Aeshna subarctica is rare in the old-glacial lowlands of Poland, i.e. in the Central Polish Lowlands and the Saxonian-Lusatian Lowlands, which occupy the central latitudes of the country and its southwestern areas (Fig. 1). Only thirteen localities of the species have been found in this area (Fig. 1);they have been presented so far only in the form of occupied UTM-squares (Bernard et al. 2009). These localities are described in detail (geographic position, habitat, data concerning A. subarctica, accompanying species). The rarity of A. subarctica reflects the small number of habitats which are appropriate for it. This unfavourable conservation status is partly naturally conditioned as the old-glacial plains are situated to the south of the last glaciation (Würm) range. Hence, they are much poorer in natural water bodies than the northern postglacial lake districts. However, human impact has also contributed to the rarity of A. subarctica habitats. These areas have been long inhabited and intensively exploited by man and thus are among the most transformed regions in Poland. Over the last two hundred years the area of Sphagnum bogs has decreased drastically (Herbich, Herbichowa 2002). As a consequence, the distribution of A. subarctica in the study area has been severely fragmented – restricted to largely isolated single localities or small groups of them, such as 6 localities in an area of 25 km2 near Pabianice (No. 3–8) or 2 (No. 9 and 10) near Białobłoty. These groups are especially valuable as they give A. subarctica an opportunity to exchange individuals between local populations (the metapopulation structure) and to restore reduced/extinct local populations on the basis of neighbouring populations. All the presented localities are situated in woodland and are surrounded with mostly pine forest or occasionally with heath. On sandy grounds and a thin peat layer, a mosaic of shallow Sphagnum bogs, transition mires and acidic sedge fens most frequently occur. The abundant vegetation is predominated by Carici-Agrostietum caninae, Sphagno recurvii-Eriophoretum angustifolii, and also locally by Ranunculo-Juncetum bulbosi. Large amounts of Sphagnum occur in the form of both floating ‘soup’ and thin mats covering the bottom/ground. The water bodies are shallow – only rarely deeper than 0.5 m – and frequently astatic, larger in the spring and partly drying out in the summer. As a consequence, the A. subarctica habitats are much more liable to desiccation than those situated in more stable, deeper water bodies in the postglacial landscape in northern Poland. At some localities (No. 3, 8 and 12), an advanced eutrophication process was recorded, indicated by the replacement of the boggy vegetation with Phragmites australis and Typha latifolia. At locality No. 8, the population of A. subarctica was already almost extinct. In contrast to the mostly primary (natural) habitats of A. subarctica in northern Poland, the habitats in the study area survived or were formed, at least in several cases, due to human activities. So they are actually partly secondary – anthropogenic, but completely or to a large extent renaturalized. At locality No. 13 they have developed in an excavated fire-fighting pool and at No. 7 in shallow peat excavations. Though forms left by extensive peat digging are already unrecognizable, we believe that this human activity also resulted in the formation of favourable habitats at several other studied localities. The occurrence in partly anthropogenic habitats is a chance for A. subarctica to survive in lowlands poor in natural water bodies. What is more, conservation policy should use this opportunity for habitat-based actions. Existing habitats could be restored or regenerated in the future – and new ones formed – due to shallow peat digging in small areas of selected localities according to the rotation model (Wildermuth 2001). Plant succession in such shallow peat excavations leads to various forms of moorlands, especially to Sphagno recurvii-Eriophoretum angustifolii, often inhabited by A. subarctica. The conservation of A. subarctica habitats would also be favourable for other tyrphobiontic and tyrphophilous species, which are fairly rare or rare in these regions, as e.g. for 4 Leucorrhinia-species occurring at the studied localities. At five localities (No. 1, 9–12) colour morphs were analysed. Five individuals represented the pale f. interlineata and five were intermediate – due to slightly smaller spots on the thorax – between interlineata and the dark f. elisabethae. Considering the occurrence of intermediate forms, it is better to use the term ‘paler individuals’ – or describe the tendency to be significantly paler (Dijkstra 2006) – than to sharply distinguish between the pale f. interlineata and the dark f. elisabethae. Considering: (a) the significantly paler individuals in central European bogs than in boreal and alpine regions (Dijkstra 2006) and (b) the absence of the dark f. elisabethae from the presented shallow and warm localities in the southern, marginal zone of the species range, it can be concluded that the paler individuals of A. subarctica are associated with warmer habitats. The simple and direct correlation between the habitat temperature and existing colour morphs was not confirmed experimentally (Sternberg 2000). Therefore, we believe that the occurrence of colour morphs depends on a set of conditions with the habitat temperature as the leading (but not sole) factor. Contrary to Bönsel’s (2001) suggestion, paler individuals of A. subarctica coexist with Aeshna juncea as recorded at all five of these localities.
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