Soil Ecology and Research Group last update December 23, 2002

Peñasquitos Canyon

Dry lands and deserts are damaged and made less productive by poor management of many kinds, including; overgrazing, over-cutting firewood and timber, inappropriate farming, urbanization, recreational activities, utility corridors, fire suppression, air pollution and the introduction of exotic animals and plants. Although it can be done, damaged dry lands are extremely difficult to restore.

Globally, the most common problem affecting dry lands is overgrazing. The dry lands of the southwestern United States offer a perfect lesson in the perils of persistent overgrazing. Only
1-2% of the western range is in excellent condition while two-thirds of it is in poor to very poor condition. As Costello and Turner wrote in 1941, "The most widespread and cataclysmic change in the desert (of the United States) in modern times has resulted from unrestricted grazing... The desert in many places is one-tenth as productive for wildlife as when white men first came on the scene".

The lands within Los Peñasquitos Canyon Preserve exhibit the classic symptoms of overgrazing. The restoration of these damaged soils and the return of native grasses, flowers and other plants to these degraded areas would improve the beauty, function and biological value of these lands. It would also provide lessons for the restoration of other disturbed arid lands around San Diego County and around the world. This research would be particularly helpful for the other local park and reserve managers at Mission Trails, Tecolote Canyon, Cabrillo National Monument and Torrey Pines State Reserve

The primary problem that appears to delay or prevent the recovery of dry lands is damage to the soil ecosystem. Soil structure and function are degraded and severely damaged. The soil no longer captures rainfall, critical nutrients are missing, soil is compacted and overall recovery is very slow. This proposal addresses the need for research on economical and effective methods of repairing soil structure and function. It will compare the effects of adding different organic materials and nutrients, soil surface shaping and the effect of these treatments on the success of replanting with container plants.

Two highly degraded areas will be selected in the reserve in conjunction with the park rangers. Soil structure and function will be analyzed before the experiment starts and then monitored over the course of the experiment. The treatments will include eight different amendments and application methods, three different fertilizer levels and two surface-shaping methods. After the treatments are completed, weed invasion will be monitored and in the winter of 2001/2002 native species planted in all plots. The plot size and layout will depend upon the sites chosen, but individual treatments will be at least 10 m2 with six replications to provide for statistical power.

Analyses will consist of soil chemistry, soil strength, soil infiltration, weed/native plant composition and container plant survival and growth. Soil amendments used will include compost (from the city landfill) cocoa hulls and a control. Each of these amendments will also be treated with a complete organic fertilizer, a complete chemical fertilizer or a control (no fertilizer). Application of the above will include surface spread, tilled in, or tilled and then surface spread. Surface shaping will include either raked flat or left rough and uneven.

Container plants will be initially grown by the Friends and at the SERG facilities at SDSU and USIU. The species chosen will depend on seed availability, but should include purple needlegrass (Nassella pulchra), blue eyed grass (Sisyrinchium bellum), wild hyacinth (Dichelostemma pulchellum), owl's clover (Castilleja densiflora), shooting stars (Dodecatheon clevelandii) and Mariposa lily (Calochortus splendens). These will be planted in midwinter or early spring depending on rainfall patterns.

Maintenance and monitoring will begin immediately after planting and continue for three years. Collected data will be statistically analyzed to determine significant differences between treatments for both above ground and below ground parameters. Results will be published on both the SERG web page and in a scientific journal for use by others involved in the restoration of dry land communities.