A new method for assessing dispersal and colonization of bryophytes

Recently, a new type of artificial trap was established for studying seed banks and seed dispersal in harsh environments (Molau & Larsson, 2000; Larsson & Molau, 2001). It also seemed to work well for collecting fragments of dispersed bryophytes and lichens (E.-L. Larsson, pers. comm.) but until now it had not been used to assess colonization or dispersal of bryophytes. The artificial traps are made of plastic FinnTurf doormats that are fixed to the ground with large nails through the corners. This study examines if the mat functioned as an artificial trap and colonizing substrate for bryophytes under harsh environmental conditions. Studies of the colonization of bryophytes have previously mainly focused on epiphytic bryophytes (Nadkarni, Cobb & Solano, 2000; Sillett et al., 2000; Cobb et al., 2001; Snäll, Ribeiro & Rydin, 2003; Snäll, Ehrlen & Rydin, 2005) or on forest habitats (Jonsson, 1993; Lloret, 1994; Frego, 1996; Jonsson & Esseen, 1998; Rydgren, Økland & Økland, 1998; Heinken & Zippel, 2004). In the forest studies, colonization was examined after the habitat had been experimentally disturbed. This experimental approach of clearing gaps is suitable for use in forests, on branches or on the forestfloor, but it does have limitations in tundra and polar areas where re-colonization may take several years or decades (see, for example, lichen colonization in the Antarctic; Smith, 1995). Consequently, there is a need for a new way to study the dispersal and colonization of bryophytes in situ. The new mat has several advantages, it is possible to use in different stages of the succession as well as in different positions, e.g. directly on the ground, on branches, or on tree trunks and it needs no artificial disturbance. Thus, if the method works efficiently on trapping bryophytes, studies on the colonizing processes and vegetation dynamics would be technically and experimentally less difficult to perform in harsh environments. This study was carried out in Thingvellir National Park (64u17’N, 21u05’W, at 120 m a.s.l.), situated in southwest Iceland. Thingvellir has a typically oceanic and subarctic climate (Einarsson, 1992; Thorsteinsson & Arnalds, 1992), with a mean temperature between 1997 and 2002 of 3.5uC, and a mean annual precipitation of 1196 mm between 1999 and 2002 (Jónsdóttir et al., 2005). The species-poor vegetation consists mainly of a well-developed Racomitrium lanuginosum moss heath with scattered patches of dwarf shrub heath (for a more detailed description, see Thorsteinsson & Arnalds, 1992; Jägerbrand, 2004). In September 1998, 20 mats (20630 cm, ca 18mm thick) made of plastic FinnTurf were divided into five groups of four mats and then placed at intervals of 1 m, each group ca 20 m apart, and fastened with 10-cm-long nails in each corner on top of the moss surface. In late June 2004, the mats were collected from the field and carefully put in sealed plastic bags. However, eight of the mats were excluded from the study as they could not be found in the field or had been moved from their original position, leaving only 12 in this study. Some of the mats were heavily colonized by moss (i.e. Racomitrium lanuginosum), making it impossible to distinguish isolated events of colonization by individual shoots or fragments. Due to these circumstances, 10 shoots from each mat were