The concept and the reality of this habitat restoration approach are simple: by arresting the force of erosion, more soil is retained and more water can be retained in the soil. This water is available for animals, plants, germinating seeds, and ultimately trickles down into the aquifer.
The heart of Cuenca los Ojos' (CLO) restoration work started in the San Bernardino Valley in the Madrean Archipelago of northern Sonora, Mexico. From the northwest, the valley collects water from the Chiricahua Mountains in southeastern Arizona and from the Peloncillos Mountains to the northeast. Historically, these waters drained into the San Bernardino Valley and created a rich wetland or cienega that provided vital habitat for resident and migratory species.
In the 1880's the ecology of the borderlands region was severely altered by logging in the Chiricahua Mountains and large-scale cattle operations in the Valley. A detrimental side-effect of these industries was erosion that resulted from the removal of trees and grasses that functioned to hold soil in place and allow rainwater to penetrate into the ground. Years of severe drought further exacerbated the situation. The bare ground caked into a cement-like crust. When the rains finally came water rushed over the impenetrable ground gaining speed and force. Deep cuts opened up in the San Bernardino Valley floor. As the cuts eroded deeper and deeper the wetlands were drained dry.
Before the end of the century the logging operations had closed and by the 1890's there was not enough forage to sustain large cattle numbers. But the forces that cause erosion were already in place; topsoil continued to erode at an alarming rate and subsurface water levels continued to drop.
In the 1960s, gravel was excavated for the construction of Route 2, the main east-west highway of northern Mexico. The mining lowered the level of the Creek, causing the water to flow faster and increase the rate of streambed erosion.
Historical photos and literature document the San Bernardino cienega extending approximately 20 miles north and south and a mile wide at the international border narrowing to a quarter mile wide at the southern end. By 1990, when the founders of CLO, Josiah and Valer Austin first explored northern Sonora, the cienega had been reduced to a fraction of its estimated original size. The Austins came to Sonora with an eye for what could be done to bring the land back to its natural condition. They had extensive experience restoring land just north of the border in the Chiricahua Mountains of Arizona. There, they had seen the beneficial effects of building small rock structures (called trinceras) in the hills to prevent erosion. They also saw changes when they managed the cattle by moving the herd constantly to allow the grasses time to recover from grazing. (for more on this please see about the founders).
Grasslands and Hillsides
In 1999, CLO acquired land in the San Bernardino Valley and began repairing the landscape. They removed cattle and began to put into practice the erosion control methods that they had been using for over 15 years in AZ. In hilly or mountainous areas transected by washes and canyons, CLO sent out teams to construct loose rock structures (trinceras) up hillsides (side bar on trinceras). In the more open grassland areas, CLO brought in heavy machinery to plug the eroding washes by pushing up dirt to form a berm. A series of berms in each wash can capture a lot of water. Both trinceras and berms serve the purpose of slowing down the flow of water (from monsoon rains) over the earth and catching sediment that would otherwise wash away.
Restoration results were tied to rainfall. At first, the ground lay scarred and dormant. However as predicted, when the first significant monsoon rains came, instead of rushing over the landscape and washing topsoil away, rainwater was caught in the loose rock dams that now dotted the hillsides. With each raining season, more and more soil was deposited behind the trinceras and berms. Because the soil below and above the structures remained wet, native grasses could become established. Eventually, once latent seeds began to sprout and a blush of green could be seen extending throughout the valleys and up the sides of hills.
In the open grasslands, the berms collected water, creating seasonal waterholes. These mini-oases provided vital water to the wildlife and allowed water to slowly soak into the ground and replenish the aquifer. After a number of years there was enough water that in some areas there was water year-round. Now, some of these spots are considered permanent water sources. "It is exciting to recreate cienega-like conditions," says Valer Austin.
"Now that we have soil and water back on the land, grass is beginning to appear on the uplands and trees are growing in the riparian areas" says Austin. "Bringing the grasses back is the most significant marker of our work. It speaks to the health of the landscape. Every blade of grass helps bring water back into the soil and every drop of water in the soil means more grass can grow. It has been a learning process. We have been at this for several decades now and are better able to predict what needs to be done to prevent erosion and to bring back the water. We are fortunate to have a great team."
In some areas where erosion was severe (cuts of 10 meters deep), CLO's team built large structures with wire baskets, which they filled with rocks (these structures are called gabions). These structures allowed water to pass through but slowed the force of flow during flood events. Silt and soil was captured behind the permeable wall and accumulated over time. The first year after the large gabions were built was challenging. Torrential rains came and blew out some of the structures. "It was difficult because we were working in the center of the system. There was a lot of room upstream from where water could pick up speed. By the time it reached us it was a real force to be reckoned with," says Austin. Lesser floods would have allowed soil to build up gradually and secure the structures. CLO repaired the structures, which fortunately held through the following seasons. Eventually the gabions became buried and the riverbed was raised. Now each year the gabions are being built higher. Eventually the soil will build up to the point where water can once again run over the surface of the terrain, thus re-forming the wetlands.
The second phase of CLO's habitat restoration work was to reintroduce native grasses and trees. As mentioned earlier, in many areas grasses came naturally, but CLO biologists noticed that some fields lay fallow even after they had been rested and water was available. The earth was too hard for seeds to penetrate. These areas were largely dominated by brush, such as mesquite. CLO brought in a Lawson aerator/seeder to break up the soil and knock back woody species. The large, spiked drums crushed the brush and churned up the rock hard soil. The seeder deposited seeds in the small trenches. As soon as the rains came, the now-familiar blush of green could be seen spreading over the aerated areas.
CLO's restoration team realized that a more aggressive approach of mechanical removal combined with burning and a liquid vegetation control campaign would be more effective. CLO will begin this new 3-pronged approach in 2011. According to Austin: "burning is most effective in eradicating brush when there is enough grass to carry the fire. But in some areas we don't have that kind of fuel load yet, so I think we need to start with a ripper and chemical treatment."
The riparian zones responded very well to CLO's soil stabilization efforts. Trinceras and berms served to catch sediment and slow water over the upland areas and the large gabions worked similarly in the riparian areas. Slower water flows protected the sides of streams and washes from erosion and year-round ground moisture meant that trees could become established along the banks. CLO has strategically planted more than 700 trees every year for the last five years, along stream banks and berms. The water allows the trees to take hold and in turn, the roots help stabilize the soil. "In some areas, things have gotten pretty thick," reflects Austin, "it's tough to get good before and after photos because the after photos are too thick with vegetation you can't tell it's the same place."
CLO manages its montane forests in the Sierra San Luis based on the findings of forest biologists who study the ecological health of the trees, pine cone crop, and evaluate the presence of dead trees which provide important habitat for nesting birds. In addition, they assess the need for fire to reduce fuel load to prevent catastrophic fire which can devastate an entire ecosystem.
"This land and its associated fish and wildlife are recovering from historic abuse and neglect. Yet, even in a degraded state, this land was hugely important and had great potential for recovery. With the ongoing restoration work being accomplished by Cuenca los Ojos, ecosystem repair is now well underway and the benefits to fish, wildlife, and humans have obviously been enhanced beyond what natural processes could have repaired. It is the difference between a raw diamond and a cut and polished diamond. The intrinsic value of this neglected landscape was recognized and refined by CLO."
- Bill Radke, Refuge Manager for San Bernardino National Wildlife Refuge in Arizona.