Introduction of native tree species in sites invaded by Japanese Knotweed Taxa and a study of its affect of the seedbank.

Abstract

The invasion of three closely related taxa of knotweeds: (Japanese knotweed) Polygonum cuspidatum, (giant knotweed) Polygonum sachalinensis, and their hybrid Polygonum x bohemica in riparian corridors throughout the eastern U.S. has a negative impact on native plant communities. In the study the following research objectives were addressed: 1) To determine if forms of mechanical control (cutting and tilling) could be used to allow tree saplings to become established in knotweed invaded sites. 2) To compare height and leaf number of saplings of four native tree species inside and outside of Japanese knotweed stands. 3) To compare the soil seed bank density and composition in knotweed invaded versus noninvaded sites. No significant differences were found in the growth or survival among the saplings of four native tree species across treatments. Although treatments did not significantly affect sapling growth trends showed that saplings in the tilled treatment had the greatest growth across treatments over the growing season. A longer running experiment is needed to establish any emerging patterns in the data. Significantly greater densities of seedlings were observed in non-invaded than invaded sites and significantly greater densities of native seedlings were observed in non-invaded than invaded sites. Knotweed invasion does significantly affect the seedbank.