We passed five Orcas (Orcinus orca) on the passage to Santa Rosa Island
After a two hour boat ride from Ventura Harbor that included sightings of gray and killer whales, passengers disembarked onto a newly-built pier and subjacent white sand beaches. We had arrived. Once unloaded, the park ranger offered an orientation rejoicing in our good fortunes. The high winds and thick fog which had typified the previous few weeks had now subsided. The forecast for the coming days included sun, low winds, and perfect temperatures.
Fog and wind are omnipresent on Santa Rosa Island and play a major role in shaping the landscape. Any plants with a propensity for upward growth are restricted to canyons, particularly north sloping ones. Here they find refuge from the wind and often more available moisture provided by the meager 15-20 inches of annual rain. However near the highest island peaks–like Black Mountain at 1,300 feet plants have adapted to wind and fog in different ways.
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.
The National Science Teachers Association conference brought me to Los Angeles and after two days, I needed to find some green space. Linking up MacArthur Park, Vista Hermosa Natural Park, and Whole Foods (to prep for a trip to Santa Rosa Island) defined a route for me to visit the urban wildlands of the city.
Stroll to the sparse urban wildlands near downtown Los Angeles .
My elegant crossing Tule Creek. Photo by Josh Smith.
Last weekend, I hiked in Trinity County along a low-elevation, fire-prone section of the Bigfoot Trail between Highway 3 and Hayfork and was able to witness obligate & facultative seeding in action.
One-third of manzanita species are facultative seeders. These are species that regenerate post-fire by both seed and burl resprouting. The remainder are obligate seeders that lose their entire adult population in a fire and depend on a seed bank for regeneration. Obligate seeding is the current model in manzanita evolution.
To understand why, consider the climatic dynamics over thousands, or tens of thousands of years or more. In the case of the resprouting species, particular individuals can live for centuries, resprouting over and over, cloning new individuals as the burls expand with each fire cycle. But in that population, the rate of genetic change is limited, because most individuals live a long time by way of asexual reproduction. This suggests that populations may be unable to respond to rapid climatic changes that might occur in only hundreds of years. The obligate seeders, on the other hand, lose all adults in stand-replacing fires and new post-fire generations have to establish from more genetically diverse seeds. Those populations consequently have greater flexibility to shift and adjust as circumstances require; traits that might have been rare and less important in older generations can emerge through natural selection and become critical in the newer generations within the lifetime of resprouting manzanitas.
Much of this area burned in the summer of 2015. While evidence of the fires were everywhere, there are many signs of the next generation of plants returning to the landscape. This was particularly true on some of the south-facing slopes above Philpot Campground where two species of manzanitas were exploring different reproductive regimes– both obligate & facultative seeding.
Arctostaphylos manzanita is a facultatative seeder. It can resprout by seed but also from dormant buds. When present, these structures are often prominent and are called burls (also ligno tubers)–seen in the middle of the sprouting leaves.
Arctostaphylos canescens is an obligate seeder and does not have a burl. Instead, genetically unique seedlings resprout from a well-stocked seed bank.
