Agricultural land-use history increases non-native plant invasion in a southern Appalachian forest a century after abandonment

Land-use history can play a significant role in shaping forest communities. We considered the effects of agricul- tural land-use legacies on the distribution of non-native invasive plants a century after abandonment in a watershed in west- ern North Carolina, USA. Forest sites that were previously in cultivation and abandoned ca. 1905 were compared with nearby reference sites that were never cultivated. The most common invasive plants were Celastrus orbiculatus Thunb., Mi- crostegium vimineum Trin., and Lonicera japonica Thunb. Formerly cultivated sites and plots positioned downslope from roads had the most invasives. Soil cation concentration and pH were positively correlated with invasive presence and abun- dance. Historic agricultural plots where the successional tree Liriodendron tulipifera L. was dominant had the highest soil cation concentrations and soil pH and the greatest abundance of invasive plants. Disentangling the cause-effect relationships between land-use history, the biotic community, and the abiotic template presents a challenge, but understanding the role of land-use legacies may provide important insights regarding the mechanisms underlying the establishment and spread of inva- sive plants in forest ecosystems. Our results suggest that land-use history at Bent Creek may be facilitating plant invasion in- directly by causing a shift in overstory community composition that in turn creates more suitable understory conditions for shade-tolerant invasive plants. Resume : L'utilisation passee des terres peut jouer un role important dans la formation des communautes forestieres. Nous avons examine les effets de l'utilisation passee des terres a des fins agricoles sur la distribution des plantes exotiques invasi- ves, un siecle apres l'abandon de l'agriculture dans un bassin versant le l'ouest de la Caroline du Nord, aux Etats-Unis. Les stations forestieres precedemment cultivees et abandonnees autour de 1905 ont ete comparees a des stations temoins situees a proximite et qui n'ont jamais ete cultivees. Les plantes invasives les plus frequentes etaient Celastrus orbiculatus Thunb., Microstegium vimineum Trin. et Lonicera japonica Thunb. Les stations precedemment cultivees et les parcelles situees en aval d'un chemin avaient la plus grande quantite de plantes invasives. La concentration des cations et le pH du sol etaient positivement correles avec la presence de plantes invasives et leur abondance. Les parcelles jadis occupees par l'agriculture, ou dominait l'espece successionnelle Liriodendron tulipifera L., avaient les plus fortes concentrations de cations dans le sol, le pH du sol le plus eleve et la plus grande abondance de plantes invasives. C'est un defi de demeler les relations de cause a effet entre l'utilisation passee des terres, la communaute biotique et la plate-forme abiotique mais la comprehension du role de l'heritage laisse par l'utilisation des terres peut fournir de precieuses indications concernant les mecanismes sous-ja- cents a l'etablissement et a la propagation des plantes invasives dans les ecosystemes forestiers. Nos resultats indiquent que l'utilisation passee des terres a Bent Creek pourrait indirectement faciliter l'invasion des plantes en provoquant un change- ment dans la composition de la communaute de l'etage dominant qui a son tour cree des conditions plus favorables en sous- bois pour les plantes invasives tolerantes a l'ombre. (Traduit par la Redaction)