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Soil Amendment Study Underway in Winters Putah Creek Nature Park

Wood chips and walnut hulls…flags and cages…things are happening at Winters Putah Creek Nature Park. If you have visited the park in the last few months, you may have wondered about the lumps on the floodplain - raised areas where the soil has been tilled and mixed with other materials. You may have noticed flags of different hues grouped sporadically, like colorful flocks of birds. Or you might have seen a group of boisterous volunteers installing plants and cages in an ongoing effort to revegetate the floodplain. These plantings are part of a soil amendment study to address the problem of soil compaction in some areas of the park.

The goal of the Winters Putah Creek Nature Park restoration project, started in the fall of 2011, is to improve the condition of a highly degraded creek channel and streamside forest, and to reconcile its function to meet the needs of both humans and wildlife alike. This plan involved narrowing the channel, lowering the floodplain to facilitate overbank flooding, and replacing invasive plants with native riparian species. The project, along with others upstream in Putah Creek, has been wildly successful in bringing back salmon to the creek, but has faced challenges regarding the re-establishment and growth of native floodplain vegetation. Some of these challenges include four consecutive years of drought, severe damage to plantings by beaver, and soil compaction. 

To address some of these issues, Rich Marovich and Solano County Water Agency (SCWA), in partnership with soil scientist Michael Hogan and rangeland ecologist Craig Thomsen, have developed a trial to test the effectiveness of different soil amendments in promoting plant growth. Last summer SCWA created the first 17 trial plots, loosening soil to a depth of two feet and mixing in wood chips and walnut hulls. This February, Putah Creek Council staff, SCWA interns, and 52 volunteers came out over the course of six days to install almost 1000 native plants in the test plots, including willows and other trees, California wild rose, white root sedge, and mugwort. Many of the trees and shrubs were also caged to protect them from excessive browsing by beavers. 

Meanwhile on the south banks of the creek, the next phase of test plots is underway. SCWA began by deep planting large diameter cottonwood, willow, and mulefat cuttings, installing them to a depth of eight to ten feet to ensure contact with the water table. New trial plots adjacent to the pole plantings were dug to a similar depth. Here, the effects of planting riparian trees in soils that have been loosened down to the water table and amended in the top two feet will be evaluated. The pole cuttings are already leafing out and it may not be long before a line of fast growing trees and shrubs will be visible from the north bank of Putah Creek!

If you would like to learn more about and be a part of this Winters Putah Creek Nature Park project, check the Putah Creek Council Event Calendar on our website for upcoming volunteer opportunities this spring.

Photos:  Top - SCWA intern Galen Hoshovsky helps a community volunteer cage a box elder, by Amy Williams. Middle - Humphrey Fellows Harum Mukhayer and Kelsey Hutchinson plant California wild rose in the Winters Putah Creek Nature Park amended plots, by Amy Williams. Bottom - Large diameter pole cuttings of willow, cottonwood, and mulefat are beginning to sprout on the south banks of Winters Putah Creek Nature Park, courtesy of SCWA.