At the end of the day on Monday, as we finished up looking at and measuring trees in our plots, the 104-degree heat in the north coast interior was a bit distracting. But I noticed this guy growing on a black oak and wanted to take his picture (sorry for the blurriness) before he gets old and dried-out.
Most people interested in ecology already know this, but you can't mention it too often: some of the most valuable members of our forest communities are the ones that decay others, recycling nutrients through the greater ecosystem and basically cleaning up the messes--like accumulations of dead branches and trees that could serve as fuel for fires--attendant on the normal processes of animal and plant death.
Plus, fungi are simply interesting in their own right. They have myriad strategies for inhabiting and digesting other living and dead things, and they come in a variety of fascinating shapes and colors. Here is a mini-salute to some of the other decay fungi we sometimes come across in the Douglas-fir/hardwood forest up here in the north coast.
Unfortunately, some of the fungi that decay hardwoods are much more obvious now that P. ramorum has killed so many trees in our region.
Well, OK, maybe that's a little much. Admire a forest pathogen? But bear with me.
Armillaria is the genus name for a group of fungi that are found in forests worldwide. Some species of Armillaria are virulent tree-killers, while others mostly play a role in forest recycling by decaying dead wood. In coastal California, the most common species of Armillaria can produce bleeding symptoms on hardwood trees that look exactly like the symptoms caused by P. ramorum.
Armillaria (white) beneath bark, with typical bleeding symptoms above (photo courtesy of Jack Marshall)
So what is there to admire? Well, for one thing, Armillaria is native to California. Researchers from UC Davis sampled Armillaria species throughout California and found four species. The overwhelming majority of their samples, though, consisted of only two of these species: A. mellea and A. gallica.
A. mellea is primarily found in developed areas. It causes a root rot that kills trees, although it rarely kills large numbers of trees at a time. A. gallica is found throughout coastal forests and is the species of Armillaria that I most commonly come across. (At least, I think that it is the species I most commonly come across. Definite identification of Armillaria to the species level requires DNA analysis and/or sophisticated morphological diagnostic skills that I don't have.)
In any case, A. gallica causes a heart rot that slowly develops inside the tree, causes bleeding lesions that show up on the bark, and eventually produces a more or less open column of rot within the tree. It can also decay tree roots and butts, but not as swiftly or commonly as A. mellea.
Since it is a native fungus, A. gallica behaves much as we would expect something to behave when it has evolved over thousands of years in the same environment with its hosts. It is ubiquitous in the forest environment, surviving on what dead woody material it can and picking off the occasional small tree that is stressed because of having to grow under a dense canopy with insufficient light. Healthy, mature hardwood trees apparently resist it easily.
In other words, A. gallica is one of nature's cull and decay agents. Not like P. ramorum at all! Since P. ramorum is not native, its host trees have not evolved defenses adequate to resist infection. This enables the rapid epidemic spread of P. ramorum in our coastal forests.
In other areas with different forest stresses, Armillaria species, even though native, can cause far greater problems. A. ostoyae, for example, kills large numbers of trees in the high-elevation forests on the east side of the Cascades and up into Canada. In these areas, trees have to compete for much more limited water resources and are much more susceptible to a variety of insect and disease problems. Our coastal forests have it easy in comparison.
So far, I have admired Armillaria for (1) being a native member of our Western forests and (2) for being a versatile survivor that plays an important role in forest nutrient cycling. I also admire the fact that the mycelium (main fungal body) of many Armillaria species glows in the dark--i.e., it's "bioluminescent." Pretty cool, huh? And there are plenty of other nifty things about this fungus--material for another blog entry someday.
California black oak with Armillaria mycelium (below left); symptoms at top right could be caused by Armillaria or P. ramorum (photo courtesy of Jack Marshall)
All this blogging about California’s oaks has got me thinking about . . . Arkansas’ oaks!
Northern red oak. Photo courtesy of Susie Lee
Preventative treatments for Sudden Oak Death, and the hard working researchers that discovered them, are prominently featured in the latest edition of California Agriculture.
A misty shot of tanoaks, decorated with spring-loaded injectors, filled with Agri-Fos, the phosphonate compound which protects healthy red oaks from the disease, adorns the cover. Researchers from Matteo Garbelotto’s lab are now trying to discover if Agri-Fos can also protect healthy tanoaks. Though much of the attention on Sudden Oak Death has been focused on true oaks killed by Phytopthora ramorum- coast live oak, black oak, interior- live oak and shreve oaks - tanoaks have been severely impacted by the disease, with up to 100% of trees dying in some areas. Researchers speculate that this may be due to tanoak being both a foliar host and a bark canker host.
California’s drier winters have slowed the spread of Sudden Oak Death and perhaps taken it out of the media spotlight, but outreach specialists - Chris Lee in Humbolt, Janice Alexander and Nicole Palkovsky in Marin and lead researcher Matteo Garbelotto in Berkeley - are trying to stay on top of things so that when the rains come, and Phytopthora picks-up, the preventative work will already be in place.
As the CalAg article points out, “One of the biggest challenges in controlling Sudden Oak Death is that prevention is the best treatment, but most efforts begin only after trees are already infected.” There is a great deal of science based outreach taking place so that the disease can be addressed before it’s a full emergency.
Here are just a few examples of trainings open to professionals and the general public:
Fourth Sudden Oak Death Science Symposium The California Oak Mortality Task Force is organizing its' fourth symposium which brings together scientific and management communities from throughout the world working on Phytophthora ramorum and Sudden Oak Death. This forum provides a scientific overview on the state of our knowledge about Sudden Oak Death and P. ramorum in forest, woodland, urban forestry, nursery, and horticultural settings.
Treatment Workshops Matteo Garbelotto offers treatment workshops on the UC Berkeley campus targeting not only tree care professionals and the general public. He makes the information accessible and questions are encouraged. The 2hr sessions, offered monthly during the academic year, cover preventative treatment for the disease. Participants learn which trees to treat, when and how to treat them and are able to see exactly how the treatments are done.
