The effect of Polytrichum piliferum on seed germination and establishment on iron mine tailings in New York

Seedling establishment on iron mine tailings in New York State's Adirondack Park was studied to determine if cover by the bryophyte Polytrichum piliferum Hedw. facilitated or inhibited seed germination and seedling survival, relative to other substrates present on the site. The occurrence of vascular vegetation on the four most commonly occurring substrates (bare tailings, cryptogamic crust, grass litter, and Polytrichum piliferum) was compared. An association survey detected preferential association between vascular vegetation and cover of Polytrichum piliferum, particularly for winter annual and biennial species. Seeds of Panicum virgatum L. and Melilotus officinalis (L.) Pallas were experimentally sown onto the four natural substrates, as well as on artificial substrates designed to mimic bryophyte turf. Germination on Polytrichum turf exceeded that of other substrates. However, seedling survivorship was low on all substrates, with no seedling surviving past 13 wk. Shade treatment on natural substrates significantly increased germination and somewhat extended survival. The results suggest that Polytrichum cover acts as a safe site for species that germinate and establish in cooler weather. However, even experimental shading of moss turf does not ameliorate summer heat stress sufficiently to permit establishment of seeds that germinate in early summer.