Which of the following is a common invasive species in New Hampshire?

Japanese knotweed is considered a common invasive species in New Hampshire. This plant is not native to the region and has the ability to spread aggressively, often outcompeting native vegetation. It forms dense colonies that can significantly alter ecosystems, reduce biodiversity, and even impact soil quality. Japanese knotweed is particularly problematic because it can thrive in a variety of habitats and is difficult to control once established. Efforts to manage this invasive species typically require ongoing treatment, as its robust root system can survive traditional removal methods.

In contrast, the other options listed, such as eastern hemlock, white-tailed deer, and American beech, are native species. While white-tailed deer can have significant ecological impacts due to overpopulation and their browsing habits, they are not classified as an invasive species. Eastern hemlock and American beech are integral parts of New Hampshire's native ecosystems and play vital roles in supporting local wildlife and maintaining ecological balance.