementation Steps:

Step 1: Site assessment
Assess the site conditions relevant to natural regeneration. Focus on the size, shape, slope, soil characteristics, hydrological conditions, availability of seed sources, and other key features of the clear-cut. Use both field observations and existing typological and forestry maps. Document natural and artificial terrain boundaries (e.g., watercourses, terrain breaks, skid trails, erosion gullies), as well as trees or tree groups retained after harvesting, standing and downed deadwood, and other biological legacies such as existing natural regeneration or ingrowth. These biological legacies and all elements that support biodiversity should be taken into account in the subsequent functional zoning of the site. Recommended timing: Conduct this assessment as soon as possible after the salvage harvest.

Step 2: Spatial zoning for restoration
Divide the clear-cut into functional zones based on site assessment. Designate areas with high potential or existing natural regeneration of desired tree species. Prepare a detailed site map with these zone’s boundaries and surface areas. Timing: immediately after site assessment.

Step 3: Measures to support natural regeneration
Silvicultural measures to enhance natural regeneration focus on preparing the soil to improve seedling establishment and regulating ground vegetation. Each measure is site-specific and must be based on detailed knowledge of local conditions. Timing: immediately after site assessment, up to 5 years after the salvage logging.

Step 4: Condition control, improvement, and follow-up care
Regularly monitor the condition of naturally regenerated seedlings and saplings, recording survival, growth, and signs of stress or damage. Check the growth rate, and, if necessary, regulate weed competition and the stand development by applying appropriate tendings. Conduct these activities annually during the first 5–10 years to ensure a successful establishment and a balanced species composition. Timing: first 5–10 years after the initial restoration activities.

Knowledge Types:

Scientific knowledge 
General recommendations for supporting natural regeneration on calamity fellings are based on well-established scientific evidence, which consistently highlights the importance of promoting natural processes throughout all levels of the forest ecosystem.

Practical knowledge
Forest restoration after bark beetle calamities also draws on practical, long-standing forestry experience that helps ensure restoration measures are workable in the field. This includes proven silvicultural practices, such as selecting appropriate sites for natural regeneration and applying suitable soil preparation and cleaning techniques.

Replicability:

YES, the practice has been tested and replicated in multiple contexts and scales and therefore, can be easily transferred and/or adapted to other initiatives with similar goals.

The restoration practice was applied within the implementation of the project SUPERB – Systemic solutions for upscaling of urgent ecosystem restoration for forest-related biodiversity and ecosystem services (Horizon 2020). 

Key Success Factors:

The utilisation of natural succession, in which pioneer species such as Betula, Populus, Alnus, Sorbus and Salix play a key role in the early stages of forest restoration. It accelerates the re-establishment of forest cover, improves conditions for the regeneration of late-successional species, helps mitigate shortages of planting material, and reduces the costs associated with artificial regeneration.

Key success factors include the selection of suitable sites for natural regeneration based on edaphic, morphological, and microclimatic characteristics. In the medium term, effective monitoring and subsequent silvicultural measures are essential to regulate stand composition and achieve the maximum effect of the pioneer species. 


Common Constraints:

Common constraints in the use of natural regeneration include uncertainty of success and temporal as well as spatial variability, which stem from the fact that we rely on natural processes that cannot be fully controlled. Therefore, monitoring and timely interventions are crucial to correct unsatisfactory conditions or guide the further development of stands. Social challenges primarily stem from the public’s negative perception of large clearings; therefore, emphasis is placed on effective communication with municipalities, education, and the active involvement of local communities. The use and promotion of pioneer tree species, which are capable of rapid regeneration and restoring the typical character of forest environments, is beneficial.

Positive Impacts:

  • Increased climate suitability of tree species
  • Increased soil health
  • Increased structural diversity

Increased structural diversity
The use of tree species with differing growth dynamics, combined with spatial and temporal diversification of regeneration, promotes the development of higher structural diversity within a relatively short time after reforestation. By combining species that grow at different rates, forest stands can rapidly form a multi-layered structure, thereby increasing ecological stability and resilience. A typical example is the incorporation of fast-growing birch in the upper canopy paired with silver fir developing in the lower layers.

Increased climate suitability of tree species
Pioneering species improve microclimatic conditions, stabilise the soil, and accelerate humus formation, thereby creating an environment more favourable for species that are better adapted in the long term to changing climatic conditions.

Increased soil health
The described approach puts a stronger focus on tree species that have a proven positive effect on soil’s physical, chemical and biological properties, thereby enhancing fertility, stability and resilience. These are mainly litter-rich species such as birch, alder and poplar contributing significantly to soil organic matter content and nutrient cycling. 


Negative Impacts:

  • Reduced timber quality or quantity

Relying solely on natural regeneration may lead to stands with lower proportions of commercially valuable tree species, resulting in reduced long-term timber production potential. At the same time, the establishment of mixed and structurally diverse forests places higher demands and costs on forest managers, and may be associated with lower expected revenues from timber harvests. A fundamental shift in species composition and an increasing share of harvests from smaller diameter classes will also require considerable adaptation within the wood processing sector, including changes in processing technologies and supply chains. Lower harvest volumes and smaller log dimensions may further increase economic pressure on forest owners, highlighting the need for more efficient and cost-effective forest management strategies.

Source/Author(s)
  • Lukáš Bílek
  • CZU Róbert Marušák
  • CZU
Topic
  • Implementation
Stakeholders
  • Landowners & Practitioners
Purpose
  • Afforestation, reforestation
  • Natural processes and ecosystem preservation
  • Restoration after natural disturbances
Biogeographic region
  • Continental
Countries
  • Czechia
Degradation Driver
  • Environmental
Scale Area
  • The restoration practice was applied within the implementation of the project SUPERB – Systemic solutions for upscaling of urgent ecosystem restoration for forest-related biodiversity and ecosystem services (Horizon 2020).