(web version revised August 2005)

Figure 2. Leafy spurge was sighted in Park County as early as 1925
and is now in every county in Montana.

Figure 3. Common tansy and other invasive weeds spread along waterways.
Noxious weeds are spread along hiking trails by hikers and pets.

Figure 4. Seeds are transported along highways and railways.

Noxious weeds
cause the loss of wildlife habitat

Figure 5. Deer and elk populations are common to Montana's native
landscapes. Noxious weeds destroy wildlife habitat.

Montanans enjoy large and diverse wildlife populations (Figure 6). Dense infestations of noxious weeds have major impacts on ecological conditions that support the existence of wildlife.

noxious weeds reduce wildlife forage

noxious weeds alter thermal and escape cover

noxious weeds change water flow and availability to wildlife

noxious weeds may reduce territorial space necessary for wildlife survival

Areas dominated by leafy spurge receive three times less use by deer and four times less use by bison compared with similar uninfested areas. On native bunchgrass sites in Montana, dense spotted knapweed populations reduce available winter forage for elk by 50 to 90 percent. Elk use increased almost four times after dense spotted knapweed infestations were controlled on these sites. On wetlands, invasions of purple loosestrife and saltcedar degrade habitat for furbearing animals and waterfowl. In the intermountain west, medusahead and cheatgrass invasions have increased the frequency of fires and reduced native shrub communities important for wildlife winter habitat.

Noxious weeds
displace threatened and endangered species

Rare species are vulnerable to the environmental changes caused by infestations of noxious weeds. In California, many endangered plant species are threatened by noxious weeds. In Montana, they pose large risks to many rare species, such as Sapphire rockcress, Missoula phlox, and Ute ladies'-tresses.

Noxious weeds
alter the functioning of riparian areas

Figure 6. Healthy riparian areas provide habitat for endangered species,
wildlife and fish.

Riparian areas are the green zones along rivers and streams and around potholes, springs, bogs, lakes, and ponds (Figure 6). They are some of the most productive ecosystems in the West, with a great diversity of plant and wildlife species. Healthy riparian systems purify water by removing sediment as it moves through vegetation. Streambank erosion is prevented as riparian vegetation absorbs and dissipates the energy of flood waters. They also provide critical habitat for wildlife and fish.

Invasive weed species, such as purple loosestrife, can be extremely competitive in a riparian setting. Invasive weeds crowd out valuable native species by forming solid stands. Noxious weeds can alter the hydrologic cycles of riparian areas. For example, saltcedar, which has invaded wetlands and riparian areas throughout the United States, uses large quantities of water and traps more sediment than native species. This weed lowers water tables and, in some areas, has eliminated surface water and native vegetation needed buy wildlife. Saltcedar infestations alter the shape of waterways, affecting carrying capacities and flooding cycles.

Noxious weeds
reduce forage production for livestock and crop production

Agriculture is the largest industry in Montana. Livestock production, especially beef cattle, is a major contributor to our agricultural economy. Leafy spurge and spotted knapweed can render many range sites useless for cattle production by displacing valuable forage. Grazing capacities for livestock can be reduced 65 to 90 percent from the original productivity. In 1994, knapweeds alone cost Montanans $14 million. If spotted knapweed is allowed to continue to spread to the fullest extent of its range, it will cost Montana's agricultural industry $155 million each year. Currently, weeds cost farmers over $100 million each year in expenses and cro production losses in Montana.

Noxious weeds
displace native plant species

Figure 7. Noxious weed monocultures fill al lniches for soil nutrients and
water and choke out most native plants.

Noxious weeds outcompete most native plants for soil, nutrients, and water. In Glacier National Park, spotted knapweed reduced the frequency of six native species and totally eliminated seven other rare and uncommon native species in a three-year period. On native, intact Idaho fescue/bluebunch wheatgrass rangelaneds, each additional spotted knapweed plant reduced the number of Idaho fescue stems by five. On a mixed-grass prairie, most native species were absent where leafy spurge was most abundant. Eleven native species were found adjacent to a dense leafy spurge infestation, but only three native species remained inside the infestation. The invasion of our rangelands by noxious weeds poses a serious threat to the conservation of native plant communities.

Figure 8. Healthy plant comunities include diverse species with root
systems occupying all niches for aoil nutrients and water.

Noxious weeds
lower plant diversity

Plant diversity is needed to maintain healthy plant communities that resist weed invasion. Many noxious weeds, such as Russian knapweed, leafy spurge, and spotted knapweed, reduce plant diversity of native rangeland. For example, as spotted knapweed increases, biodiversity decreases. Plant diversity is needed to maintain the ecological integrity of the habitat, provide resistance to weed invasion and preserve genetic material necessary to adapt to long-term changing environmental facotrs, such as elevated carbon dioxide levels or changes in temperature or moisture patterns.

Noxious weeds
change the way a plant community works

Each plant community has evolved certain ways to cycle nutrients, cycle water, capture energy from sunlight, and store energy in a form useable by animals. Noxious weeds alter the way these processes work. By increasing surface erosion, noxious weeds cause a loss of organic matter and nutrients that are normally concentrated in the surface soil layers. These nutrients necessary for growth are gone forever from the ecosystem. The removal of organic matter also reduces infiltration capacity, thereby making water less available for plants. Because many noxious weeds have relatively sparse plant canopies, more water evaporates from the soil surface, which makes even less moisture available for desirable plant growth.

Noxious weeds
increase soil erosion and soil sedimentation

Protecting and conserving the surface soil are critical to the long-term sustainability of healthy, functioning ecosystems. Soil provides nutrients and moisture necessary for plant growth. When spotted knapweed invades rangeland dominated by native bunchgrass, protection of soil and water resources is compromised. In one study, runoff was 1.5 times higher and sediment yield was three times higher on spotted knapweed-dominated plots than on plots dominated by the native bluebunch wheatgrass. Loss of soil because of noxious weeds may have very serious consequences in the future.

Noxious weeds
affect recreational value and uses

Montana's environment provides a wide range of recreational opportunities. Fishing, hunting, hiking, backpacking, camping, horseback riding, and off-road vehicle recreation are all important to the lifestyle of Montanans. For most recreationists, the enjoyment of being outdoors is diminished in areas dominated by noxious weeds. For example, hikers in the Beartrap Recreational Area along the Madison River often express the need to control spotted knapweed along the river. Riding horseback through houndstongue promotes husbandry problems for horses when seeds attach to the hide. The invasion of spiny weeds, such as Canada thistle and musk thistle, limits river access, and the sharp spines make walking difficult.

Noxious weeds that displace non-game wildlife lower the quality of the outdoor experience for many recreationists. Loss of habitat for game animals and fish decreases success of hunters and anglers. This reduces the value of areas used by recreationists.

Noxious weeds
can reduce the value of land

Noxious weed infestations have reduced the appraised value of land in Oregon. On one $2 million recreational land transaction, the purchase price was reduced by $200,000 because of the level of sulfur cinquefoil infestation. Noxious weeds may not have a major effect on land values in western Montana because buyers may be "paying for the view", but real estate licensees are seeing more potential buyers scrutinize weed infestation and management practices before closing. On production-oriented land, noxious weeds are usually considered in land appraisals. In one analysis, the presence of a noxious weed that reduces carrying capacity by 60% lowered the value of the land fro the original $220 to $100 per acre.

Noxious weeds
cost Montanans millions of dollars every year

Figure 11. Wildlife habitat value decreases as noxious weed infestations increase.

Noxious weeds have a substantial impact on the economy and may cause job losses. Unfortunately, the economic impact of noxious weeds is poorly understood. It has been estimated that the economic impact of leafy spurge in Montana, North Dakota, South Dakota, and Wyoming totals $129.5 million each year and may result in the loss of 1,433 jobs. In Montana alone, spotted knapweed is estimated to cost $42 million each year. This could support about 500 jobs. If this weed is allowd to expand to its fullest range, it could cost Montanans over $155 million each year.

Currently, all weeds cost farmers over $100 million each year in expenses and crop production losses in Montana alone. Degraded wildlife habitat also reduces wildlife-associated recreational expenditures in most states. Their secondary impact on the economy is unknown, but likely range between $200 and $300 million each year.

SUMMARY

Noxious weeds are invasive plants that require immediate attention because of their impacts on the ecology and economy of Montana. These weeds are spreading rapidly. Many scientists believe that if the spread continues at its current rate, noxious weeds will dominate much of our rangelands and forests in a few decades. Noxious weeds outcompete and displace most native plants. This lowers plant and animal diversity essential to a healthy native ecosystem. Their invasion changes the way ecosystems work and degrades habitat for native wildlife and fish. Noxious weeds also affect threatened and endangered species. Some weeds increase soil erosion and stream sedimentation that threatens long-term sustainability of land. Noxious weeds cost the agricultural industry millions of dollars each year in forage and crop losses. It will take all Montanans working together to protect our state from the invasion and spread of noxious weeds.