Germination, survival, and early growth of three invasive plants in response to five forest management regimes common to US northeastern deciduous forests

Abstract

The association between invasive plants and disturbance is well-documented. Most forest management regimes include disturbance (i.e., harvesting and fire) to improve regeneration of native plants, such as oaks. There is a need for land managers of northeastern forests to foster regeneration of native species without promoting invasive species establishment. We evaluated the germination, first-year survival, and growth of three exotic plants (Ailanthus altissima, Alliaria petiolata, and Microstegium vimineum) in 56 uninvaded forest stands located in five management regimes (control, single burn, repeat burn, diameter limit cut, and shelterwood) across two provinces (Appalachian Plateau, AP, and Ridge and Valley, RV) and two slope aspects (north-to-east facing, NE, and south-to-west facing, SW). These results were compared with the native Quercus rubra survival and growth under the same conditions. Two-hundred-fifty seeds and 30 transplants for each species were planted at each site. Germination, survival, and growth were measured three times over one growing season and analyzed using generalized linear mixed models.RV sites had more open canopies, lower soil fertility, and lower plant species richness than AP sites; NE aspects had higher soil fertility and plant species richness than SW aspects. The shelterwood sites had the most open canopies. Germination rates were below 25%, but lowest in the control sites and higher in the RV and on NE aspects for all three species. Survival was above 70% for A. altissima, M. vimineum, and Q. rubra but below 20% for A. petiolata, with little difference among province, aspect, or management regime for all three species. Survival decreased significantly between measurements. Microstegium vimineum grew the most of the three species. Microstegium vimineum and A. petiolata grew best in shelterwoods and better in the RV and on NE aspects. Ailanthus altissima had more root growth in the RV than the AP and the least root growth in the control sites. Quercus rubra survived better in the RV and best in the harvested sites, though growth did not differ among the management regimes. These invasive species are similar to many native species during the early stages of colonization; their germination, survival and growth are initially precarious and dependent on adequate resources (NE aspects) with minimal competition (RV province). Our results suggest that the likelihood of colonization by invasive plants could be reduced by keeping canopy openings below 15% and encouraging native understory competition with deer exclusion and artificial regeneration where native seed sources are depleted.