Harmonised evaluation of FFH forest habitat types for a nationally coordinated data basis for FFH reporting and for improving the conservation status, including recording of the herbaceous layer as a supplement to the 4th Federal Forest Inventory (LRT-BWI)

Targeting, delimiting and assessing forest habitat types according to Annex I of the Habitats Directive are an essential part of nature conservation monitoring and an important prerequisite for fulfilling the reporting obligations in the European protected area system Natura 2000 (Ssymank et al. in prep.). As a Germany-wide national inventory of forest area and productivity required by forest law, the BWI provides a basis for forestry and environmental policy decisions (BMEL 2014) and, in view of the growing importance of forests for biodiversity conservation, is increasingly being evaluated and interpreted from a nature conservation perspective (Reise et al. 2017).

A total of 19 of the forest habitat types listed in Annex I of the Habitats Directive occur in Germany. They are defined in the EU Interpretation Manual for the FFH-habitat types (European Commission/ DG Environment 2013) and described in detail for Germany in the second volume of the BfN manual (Ssymank et al. in prep.). Although the German Länder base their forest habitat type descriptions on these specifications, their definitions differ significantly from each other in some cases, especially with regard to the habitat-typical species composition, the occurring plant species and their dominance ratios. These differences are mainly due to the states' efforts to reflect the variability in the biogeographical composition of the natural areas. Even greater differences in the interpretation of forest habitat types can be assumed between neighbouring EU Member States.

In addition to the nature conservation data of the Länder, the survey and assessment of the conservation status according to the Habitats Directive is based on data from the Habitats Monitoring, which was introduced in 2007 for the Atlantic and continental regions of Germany (cf. e.g. Sachteleben & Behrens 2010). The EU does not specify any methodological requirements for the survey, but recommends the use of certain sampling methods for common or widespread protected species. In Germany, the procedure for surveying and assessing the individual protected goods has been documented in the form of assessment schemes coordinated across the Länder (BfN & BLAK 2017). The criteria for the "completeness of the habitat-typical species composition" were documented in a database.

For the common forest habitat types 9110, 9130, 9160, 9170 and 9410, data from the BWI have been used regularly since 2013, in addition to data from the Länder, to derive the parameter "specific structures and functions" (sS&F) of the national FFH reports.

However, the year-round recording period of the BWI results in major gaps in the recording of the feature "species composition" (herbaceous vegetation) as part of the parameter sS&F and in the addressing of the oak-hornbeam forest habitat types 9160 and 9170 (Kroiher et al. 2017, cf. also Maciejewski et al. 2022). An improvement of the approach and assessment methodology therefore requires a complete recording of the species inventory by vegetation surveys (cf. Chytrý et al. 2020).

Vegetation surveys according to the standard introduced by Braun (1913) have been collected in Germany for more than 100 years and are today often archived in databases (e.g. vegetweb.de, Ewald 2005, Jansen et al. 2015). However, their spatial distribution does not usually follow a statistically representative sampling design, so that analyses in the course of monitoring are only possible to a limited extent.

Federal vegetation inventories of forests, which were collected according to a statistically representative sampling design, are so far only available from the plots of the Soil Condition Survey in Forests (BZE II) (Ziche et al. 2016). However, due to the coarse inventory grid, the latter cover the forest habitat types protected under the Habitats Directive only insufficiently. In addition, the FFH module of the BWI already collects data on other features that are required for the assessment of the sS&F. The use of the FFH module is therefore proposed in this project. Therefore, the use of the BWI sample proposed in this project is necessary.

The project aims to develop concrete recommendations for a nationally harmonised approach to the forest habitat types (WLRT) of the Habitats Directive as a basis for management, the reporting according to Art. 17 and, within the framework of monitoring according to Art. 11 Habitats Directive, to supplement the data of the 4th Federal Forest Inventory (BWI-2022) on common forest habitat types with a survey of herbaceous ground vegetation and to integrate these data into the assessments of the conservation status of the habitat types. So far, the Länder have used forest habitat type definitions in their mapping instructions or in the site reports, which are based on the specifications of the EU Interpretation Manual, but still differ significantly from each other in some cases with regard to essential aspects - especially the habitat-typical species composition and the dominance ratios. With regard to the FFH reporting obligations, different interpretations of "primary" and "secondary" expressions of the WLRT 9160 and 9170 also play a role.

In order to significantly improve the evaluation and assessment of frequent forest habitat types, the project pursues the following operational objectives:

1. Development of a comprehensive review of the evaluation criteria of the Länder with a view to the decisive categories of site requirements, pnv reference, tree species proportions, herbaceous layer, evaluation of age and juvenile phases, etc.
2. Derivation of concrete recommendations for the unified evaluation and assessment of the individual forest habitat types with method testing in the field in different federal states.
3. Supplementation of the BWI-2022 with a recording of the herbaceous ground vegetation of the common forest habitat types (9110, 9130, 9160, 9170, 9410) separated according to biogeographical regions as a support in the assessment of the criterion of completeness of the habitat-type species inventory.
4. Integration of the additionally collected data on herbaceous ground vegetation into the existing forest habitat type assessments, further development of the assessment methodology for the common habitat types for the upcoming FFH report in 2025 and derivation of conclusions for an improvement of the conservation status of the common habitat types.
   

The project is divided into the following work packages (WP):

WP 1: Comparison of procedures and harmonisation of WLRT addresses
WP 1 will be carried out by HSWT and includes a comparison of the interpretation and address of forest habitat types 9110, 9130, 9160, 9170 and 9410 in a) the federal states and b) selected neighbouring states as well as c) a synoptic review of the procedures with recommendations for harmonisation.

WP 2: Vegetation surveys at BWI plots
In the framework of the BWI-2022, a standardised vegetation survey with complete coverage of ground vegetation will be carried out in 2023 in a sub-sample of those tract corners that are assigned to the common forest habitat types (9110, 9130, 9160, 9170, 9410) and verified as such on the basis of forest ground vegetation.

WP 3: Evaluation, expert system, monitoring concept
In this WP, the data from WP 2 are evaluated with regard to the habitat-typical species composition, the algorithms of the BWI are further developed into an expert system and combined with the findings from WP1 into a monitoring concept.

WP 4: Project-accompanying working group, workshop, publications, final report
In addition to the ongoing information of the client, WP 4 comprises the establishment and integration of a project-accompanying working group (PAG), the organisation of a workshop at the federal level and the publication of the results.