How to effectively manage forests in water-affected habitats

In the Czech Republic, 19% of forests are found in water-affected habitats, including peat bogs, waterlogged forests, and floodplains along watercourses. The challenging conditions for forest cultivation in these areas have led to the construction of technical drainage systems, known as melioration networks, since the end of the 18th century. These networks were primarily designed to partially drain the soil, at least during the forest regeneration period. However, their effects were often viewed as long-term.

Given the ongoing climate change, it is important to evaluate the significance of technical land reclamation in specific areas. This evaluation is related not only to the geomorphology of the region, the local climate, and the nature of the soils, but also to the condition of the forest stands and the methods used for their management.

In 2020, the Forest Grant Service of the Czech Republic announced a research initiative titled “Optimization of the Hydrological Regime of Existing Land Reclamation Networks in Forests.” This initiative aims to develop comprehensive guidelines and information for assessing and optimizing forestry management in water-affected sites where forest hydromelioration has been implemented in the past.

The project titled “Methods of Adapting Existing Forest Drainage Structures to Changing Climate Conditions” was addressed between 2021 and 2023. The outcomes of this project served as the foundation for the certified methodology titled “Restoration and tending of forest stands on groundwater-influenced sites“ (Obnova a výchova lesních porostů na lokalitách ovlivněných hladinou podzemní vody). This methodology was developed by a team of authors from the Opočno Research Station, the Forestry and Game Management Research Institute, v. v. i., and the Czech University of Life Sciences in Prague.

The methodology outlines specific procedures and principles for the restoration and cultivation of forest stands in water-affected habitats, tailored to various natural conditions. It places special emphasis on enhancing the stability of these stands, especially considering ongoing climate change. The approach seeks to balance the expected functions of the forest, particularly the interplay between production and water management.

The methodology consists of three complementary components. It begins with silvicultural principles tailored for the main commercial tree species found in water-affected habitats. The second part includes catalogue sheets that provide framework guidelines for management based on specific habitat conditions. The final component offers a brief guide on the use of mechanization in forest cultivation.

In water-affected habitats, implementing appropriate silvicultural practices is essential for effective management. Technical measures to regulate the water regime are only applied when standard management practices fail to create forest stands that meet expected functions. The specific growth conditions in these habitats can complicate restoration efforts and subsequent stages of forest cultivation. Therefore, the key is to make the right choices regarding species composition and the intensity of management practices.

The authors of the methodology recommend the following for forest restoration:

Support the establishment of mixed stands, primarily by grouping habitat-appropriate tree species, with certain exceptions.

Adjust the intensity of restoration procedures based on the current stand type, the health of the trees, and the potential to achieve the desired species composition.

Favor gentle management methods that maximize the natural regeneration of existing mother trees. When possible, apply the undergrowth management method, incorporating small-scale elements, and ensure that the size of any necessary clear-cut areas complies with applicable legislation.

To maintain a high level of forest cover stability, which is essential for the proper functioning of the “biological pump” (i.e., evapotranspiration) within the stands, it is important to limit waterlogging on the site. This approach involves reducing mowing frequency and extending the renewal period, tailored to the specific type of forest stand.

Additionally, small clearings and areas devoid of tree vegetation, up to approximately 0.04 hectares, can be left untouched (without planting) in situations where there is a high demand for regeneration due to elevated groundwater levels. This strategy will not only enhance the diversity of forest habitats but is also expected to increase biodiversity in the surrounding area, thereby strengthening the overall fulfilment of various forest functions.

For soils that are not fully capable of supporting heavy forestry machinery, or only partially capable, follow these recommendations for mechanized cultivation interventions:

• Harvest timber and transport it during the winter when the ground is frozen, provided the snow cover is adequate.
• In areas that can only partially support timber operations, dry periods can also be utilized for harvesting.
• Avoid using unsuitable tree harvesting methods.
• Choose the most direct routes for machinery operation.
• Ensure that the trees along the edges of the approach routes are consistently protected from damage.
• It is advisable to limit the use of clear-cutting methods for restoration.

Conclusion

The methodology being applied aims to enhance species and structural diversity, which in turn is expected to improve the stability and resilience of forest stands in water-affected habitats. It is essential to ensure that all anticipated forest functions are met, especially the non-production functions related to hydric and water management.

Implementing this methodology is expected to improve production safety and increase both the quantity and quality of wood mass. This improvement could lead to increases of a few percent, potentially generating tens of thousands of CZK per hectare of forest land in water-affected habitats.

The methodology titled “Restoration and tending of forest stands on groundwater-influenced sites“ (Obnova a výchova lesních porostů na lokalitách ovlivněných hladinou podzemní vody) can be downloaded here.

Authors: Ing. Ondřej Špulák, Ph.D., Ing. Dušan Kacálek, Ph.D.; VÚLHM, v. v. i., Research station Opočno (Výzkumná stanice Opočno); doc. Ing. Lukáš Bílek, Ph.D., Czech University of Life Sciences in Prague (Česká zemědělská univerzita v Praze); e-mail: spulak@vulhmop.cz

Prepared following the original by Ing. Jan Řezáč, VÚLHM, v. v. i., e-mail: rezac@vulhm.cz

Illustrative photos: Forests in water-affected habitats, the archive of Opočno Research Station, FGMRI.