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We use computer modeling to estimate how much forage goes to livestock,
other uses, and other animals.   What is left we use to calculate how many
deer and elk can be supported.
Wildlife managers that set population objectives for wildlife in Colorado, and the researchers that provide information to the managers, have been hoping for many years to include a strong habitat component. The Colorado Wildlife Habitat Assessment Project has made that possible. Our project uses modeling with computerized maps that include how much food is produced, and how much is needed by animals, to estimate how many elk and deer should be in an area. We do that based on the wildlife's wintering habitat, the time of year when they are most food-stressed. The logic is that if they are provided with adequate forage through the winter, finding enough forage through the other seasons will be easier.

The Northwestern model application area, including most of three HPP committee boundaries.

The forage production map.

One way to understand how the model works is through the spatial data it uses. We will use images from the Northwestern Habitat Assessment Model Application to illustrate. The data include a:

Forage Production Map
The forage production map represents how much vegetation is produced in an area that is suitable for grazing animals. One good source of forage production is from the soils databases produced by the USDA Natural Resource Conservation Service. They use soils to estimate vegetation types on within patches of the land, then estimate the amount of forage produced based on vegetation. They are updating the information as well. We merge databases and make updates when better data are known.

Livestock Offtake Map
Agricultural databases compiled by the federal government based on numbers farmers provide to them give us estimates of livestock by county. Indeed, in some small HPP regions, the number of livestock owners has been small enough for us to simply ask how many animals they had. Regardless, we use the number of livestock (usually cattle and sheep) on an area and estimates of how much forage each animal needs per day to calculate how much each animal needs throughout the entire year. We distribute the livestock and their offtake onto the landscape based on forage production, both reported in databases and as seen from satellite images.

The livestock offtake map.

The winter distribution of elk and deer, combined, shaded in green.
Wildlife Winter Distribution Maps
The Colorado Division of Wildlife creates maps showing the winter distributions of elk, deer, and other wildlife species. HPP committees help us update the maps, if necessary, then we use them in modeling.

With these important layers, plus other information, in place, we then use a spatial modeling process. We subtract from the forage that is available, the forage that livestock will use. We then subtract an amount of forage that should stay on the landscape, to keep the system sustainable. This component of forage is used by small animals, is decomposed to enrich the soil, protects against excessive runoff and flooding, etc. We then remove forage that may be used by other wildlife species, such as pronghorn or wild horses. Lastly, we use whatever forage is left to calculate how many elk and deer may be supported.

There are more details about what we do, such as different levels of forage production based on rainfall and different estimates for elk and deer based on whether managers are risky or conservative, but the general idea has been described. For more detail, you may read a write-up by N.T. Hobbs that describes the general approach. Our manual, provided on the products page provides the most detail. Feel free to contact us if you have further questions.

Last changed: August 5, 2005 Contact us