Identifying pathways of biological invasion: can commercial moss harbor potential stowaways?

Abstract

Wild-harvested ‘‘moss’’, typically a mixture of mosses and liverworts (Peck 2006), is gathered from the forests of the Pacific Northwest (PNW) and Appalachians and distributed within the continent and to at least 44 international destinations (Muir et al. 2006) with no processing beyond air-drying (ca. 15% moisture content) and packaging in sealed plastic bags. Some companies also distribute ‘‘fresh’’ moss, which usually contains portions of the O horizon (organic matter or humus) and sometimes of the A horizon (i.e., actual soil) and is not allowed to air dry. Previous work examining commercially harvestable PNW moss mats has identified over 200 morphotaxa of associated macroinvertebrates, with any given moss mat bearing a dozen taxa and hundreds of individuals (Peck and Moldenke unpublished data). We conjecture that some of these taxa become trapped within the plastic retail bag, confined to a closed ecosystem that may have no inputs for weeks to months, until they are released at the final retail destination. Because many invertebrates are tolerant of environmental extremes, responding through cryptobiosis (Polgar and Darvas 1995) or anhydrobiosis (Watanabe 2006), we hypothesized that at least some invertebrates inhabiting commercially harvested and processed moss are likely to survive and be capable of emerging after the moss has reached the final consumer. Furthermore, we anticipated that many more individuals and taxa would be capable of surviving in minimally processed ‘‘fresh’’ moss.