Water in the forest – from monocultures to diversity in National Forests

Poland’s forest area is more than 9.2 million hectares, much of which is managed by a single institution – the State Forests. Forests are not only the green lungs of our country, but also people’s silent allies in the fight against the elements. What measures are State Forests taking to counter droughts and floods? Which tree species best promote water retention? Do monocultures really increase the risk of natural disasters?

Krzysztof Rostek, head of the Department of Silviculture at the General Directorate of State Forests, talks about the role of water retention in Polish forests, especially in the face of accelerating climate change.

Agnieszka Hobot: Could you explain how the State Forests view the relationship between forests and water management?

Krzysztof Rostek: State Forests is deeply aware of the interdependence between forests and water management, and our work on small-scale retention dates back to the 1990s. last century. We were one of the first institutions in Poland that not only noticed the need for water conservation, but also took concrete steps towards its implementation. We carried out the initial projects with our own resources and with the support of the National Fund for Environmental Protection and Water Management, the Provincial Funds for Environmental Protection and Water Management, the EcoFund.

From the late 1990s to 2005, we built and restored more than 1,100 water reservoirs with a capacity of more than 8 million^{cubic meters}, as well as more than 2,000 water damming facilities. The effectiveness of these activities prompted us to create nationwide programs – the Small Lowland Retention Project and the Small Mountain Retention Project, which were implemented from 2007 to 2015. Under these initiatives, more than 7,000 facilities were built to store and/or slow down water runoff, with a total capacity of about 45 million^m3. Funding for these activities came 85 percent from EU funds, with the State Forests financing the remaining 15 percent.

The popularity of the program led to its continuation in 2016-2023. Although the number of new or upgraded reservoirs was smaller at the time – about 800 facilities – a number of solutions to prevent erosion in lowland and mountainous areas emerged, with a significant impact on the protection of aquatic ecosystems.

It is worth noting that a total of more than 15,000 facilities built and planned for construction will store about 62 million^{cubic meters of} water, and the total cost of small retention projects will be more than PLN 1.5 billion.

We are currently working on the third edition of the project, and are planning a new initiative to protect and restore hydrogenic habitats. These activities are intended not only to support water management, but also the long-term protection of valuable habitats. The project, which is being carried out in cooperation with other entities under the LIFE program, will also include the identification of non-treasury lands, which will enable us to take a comprehensive approach to the protection of forests, and thus water resources.

A.H.: What specific activities under this project are planned and in what area?

K.R.: The latest project will be implemented nationwide, and will be coordinated by the Center for Coordination of Environmental Projects. We have already conducted a preliminary identification of the possibility of implementing the activities, which will first focus on Natura 2000 areas and the so-called green infrastructure elements.

We have also introduced a major innovation in the area of water management – with the amendment of key documents on state forest management, such as silvicultural principles, the forest protection manual and the forest management manual, we have added the possibility of creating water management plans in individual forest districts. These plans will allow for more comprehensive management of water resources. We realize that expert support is necessary to make these activities substantive and effective. Our goal is for the documents to translate into concrete results.

A.H.: What about the effectiveness of the activities you are implementing? Especially in the context of monitoring their effects. You mentioned the value of water retention, but after all, there are many activities other than the construction of reservoirs that are crucial for water management in forests. How do you assess their effectiveness? How long does it take to determine that an improvement has occurred in a given forest area?

K.R.: Small water reservoirs are limited in scope, so monitoring is mainly based on scientific studies of their environmental impact. Importantly, we also focus our activities on facilities that have retained value and can perform retention functions. Traditional land reclamation from the post-war period until the 1990s was often carried out incorrectly, so we now ensure that all land reclamation work is carried out with the utmost care and in a way that benefits the environment. Modern, well-conducted land reclamation can bring tangible benefits, strengthen resilience to climate change threats in lowland and mountain forest ecosystems.

We monitor the effects of our activities in a number of ways – we use the results of scientific research and observe the impact of the implementation of the completed facilities on forests. It is worth noting that water management is not the only aspect of our work. We also carry out reconstruction of forest stands – especially where spruce and pine monocultures dominate, often unsuitable for the habitat. Unfortunately, this is not always met with understanding from the public. Reconstruction of forest stands is a long-term process, lasting up to 100-150 years, because we implement it during the generational replacement of the forest. Reconstruction of younger stands is carried out only where forests are dying.

We realize that timber harvesting is a topic of public controversy, but we believe that consistently explaining the goals and showing the results of our activities will help to better understand the issue.

A.H.: You mentioned the monoculture prevailing in Polish forests. What species play a key role in terms of drought or flood protection? Does the choice depend on regional conditions, or mainly on catchment areas and habitats?

K.R.: The choice of tree species depends not so much on regional conditions as on specific habitats. First of all, we have a very high proportion of pine trees – more than 60 percent of the stands in Poland. Mainly because it was planted in areas marginal for agricultural production, with poor boning (sixth class). Often nothing else will survive in such areas, although we sometimes introduce deciduous admixtures there, such as birch or sessile oak.

In more fertile habitats, however, we have more options, and there we plant deciduous species, such as oaks, beeches and alders – the latter are particularly water-bound and tolerate periodic flooding well. As for spruce, it is a species that arouses a lot of emotion at the moment, especially in mountainous areas, where it was often planted on a massive scale in the 19th and 20th centuries, in pursuit of quick profit, and at the expense of species more adapted to local conditions, such as fir or beech. We now have serious problems with spruce throughout Europe – as do the Czechs, Slovaks, Austrians, and Germans. These countries, too, are now moving away from spruce monocultures.

Spruce has a shallow root system and is sensitive to lowered groundwater levels, so it suffers when there are moisture deficits in the upper soil layers. However, we are not giving it up completely. In silviculture, we apply the principle of species diversity, planting stands as diverse as possible. This way, when a species begins to show adaptation problems, others will be able to take over its functions in the ecosystem.

A.H.: Following up on what you said about shallow groundwater shortages and drought, do you think climate change has had a significant impact on the condition of forests over the past 10 years?

K.R.: Undoubtedly, climate change is having a significant impact on the condition of forests. The turning point was 2015, when the drought phenomenon made itself known in an exceptionally severe way. At the same time, it should be noted that trees respond to drought more slowly than other plants. In the following years, 2017-2019, the drought led to a massive drought in various regions of the country. At that time, about 25 percent of the timber harvested came from trees dying due to lack of water.

We are also seeing an increase in the activity of pests that previously did not pose an economic problem. An example is the bark beetle, which years ago was only marginally mentioned in entomology textbooks. After the droughts of 2015-2016, it initially began to overrun the stands of eastern Poland on a massive scale, causing them to die. Later, the phenomenon spread throughout the country. Another example is mistletoe, which until a dozen years ago did not cause damage. Now it is found en masse in stands all over the country, and it is very worrying that it is starting to attack even young, 5-6 year old trees, which was unthinkable not long ago.

Extreme weather events, such as hurricanes and tornadoes, are also becoming more frequent. An example is the 2017 hurricane that swept through the Tuchola Forest, damaging more than 120,000 hectares of forest and leaving behind 10 million^{cubic meters of} fallen and broken trees. Many forest districts almost ceased to exist. In such situations, the force of the wind is enormous, and regardless of the species of trees, losses are inevitable.

A.H.: In the context of the recent flooding, there have been reports that water retention in forests can support flood protection. I wanted to ask about the experience of the State Forests in this regard – to what extent can forests slow down surface runoff and how does stand composition affect this relationship?

K.R.: Indeed, there have been allegations that the flooding may have been the result of poor forest management by the State Forests, which is completely unfounded. With precipitation in excess of 470 mm in four days, or nearly 500 liters per ^1m2, no forest can help or manage to retain such a huge amount of water. Forests have natural retention capacities – tree crowns, trunks, undergrowth and soil help store water – but not with such intense and sudden precipitation.

In the Sudetenland, where spruce trees predominate, accusations of inadequate stand reconstruction are also unjustified. Even if we started changes on a massive scale, the effect would be similar in the face of such a downpour. I would add that dead wood and soil can also absorb water perfectly well, but in this case they were so dried out that their retention capacity dropped to almost zero. Imagine that after five days of heavy rainfall, the soil at a depth of 30 cm was still completely dry.

As for the future, we plan to continue measures to prevent the effects of drought and flooding – as we have been doing for years. The forest has its natural retention capacity, but it is not unlimited. Countering the effects of drought and flooding requires extensive measures, such as age-differentiation of forest stands to ensure a healthy forest structure. Every year, Poland’s forest area increases, even though the land for afforestation is gradually shrinking. Our goal now is to preserve healthy stands of different ages so that forests can serve future generations in the best possible condition.