Home & Garden Columns

Nearly Native, Cosmopolitan and Threatened

Ron Sullivan, Special to the Planet
Tuesday September 05, 2006

All over the hills and in many yards, we see the plentiful and familiar Monterey pine. It’s one of the key tree species of our parks and urban hill forest, part of our natural surroundings. 

Except for the “natural” part. Pinus radiata is no more native right here than Eucalyptus globulus—at least in this eon. It’s a species in trouble on its home turf, a small part of the coast south of here approximately from Año Nuevo to Cambria and not very far inland, six or seven miles up the Carmen River valley. Even there, its populations aren’t contiguous, but in three disjunct areas.  

In other epochs, its range was longer though about as narrow, along the coast from the La Brea Tar Pits to Marin County and north, to judge from the locations of fossil cones. To judge by those cones’ ages, though, it seems never to have been widespread at any one time; it just grew in small but varied ranges as climates shifted between glacial periods. 

There are two natural varieties of the species on small Mexican islands: binata on Guadalupe Island, and cedrosensis on Cedros Island. The population on Guadalupe Island is in trouble because feral goats eat all the seedlings. Fewer than 100 individuals remain. 

The base stock is now also threatened by pine pitch canker, an introduced fungus.  

At the same time, it’s one of the most widely distributed and most-planted—by humans—tree species in the world. You’d think a species with such a small and precise original range would be demanding about living conditions, but Monterey pines thrive on timber plantations in Hawai’i, Australia, New Zealand, Chile, Spain, the British Isles, and South Africa, and as ornamentals elsewhere.  

Including here in the San Francisco Bay Area. And therein lies the rub, genetically. 

The trees planted as ornamentals are mostly from the stock grown in New Zealand for timber. As they’re planted here, over the years closer and closer to the native foundation stock, they’ve been “cross”-breeding with the homeboys. What long-term effects this genetic sorting and re-mixing will have are a toss-up.  

The timber trees get selected over generations for qualities like fast growth and straight trunks that make easy-to-mill lumber. Whether these characteristics, if they get passed on to new generations in the wild, are good things to have if you’re a tree trying to make a living in the wild along windy coastlines and in coastal soils—good question! 

One might reasonably speculate that fast growth, which usually results in weaker wood and a tendency to drop branches, wouldn’t be so wonderful. Straight trunks, same thing, though that might be more environmentally malleable; it’s easier to be upright in a plantation full of your brethren than on a wind-sleeked shoreline.  

The ornamentals seem just as susceptible to pitch canker as the original stock, and might be a reservoir for the disease. 

In the older population of Monterey pines in our hills, we’ve already noticed their tendency (like many trees’) to self-prune. When a low branch (or even a leaf) is shaded to the point where keeping it is more expensive metabolically than giving up its “income,” a tree will drop it. (This is hardly an exact calculation, of course; it’s just that wood gets weaker when the leaves directly outward/up from it nourish it less.)  

Monterey pines make great big heavy limbs. When they fall, look out! One calm night many years ago, Joe and I noticed the lights flickering, and the power went off completely as we grabbed flashlights and went up the front path to see what was happening. Then, with a memorable and eloquent groan, a low limb bigger than the average Yule tree split off the tree and fell onto the garage.  

The valiant PG&E crew had our power back on within a couple of hours, but it took us and the landlady’s son most of the next day to excavate the undamaged but suddenly verdant garage. The tree’s still there, 20-some years later.  

If you have a Monterey pine and worry about its health, call in a pro—a real ISA-certified arborist, not some clown who advertises “topping” trees. They should be pruned only when the canker’s least virulent, a short window in midwinter, and with care and knowledge.