Dry-season grazing with small ruminants enhances native diversity in invaded oak woodlands

Oak woodlands are biodiversity hotspots that provide critical ecosystem
services and hold significant cultural value. However, these ecosystems
are increasingly threatened by invasive grasses, which suppress native
plant diversity, elevate fire risk, and disrupt ecosystem processes. While
targeted grazing is gaining popularity as a management technique for
controlling invasives, the ecological impacts of dry-season grazing are
understudied, as are outcomes for native species. We evaluated the
effectiveness of targeted summer grazing with small ruminants for reducing
invasive grass fuel loads and enhancing plant diversity in oak woodlands
of California by comparing plant species richness and abundance in paired
grazed and ungrazed plots over multiple years. Grazing substantially
increased richness and cover of native forbs. Nonnative cover was
unaffected, though minor increases in nonnative forb numbers were
observed. Ordination analysis revealed that grazing shifted plant
community composition, largely driven by increases in native forb species
and to a lesser extent nonnative forbs. Indicator species analysis
revealed similar patterns, with increases in multiple forb species
detected with grazing, highlighting the potential for grazing to support a
diversity of plant species. These benefits likely stem from reduced thatch
accumulation, improved light availability, and the creation of favorable
microsites for seedling establishment. Practical application: Dry-season
grazing with goats and sheep presents a multi-benefit strategy for land
stewardship, helping to reduce invasive grass thatch, enhance native plant
diversity, and lower fire risk in invaded woodlands. While grazing alone
is unlikely to effectively suppress invasive grasses and may encourage
certain nonnative forbs, it can dramatically improve the ability of native
species to coexist with nonnatives. To maximize benefits, practitioners
should integrate grazing with complementary management strategies when
controlling nonnative plants is a priority. Careful management of grazing
intensity, timing, and duration, coupled with long-term monitoring, will
aid in balancing these ecological trade-offs. Incorporating targeted
dry-season grazing into a broader restoration framework could aid in the
conservation of biodiversity in grass-invaded dryland ecosystems
worldwide.