Use of Spectral Mixture Analysis for Characterisation of Function and Structure of Heathland Habitat Types

Habitat monitoring of designated areas under the EU Habitats Directive requires every 6 years spatially explicit information on area, range, structure and function for the protected (Annex I) habitat types. Hyperspectral remote sensing could be an important technique to assist in the evaluation of the habitat conservation status by providing continuous maps of habitat quality indicators (e.g., structure types, age distribution, invasive species, management activities). This paper assesses the use of hyperspectral imagery to study the structure and function of a heathland ecosystem in the Veluwe nature reserve in the Netherlands. Spectral mixture analysis (SMA) was applied on AHS-160 (Airborne Hyperspectral Scanner) imagery to investigate their appropriateness to characterize the spatial coverage and configuration of relevant heathland habitat types (wet and dry heathlands and inland sand dunes). For the Calluna vulgaris dominated dry heath there was a specific emphasis on the characterization of different development stages of the heather (pioneer, developing, climax and degenerating). In addition, fraction maps for the endmembers grass and coniferous forest (e.g., Pinus spp.) were made to assess the process of grass and forest encroachment in the heathland which are considered as unfavourable developments. Results indicate that SMA is suitable for mapping the main components of the heathland ecosystem. However, additional research is required to assess the influence of sensor type and phenology of the vegetation. The results of this study show that hyperspectral remote sensing can complement the traditional vegetation field surveys. Remote sensing derived continuous habitat maps and their associated quality indicators can help to optimize sampling schemes and focus effort on rare and often inaccurately mapped habitat types. Moreover, the remote sensing derived information does not only provide useful information for the habitat reporting obligations but also provides useful (site specific) information for the nature reserve managers. In this way costly fieldwork effort can be employed in a more efficient way.