The Green Grass Initiative
Friends of Edgewood began the Green Grass Initiative with the goal of restoring Edgewood’s non-native grasslands to their former floral beauty and species diversity by reducing or eliminating weeds and promoting greater cover of native plants.
Finding the Best Restoration Approach
Friends of Edgewood is working with its long-time partner, Creekside Center for Earth Observation, to conduct a multi-year experiment testing methods for removing invasive plants so we can make room for native plants to once again take hold in Edgewood’s grasslands. This project began by surveying and inventorying the grassland species at various locations and analyzing soil conditions and topography to determine which sites might provide the best habitat for experimentation and which native plant species were most promising for future restoration efforts.
Test Plots Hold the Key
In 2021, the first season of treatment, we made 8 test blocks in different locations in the preserve. Each test block contained six test plots (five treatment alternatives and one control plot). Color-coded stakes indicate which plot was getting which treatment. We examined the results of a process called hydromechanical pulverization (HMP), a high-pressure water treatment that destroys above-ground plant matter and creates space for new native plant seedlings. This treatment does not adversely impact native perennials in the treatment plot. You can see how effective HMP is in removing above-ground plant matter without disturbing perennial roots in this short video. We also compared HMP to both a post-germination scrub mowing and a later spring mowing to identify the best treatments to scale up in different areas in future years.
Key to Our Grassland Restoration Test Plots
Native Seeds for Edgewood’s Grasslands
Once we reduced the density of invasive species, we seeded some of the plots with either a native seed mix or “boutique” seeds which have been matched to specific locations based on the soil, moisture, and sun conditions of each test block. The seed mix is purchased from a specialty grower, Hedgerow Farms, and includes native yarrow seeds propagated specifically for Edgewood, along with other wildflowers appropriate for our area. The “boutique” seeds have been hand-collected by Friends of Edgewood volunteers under a special permit from San Mateo County Parks. Plants from some of these seeds are growing at our own Edgewood Farms (near the Day Camp picnic area) so that we can create more seeds to collect for future efforts.
Here are some of the native plants that make up the “boutique” seeds being used in our experiment.
|“Boutique” Seeds Collected at Edgewood
|Clay Mariposa lily
|California oat grass
|Blue wild rye
|Big squirreltail grass
|Heterotheca sessiliflora ssp. echioides
|California canary grass
|Henderson’s shooting star
|Foothill needle grass
|Purple needle grass
|Narrow-leaved mule ears
What Have We Learned?
The first set of treatments began in January 2021. The results from the 2021 growing season showed that the HMP plus seeds treatment was clearly superior. The plots bounded by the blue and yellow stakes saw the greatest increase in number of native species, while the densities of non-native species decreased.
Based on these results, we decided to focus solely on the HMP plus seed treatment for the 2022 growing season. The HMP plus seed treatment was applied in November 2021 at five of the test sites. The plot size was increased from 49 sq. meters to 900 sq. meters per test plot. After recently germinated plants were eliminated using HMP, a seed mix was distributed over the area which was then covered with a thin layer of rice straw, which will keep the seed from being eaten by birds and help retain moisture. In the areas bounded by yellow and pink flags, we added a variety of boutique seeds collected from Edgewood and amplified at Edgewood Farms.
It will take several years to fully evaluate the effects of the treatment experiment. We will be monitoring the new 2022 treatments, as well as the test plots from 2021, and report on our overall findings later in the fall.