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Boerne Chapter

Native Plants and the Drought — Some Random Observations

Author: Bill Ward

Everyone complained about the poor crop of wildflowers in the Hill Country last spring, but the lack of wildflowers was expected in the midst of our prolonged drought. No rain, no flowers. However, from my random and non-expert observations, it seems to me the reaction of many native plants to our exceptional dry spell is not necessarily so straightforward.

Last spring, after a year and a half of drought, certain trees and bushes bloomed more profusely than they do during wetter years. For example, the mountain laurels (Sophora secundiflora) in our yard were covered with blooms more than ever before, and now they are heavy with seedpods.

Plant with purple flowers
Correll’s false dragon-head flowering in northern Bexar County.

Some legumes, such as huisache (Acacia farnesiana) and golden-ball lead tree (Leucaena retusa), also had dense flowers last spring. Another tree that bloomed profusely in our part of the Hill Country this year is basswood or linden (Tilia americana). So did the bigtooth maple (Acer grandidentatum). The largest two maples in our yard and many in the canyons just west of Boerne now are laden with brown seedpods.

Even century plants (Agave americana) sent up an unusual number of bloom stalks this year. And at one point during late spring, it seemed this would be the “year of the antelope-horns milkweed (Asclepias asperula).” They were coming up and blooming in greater numbers than usual.

Some of my botanist friends think this profuse flowering by some plants during the severe drought probably is a mechanism for survival of the species. The dry period seems to send a message to some plants that it is time to expend their energy producing abundant seeds to increase the chance that some offspring will survive, even if the drought kills off many individuals.

Even during a drought as prolonged as the current one, many seemingly dry stream beds still hold moisture. These are stream bottoms and banks that have been left undisturbed, and their natural native vegetation has stored moisture in the root masses. Last week, Jason Singhurst (Texas Parks and Wildlife) and I visited a couple of nearby sites where rare plants grow along the banks of now-dry streams.

Northern Bexar County has one of the very few spots in Texas known to grow Correll’s false-dragonhead (Physostegia correllii). We were surprised to see numerous plants thriving and blooming during this second summer of drought, even more than last year. So far, the prolonged drought apparently is not making a dent in the population of that rare plant.

Plant with red flowers
Big red sage bloom stalks are much fewer this year.

In a little canyon west of Boerne, we found a different story for the population of big red sage (Salvia pentstemonoides). We visited the second-largest known population of big red sage in Texas (the largest is also in Kendall County, southeast of Boerne). We counted 107 plants, half of which were very small rosettes. Last year there were many blooming plants at this locality, but after almost two years of drought, now there is only one plant with a bloom stalk. This is significant for a species that numbers less than 350 known plants in Texas (and the Texas Hill Country is the only place they occur in the world).

My friend Delmar Cain posed an interesting question in light of the fact that many Texas native plants apparently have evolved a way of survival by shutting down during the hot, dry summers. He asked, “Are we doing our cultivated native plants a favor by giving them water during the droughts? Is watering causing certain plants to suffer and perhaps die, when leaving them alone might be better for the long-term survival of those plants.”

Probably it depends on the plant, but some plants do seem to decline with irrigation. I can imagine that root hairs, already trying to filter out the excess calcium carbonate dissolved in our soil water, might not welcome a dousing with our alkaline aquifer water. Another good reason for installing rain-catchment tanks.

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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