Is it worthwhile to obtain thermal energy from stands of preparatory tree species?
As the area of disaster clearings increases, there is a growing emphasis on promoting spatial, species, and long-term age diversity in subsequent forest stands. One promising approach to achieving this is the use of preparatory tree species that exhibit a pioneering growth strategy for restoring these cleared areas.
Depending on the silvicultural methods employed, preparatory stands can have ecological benefits and yield a considerable amount of wood mass (dendromass) that can be utilized and assessed.
Photo: Preparatory stands of silver birch, 6 years old, established by planting on a calamity clearing in northern Moravia (Huzová research trial); photo by J. Černý.
In the case of faster restoration with targeted tree species, it is advisable to fully retain the harvested biomass of the preparatory stand as a means of recycling nutrients. Conversely, when it comes to long-term care, the stands of preparatory tree species can be utilized to produce high-quality wood. The characteristics and economic ties of this wood often create opportunities for its use in energy production, for instance. Additionally, energy chips or fuelwood derived from preparatory tree species, particularly birch, are in high demand in the region.
The promotion of using forest biomass for energy is supported by the National Forestry Programme II (NLP 2008). The main regulation governing the use of energy from renewable sources is the European Union Directive on the promotion of renewable energy, known as the Renewable Energy Directive (RED), which was revised in 2003 (Directive of the European Parliament and the Council (EU) 2023/2413). According to this plan, it is expected to be incorporated into the legislation of all EU Member States by the end of 2025.
Photo: Preparatory stand of European larch in a calamity-clearing area in northern Moravia (research trial Huzová); photo by J. Černý.
Scientists from the Opočno Research Station, part of VÚLHM, v. v. i., have published a certified methodology on the determination of thermal energy in the biomass of preparatory stands of tree species (Stanovení množství tepelné energie v dendromase porostů přípravných dřevin). This methodology was developed during the NAZV project NAZV QK22020008 titled “Comprehensive Evaluation of the Fulfilment of Production and Non-Production Functions of the Forest in Preparatory Tree Species Stands” (Komplexní vyhodnocení plnění produkčních a mimoprodukčních funkcí lesa u porostů přípravných dřevin).
The methodology provides procedures for the effective utilization of biomass derived from tree species in preparatory stands, primarily in areas severely impacted by large-scale forest degradation. This approach supports decision-making in forest management and energy sectors by adhering to the principles of sustainable forestry. It emphasizes minimizing the risks that could threaten the ecological resilience of forest ecosystems. The objective is to contribute to the effective utilization and development of renewable energy sources, making it a valuable tool for professionals in forestry and energy.
A preparatory forest is a type of secondary forest that emerges through natural succession or artificial regeneration after the original forest has been lost, either due to natural disasters (such as wind, fire, or insect infestations) or intentional activities (like logging or deforestation). The economic goal of utilizing a preparatory forest is to rapidly establish a canopy that provides shading and reduces climatic extremes in previously bare areas.
Photo: preparatory stand with a predominance of alder, approximately 20 years old, created by natural regeneration; photo by O. Špulák
Positive effects of preparatory trees include the reduction of direct sunlight, temperature fluctuations, and wind speed. They also help decrease competition from weeds, regulate the water regime, promote rooting, reduce erosion risk, and improve the physical, chemical, and biological properties of the soil.
The most suitable species for preparatory stands are those that require fewer nutrients, exhibit rapid growth, can naturally regenerate, and thrive in bare areas. Additionally, these trees should have abundant and regular fertility. In the Czech Republic, the most common preparatory tree species include silver birch, black alder, poplar, aspen, wild service tree, and willow.
The biomass of preparatory tree stands, mainly consisting of silver birch and poplar aspen, increases rapidly due to their fast growth in early years. By the time they reach 30 years of age, these trees can produce between 180 and 250 m³/ha of rough timber, which translates to a total biomass production of 216 to 300 m³/ha, depending on the quality of the habitat. After utilizing their “preparatory function,” cultivation practices focus on either single or gradual harvesting of these stands. This process aims to release target tree species or introduce them at ages ranging from 20 to 50 years following the establishment of these preparatory stands.
Photo: A stand of naturally regenerated trees approximately 30 years old, where birch is designated as both a target species and a preparatory tree species; photo O. Špulák
When calculating the potential use of harvested dendromass from the preparatory stand for energy purposes, it is essential to consider not only the economic balance of anticipated costs and revenues but also the impact of this intervention on the site’s nutrient balance. This is particularly important when assessing the use of all above-ground dendromass, including thinner wood (up to 7 cm of DBH). Most nutrients are stored in the bark and the tree’s leaves and branches, making the non-wood mass a significant reservoir of these essential nutrients.
Energy chips, which consist of wood, bark, and coniferous materials often mixed with impurities such as soil, are in high demand for use in various power plants, central heating facilities (including cogeneration units), and household heating systems. This growing demand for dendromass is supported by subsidies that help offset the costs of acquiring combustion technology and generating electricity from this renewable source.
Utilizing wood biomass from preparatory forest stands can be an economically advantageous strategy, depending on the habitat and stand conditions. This approach can yield short-term profits, diversify income, and contribute to the support of the regional economy.
Photo: Energy chips of wood biomass, VÚLHM archive
The yield from harvesting preparatory stands can offset economic losses linked to disasters or long-term forest restoration. Unlike fossil fuels, the CO₂ released from burning dendromass can be gradually balanced by the growth of new forest biomass, making it a potentially carbon-neutral energy source over time.
Using dendromass for energy also offers ecological benefits, such as supporting renewable energy sources and helping to mitigate climate change. However, in nutrient-poor areas, it is essential to leave a certain amount of dendromass in place, for example, in the form of wood chips.
The dominant tree species in preparatory stands, primarily birch, have a high calorific potential, making them attractive in the renewable energy market. The yield from a hectare of these stands can amount to tens or even hundreds of thousands of CZK, depending on the amount of dendromass available and the costs of harvesting.
The methodology for calculating the thermal energy in preparatory tree stands (Stanovení množství tepelné energie v dendromase porostů přípravných dřevin) can be downloaded here.
Authors of methodology: Ing. Ondřej Špulák, Ph.D., Ing. Jakub Černý, Ph.D., Ing. Jan Leugner, Ph.D.; VÚLHM, v. v. i., VS Opočno, e-mail: spulak@vulhmop.cz
Prepared by Ing. Jan Řezáč, VÚLHM, v. v. i., e-mail: rezac@vulhm.cz