Project looks at social values of removing brush
A study in central Texas is proving the social value of brush control on rangeland.
In recent years it’s become a hot topic, especially in San Antonio, where more than 1.7 million people rely heavily on groundwater from nearby rangeland. The debate is whether removing millions of acres of brush, mostly cedar species, could provide more and better drinking water, and whether this is the right and “natural” thing to do.
Part of the argument depends on whose interpretation of history you read. But it appears the Edwards Plateau, feeding the Edwards Aquifer, was once an oak savanna with Ashe juniper which, so omnipresent today, was mostly confined to steep-sided canyons where then-frequent fires could not reach. Overgrazing and fire suppression helped the juniper expand to typically cover 35% to 50% or more of the land.
Clearing much of that juniper and restoring the oak savanna might offer multiple benefits for agriculture, ecology and cities. Proponents argue it could provide more grazing, help endangered species, and improve water quality, stream flow and aquifer recharge.
Among the arguments made by the brush-loving contingent is that water usage by cedars is not as high as has been claimed.
But a group of conservation and civil agencies is disproving that argument.
The USDA Natural Resources Conservation Service and the U.S. Geological Survey, in cooperation with five other Texas agencies, began such a study in 1999.
That study was based on a previous study conducted from 1991-95 on a 47-acre site on the Seco Creek watershed. It’s in the Honey Creek State Natural Area, a state-owned park currently not grazed.
In the earlier study, about 60% of the Ashe juniper was removed from that watershed. The USGS measured rainfall, stream flow, evapotranspiration and water quality in Seco Creek and the adjacent watershed before and after juniper removal.
In the two years of post-treatment monitoring, stream flow increased about 49,000 gallons per acre each year.
Such promising results indicated need for a repeat of the data and on a larger area.
For the current study, the NRCS selected two adjacent watersheds in the Honey Creek area. Land cover was 40% grassland, 35% Ashe juniper and 20% other woodland species.
On 358 acres, selective cutting removed about 80% of the Ashe juniper from the treatment watershed. The “reference” or control watershed nearby is 230 acres.
The Ashe junipers were cut near ground level with hydraulic tree shears on a skid loader. This method kills the tree with minimal soil disturbance compared with tree dozing. Cut trees were left in place. Ashe juniper was left in ravines and on steep slopes — the niches it may have occupied prior to European settlement.
In this new project, final data won’t be published until late this year or sometime next year, but early indications from measuring instruments show promise of duplicating earlier successes.
For example, stream flow after rainfall seems to be less intense and cleaner. It also seems to last longer and to have greater volume. Evapotranspiration over the grassland is less than over the juniper forest. And groundwater flow from the treatment area is significantly higher than from the forested area.
Once the data from this study is in, it should offer city officials and environmentalists something they’ve never had before: real return value to weigh against the costs of landscape clearing. In other words, someone might be able to figure a cost-return benefit analysis and decide whether to pay thousands of landowners to do such juniper removal.
Read more online at pubs.usgs.gov/ds/2006/200.
This article published in the March, 2010 edition of BEEF PRODUCER.