Boerne Chapter

Sustaining Mother Nature with Native Plants

Douglas W. Tallamy wrote a whole book on what this column has mentioned too briefly and too few times; namely, that growing native plants in your garden concerns a lot more than conserving water. Of course helping sustain Hill Country aquifers is indeed ample justification for us to “grow native,” but native plants in the garden also are helping sustain nature in a time when the wild is disappearing.

Tallamy’s book is “Bringing Nature Home? How You Can Sustain Wildlife with Native Plants.” This 2009 paperback edition is an updated and expanded version of his 2007 first edition. To make his points about biodiversity, alien species, and balanced ecosystems, Tallamy focuses on insects.

Image of black, yellow, and white striped caterpillar munching on a leaf
Monarch larvae survive only on milkweed. Texas milkweed, shown here, is one of the Hill Country milkweeds that feed monarch larvae.

He writes, insects are “the most important herbivores in our suburban ecosystem in terms of passing energy from plants to other animals.” Bugs in native-plant gardens are helping to sustain the ecosystem by supporting a diverse and balanced food web. The same cannot be said about yards landscaped with predominantly exotic plants.

Native insects prefer native plants, because alien plants do not support growth and reproduction of many of our native insects. Imported plants commonly are introduced specifically because they tend to be “pest free.” The invasion of such exotic species into many parts of the country has drastically reduced native insect populations, inevitably leading to seriously imbalanced ecosystems.

Many gardeners prefer “sterile” gardens, free of anything that eats plants. Those gardens do not function as a “dynamic community of interacting organisms, all working smoothly to perpetuate their interactions.” Tallamy believes that a plant that has fed nothing has not done its job in helping sustain a balanced community.

In general, people seem to have a bad opinion of insects. According to Tallamy, only one percent of insects interact with humans in a negative way. The rest are worth billions of dollars to man, because they pollinate plants, enrich and aerate the soil, keep populations of insect herbivores in check, and provide food directly or indirectly to most other animals.

Image of a caterpillar on a leaf
In the Boerne area, caterpillars of spicebush swallowtails eat only spicebush.

The one insect that many people do seem to favor is the butterfly. To have butterflies in our environment, it is necessary to make butterflies. Many different flowering plants, both native and alien can provide nectar, but only certain plants provide larval food to perpetuate the species. This means that butterfly species depend on the certain native plants which their larvae have evolved to eat.

For example, our giant swallowtail lays its eggs on members of the citrus (rue) family. In the Boerne area, wafer ash ((Ptelea trifoliate) and tickle tongue (Zanthoxylum hirsutum) are the host plants for giant swallowtail larvae. These are local native plants easily incorporated into a Hill Country native-plant garden.

Another local example is the spicebush swallowtail, which needs the spicebush (Lindera benzoin) to feed its larvae. Spicebush is another good-looking shrub that can be used to advantage in a home landscape.

After arguing his points about the importance of biodiversity and the dangers of alien vegetation, Tallamy presents chapters on garden design and on trees and shrubs that promote insect diversity. He then describes the characteristics and habits of a number of insects that are prime bird food.

Appendices in the back of this book list information on “native plants with wildlife value and desirable landscaping attributes by region,” “host plants of butterflies and showy moths,” and experimental evidence on the much greater biomass produced by insects feeding on natives compared to those feeding on exotic plants.

The common theme of the various points made in Tallamy’s book is that humans have disrupted the natural habitats in so many ways and in so many places that the future of our nation’s biodiversity is dim unless we share our cities and suburbs with the plants and animals that evolved there. “Because life is fueled by the energy captured from the sun by plants, it will be the plants that we use in our gardens that determine what nature will be like in 10, 20, and 50 years from now.”

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About the Region

New Braunfels, the location of our Fall 2024 Symposium, straddles both the Edwards Plateau Ecoregion and the Blackland Prairie ecoregion. Interstate 35 divides the city of New Braunfels; its path through the city closely parallels the boundary of these two ecoregions, with the Edwards Plateau on the west side and the Blackland Prairies region to the east. The Edwards Plateau area is also called the Hill Country; however, this general term covers a much larger area extending farther north. Spring-fed creeks are found throughout the region; deep limestone canyons, rivers, and lakes (reservoirs) are common. Ashe juniper is perhaps the most common woody species found throughout the region. Additional woody species include various species of oak, with live oak (Quercus fusiformis) being the most common. Sycamores (Platanus occidentalis) and bald cypress (Taxodium distichum) border waterways. This area is well known for its spring wildflower displays, though they may be viewed in spring, late summer, and fall, as well. According to Texas Parks and Wildlife, average annual rainfall in the Edwards Plateau ranges from 15 to 34 inches.

The Blackland Prairie extends from the Red River south to San Antonio, bordered on the west by the Edwards Plateau and the Cross Timbers, and on the east by the Post Oak Savannah. Annual rainfall averages 30 to 40 inches, with higher averages to the east. This region is dominated by prairie species. The most common grass species include little bluestem (Schizachyrium scoparium) and Indian grass (Sorghastrum nutans) in the uplands and switchgrass (Panicum virgatum) in the riparian areas and drainages. Common herbaceous flowering plants include salvias, penstemons, and silphiums. This area has suffered greatly from overgrazing and agricultural use. Few intact areas remain, though many of the plants can be found along county roadsides throughout the region.

Our four host chapters (New Braunfels, Lindheimer, Guadalupe, and the Hill Country chapters) are located in one or both of the ecoregions above. However, the eastern portion of Guadalupe County also falls within the Post Oak Savanna ecoregion. Annual rainfall averages 35 to 45 inches, with higher averages to the east. A wide variety of hardwood trees are found, including several species of oaks, elms, and in the Bastrop area, loblolly pine (Pinus taeda). Grasses and forbs dominate in the open savannas, with most common grass being little bluestem. Ranching, agriculture, and fire suppression have allowed woody species to encroach on the once-open savannas.

Source: Wildflowers of Texas by Michael Eason