- Author: Michelle Davis
Torrey pines are the rarest conifers in the United States. We are lucky to have a few in the UC Davis Arboretum, but these trees did not arrive here on their own. The trees' native locations are the California coast from San Diego to Del Mar (now Torrey Pines State Natural Reserve) and another subspecies 175 miles away on the eastern coast of Santa Rosa Island, now part of the Channel Islands National Park. The tree was first “discovered” in 1850 by Charles Parry M.D. who named it after his professor John Torrey M.D.
Almost all California pines grow in higher altitudes with cooler climates. Amazingly, these trees survive on 10 inches of rain/year in a hot, semi-arid Mediterranean climate at 100 – 500 feet above sea level. They have adapted by developing deep and extensive root systems, often at least twice as deep as the height of the tree, and growing longer needles (9 – 13 inches) in usually bundles of 5 needles per fascicle to catch more of the morning fog common along the San Diego coast. They are found along canyon ridges, mesa tops, or seaside slopes with sandy or sandy-loamy soil. When the soil erodes, the extensive root system emerges. Trees that have more wind protection grow to about 70 feet, but those exposed to the ocean winds are “salt-pruned” growing prostrate and/or contorted.
One of the reasons this tree is so rare is that its seed dispersal system isn't all that efficient. The male cones grow upright on the bottom of the tree and the female cones on the upper part of the tree. The male cones need a good crosswind to float the pollen from the next tree. The scales on these large cones stay open until the seeds are pollinated. They then close and turn downward. When the seeds are mature, the scales open very slowly and the seeds fall down. The seeds don't all come tumbling out at the same time. The large, heavy cones can stay on the tree for 15 years! Seeds can be released slowly from 15 months after pollination through the time they remain in the cone on the tree. True for all pine trees, it takes 15 months from pollination to fertilization. Blue jays have been found to be helpful in seed dispersal.
Another factor leading to Torrey pines' rarity is that the trees are dying from damage due to bark beetles. These beetles co-evolved with the pine trees. The two causing the most damage are the California 5-spined engraver beetle (Ips paraconfusus) and the Red Turpentine beetle (Dendroctonus valens). When a tree is bored by a beetle, the sap is released. If the tree has been getting enough water to produce a good amount of sap, the beetle is drowned by the sap. In drought years, however, there isn't as much moisture for the tree to produce the needed amount of sap. California 5-spined engraver beetles bore into the upper part of the tree and can be recognized by the frass they leave on the tree's bark from the borings. Red Turpentine beetles mine under the bark at the tree's base large roots. They leave large pitch tubes made of the borings mixed with the pine's sap. The tunnels are pinky-brown to white. Both beetles mine the phloem-cambium region under the bark and lay their eggs in the tunnels they create. Beetle traps are used to monitor the trees in the reserve and in the national park for evidence of the beetles. The area covered by one trap for purposes of killing the beetle is not very big, so a vast number of traps would be needed to contain the problem.
The Torrey Pines State Reserve gets 9000 visitors a day and up to 15,000 on the weekends. (pre-COVID statistics). If you go, go early in the day and in the middle of the week. Otherwise, go locally. One Torrey pine can be found in the UCD Arboretum redwood grove. A group of Torrey pines is located just off the decomposed granite pathway about 100 feet east of the acacia grove. It's a little closer and a lot less crowded to see the rarest and one of the most remarkable California conifers.