The rolling pastures peppered with shrubs and rock outcroppings along the 405 between Sand Canyon and University are a stark contrast to the usual freeway scenery. This not-so-hidden spot is Quail Hill, a 733-acre area of permanently protected open space that is part of the City of Irvine Open Space Preserve.
Like much of the historic Irvine Ranch, cattle grazed Quail Hill for decades in the twentieth century. Grazing likely transformed the original plant community from one composed of native perennial flowers, grasses, and shrubs to one dominated by annual grasses and other invasive plants. After the cattle left the hills, the invasive artichoke thistle(Cynara cardunculus) has thrived, blanketing the hills around the Quail Hill Loop trail. Originally from Spain, this plant is a wild ancestor of the globe artichoke found in the supermarket.
With the aim of reducing the cover and spread of artichoke thistle at Quail Hill, the Conservancy began a volunteer-led weed removal program in 2008. Armed with this research (and shovels!), Conservancy staff and volunteers have spent more than 1,300 hours battling artichoke thistle and other invasive species at Quail Hill. The key to killing off this weed is attacking the base every 4-6 weeks.
“Studies elsewhere in Orange County found that repeated removal of above-ground plants would gradually deplete carbohydrate resources stored in the artichoke thistle’s long tap root, starving a plant within a few years without the use of herbicide,” says Conservancy Ecologist and Project Manager Riley Pratt, Ph.D. “Similarly, removal experiments established by Irvine Ranch Conservancy on behalf of the City of Irvine are showing that regular, repeated cutting at the base of the plant is very effective.”
In 2013 alone, volunteers spent 68 days removing thistle in Quail Hill, treating a net area of 447,615 square meters and lopping off more than 93,000 thistle rosettes and flower heads. As a result, there have been obvious decreases in the number and density of artichoke thistle every year since the removal campaign began. This year, almost every artichoke thistle in and around the Quail Hill Loop received at least one cut, most received multiple cuts, ensuring no plants will spread seed.
Despite these gains, eliminating artichoke thistle from Quail Hill requires a sustained effort in the coming years. As long-lived perennials, most thistles treated this year will indeed re-sprout next winter. The good news is that with a shrinking thistle population, the fight will be easier each season, freeing up more time to plant native species. You can help bring more wildlife back to Quail Hill -- look for upcoming public volunteer opportunities in Quail Hill by visiting www.LetsGoOutside.org.