Cross Timbers Research Natural Area, 
LBJ National Grassland, Texas
Don Bragg
Jan 25, 2005
Ed-- Here are a couple pictures and some materials that ENTS members may be interested in... These pictures were taken on January 21, 2005 at the Cross Timbers Research Natural Area of the LBJ National Grassland just north of Decatur, Texas. Most of the RNA is encompass by a small valley with an intermittent stream carving a narrow gorge through the weakly cemented sandstone and conglomerates common to the area.  The site is relatively atypical for older Cross Timbers sites, as the deep sands that cover the uplands are level and rarely rocky.  The area receives approximately 28 inches of precipitation per year, and high evapotranspiration makes the site droughthier than it may otherwise seem.

Vegetation is dominated in the higher, drier portions of the RNA by mature post oaks with a scattering of blackjack oak and several other hardwood species.  Eastern redcedar is becoming invasive over much of the area, and is starting to dominate in the lower, moister slopes currently occupied by a mixture of elm, Nuttall oak, and post oak.  Most of the area has been cutover and grazed, and the Forest Service is attempting to reintroduce fire to the stands.  A scattering of old, gnarly post oaks 150 to 300 years old can still be found.  

The first picture is of Dan Griffin, a student working for Dr. David Stahle of the University of Arkansas, coring one of the old post oaks (probably a 300+ year old tree). 

xtimbers01a.jpg (103282 bytes) xtimbers02a.jpg (112166 bytes)

The second image is of a younger post oak (probably ~ 150 years old) more commonly found in the RNA. These old post oaks, while relatively short (less than 60 feet tall) and not very large in diameter (1 to 2 feet DBH) are often impressively old, with some individuals exceeding 300 years old.  

Dr. Stahle has found other post oaks in other Cross Timbers stands that exceed 400 years, and eastern redcedars on some protected bluff sites have exceeded 600 years old. 

Don **************************************************************

Don C. Bragg, Ph.D. Research Forester 
USDA Forest Service, 
Southern Research Station 
P.O. Box 3516  UAM 
Monticello, AR 71656 
http://www.srs.fs.fed.us/4106/