The 2008 Joint Meeting of the Society for Range Management and the America Forage and Grassland Council.

Tuesday, January 29, 2008 - 2:40 PM

Plant Community Dynamics in the Northern Great Plains - Recognizing the Impacts of Invasive Species

Jeffrey L. Printz and Stan Boltz. USDA Natural Resources Conservation Service, 220 East Rosser Avenue, Bismarck, ND 58502-1458

Since development of ecological site descriptions on the Northern Great Plains (NGP) began in 1999, the question of plant community thresholds has been debated.  NGP native plant communities have been considered very resilient due to their evolution with various disturbance factors including large herds of free-ranging grazing herbivores, frequent fire and periodic drought.  Reduction in fire frequency, the switch from large free-ranging herds to small herds of confined domestic grazing animals and the introduction of exotic plant species has dramatically modified the disturbance regime.

Elimination and/or changes to the frequency of these disturbances has functionally altered the ecological processes and resulted in shifts in plant community composition.  Major reduction in the frequency of wildfires and limited adoption of prescribed fire has resulted in an increase in the shrub component of some ecological sites.  This would include willow species (Salix species.) and quaking aspen (Populus tremuloides) invasion to subirrigated and wet meadow ecological sites in southeastern North Dakota.  In western North Dakota, Rocky Mountain Juniper (Juniperus species) is invading the loamy and clayey ecological sites from adjoining very shallow ecological sites.  In these cases, thresholds are theorized to correlate to shrub size and density.

The introduction of exotic plant species combined with the altered disturbance regime has further compounded the threshold issue and added a greater degree of urgency to this debate. A majority of the ecological sites across the NGP have been invaded to some degree with exotic plant species.  Kentucky bluegrass (Poa pratensis) is the primary species of concern with smooth bromegrass (Bromis inermis), and leafy spurge (Euphorbia esula) further impacting the ecological processes and plant community composition.  A limited amount of research and a considerable amount of anecdotal evidence would seem to support the existence of plant community thresholds in relation to exotic plant species invasion.   


See more of State-and-Transition Models: Triggers, Feedbacks and Thresholds
See more of Symposia

See more of The 2008 Joint Meeting of the Society for Range Management and the American Forage and Grassland Council (January 26 - 31, 2008)