Confronting the Issue of Invasive Native Tree Species Due to Land Use Change in the Eastern United States

Abstract

The increased abundance of historically rare native tree species is symptomatic of land-use change, which causes ecosystem regime shifts. I tested for an association between mean agricultural area, a proxy for land-use change, and native tree species. I first modeled agricultural area during the years 1850 to 1997 and the historical and current percent composition of tree genera, along with the dissimilarity and difference between the historical and current composition, for the northern part of the eastern U.S. I then modeled agricultural area and current genera and species for the eastern U.S. and regionally. For the northeast, agricultural area was most associated (R2 of 78%) with the current percentage of elms and a diverse, uncommon “other” genera. For the eastern U.S., Ulmus, Juglans, Prunus, boxelder (Acer negundo), black cherry (Prunus serotina), and hackberry (Celtis occidentalis) best predicted agricultural area (R2 of 66%). Regionally, two elm and ash species, black walnut (Juglans nigra), mockernut hickory (Carya tomentosa), red maple (Acer rubrum), sweetgum (Liquidambar styraciflua), and American sycamore (Platanus occidentalis) increased with agricultural area. Increases in historically rare and diverse species associated with agricultural area represent an overall pattern of invasive native tree species that have replaced historical ecosystems after land-use change disrupted historical vegetation and disturbance regimes.

Potential Interactions between Climate Change and Land Use for Forest Issues in the Eastern United States

“…Fire exclusion had increased tree densities (see fire section above). Additionally, composition generally has shifted from a few relatively slowgrowing, long-lived tree species that are stress-tolerant to numerous early-seral species that grow quickly in response to severe disturbance, reproduce young, and die within 100 years in the eastern U.S. [62]. Perhaps in consequence, mortality is seven-fold greater in diverse stands than monospecific stands [63].…”

“…Inconsistent changes in moisture availability, which are within the range of natural variation, have not provided correlations with comprehensive tree expansion, but land use change has corresponded with tree changes based on timing, magnitude and direction of change, and mechanism [15,22]. Native tree species have increased within U.S. forests and grasslands, arguably with much greater effects, by replacing historical ecosystems, than non-native invasive species [62]. Shifts in tree species composition occurred due to land use change, from a regime of frequent surface fires combined with infrequent overstory disturbance to a regime of fire exclusion combined with chronic overstory disturbance.…”