- Effects of reindeer grazing on understorey vegetation in dry Pinus sylvestris forests - 523 Journal of Vegetation Science 6: 523-530, 1995 © IAVS; Opulus Press Uppsala. Printed in Sweden Abstract. Data on floristic composition and environmental variables were collected in floristically homogeneous oligo- trophic pine (Pinus sylvestris) forests with heath-like under- storey vegetation in eastern Fennoscandia, and ordinated by non-linear multidimensional scaling (NMDS) in order to study the effect of lichen grazing by reindeer on the understorey vegetation. The study sites included areas with varying graz- ing pressure, as well as 50-yr old grazing exclosures. Sites rich in respectively bryophytes and lichens were placed at opposite ends of the ordination axes, and heavily grazed sites were placed in between them. Reindeer grazing increased the abundance of bryophytes, especially Dicranum spp. and Pleurozium schreberi. Grazing changed the vegeta- tion to the extent that it resembled more mesotrophic sites, but this did not show any relationship with tree volume or other site productivity indicators. This was observed both in the ordination and, in a more compelling way, when exclosures with adjacent grazed areas were compared. No such signs were evident at ungrazed sites, where especially Cladina spp. spatially replace Cladonia spp. and tiny bryophytes like Barbilophozia spp., Polytrichum spp. and Pohlia nutans dur- ing succession. Cladina stellaris had almost disappeared from the most intensively grazed sites. The soil at ungrazed sites was characterized by high Al and Fe concentrations and bryophyte-rich sites by high Mn concentrations. Shannon’s diversity index, depth of humus layer and proportion of bare ground also increased in sites getting richer in bryophytes. Keywords: Boreal ecosystem; Cladina; Cladonia; Dicranum; Non-linear multidimensional scaling; Rangifer tarandus; Suc- cession. Nomenclature: Hämet-Ahti et al. (1986) for vascular plants, Ahti (1981) for lichens, Koponen et al. (1977) for bryophytes, except for Dicranum in which Nyholm (1986) is followed. Introduction Lichen-rich forests, usually with Pinus sylvestris as a dominant tree, occur on dry sandy soils in Finland. They are heavily grazed by semidomestic reindeer. In Effects of reindeer grazing on understorey vegetation in dry Pinus sylvestris forests Väre, Henry 1* , Ohtonen, Rauni 1 & Oksanen, Jari 2 1 Department of Botany, University of Oulu, P.O. Box 400, FIN-90570 Oulu, Finland; 2 Department of Plant Ecology, Institute of Biology and Geology, University of Tromsø, N-9037 Tromsø, Norway; * Fax +358 81 5531500; E-mail HENRY.VARE@OULU.FI the beginning of the 1900s the number of reindeer was above 100 000 (Kautto et al. 1986), and by 1959 - 1960 it had reached 140 000 (Alaruikka 1964). In 1983 - 1984 the number exceeded 200 000 (Kautto et al. 1986) and in the winter of 1991 - 1992 it was 265 000 (Anon. 1993). As a consequence reindeer have to be fed with hay or imported lichens during winter (Mattila 1981; Helle & Aspi 1982; Kojola et al. 1993). Today, trampling and grazing of lichens by reindeer is a major factor control- ling the vegetation cover and has led to significant variation in the forest floor plant cover in northern Finland. Several authors (Du Rietz 1925; Söyrinki 1939; Nord- hagen 1943; Skuncke 1969; Brown & Mikola 1973; L. Oksanen 1978; Helle & Aspi 1982; Leader-Williams et al. 1987; Staaland & Olesen 1992; Staaland et al. 1993) have described the effects of reindeer grazing on vegeta- tion. Many studies are speculative in nature, however, since exclosures were only rarely used (L. Oksanen 1978; Leader-Williams et al. 1987). The response of vegetation to grazing depends on the geographical location. In oceanic areas a change in vascular plant abundance has been reported, e.g. native Poa flabellata was replaced by introduced weedy Poa annua in South Georgia (Leader-Williams et al. 1987), in St. Matthew Island in the Bering Sea, and in Scan- dinavian mountains, lichens were replaced by grami- noids like Carex bigelowii and Festuca ovina (L. Oksanen 1978; Klein 1987). In continental and intermediate parts between continental and oceanic sectors of the Fenno- scandian mountains the thick Cladina stellaris carpet is replaced by vascular plants, bryophytes and other li- chens (Du Rietz 1925; Nordhagen 1943; Söyrinki 1939). However, in the absence of ungrazed control areas, it is impossible to say which of the characteristics of vegeta- tion are due to reindeer grazing and which are natural (Oksanen & Ahti 1982; Oksanen 1983). Succession in vegetation is very slow, according to Jalas (1953) it takes at least 50 to 80 years after fire to reach the mature Cladina stellaris stage in central Finland. In northern Finland this may be even longer.