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Native Plant Society of Texas

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.