MACROARTHROPOD-HABITAT RELATIONSHIPS IN OAK FORESTS IN SOUTH BELGIUM .1. ENVIRONMENTS AND COMMUNITIES

Woodlouse and millipede assemblages were studied in nine deciduous oak -forest stands located in the three geomorphologically distinct region s of the Viroin-Hermeton Natural Park, South Belgium (Ardenne, Calesti enne and Fagne-Famenne). Principal component analysis revealed marked regional structure of the edaphic conditions linked to humus type and soil texture. During the present study and additional surveys, 70% of the saprophagous macroarthropod species known in Belgium were found in the park, which suggests a very high biodiversity in this area. Numer ical size of populations was estimated using two sampling methods, i.e . extraction from soil samples (abundances) and pitfall trapping (acti vities). Although a quite good relationship was registered between abu ndances and activities estimated in spring and autumn, pitfall efficie ncy greatly depended on the taxa concerned. Multiple multivariate regr ession analysis and canonical correspondence analysis were used to stu dy spatial community structure. The most significant variables influen cing the distribution of species are: (1) available water in the Ah la yer correlated with C/N ratio of the litter layer (related to both the litter structure and humus type); (2) the textural soil conditions (s ilt content); and (3) the local biogeographical structure. Mull specie s are essentially macrosaprophagous taxa belonging to ''bulldozer'' an d ''roller'' ecomorphological types or small hypogeic species able to resist summer drought whereas microsaprophagous epigeic taxa with high water requirement are linked to moder soils. Finally, the results are discussed in keeping with regard to the patchiness concept and the lo cal edaphic and floristic conditions.