Yaupon Management for Habitat Improvement in the Post Oak Savannah

A substantial and increasing amount of rural land in the Post Oak Savannah region in Texas is (or is becoming) dense oak forest with an even denser woody understory of predominantly yaupon. The picture on the right shows what it looks like at the ground level in these forests. The ground is covered with leaf litter and quite open for the bottom few feet. This provides almost no food value for wildlife. It is so open at ground level, it is not even good cover for animals as their predators can see right through it. The ground looks like this because almost no sunlight is making it to the ground. The lack of ground-level solar energy means that even most insects (and the small animals that prey on them) struggle to survive.  A recent study has shown that "thicketization" of oak forest even reduces groundwater recharge to almost nothing.

One might argue that this is the natural state of land when human management (interference) is removed, but this is not the case. In earlier times, when bison roamed the area, there were periods of intense grazing and frequent wildfires. Wildfires and bison would reduce the oak forests and suppress the woody growth dramatically while favoring a diverse mix of tall grasses (mostly little bluestem) and forbs. 

Modern people have greatly altered the land, reducing its habitat value for all kinds of wildlife, mostly for good agricultural reasons. However, an emerging trend is to let an increasing amount of land fall out of agricultural use. Unfortunately, as discussed above, just “letting the land go” does not return it to high-quality habitat. We cannot return to the wildfires and roaming herds of bison of past years, but we can do much to improve the habitat quality of our post oak savannah forests by using proper active management. 

The goals of good management should be to: greatly reduce the woody understory, moderately reduce the forest density, and encourage diverse mix of native grasses and forbs to grow in open areas and under the trees. The following discusses how to do this in the Post Oak Savannah region of Texas, but much of what is described can be applied to other forest areas with a dense woody  understory. 

This stage consists of using special forestry mulching equipment to mulch the woody understory. This is the most expensive stage and costs (in 2022) about $1,200 per acre actually mulched. We mulched about 75% of the project area, leaving strips and clusters that hopefully will be reduced over the years by prescribed fire. In a project with TPWD funding, mulching can only be conducted between July 1st and December 31st to avoid any possible overlap with the Houston Toad breeding season. 

The goal of the mulching is to clear the woody understory just to the level that a UTV can drive over it.  

The mulching work at the Nature Preserve was done by Shuffield Land Clearing, Cameron, Tx, (254)-482-0697.  They did a great job and have established an excellent reputation on numerous projects for local landowners and government agencies.

Yaupon will re-sprout denser than before if it is just mulched. Re-sprouts must be properly treated with a Triclopyr (Remedy) herbicide mix. This should be done in May through September after the year in which the mulching was done. For smaller projects an individual plant treatment (IPT) process is practical and preferred. For larger projects a broadcast treatment is more practical.  However, the determination of an herbicide mix and application schedule (1 or 2 applications) is an ongoing process. The mix discussed below was used in our project, but it only top-killed much of the yaupon. This still knocked down almost all the yaupon, allowing substantial growth of native grasses and forbs and setting the stage for a future successful prescribed burn.  

Mix: 10% Triclopyr, 90% diesel and blue dye as needed 

Application: about 2.6 oz of mix per plant applied to stems at the rate of 100 plants per labor hour. A diesel compatible sprayer must be used. 

Cost: at 300 stems per acre this will take about 6 gallons of mix per acre. At this rate the mix will cost >$65 per acre. You may have much more than 300 stems per acre.

Mix: 2.8% Triclopyr, 2.8% Methylated Seed Oil (as a surfactant), 94.4% water, blue dye as needed. Note: This formula gave us a very good top-kill of yaupon  but we estimate that it completely killed about 30%-50% of the yaupon. This formula  caused minimal suppression of forbs and grasses.  There is some thought that a lower percentage of MSO (say only 1%) might be more effective at giving a complete kill. More research is needed in this area.

Application: Broadcast 20 gallons per acre using appropriate broadcast spray equipment. It may be necessary to do a follow-up spraying that targets missed areas as the open, rough terrine of most natural areas makes it very difficult to follow a perfect spay route.

Cost: The chemicals will cost > $48 per acre. (Using a lower percentage of MSO will reduce this somewhat.) Due to the difficulty of our terrain,  chemicals ran about $67 per acre as we applied nearly 28 gallons of mix per acre. Labor is difficult to estimate, but our project achieved about 2.25 acres per labor hour at $125 per hour for labor and equipment. 

Chancey Lewis also did our spraying using the equipment shown. Again, Chancey proved to be very professional and competent carrying out this very difficult task.

IPT, as described above, is almost 100% effective, but everything that is sprayed dies, except rough barked trees. IPT is even effective on large yaupon if sprayed on the trunks. The chemical and labor cost is much higher. IPT is preferred for follow-up and spot treatment. It may be very difficult to contract for a large (> 25 acres) project. 

Broadcast is cheaper per acre, but the process misses a significant number of plants due to shading by other plants and errors in the spray route. A second spot treatment will probably be necessary. Broadcast will kill most other woody brush but may not kill grass and some forbs. Broadcast is only effective on smaller, bushy yaupon - it is not effective applied on the trunks of larger yaupon. 

Once the woody understory is well surpassed and native grasses and forbs are well established it is believed the periodic prescribed burns (every 3-4 years) will maintain diversity and quality of the habitat. On smaller areas periodic shredding will work but habitat diversity may be reduced.