Daniel F. Brunton
There are 114 taxa of ferns and fern allies (including interspecific 25 hybrids) known from the Mixedwood Plains Ecozone (Appendix 1). Most are widespread species found in woodlands, on cliffs, in sand and rock barrens, and in aquatic habitats across northeastern North America (Cody and Britton 1989; FNA Editorial Committee 1994). Pteridophyte spores are aerially dispersed for great distances, even transcontinentally (Wagner and Rouleau 1984), resulting in full occupation of suitable habitat. Biophysical site restrictions, therefore, constitute the main limitation to pteridophyte in and beyond the ecozone.
Pteridophytes have the highest incidence of natural biodiversity (99.1%) of any large group of vascular plants in the Mixedwood Plains Ecozone. Only one non-native taxon, the Water-clover Fern (Marsilea quadrifolia) is known in the ecozone.
Pteridophytes typically maintain relatively inflexible ecological requirements. Populations frequently vary in direct relationship to changes in their habitats. Population fluctuations in the Mixedwood Plains Ecozone, therefore, largely reflect natural and/ or non-natural alterations to indigenous habitats.