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Why Do the Exotics Beat the Natives: Where Is the Home-Team Advantage

Experimental disturbance killing native plants facilitates invasion by tall tumblemustard, cheatgrass, lamb's quarters, prickly lettuce, Canada thistle, bull thistle, sweetclover, bulbous bluegrass, and herb Sophia. Forest ServiceSnapshot : New research sets forth a framework for understanding why exotic plants invade and how to fight the invasions

Principal Investigators(s) :
Pearson, Dean E.  
Research Location : West-central Montana, southwestern Turkey, central Argentina
Research Station : Rocky Mountain Research Station (RMRS)
Year : 2012
Highlight ID : 142


Exotic invasive species cause approximately $120 billion in lost revenue, mitigation costs, and infrastructure and resource damage in the United States each year. Natural resource agencies and private land managers expend tremendous efforts to manage such invaders, but progress is slow because we often do not know why these invaders become so successful in their new ranges. The primary reason for this knowledge gap is the lack of comparative studies that examine how these species' behaviors differ between their native and invaded ranges.

The current dogma surrounding invasive species is that they experience population release in the invaded range that results in larger populations and or larger plant sizes because they are released from constraining factors such as insect herbivores, pathogens, or other natural enemies when introduced, and that allows them to outcompete native plants. Remarkably, however, few studies have compared populations between the native and invaded ranges.

In 2010, Forest Service scientists initiated an international collaboration to examine more than 35 species of exotic plants in their native range of Turkey and two invaded ranges, west-central Montana and central Argentina, to understand which species experience population release after invasion and why. Results suggest that, although some exotic plants do appear to become more abundant and larger in the invaded range, suggesting their release from some population limitations, others occur at comparable abundance or reduced abundance in the invaded range. This suggests that the species experience no net change in resistance or experience greater resistance where introduced.

Findings show that identifying and managing for natural sources of biotic resistance can increase natural resistance to invasions at a relatively low cost, while more active managements such as biological, mechanical, or herbicide controls can be improved by directing the appropriate action at the right target species based on understandings of why it is released. This research sets forth a framework for understanding why exotic plants invade and how best to mitigate the undesirable effects of invasions.

Forest Service Partners

External Partners

  • Bitterroot National Forest
  • Adnan Menderes Universitesi, Ayden, Turkey
  • Bureau of Land Management
  • Confederated Salish and Kootenai Tribes
  • La Universidad Nacional de La Pampa, La Pampa, Argentina
  • MPG Ranch, Stevensville, MT
  • Montana Department of Natural Resources and Conservation
  • Rimel Ranch

Program Areas