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Grazing Megafauna Return to Jasper Ridge

Goats grazing at Jasper Ridge

As part of a new experiment aimed at reducing fire fuels and controlling invasive species, goats temporarily will be filling the ecological niche of grazing megafauna at Jasper Ridge Biological Preserve at the old Boething nursery site located in the northeastern edge of the preserve. This is part of a larger Stanford University effort to reduce fire-fuels in the area, and provides an opportunity to understand the effects of re-introducing large grazing animals into an ecosystem that evolved with them as a critical component.

Megafauna are animal species whose adults average 100 pounds or more, and up until the 20th century a wide variety of such species were integral for maintaining vegetation structure in ecosystems throughout California, including Jasper Ridge. In Ohlone times, the local megafauna included not only the two species that still use the preserve—black-tail deer and mountain lions­—but also Tule elk, antelope, grizzly bears and black bears.  And before that, going back ten thousand years or more, mammoths, mastodons, horses, camels, and saber-toothed cats were in the mix.

In fact, a rich assemblage of megafauna coevolved with California flora for millions of years. The vegetation influenced where plant-eating megafauna and the carnivores that preyed on them could live, and in turn the megafauna shaped plant distribution and abundance through profligate browsing, grazing, and fertilizing the soils with the waste products of their digestion. When the largest megafauna disappeared with first human contact near the end of the last ice age, the reduced pruning by large animals resulted in increased undergrowth, creating a new normal that persisted until the time of Spanish contact. At that time, domestic livestock including cattle, sheep, goats, and horses replaced most of the native large herbivores, while concurrently many of the large carnivores were eliminated.  The result was overgrazing in many places and introduction of non-native grasses and herbs, once again resetting the stage for what was normal for vegetation composition, abundance, structure, and seasonal growth.

With the cessation of livestock grazing within Jasper Ridge some 50 years ago, yet another “new normal” is emerging. This time the typical situation is characterized by seasonal proliferation of undergrowth—much of it non-native and fire-prone—that the only remaining native mega-herbivores, deer, are incapable of keeping in check given evolutionary constraints on their teeth and digestive system.  

Enter the goats, which essentially act as an ecological analog to long-gone native antelope. Unlike deer, goats and antelope have high-crowned teeth that can withstand the wear that results from eating gritty, abrasive plants, and a digestive system that can handle the tough vegetation. These adaptations mean that he goats can rapidly consume understory that is unpalatable for deer, but if left standing, becomes tinder for wildfires.

While grazing goats clearly reduce wildfire risk, it is still unknown whether they will change vegetation over the long term in areas where they are introduced. To assess this, Jasper Ridge researchers will be carefully monitoring the before-and-after condition of the grazed areas. Among the ongoing studies are qualitative and quantitative assessments of vegetation composition in grazed plots compared to ungrazed ones, and germination experiments to determine if and how seeds in the goat droppings might be expected to favor expansion of certain plant species at the expense of others. The results will be important not only for maintaining ecological health at Jasper Ridge as the future unfolds, but also for understanding how re-introduction of ecological analogues for lost megafauna might be used to enhance the health of ecosystems in general.

Photo and video: Goats working to reduce wildfire risk at Jasper Ridge Biological Preserve.  Note the difference in understory height in the area where the goats are grazing relative to the ungrazed vegetation to the right of the temporary fence.