BAMS! October meeting: SOD, Fond Memories, Friends and Fungi
- View SourceIf you missed our first BAMS meeting last night, you missed out.
We started with a series of photos of Larry Stickney, from early NAMA days to his last, triumphant scaling of Lafayette Ridge this past spring, to scenes from his recent Memorial at the Randall, including the wonderful banner of Larry in an eternity of mushrooms, produced by Mike McCurdy and his family. His faithful presence at the head of our table at UCB, tapping away on his laptop as he took scrupulous notes, was sorely missed.
We then segued to a very interesting update on the scourge of SOD, by one of the primary SOD field researchers in the East Bay, Brice McPherson of UC Berkeley. SOD, or sudden oak death, a recent (1990s) arrival to California, is caused by an introduced pathogen called Phytophthera ramorum, a motile oomycete in the brown algae group.
This species of Phytophthera (it was also a Phytophthera sp. that caused the Irish Potato Famine) is native to Asia, and was inadvertantly brought here on cultivated rhododendron shrubs for the nursery trade. Then, like our invasive, mycorrhizal Amanita phalloides, also brought in on ornamental trees, it escaped into the wild, and has caused and continues to cause widespread death among our native live oak, black oak and tanoak forests.
A grim topic, but an important one for those of us who care deeply about our forests and will sorely miss those irreplaceable MR tree hosts...
SOD symptoms leading to tree death in oaks and tan oaks follow a distinctive pattern:
Bleeding and Beetle Attacks
Bleeding and Beetle Attacks and Hypoxylon
Attempting to treat preventatively for beetles early in the process has helped some trees to survive. Ambrosia Beetles are one of the important beetle species in this process, and fascinatingly enough, like our old friends the attine ants, they apparently also farm fungi within the chambers and tunnels that they bore within the wood. These fungi provide food for the beetles and their young. It is the beetle-introduced fungi that ends up hollowing and weakening the trees, causing them to break off, many feet above the ground, even while their crowns are still green.
The larger the canker (an open wound) on a tree, the more likely that tree will die. Trees of small diameter (older, larger trees are more susceptible) or that have small cankers, regardless of tree size, seem to have much better survival rates.
There is some good news. Despite the widespread devastation of tanoaks in the Santa Cruz mountains, the live oaks have been much less affected. Turns out the species of live oak down there is NOT primarily Coast Live Oak, but a related (and sometimes cross-breeding) species called Shreve's Oak. And as luck would have it, the Shreve Oak, unlike Coast Live Oak, is fairly resistant to Phytophthera ramorum.
Dying and dead stands of Tan Oaks in many places are giving way to healthy Doug Fir replacement forests. As painful as it is to see our beloved hardwood forests dying in mass, the natural world is constantly changing and evolving, and will eventually form a new balance. And even Doug Firs have many interesting and even delicious MR fungi (see MDM pages 35-36).
In the broadly devasted Marin County landscapes where SOD has been working its deadly way through Coast Live Oak stands, there do appear to be some pockets of natural resistance. Despite a steadily eroding population of native oaks, there are healthy trees, without disease symptoms, still standing in plots of SOD destroyed trees that have been monitored for over a decade. There is also experimental evidence that some trees can fight off infections: a few trees that were innoculated with the SOD organism but remained asymptomatic, with no observed bleeding, showed a visible walling off of the infection when the bark was peeled back.
The phloem of trees can contain varying amounts of phenolic compounds, which seems to inhibit the growth and spread of the SOD organism, at least in vitro. This indicates that SOD susceptibility may be a function of the phloem chemistry of individual trees.
Despite many minds and many dollars getting thrown at the study of SOD here in California, we still don't know exactly how it is spread...it may well be a foliar infection in tan oaks, but is probably a bark infection in Live Oak, altho how it enters intact bark is unknown. We do know that it spreads more quickly in rainy years, and that it needs moisture to survive and spread, with fog drip even in lieu of rain being a major factor towards its spread.
Despite CA Bay Laurel getting cast as the villian in this scenario (towering Bays catching fog and rain and dripping down on innocent oaks), and even funds getting earmarked to kill these trees as a "preventative", we really don't know how SOD works its way thru our forests. Bay Laurels seem to be a more important SOD vector early on in the infection process, and as Brice stated, it is arrogant of us to think that we know better that the forests themselve as to which native trees are important to the health of the forests and which are not.
As to current SOD hosts in CA, or those plants and trees that have non-fatal, mildly symptomatic infections, it is now so widespread here that the list of non-SOD infected species is shorter than the list of known hosts!
SOD is here to stay, and we, like the forests themselves, must learn to adapt to it.
And, as always, in death there is also life...the falling of the largest trees, perhaps already at their time to pass on to that great Arbor in the sky, fall to the ground and are quickly decayed by saprobic fungi, opening up formerly tree-choked areas to vastly increased sunlight, and providing a big boost of nutrients for the growth of new trees and plants of all kinds. Indeed, young Coast Live Oaks have been observed taking advantage of the sunlight and growing steadily, deer browsing notwithstanding, and at this point in time are not showing signs of disease. Apparently, older, larger oaks are far more susceptible to succumbing to SOD.
So, it's kind of a classic good news/bad news joke, without a whole lot of laughter and an elusive punchline.
Many thanks to Brice McPherson for creating such an interesting and informative synopsis of current SOD research. Seeing your show and tell examples of SOD damaged trees and those devastating but teeny tiny Ambosia beetles in a box was illuminating.
And thanks to Erin Blanchard and others who brought so many interesting fungal specimens to share with the group. Your efforts were appreciated by all!
See you at our next BAMS event: the Salt Point camping foray on November 13. Details on the BAMS website here: http://www.bayareamushrooms.org/calendar.html
and on this list closer to the date.
Yay, Rain! Can't you feel that mycelia stirring? ;)
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