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Science

Rangeland provides habitat for pollinators

Increasing host plants impacts butterfly populations

PORTLAND, Ore. — Food, shelter, connectivity and absence of insecticides are the four general components of pollinator habitat.

“The good news about rangeland is it often has all four components of pollinator habitat,” said Ray Moranz, grazing lands pollinator ecologist for the Xerces Society, as well as the Natural Resources Conservation Service.

Although the amount of rangeland in the United States has decreased, Moranz said, vast amounts still remain.

“There are over 700 million acres, so one of the best things we can do for pollinators is manage our rangelands in the manner that provides them with good habitat,” he said.

The diversity and abundance of insects are decreasing in most places studied, Moranz said during the Monarch Conservation Webinar series.

“Twenty-eight percent of the bumble bee species of North America are considered threatened,” Moranz said. “This is significant because bumble bees are good pollinators.”

Butterflies also are declining in the United States.

“A study in California that includes 45 years of monitoring found butterflies are declining at all sites and in all groups of butterflies in northern California,” Moranz said. “In Ohio, butterfly abundance has declined by 33% over 21 years.”

One of the challenges is butterflies tend to be host plant specialists.

“Monarch caterpillars only feed on milkweeds,” Moranz said.

However, bees do not need host plants when they are young.

“Bees eat pollen and nectar and they are the only pollinators that consume both pollen and nectar,” Moranz said.

About 4,000 species of native bees are in North America.

“Seventy percent of them nest underground, 29% nest in stems and 1% are the bumble bees that tend to nest in cavities,” Moranz said.

In the Great Plains, Moranz said, there is a lot of private and very little public rangeland.

“There are risks of over grazing that can cause highly palatable wildflowers to disappear, the stems bees nest in and butterfly caterpillars live on will be trampled or eaten and livestock can compact the soil,” he said.

However, there are benefits to prescribed grazing.

“It will maintain healthy grass, provide a diversity of habitat for pollinators and promote wildflower diversity,” Moranz said.

Best management practices for prescribed grazing include the importance to allow for plant recovery after grazing and to determine the proper stocking rate.

“The factors differ for proper stocking rate, so you should consult with your local NRCS staff,” Moranz said.

There are vast regions of the Great Plains where prescribed fire is rarely performed, Moranz said.

“In my experience, most of the best pollinator habitat I’ve seen are the ones that are getting burned,” he said.

“Fire has lots of positive aspects on the landscape and the most important one is killing invasive trees,” he said. “Cedar and juniper trees are taking over most of Texas, Oklahoma, Kansas, Nebraska, Iowa and Missouri and if these trees take over we lose many of our grassland pollinators.”

Since fire also kills pollinators, Moranz advises landowners to only burn one-third of their area each year.

“Our hope is by only burning one-third, while you’re causing some negative effects to pollinator populations, you’re improving the habitat dramatically so in following years that burned area gets increased populations of pollinators,” Moranz said.

“Try to burn whenever you can because anytime of the year you burn, you’re going to be helping some species and harming others,” he said. “There are advantages to burning in the winter, there are pollinators helped by burning in the spring and others in the summer.”

After burning a rangeland, the burned vegetation that re-sprouts is green, fresh, highly nutritious and palatable.

“Livestock are attracted to these areas,” Moranz said. “Patch burn grazing is an excellent way to generate habitat heterogeneity.”

A 1,700-acre ranch in southern Oklahoma was invaded by Cedar trees which resulted in the disappearance of wildflowers and a reduction in pollinator populations.

“The NRCS provided funding to bulldoze the trees, prescribed fire was used to burn the trees and that reinvigorated the vegetation,” Moranz said. “With the use of prescribed grazing, hundreds of acres of Monarch habitat was restored in two to three years.”

The Xerces Society and NRCS have developed plant guides that list the best plants in a region for Monarch butterflies.

For more information about the Xerces Society, go to: www.xerces.org.

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