Distribution and habitat ecology of the threatened forest lichen Lobaria pulmonaria in Estonia

Lobaria pulmonaria is a widely used as an indicator species of undisturbed old-growth forests ecosystems, but the knowledge about its habitat ecology is still highly fragmented. To quantify the distribution, habitat preference and host tree specificity of Lobaria pulmonaria we utilised data from databases and field surveys in Estonia. The number of L. pulmonaria localities is the highest in the densely forested regions, concentrated mainly in small forest patches defined as ‘ecologically highly valuable’. The species grows mostly on deciduous trees, particularly on aspen (Populus tremula). L. pulmonaria is most common in oligo-mesotrophic boreal, eutrophic boreo-nemoral and in eutrophic paludifying forests, and prefers forests with an average age of trees more than 100 years. In addition, we found that younger stands could be suitable habitats for L. pulmonaria if the structure of the stand is comparable to mature stands. In spite of the many localities of L. pulmonaria in Estonia, the species is still threatened because (1) the rotation period of tree stands is short, (2) it is abundant in forest types which are rare or under strong economic pressure, (3) and it prefers host trees which have a restricted distribution in Estonia or are not favoured in forest management practice. Kokkuvõte: Hariliku kopsusambliku (Lobaria pulmonaria), ohustatud metsasambliku levik ja kasvukohanõudlus Eestis. Harilikku kopsusamblikku (Lobaria pulmonaria) on laialdaselt kasutatud looduslike vanade metsade indikaatorliigina, kuigi teadmised tema kasvukohanõudlustest on piiratud. Et saada ülevaadet h. kopsusambliku levikust, kasvukohaeelistustest ja puuliigi spetsiifilisusest Eestis, kasutasime erinevatesse andmebaasidesse koondatud andmeid. Hariliku kopsusambliku leiukohtade arv on kõrgeim suurema metsasusega piirkondades, peamiselt väikestes metsaosades, mis on defineeritud kui ökoloogiliselt väärtuslikud. See liik kasvab peamiselt lehtpuudel, eriti harilikul haaval (Populus tremula), olles kõige tavalisem palu-, saluja soostuvates metsades, ning eelistades puistuid, kus puude vanus on üle 100 aasta. Siiski võib h. kopsusamblik kasvada ka nooremates metsades, kui puistus on piisavalt suuri puid. Hoolimata h. kopsusambliku arvukatest leiukohtadest Eestis on see liik siin siiski ohustatud, kuna (1) metsade raiering on lühike, (2) ta on arvukas metsatüüpides, mis on Eestis haruldased või majandusliku surve all, (3) ning ta eelistab peremeespuid, mis on Eestis piiratud levikuga või mille kasvu ei soodusta metsamajandus. 56 Folia Cryptog. Estonica where the lichen has been recorded mainly in small and fragmented old-growth patches in the landscape of managed forests (Auzinš & Ek, 2001; Gu et al., 2001; Andersson et al., 2003; Pykälä, 2004). Lobaria pulmonaria has been widely used as an indicator species of undisturbed forest ecosystems and forest areas of a high ecological continuity (Rose, 1976; Andersson & Appelqvist, 1987; Nilsson et al., 1995; Andersson et al., 2003; Campbell & Fredeen, 2004; Liira & Sepp 2009), owing to the evidence of the low dispersal ability of the diaspores (Scheidegger, 1995; Walser et al., 2001) and long generation time (Scheidegger et al., 1998). During the long life-cycle of L. pulmonaria, in average 35 years, the dispersal by the vegetative diaspores (soredia, isidioid soredia) and by the thallus fragments predominates (Scheidegger et al., 1998; Scheidegger & Goward, 2002). That causes high density clustering of specimens within a habitat patch (Walser et al., 2003; Öckinger et al., 2005). In the later stage of the life cycle ascospores become available (Scheidegger et al., 1998; Scheidegger & Goward, 2002) and ensure long-distance dispersal (Wagner et al., 2006; Werth et al., 2006b). The quality of the habitat, e.g. ecological conditions at stand and tree level may hinder successful establishment and colonization of L. pulmonaria (Werth et al., 2006a). Until now, the effect of the forest site type on the distribution of L. pulmonaria has received little attention (Gu et al., 2001; Nascimbene et al., 2006). Within a stand density of host trees and availability of large trees are positive predictors for presence of L. pulmonaria (Gu et al., 2001; Öckinger et al., 2005). At tree scale, colonization and reestablishment of individuals is dependent very specific pH levels of tree bark (Wolseley & James, 2000) and extent of bryophyte cover on host trees (Öckinger et al., 2005). The aim of this study is to evaluate the importance of different forest site types for the presence of L. pulmonaria in hemiboreal forests in north-eastern part of Europe. We also addressed our interest to assess some stand-scale habitat characteristics and the preference of the host tree species for the distribution of L. pulmonaria in forestland. We will provide an overview of the present distribution of L. pulmonaria in different habitats and forestland categories in Estonia and estimate the risk factors related to the forest management for the long-term presence of L. pulmonaria in