Distribution and dynamics of two ferns: Dennstaedtia punctilobula (Dennstaedtiaceae) and Thelypteris noveboracensis (Thelypteridaceae) in a Northeastmixed hardwoods-hemlock forest

Dennstaedtia punctilobula and Thelypteris noveboracensis are two native spe cies that often arrest forest succession and reduce understory diversity. A s part of a project to examine the feedback between forest understory and c anopy dynamics, we studied the patterns of distribution and dynamics of the se two fern species in an oak-transition hardwoods-hemlock forest. Dennstae dtia was least abundant under shade-tolerant tree species and most abundant in small (1-2 trees) canopy gaps, but did not show any distinct patterns a cross the sampled moisture regime. The light response was verified using li ght manipulation experiments and examination of plant size-abundance patter ns across light environments. Thelypteris tended to be most prevalent under maple canopies and appeared to be more sensitive to soil moisture regime b eing restricted to more mesic sites than Dennstaedtia. Seasonal and year-to -year changes in abundance of established clones of both fern species were small, suggesting that once established, both species can maintain a strong hold on a site. Further work on the niche requirements of the two species is warranted, but any event that maintains or promotes canopy openness (tre e death by disease or windthrow, forest harvesting, or the elimination of a shrub layer by browsing) will promote persistence of Dennstaedtia.