Boerne Chapter

Driven Up the Wall by Herbivores

Author: Bill Ward

There is an interesting story about the rare Texas snowbell (Styrax platanifolius subsp. texanus) in “Water from Stone” by Jeffrey Greene. That is the book about David and Margaret Bamberger and their Selah Ranch north of Blanco. For many years, David Bamberger has worked tirelessly to increase the number of Texas snowbells by reintroduction into the watersheds of the Nueces and Devil’s Rivers. That is the only area in the world this endangered plant exists in the wild, and most of the wild populations are not growing.

On one trip to search for snowbells in steep-walled creeks off the Nueces River, a member of Bamberger’s snowbell-recovery team made a surprising discovery. Scott Gardner happened onto a large patch of snowbell saplings growing on the floor of a canyon.

This turned out to be the second largest population of Texas snowbells found in the wild. Amazingly, it is not growing on steep cliffs as all previously found snowbells are in that area. And, most significantly, regeneration is taking place at that site.

At the usual snowbell localities in the Nueces watershed, mature flowering snowbells are growing from steep cliffs, and any saplings sprouting from seeds that drop to the canyon floor are eaten by deer. There is no regeneration of the species.

Where Gardner had found this regenerating population, no sheep were kept on the land and anthrax had killed 80% of the deer in the area. Without browsing animals, how many other habitats might the Texas snowbell occupy?

Apparently, there is some debate among botanists about whether certain Hill Country plants are confined to limestone canyons mainly because they require the extra moisture provided by those habitats or mainly because browsing ungulates have eaten them back to the most inaccessible sites.

Jackie Poole, Texas Parks and Wildlife botanist, probably has studied Texas snowbells longer and more thoroughly than anyone. She writes in “Rare Plants of Texas” that snowbells in the Devil’s River watershed show little damage from herbivory. Along the Devil’s River and its tributaries, Texas snowbell grows in several habitats, not just on inaccessible canyon walls as it does in most of the upper Nueces system.

This might make us wonder about some of the local uncommon native plants that seem confined to stream canyons. For example, sycamore-leaf snowbell (Styrax platanifolius subsp. stellatus) in the Boerne area grows hanging out over the rims of steep canyons and creek banks. There are four or five sycamore-leaf snowbells along Cibolo Creek at the Cibolo Nature Center (CNC). Although these little trees flower every spring and produce viable seed, no saplings are taking hold under the mature plants.

Probably the overabundant deer population will never allow sycamore-leaf snowbells to regenerate here. This species seems destined to eventual extinction at the CNC as long as the pressure from browsing deer is so intense. Perhaps it is time for a little assistance from man to avoid this.

From seeds collected nearby on a high bluff over Cibolo Creek, we are growing snowbell seedlings to plant at the CNC. It is hoped that in time, there will be healthy self-perpetuating populations at the nature center.

Growing snowbells will require strong exclosures to keep away the munching critters. With good wire-fence exclosures, we can experiment with several different habitats to see where sycamore-leaf snowbells might be thriving if this area hadn’t suffered through many decades of sheep and goat browsing, followed by the current severe overabundance of deer.

Other local canyon plants that might have a wider distribution if it were not for abundant browsing animals are big red sage (Salvia pentstemonoides) and canyon mockorange (Philadelphus ernestii). We’ve already begun an experiment to see what different habitats at CNC will support big red sage. I’ll keep you posted on the results our endeavors.

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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