CRP Oak Regeneration Study

Oaks ‘n’ Folks – Volume 13, Issue 2 – August, 1998

The federal Conservation Reserve Program (CRP), administered by the Farm Service Agency (FSA) (formerly the Agricultural Stabilization and Conservation Service [ASCS]), was begun in 1985 to conserve and improve natural resources by taking highly erodible cropland out of grazing and crop production for at least 10 years. In California, San Luis Obispo County and southern Monterey County lead in CRP participation, with more than 100,000 acres of privately owned land entered in the program. Much of this land is blue oak or valley oak rangeland. During autumn 1995, I surveyed the effects of the CRP on oak regeneration.

CRP and non-CRP sites for this survey were established on ranches in northern San Luis Obispo and southern Monterey Counties. Criteria for selection were that the ranch was in the oak woodland vegetation type and that ithad been in the CRP for at least 5 years. I identified eight ranches from aerial photographs obtained at the FSA office in San Luis Obispo County. On three of the ranches, a CRP site was compared with a nearby non- CRP site that was similar in tree cover and topography but was grazed by cattle.

At each ranch, I explored the use of two techniques to detect the amount of oak regeneration: (1) strip transects, 25 m long and 6 m wide, established in the four cardinal directions at randomly selected mature oak trees within the CRP and non-CRP sites, and (2) timed searches of the CRP and non-CRP sites.

The number of seedlings found per 120 minutes during timed searches varied from 0 to 299 for three non-CRP sites and from 0 to 150 for nine CRP sites. Both CRP and non-CRP sites generally had a low percentage of tree cover, and the trees were located mainly in riparian areas, along fences,and on steep hillsides. Most seedlings were found within 15 meters of the driplines of mature oak trees. Because of the great variation in seedling counts and the small number of non-CRP sites, no statistically valid comparison of oak regeneration could be made between CRP and non-CRP sites.

This pilot study demonstrated that, of the two seedling sampling techniques used (transects and timed searches), timed searches would be a good wayto evaluate whether retiring lands from grazing under the CRP stimulates oak regeneration. Importantly, this study only preliminarily suggests that oak regeneration is not stimulated on CRP land, probably because of the development of thatch (a mat of undecomposed plant material). During growth,grasses and forbs that comprise thatch compete with oak seedlings for moisture and space. Moreover, once developed, thatch often provides habitat for rodents,especially voles, which may feed on roots or girdle stems of oak seedlings. Both of these factors (increased plant competition and increased rodent populations) may outweigh any benefits to oak regeneration provided by the removal of livestock grazing.

prepared and edited by Richard B. Standiford and Pamela Tinnin