Ecological Restoration and Invasive Species Management

Or, Why We're Cutting Down Trees and Shrubs in Austin Parks

When passers by see Austin Parks Foundation volunteers cutting down trees, they are often alarmed. "We need the shade," they say, "And trees make the park feel natural". It's true, we tell them, but there are times when cutting down specific trees or plants can be good ecologically.

Austin is facing an ecological crisis. Not only is wild land rapidly disappearing because of development, those areas protected as preserves and parks are being overgrown with non-native, invasive plants. At many creek-side areas throughout Austin, including many of our greenbelts including Barton Creek, Shoal Creek, Walnut Creek, and Bull Creek, non-native trees such as Ligustrum and Chinaberry have become the majority of the canopy. These fast-growing, adaptable plants are quite attractive, but they have many negative impacts. Here's a quick overview:

Invasives shade out understory plants, leaving bare dirt that erodes easily or is washed by periodic flooding along creeks.
Invasives grow quickly, out-competing native plants that feed and shelter wildlife.
Invasives produce astronomical quantities of seeds, allowing them to spread rapidly throughout the area.

When volunteers remove the invasive trees, native understory begins to rebound. For example, when Carl Brockman of Natural Texas donated his time and equipment a few years ago to clear an area of Shoal Creek Greenbelt, he revealed a grove of red buds, bald cypress, bois d’ arc, and other trees that had been completely hidden and smothered by invasive plants.

We also have found with recent efforts to remove concentrated thickets of ligustrum (one of the big 3 invasive species in central Texas), native grasses immediately begin sprouting and growing. A good example of this is portions of the Barton Creek Greenbelt Trail including the trailheads at Zilker Park, Spyglass Drive, Loop 360 Access Homedale Drive and Gus Fruh Access.

Invasive trees and plants are really a form of biological pollution. While they may not seem as threatening as smog or a chemical spill, the effects are similiar.

A forestry mower at Pease Park. This very cool machine can bore through a tree, knock it down, and turn it into mulch. The machine is precise enough to allow the user to carefully select which trees to remove. The weight of the machine is very evenly distributed, with the same impact on the soil as a person pushing a wheelbarrow.

We can further restore our ecosystem by replanting some of the diverse species that once grew along Austin area creeks. The foundation gets continuing advice and approval from the Austin Parks and Recreation Dept (especially Rene Barrera, who manages the central and eastern preserves), the Ladybird Johnson Wildflower Center, and APF board members Glee Ingram and Jill Nokes, both native landscape designers.

How We Do It:

First, we remind ourselves that removing invasive trees and plants is a multi-step process, working with both volunteers and professionals. We assume that we'll need to return to check for newly sprouting seeds or new growth on a tree or shrub stump that we thought that we had completely removed.

Second, we want to make sure that we are only removing invasive species. The big three in Austin parks and greenbelts are ligustrum (a multi-trunked evergreen tree) Chinaberry, a tall, fast growing tree with purple spring flowers and fall yellow color) and nandina, a waist high red and green shrub with red berries in the winter. All three are from outside the USA, have no natural enemies and can really take over, out-competing our native plants and trees for sunlight. The biggest issue is that all produce berries that are tasty to our native birds and other wildlife and thus they spread like wildfire. Ligustrum is especially troubling, as its canopy grows so dense, so no grasses or plants grow beneath them, resulting in bare ground. This is bad in greenbelts and along creeks, where the potential for erosion and flood damage increases as a result.

With a little training, volunteers will easily recognize these non-natives and target only those, leaving the natives behind.

Third, when we remove the invasives, we want to remove them roots and all if possible. A weed wrench, as well as picks and sharpshooter shovels are great tools. Weed Wrenches can remove trees and shrubs up to two inches in diameter. For multi-trunked or stemmed plants or trees, such as nandina, a weed wrench can snap off the stems. Often a sharpshooter shovel and pick can be used to dig around the base of the plant, allowing you to dig it up like you might transplant it.

When we removed these plants and trees roots and all, we shake out the soil from the roots and pile them in windrows (long neat piles) parallel to trails or creeks to serve as a natural silt fence as they decay.

If we cannot pull them out roots and all, trees that are too big can be cut at knee height by volunteers, cut up and piled into windrows. We then hire professionals who are certified in chainsaw use and herbicide application to come and cut the stumps flush to the ground and treat the stumps.

Fourth, if the cut and wrenched trees are not needed for windrows, we prefer to turn them into mulch. Again, we hire professionals who operate chippers to do the job.

Fifth, we return several times a year to check for new seedlings or re-sprouting from stumps or maybe a tree or shrub we missed.

Sixth and finally, we work on efforts to replant native grasses, plants and trees, working parks and forestry staff to plan out our efforts. Often, in more natural areas, natives immediately begin to re-sprout from soil that now has sunlight. In some cases, we need to re-plant and we work to ensure that newly planted grasses, plants and trees have the water necessary to survive.

Some of our current ecological restoration projects include:

Zilker Preserve - Volunteer and EcoTexas effort working with the parks dept to remove all invasives from this 60 acre site. 2009 Grant Funded Project.
Bull Creek Greenbelt - Bull Creek Foundation regularly removes invasives.
Shoal Creek Greenbelt - ongoing foundation efforts to remove invasives and replant native species.
Barton Creek Greenbelt - Ongoing Greenbelt Guardians working to remove and treat invasives between Zilker trailhead and Gus Fruh, Separate Austin Parks Foundation funded projects to remove invasives from other portions of the greenbelt including the area near Loop 360 acccess and the Hill of Life.

Some of our completed ecologocial restoration projects include:

Country Club Creek Trail -15 acres of invasives removed by Natural Texas, new trees planted and ongoing efforts to manage bamboo andother resprouting trees. (2007-2008 funded projects)
Red Bud Isle - Large stands of Ligustrum have been removed. (2007 Grant funded project)
Little Stacy Park - Invasives removed and natives replanted. (2007 Grant funded project)
Mayfield Preserve - A combination of volunteers and grant funded American Youthworks E-Corps removed and treated invasives from this 22 acre site surrounding the Mayfield Cottage and Gardens (2008-2009 Grant funded project.)

What You Can Do

Choose native plants when landscaping your property. Visit Austin Grow Green for advice on some great alternatives.
Remove non-native invasives on your property, when possible. You can download a photographic guide here. (Also from Austin Grow Green.)
Educate your friends, neighbors, and favorite plant nursery about non-native plants
Attend a volunteer event to help remove unwanted plants and restore native habitat!

For further information on invasive plant species issues, visit:

Austin's Least Wanted - a very useful presentation by René Barrera, Environmental Conservation Information Specialist for the Austin Nature Preserves System, Natural Resources Division, City of Ausitn Parks and Recreation
Austin Grow Green - plant guides, gardening tips, pest management information, and more.
Texas Invasives Website
Ladybird Johnson Wildflower Center - article about repairing riparian (creekside) areas
Union of Concerned Scientists - Invasive species basics

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