PS 46-58 - Landscape and successional influences on plant invader success in a primary successional riparian zone

Wednesday, August 8, 2012
Exhibit Hall, Oregon Convention Center
Sean R. Satterlee, Biology, Youngstown State University, Youngstown, OH, Ian J. Renne, Biological Sciences, Youngstown State University, Youngstown, OH and Thomas P. Diggins, Department of Biological Sciences, Youngstown State University, Youngstown, OH
Background/Question/Methods

The Zoar Valley Canyon of 6th-order Cattaraugus Creek in western New York State contains a pristine riparian zone that encompasses >11 river km and 500 ha of publically protected old- and first-growth hardwood forest, with stand ages from <10 to >300 years. We explore here the roles of disturbance and diversity in invasibility of riparian successional forest at the landscape scale (~100ha). Specifically, we are addressing the following: 1) Does invader success (e.g. bush honeysuckle, multiflora rose, black locust) change over successional time? 2) Are there biotic and/or abiotic stand characteristics associated with recipient community invasibility? 3) What are the influences of Eltonian ecological resistance vs. invasive species access via the river corridor? In addition to distribution/abundance of major invasives, recipient ecosystem variables such as stand age and composition and landform history were quantified on four raised terraces (understory reinitiation/multi-aged), six lower terraces (stem exclusion/understory reinitiation), and seven active channel margins/mid-channel islands/abandoned channels (stand initiation).

Results/Conclusions

Invasives, even black locust, were rarely found on landforms >80 years old (i.e. stand ages >60 years), which may reflect both a successional threshold and/or the historical introduction of the invaders. In contrast, active channel margin and mid-channel island stands <30 years old were extensively invaded, with aerial coverage by bush honeysuckle in particular exceeding 30%. Minimally wooded old channels (40 – 60 years old) were also heavily invaded, whereas mature-forest canopy gaps were not. Multi-aged (150 – 300+ years) stands were uniformly free of invasives, except at very localized natural disturbances such as alluvial fans and seepage-created nascent wetlands, where isolated individual clumps of honeysuckle and multiflora rose have colonized. Results thus far suggest distinct, perhaps even punctuated, changes in invasibility over successional time, with mid- and late-seral stands and their canopy gaps uninvaded. The youngest and most invaded landforms/stands were subject to the highest impact of hydrologic disturbance, whereas the least invaded successional stages actually displayed the highest native species diversity.