Developing a forest naturalness indicator for Europe - Concept and methodology for a high nature value (HNV) forest indicator

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Courtesy of European Environment Agency (EEA)

Background
In Europe, forests cover around 40 % of the land area (190 million ha), making Europe one of the most forest-rich regions in the world. Forests are important habitats for many species of wildlife. Yet, forestry can also have negative impacts on biodiversity as unsustainable forest operations can lead to forest degradation and loss of biodiversity. In more recent times increased land use, expanding urban areas, and climate change have all contributed to place more pressure on forests.

The European Union (EU) has long been committed to biodiversity conservation in the EU. EU nature legislation dates back to 1979 and its biodiversity strategies have been in place since 1998. Forests and biodiversity are strongly related. Forest biodiversity depends on the health and vitality of forested areas. A main threat to forest biodiversity is the loss of 'naturalness' of forest ecosystems as a consequence of intensive and inappropriate ecosystem management.

Measuring the level of naturalness can be defined as 'the similarity of a current ecosystem state to its natural state' (Winter, 2012). A virgin forest, for example, would be considered to have a high level of naturalness as it is as close to its original state as is possible. Meanwhile, a plantation could be considered to have a low level of naturalness as it often contains only one species of tree of a similar, if not exactly the same age, and planted in a uniform manner.

The high nature value (HNV) concept
A number of EU strategies and regulations are related to the protection of nature and environment as well as to halting the loss of biodiversity. Forest protection is viewed as an important tool to conserve and generally maintain and enrich biodiversity. As part of this broader discussion the HNV concept emerged in the early 1990s. It aimed to support farming and forestry practices in order to maintain and protect biodiversity in rural landscapes. Much effort was put into developing a system to monitor the level of naturalness in agricultural areas in Europe.

Several studies and initiatives have been launched to develop a HNV indicator for forest areas, some of them by the European Environment Agency (EEA). A first definition for HNV forest areas was proposed by the Institute for European Environmental Policy (IEEP) in 2007 as a parallel to the HNV farmland process: all natural forests and those semi-natural forests in Europe where the management (historical or present) supports a high diversity of native species and habitats, and/or those forests which support the presence of species of European, and/or national, and/or regional conservation concern.

As both naturalness and biodiversity are complex concepts they should be monitored through the use of several indicators. If only one or a limited number of indicators are used, erroneous conclusions may be drawn.

This EEA technical report aims to clarify the HNV concept for forests. It also proposes a feasible and replicable methodology to define and identify HNV forest areas in Europe. The proposed methodology, and by extension the ability to measure and monitor changes in HNV areas, is considered essential for supporting European environmental protection and policy implementation.

The report reflects on the work carried out since 2011. To simplify the work and for the sake of transparency, the methodology was applied to beech forests only. Beech forests are well documented and rather homogenous forest types and were considered appropriate for such a test.

The present work focuses on identifying areas of forests that approximate to a certain level of naturalness. Only countries where beech forests are found are represented. These countries are: Austria, Belgium, Bulgaria, Croatia, the Czech Republic, Denmark, France, Germany, Hungary, Italy, the Netherlands, Norway, Poland, Slovakia, Slovenia, Spain, Sweden, Switzerland, and the United Kingdom. Work is ongoing to extend the concept to cover all forest areas in the EEA-39 countries (1).

In Chapter 1, an overview of the policy context is provided. The HNV concept is defined and discussed in comparison with other relevant concepts: naturalness, biodiversity, high conservation value forests (HCVFs), and biologically important forests (BIFs). Other international and country experiences are reviewed.

The chapter reflects on nine case studies carried out in 2011 as part of an EEA project to explore how a HNV forest indicator could be developed. These studies took into account existing national level assessments and underlined the need for a clearer definition of the HNV concept as applied to forests.

These case studies revealed several important issues:

  • some confusion exists about the monitoring target . biodiversity, naturalness and conservation status are mixed up;
  • in the absence of a clear definition of HNV forests, local monitoring systems tend to be based on multiple criteria with different sets of indicators; and
  • the availability of data in the investigated area often determines the choice of indicators.

It is therefore clear that there is a need for pan.European agreement on the monitoring target, with clear definitions for the different concepts. Two strategies may be followed in setting up an operational monitoring framework: (i) aggregating national efforts and products, or (ii) developing a new system based on information commonly available across Europe.

As a result of the diversity of country approaches and the lack of available harmonised data, it was considered more feasible to develop the HNV forest area based on available data at the European level rather than at an individual Member State level. Chapter 2 discusses such an approach, which was applied to beech forests only, and included a selection of existing and available spatial data sets. The assessment of HNV forest area is based on five indicators:

  • naturalness;
  • hemeroby (the degree of human influence on the ecosystem);
  • accessibility (expressed by the steepness of terrain and thus how accessible the forest is for management);
  • growing stock (the volume of living trees);
  • connectivity (forest availability and distance between patches of forests i.e. the extent to which the landscape facilitates or impedes the movement of species).

The chapter describes these indicators and the multi.criteria approach used to assess HNV.

Chapter 3 presents the results of this multi-criteria approach applied on beech forests in Europe. The report suggests that using such a multi-criteria approach means that defining a HNV forest area is now possible. Aggregate results from the five indicators led to a first HNV beech forest assessment. After validation against site data and various statistical tests, it was decided to simplify the approach to include the 'naturalness' of tree species' composition, accessibility and connectivity.

A map of HNV beech forests for Europe was produced covering 19 countries within the EEA region. A plausibility test was carried out by comparing the map to three independent information sources on potential natural vegetation. These were the European Forest Genetic Resources Programme (EUFORGEN); an analysis on habitat suitability carried out by the Joint Research Centre (JRC) for European forest types (JRC, 2012c); and the map of potential natural vegetation in Europe, the so-called 'Bohn map' (Bohn et al., 2004). A first comparative analysis with existing networks of protected areas (Important Bird Areas (IBAs), Natura 2000 and Common Database of Designated Areas (CDDA) sites) was also conducted.

This comparison resulted in further refinement of the definition of HNV forest areas to an area covered by forests or other wooded lands having a current ecosystem state similar to its natural state. Chapter 4 presents conclusions, challenges and the way forward for developments of HNV forest areas. The study carried out for beech forests demonstrated that some pan-European data sets already exist for developing analysis of HNV forest areas. The results for beech forests were contrasted against observations in mature forests with no significant signs of human activity (known as 'old.growth' forests), demonstrating that some of the tested indicators have promise. However, the test also highlighted the complexity of a multi-criteria approach based on several indicators.

One main outcome of the study was to further simplify the approach to assess naturalness by analysing each of the five indicators one at the time. A follow-up study considered the naturalness of tree species composition only, and enlarged the analysis, considering the overall forest area for specific forest types according to the EEA European Forest Type (EFT) classification. A first test and mapping were successfully carried out for forests within the 'boreal' region of Scandinavia, a region with a subarctic climate.

Both proposed outcomes are under further development to produce HNV forest area maps for the all forest areas in Europe. The approach and its results will be presented and compared with country level estimates of HNV forest areas based on more detailed forest data and information. The approach will be further refined as soon as more forest information is made available at the European level with the support of data and information from the European Forest Data Centre (EFDAC).

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