Mowing to Mimic Nature
Published May 7, 2026
Each year when spring arrives and the grasses begin to grow tall throughout the preserves the annual practice of timed mowing occurs in select areas of Midpen preserves. The mowing mimics natural disturbances, such as wildlife grazing and fire, to benefit grassland health and resilience by reducing invasive, non-native plants.
Mowing fast-growing non-native grasses and thistles, which sometimes comprise up to 90 percent of vegetative cover in areas, prior to their seeds becoming viable helps prevent them from further spreading. The timed mowing also gives the native grasses and wildflowers that are often crowded out more resources to grow.
This work has significantly reduced yellow-star thistle at the Hawthorns area of Windy Hill Open Space Preserve. At Rancho San Antonio Open Space Preserve, a series of annual timed-mowing treatments are used to reduce annual grass competition with native plants as well as to reduce vegetation for wildland fire safety. Midpen staff have observed an abundance of the native tar plant (Hemizonia congesta) in areas where the timed mowing occurs. This late-blooming native wildflower provides important resources to numerous native pollinators.