Abundance of Viable Hay-Scented Fern Spores Germinated from Hardwood Forest Soils at Various Distances from a Source

-The abundance of viable fern spores in the forest floor of undisturbed central Pennsylvania mixed oak stands was assessed at various distances from hay-scented fern (Dennstaedtia punctilobula) spore sources before and after seasonal spore dispersal. Intact soil samples were collected at distances up to 50 m from large, reproductive fern communities and placed in a greenhouse to induce spore germination. Spore abundance was estimated by counting the number of gametophytes that germinated in the top 1 cm of samples. Hay-scented fern was the predominant or only fern species present on sites. Hay-scented fern has cordate, naked (glabrous) prothalli. Fewer than ten hairy (trichomatous) prothalli were germinated in all samples and only glabrous prothalli were counted. Sixty other samples collected from sites in the pre-dispersal season were allowed to grow for one year. Only one sample produced a sporeling that was not hay-scented fern. The majority of prothalli that developed were most likely hay-scented fern. Large numbers of viable hay-scented fern spores were found at all sample locations. Viable spores occurred in 98% of the samples, and site estimates varied from 7 to 15 viable spores cm-2 during the preand post-dispersal trials. Viable spores occurred at all distances within 50 m, the greatest distance sampled, from all sources. Highest abundance of spores always occurred within 4 m of the source and generally declined with increasing distance from a source. These data indicate that hayscented fern spores remain viable for at least one year, and the potential exists for the establishment of hay-scented fern from a viable spore bank in central Pennsylvania mixed oak or hardwood stands. Hay-scented fern (Dennstaedtia punctilobula (Michx.) Moore; Dennstaedtiaceae) is a common forest understory species in the northeastern United States and eastern Canada (Cody et al., 1977). In Pennsylvania, hay-scented fern is considered a forest weed, because it interferes with the regeneration of Allegheny hardwood and mixed oak stands (Bowersox and McCormick, 1987; Horsley, 1988, 1993; Horsley and Marquis, 1983). Dense, highly competitive colonies of hay-scented fern capable of excluding most other vegetation often become established in forest areas following harvesting or natural disturbances (Allen and Bowersox, 1989; Hall, 1955; Kolb et al., 1990). An inventory of Pennsylvania's forests completed in 1989 found that 30% of the areas sampled had sufficient fern cover to inhibit the establishment of hardwood regeneration (McWilliams et al., 1993). Recent studies have emphasized the importance of sporebanks in the colonization of sites by ferns (Dyer and Lindsay, 1992; Hamilton, 1988; Schneller, 1988). Under favorable conditions, spores of hay-scented fern can germinate to form prothalli (gametophytes) capable of reproducing sexually and produc1 Author to whom correspondence should be addressed. This content downloaded from 157.55.39.215 on Wed, 31 Aug 2016 04:19:49 UTC All use subject to http://about.jstor.org/terms AMERICAN FERN JOURNAL: VOLUME 86 NUMBER 3 (1996) ing young sporelings (sporophytes) (Conard, 1908). Once established, the sporophyte spreads aggressively from an underground rhizome (Anderson and Egler, 1988; Horsley, 1984). Soil disturbances associated with timber harvesting facilitate the establishment of hay-scented fern by creating favorable microhabitats for spore germination (Groninger and McCormick, 1992). Establishment of spore-origin hay-scented ferns occurs commonly on moist, exposed mineral soil or moss colonies along exposed banks of skid trails, in drainages, and on root mounds of trees overturned by wind, road construction or tree felling (Groninger and McCormick, 1992; Horsley, 1988). Because spore-origin hay-scented fern often contributes to the colonization of forest stands and subsequently interferes with hardwood regeneration (McCormick et al., 1992), it is useful to have an understanding of the spore bank, spore viability, and spore distribution of hay-scented fern. This study was designed to determine whether viable spores of hay-scented fern exist in the soil of undisturbed mixed oak stands of central Pennsylvania and to quantify the abundance of viable spores in stands adjacent to large, well-established populations of hay-scented fern relative to distance from a spore source. Abundance of viable spores was measured by counting the number of gametophytes that developed in soil samples collected from forest stands before and after spore dispersal. Fern species differ in the ability of their gametophytes and young sporophytes to persist and become established on sites (Peck et al., 1990). Although spore abundance cannot directly indicate future establishment of the species, the presence of a viable spore bank dormant in the soil infers a potential of these spores to further colonize stands. This is particularly true when stands are cut or otherwise disturbed and conditions are favorable for spore germination and sporeling survival. METHODS AND MATERIALS STUDY SITES.-The study was conducted at two forest sites in central and south central Pennsylvania. One site (Tram Road) was located in the Rothrock State Forest and the other site (Clear Shade) was located in the Gallitzin State Forest. Two plots were established at each site and were identified as TR1 and TR2 at Tram Road and as CS1 and CS2 at Clear Shade. Each plot was established adjacent to a reproductive population of hay-scented fern. The fern populations occurred along roadsides or in clearcut areas adjacent to undisturbed hardwood stands with little or no fern invasion. The Tram Road site was located along a southeastern facing side slope in the Ridge and Valley Province at an elevation of 365 m. The site was occupied by an 80 year-old, undisturbed, mixed oak stand with an average stand density of 20 m2/ha. Overstory species included northern red and white oaks (Quercus rubra and Q. alba), hickory (Carya spp.), yellow birch (Betula alleghaniensis), red maple (Acer rubrum), and white pine (Pinus strobus). Woody understory species included red maple, yellow birch, white pine, witch hazel (Hamamelis virginiana), and blueberry (Vaccinium spp.). The ground layer included woodland herbaceous plants, grasses, mosses and lichens. New York fern (Thelyp70 This content downloaded from 157.55.39.215 on Wed, 31 Aug 2016 04:19:49 UTC All use subject to http://about.jstor.org/terms PENROD & McCORMICK: HAY-SCENTED FERN SPORE GERMINATION teris noveboracensis ) occurred only at TR2. Soils at the site were well to moderately drained, silt to sandy loams derived from sandstone, siltstone, and shale parent material (Hazleton-Laidig-Buchanan association) (Merkle et al., 1978). At Tram Road, one plot (TR1) was located in a hardwood stand directly adjacent to a hay-scented fern-dominated clearcut. The second plot at Tram Road (TR2) was located several hundred meters from TR1 along a road rightof-way adjacent to a 7 m wide and 60 m long patch of hay-scented fern. No other fern species was observed in the source patch at TR2. Scattered patches of New York fern occurred at TR2 in forest gaps at 25-50 m from the source. No other fern species was present and there was no invasion by any ferns beyond the source at TR1. The Clear Shade site was on a ridge top on the Allegheny Plateau at an elevation of 730 m. The site was occupied by an 80 year-old, undisturbed, mixed oak stand with an average stand density of 24 m2/ha. Overstory species included northern red oak, white oak, beech (Fagus grandifolia), yellow birch, sweet or black birch (Betula lenta), sugar maple (Acer saccharum), and red maple. Woody understory species included striped maple (A. pensylvanicum) and beech. The ground layer included ground pines (Lycopodium spp.), herbaceous woodland plants, grasses, mosses, lichens, and small populations of ferns. Soils at the site were well to moderately-well drained, silt to sandy loams derived from sandstone parent material (Hazelton-Cookport association) (Yaworski et al., 1983). At Clear Shade, the two plots (CS1, CS2) were located on opposite sides of an improved dirt road with a 3-4 m wide strip of hay-scented fern growing along both sides of the road. Hay-scented fern was the predominant fern species at the site with minor amounts of New York fern and wood ferns (Dryopteris spp.). Scattered patches of hay-scented fern or woodfern at CS1 and CS2 occurred in forest gaps at 25-50 m from the fern sources. At CS2, heavier invasion by ferns occurred where stands were thinned at 50-200 m from the