Restoring the "Hogwallows".
Imagine you're on a trip through the San Joaquin Valley in California, traveling south down State Highway 43 in southwestern Tulare County. If it's winter, you probably can't see much because the "tule" ground fog is too thick to see even the lines on the highway. If it's summer, the temperature passed the 100-degree mark at 8:30 a.m. But this scrubby, desert environment contains an unusual type of habitat--"hogwallows"--supporting several vulnerable species, including three listed as threatened or endangered by both the State and Federal governments.
The California Department of Fish and Game (CDF&G) recognized the importance of hogwallow habitats to threatened and endangered species as early as the 1970's. The Wildlife Conservation Board, the real estate branch of CDF&G, purchased the first three 160-acre (65-hectare) parcels in the early 1980's. These parcels became the cornerstones of the Allensworth Ecological Reserve. Biologists from CDF&G and The Nature Conservancy developed a Conceptual Acquisition Plan for the reserve in 1989, which sets priorities for the acquisition goal of a 10,000-acre (4,047-ha) area. CDF&G currently owns and manages 4,810 acres (1,945 ha).
Hogwallows, a unique geographical feature of this area, are caused not by the presence of pigs but by the area's natural topography: an undulating terrain with hummocks that can be as much as three feet (0.9 meter) higher than the adjacent swales. The hummocks are an important habitat feature for the animals that live here. Winter rains fill the swales, and water can stand on the clay soils for several weeks. If you are a burrowing animal, you would choose to build your home on a hummock and avoid the winter floods. Burrowing behavior has helped several endangered species--including the San Joaquin kit fox (Vulpes macrotis mutica), Tipton kangaroo rat (Dipodomys nitratoides nitratoides), and blunt-nosed leopard lizard (Gambelia silus)--adapt to the extreme temperatures typical of this environment. All three live in burrows, which are cool in the summer and warm in the winter. These species also restrict their activities to avoid the hottest part of the day.
Also of significance in the Allensworth area is one of the best remaining examples of alkali sink scrub, a natural vegetation community that has been reduced to only two percent of its original range in California. Alkaline soils, which typify this community, are easy to identify because the salts often form a white crust on the surface. The plant species that occur here are adapted to the salty and hot conditions. Characteristic plant species include succulent shrubs such as iodine bush (Allenrolfea occidentalis) and bush seepweed (Suaeda moquinii), as well as salt tolerant grasses such as alkali sacaton (Sporobolus airoides) and saltgrass (Distichlis spicata).
Some habitats now owned by CDF&G at Allensworth Ecological Reserve were disturbed in the past. Under previous owners, experimental agriculture expansion included leveling the hogwallows on several parcels. During the wet winter of 1994-95, sheet flooding was observed on leveled land, confirming the theory that it was unsuitable for burrowing animals. CDF&G has undertaken a program to restore the hogwallow topography on these parcels to enhance their value for threatened and endangered species.
The first step in this program involved a pilot project of 160 acres on previously farmed and leveled land, using earth-moving equipment such as bulldozers to reestablish the hogwallow topography. To begin the process, CDF&G biologist surveyed the project site to identify areas of endangered species activity. The biologists marked areas containing concentrations of active Tipton kangaroo rat and blunt-nosed leopard lizard burrows and surveyed for potential kit fox dens. These efforts were designed to avoid any incidental take of these species during project construction. Through a cooperative agreement, the U.S. Fish and Wildlife Service lent assistance and helped State workers avoid take of the listed species.
The next step was to inspect a nearby parcel containing natural topography to estimate the number of hummocks per acre that occur naturally in the area. The estimate was used to calculate the amount of earth that would need to be moved to restore the hogwallows.
Work began in the winter of 1995-96. The earthmoving equipment operators were instructed to scrape soil from an area and pile it up in a series of random shapes and sizes, mimicking the natural hogwallows. The mounds were constructed a bit taller than natural ones to account for erosion and settling. Conveying this idea to workers who were used to following blueprints road and foundation construction was difficult at first, but once they got the hang of it, they were constructing up to 100 hummocks per day. And they were having fun doing it! Biologists were present on-site throughout construction to monitor compliance with the terms of the CDF&G/FWS agreement. In the end, 655 hummocks were created, and except for the lack of vegetation, the topography looked very natural. Additionally, no take of endangered species occurred. The proof of success, however, is in monitoring species activity on the site.
By the following spring, burrowing animals had already begun to recolonize the area. More San Joaquin pocket mice (Perognathus inornatus), a California Species of Special Concern, were captured on the project site in the spring of 1996 than at any of the natural habitat sites within Allensworth Ecological Reserve. Plant growth also had begun (primarily annual grasses), and in the winter of 1997 almost all of the hummocks were covered with vegetation. Unfortunately, no Tipton kangaroo rats or blunt-nosed leopard lizards were observed on the project site, but very few of these were seen anywhere on the reserve in 1996. It will take several more years to completely evaluate the effectiveness of the project, but so far we consider this first phase a success. We will continue to monitor the site at least annually for species activity.
Phase Two and Beyond
Phase two of the project began in April 1997 and will result in another 160 acres of restored topography. This habitat restoration project is one of several planned at the Allensworth Ecological Reserve. Our goal is to restore the hogwallow topography on all 1,100 acres (445 ha) of the leveled CDF&G owned land. The reserve will serve as a testing area to evaluate the effectiveness of this and other endangered species habitat management tools, such as controlled burning and grazing. We hope that what we learn at the Allensworth Ecological Reserve can be applied to other CDF&G lands containing alkali sink scrub habitats.
The Allensworth Ecological Reserve is open for passive public uses such as hiking, bird watching, and nature study. For more information, please contact the California Department of Fish and Game office in Fresno at (209) 243-4017.
Gail Presley is an Associate Biologist (Wildlife) in the Wildlife Management function of the California Department of Fish and Game in Visalia. Martin Potter is an Associate Biologist (Wildlife) in the Natural Heritage function of the California Department offish and Game in Hanford.
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|Title Annotation:||California central valley|
|Author:||Presley, Gail; Potter, Martin|
|Publication:||Endangered Species Bulletin|
|Date:||Nov 1, 1997|
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