Effects of logging history on invasion of eastern white pine forests by exotic glossy buckthorn (Frangula alnus P. Mill.)

The extent to which forests can be invaded by exotic plants and the role of tree harvest in facilitating such invasions are important issues in invasion biology. Our objective was to determine: (a) whether a widespread exotic shrub, glossy buckthorn (Frangula alnus), can invade a common northeastern US forest type, (b) the extent to which logging facilitates buckthorn invasion, (c) whether buckthorn invades gaps through pre-disturbance (‘advance’) regeneration, (d) whether or not it forms uneven-aged populations in invaded stands. We selected nine eastern white pine – hardwoods stands in Durham, NH. Three were undisturbed, three were clear-cut, and three were partially cut. Cutting occurred ⩾6 years prior to sampling. Glossy buckthorn (⩾0.5 m tall) was present in all stands at the time of sampling and most buckthorn populations were all-aged, suggesting that recruitment by seed continued after initial establishment and that long-term persistence in these stands is possible. Buckthorn was present in four of six cut stands prior to cutting, indicating some advance regeneration. The results support the view that forests are not inherently resistant to invasion by exotic plants. Compared to uncut stands, however, buckthorn had higher densities in clear-cut and partially cut stands. In partially cut stands, buckthorn density was greater in canopy gaps than in adjacent uncut areas. Thus, logging facilitated buckthorn invasion. Given this result and the known negative effects of buckthorn on tree regeneration, control measures should be considered when logging stands where buckthorn invasion is likely.

► We relate the density and age structure of an exotic shrub to logging history.
► Frangula alnus was present in all sampled white pine stands, even if uncut.
► F. alnus density was greater in partial- and clear-cut stands than uncut stands.
► In partial cuts F. alnus density was greater in canopy gaps than uncut areas.
► F. alnus populations were all-aged, even in uncut stands.