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Native Plants are losing the battle

Picture of a native plant community along a roadway
Great Basin sagebrush steppe communities have considerable plant species diversity. A short supply of water and limited nutrients required plants to adapt strategies to capture what is available and hang onto it. These native plant communities are now facing new challenges brought on by invasive weeds. Picture of a cheatgrass monoculture
Invasive weeds have innovative and aggressive survival strategies, but lack natural predators. These weeds injure, overwhelm and out-compete native plants in various ways. This results in the loss of local plant diversity.Image depicting the cheatgrass/fire cycle

The cheatgrass-wildfire cycle reduces the ability of native perennial grasses, forbs, and shrubs to re-establish. Cheatgrass germinates at low temperatures and seedlings mature quickly and gain an advantage over the slower growing native species. This weed also does especially well with more nitrogen…which is released from burned plants and litter. Native perennial seedlings don’t compete well with cheatgrass, and native plants are being resigned to ever shrinking territory.

Many invasive weeds form dense stands that crowd-out native plants. Some species notorious for this include knapweeds, yellow starthistle, Canada thistle, perennial pepperweed, and rush skeletonweed. Through either vegetative spread or prolific seed production, these plants greedily hoard space, water, nutrients, and sunlight. Drawing of a knapweed flowerheadWith each new stem or plant, native plants are confined to fewer and fewer resources until they simply can’t compete.

Some plants have novel weapons that they use against native plant species. Some invasive weeds like Russian and spotted knapweed, release chemicals from roots or accumulate substances in litter that inhibits growth of other plants. This is called allelopathy.

Picture of thick medusahead rye thatch with a hand for scaleMedusahead creates a thick layer of silica-rich litter that breaks down very slowly. Other plants have a tough time growing under the accumulated thatch. Soils under prolonged weed invasion can experience changes that make reintroduction of certain native plants impossible.

Because it is cheaper and more successful, exotic crested wheatgrass is often planted in areas infested with weeds. This practice has indirectly resulted in additional loss of native plant diversity.

Images:
-Native plant diversity:USDA, Agricultural Research Service, Blair L. Waldron.
-Cheatgrass monoculture: Bob Blank.
-Spotted knapweed drawing: Maria Fonnesbeck.
-Thick medusahead thatch: Paul Doescher.
-Sidebar photo: Mike Pellant.

Text references:
-Archer, Amy J. 2001. Taeniatherum caput-medusae. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: (http://www.fs.fed.us/database/feis/, 26 September 2006).
-Entwistle, P.G., A.M. DeBolt, J.H. Kaltenecker, and K. Steenhof, compilers. 2000. Proceedings: Sagebrush Steppe Ecosystems Symposium. Bureau of Land Management Publication No. BLM/ID/PT-001001+1150,Boise, Idaho, USA.
-Pellant,M. 1996. Cheatgrass: the invader that won the west. Unpublished report. On file with: U.S. Department of Agriculture, Forest Service; U.S. Department of Interior, Bureau of Land Management; Interior Columbia Basin Ecosystem Management Project, 112 E. Poplar, Walla Walla, A 99362.
-Young, J.A., and R.A. Evans. 1978. Population dynamics after wildfires in sagebrush grasslands. Journal of Range Management. Vol. 31 No. 4 pp. 283-289.
-Zouhar, Kris 2001. Acroptilon repens. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: (http://www.fs.fed.us/database/feis/, 26 September 2006).