Summary
The proposed assessment system evaluates the biological status of habitat types and species. The system uses measurable and objective indicators to evaluate the impact on the EU habitat types and species. In the past, management of natural areas has generally been based on the subjective and individual judgements of biological experts, with little or no possibility for others, including other experts, to gain insight in the assessment. The system presented here is based on relatively few, simple and visible indicators, that within a half to one-and-a-half hours of field survey can characterise the biological status of an area. The indicators are evaluated in the field by identifying the appropriate, relatively broad assessment category. This ensures a robust and simple system. The calculation of the biological status is based on these data and assessed on a reference scale from 0 to 1, where 1 is the optimal condition. Subsequently, this value can be translated to one of the five status classes analogous to the ecological status classes of the EU Water Framework Directive, ranging from poor to high status.
This report covers the use of the assessment system on the habitat types and species on the EU Habitat Directive. The use of the system in relation to the newly implemented Danish Law of Environmental Targets is an important issue within the report. The system can directly be transferred to other habitat types and species under the condition that indicators, valuation values and importance weights are developed for these parts too.
Data for structural elements and species composition are used to calculate a structural index and a species index used in the final assessment of the biological status. Both indices use the same reference scale between 0 and 1, where 1 is the optimal condition. Information on the area size is not part of the assessment biological status. There is a risk that information on small areas with very high biological status are lost if these information’s are mixed.
The structural elements are simple to observe visually and hold important information on the present biological status of the habitat types. Based on the indicators developed in the NERI –report 457 "Kriterier for gunstig Bevaringsstatus" (a draft English version available, see reference list), the following five indicator groups are used to characterise the structure and function of the habitat types:
In each group the indicators are registered in the field survey by a tick mark in the appropriate desriptor category from a pre-defined list. In advance, each category is assigned a score, where high scores equal optimal conditions for the indicator in the given habitat type. As the indicators are not all equally important in the assessment of the biological status of the different habitat types, each indicator is also assigned in advance an importance weight for the different habitat types. The final structural index is calculated as the average of the weighted indicator scores.
The species composition is an important source of information in the identification of the habitat types and the characterisation of the biological status. The non-mobile species, such as the flora, are especially important in their complete dependence on the specific and local biological status. All species, both flora and fauna, assigned a species score can be used in the calculation of the species index of the habitat types. The species composition of the vegetation is registered in a circle of 5-m radius, centered in a homogeneous area characteristic of the habitat type. In advance, the species are assigned species scores between 1 and 7. Species with low scores contribute only little to the information on the biological status, whereas species with high scores contribute more. Rare species often have higher demands with regard to the biological status, and their presence is often a good indication that the anthropogenic impact is low and the biological status are high. Therefore the species scores are based on their general rarity and distribution in Denmark. However, in many cases there is a need to adjust these rarity-based values.
The assessment system is also capable of evaluating the biological status of the habitat of a single species. The evaluation is based on the assessment of the habitat types used by the species supplemented by a number of indicators influencing the long-term survival of the species. The survival prospects of some species are closely related to the general status of the habitat types they occupy, i.e. there is total correlation between the biological status of the habitat type and the biological status for the species. These species need no supplementary indicators. Other species may have very specific demands not necessarily reflected in the biological status of the habitat types. These specific demands should instead be reflected in the supplementary indicators. The supplementary indicators are assigned scores and weights as described for the structural indicators. A "supplementary index" is calculated as the mean value of the weighted supplementary indicators, and contributes together with the structural index and the species index of the habitat types to the final assessment of the biological status of single species habitats.
TILDA is newly developed Access database by NERI, designed to calculate the described indices. Data from the field survey can be inserted directly in the database, or linked from e.g. Excel data sheets. The database holds all relevant information on scores and weights for the different habitat types. The database will be released when finally tested and calibrated against data from known localities in Denmark.
Full report in pdf-format (1,180 kB).
