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Brush Management Most
of the catchment area for the Edwards Aquifer recharge zone lies on the
Edwards Plateau, high in the Hill Country of south central Texas.
When people discuss brush management they almost always end up talking
about the Hill Country in its natural, prehistoric state, and th For more online info regarding the Ashe juniper, see Untwisting the Cedar by Elizabeth McGreevy Seiler.
The interest in brush management as a means to increase water supply is rooted in the belief the area was originally open grasslands and the idea that brush such as cedar and mesquite cause more runoff and less infiltration than grasses. So the theory is that streamflows and Aquifer recharge might be increased by controlling and limiting growth of brush and trees in areas where grasslands would have naturally dominated. There are at least two ways this might happen: 1) removal of brush would mean less interception of rainfall, so there would be more runoff to streams and consequently more recharge; and/or 2) brush clearing would result in more infiltration of rainfall into the ground, thereby causing higher flow in small springs and seeps that feed the recharge streams. Rangeland ecologists I have talked to about this are deeply divided and there is disagreement on very basic issues such as whether cedar increases or decreases runoff. The bottom line is no scientist claims to be able to say for certain that brush clearing would result in more water in the Aquifer. Brush management is one of the options that made the June 2000 draft report of the South Central Texas Regional Water Planning Group, but the document notes that quantity of water in terms of firm yield cannot be determined. Rangeland ecologists do agree that heavy grazing does indeed promote an increased dominance of brush and trees in what was previously grassland. However, all the earliest descriptions of the Hill Country make it abundantly clear the area was not originally an open grassland. In The Explorer's Texas, Del Weniger collected a number of compelling, first-hand, eyewitness accounts of the original condition of the Texas Hill Country when Europeans arrived. The explorer's accounts tell us it was a prairie, cedar-rich and thickety, where tall thin grasses and trees coexisted, where groves and woods mixed with open spaces. There was hardly any of the boot-high, short grasses that predominate today where brush and cedar have been cleared. One of the most reliable eyewitnesses, expert naturalist and landscape designer Frederick Law Olmsted, stated the proportion of grass decreased and trees increased from west to east across the prairies (Olmsted, 1857). This is as expected given the Hill Country is the zone of juncture between the eastern forests and the western grasslands - the area between them which neither can claim. Contributing to the diversity of the prairies was a third great ecoregion to the south, the Gulf Coastal Plain. South central Texas is the only place where all three ecoregions converge, and the various prairies that existed had characteristics of all three. Those who believe the Hill Country was an endless sea of grass have to deal with eyewitness accounts such as one made by C. Hugo Claus about 1875:
By 1860, grazing by domestic livestock and fires set by settlers had already vastly changed the prairie. Many of the trees had been cut and much of the tall grasses had disappeared. The last half of the 19th century was an era of great cutting and burning and saw a well-documented decline of trees under the assault of field-clearers, fence and cabin builders, cedar choppers, charcoal burners, and shingle makers. The modern myth of an open, practically treeless Hill Country where cedars are unnatural invaders developed in the first half of the 20th century, when cedars began reclaiming what had always been theirs. By the middle of the 1900s many were claiming the cedar was not even native, a myth that is common even today. Proof positive that cedars are native can be found in ice age pollen. In the September 1995 issue of Quaternary Research, Stephen Hall and Salvatore Valastro presented a report on the southern great plains vegetation during the last ice age. The Friesenhahn Cave, located in northwest Bexar county, is included in the report as a site that produced juniper pollens dating back to the late ice age.
George Catlin: Elk and Buffalo Making Acquaintance on the Texas Prairie, ca 1834. The essential feature of prairie is that it is a mixture of trees and grasses. The Hill Country in its natural condition was far from being an open grassland.
A study that began in 1991 in the Seco Creek watershed near Hondo involved looking at the effects of removing Ashe juniper. Eighty percent of the cedar canopy was removed from an 8 acre tract, and flows from a nearby spring increased 20%. In a soil water balance study, all regrowth cedar was removed from rangeland in a 40 acre watershed. Three years of data showed an average increase in water yield of around 35,000 gallons per acre per year. The increase in water yield was significant, but it declined over time as grasses and other plants became established where the cedar had been. This suggests that cutting cedar could indeed help increase infiltration of water and increase local springflows, but maintenance would certainly also be required. It is unknown whether increased infiltration produced by cutting cedar on the Edwards Plateau would actually result in more water in the Edwards Aquifer. The Seco Creek project demonstrated that cutting cedar can result in more water infiltrating down into the ground instead of running off the surface into nearby streams. However, these are the streams that carry water to the Edwards recharge zone, so reducing water in those streams could actually result in less recharge after a rain event. On the other hand, in the long run, recharge might increase. This is because when water infiltrates into the ground on the Edwards Plateau, that which is not used by plants can later emerge from nearby springs, or it can travel long distances through the limestone and emerge from water table springs on the Balcones Escarpment (see the cross-sectional view on the Intro page). Both the local springs and the water table springs feed the recharge streams for the Aquifer, and they do it much more slowly than water that ran over the surface instead of moving through the ground, so increasing their baseflow might provide a more reliable and stable flow of water toward the Aquifer's recharge area. The success of the initial study prompted officials to organize two new studies in February of 1999. Both of these will be eight year studies. One involves a 380 acre test plot at the Government Canyon State Natural Area near Helotes in northwest Bexar county, and the other will study a plot at the Honey Creek State Natural Area near Bergheim in eastern Kendall county. These studies have been designed to look more at the quality of runoff water than at the quantity. On Cedar Loving and Hating
Besides the potential for increased recharge, there
are several other reasons some people are in favor of cutting cedar.
Some point to cedar chopping as a tool that will help restore the
hillsides to something more closely
resembling their native condition (the myth of a cedar-less Hill Country
is still pervasive and widely believed). Some point out that eliminating thick stands
produces more grazing for livestock. And some people just flat don't
like cedar because it produces copious amounts of berries and pollen. On the other
hand, there are also
people who really love cedar, so the pro and con
arguments regarding cutting it get tossed around quite a bit. Some worry that since long strips of bark from old-growth
trees are required for nest building by the endangered Golden-cheeked
warbler, cutting cedar won't ensure enough habitat exists to support
healthy populations. Others point out that cedar is a great cover
for wildlife and produces an important food during critical periods.
And some worry that between
the time cedar is cut and other plants start to grow, there could be an increased
potential for flash flooding, erosion, and stream siltation. Both
sides also have counterarguments: numbers of warblers can be increased by
carefully planned programs of prescribed burning and improvements in
cattle grazing systems; reducing cedar would increase diversity of plants
and animals and improve habitat instead of reducing it; recharge might
also be increased by encouraging more cedar and collecting and
channelizing the increased runoff toward the recharge area. Some people really love the graceful, stately appearance of old-growth cedars, which no longer have the squat, bushy appearance that characterizes most cedar trees in the Hill Country today. Old-growth cedars lose their lower, dead branches and develop shaggy, twisting trunks and branches. There is hardly any old-growth cedar left since most of it was mined for charcoal and for building materials in the mid-1800's. A medium-sized old-growth cedar like this one is 200-300 years old. Implementation Issues One thing that's clear is cutting very large areas of second growth cedar to increase infiltration or increase runoff would involve environmental trade-offs. This is always the case when humans take actions that affect the environment. Another thing that's clear is all the issues and ecosystem impacts of cutting cedar have not been fully studied, perhaps not even completely listed. There are plenty of implementation issues that would have to be worked out. The cheapest methods of clearing cedar such as chaining and cabling also remove wildlife habitat and expose surfaces to erosion by wind and water. Low impact, hand techniques are much more expensive. Chemical methods could be employed, but there's a risk they could runoff into streams and affect air quality if they are sprayed. Also, it has not been shown that a large-scale brush control program would be practical because it would require the cooperation of many different landowners having different interests in their property. To have a significant impact on increasing recharge to the Edwards, brush control would have to be practiced over a very large area. Property owners who are not dependent on grazing income might have little interest in brush control. On hunting ranches, owners might actually prefer keeping thick stands of vegetation. |
is essay
will be no different. Some of the most hardened and persistent
modern myths to be found anywhere deal with what this area was like in the
beginning of the historical period. Today, Ashe juniper (cedar) and
other woody species grow thick on the Edwards plateau. Yet, most of
the cedar that covers hillsides today in the Edwards region is regrowth.
Almost all the old-growth cedar in the region was mined for charcoal and
for building materials in the mid-1800's. The thick stands that
exist today have grown up since then.
