Water sensitive forest management

At European level, forests are closely connected to the hydrological network, and provide more than 4 km³ of water to European citizens annually by hosting 870,000 km of rivers (the total length of European rivers is about 3.5 million km). Moreover, almost 33% (or 92,000 km²) of 71,000 lakes are located in forested catchments (EEA technical report 13/2015). Forests greatly contribute to proper management of water quantity and quality aspects: 

• by intercepting precipitation, evaporating moisture from vegetative surfaces, transpiring soil moisture, capturing fog water and maintaining soil infiltration, forests positively influence the amount of water available from groundwater, surface watercourses and water bodies;  
• by maintaining or improving soil infiltration and soil water storage capacity, forests influence the timing of water delivery;  
• by minimizing erosion, forests minimize impairment of water quality due to sedimentation; 
• by retaining excess rain water, forests help to moderate run‑off patterns, preventing extreme run‑offs, thus reducing damage from flooding, and help in mitigating the effects of drought. 

Forests can also protect water bodies and watercourses by trapping sediments and pollutants in runoff waters from upslope land use. In addition, along streams, forests provide shade, thus reducing the water temperature. Finally, forests are also essential to mitigate and adapt to the impacts of climate change, as well as to contribute to the Sustainable Development Goals (SDGs) n. 3 (Ensure healthy lives and promote well-being for all at all ages), n. 6 (Ensure availability and sustainable management of water and sanitation for all), and n. 15 (Sustainably manage forests, combat desertification, halt and reverse land degradation, halt biodiversity loss). In the international community, these multitudes of water-related benefits that forests provide to society are referred as the forest–water nexus, which has been recently highlighted as a human issue that requires urgent socio-political attention. 

At the same time, forests make important use of water. Trees use water at their highest rate when they have reached their final height and during the most intensive growth stage. The amount of water used by forests is influenced by climate, topography, soil, forest age, species composition and management practices. Either too little water (as a result of insufficient precipitation or a reduction in groundwater availability), or too much (i.e. waterlogging), can have a negative effect on forest health. These aspects can be influenced by climate change, which are expected to affect precipitation regimes differently, depending on the specific location. Under climate change conditions drought and wet extreme events are expected to intensify in the next decades.  

Forest management measures can increase water yield, regulate water flow, and reduce drought stress for a forest. One of the challenges for forest managers is therefore, to maximize forest benefits while conserving water resources. In this perspective, important water management goals in forests include: 

• maintaining the ideal height of groundwater (i.e. water in saturated soil, the top of which is known as the water table) to create stable (growth) conditions for trees; 
• ensuring that water quantity and quality are maintained or improved; 
• protecting natural resources and human-made infrastructure against water damage;  

• maintaining or improving conditions for rest and recreation in forests.  

Forest conservation measures are especially important in areas closed to water streams. Studies report a wide range of water quality impacts after forest operations associated with logging, including sediment delivery, nutrient losses and changes to acidity and temperature. 

Water infiltration and retention are encouraged in forest soils by dense, deep root systems and a thick and porous organic top layer. To support this regulating function, forest managers should aim to maintain permanent vegetation cover, limit the compaction of soils, maintain a high amount of organic matter in the soil, and increase the “surface roughness” (that is, the unevenness of the soil surface, which helps increase water infiltration). Maintaining a good tree cover, with healthy undergrowth, is effective for minimizing sediment loads and soil erosion, thus improving or maintaining good water quality in a forest area. 

Afforestation and reforestation bring benefits for the regulation of water flow and the maintenance of water quality, reducing the intensity of floods and the severity of droughts. Particularly relevant, in this context, are practices such as harvesting, thinning and species mix choice. Canopy structure of mixed species plantations reduce transpiration, imposing less pressure on water if compared to mono-species plantations. By decreasing the number of trees in the stand, thinning may also be used to mitigate excessive forest water use. The positive impact of this measure may however be offset by increased water consumption due to increased growth of the remaining trees. Depending on the fraction of harvested land and on harvesting patterns, water yield usually increase after timber harvest. Different harvesting regimes may therefore impact differently on water resource security. Finally, shorter rotations decrease the period of time for which canopy is completely closed and may therefore also reduce water forest consumption. A relatively constant population of the stand by young trees may, however, counterbalance this effect. In addition, the use of fast growing species is usually more water intensive than slow growing species with higher rotations. The last point is something to consider in landscapes with a water deficit. Unmanaged or overstocked forests may reduce downstream water supply. The desirable trait of inhibiting water runoff may become undesirable in circumstances where water is particularly scarce.  

IPCC categories

Structural and physical: Ecosystem-based adaptation options

Stakeholder participation

The implementation of this adaptation option requires the involvement of various actors (river managers, farmers, forest services, policy-makers, private owners, etc.) who should be involved to make the adoption of the adaptation option feasible. Stakeholders also have a crucial role for the management of the implemented measures. Information campaigns, and other specific activities, about the role of wetlands and forests as water suppliers should be promoted to raise awareness among the different stakeholders in the whole watershed (national authorities, the public and the private sector).  

Success and Limiting Factors

A key challenge for land, forest and water managers is maximizing the wide range of forest benefits without detriment to water resources and ecosystem function. To address this challenge, there is urgent need for better understanding of the interactions between forests/trees and water (particularly in watersheds), for awareness raising and capacity building in forest hydrology, and for embedding this knowledge and research findings in policies and actions. The benefit to upstream and downstream populations should be also publicised, so that the forest management options will be recognized as essential and accepted. There is also need to develop institutional mechanisms to enhance synergies in forests and water issues, and to implement and enforce national and regional action programmes. 

Costs are a potential limitation of adapting management rules in silviculture to improve the tree water balance. Market-based arrangements are a way for upstream land users to recover the costs of maintaining forest cover, and a way of funding other land management practices to protect watershed services. Especially on private land, incentives are required to guarantee forest conservation. Though the vast majority of experiences have been outside of Europe, market-based approaches in which payments are contingent on achieving desired outcomes (e.g. Payment for Environmental Services, PES) can lead to more efficient resource allocation and more cost-effective solutions. They are recognized as incentives to regulate and maintain forests services. The new EU Forest Strategy specifically encourage member states, as relevant to their national circumstances, to set up a payment scheme for ecosystem services for forest owners and managers. PES initiatives take various forms depending on the characteristics of the service, the scale of the ecosystem processes producing them, and the socioeconomic and institutional context. They range from informal, community-based initiatives, through more formal, voluntary contractual arrangements between individual parties, to complex arrangements among multiple parties facilitated by intermediary organizations.  

Property rights also play an important role in economic incentives because they define who has access to benefits and who has responsibility for the costs of delivering those benefits. If the distribution of costs and benefits is not perceived as equitable, and if significant stakeholders are excluded or disadvantaged, they will have little incentive to cooperate. For example, without clear land title, upper watershed land users lack the authority to enter into contractual agreements and are thus unable to benefit from payments. 

However, demonstrating and quantifying the actual benefits of the forest management options to those who are asked to pay for them is quite challenging. This requires an understanding of complex ecosystem processes, over time in specific places, the identification of effective management actions to maintain these, and reasonable assurance that buyers will have access to benefits in the future. Finding the most efficient and effective approaches also requires the capacity to learn and adjust to new information.

Costs and Benefits

Forests are serving multiple functions and providing several ecosystem services, including those related to water management, as: 

• conservation and provision of freshwater for diverse human uses; 
• flow regulation and filtration, which help to maintain base or dry-season flow, allow the recharge of water stored in soil, groundwater, wetlands and floodplains, and control the level of groundwater tables.  

• Control of water runoff, preventing extreme run‑offs, thus reducing damage from flooding 
• trapping of pollutants and sediments that affect water quality; 
• maintenance of habitat diversity and ecosystem resilience;  
• conservation of cultural values, including aesthetic qualities that support tourism, recreation and traditional ways of living.  

Moreover, management measures that safeguard the water related functionalities of forests can save the costs associated with water treatment for different uses. Indeed, it is recognized that water from forest sites require less treatments than water from other water polluting sectors (Miettinen, 2020). For every 10% increase in watershed forest cover, water treatment costs decrease approximately by 20%, up to about 60% forest cover (Centre for Watershed Protection – Forest and Drinking Water). Treatment costs level off when forest cover is between 70 and 100%. Cost saving evaluations can vary from site to site and need specific studies supporting the design of cost-effective policies. 

Legal Aspects

The new EU Forest Strategy, published at the end of 2021, aims to improve the quantity and quality of EU forests and strengthen their protection, restoration and resilience. This will increase the forests potential in providing several ecological and socio-economic services, including those related to the forest – water nexus. In addition, the recent adopted EU 2030 Biodiversity Strategy includes among its objectives restoring degraded European ecosystems by planting at least 3 billion additional trees by 2030, which will enhance the forest cover across Europe. 

The main EU funding source for forestry measures is the Common Agricultural Policy (CAP) and in particular its “second pillar” Rural Development Programme. Within the reformed CAP post 2020, Member States are able, through their national strategic plans, to encourage forest managers to maintain, grow and manage forests in a sustainable way. The Water Framework Directive requires the Member States to prepare River Basin Management Plans including Programmes of Measures (PoMs) for each River Basin District. Measures within the PoMs are directly linked with measures under axis 2 of the Rural Development Programme and other EU policies related to forest issues, such as EU Forestry Action Plan (FAP), Natura 2000 and the Biomass Action Plan (BAP). 

Implementation Time

The implementation time of this option is highly variable, because it depends on what measures are undertaken to protect and restore forests and their ecosystem services. The implementation time of some measures may be very short but may also require proper maintenance in the long-term period. Moreover, the full recovery of water quality and quantity after forest restoration can require many years (more than 25 years).  

Life Time

Endless if the management scheme is maintained and adapted  

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