Invasive Brush Plants - Part 6 - Juniper or Cedar

Juniper, also called Texas cedar (Juniperus virginiana) has a few redeeming qualities: 1) it makes good fence posts; 2) we can build things from it and 3) the barred owl roast in them during the day for cover. Nonetheless, for the most part, the cedar is not good in invasive qualities.  Here is a real world example. On the my blog post dated September 11, 2010, there is photo of the American flag in a holder mounted on a juniper stump. The trunk is about 6 inches in diameter and the tree was probably 30 feet tall and sported thick green foliage. The grass under the tree and in its dense shadow never really grew well, didn’t turn deep green and was thin. We cut off the top of the tree in the winter. The following spring the grass around the stump and where its dark shadow used to fall was thick and green like never before.


Thick shade of juniper trees



Regardless of our obversations and the opinions of the county AgriLife agent and biologist, some family and friends are unconvinced that we should remove so much juniper. They feel the trees are pretty and that destroying them is not environmentally appropriate. Therefore, before discussing our methods of juniper removal on Dogwood Ranch, I will review some scientific information provided some folks much smarter than me.  Recall from the post describing the Blackland Prairie vegetation zone that although juniper may be native to the area, before European settlement, the brush was controlled by frequent naturally occurring fires so it did not become invasive.

According to Thomas L. Thurow and Justin W. Hester in their paper “How An Increase or Reduction in Juniper Cover Alters Rangeland Hydrology”, http://texnat.tamu.edu/symposia/juniper/TOM2.htm : “Increased dominance of juniper in what had previously been grasslands or savannas substantially alters the fate of precipitation on rangelands. This has very important ramifications because water is a direct or indirect limiting factor to all aspects of production on semi-arid regions.” Thurow and Hester explain that the increase or decrease of juniper changes the natural hydrologic cycle. You may remember studying the basic hydrologic cycle in 5th grade science class but see the USGS’s diagram as a quick refresher.

Thurow and Hester describe how changes in juniper cover disrupt several processes of the natural hydrologic cycle: interception, infiltration, herbaceous production, evapotranspiration, runoff, deep drainage and erosion.

Interception loss is loss due to interception of rain before hits the ground. Thick juniper canopies intercept the rain drops and reduce the amount of rain that reaches the ground.


Infiltration is the process by which water moves into the soil. Increased infiltration is one cause of increased erosion when juniper invades the range.

Herbaceous production, or growth of other plants such a grass, are often negatively impacted due to juniper-induced reduction in light, soil moisture and nutrients. What we observed unscientifically on Dogwood Ranch, Thurow and Hester describe as follows:



“Juniper is an evergreen with extensive lateral and deep roots, and it has physiological adaptations which enable it to extract water from very dry soil. In addition, juniper also has a dense mat of fibrous roots at the soil surface. These traits make juniper a very strong competitor with grass for water, both underneath the canopy and in the tree interspace. Numerous studies have documented significant reductions in grass production due to increased woody dominance underneath the canopies. . . .When juniper roots grow into the spaces between trees to compete for water and nutrients, this competition, especially when combined with grazing pressure, puts extreme stress on the grass. This can explain why grass in the juniper interspaces may often be sparse, lack vigor and are difficult to reestablish as long as the juniper is present. Another competitive advantage of juniper is that it is not as quickly affected by drought as herbaceous species because the trees have a deep root system which gives them access to a water source that the herbaceous species cannot effectively tap.”

Evapotranspiration consists of evaporation and transpiration. Transpiration is water vapor released in to the atmosphere by plants while evaporation is water vapor released from water sources or the soil into the atmosphere. Although water evaporation is less under the juniper tree due to the thick canopy creating a microenvironment of shade and reduced wind, the increase interception caused by the thick canopy increases evaporation. This is because the water on leaves and branches evaporate quickly before it can be transpired by the plants. More precipitation is lost to evaporation in juniper woodland than grass land. “Juniper has a very extensive rooting system compared to herbaceous plants, and therefore when it invades a site, it has access to a greater volume of soil water. . . .Juniper can continue to remove water from the soil long after grasses have gone into a drought or temperature induced dormancy.

Juniper seems to have little effect on runoff but negatively impacts deep drainage. “The combination of less water entering the soil and strong ability by the juniper to extract water means that little water has a chance to drain beneath the root zone.”

Finally, juniper invasion also can cause increased erosion in the interspace between the trees because the juniper often has out competed the grass and bare soil is exposed.



I hope the above explains why we are aggressing removing juniper from Dogwood Ranch. We hope to improve our chances of restoring the Blackland Prairie grasses with the juniper held closely at bay, if not totally gone. Never fear though, as we will never be able to eliminate all the juniper on Dogwood Ranch by our manual methods. Also, some of the tall old juniper in the woods we will not disturb as the barred owl uses it for cover during the day.