The climate crisis is no longer a grim vision for unspecified future generations. He is already taking place here and now, which we are all witnessing. Its consequences are extreme weather events, more frequent and prolonged heat waves, droughts, heavy rainfall and the accompanying massive reduction in biodiversity.

In Poland since 1951. the increase in annual temperature is estimated at about 1.5 – 2ºC, with annual precipitation not changing significantly, which consequently translates into a significant increase in field evaporation and water shortages also in forests, which are its natural reservoir.

According to the latest report of the Central Statistical Office, “Poland on the path of sustainable development,” we rank 24th in the European Union in terms of renewable freshwater resources per capita, just ahead of the Czech Republic, Cyprus and Malta. The volume of renewable freshwater resources per capita in Poland is less than 1,600m3, indicating the threat of water stress. According to the UN, the limit below which a country is considered at risk of such a shortage is 1,700m3 per capita.

Climate change is therefore a significant threat to the stability of forest ecosystems, with the potential to adversely affect their resources and ability to perform social functions, as well as the profitability of the forestry sector and related industries. Among the greatest water-related threats, from the point of view of the stability of the functioning of forest ecosystems, are currently considered long-term climatic droughts. Swamping of forest habitats is a much rarer phenomenon than desiccation, nevertheless, the damage caused by excess water can be large and permanent, as it causes local transformation of ecosystems. Floods are among the phenomena whose frequency has been increasing markedly in recent times, and their effects are increasingly severe.

Some processes we can no longer stop, but we are able to adapt to them. And although it may seem that today’s world is beyond our imagination, a certain, determined group of professionals – Polish foresters, but also enthusiasts – actively and effectively carry out a number of activities every day that adapt forest ecosystems to climate change, thus counteracting the negative effects of this phenomenon.

Forest-Water, Water-Forest

Water is the lifeblood of ecosystems, including forests, lakes and wetlands, on which our current and future food security depends. The forest as an ecosystem should be prepared for both periods of excess water and water scarcity.

The stakes are high, as Poland is at the forefront of Europe in terms of forest area, which currently stands at more than 9.2 million hectares, equivalent to nearly 30% of the country’s area. The vast majority are state forests, with more than 7.3 million hectares managed by the State Forests National Forest Holding. And the forest provides numerous ecosystem services, essential to the anthroposphere and biosphere, and performs many key functions, such as water-protection.

Green sponge

Forests play an extremely important role in the circulation and storage of water. This is aptly illustrated by the metaphor of the forest as a sponge, collecting and accumulating water during the rainy season and giving it back during the dry season. Wetlands and peatlands are also natural sinks and stores of water, for which it is a to be or not to be. This ability of the forest to retain moisture makes it a specific microclimate, creating favorable conditions for the organisms that inhabit it, as well as affecting neighboring areas.

Forests and wetlands have a significant impact on the circulation of water in the atmosphere and the water balance on a geographic scale. High forest cover and the presence of wetland habitats increase terrain evaporation, and therefore the water vapor content of the air. They thus create a hydrological pump that sustains precipitation in the form of rain, dew or fog deep in the continents. This is particularly important in temperate latitudes, where about 70% of summer precipitation is the direct result of land evapotranspiration rather than the transport of water from the oceans. The higher the air temperature, the more water vapor it can hold and the faster terrestrial ecosystems dry out, especially agricultural land with poor retention.

This is also why a warming climate is making droughts more severe. In such cases, the lifesaver is the proximity of wetlands, which, by increasing humidity, effectively reduce the drying out of other surrounding areas.

Water shortages and their consequences for forest ecosystems

Poland has both forests adapted to very wet soils, such as forests or swamp forests, as well as to extremely dry conditions, such as pine forests developing on loose sands. In both cases, a radical change in moisture content has a negative impact on the viability of trees and other ecosystem-building organisms. Reductions in water resources often have a more negative impact on the functioning of heavily moistened wetland habitats than dry ones, where trees are inherently better adapted to cope with shortages.

The above changes have and will continue to have an impact on the health of most native tree species, especially those attached to the cool and humid climates of northern Eurasia or high mountains (such as spruce).

Coevolutionary mechanisms gradually intensify the water cycle toward internal forest ecosystems, promote the substitution of species with distinct water needs, and thus maintain the balance between supply and demand, and even reduce water consumption. However, co-evolving hydrological and functional processes may prove asynchronous and delay the emergence of a water-saving effect. Various processes that can negatively or positively affect water resources are constrained by energy and water supplies both inside and outside forest ecosystems, which creates uncertainty in the forest-water relationship

Water scarcity is a factor that affects both the physiological condition of trees and the population dynamics of other organisms that make up the complex forest ecosystem (bacteria, fungi, insects, birds or mammals), as well as the interrelationships between trees and these organisms. Changing these interdependencies is a common cause of health deterioration and even decline of some tree species. Long-term water deficit weakens the natural defense capabilities of many plant species. Trees become more susceptible to diseases and pests, become weaker, and consequently show less resistance to damage from wind, frost or rain.

High temperatures and drought also result in increased fire risk. Dry litter and the presence of downy (withered trees) and the dominance of conifers make the fire spread rapidly. Drought in the forest also means limited access to water and food for animals. Dry litter and dried-up bodies of water mean deterioration of living and reproductive conditions, for species associated with them. In extreme cases, they can mean their extinction. Prolonged and repeated drought leads to the death of some tree species, such as oaks and ash trees, which need much more water.

The symptoms of the response of forest ecosystems to a warming climate are many. These can include the mass release of spruce trees (climate warming is causing water stress in the trees and an increase in the generation of the printworm, whose larvae feed in the phloem), as well as the mass colonization of pines firs and poplars (and, more recently, linden and fruit trees) by semi-parasitic mistletoes (their seeds are spread by thrushes, whose population is increasing due to mild winters), as well as the emergence of insects from the group of scrollworms that feed on oak leaves. Direct signs of drought can also be observed in the crowns of trees (e.g., beech trees), especially the tallest ones, growing on dry and sunny sites.

Water shortage interacts comprehensively and in conjunction with other factors, most notably higher temperatures during the growing and resting (winter) seasons. A strong and permanent change in habitat conditions leads to the activation of processes that eventually initiate the remodeling of the entire ecosystem and its better adaptation to new, such as drier habitats. From a human perspective, however, such a natural adaptation process can have negative consequences: the extinction of the forest over vast areas and the loss of some of its ecosystem functions, such as recreation, soil conservation, etc.

The question then arises, how to manage the area of the “forest water body” without violating the basic management goal of preserving water relations as close to optimal as possible?

Adaptation to climate change

For foresters, constantly under pressure from public expectations, this is a difficult challenge. Polish foresters, despite the complexity of the process, as well as many uncertainties, steer the development of forest ecosystems in such a way that the process of adaptation to changing conditions is as smooth as possible and does not limit the functions of forests.

Concrete steps in this direction are being taken early and focused on areas where the risk is greatest. They also take into account the different purposes fulfilled by forest areas, which are sometimes difficult to reconcile, such as: biodiversity conservation, social functions and timber production. An excellent example is the projects implemented by the State Forests, with the support of EU funds, aimed at increasing the natural retention capacity of forests in lowland and mountain areas.

What is water retention?

As signaled above, forests and wetlands have a significant impact on the circulation of water in the atmosphere and the water balance on a geographic scale. However, not all the water remains in the forest. Some evaporates into the atmosphere, some penetrates the soil and feeds ground and deep-sea resources, and ends up in streams, rivers or reservoirs. In this way, the forest is part of the so-called “forest”. a small water cycle in nature, which is important for local hydrological conditions. In a situation where we want to take some part of the water out of this cycle by storing it or slowing its outflow, then we are dealing with retention. In the forests, we have the so-called. small retention – water is stored in small reservoirs and ponds, as well as in wetlands.

History of retention in forests

Conservation activities in the field of forest and forestry adaptation to climate change, consisting of small-scale retention investments, began on a somewhat larger scale in the 1990s. 1920s. Conducted earlier, back in the pre-war (Sudetenland) and 1970s. Last century, investments in hydrotechnical infrastructure in forests were aimed at regulating the water relations of habitats with a view to increasing the productivity of forest stands.

As a result of small retention activities in the State Forests, a total of 1124 small retention reservoirs with a total area of approx. 1360 hectares and a capacity of approx. 8.4 millioncubic meters, and 2216 damming structures such as levees, sills, small weirs and rapids. Outlays for the implementation of small-scale retention in forests amounted to about PLN 38.6 million in these years, comprising mainly funds from the State Forests, with minor support from the National Fund for Environmental Protection and Water Management, the National Fund for Environmental Protection and Water Management, the EcoFund and foreign funds, including PHARE.[1]

In the financial perspective 2007 – 2013, within the framework of the Operational Program Infrastructure and Environment, organizational units of the State Forests have undertaken two projects. These were the first small-scale retention and runoff slowing projects in Europe, carried out on such a large scale in mountain and lowland catchments. They have contributed to better adaptation of forests and forestry to climate change, manifested mainly through intensification of violent weather events.

Great small retention – LP projects implemented under the Operational Program Infrastructure and Environment.

Forests are and will continue to be one of the key beneficiaries of European funds for climate change adaptation and nature conservation. Two small-scale lowland and mountain retention projects are currently being finalized under OPI&E 2014 – 2020, namely.

  • Comprehensive project for adaptation of forests and forestry to climate change – small-scale retention and prevention of water erosion in lowland areas;
  • Comprehensive project for adaptation of forests and forestry to climate change – small-scale retention and prevention of water erosion in mountainous areas.

Both of the aforementioned projects are part of the trend of early adaptive action by increasing the natural retention of forest land and protecting existing infrastructure from increased erosion processes.

In order to retain water in forested areas, a number of activities have been carried out in the above-mentioned projects to create and restore small reservoirs, polders and natural floodplains, wetlands. Measures have also been taken to slow the outflow of water from the catchment area and retain it in the forest litter and soil.

The projects also implemented measures to protect infrastructure from excessive erosion caused by flood waters. The projects involved securing or reconstructing infrastructure unsuitable for flood waters and protecting slopes, roads and trails from excessive water erosion.

These activities have a positive impact on water levels and biodiversity, as on the one hand they reduce the supply of debris, and on the other they contribute to restoring the biological continuity of watercourses (in the case of culverts, reconstruction to facilities with a larger light and natural bottom, removal of sills and steps, and reconstruction of weirs on watercourses). The total value of the currently implemented lowland and mountain small retention projects carried out by the State Forest Service under OPI&E 2014 – 2020 is PLN 538.36 million, of which EU funding accounts for PLN 338.37 million.

It doesn’t stop there. More projects are in the pipeline and will be submitted to the European Funds for Infrastructure Climate and Environment Operational Program(FEnIKS) 2021 – 2027. They will be a continuation of retention projects, but there will also be new initiatives for hydrogenic habitats, including the project “Restoring the function and improving the condition of hydrogenic habitats on lands under the management of the State Forest Service in Natura 2000 and Green Infrastructure areas.”

The main objective of the project is to protect and restore biodiversity and promote adaptation to climate change by creating conditions for the implementation of the Priority Action Framework for Natura 2000 and Green Infrastructure. Achieving the aforementioned goal will serve to better protect the natural habitats and species associated with heavily wetted (marshy) areas, especially Natura 2000 habitats.

Small-scale water retention projects extend far beyond forest management with their scope. The effect of these measures is to generally mitigate the effects of the already widespread decline in groundwater levels, to supply the forest with life-giving water and improve the water balance, and thus to have a positive impact not only on the functioning of the entire forest ecosystem, but also on adjacent areas (including elements of the agricultural landscape). Small-scale retention contributes to increasing the moisture content of forest habitats by raising the groundwater table in areas adjacent to water reservoirs, significantly increasing biodiversity in the adjacent forest. Indeed, around small bodies of water and in wetlands, habitat mosaics are much richer. Small-scale retention also has a beneficial effect on hydrogenic habitats, i.e. water-dependent peatlands, alders and riparian forests.

[1] U. Zabrocka-Kostrubiec, Small retention in National Forests – Status and prospects, Studies and Materials of the Center for Nature and Forestry Education, R.10. Vol. 2 (18)/2008

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