Management and Conservation
Wildlife conservation is at the heart of the National Wildlife Refuge System. It drives everything on U.S. Fish and Wildlife Service lands and waters managed within the Refuge System, from the purposes for which a national wildlife refuge is established to the recreational activities offered to the resource management tools used. Using conservation best practices, the Refuge System manages Service lands and waters to help ensure the survival of native wildlife species.
The Crosby Wetland Management District administers the management actions for Lake Zahl National Wildlife Refuge, 99 Waterfowl Production Areas, and numerous wetland and grassland conservation easements. The district is part of the Northwest North Dakota Wetland Management District Complex. A project leader oversees the general management of all refuge lands within the complex, and refuge managers are responsible for using habitat management tools to best manage the lands for wildlife.
Livestock Grazing
Herds of bison once grazed the grasslands of this region, greatly influencing the structure and composition of prairie communities. Grassland plants are adapted to disturbances caused by bison and other herbivores grazing, trampling, and depositing feces. As bison herds diminished, the composition of grassland plant and animal species began to change dramatically.
Today, cattle are used to mimic the effects of grazing bison. Grazing, based on the bison model, is now used to maintain a diverse and healthy prairie.
By varying the intensity, frequency, and timing of grazing, Refuge staff can target different plant species (such as invasive cool season grasses), reduce the amount of ground litter, and increase the structural diversity (range of heights and plant forms) of a prairie. This practice can be used to prepare ground for restoration, to increase the attractiveness for ground-nesting migratory birds and waterfowl, and to mimic a time when bison trampled and grazed large expanses of prairie.
Noxious Weed Control
Invasive plants are a persistent threat to the native grassland and wetland ecosystems in North Dakota. The spread of noxious weeds has been difficult and expensive for refuge managers to control.
Canada thistle and leafy spurge are the top two noxious weeds by acreage in the Crosby Wetland Management District. Baby's breath, a popular ornamental plant often used in flower arrangements, is another invasive plant that has spread into the District.
Leafy spurge is perhaps the most difficult to control, requiring treatment beyond prescribed fire and grazing. Current techniques include herbicide application and biological controls.
Prescribed Fire
Historically, the North American prairies were subject to both regular fires caused by lightening and fires used as a hunting tool by Native Americans, in addition to short bursts of intensive grazing as huge herds of bison moved across the plains. Frequent fires maintained native grasslands by preventing most trees and shrubs from becoming well-established.
However, during the 1900's, these fires also destroyed the homes, possessions, and crops of European Americans. These settlers began preventing fires as much as possible, suppressing this natural process for more than 100 years. This allowed shrubs and aspen trees to expand over the prairie landscape, leading to changes in habitat and wildlife communities.
Over the years, changes in wildlife populations and habitat were recognized, and the importance of fire as a management tool became understood.
Fire is an important aspect of prairie restoration and maintenance. Refuge staff use prescribed burning to mimic the effects of natural fires and maintain the health of a prairie. Fire, when used correctly, removes vegetation litter, sets back the succession of invasive cool-season grasses, and stimulates new plant growth.