In Touch: Torrey pines, the rarest pines in North America
In my garden, is it a native plant? Plus new science on these remarkable trees
At the zoo/aquarium where I work, we feature a native pollinator garden. Although the landscaping and plants of the garden don’t really differ much from the native landscaping of the rest of our grounds, the garden allows us to spotlight our pollinators and encourage folks to plant their own pollinator gardens.
In the garden is an outdoor classroom with a shade structure, and growing up through the timbers of the shade structure is a Torrey Pine. The tree predates the installation of the garden and the construction of the shade structure. It even predates me, having been planted long before I was hired at the organization.
One of the branches of the pine started to droop, making it difficult for folks to sit in the shade; so I trimmed the branch and freed up the space. It was a quick, mundane task, but nonetheless a little odd, because Torrey pines are the rarest pine trees in North America, numbering just a few thousand. They only grow along the northern coast of San Diego County and two of the Channel Islands off the coast of southern California. The rarest pine in North America, and I was chopping away at one of them.
Once you consider that I sawed a branch off a member of the subspecies Pinus torreyana ssp. torreanna, the subspecies whose small numbers—two to three thousand—occupy a bluff and some surrounding areas along San Diego County’s coast, it can seem even weirder.
If this tree had not been planted on this island where I work, It would not be growing here. They like the sandstone soil of coastal northern San Diego County. They also thrive on the thick fog banks that envelope that piece of geography. At the zoo/aquarium the soil is almost entirely made of clay, and we don’t get the thick fog, either. It’s remarkable that this tree was able to take root at all on this island.
So there is a funny question: this Torrey pine growing in the pollinator garden where I work, is it a native plant? It is quite outside of the habitat that is conducive for it survival, yet it is only about 20 miles away from that habitat. Eucalypti from Australia are certainly nonnative to southern California, as are the South African ice plants that line our freeways and invade our canyons. But can a plant that is only 20 miles removed from its native landscape be considered nonnative?
The promontory where these trees naturally grow has been set aside as a state reserve, where they have been protected since the early 20th century. At the time that the reserve was created the trees numbered only around 100.
One of the most curious things about the Torrey pines is how much the trees can differ within the 1750 acres of the reserve. Next to the cliffs that drop 100 to 200 feet to the ocean, along the wind swept bluffs, the Torrey pines grow almost like shrubs and stand no more than a few feet tall. If you walk from the bluffs inland, about a quarter mile to the canyons where the trees are shielded from the ocean winds, the trees grow straight and tall, some towering more than 70 or 80 feet and having trunks more than four feet in diameter. In some areas of the reserve, the trees are tall and plentiful. It can seem odd to be in southern California, a landscape dominated by coastal sage scrub and the shrubs of coastal chaparral, and walk through one of these native pine forests.
Evolved to live in a fog
Coastal San Diego receives about 11 or 12 inches of rain a year, so little precipitation that it could almost be considered a desert, and too warm and dry for a large pine tree to call home. As it turns out, the fog that frequently settles in along northern San Diego County is the key to the trees’ survival. The pines’ needles, which grow in groups of five, have microscopic cupping that face downward as the needles hang from the branches. These cups collect the fog that condenses on the needles. The water then travels down the needle and drips off as a tree raindrop. I can attest from personal experience that the fog need not be very thick for each Torrey pine to turn into its own private rain cloud. It can seem like a light rain falling under each tree when the fog comes in.
The trees make their own rain. Recent research also finds that the pines’ needles can directly harvest moisture that collects on them during fogs. In a paper published in February of this year, in the journal Plant Ecology, scientists determined that Torrey pines can absorb water on their needles. They also found that compared to most of the other evergreen plants that live in the coastal sage scrub environment, Torrey pines were also better than the other plants at retaining water, another secret to their ability to thrive in such a dry environment.
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