Land Stewardship in a Time of Climate Variability
Habitat Enhancing Land Management
Stressed Red Oak Tree
"Don't think about the entire planet’s problems—you’ll get depressed. Instead, focus on the piece of the earth you can influence.” —Doug Tallamy, Homegrown National Park
Christine Middleton
Read the article below or listen to it narrated by Hays County Master Naturalist Allison Buckner.
It’s been a wild ride! Just thirty days into 2023 the Austin area experienced a tree-ravaging ice storm. Otherwise, very little precipitation—four inches less than normal in the first half of the year and very little more until October. Summer came on with a bang—heat like we have never experienced before. In June, we broke an all-time record heat index when the “feels like'' temperature topped 118 degrees. July 2023 was the hottest ever recorded. And the heat didn’t let up—eleven straight days above 105 degrees Fahrenheit. The heat continued through September and early October with a record-setting high of 100 degrees on October 4th. But by the end of that same month, we’d set a new record low.
While no single crazy weather event can be blamed on climate change, it is important to understand the forces responsible for more volatility in our weather systems. Warmer temperatures produce more evaporation, and a warmer atmosphere holds more moisture. Thus, longer periods of drought followed by heavier than normal rains are almost certainly in the Texas Hill Country’s future. More rain means more heat is released, resulting in stronger winds. And even as overall average temperatures go up, freak winter storms are likely to increase in both frequency and intensity due to an unstable polar vortex.
Plants have suffered along with us. Ice brought down lots of tree limbs and a few trees. Then the combination of heat and drought caused plants to look more stressed than ever—like they were ready to die. Even prickly pear cactus became quite scrawny.
Have you thought about what you can do to make your property more resilient to the vagaries of our changing climate? How you can protect what you have and restore what will be damaged by future weather extremes? How can you insulate yourself and your community from the consequences of future floods, fires, and other disasters exacerbated by a changing climate?
Intense Heat Amplifies Drought
Droughts have always been a part of the climate of Central Texas. Plants experience drought stress when water loss exceeds the ability of the plant’s roots to absorb water. Drought-tolerant plants have a variety of adaptations that enable them to withstand long periods without appreciable rain. We talk about the drought of the 1950s as our benchmark. But evidence shows that in the past 1,200 years there have been at least four local megadroughts that lasted between 15 and 30 years. Much of our native flora evolved by surviving those droughts. Want to know more about how they do it? We explored that topic last August in Hill Country Natives Are Smarter Than You Think (Drought).
One of the main strategies plants use to conserve water is closing small openings on the leaf surface called stomata. These are the openings through which carbon dioxide enters and oxygen and water are expelled. This process is called transpiration. Transpiration also cools the leaves. But when plants close their stomata to conserve water, they lose that cooling effect. This means the plants are even more vulnerable to heat stress. Heat stress occurs when air temperature rises above a certain threshold for a period of time sufficient to cause permanent damage to plant growth and development. Heat stress causes leaves to dry out or curl at the edges. The leaves often turn pale or reddish in color as the green chlorophyll begins to break down.
Heat stress on Red Oak
To protect themselves from adverse circumstances, plants cease growing as they begin moving chlorophyll out of their leaves. When deciduous trees lose their leaves in the fall, we don’t jump to the conclusion they are dying. Rather, we are confident they will recover come springtime. Perhaps we need to extend that optimism to natives that go into summer dormancy. In summer of 2023 many of us lamented that our trees and other vegetation were dying. But as temperatures slowly dropped and even before much fall rain, many native species, such as the Frostweed in the photo, showed distinct signs of recovery. So let’s wait a full season before prematurely declaring a Texas native lost.
Recovering Frostweed
There are simple tests for life you can use on woody vegetation. The easiest is to simply grab hold of a small branch and bend it. If the branch breaks easily, the shrub or small tree may be dead. If the branch is still springy to the touch, there is a good chance the plant will come alive again as soon as conditions become more favorable. The second is a scratch test. Simply use your fingernail or a small knife to scratch a small section of bark on the trunk or a branch. If the tissue underneath is green and moist, the tree or shrub is still alive. If the tissue is brown and dry, the plant may well be dead.
The big question is whether the strategies Central Texas natives evolved for surviving hot dry summers will start to lose their effectiveness as extreme temperatures extend over longer periods. Plants that go into a summer dormancy draw from nutrients stored in their roots once conditions improve. But longer periods of extreme heat are likely to raise soil temperature. This can extend heat stress underground. Slower root growth potentially impairs the plant’s ability to take up water. Extreme heat can alter soil making it harder for plants to access nutrients. So potentially even our hardy natives may find the going just a bit tougher.
Drought Increases Fire Danger
Oak Grove Fire - Hays County - August 2023
Photo: Constance Quigley
Wildfires are not a direct result of climate change. But the severity and rapidity of spread is influenced by more intense drought and stronger winds. Here in Hays County we were reminded of this fact this past August when the Oak Grove fire scorched about 400 acres and destroyed one home. Healthy vegetation contains moisture that helps keep a small brush fire from getting out of control. But when landscapes are fried to a crisp and strong winds are blowing, small brush fires can quickly get out of control.
One tool widely used to understand fire risk is the fuel moisture index. Fuel moisture content is the percent of a given fuel’s weight relative to the weight of water divided by the fuel’s dry weight. So, for example, a green leaf with three times as much water compared to its dry weight would have a fuel moisture content of 300%. By comparison that same leaf after it dies might have a fuel moisture content of 30%.
% Fuel Moisture Content = Water Weight / Oven-dry Fuel Weight X 100
When the moisture content of an area is high, a wildfire has trouble igniting because heat energy is required to drive water from the plants before they begin to burn. That’s why wildfires sometimes stop and burn themselves out when they reach a point where the fuel moisture content of the vegetation is high. But when moisture content is low, heat energy goes directly into the burning flame. Under such conditions, wildfires start easily and spread rapidly.
Thus, what is growing where can make a difference. Some plant species naturally hold more water than others. Some species contain resins, oils or other volatile substances that are more likely to ignite. The amount of vegetation a plant produces is also a factor. Plants that grow close to the ground or that have open structures produce less burnable material. For example, American Beautyberry (Callicarpa americana) will burn less intensely than Texas Sage (Leucophyllum frutescens). On the other hand, Ashe Juniper (Juniperus ashei) saplings or Agarita (Mahonia trifoliate) bushes growing under oaks can be ladder fuel, capable of extending the fire into the tree canopy.
Fear of wildfires does not translate to clearing your entire property of Ashe Juniper, Agarita, or other vegetation. After a wildfire, land will recover on its own. In fact, because our vegetation evolved with fire, the property may well ultimately benefit from the conflagration. But your home and other structures would be much harder and more expensive to replace. So prioritize the “hot ignition zone.” That’s the first 30 feet around your home. If you have dense, woody undergrowth beneath the tree canopy close to a structure, reduce it as much as possible. In its place plant shade tolerant grasses and other perennials, such as frostweed, buckeye, Turks cap, mistflower, and mountain laurel. For more, check out this excellent brochure from the Texas A&M Forest Service entitled Firewise Landscaping in Texas.
Heavier Rains Exacerbate Erosion
Many of us remember the Central Texas flood disasters that punctuated the 2010-2015 drought years. In that short space of time, there were three historic floods: October 2013, May 2015, and October 2015. Flooding has long been a problem in Central Texas. But now with more water in the atmosphere and less vegetation due to more frequent droughts and excessive heat, it is quite possible we will begin seeing one-hundred-year floods become ten-or twenty-year floods. Or even worse.
The rate at which water flows off of a property, even if it is nowhere near a stream, contributes to the intensity of a flood. The topology of a property, combined with the amount and type of vegetation, determines how quickly the runoff joins the floodwaters. Healthy, well vegetated upland areas can delay the flow by a few hours—a function that can be instrumental in reducing the severity of a flood. And even better is the fact that more of the water will soak in and recharge our aquifers. That means there will be more water available to help see us through the next long drought. So it is incumbent on all of us to slow and capture as much of the water flowing across our properties as possible.
Displaced juniper litter is indicative of path and speed of rain runoff.
Heavy rains leave evidence of the path and speed of runoff—grasses laid down, displaced juniper litter such as that in the picture. Erosion is an even clearer indicator that water moved too quickly through a property. Once erosion starts, each heavy rain only makes the problem worse because there are fewer roots to hold the surface. Correcting the problem when it first starts is a lot easier than trying to repair a deep gully. So a good practice is to walk your property after a heavy rain. When you spot an area beginning to erode, look for ways to slow and spread the water. Sometimes the solution is as simple as laying down a few branches, disrupting the flow. Or you can relocate a few rocks to create a small berm. An earlier HELM Network News article, Don’t Go With the Flow, talked in depth about how erosion happens and what you can do about it.
Extreme Temperatures and Drought Take a Toll
Hotter temperatures such as we had this summer were not unexpected. What has surprised us were the colder ones. Both have taken and will continue to take a toll on our plants. Generally, natives have fared much better than non-native nursery plants. But we should expect to lose some native plants and eventually some species will disappear from our part of the Hill Country. Flowering plants are and will continue to bloom earlier and later than they have in the past. And flowers, fruits, and nuts such as the acorn in the picture will sometimes be smaller than normal.
Climate variability also threatens the survival of wildlife that depend on native vegetation. Have you ever heard the term “phenology?” It’s the study of cyclic and seasonal patterns, especially in relation to climate and plant and animal life. Some of the biological responses most sensitive to climate change are phenological events, such as when plants flower or when animals migrate. The risk is that cycles that have evolved together will be thrown out of whack, creating mismatches. Some animal species, particularly generalists (animals that depend on a variety of plants), will switch their allegiance and survive. But the populations of others, particularly specialists (who depend on one particular plant species), are likely to decline. And, as key species decline, the impact could potentially ripple up the food chain.
Monarch butterflies are milkweed specialists. They require milkweed to complete their life cycle. This photo of a migrating monarch depositing an egg on Antelope Horns Milkweed was shot at Jacob’s Well Natural Area in April. When the caterpillars hatch from the egg, they will consume the milkweed leaves. Photo: Betsy Cross
Antelope Horns Milkweed patch at Jacob’s Well Natural Area Photo: Betsy Cross
In Variety is the Spice of Life and That Goes For Plants Too! (Diversity), we discussed why diversity is an essential part of stable, healthy ecosystems. Think about the difference between losing one species out of thirty versus one out of just five. So as our climate becomes more variable, the importance of restoring and maintaining diversity will only increase in importance. But what should you plant? Hard to say. When we’ve asked this question, experts we spoke to all suggested that species that grow just to the west of us are the most likely to survive. The Native Plant Society of Texas has just introduced a great new database, where you can find the range of many of the Texas natives: https://www.npsot.org/resources/native-plants/native-plants-database/
Trees, particularly red oaks, were hit hard by this past summer’s combination of extreme heat and drought. The loss of trees is particularly devastating because trees take decades to reach maturity. Drought stressed oaks, elms, pecans, sycamores, and other trees are particularly susceptible to diseases and other pests. For example, a secondary pathogen, hypoxylon canker, is a fungus that is not aggressive enough to attack healthy trees. But once the fungus invades a weakened tree, it attacks the sapwood, causing the tree to die.
Of concern is the decrease in young trees to replace the dead ones. Sprouts and saplings are being decimated by our hungry out-of-control deer population. Planting trees is something we all should be doing for the next generation. The full range of native trees will continue to be viable if planted in the right spot, watered for the first few years as needed, and protected from deer. Walter Flocke with the Texas A&M Forest Service suggests that “For many species, it may be necessary to find microsites where they [trees] can grow, such as shaded canyons and hillsides, near sheltering trees and shrubs, or in depressions that get extra water.”
Want more help with how you might refine your land management practices to account for the impact of climate change? As part of our HELM (Habitat Enhancing Land Management) program, we will send a team to walk your property and talk about this and other issues related to land stewardship. We are currently taking requests for Spring 2024 HELM visits. So, if you or one of your neighbors would like the HELM team to visit your/their property, simply go to https://www.beautifulhayscounty.org/helm/ and fill out our request form. And please help us spread the word!
Master Naturalists lead a tree planting event at Dripping Springs Ranch Park. Photo: Tom Hausler