Have you ever startled a deer mid-snack or sent a quail fluttering into the brush? In moments like these, the forest comes alive—full of movement, sound, and timeworn routines. They also raise a big question: how do animals respond when their rhythms are disrupted?
At San Vicente Redwoods, a nearly 9,000-acre forest in the Santa Cruz Mountains, we set out to capture that hidden rhythm. That’s why, in 2019, POST partnered with Sempervirens Fund, Save the Redwoods League, and the Land Trust of Santa Cruz County to install dozens of acoustic sensors and trail cameras around the property. Our plan was to collect data before and after a new trail network opened. We hoped to learn how human presence—from footsteps to bike tires—might ripple through local animals’ daily lives.
Then, in 2020, disruption arrived on a far larger scale. The CZU Lightning Complex Fire swept through the forest, reshaping the landscape—and our research along with it.
What began as research into human impacts became an unexpected window into how wildlife adapts, returns, and rebuilds after wildfire. As POST’s Director of Conservation, I see this not as a setback, but as a rare opportunity to learn how animals rebound from disturbance—and how we can design trail systems that better coexist with the forest’s wild residents.
BUT FIRST, A WORD ABOUT WILDFIRES
Wildfires are a natural part of California’s landscapes, and plant and animal species have evolved over millennia to coexist alongside seasonal fires. Some plants you may see in the park have special adaptations to fire. Redwoods, for example, have thick bark that insulates their sensitive inner tissue from heat damage. Others actually rely on the heat from fires to disperse their seeds.
That’s one reason why land managers have for many years carried out prescribed burns on POST properties, including San Vicente Redwoods. Fires that burn in well-managed forests move more slowly and burn at a lower temperature. This makes them less catastrophic than the infernos that rip through dense undergrowth. Animals are less likely to become trapped by flames, while plants are more likely to survive the heat. Some of the most spectacular wildflower blooms follow periods of fire.
HOW WE PIVOTED: MONITORING WILDLIFE AFTER WILDFIRE
Despite the unexpected challenges posed by the wildfire, we wanted to continue our research. An added benefit: we can now use the information we collected to learn how the animals of San Vicente Redwoods are recovering following the fire.
Because the blaze destroyed our equipment, we had to start fresh. We set up a new network of 50 sensors and 50 cameras to coincide with a new system of trails. The array was laid out in a grid pattern, including areas near the trails as well as more remote areas. This setup lets us compare how animals behave close to the trails versus farther away, where human impact should be lessened.
TECHNOLOGY MATTERS
Sending biologists out into the woods risks disrupting animals’ natural behaviors. Plus, our field technicians can’t monitor wildlife at all times. That’s why we settled on tools that remotely identify species and track their movements in the park.
Here’s how it works. The acoustic sensors record bird calls over five-hour intervals each dawn and dusk, while the cameras capture images of mammals who frequent the forest. To the best of our knowledge, we’re among the first to pair acoustic sensors with cameras to follow both birds and mammals.
Here are some of the animals our cameras recorded across San Vicente Redwoods:
WE HAVE DATA, NOW WHAT?
To identify birds in the area, we turned to our partner, Conservation Metrics. Their software analyses the calls and can make a species identification for any bird in North America. For mammals, Wildlife Ecologist Sue Townsend, used a program called Wildlife Insights to capture images, which were then reviewed by our experts.
We analyzed thousands of hours of audio, flagging 61 different species frequenting San Vicente Redwoods during the spring months. This allows us to calculate a value, called the Avian Biodiversity Index (ABI), that tracks changes in bird communities over time. Similarly, we used Wildlife Insights to analyze nearly 2,000 photos and calculate a mammal diversity metric called the Wildlife Picture Index (WPI).
WHAT WE FOUND
As is often the case in scientific research, the results were not as tidy as we expected.
Animals don’t respond uniformly to disturbance; species-level nuance matters.
We anticipated from the outset that wildlife responses to disruptions would not be uniform. Indeed, our findings varied from species to species, with some creatures remaining more sensitive to disturbance and others acclimating over time.
This at least appears to be the case based on the data from our grid sensors. Following the construction of new trails, the diversity of birds in more remote areas increased by about 30 percent compared to areas near the trails. Mammal diversity generally declined across the length of the study period, but had begun to creep upwards again towards the end of the experiment. We didn’t see any noticeable differences between trail areas and more remote areas.
Birds and mammals both respond to changing habitat conditions that follow fire.
When you look at the fire data, bird biodiversity metrics remain somewhat consistent across grid sites until about 2022, when more birds begin appearing in remote areas. Now, it could be that these birds are moving into these areas because of the trails, which crews completed that year. But following a fire, forests undergo a period of regeneration. Early on, quick-growing plants will be the first to show up, and they may dominate for years before slower-growing species like trees and shrubs grow large enough to shade them out. These two states represent very different habitat conditions for birds.
Mammals also seemed to respond to changing conditions following the fire. Smaller species, such as squirrels, chipmunks, and rabbits, declined after the burn. So did larger herbivores like deer. This led to a subsequent decline in their predators, including bobcats, coyotes, mountain lions, and raccoons. But as the forest recovered, WPI measurements began ticking upwards. Animals repopulated the landscape, including some rare species like the American badger and the long-tailed weasel.
San Vicente Redwoods is an ecosystem in flux.
Collectively, what we’re seeing is that the fire seems to have had a much larger impact on animal communities than the trail building did, although the constantly changing conditions in the fire’s aftermath make it difficult to interpret many patterns in the data. It’s not possible to fully tease apart whether it’s the trail building, opening, and use or the regrowth of the forest driving the changes in animal diversity and abundance that we observed, for example. What we’re seeing is an ecosystem in flux, readjusting in the wake of the fire. It will likely be many years before this system reaches a new equilibrium.
WHAT’S AHEAD
Now that we know a bit about wildlife monitoring after wildfire, what’s next? POST and our partners will keep these findings in mind as we move forward. By comparing our results with those of other public lands in the Bay Area, we can also learn more about what makes San Vicente Redwoods unique. It’s not clear, for example, what sorts of animal interactions are influencing the makeup of the community. Is the presence of mountain lions in the area affecting how many coyotes we have, for example? But with the camera trap data, we can start to answer those questions.
As stewards of the land, it’s our job to balance the needs of all of the park’s visitors. We’ll use this information to inform any future stewardship. In addition, we’ll make it a priority to ensure that our trail designs leave enough remote, hiker-free forest for animals to use as a refuge. The chance to view wildlife is a gift, and it’s one that we hope to continue sharing for many years.
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About Post
Peninsula Open Space Trust (POST) protects open space on the Peninsula and in the South Bay for the benefit of all. Since its founding in 1977, POST has been responsible for saving more than 97,000 acres as permanently protected land in San Mateo, Santa Clara and Santa Cruz counties. Learn more
