Texas A&M Forest Service surveyed the health of bald cypress trees along a 7-mile stretch of the Guadalupe River this summer after a significant decrease in water levels over the last four years.
On May 14, 2019, the middle section of the hydroelectric dam on Lake Dunlap outside of New Braunfels collapsed, releasing a torrent of water that subsequently dropped the level of water in the lake and upstream of the Guadalupe River by 8-10 feet.
In the wider and shallower sections of the lake, as the water retreated from the shoreline toward the river channel, many bald cypress trees were left high and dry with sections of roots that were once underwater exposed to the air. These exposed roots left many shoreline property owners concerned about the health of their bald cypress trees.
This July, over four years later, a replacement dam was completed, and water levels are slowly returning to normal.
“Bald cypress are ancient trees that have been around for millennia,” said Jeff McFall, Texas A&M Forest Service staff forester. “In Central Texas, the bald cypress is, fortunately, adapted to the recurrent periods of extremely dry weather.”
During drought, or times with no water, the trees go into a semidormant state and appear as if they are dying, with leaves browning and falling. However, the trees hold on to water internally. When rain or water returns, many seemingly dead trees come out of dormancy and begin to leaf out again.
The numbers are good
The resiliency of bald cypress trees led foresters to wonder how many trees died during this window with low river levels.
Of the 1,195 trees found in the stretch of the river from the Interstate 35N access bridge to the Lake Dunlap Dam, 88.3% were alive and 11.7% were dead.
“The tally of trees was conducted from the river by kayak,” said McFall. “All bald cypress trees 5 inches in diameter at chest height and larger were tallied.”
Additionally, the survey found no evidence of widespread disease or pest infestation in the trees, though wood borers were present in already dead-standing trees.
“Tree mortality can often be attributed to an accumulation of stressors over time,” said McFall. “However, in this case, the most likely scenario is a significant departure from normal water availability, especially for trees directly along the shoreline with root systems adapted for constant contact with water.”
Of the 159 dead trees, approximately 97% were located in clusters on undeveloped lots or farm and ranch lands that received no supplemental irrigation, and only five were found on property that received landscape irrigation, despite two drought-stricken years.
Texas A&M Forest Service has worked directly with landowners over the past four years, developing irrigation techniques to keep trees alive.
“During dry times, we recommend watering bald cypress at a rate of 0.6 inches per week to simulate an approximate normal annual precipitation for the area,” said McFall. “The goal is to keep the soil lightly moist 6-8 inches deep throughout the critical root zone.”
Plans are underway to dewater downstream Lake McQueeney and Lake Placid in anticipation of construction to replace unsafe and aging dams. With many bald cypress trees in the upcoming dewatered area, these survey results are a glimmer of hope.
“Based on this survey of bald cypress survival, the majority of bald cypress trees located on developed property on Lakes McQueeney and Placid should survive the dewater and dam rebuild process with just a normal amount of landscape water,” said McFall.
For extra protection of trees that were once growing at the edge of water and now have exposed roots, McFall recommends covering newly exposed roots with mulch and keeping the mulch moist with a dripper hose or sprinkler during dry periods.