PRESENCE AND ABUNDANCE OF 4 EPIPHYTIC BRYOPHYTES IN RELATION TO DENSITY OF ASPEN (POPULUS-TREMULA) AND OTHER STAND CHARACTERISTICS

The influence of the local density of aspen on the presence and abunda nce of four epiphytic bryophytes was investigated in four mixed forest stands in Central Sweden, each about 30 ha and aged 70-120 yr. Cover of the bryophytes Nyholmiella obtusifolia, Orthotrichum speciosum, Pyl aisia polyantha and Radula complanata (the four most frequent aspen-sp ecific epiphytic bryophytes in this region) was recorded on the bark o f 155 systematically sampled aspen stems. Ln circular plots with 10 m radius surrounding each sampled aspen, information on ground vegetatio n, soil moisture and stand density was collected. in these plots, and also in plots with 5 m and 20 m radius, stem number and diameters of a spen trees were recorded together with an observation of the presence/ absence of the four bryophytes. There was no general and consistent re lation between aspen density and presence or abundance of the studied bryophytes. Site, host aspen diameter and forest stand structures were mole important for the bryophytes. The site factor explained more of the Variation than any of the studied variables. All species except N. obtusifolia were favoured by a large diameter of the host tree, and t he density of the surrounding forest stand had a positive effect on th e cover of Pyl. polyantha and R. complanata. The practical implication s of the results are discussed. (C) 1998 Elsevier Science B.V.