“I speak for the trees” – the Lorax
Cowan sits in a fire tower at the top of Palomar Mountain.
From his perch, Cowan — a freelance columnist, outdoor writer for the San Diego Union-Tribune, former mayor of Escondido and avid nature-lover — looks out on the vast untouched wilderness below him.
Cowan’s been there the whole day. He’s watched how animals in the park have woken up, how a quail walked with her chicks and a bobcat with her cubs — how nature proceeds in the absence of humans.
“Watching the animals and the seasons evolve, it’s a wonderful way to connect with the outdoors,” Cowan said.
But what Cowan observes from his vantage point in the mountains is just a fraction of the life that is teeming in San Diego County’s natural ecosystems.
This is because our county is one of the world’s few biodiversity hotspots — regions with incredibly high numbers of endemic vascular plants. In fact, San Diego is the most biodiverse county in the continental United States.
“[There are about] 3,000 different kinds of plants that occur in our county,” Jon Rebman, Curator of Botany at the San Diego Natural History Museum, said. “To put that in perspective, that is more diverse than most of the states in the northern tier of the United States. That’s a lot of diversity in a very small area.”
Out of these thousands of plants, close to 1,700 are native to San Diego, according to the California Native Plant Society. These indigenous plants work in harmony with each other and the surrounding fauna to create San Diego’s lively ecosystems.
But there’s another side to the biodiversity hotspot designation: a region must have less than 30% of its original vegetation.
San Diego certainly meets this criteria. According to the Earth Discovery Institute, it is home to the most plant species threatened with extinction in the country.
According to Christa Horn, the Conservation Program Specialist in Plant Conservation at the San Diego Zoo Wildlife Alliance, San Diego County has 139 plant species that are rare and threatened, an “overwhelming number.”
And many of these are very close to home. According to Calflora, an online, nonprofit database of California’s wild plants, close to 20 rare plant species exist in the Gonzales Canyon Open Space Park, situated just behind TPHS.
“[There’s] really special stuff right in our own backyard,” said Sarah McCutcheon, Program Coordinator at the San Diego Management and Monitoring Program.
A quick trip down Del Mar Heights and a left turn on North Torrey Pines Road takes us to a treasure trove of San Diego’s natural wilderness: the Torrey Pines State Natural Reserve.
The 2,000-acre reserve, which is one of the last to exist on San Diego’s highly urbanized coast, represents around 20% of the flora in San Diego County, with some 370 native plant species and 50 rare ones, according to Darren Smith, a Senior Environmental Scientist for California State Parks.
“Two of the reasons it’s so biodiverse is because we’ve developed most of the coastline of San Diego, so most of the similar habitats have been wiped out … and Torrey Pines also has this really unique geology that has odd soils and coastal fog influence,” Smith said.
It is precisely this geology that allows its namesake, the Torrey pine tree, to grow. The pines, which rely on the moist fog drip from the coast to survive in San Diego’s Mediterranean climate, grow exclusively in the reserve and on Santa Rosa Island, off the coast of Santa Barbara. They are found nowhere else in the world.
But the pines are becoming increasingly rare for another reason: an infestation of a native species of bark beetle called the California five-spined engraver.
Between 2006 and 2018, the park lost 12% of its adult and subadult Torrey pines to the beetle, according to Monica Stupaczuk, Environmental Scientist at California State Park’s San Diego Coast District. Another 5-10% were lost between 2018 and 2022.
But according to Stupaczuk, the beetle’s relationship with the pines is normally a healthy, balanced one.
“The five-spined engraver is a native and it’s co-evolved with these trees over who knows how many thousands of years,” Stupaczuk said. “They’re a natural part of the system.”
So what’s the problem? It’s the rapid rate at which the pines are crashing, something caused by prolonged droughts in San Diego: a direct consequence of human-induced climate change.
“It’s definitely beetles and climate change in tandem,” Horn said. “The beetles attack trees that are weakened by drought and heat stress, and they no longer have the capability to defend themselves.”
Smith echoed this.
“The tree’s best defense mechanism against the beetles is a pitch they produce that pushes them back out,” Smith said. “But when there’s drought, the trees don’t have as much water in their vascular system, and they can die and they do die regularly.”
The beetles are not the only nuisances to the pines. Another climate-change-related menace is a pitch canker of non-native fungus, which is “beating up the trees, making them misshapen,” and causing them “to lose some of their branches,” according to Smith.
“One of the other [effects of] climate change in Southern California is less predictable precipitation patterns,” Smith said. “The last two years we’ve gotten these pretty intense summer rains, and when you get moisture in the summer, you’re more likely to get fungi and pathogens introduced to the trees.”
But the Torrey pines are just one of the rare plant species in the reserve. The two rarest ones, according to Smith, are the short-leaved dudleya, a succulent, and the Orcutt’s spineflower that Smith said only has two known populations left in the reserve.
The main reason for their decline is invasive, non-native plants, which occupy specific, unchecked ecological niches and spread rapidly.
“We have about 800 species of plants that are reproducing on their own in natural environments that are not supposed to be in our flora,” Rebman said.
And this is all occurring on the land we haven’t even developed. San Diego, with its rapid urbanization, is losing the untouched wilderness that houses so much of its biodiversity.
“Anyone that lives here knows our development is extreme,” said Rebman. “Look at any Google map or satellite map, and you can see all the [wilderness] that is now housing and pavement.”
This is especially serious for species whose habitats are already rare to begin with. These include the Del Mar manzanita — a tree endemic to San Diego found in only a couple of spots along the coast — the dudleya and the endangered San Diego thornmint, according to Justin Daniel, President of the San Diego CNPS Chapter.
“The soils the [thornmint] lives on are rare and those soils happen to also be high development areas,” Daniel said. “Those areas are really desirable for recreation activities like mountain biking, horseback riding and hiking.”
Another rare plant in San Diego may be less obscure to the public: the palm tree.
According to a University of California news article, since 2011, the invasive species of the South American palm weevil has killed more than 20,000 palm trees in San Diego County. The population decline has been even more dramatic in areas closer to TPHS like Rancho Santa Fe and Carmel Valley.
“It was about three years ago, I can remember flying into the San Diego Airport and looking out an airplane window and I was just blown away at how many [dead palm trees] were downtown,” licensed arborist and palm tree applicator Mike Grande, said. “It was probably 10 to 20 just in my view.”
According to Grande, even though there are lots of preventative methods and removal procedures, by the time the palm trees exhibit any sign of disease, it is most likely too late.
The palm weevil was brought to San Diego, in part, by humans traveling up north. But the reason the weevils have been able to live and thrive here is California’s adaptable climate and global warming.
“As [our climate] warms up, it might be within the edge of an insect’s range of tolerance to move further north and invade places that they weren’t before,” AP Environmental Science teacher Michael Rall said. “When a new species invades a new ecosystem, oftentimes there aren’t predators or natural defenses to keep them down.”
From invasive species to climate change to urban development, San Diego’s rare plants are threatened from all angles.
But why are scientists focusing on these niche species? Because they all have a part to play in the complex webs of San Diego’s ecosystems; and the loss of one could be detrimental to the entire structure, according to Horn.
“There’s an analogy that ecologists will sometimes use: an airplane with all of its rivets. The airplane wing has one little rivet every few inches that holds the wing of the plane together, and you can lose one or two or three of those, you don’t really know,” Horn said. “But then at one point you’ll lose one and the whole airplane will fall apart. We just don’t know enough about these systems to know which of those rivets is important, which of those species is important and how many we can lose.”
Caught in the bustle of urban life, it can be difficult to remain cognizant of the crisis facing our native plants, and perhaps even more so, why their conservation matters in the first place.
“[These plants] have a right to be there. This natural world has evolved very complex interactions and situations, and it’s spent tens of thousands of years developing them,” Smith said. “There’s a little more power to something that’s been around for [that long] and formed these relationships with us. If you look at them carefully, they’re like music or art.”
And this music and art is something humans depend on.
“We learned from COVID that when we’re trapped inside, it affects our mental health,” Rall said. “Until you get outside and start enjoying a little bit of free space, clean air, clean water, healthy ecosystems and birdsong, you don’t feel that connectivity.”
The good news? There is a vibrant scientific community in San Diego working to preserve the access to that connectivity.
Back at the Torrey Pines reserve, Smith and Stupaczuk are working closely with Horn’s team from the SDZWA to monitor the pines’ health, growth rates and population sizes in different areas of the park, aided by aerial imagery technology and precise measurement tools.
This information tells the scientists which populations of the pines are doing well, and thus where to center conservation efforts.
“We want to know what types of habitats [the pines] are doing very well in under stress,” Horn said. “Those are the areas we’ll want to focus any reforestation efforts on if a beetle comes through because we don’t want to grow plants where they’re going to … get stressed again.”
This reforestation is made possible by the SDZWA’s seed banking efforts — the process of collecting seeds from rare plants like the Torrey pines that could be planted in the future — an “insurance policy” of sorts, according to Horn.
“We lost maybe another 5-10% [of our pines] between 2018 and 2022, but in the meantime, we planted around 464 new trees, and that’s a whole project [called] the Climate Ready Reforestation Project,” Stupaczuk said. “That’s kind of our way of addressing the loss of Torrey pines.”
But protecting existing pines is essential, too. The reserve/SDZWA team is using bark beetle traps with specific attractive pheromones, spraying chemical beetle deterrents, collecting genetic samples to test fungal resistance and minimizing other stresses to the pines like invasive grasses.
Similar measures are being taken to slow the loss of the myriad of other rare plants across San Diego County.
And numerous local organizations, such as San Diego’s CNPS chapter that Daniel leads and the San Diego Management and Monitoring Program that McCutcheon coordinates, are dedicating themselves to the collection of data about the number of rare plant occurrences and the severity of their threats, an essential component of conservation.
“We want to be able to monitor and manage things at a more regional level,” McCutcheon said. “We go in and we count all the plants of a rare species in the survey area…but we’re also taking note of the threats and what level each individual threat category is, [if it’s] a high, medium or low.”
Preserving the access to that connectivity is not just for environmental scientists like Smith and Horn, however. Everyday San Diegans can get involved in the fight to preserve our community’s robust ecology.
Environmental activism is already apparent within the TPHS community, especially in the student run Garden Club and Urth Club.
“Since the beginning of our club we’ve been doing crafts, educating our members on how to take care of our garden, all those kinds of things,” Vice President of Garden Club Christine Chinnappan (12), said. “Just raising awareness about plants in general.”
The Garden Club promotes sustainability and spreads awareness on the TPHS campus by planting native species in the gardens near the Chemistry buildings.
Similarly, Urth Club focuses on getting students involved and finding ways to promote awareness.
“It does have to be kind of forced on most students,” Co-President of Urth Club Charlotte Sach (11), said. “The best way to raise awareness for environmental protection would be through SC time or something that’s more exciting to engage them … and I’d encourage students to join clubs. There are lots of programs on campus.”
But students can get involved off campus, too. Even moments spent connecting with nature — going on a hike or taking a walk through a local canyon — can prove to be an opportunity to support native fauna. Free apps like iNaturalist allow users to take pictures of plant species in their local ecosystems, which directly feed into databases that environmental scientists like Rebman use.
“Once I verify that data and download it into our databases, we can map it out with our own specimens, adding more distributional knowledge or possibly new diversity,” Rebman said. “You might have found something new to science or you might have found a new weed that we need to deal with.”
And while out in nature, the most important thing is to be conscientious of the fragile, complex ecosystem around us and how we interact with it.
“You can take it down to a personal level,” Rebman said. “When something’s fenced off and you’re like, ‘oh, that’s a nice natural place, I want to go hike that area,’ you personally impact that area. Every footprint you make causes disturbance.”
Horn agreed.
“Wherever you step, be a conscientious appreciator of nature,” Horn said. “That actually helps a lot.”
