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Northern Research Station
11 Campus Blvd., Suite 200
Newtown Square, PA 19073
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Forest Disturbance Processes

Forest Vulnerability to Invasion by Exotic Plants

Research Issue

[photo:] Rosa multiflora, one of the most common invasive exotic species found in West Virginia, Ohio, and Pennsylvania closed-canopy forests, though it is rare to find the shrub flowering under the closed-canopy.Forest site conditions resulting from disturbances that increase the probability of invasion by exotic plants need to be better defined for improved risk analyses.  These disturbances include unplanned natural and anthropogenic disturbances, planned forest management, and multiple stressors, such as deer herbivory and insect and pathogen infestations.  We must also be able to evaluate these disturbances within existing forest abiotic and biotic conditions.

 Our Research

We have approached this issue by first simplifying a complex list of possible variables into variables defined by biotic, abiotic, or disturbance factors.  Variables within each category are evaluated against abundance and presence/absence invasive exotic plants as well as all exotic plants.  The most important variables within each category are then evaluated together.  We also haven chosen to evaluate early stages of establishment and spread stages separately.  This is important because the spread stage may reveal site conditions that are products of the invasion rather than characteristics that enabled the invasion.  We also approach this from a gradient analysis perspective as well as incorporating multiple stressors, such as deer herbivory and invasive insect or pathogen outbreaks. Using a sampling design that will detect these early invaders is critical.

Expected Outcomes

We expect disturbance to play a key role in successful early invasions.  However, we also anticipate exotic plants to show a preference for resource-rich sites (i.e., ample water, light, and nutrients), which may or may not be a result of a disturbance.  Because many native species also are more likely to be found on resource-rich sites, we expect to see a correlation with native species richness and establishment of exotic plants.  We predict that there are thresholds of disturbance (and the changes in resources associated with these disturbances) that are more likely to result in invasions.

Research Results

Huebner, C.D., R.S. Morin, A. Zurbriggen, R.L. White, A. Moore, and D. Twardus. 2009. Patterns of exotic plant invasions in Pennsylvania’s Allegheny National Forest using intensive Forest Inventory and Analysis plots. Forest Ecology and Management 257: 258-270.

Huebner, C.D. 2007. Detection and monitoring of invasive exotic plants: A comparison of four sampling methods. Northeastern Naturalist 14(2): 183-206.

Huebner, C.D. and P.C. Tobin.  2006.  Invasibility of mature and 15-year old deciduous forests by exotic plants.  Plant Ecology 186:57-68.

Huebner, C.D. 2003.  Vulnerability of oak-dominated forests in West Virginia to invasive exotic plants:  Temporal and spatial patterns of nine exotic species using herbarium records and land classification data. Castanea 68(1): 1-14.

Research Participants

Principal Investigator

  • Cynthia D. Huebner, Research Botanist/Ecologist, U.S. Forest Service, Northern Research Station

Research Partners

  • Daniel Twardus, U.S. Forest Service, Northern Area, Forest Health State and Private
  • Jim Steinman, U.S. Forest Service, Northern Area, Forest Health State and Private
  • Robert L. White, U.S. Forest Service, Allegheny National Forest

Last Modified: 04/06/2016