Santa Rosa Island Torrey pine (Pinus torreyana ssp. insularis)
The first time Santa Rosa Island landed on my plant exploring radar screen was when I learned about the Torrey pine some time in the early 2000s. I had never even seen this tree until I took a trip to Torrey Pines State Reserve north of San Diego in early 2012. It is the rarest pine in North America with several thousand “mature” trees on both the mainland and island. My bucket list for understanding the ecology of this species is complete now that I have visited the island.
As mentioned in an early post, pigs were first introduced on Santa Rosa in the mid 1800s. By 1888 it is estimated, based on historical records, that there were only 100 Torrey pines on the island. Today, all herbivorous megafauna have been removed (minus 5 sterile horses from the old ranch) and the Torrey pine are thriving–with an estimated 12,300 trees–one-quarter of which are saplings!
Researchers debate the arrival time of the Santa Rosa Torrey pine, estimating anywhere from 6,000 to over 1 million years. Disagreement also exists as to whether these two population represent subspecies or varieties of each other. Some argue the two populations are genetically different enough to be considered a subspecies, others prefer distinction at the variety level. Regardless, it is a beautiful species and well worth seeing in the wild.
In 1998 I first visited the Channel Islands. This was early in my naturalist career but I was struck, none-the-less, by the beauty and isolation I found on Santa Cruz Island. On that trip I first saw the endemic island scrub jay (Aphelocoma insularis) and began to develop an understanding and interest in island biogeography. Twenty years later this experience brought me to Santa Rosa Island–in major part to see the Torrey pine grove–but also for the opportunity to explore one of the least visited places in Southern California.
Santa Rosa Island is separated from the mainland by over 25 miles of water. The next closest landmass is San Miguel, which is now isolated from Santa Rosa by three miles of water. Isolation has nurtured endemism on both a localized island level as well as on a unifying level between islands. Combined, all the Channel Islands are home to 150 species of unique plants and animals. Santa Rosa hosts 46 of those, including six endemic plants that grow nowhere else.
Work occasioned a trip to southern California which, of course, also required me to spend some time with a few regionally endemic conifers. I had never visited the Torrey pine or Cuyamaca cypress, so in planning the trip to Palm Springs for a conference, Allison and I took a few extra days–looping south toward the Mexican border–to see North America’s rarest pine and cypress.
Rarity is a new endeavor for the Torrey pine. Though it is the current record-holder for “rarest North American pine” it has not always been that way. It is an ancient pine, whose lineage (or at least that of a near ancestor) extends back as far as the Oligocene or Miocene with a range that extended as far north as Oregon (Kral 1993). In the Pleistocene, the species probably ranged throughout the coastal basins of Southern California but became restricted to coastal San Diego County and Santa Rosa Island over the last 12,000 years or so, during Holocene warming (Waters and Schaal 1991). Its closest extant relative is probably the Coulter pine (Pinus coulteri).