In a first step to find information on the approaches and methods of selected EU Member States concerning the assessment of the parameter ‘structure and functions’, an internet search was conducted for 15 countries which are part of the same biogeographical regions as Germany. The relevant data sources were considered regarding the accuracy of data aggregation and derivation of assessments, as well as validity of trends and amount of data (e.g. sample sizes for monitoring) and searched for further literature indications. Source documents were the Article 17 reports of Member States (EU obligations: Habitats Directive: Report on Implementation Measures) for the reporting period 2007–2012 (http://cdr.eionet.europa.eu), especially information on the ‘most important achievements in the implementation of the Habitats Directive’ (Annex A, field 1.1 or 1.2), as well as the collections of Internet links (especially field 2.3). German, English, French and Spanish homepages could be analysed directly, while information in other languages were examined for potentially relevant content by using translation aids like ‘Google translate’. However, the internet search of publicly accessible documents did not yield sufficiently precise information on the assessment methodology used for the parameter ‘structure and functions’ for any of the selected Member States.

In addition to the internet search, a standardised questionnaire was compiled for the selected EU Member States to answer essential questions. The questionnaire was in two parts (see Suppl. material 1: Table S1).

The first part focuses on sample selection and monitoring methods in general (e.g. monitoring scheme, number of habitat types monitored, number of sample plots, location of sample plots within or outside Special Areas of Conservation (SACs), utilisation of already existing monitoring systems).

The second part addresses assessment methods for the parameter ‘structure and functions’ at the level of biogeographical regions, based on the assessment of single habitat type occurrences (single plots). The objective of the analysis was to determine if Member States implement the assessment of conservation status based on individual habitat type occurrences (analogous to the standard data forms) similar to Germany or if the assessment is conducted based on other data.

The questionnaire contained 22 questions in total, as well as explanations on the approach in Germany. The questions related to monitoring in the reporting period 2007–2012, but some Member States have given outlooks for the current reporting period to show what will change.

In mid-August 2015, the German Federal Agency for Nature Conservation (Bundesamt für Naturschutz, BfN), which is responsible at a national level for monitoring under Article 11 of the Habitats Directive, sent the questionnaire to members of the Expert Group on Reporting (EGR) and the Habitat Committee, overall to 26 of 28 Member States. Croatia was not included because the country only joined the EU in 2013. Representatives of 13 Member States (Austria, Belgium [only Wallonia], Czech Republic, Denmark, Finland, Hungary, Ireland, Latvia, Lithuania, Portugal, Romania, Slovenia and Sweden) answered the questionnaire. The authors of this paper compiled the answers for Germany.

Additionally, Bijlsma and Jansen (2014) yielded relevant aspects of the approach in the Netherlands. Information from the region of Wallonia has been used for Belgium, although assessment requirements and algorithms for conservation status differ in the regions of Flanders and Brussels (Westra et al. 2018).

The answers of the Member State representatives have been compiled in a table (as of May 2016, after queries to individual States), with their consent for publication of the data.

Analysis of the questionnaires revealed that only two of the selected Member States (Portugal and Slovenia) had not yet carried out monitoring according to the Article 11 requirements in the reporting period 2007–2012. Slovenia planned to establish monitoring for Natura 2000 areas in 2015 for the first time. Only a little information on Slovenia has been available from other sources so far. Thus, replies to the questions have been omitted for these two countries. Finland only answered some of the questions.

The Czech Republic assesses data from a nationwide biotope mapping programme. The complete update of all data takes place there over 12 years. This means that only part of the data is newly collected for each reporting period.

I. Was the assessment of the parameter ‘structure and functions’ for the biogeographical regions conducted on the basis of a monitoring programme?

Most Member States assess the parameter ‘structure and functions’ by monitoring similar to Germany, at least for some of the habitat types. Wallonia (southern part of Belgium; four ecologically grouped monitoring schemes – forests, waters, grassland and other semi-natural open landscapes) and Denmark have implemented comprehensive monitoring programmes.

Monitoring programmes for a part of the habitat types or just subparameters exist in Finland, Ireland (monitoring schemes for ecological groups [e.g. upland habitat types, dune habitat types and raised bog habitat types]), Latvia, Romania (part of the forest habitat types as part of the nationwide forest inventory), Sweden (nationwide forest inventory; inland waters as part of monitoring according to the Water Framework Directive; Article 11 requirements are integrated into a general landscape monitoring which is still under development) and Hungary (grassland habitat types since 2009, forest habitat types since 2011, wetland habitat types since 2014).

Lithuania and Austria are still developing monitoring programmes. In Austria, the monitoring programme has so far only been tested in the forest inventory for forest habitat types. The Czech Republic does not conduct separate monitoring but uses repeated biotope mapping of their entire land area instead.

I.a) When (year) was the monitoring programme installed?

The starting points in time differ between Member States. The first monitoring was established in Wallonia (Belgium), where monitoring forests as part of the forest inventory has existed since 1994. The second monitoring was implemented in Hungary in 1997. Most Member States established their monitoring in the first decade of the 21^st century. Of course, older monitoring schemes for biotopes or landscapes existed in some Member States before the Habitats Directive came into force (e.g. the UK Countryside Survey).

The very different initialisation phases are a first indication of the varied development progresses and different methodical approaches of Member States. Like Germany, Denmark, Latvia and the Czech Republic used their monitoring results for the assessment of the parameter ‘structure and functions’ for the reporting period 2007–2012. In other countries, this has only been done for part of the habitat types (e.g. in Ireland) or has not yet been applied or just tested, as in Lithuania or Austria.

I.b) In which biogeographical region is the monitoring programme carried out?

Most of the Member States surveyed are conducting, or planning to carry out, a monitoring programme in all biogeographical regions. The marine parts of the biogeographical regions, which are recorded separately by the EC as marine regions, were not explicitly queried. So far, Ireland has conducted monitoring merely for the Atlantic region and the monitoring programme for marine-Atlantic habitat types only started in 2015.

I.c) How many habitat types occur in your country? How many habitat types have been processed in the monitoring?

Depending on country size and biogeographical setting, the Member States surveyed have between 41 (Wallonia) and 89 (Sweden) habitat types. The States with an already existing monitoring programme include all or a majority of the terrestrial/inland habitat types in their respective programmes (minimum 87% of the habitat types in Hungary).

I.d) Was the assessment conducted on selected sample plots or on the total habitat area (total census)?

Most of the monitoring approaches are based, at least partly, on sampling as undertaken in Germany. The assessments of habitat types in Wallonia, Denmark, Ireland, Lithuania, Sweden and Hungary are conducted fully with samples. In Austria and Romania, selection is carried out similar to Germany on the basis of sampling for widespread habitat types and total census for rare habitat types. Finland uses sampling for widespread habitat types (e.g. 9010 and 9050). In Lithuania, monitoring is carried out in transects.

In the Netherlands, the conservation degree of each habitat type of each Natura 2000 site is considered, weighted according to its area in the site (Bijlsma and Jansen 2014, page 12) and it is assumed that the area of the habitat type outside Natura 2000 sites is very small. If this assumption proves to be false for a habitat type, one or two virtual Natura 2000 sites with an estimated degree of conservation are added. In the Czech Republic, the entire area is considered.

I.e) What was the sample size per habitat type in each biogeographical region?

In most Member States, the number of sampling areas depends on the frequency of habitat type and other ecological and methodical factors, as well as effort and costs. The other States do not apply a standardised sample size with an upper limit like the 63-sample in Germany. For frequent of habitat types, the number of samples and sample size generally exceed those in Germany to achieve the necessary accuracy of results. Table 1 lists detailed information on the samples in Member States.

I.f) Which methods were used for the selection of sample plots (connected or unconnected, stratified or unstratified, weighted or unweighted samples)?

Each Member State selected sample plots differently. Overall, most Member States conducted at least a partly systematic selection based on distribution, size and characteristics of habitat types and/or other factors. Random samples without an expert assessment of their representativeness have not been used by any Member State.

I.g) Is the monitoring permanently repeated on the same sample plots once selected?

Apart from Ireland, all Member States use permanent observation plots at least for the majority of investigated habitat types or a total inventory of habitat types as in the Czech Republic.

I.h) How often is the monitoring carried out (survey intervals) during one reporting period?

Most Member States implemented at least one survey per reporting period. Several surveys per reporting period are mainly conducted in habitat types which depend on management, for example in Wallonia (aquatic monitoring) and Ireland (grassland). In the Czech Republic, one mapping cycle requires 12 years, thus only half of the land area is updated for each report.

I.i) Were only Natura 2000 sites included in the monitoring or also sites outside the Natura 2000 network? Can differences inside/outside Natura 2000 be detected from the monitoring?

Most Member States included areas within and outside Natura 2000 sites. So far, none of the Member States could find statistically reliable differences or the sample size was not large enough to allow a differentiation. Only a few Member States (Wallonia, Czech Republic, Denmark, Finland, Hungary and Sweden) assume that this will be possible for the next reporting periods.

I.j) Are there already existing monitoring systems and are they used for the Article 11 monitoring?

In a few States, the data for the National Reports are based on different monitoring systems and data. Monitoring according to Article 11 has been partly integrated into already existing procedures or only data has been extracted from already existing procedures. Independent monitoring programmes specially developed for Article 11 monitoring exist merely in a few countries (Germany, Denmark, Latvia, as well as the Czech Republic). Austria is currently developing Article 11 monitoring.

II.a) How is the evaluation of single habitat plots (degree of conservation) included in the assessment of the parameter ‘structure and functions’ as part of conservation status at biogeographical level?

The assessments of single monitoring plots are integrated into the assessment of the parameter ‘structure and functions’ in all examined monitoring approaches. However, the employed methods differ between States and are elaborated in the following questions. Table 2 shows a summary of all answers.

II.b) Is there a uniform assessment scheme for each habitat type on site or plot level in your State?

Wallonia, Germany, Denmark, Latvia, Lithuania, the Netherlands, Austria, Romania, Sweden, the Czech Republic and Hungary have a standardised assessment scheme. Denmark, Hungary and Germany revised their schemes for the reporting period 2013–2018. In Ireland, the assessment methods for each habitat type are similar but not always the same because different approaches work better for some habitat types depending on the heterogeneity of habitat type. Some countries, like Sweden or Hungary, have standardised assessment schemes for groups of habitat types, such as forest and grassland habitat types.

II.c) If no uniform assessment scheme exists: How is the evaluation of habitat types carried out?

Most Member States have standardised assessment schemes. In Hungary, assessment schemes are lacking only for a few habitat types. For these habitat types, experts conduct the assessment by using other data from nationwide biodiversity monitoring. In Sweden, habitat types without standardised assessment schemes are evaluated by experts based on existing data and expert opinion.

II.d) How is the review of the criteria/the degree of conservation on site or plot level carried out?

Except for Wallonia (Belgium), Member States calculated a degree of conservation (as in Germany) or a comparable assessment for each sample plot. In Wallonia, all features are aggregated at a biogeographical level and combined afterwards to a degree of conservation.

II.e) How was the assessment of the typical species referred to in Appendix V of the guidelines (Assessment and reporting under Article 17 of the Habitats Directive, Explanatory Notes & Guidelines) carried out for the period 2007–2012)? Which species groups were investigated?

The considered Member States, except for the Netherlands and Sweden, investigated plant species only; animal species are solely considered for assessment in special cases or as additional information. Member States either apply complete species lists or just use species typical for a habitat type or indicator species. In Germany, the assessment of habitat types dominated by vegetation is also conducted solely via number of typical plant species. Animal groups are included in the assessment of a few habitat types only (see question II.g in Suppl. material 1: Table S1).

II.f) What method for monitoring the vegetation is recognized: Compilation of a complete list of species, phytosociological relevés recording according to Braun-Blanquet, or other methods?

Many Member States compile, at least for some habitat types, lists of typical species. Only Denmark records complete species lists and three Member States perform phytosociological vegetation mapping (Wallonia, Ireland, Lithuania).

II.g) Is a faunistic list also recorded – a complete list or only for certain groups of species? From which faunistic groups are typical species recorded?

Most Member States rarely used animal species, especially for assessment of habitat types with sparse or no vegetation of higher plants. Only Sweden lists animal species for assessment of a few habitat types. The most frequent animal groups are birds, butterflies and beetles (see also question II.e).

II.h) Are the assessments of the criteria ‘habitat structures’, ‘typical species’, and ‘pressures and threats’ calculated separately for all sample plots? Or is the separately calculated degree of conservation of each sample plot used for aggregation?

Germany, Denmark, Ireland, Latvia, Austria, the Czech Republic and Hungary aggregate the degree of conservation which has been calculated for each sample plot separately. Denmark is revising the method for calculating conservation status for the next report according to Article 17. Ireland is testing another method with an indicator-based instead of plot-based assessment. For this method, individual features or criteria of many sample plots are directly aggregated at a biogeographical level without combining all relevant features or criteria of a single sample plot to a degree of conservation. Similar assessments are already underway in Sweden. In Wallonia, assessments of some features are aggregated at the biogeographical level, while others are aggregated at the level of single sample plots.

In the Netherlands, the conservation degree of a habitat type (based on the requirements of the standard data forms) of each SAC is assessed separately and conservation degrees of respective habitat type of several SACs are subsequently aggregated according to their area percentage (see question II.d).

II.i) How is the parameter ‘structure and functions’ calculated at biogeographical level?

From the information supplied, it is concluded that four different approaches can be distinguished regarding the methods of Member States (see Table 2):

• Holistic assessment of single plots or single Natura 2000 sites and aggregation of the parameter ‘structure and functions’ according to a threshold for percentage of single assessments (Denmark, Wallonia – grassland habitat types, Ireland, Latvia, Austria, Romania, Czech Republic). This corresponds to monitoring of sample plots in Germany and assessment of the parameter ‘structure and functions’ according to the proportion of C assessments of conservation degree.

• Calculation of an assessment at a biogeographical level of each individual feature and subsequent derivation of the parameter ‘structure and functions’ (Wallonia – forest habitat types). In Germany, a consistent value at a biogeographical level is only determined for the features ‘forest development phase’, ‘habitat trees’ and ‘dead wood’ of frequent forest habitats which are assessed based on data from the National Forest Inventory.

• Expert evaluation of the parameter ‘structure and functions’ without fixed rules for aggregation but based on individual features of all sample plots (Sweden). This method was occasionally used in Germany if monitoring would have resulted in ‘unknown’ for some reasons (missing data for a part or all of sample plots).

• Assessment of conservation degrees in single Natura 2000 sites and aggregation to a status of the subparameter ‘structure and functions (without typical species)’ according to a threshold value for the area percentages of conservation degrees at a biogeographical level. Furthermore, determination of the status of the subparameter ‘typical species’ at a biogeographical level based on the categories of the Red List of all typical species and subsequent aggregation of both subparameters at a biogeographical level to the parameter ‘structure and functions (including typical species)’ according to the EU evaluation matrix. Only the Netherlands uses this method.

Although most Member States apply the first method, considerable differences exist between threshold values (see Table 2 and section 3.2). In Wallonia, the first two methods are used.

II.j) What is the significance and the statistical power of the monitoring/the assessment? How big is the minimum detectable difference between two reporting cycles (six years)?

None of the Member States surveyed made a statement on theoretical statistical strength of the samples or the monitoring. Either they did not understand the question or no calculations exist. The question did not aim at complete determined differences, but at the size of possibly detectable differences between two reporting periods.

Germany specified a significance level (α error) and a β error of 0.2 each. The power is 0.8. The applied Chi² test yielded a minimum detectable difference of ≥ 30% for a sample size of 63 (Sachteleben and Behrens 2010).

II.k) Are reference documents or websites available for methods used? Is it possible to provide digital documents?

The information and further literature of Member States differ considerably. Additional information on Article 17 methodology beyond the questionnaire replies is not included. Lithuania, Denmark and Hungary only have information in their respective national language. The Czech Republic added all relevant information which has been integrated into the answers above. For the Netherlands, the documents from Bijlsma and Jansen (2014) and Jansen et al. (2014) were analysed.

Besides the design of data collection (questions to point I), the assessment methods of the parameter ‘structure and functions’ at a biogeographical level are also particularly important. The approaches of Member States differ considerably (see Table 2). However, most Member States who replied use the three grades of the EU assessment system for the conservation degree. The assessment of the degree of conservation comprises three grades: A – excellent; B – good; and C – average or bad. Some States assess degrees of conservation at the level of single plots; others assess degrees of conservation of habitat type areas in the respective Natura 2000 sites (Netherlands) and some States evaluate subparameters for assessment of the structure and functions directly at site or biogeographical level (Ireland, Wallonia – e.g. structural diversity in forests). Sometimes, experts are consulted in borderline cases or for subparameters which are difficult to obtain.

Only four Member States (Germany, Ireland, Netherlands, Czech Republic) apply the threshold value defined in the reporting format for an inadequate-bad status if more than 25% of the area is inadequate (Table 2), but in the Netherlands, it is linked to additional conditions. Another three Member States (Denmark, Austria, Romania) also assess the proportion of C assessments but use different threshold values and consider the proportion of A assessments as well.

The 25% specification of the reporting format is unclear if individual features are assessed at a biogeographical level and then aggregated to the criteria or directly to the parameter ‘structure and functions’. Although it is possible to aggregate individual features according to their proportion (based on area or quantity) of the respective assessments (A, B or C), Member States can decide if one or more features of a criterion have to exceed 25% for a U2 assessment of the criterion.

If assessment of the individual features of conservation degrees is conducted by averaging for assessment of the three features of the criterion ‘species composition of the vegetation’ (as in Wallonia), the proportion of A assessments partly balances the C assessments. Thus, the ‘unfavourable’ status of a feature shows only with a much higher proportion of C assessments. The described example of Wallonia tries to compensate for this effect by weighting the proportion of C assessments higher than the other assessments.

An assessment of single features of the parameter ‘structure and functions’ may not be appropriate at the level of single plots (e.g. proportion of dead wood or habitat trees on very small sample plots of a few 100 m²). In this case, averaging of the value of the feature is conducted for all sample plots (e.g. forest habitat types in Wallonia, frequent forest habitat types in Germany). The assessment is ultimately carried out via a threshold for the calculated average values. In these cases, it is not possible to apply the 25% rule.