Khalil and Vera are visiting a region of land that is unfamiliar to them. They observe a community of grasses and shrubs, as well as a variety of insects, birds, snakes, and small mammals such as mice and rabbits. Khalil claims that they are visiting a meadow ecosystem that, if undisturbed, will remain stable for many years. Vera argues that Khalil is incorrect. She claims that the ecosystem is undergoing ecological succession, and that it likely will become a hardwood forest. Which observation from this region would provide the strongest evidence in support of Vera's claim