Identifying cost-effective indicators to assess the conservation status of forested habitats in Natura 2000 sites

Abstract

The Natura 2000 (N2000) network represents one of the most important actions for biodiversity conservation in Europe; its main aim is to assure the favourable conservation status of Europe's natural habitats and wild species. Monitoring of N2000 sites is required under the Habitats Directive, and Member States are required to report monitoring results to the European Commission. However, there is a widespread lack of understanding about precisely what should be monitored and which methods should be used. This research aimed to identify potential indicators and evaluate their suitability for evaluating the conservation status of forested habitats in N2000 sites. In addition, the cost-effectiveness of monitoring methods was assessed. Three monitoring methods were assessed in two N2000 sites, the Foresta del Cansiglio (IT) and the New Forest (UK): (i) sample plots, (ii) a point-transect method and (iii) a visual assessment method. Indicators were selected on the basis of a literature review, and related to forest structure and composition, dead wood volume, tree regeneration and ground flora composition. Results suggested that mean values of indicators did not differ between the plot and the point-transect-based methods ( P > 0.05; paired t-test and Wilcoxon signed rank test). However, the survey method employed influenced the extent of variation within the indicators (as indicated by Z scores), a measure of their sensitivity. Correlations between indicators differed between the two sites. Of the three methods considered, the point-transect method was the most efficient in terms of set-up and total time required, but required the longest time per indicator and surveyed the smallest area ( P < 0.001, Kruskal–Wallis test). The visual assessment method assessed the largest forest area; however, total scores of the reference values obtained from the plot-based and point-transect methods were poorly correlated with those obtained from this subjective approach. The contrasting results obtained between different methods and between different sites suggest that a general approach to monitoring N2000 sites may be difficult to develop; rather, a framework that can be adapted to the specific needs and characteristics of individual sites may be required.