Terrestrial molluscs as indicator species of natural forests Digna Pilâte Nature Museum of Latvia, Kr. Barona iela 4, LV-1712, Rîga, Latvia, [email protected] Introduction During the last 100-200 years, more and more intensive destruction of the natural fo- rests as well as their replacement with planted tree cultures, can be observed in Latvia (Zunde 1999, Suško 1997). Land molluscs are among those animals, which are very sensitive to human caused disturbances in the forest and therefore can be used as bioindicators of anthropogenic influence (Ehnström & Waldén 1986, Ssymank 1994, Møller 1997, Niemelä 1997, Ëèõàðåâ1962, Ëèõàðåâ & Âèêòîð 1980, Øèëåéêî 1978). The aim of this study was to find out mollusc species most sensitive to forest manage- ment, which therefore could indicate biologically valuable forests in Latvia. Approba- tion of indicator species of natural forests is still continued in a course of forest key habitat inventory started in Latvia in 1998 (Ek et al. 2000). Materials and methods The studies were curried out in 1995 and 1997 as part of complex investigation on natural forests of Latvia conducted by Suško (1997). Material was collected in four distant areas having different climatic features, topography, soil conditions and forest management history (Table 1). Altogether 42 study plots were set in following groups of forest biotopes: forests with natural or human caused disturbances /CDF/ (wind- falls, clear cuts, young naturally regenerated stands after clear-cutting, plantations), forests of pioneer tree species /PTSF/, pine forests /PF/, spruce forests /SF/, wet deciduo- us forests /WDF/ and broad-leaved forests /BLF/. Each study plot has different history of forest management and different amount of key elements supporting biodiversity as well as different tree and log continuity (Suško 1997). Investigations were carried out in all three classes of natural forests represented in Latvia (Priedîtis 1999): Cl. Vaccinio-Picetea, Cl. Querco-Fagetea and Cl. Alnetea glutinosae. Two methods – volume method and square method (Balogh 1958, Dunger & Fied- ler 1997) were used to collect samples of the litter. The volume sample was collected from plot sized 20 x 10 m. In total, 3 litres of forest litter (decomposing leaves and humus) were sifted at random from ground cover in each relevé using a soil sieve with 1 x 1 cm mesh. In square method 25 samples sized 20x20 cm were collected along the transect set in each study plot. Later the litter was sifted using soil sieve with 1 x 1 mm mesh. Besides that, molluscs were collected from relevant substrata (tree trunks, snags and logs and under their bark, different parts of fungi, lichens, bryophytes and vascular plants) as recommended by Ëèõàðåâ (1962) and Øèëåéêî (1978). Altogether 1260 l of the litter were sifted and 11 421 mollusc specimens were counted. Species of molluscs were identified using guidebooks of Kerney et al. (1983) and Ëèõàðåâ (1962). 216 ○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○The Finnish Environment 485 The species requiring specific conditions in prolonged time period (e.g., forest continuity, stable microclimate, large diameter logs and old trees) as well as endange- red by certain forest management practices (e.g., clear-cuttings, soil tillage, establish- ment of plantations and artificial regeneration, land drainage, removal of dead wood and injured trees) were chosen as indicator species (Suško 1997, Ek et al. 2000). Table 1.Characterization of natural forest study sites (from Suško 1997) Study site Slitere Livberze Aizkraukle Mezole Area (ha) 715 632 616 716 Location in North-western Southern Southern North-estern Latvia part (coastal) part (central) part part Climate Moderately warm, Warm Warm Cool, the most oceanic the most region continental region Forests Outstanding nemoral One of the main One of the main One of the main broad-leaved and nemoral broad- nemoral broad- boreal spruce boreal coniferous leaved forest leaved forest forest forests distribution areas distribution areas distribution areas in Latvia in Latvia in Latvia Biological High ecosystem Presence of little High ecosystem High ecosystem values naturalness, influenced wetland naturalneness, naturalneness, extremely high forests, oldgrowth unique forest-bog presence of little biodiversity, broad-leaved mosaic and influenced wetland standards of forests, significant transitional com- forests, oldgrowth Eurosiberian alder community samples munity complex, spruce and pine swamp and of ash wetlands little influenced forests around European broad- (mixed decidious broad-leaved tracts of bog, a leaved forest wetland forests), forests on islands great number of communities, a a great number of in the bog, a great rare species great number of rare species number of rare rare species species Management Not managed in Under intensive Under intensive Not managed in status the last 75 management management the last years 30-35 years Conservation Strict Nature Not protected Not protected Restricted Nature status Reserve since area since late 1921 1960-s Results and discussion More than 60 of the 85 terrestrial mollusc species found in Latvia inhabit forests (Rudzîte et.al 1997). 52 land mollusc species representing 16 families were found in forest areas studied. Three species: Discus ruderatus, Euconulus fulvus and Nesovitrea hammonis were recorded in all study plots regardless of biotope‘s transformation stage and it’s biolo- gical features. In the same time 15 species were recorded only in those study plots having high biological values (Suðko 1997). Results of studies in other forest areas (Pilâte 1997, unpubl. data) reveal that additional 5 species are closely connected with structures supporting biodiversity in forests. Therefore, altogether 20 species were ○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○ The Finnish Environment 485 ○○○○○○○○○○○ 217 chosen as indicators for natural forests (Table 2). Due to practical reasons (easiness to find and identify) 15 species of them are used in the fieldworks of general forest key habitat inventory. Table 2. Mollusc indicator species of natural forests in Latvia (PF- pine forest, SF- spruce forest, BLF- broadleaved forest, WDF- wet deciduous forest). Species name Forest biotopes Forest key Protected Red-listed inhabited habitat (category) inventory Acicula polita BLF, WDF, SF X 4 Aegopinella nitidula BLF, WDF 4 Bulgarica cana BLF, SF X X 3 Clausilia bidentata PM, SF, WDF, BLF X X 3 Clausilia cruciata SF, WDF, BLF X X 3 Clausilia dubia SF, WDF, BLF X X 3 Clausilia pumila WDF, BLF X X 3 Cochlodina orthostoma SF, BLF X X 3 Ena montana BLF X X 3 Ena obscura BLF X X Isognomostoma isognomostoma BLF X X 3 Laciniaria biplicata BLF Laciniaria plicata SF, BLF X X Lehmania marginata BLF Limax cinereoniger WDF, BLF X X Macrogastra latestriata SF, BLF X X Macrogastra plicatula SF, WDF, BLF X X Macrogastra ventricosa PF, SF, WDF, BLF X X Ruthenica filograna WDF, BLF X X 3 Spermodea lamellata SF Factors determining the occurrence of indicator species Long lasting relationship of indicator species with biologically valuable forests are determined by several natural factors: shadowness of forest, stable microclimate, richness of vegetation, deadfall, decomposing stumps, old trees, ravines covered by forest (Ehnström & Waldén 1986, Ssymank 1994, Møller 1997, Niemelä 1997, Suško 1997, Ëèõàðåâ1962, Ëèõàðåâ & Âèêòîð 1980, Øèëåéêî 1978). Most of the indicator species are found in broad-leaved forests and in forests of pioneer tree species. Less species occur in wet deciduous forests, in spruce forests and in forests with natural disturbances. Minor part of the species are found in pine forests and in forest with human caused disturbances. In Latvia, indicator species of molluscs are most threatened by planting the spruce plantation on rich deciduous woodland soils and the cultivation of these cultures. In forests where forest management activities during the long period (the last 50-90 yea- rs) were less intensive (selective cutting or single clear-cut), the number of indicator species does not decrease. It is observed that indicator species decolonise 80-90 years old, unmanaged plantations, if the ecological corridors are maintained or if the planta- tion is adjacent to natural forests (Suško 1997). 218 ○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○○The Finnish Environment 485 Characteristics of indicator species The larger part (12 species) belongs to Clausiliidae. Almost all of them are included in the Red Book of Latvia (Spuris 1998). In Latvia almost all indicator species inhabit exclusively in forests (Suðko 1997, Pilâte unpubl. data). Some species (Macrogastra ventricosa, calciphilous Macrogastra plica- tula, Aegopinella nitidula and Limax cinereoniger) can be found also in old, unmanaged estate parks. Limax cinereoniger sometimes is found in cellars of old houses. These snails favour moist conditions as well as rich microflora and mycoflora serving as food. Aegopinella nitidula, Arion circumscriptus and most species of Clausiliidae are typi- cal for broad-leaved forests. Almost all species of Clausiliidae are found also in moist spruce forests. Ena montana, Lehmania marginata and Isognomostoma isognomostoma inha- bit particularly old broad-leaved forests, mainly in ravines (Pilâte et al.1994). Clausilia pumila and calciphilous Ruthenica filograna are typical for moist broad-leaved, spruce and black alder forests. Laciniaria plicata and Ena obscura can be found mostly in river valleys and in ravines covered by trees. Spermodea lamellata, Laciniaria biplicata, Ena