Belg. J. Zool., 137 (2) : 137-146 July 2007 Ant biodiversity conservation in Belgian calcareous grasslands: active management is vital Dekoninck W1,2, De Koninck H3, Baugnée J-Y4 & J-P Maelfait2,5 1 Royal Belgian Institute of Natural Sciences, Department of Entomology, Vautierstraat 29, B-1000 Brussels 2 Terrestrial ecology unit, Ghent University, K.L. Ledeganckstraat 35, B-9000 Ghent 3 Smalvoortstraat 47/2, B-2300 Turnhout 4 Zoologie générale et appliquée, Faculté universitaire des Sciences Agronomiques, Passage des Déportés 2, B-5030 Gembloux 5 Research Institute for Nature and Forest, Kliniekstraat 25, B-1070 Brussels Corresponding author : e-mail: [email protected] ABSTRACT. A list of ant species collected in eight calcareous grasslands in the Viroin valley (Viroinval, Belgium) is presented. Thirty species were identified, including Temnothorax albipennis, for the first time recorded in Belgium. Ant community composi- tion and chorology of some ant species are discussed. Recommendations on how to use ant community composition and nest densi- ties of several ant species to evaluate management in calcareous grasslands are given. It appears that in locations with encroach- ment of tall grasses (especially Brachypodium pinnatum) and spontaneous afforestation, due to a complete lack of or to inadequate management, most of the often rare xerophilic ant species are replaced by mesophilic, rather common species. KEY WORDS : ant biodiversity conservation, calcareous grassland, nature management, Belgium ABSTRACT. Un inventaire des fourmis collectées à l’aide de pièges d’activité dans huit pelouses calcicoles de la vallée du Viroin (Viroinval, Belgique) est présenté. Trente espèces ont été identifiées dont une, Temnothorax albipennis, est signalée pour la pre- mière fois de Belgique. Des remarques sont données sur les communautés de fourmis et leur composition spécifique, ainsi que sur la chorologie de certaines espèces. Des suggestions sont émises à propos de la prise en compte des communautés de certaines espè- ces de fourmis et des densités de leurs nids dans le cadre de l’évaluation des effets de la gestion des pelouses calcicoles. A cet égard, nous pensons que dans les sites où le tapis graminéen (comme le Brachypodium pinnatum) se densifie ou que la recolonisa- tion préforestière s’amorce, la plupart des espèces xérothermophiles, souvent rares et très localisées, seront remplacées par des élé- ments plus mésophiles, largement plus répandus et communs. INTRODUCTION diversity and they often contain many rare species (MITCHLEY & XOFIS, 2005). Regions which have this rich floristic diversity are often biodiversity hot spots for a The calcareous grasslands of northwestern Europe wide variety of invertebrates. In Belgium the calcareous comprise the dry grasslands on limestone and chalk as grasslands of the Viroin valley are such habitats (ADAM et well as those on calcareous loess. These grasslands origi- al., 1991; HONNAY et al., 2004; BUTAYE et al., 2005a,b). nated after felling of primordial forest, which had already They are catalogued as a Belgian hot spot for several started in prehistoric times. Since these habitats are semi- groups, i.e. Heteroptera (DELESCAILLE et al., 1991), Salta- natural, they require some form of management by graz- toria (DECLEER et al., 2000), butterflies (GOFFART & DE ing or mowing to prevent afforestation. They were once BAST, 2000; VANDEWOESTIJNE et al., 2005), bees and widespread in the hilly calcareous regions of Europe, but wasps (CLAESSENS, 1992; LONGO et al., 1992) and spiders because of changes in agricultural practice their extent (BARA, 1991). has decreased dramatically. Since World War II urbanisa- tion, abandonment of grazing practice and fertilisation In Belgium the ant fauna of these habitats is rather resulted in a dramatic decrease of these grasslands in poorly investigated. Elsewhere in Europe calcareous Belgium. Everywhere in Europe this habitat type is grasslands and other similar thermophilic grasslands are severely pressured by threats that impinge upon several known to have a rich ant fauna often including very rare ecological communities. A shift in land use is one of the species (MABELIS, 1983; GALLÉ, 1986; SEIFERT, 1996; most important among these. Moreover the remaining MEYER-HOZAK, 2000; BRASCHLER & BAUR, 2003; 2005; areas are often strongly fragmented. This poses threats of OTTONETTI et al., 2006). In the northern part of the coun- extinction and inbreeding for the remaining characteris- try (Flanders), calcareous grasslands are scarce and the one that was recently well studied at the Sint-Pietersberg, tic arthropod populations (WALLISDEVRIES et al., 2002; was indeed a hot spot of ant biodiversity (more than VANDEWOESTIJNE et al., 2005). 25 species) in Flanders (DEKONINCK et al., 2003; 2005). Calcareous grasslands, especially the ones on dry In the southern part of Belgium (Wallonia), calcareous slopes and plateaus, are known as being rich in plant grasslands are more widespread but their ant fauna is 138 Dekoninck W, De Koninck H, Baugnée J-Y & J-P Maelfait poorly known. GASPAR (1965; 1971) investigated the MATERIALS AND METHODS habitat type in the Famenne region, whilst the Viroin val- ley has been studied by LEMAL (1978) and later by Study area DELESCAILLE et al. (1991). But others have never been sampled for their ant fauna. Recently, two localities in the The Viroin valley is located in southwestern Belgium, Viroin valley, respectively at Treignes and Vaucelles, mainly in the municipality of Viroinval (province of were studied by BAUGNÉE (2004). He recorded Campono- Namur). The Viroin, a river of medium size (about 25km tus piceus (Leach, 1825) for the first time in Belgium and long and 5-10m width) flows between a succession of suggested that this interesting region still has a lot of hills and joins with the Meuse near Givet in the French entomological “secrets” to reveal. Hence, when a new Ardennes. The geological formation dates from the Devo- pitfall sampling campaign on xeromorphic and rocky nian period and occurs as limestone hills (‘Tiennes’ in soils (Xerobromion=XB and Mesobromion=MB) in the French) in the landscape. In the Viroin valley two major Viroin valley was started, rare, extinct or new species for types of calcareous grasslands are present: mesomorphic the Belgian ant fauna were expected. As different nature calcareous grasslands with five different plant communi- management types, microhabitats and vegetations were ties, and xeromorphic grassland with three different plant sampled, this study also enables us to evaluate the influ- communities (see HONNAY et al., 2004; BUTAYE et al., ence of the type or the lack of management in these grass- 2005a,b). The mesomorphic calcareous grasslands in the lands on the occurring ant communities. Viroin valley belong to the Mesobromion and show an The main aim of the present inventory is to investigate intermediate position between the Central European and if there is a specific ant fauna in the typical xeromorphic, Atlantic calcareous grassland communities (BUTAYE et rocky and calcareous grasslands of the Viroin valley and al., 2005a). The xeromorphic calcareous grassland com- to give a complete list of all known ant species of this munities on the other hand show strong affinities with the region. We also want to essay the possibilities to use ant calcareous vegetation of Central Europe and southern community composition and the occurrence and abun- Europe. The Viroin valley is a favourite region for ento- dance of several typical ant species to evaluate the effects mologists and other naturalists because some of the most of management and to make some remarks on the impor- notable Belgian calcareous grasslands occur there tance of active management for ant community composi- (DUVIGNEAUD et al., 1990). tion of calcareous grasslands in general. TABLE 1 Codes, locality, description, management, exposition, distance to other habitat and area of the sampled locali- ties (with temperature: +=cold, ++=warm, +++=hot sites) Tempera- Manage- Expo- Distance to Code Locatity (city) Vegetation and description site Area ture ment sition other habitat TdL(WO) Tienne du Lion Open woodland: Pinus nigra nigra, Brachypodium + None South- 20m open 10.000m² (Frasnes) pinnatum, Teucrium chamaedrys, mosses on NW East grassland slope. Cha(XB) Chalaine (Nis- Xerobromion: xeromorphic site with a lot of stones +++ Short South 40m forest 2.500m² mes) and bare ground; vegetation: Teucrium chamaedrys, intensive and arable Galium pumilum, Anthyllis vulneraria, Thymus prae- summer field cox, Helianthemum nummularium and Ononis grazing repens. FdC(XB) Fondry des Xerobromion: south-exposed slope with stones and a +++ None South 100m forest 4.500m² Chiens (Nismes) scarce vegetation, a sharp slope, with vegetation sim- ilar to Cha(XB). RTr(MB- Roche Trouée Meso-Xerobromion: south-exposed slope with ++ Short South 20-25m forest 2.500m² XB) (Nismes) grasses (Brachypodium pinnatum and Festuca ovina) intensive but also other typical calcareous herbs. summer grazing TaP(XB) Tienne aux Pau- Xerobromion: a lot of stones, short grassland on a +++ None South- 25m forest 2.000m² quis (Dourbes) sharp slope, Origanum vulgare, Sedum sp., Teucrium West chamaedrys and Prunella lanciniata. TaP(MB) Tienne aux Pau- Mesobromion: uniform grass layer (80%) surrounded +None South- 5-10m forest 6.000m² quis (Dourbes) by Buxus-Carpinus betulus forest, regularly chopped. (regularly West chopping) TdR(MB- Tienne des Rive- Meso- Xerobromion: