Recopied with permission - this article was originally published in the

Watershed Management Council Newsletter:

Winter 1992 Volume 4 No. 3

Riparian Systems

by Ronald L. Tiller and Reed Tollefson

TNC, Kern River Preserve

Since 1986, The Nature Conservancy has been involved in the restoration of the Great Valley cottonwood forest along the South Fork of the Kern River. The goals of the project are to supplement existing riparian habitat and to develop techniques for successful restoration of the native riparian system. Restoration of this community should provide additional habitat for a wide assemblage of riparian-dependent wildlife including the state endangered Yellow-billed Cuckoo (Coccyzus americanus) and Willow Flycatcher (Empidonax traillii extimus), and up to 40 other species of special concern.

The research focus of the restoration effort is to determine how site characteristics such as soil texture, electrical conductivity (EC), pH and depth to the water table affect the survival and growth of Fremont cottonwood (Populus fremontii), red willow (Salix laevigata), and mule fat (Baccaris glutinose). These factors are known to have profound effects on plant survival and growth, but specific tolerances are not well documented for these species.

In order to determine or refine thresholds for these species, soil and water samples are taken from 8-10% of the planting holes arranged in a stratified sampling grid. On a 50-acre site, this amounts to 400-500 sample holes, or nearly one sample per 1/10th of an acre. This sampling density is necessary to adequately represent the highly variable site conditions found in the South Fork floodplain and to develop statistically valid sample sizes.

Planting holes are augured to the water table and soil samples are taken at depths of 6 inches, 2 and 4 feet. Soil texture, electrical conductivity and pH are determined from these samples. Groundwater depth, and the EC and pH of the groundwater are also taken. These data are compared with species thresholds gathered from the literature and past trials on the preserve and is used to develop a site map and planting design. Where information is unknown or unavailable for a species (i.e., mule fat), assumptions are made regarding its tolerance. Cottonwood, willow and mule fat saplings are then randomly assigned to the sample holes and their survival and growth are tracked throughout the growing season.

Long-term monitoring of these trees and shrubs will provide important information that will aid in the accurate determination of tolerances for these species to the measured site factors. Adjustments will then be made to future planting designs that will improve the success of future restoration efforts at the preserve. Knowledge gained from monitoring at the Kern River Preserve will have application to similar riparian systems in the southwest and should ultimately lead to more and better habitats for riparian-dependent wildlife.

Reed can be contacted by calling (760) 378-2531 or E-mail