Polo Field down towards Moore’s Lake overtaken by poison hemlock before treatment in 2020. Photo by Jackson Brooke.
October 5, 2021
By Jackson Brooke, Restoration Technician
As the Restoration Manager at Santa Lucia Conservancy, my department’s goal is to remove invasive species from 500 acres of grassland on the Santa Lucia Preserve each year. Grasslands are essential to a tremendous variety of wildlife including golden eagles, burrowing owls, badgers, coyotes, California tiger salamanders, red-legged frogs, and tri-colored black birds. While grasslands cover only 10% of California’s landscape, they provide habitat for at least 75 federally listed species, as well as 90% of state-listed rare and endemic plants. To recover the natural processes that are vital to the health of our grasslands, we must give native species a chance by removing invasives that threaten to take over.
While our daily work helps us inch toward our grassland restoration work, it can be difficult to gauge how dramatic the impact is. Photography allows us to track the stark change between a field before active management and after, as the invasives disappear to allow for native species to return to the landscape.
In the first part of this photo story series, we focused on hand pulling French broom. This month, we shift our focus to mowing poison hemlock. Hand pulling is a very effective treatment but takes a long time to cover an area. Mowing, on the other hand, allows us to cover ground much faster, but often requires a follow-up treatment as it doesn’t always kill the plant right away unless it is timed perfectly. Luckily, our poison hemlock mowing has been timed very well the past couple of years and we’re seeing large reductions in population size.
1. West Pronghorn Run
BEFORE: When we arrived at the grasslands between West Pronghorn Run and Robinson Canyon Road with our seasonal field crew in the summer of 2020, we noticed that a lot of the weeds were clustered around the trees, particularly the oak pictured above. This was not particularly surprising as many invasives, especially thistles, like to grow within the drip line under the canopy of a tree, where it is cooler and more moist. Under this oak it was almost entirely Italian thistle, milk thistle, and poison hemlock.
AFTER: As summer begins each year, we shift our treatment methods to mowing. By summer, most invasive species are flowering and preparing to set seed, so time is of the essence. Herbicide takes roughly two weeks to kill a plant and hand pulling each individual plant takes a lot of time. Mowing allows us to immediately prevent the plant from setting seed and covers a larger area in a shorter period of time. When we went back to this tree in 2021, we found very few thistles and only a couple of hemlock plants, so our 2020 field crew’s mowing really paid off!
2. Polo Slope
BEFORE: Managing invasive species requires returning to the same areas year after year to continue to build on the progress of the past. Even just one year off can result in a devastating return of the invasive species populations. One reason that invasives take over so quickly is that they can produce incredible numbers of seeds every year, making it imperative that follow up treatments are done annually. The area pictured above, the slope from the Polo Field down towards Moore’s Lake, was overtaken by poison hemlock. It’s been treated by every field crew since the inception of the Grasslands Initiative in 2019. This photo shows 2020 before treatment.
AFTER: Photos like these are particularly striking as they show the dramatic improvements our team makes year over year. A field dominated by poison hemlock in 2020 opened up significantly in 2021. There were still several types of invasives present, including mustard and bull thistle, but the poison hemlock population was greatly reduced. This set of photos really illustrates the difference that our work makes on The Preserve and reminds us of the importance of continued management of invasive species.
This is the second part of our before & after photos series, covering the impact of the invasive species treatments that the Ecological Management Department implements on The Santa Lucia Preserve. If you missed the first part, check it out here!