The Mystery of the Monterey Pines: A Stewardship Story

When my colleagues and I set out to steward Burns Valley, a stunning POST-protected parcel of land atop a San Mateo County ridge line, we stumbled upon a curious mystery — and, to be honest, a potential fire hazard. How and when did a thick stand of Monterey pines sprout up next to an emergency fire road, overlooking a sweeping expanse with views of San Gregorio and the Pacific Ocean? Some trees were unhealthy, dead, or overcrowded, with natural debris amassing up to a foot high on the forest floor. As land stewards, we asked ourselves: how can we restore ecological balance while ensuring the landscape remains safe for wildlife and local communities?

FOSTERING A RESILIENT FOREST

Our main goal was clear: to foster a stronger and more resilient forest, especially as climate change and wildfire risks loom larger. Back in 2020, the CZU Fire crept down within two miles of the property, and its neighbors evacuated their homes. So we teamed up with local residents, foresters, and other experts and got to work.  In collaboration, we set out to reduce the excess vegetation to foster a safer community, improved habitat, and a healthier forest overall. (A mild spoiler: Thanks to this project, we’re proud to report that the fire road is now clear enough for CAL FIRE’s trucks to roll through if needed!)

We also had another puzzle to solve—what exactly was going on with the mysterious trees? Turns out, neighbors and long-time residents knew an intriguing backstory.

O CHRISTMAS TREE, O CHRISTMAS TREE

Did you know that choose-and-cut Christmas tree lots are a local innovation? These family-friendly destinations emerged in the Santa Cruz area in the 1940s. In the decades that followed, the fad hit San Mateo County. Locals told us that the trees at Burns Valley were intended as part of this regional trend, but the business never quite got off the ground. 

As land stewards, we wondered what the property may have looked like before these sentinels took root. What types of plants and animals thrived here, and how did the landscape shift over time? And now that this unique forest is here and established, how might we help these trees thrive? We were curious, too, what would happen if we thinned (aka removed) some of the pines. Would a new ecosystem emerge, one that had flourished in this area long before settlers interfered?

A NATURAL HISTORY OF MONTEREY PINES

Monterey pines are remarkable trees with a storied past. Long ago, these conifers grew abundantly across the state. In fact, fossilized Monterey pine cones have cropped up in 20 distinct California locations, including the burbling La Brea Tar Pits, the rugged Channel Islands, and windswept Tomales Bay.  

Today, their native range is much smaller. It includes two islands off Mexico and three foggy regions of California: Monterey, San Luis Obispo, and Santa Cruz counties. Adapted to their cool coastal climate, Monterey pines grow quickly, help stabilize soil, and regenerate with the help of low-intensity fire. It’s a spark of magic how heat opens their cones, letting seeds spread and new roots find purchase. These trees also play a crucial role in supporting rare orchids and providing wintering habitat for monarch butterflies in nearby Pacific Grove.

While Monterey pines are rare in their native range, they’ve been widely planted around the world—from Australia to Spain. In fact, they’re one of the most commonly introduced species, often becoming invasive in new places. But this particular stand of trees in San Mateo County? That’s where the mystery deepened. To get to the bottom of it, we called in some tree experts—foresters.

A FOREST IN NEED OF A CHECK UP

Foresters are a bit like doctors for trees. First, they consult existing records to piece together an area’s history. Next, they conduct a thorough check up, assessing the health of the forest. Lastly, they prepare for the future by prescribing treatments. Their prescriptions come in the form of forest management plans, ensuring trees can withstand ensuing storms, fires, and other challenges—all while preserving the landscape’s natural beauty and biodiversity.

The Science of a Stressed-Out Forest

Like all trees, Monterey pines regularly fend off many pests including parasitic fungi, mites, viruses, bacteria, and beetles. Their most common problem is a trunk-infesting fungus called pitch canker. The issues compound when pine bark beetles attack infected trees. These well-known California pests start in at the roots while pitch canker climbs toward the canopy. 

As living organisms, Monterey pines also have an immune system to help fight off these threats. But when trees are overcrowded and stressed, their defenses weaken, making them more vulnerable to disease — and in some cases, they may not survive. The good news? Healthy Monterey pines are sturdy and tough. With strong immune systems and defensive sap, they can fend off pests, keeping the forest in a flourishing state. 

Digging into the Past to Plan for the Future

Before introducing any changes, our foresters knew how essential it was to pan out and get a holistic perspective at Burns Valley. They wondered, for example, what the land might have looked like back in 1769, during the Portolá Expedition, centuries before the pines were introduced. While the available archive didn’t reach back quite so far, they did have access to aerial photos dating to 1931. An important clue stood out as they inspected the images. The dark canopy of the trees is visible in a 1991 photograph, but in shots from 1965 and 1985 it’s nowhere to be seen. In all likelihood, they concluded, someone must have seeded the trees sometime between 1985 and 1991. 

Archives can help foresters travel through time. Watch as decades of aerial photos reveal the hidden history of Burns Valley below:

Diagnosing the Forest’s Condition

Next, the foresters began identifying any diseased or dying trees. Then, they took stock of the smaller trees crowding the stand. They cautioned us that removing too many trees at once could disrupt the ecosystem’s delicate balance, possibly making fire risks even worse. 

Arriving at a Prescription

In the end, the foresters recommended a middle-ground approach: thinning out the smaller trees to give the hardier pines more space. When a stand of trees grows too dense and experiences crowding, each tree must compete for scarce sunlight, water, nutrients, and space. By making them less jam-packed, we’re able to make the remaining trees healthier and more robust, with plenty of space and resources to go around.