Improving Biodiversity in the Habitat Management Units

Published Nov. 6, 2020
shrub-steppe habitat

Big Flat is one of the Habitat Management Units belonging to the Walla Walla District. It is located about 10 miles upriver from Ice Harbor Dam.

Sprinkler in the distance. Tall grass in the foreground.

The Corps is working to remove irrigation and food plots at Big Flat, to return the habitat to a more natural space.

Praying mantis on a flower

Praying mantis spotted at Yakima Delta Habitat Management Unit.

Habitat Management Units, or HMUs, are different from other parks. While parks are maintained to provide recreational opportunities, HMUs are areas of land dedicated to environmental stewardship.

“The focus of the Corps’ environmental stewardship program is to increase biodiversity or maintain biodiversity. We’re trying to make the habitat most appropriate for all species. That’s birds, reptiles, amphibians, mammals, insects and things that live in the ground,” James Castle, Wildlife Biologist for the Walla Walla District Corps of Engineers, said.

The concept of environmental stewardship has changed over the years. Management strategies were initially developed for HMUs in the 1970s, focusing mainly on hunting and providing habitat for game species.

“It’s a lot of a few things, instead of a few of a lot of things. And that’s where a large shift in the focus in management is starting to occur,” Castle said.

Nowadays, the Corps focuses on reintegrating native plant species and providing more natural habitat that will attract a wide range of native species and allow them to thrive.


Big Flat

Big Flat is one of the Habitat Management Units belonging to the Walla Walla District. It is located about 10 miles upriver from Ice Harbor Dam.

Originally, the area was mainly shrub-steppe habitat, which is to say mostly arid grasslands. To manage for game species, the Corps planted food plots and set up irrigation. Today, Big Flat is still a popular hunting spot, but there are also efforts to improve the habitat. To do this, the Corps is replanting native grasses and shrubs like grey rabbitbrush and milkweed, while cutting back or removing non-native plants.

One non-native plant, which has lately become a nuisance, is the Russian olive tree. 

“We have a contractor that helps us with the management of some of the invasive species,” Castle said. “They remove Russian olive for us, and that’s helping create a more desirable habitat. It creates more diversity for both game and non-game species.”

Breaking up the dense clusters of Russian olive and creating wide-open spaces of grass and low-level shrubs allows animals to travel easier. It also creates a better habitat for ground-nesting birds like quail. Previously, the Corps constructed quail habitat by building artificial nesting structures out of old Christmas trees. Now, quail have plenty of natural grassland and shrub cover in which to make their nests.

“Eventually, we hope to remove irrigation and things that we’re artificially doing to improve the habitat. We want to get it back to nature, but that’s going to take some time to do,” Castle said.

The results are already apparent. Corps officials and public visitors have noticed an increase in the number of different bird and animal species making their homes in the HMU.


Yakima Delta

“The HMUs are consistently working towards improvement. We are doing things to try and maintain the HMUs to a higher level than we originally had. Some of the HMUs, like Yakima Delta, for example, was originally farmed. There are still farm roads that you can see in some of the meadows,” Castle said.

Yakima Delta is an HMU within the city of Richland, on the shore of the Yakima River. Because this HMU is in city limits, there is no hunting allowed, but the HMU still provides habitat for a wide range of birds and animals. The Corps has dramatically improved the habitat over the past couple of years by removing large quantities of Russian olive trees. Because these trees grew too thickly for anything to move through the HMU, the Corps created open meadows in a mosaic pattern to provide movement corridors for wildlife. These open meadows have allowed new species to move into the area.

“We have seen nesting bird populations out here starting to form, so within a year or so we’re probably going to have a nice established habitat out here,” Castle said.

Taking out sections of dense vegetation at this HMU is good for wildlife and people as well. Because Yakima Delta is so close to Richland and other communities, it is crucial to manage the area to reduce fire risk. Opening the space decreases the potential fuel load for fire and allows river access to fire engines that might need it.

River access is also a benefit to anglers and other people seeking to recreate near the Yakima River.

And efforts are still being made to improve habitat. When removing the Russian olive trees, the Corps made woodpiles, just a couple per acre, to create structured habitat for birds, reptiles and small mammals to use as shelter. The Corps also plans to plant willows and cottonwoods along the Yakima River to increase the natural habitat along the riverbank.

Kristen Shacochis-Brown, a biologist for the Walla Walla District, leads a team that performs habitat assessments to determine what improvements to make to structure the habitat for various birds, including the yellow warbler.

“The yellow warbler is not a rare bird. It’s what we call a keystone species,” Shacochis-Brown said. “It’s an indicator that the habitat is doing well. By seeing that bird, we know that we’re going to have habitat for other birds that use a similar type of habitat.”

Yellow warblers have lately been abundant throughout the lower Yakima River, and conditions have only improved.

“There are more birds that are coming in today versus a year ago,” Shacochis-Brown said.

“And it’s a benefit for everybody,” Castle said. “Birdwatchers can come out here now and walk through and spend hours out here. Hikers can come out; people can come out.”


A place for everybody

While Habitat Management Units are not a part of the Corps’ recreation mission, HMUs do provide recreational opportunities. Some HMUs allow hunting and fishing, while others are great for horseback riding, hiking and wildlife watching.

Bird watching is a fairly popular activity at Corps HMUs. In the Tri-Cities area, there are 60 or 70 different species of songbirds. And this doesn’t include all the other types of birds, like pelicans, cranes, geese, owls and hawks.

“We’ve had some rare birds here,” Castle said. “At the Ice Harbor Dam we had a brown pelican show up one year. There’ve only been two reports of brown pelicans ever this far inland in the state of Washington.”

Other rare bird sightings have included a black scoter, an arctic circle bird, and a broad-winged hawk. The broad-winged hawk is found primarily in the eastern half of the continent.

As efforts to improve habitats continue, Corps officials expect to see more and more diversity in the wildlife present at the HMUs.

“It’s important to us that we’re maintaining these so that it’s for the benefit of everybody,” Castle said. “And the work we’re doing on these will move us far into the future.”