"Weed calculator" estimates the landowner costs from invasive plants

Leafy spurge (Euphorbia esula L.)Scientists have developed a compelling tool for helping land managers calculate the economic impact from the invasive weeds on their property.

Matt Rinella, a rangeland ecologist with the Agricultural Research Service has developed a weed impact calculator that tells ranchers the number of additional cows they could raise if they eliminated one or two widespread exotic invasive plants.

The calculator (http://199.133.173.229/WeedImpact/) is based on a computer model that Rinella developed utilizing data from 30 weed scientists to predict invasive plant impacts on forage production. Rinella writes,

"All the rancher needs is a datasheet, a clipboard, a pencil, a yard stick, and homemade sampling frames of any size, rectangular or circular. Ranchers can download datasheets for recording weeds. They tally weeds in each frame, grouping them by their heights. The necessary data can be gathered in about 30 minutes.

When the numbers are entered into the calculator, the ranchers learn how many pounds of weed they are producing per acre and how many more cattle they could raise per acre if those pounds of weeds were replaced by forage plants."

This tool could be particularly useful to conservation extensionists by helping them illustrate to private landowners the financial benefits of controlling invasive weeds on their property.

Currently the tool can be used for spotted knapweed and leafy spurge - two of the worst invasive plants in North America. However, Rinella hopes to expand the use of calculator to numerous other species.

To add other weeds to the calculator, we would need to integrate information on the plant's impact per unit density - i.e. how the abundance of desirable plants declines as weed density increases.

This information is likely already available for other well-studied invasive species, so one would expect that more weeds will be added to the calculator application in the near future.

The calculator can also be used to come up with estimates on the economic impacts of invasive weeds on livestock production. For example, Rinella estimated that if leafy spurge were eliminate from the western U.S., ranchers in the region could graze an additional 200,000 more cows per year.

--Rob Goldstein