Toward objective assessment of the conservation status of (the Natura 2000) forest habitat types: A comparison of a qualitative and a quantitative modeling approach

To halt the loss of biodiversity in natural habitats, the EU passed the Habitats Directive and established the Natura 2000 network. The network captured forest habitats and habitat types, whose conservation status must be reported under Article 17 of the Directive. Hence, the harmonization of habitat assessment methods and reporting formats are a critical issue. So far, the EU Commission and Member States have managed to design and issue reporting guidelines. However, as many of these reports are largely based on expert opinions, they tend to be biased and incomparable. To make conservation status assessments and reporting more consistent, this study evaluated a set of indicators with two decision support models. The DEX model operated with linguistic statements derived from numerical values, while the fuzzy model utilized numeric input. Both models were tested with data from Slovenia's three largest forest habitat types (FHT), namely 9110 – Luzulo-Fagetum beech forests, 91K0 – Illyrian Fagus sylvatica forests (Aremonio-Fagion) and 91L0 – Illyrian oak-hornbeam forests (Erythronio-Carpinion), provided by the Forest and Forest Ecosystem Condition Survey. The DEX model produced uniform results and defined the conservation status of all three FHTs as least favorable. Conversely, the fuzzy model produced three different conservation status grades for the FHTs: a favorable conservation status for the 91K0 FHT, least favorable for the 9110 FHT and unfavorable for the 91L0 FHT. Its results were logical and in accord with the existing assessments. The study showed that both models could be used for the evaluation of FHT traits. However, because of its larger sensitivity, the fuzzy model allowed detecting subtle differences among the indicator values due to the use of continuous numerical data and more sophisticated mathematical procedures.