The In Defense of Plants podcast took deeper look at the most diverse woody plant lineage in western North America (Arctostaphylos spp.) with San Francisco State Professor Dr. Tom Parker who has devoted much of his career to uncovering the ecology and evolution of the manzanita lineage. From mutualistic relationships with rodents and fungi to their dependence on fire, you will soon find that manzanitas play an important role in the ecology of California’s natural ecosystems. It is time we start paying these plants the respect they deserve and I hope this episode is a good start to doing just that.
(Arctostaphylos uva-ursi subsp. cratericola)
Arctostaphylos uva-ursi is a variable taxa because of the wide range of latitudes it explores across the northern hemisphere. Guatemala bearberry (Arctostaphylos uva-ursi subsp. cratericola) is a subspecies because of its disjunction distribution in Guatemala. It is also the only taxon not included in Field Guide to Manzanitas. Fernando Tobar recently took a trip to the Sierra Cuchumatanes, in Guatemala and observed these plants in their native habitat. That trip inspired this post.Continue Reading
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.