Post Oak Savannah or Post Oak Thicket?

Recently, I visited a nearby ranch that is actively clearing yaupon, elm, and other woody plants from the understory of the post oak woodlands. This landowner understands (at least to a certain extent) the importance of creating an open understory to enhance wildlife habitat. While visiting properties in the Harvey WMA and throughout the Brazos Valley, I’ve realized that there is some confusion about the abundance of woody shrubs and vines that dominate much of the landscape. Some of the comments I hear are, “The thick woods provide cover for the deer, right?”, “Do deer eat yaupon?”, “I don’t want to kill any trees, but I can’t get to most of my property because of all the yaupon.”

Brazos County lies completely within the Post Oak Savannah Ecoregion. Merriam-Webster’s Dictionary defines a savannah as “a temperate grassland with scattered trees (as oaks)”. According to Wikipedia, the term savannah originally came from a Native American word describing "land which is without trees but with much grass either tall or short" and by the late 1800s it was used to mean "land with both grass and trees". It now refers to land with grass and either scattered trees or an open canopy of trees. Savannahs are often a transition between forests and prairies. They support a tremendous number of plant and animal species.

Much of the lands we own and manage in Brazos County today are in a condition much different from the savannahs of 100 years ago. Grasslands dotted with post oaks have been replaced by large blocks of bermuda pastures and dense woodlands. Historically, regularly occurring grass fires and periodic grazing created environmental conditions favorable for the growth of annual forbs and perennial grasses of the savannah ecosystem. When these conditions were altered by fire suppression, introduction of exotic grasses, and year-round grazing by domestic livestock, the process of succession took affect.

Succession is the process in which the same area is successively occupied by different communities over time. Through the process of succession, bare ground [created by strip-mining, land leveling, or river deposited sand bar] will, over the course of tens, hundreds, or thousands of years develop into a stable climax community of perennial [woody] plants and trees. In the absence of fire and periodic grazing, the grassland savannahs of Brazos County and surrounding areas have developed into shrub-woodlands. As a result, bobwhite quail, eastern wild turkey, Houston toad, and other desirable wildlife species have disappeared. A recent study described a post oak savannah site which in the early 1800s documented more than 28 bird species and 300 plant species. In year 2000, after undergoing the same land use changes occurring in the Brazos County area, that same piece of property recorded only 4 bird species and less than 25 plant species.

There is good news! In his 1933 textbook titled Game Management, Aldo Leopold, the father of wildlife management, stated that “…game can be restored by the creative use of the same tools which have heretofore destroyed it - ax, plow, cow, fire, and gun." In other words, activities such as mowing and cutting (ax), disking (plow), grazing (cow), prescribed burning (fire), and/or hunting (gun) can be used to return the yaupon infested woodlots and weed-controlled hay pastures to grasslands with an open canopy of trees.

Although deer and birds will eat leaves, twigs, and berries of yaupon, dense woodlots provide travel corridors for deer movements in a highly fragmented landscape, and some bird and mammal species prefer dense woodlands to an open canopy, overall plant and animal diversity increases with the removal of yaupon, elm, and eastern redcedar from the understory of your wooded properties. Thinning or removing these woody plants will allow more sunlight to reach the ground, promote grass and weed production, and allow for forest regeneration. Additional benefits include decreased erosion and increased ground water re-charge. Remember, except for the creek and river bottoms, your property used to be a savannah which supported hundreds of plant and animal species which are absent from the yaupon crowded woodlots of today.

Stay tuned for recommended methods of removing nuisance understory brush and increasing diversity on your property.