From Invasive Plants to Native Habitats

As the Center for Urban Ecology continues to grow, we want to work on expanding ecological knowledge and creating habitat. One of the ways we are working towards that goal is by practicing ecological restoration and habitat management at Quinta Mazatlan. We chose what we call “Ebony Grove” as our restoration area for two reasons:

1. Historically, Ebony Grove has mostly been dominated by invasive grass species, making it ideal for figuring out how to control them prior to establishing native plant species. Ebony Grove was not part of the original purchase of Quinta Mazatlan by the City of McAllen in 1998. It was added on as part of the park in 2004, two years prior to Quinta Mazatlan’s grand opening as the McAllen wing of the World Birding Center system in 2006. At that point most of Ebony Grove was dominated by invasive grass species – predominantly Buffelgrass (Cenchrus ciliaris) and Guinea Grass (Megathyrsus maximus) – with an assortment of scattered Honey Mesquite trees (Prosopis glandulosa) and a mixed-species tree line along the eastern edge of the tract (figure 1). This configuration of mostly open habitat, largely covered by invasive species and scattered trees, is quite common in our urban areas. If we can learn how to successfully create wildlife-friendly habitats in these areas at Quinta Mazatlan it would be applicable to many different parts of the Lower Rio Grande Valley.

Figure 1. Aerial image of Ebony Grove in December 2006. Quinta Mazatlan is open to the public, but there are no established trails to Ebony Grove. At this point, roughly half of the land area was covered by invasive grasses (49.0% per historical i-Tree Canopy survey).

2. We want to put the land we have to good use for people and wildlife. As an urban nature center, we firmly believe in the value of green space for city residents and as areas to support the native plants and animals that help maintain a healthy ecosystem. The more patches of green space filled with native plants, whether they are a small private yard or a large public park, the better quality of life in our towns and cities! Quinta Mazatlan could not leave Ebony Grove unused, so in 2014 the Friends of Quinta Mazatlan Board dedicated funding to purchase and plant over 45 Texas Ebony trees (Ebenopsis ebano) in the tract. That first step was followed by generous funding by HEB, Green Mountain Energy, and others to add native plants, a recirculating creek, a solar panel, a pavilion, and palapas. Over the next 5 years, the canopy cover in Ebony Grove increased as a result of these actions (figure 2).

Figure 2. Aerial image of Ebony Grove in December 2019. This is 5 years after the Friends of Quinta Mazatlan purchased and planted over 45 Texas Ebony trees, added a trail, created a pond, installed a recirculating creek, and built a pavilion. Tree canopy increased to 69.0% (up from 50.0% in 2006).

Creating a Wildflower Meadow
Increasing native tree and shrub cover is one part of our restoration efforts in Ebony Grove, but we also want to maintain herbaceous habitats for pollinators and other organisms. That’s why in September 2021 the Center for Urban Ecology began to the process of creating a pollinator meadow across from the pavilion. We chose this area because it is one of the first things visitors see when they enter Ebony Grove, does not have existing tree cover, and already has some native wildflower and grass seeds in its soil. Below is our step-by-step approach to creating our meadow habitat.

Step 1: Control Invasive Species
This is the first and perhaps most important part of the process. Invasive species are so named because they outcompete native species, and because Ebony Grove had been dominated by multiple invasive grass species for decades – in this particular patch Guinea Grass (Megathyrsus maximus), Buffelgrass (Cenchrus ciliaris), and Bermudagrass (Cynodon dactylon) – we needed to have a fresh start. Thanks to the pragmatic advice of the Hub of Prosperity (a sustainable, organic urban farm run by the UTRGV Agroecology Program), we decided to use silage tarps. Silage tarps work by blocking sunlight, retaining moisture, and raising temperatures (even several inches down into the soil) to kill weeds. We had tried silage tarping other parts of Ebony Grove with good results prior to this project.

First, we mowed the patch of existing vegetation. Mowing is a regular practice to maintain wildflower meadows, but in this case we mowed it very short in order to be able to spread the silage tarp (figure 3).

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Figure 3. Before (left) and after (right) photos to document meadow restoration. We mowed the patch in early September, after most of the existing wildflowers and native grasses had completed their bloom period and had already gone to seed.

Immediately after mowing, we spread several cuts of silage tarp to cover the entire 2,800 square foot area, weighing down the tarps with stones (figure 4). We left the area covered for 6 weeks, from September 9, 2021 to October 15, 2021.

Figure 4. Silage tarps in action. When walking by the tarps on a hot day, you can feel the heat emanating from the black surface.

Step 2: Uncover, Assess, and Till
After six weeks, we removed the silage tarps to see how the patch looked. It had successfully controlled over 95% of the invasive species present, leaving nothing but a mulch layer behind. The only species it did not kill (but still negatively impacted) were Bermudagrass and Nutgrass (Cyperus rotundus), so we went in and did light hand-weeding to remove the small amounts of those species left behind. After that it was time to break out the tiller! In early November (after there was some regrowth of invasive species), we tilled the entire plot to further control invasive species and prepare the site for seeding (figure 5).

Figure 5. The tilled plot. We use a rear-tine, dual-rotating tiller. A cold front brought rain that made the soil soft and easy to till.

Step 3: Seeding native plant species
Immediately after tilling, we hand-scattered a native seed mix of the following species: Arizona Cottontop (Digitaria californica), Awnless Bushsunflower (Simsia calva), Cowpen Daisy (Verbesina encelioides), Hooded Windmill Grass (Chloris cucullata), Huisache Daisy (Amblyolepis setigera), Multi-flowered False Rhosegrass (Trichloris pluriflora), Partridge Pea (Chamaecrista fasciculata), Prairie Acacia (Acaciella angustissima), Prostrate Bundleflower (Desmanthus virgatus), Redwhisker Clammyweed (Polanisia dodecandra), Sand Dropseed (Sporobolus cryptandrus), Slender Grama (Bouteloua repens), Upright Prairie Coneflower (Ratibida columnifera), and Whiplash Pappusgrass (Pappophorum vaginatum).

In the same area we have also previously planted (and seen gone to seed): Prairie Milkweed (Asclepias oenotheroides) and Texas Bluebonnet (Lupinus texensis).

Step 4: Establishing the meadow
Over the next few months we will continue to monitor how the meadow progresses and do what we can to help it get established, including watering it and weeding any remaining or regrowing invasive species. Previous meadow restorations showed the need for regular but light weeding of invasive species that germinate from the soil’s seed bank.

We hope you will come out to see how our Ebony Grove restoration projects continue to grow and support the local wildlife. If you are interested in volunteering, please fill out our volunteer registration form and email John Brush (jbrush@mcallen.net) for more information. You can also keep up with what plants and animals are being seen in Ebony Grove on our iNaturalist project, and next time you visit, snap a few photos to add observations of your own!