By Bill Ward
Published in The Boerne Star on January 21, 2003
An often-told tale in the Hill Country is the story of the rancher who removed cedar (Ashe juniper) from his land and then found that his long-dried-up springs began to flow again. The intended inference is that junipers suck up so much ground water that when they are removed, the water table will return to its pre-juniper level.
If this actually ever happened, the reasons probably were not so direct as “juniper gone; therefore, springs are back.”
More likely, removal of juniper breaks would have to be followed by restoration of nativie grasses and shrubs before the water table would rise.
Grasses, wildflowers, and woody plants tend to slow down runoff of surface water and encourage infiltration, thus helping to recharge the ground water. I suspect there is little if any scientific evidence that simply killing juniper will do much for the supply of ground water.
The natural integrated system of ground cover, understory woody shrubs, and trees is ideal for promoting infiltration and decreasing runoff. Where such natural systems are disturbed by overgrazing or urbanization, there is bound to be an increase in runoff and decrease in infiltration of rain water.
This leads to two undesirable events:
- Increase in the frequency of floods because of increased runoff and
- Increase in the severity of droughts because of decreased groundwater.
At the last meeting of the Boerne Chapter of the Native Plant Society of Texas, Rufus Stephens, Texas Parks and Wildlife biologist for Kendall and Comal Counties, discussed the role native plants play in regulating the quality of surface water and ground water.
Stephens focused on the importance of the native flora along streams, ponds, and marshes.
In the natural system, a diverse flora of grasses, sedges, reeds, low-flowering plants (wildflowers), woody shrubs, small trees, and large trees grow along the edges of most bodies of surface water.
This diversity is important in stabilizing banks and in maintaining water quality. Trees alone cannot do the job.
It is not only the above-ground foliage that is lost when plant diversity is decreased by human “improvements” or by animal over-browsing. A vast network of root systems also is removed.
A major consequence of reducing vegetative cover and root systems is less infiltration of the rainwater flowing off the land surface. This leads to increased flowing. During the fooding, stream erosion increases, because bank stability had been reduced where plants were removed.
Stephens pointed out that dense root systems are like sponges that soak up large amounts of the infiltered water, which can provide base flow to streams.
Where stream-bank plant diversity is reduced, streams more easily go dry during droughts.
Reduced infiltration also increases the volumes of contaminants that are transported by surface runoff.
Bodies of surface water that are surrounded by diverse native-plant populations are less easily polluted.
One simple way to ameliorate the consequences of destroying water-edge habitats is to fence off much of a stream bank or pond.
Browsing animals could be allowed only limited access to the water body so that a diverse flora could grow along most of the bank.
As long as native-plant diversity in riparian habitats continues to be reduced, those “500-year” floods are likely to keep coming every few years, flood damage will increase, and the dry spells will be drier.
