Dennstaedtia punctilobula (hay‐scented fern) can act as a native invasive species in forests in eastern North America where prolonged deer browsing occurs in stands with partially open overstory canopies. Ferns dominate the understory with a 60‐cm tall canopy, with little regeneration of native tree species. It has been hypothesized that, once established, ferns may continue to inhibit tree regeneration after deer browsing has been reduced. To test this hypothesis, we documented the pattern of recovery of the tree seedling understory in plantations of Pinus strobus (white pine) and Pinus resinosa (red pine) on the Quabbin Reservation watershed protection forest in central Massachusetts, where after 40 years of intensive deer browsing the deer herd was rapidly reduced through controlled hunting. Dense fern understories occur on nearly 4,000 ha of the predominantly oak–pine forest. Three years after deer herd reduction, stands with the highest density fern cover (77% of plots with>90% cover) had significantly fewer seedlings at least 30 cm in height, compared with stands with lower fern density, and those seedlings consisted almost entirely of Betula lenta (black birch) and white pine. Height growth analysis showed that black birch and white pine grew above the height of the fern canopy in 3 and 6 years, respectively. In contrast, two common species, Fraxinus americana (white ash) and Quercus rubra (red oak), grew beneath the dense fern cover for 5 years with height growth less than 5 cm/yr after the first year. A study of spring phenology indicated that the ability of black birch to grow through the fern canopy might have been due to its early leaf development in spring before the fern canopy was formed, in contrast to oak and ash with delayed leaf development. Thus, the ferns showed differential interference among species with seedling development after reduction of deer browse.

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Hay-scented fern (Dennstaedtia punctilobula) is a native species that can invade and dominate the forest understory, after thinning and intensive deer browsing. Fern colonies form a dense cover 60 to 80 cm high that intercepts light and inhibits tree seedling regeneration. Hay-scented fern can be controlled with herbicides, but some landowners (both public and private) seek alternative methods. We investigated mowing as a possible method of fern control. We tested different mowing schedules and measured the response of ferns (frond length and density) and of natural regeneration and planted seedlings. Mowing the ferns twice in one growing season (first in June when the fern fronds had reached their full height and again in August) led to a significant reduction in frond length during the next two growing seasons compared to untreated controls. Mowing four times over 2 years reduced both length and density of ferns. Mean density of naturally established tree seedlings was four times greater on these treatment plots compared to controls, but with great variability among plots. Red oak (Quercus rubra) and sugar maple (Acer saccharum) seedlings planted the year after mowing showed greater survival and height growth compared to controls.

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