When most of us think about the word "wilt," we don't picture trees. Instead, we think about green shrubs and flowering plants losing all their support and flopping over, usually from lack of water.

But many diseases of forest and urban trees are classified as wilts. The pathogens that cause these diseases grow into the water-conducting vessel elements and tracheids in the sapwood of the tree, clogging them up and stopping the flow of water. Some of the better-known tree diseases that do this include Dutch elm disease, oak wilt, blackstain root disease, and . . . Sudden Oak Death!

Douglas-fir killed by blackstain root disease in southern Humboldt County

Well, Sudden Oak Death is partly a wilt. Scientists haven't completely determined all the steps involved in pathogen infection and death of tanoak and true oak trees. For a long time, it was assumed that P. ramorum killed trees solely by consuming the cambium underneath the bark. When the pathogen had done this all the way around the circumference of the tree, the tree died because it could not produce new phloem to carry organic compounds or new xylem to carry water and mineral nutrients.

But within the past couple of years, a team led by Jennifer Parke at Oregon State University determined, with the aid of electron microscopy, that P. ramorum does grow into the vessel elements and tracheids in the sapwood of tanoak trees (read the abstract here). This invasion stimulates the tree to produce hard structures called tyloses, which are like little hardened embolisms that protrude into the vessels. These tyloses may help slow pathogen growth, but they also slow water transport.

Thus, P. ramorum's mode of killing trees appears to be a multifaceted one. The OSU team continues to investigate exactly how this works, while other scientists are investigating whether P. ramorum also produces toxic substances that help to kill plant tissue in its path. This variety of ways to survive and grow inside the tree is matched by a variety of movement and survival strategies on the part of the pathogen in the outside world, again demonstrating how tough and versatile P. ramorum is--truly a supremely difficult forest problem to tackle.

P. ramorum hyphae in tanoak xylem. Photo courtesy of Dr. Edwin Florance.

The encroaching army leaves mayhem in its wake, spreading from hillside to hillside, county to county, with alarming speed and determination. Only the strong and brave can stare into the gaping maw: educated school children.

This is one great example of citizen science at work - the AntWeb database sponsored by the California Academy of Science, one of many such projects through the Academy's Naturalist Center. More than 800 citizen scientists have participated thus far in the project, submitting ant specimens from around the Bay Area. From these submissions, the Cal Academy has indentified 34 distinct ant species, and is gaining a better understanding of how the invasive Argentine ant is affecting native ant populations.

Closer to our Sudden Oak Death roots, students at the Mount Madonna school in Watsonville are monitoring local P. ramorum infections and tree mortality as part of their own citizen science initiative. Here in Marin, the Marin Municipal Water District uses visiting student groups to track SOD on their land. I know that there is interest from other students and teachers in using Sudden Oak Death in their classrooms and during field trips - what other projects are going on out there?

Send me information on any citizen science projects that deal with SOD, or wishes for projects that might get started, and I'll post the highlights in an upcoming blog.

On Friday, I was at the Trinity River in eastern Humboldt County, watching my son splash his way through water as clear as the sky above. One hundred feet upstream, a helicopter repeatedly dipped its bucket into the river, rising up each time to carry its load to one of the fourteen fires that broke out in our county and neighboring counties last week, the results of lightning strikes. As the helicopter passed over our heads, it trailed a stream of water from the bucket, and about three minutes later, it would be raining on us very gently for a minute or two.

This got me thinking, of course, about fire hazard and the toils of keeping cleared, defensible space around one's home when one lives in the country (which I do not). This in turn evoked thoughts of a local NGO in our north coast area, the Mattole Restoration Council (MRC), which is working to encourage homeowners in the Mattole River watershed to provide that defensible space by distributing grant money to help the homeowners get the work done. When each household maintains that magical 100-foot clearance, it benefits the entirety of this remote watershed, where it's often extremely difficult for firefighters to get quick entrance and egress on steep, narrow roads in scattered neighborhoods. With less flammable space around homes (and fewer homes that are themselves flammable--but that's another subject), firefighters can concentrate on attacking the flames in the wildland area rather than spending all their time worrying about defending structures.

This led to thoughts of other worthy MRC work: the organization is working on writing a Program Timberland Environmental Impact Report, a document designed to apply to owners throughout the watershed who want to practice sustainable forestry designed to return Mattole forestlands, many of which were highly degraded by mid-20th-century timber harvest practices, to healthy productivity while protecting water quality and other important values. Having a program document like this (i.e., an already-written "checklist"-type document) will make responsible forestry, which can be an expensive proposition for a small landowner, a real possibility for many watershed residents.

Which brought me to Sudden Oak Death. P. ramorum has moved to the very eastern edges of the Mattole River watershed. Soon, the disease could be one more thing for Mattole valley residents to worry about. Along with the MRC, UC Cooperative Extension has been holding informational workshops about SOD, but concern hasn't built as high here as in some areas of coastal California. This could partly be the result of a few dry years during which the pathogen has become less visible in southern Humboldt County because it has caused less tanoak mortality. On another level, though, it's understandable that many Mattole residents may have "wildland management fatigue" from worrying for so many years about fire, fish, and forestry.

Since Sudden Oak Death has not yet impacted the Mattole, there's a real chance that, given funding and political will, residents could do something the limit the spread throughout the watershed. But the disease is tagging along behind all those other equally important concerns. The question that occurs to me at this point, then, is this: Is there a way to unite these seemingly disparate domains? Given the realities of funding, in which each relatively narrow environmental issue attracts its own funding, scientific study, and advocacy groups, could some kind of comprehensive wildland management assistance ever materialize for rural landowners who need it, like the ones in the Mattole? 

When our president talks about creating jobs to help our environment, this is what I see: an army of forest management experts and helpers, working in places like the Mattole to address all these wildland management concerns in a comprehensive manner. On any given property, these folks, organized into teams perhaps, would work on fuel hazard reduction and riparian restoration and erosion remediation and sustainable timber production and weed control and habitat protection and protection from insects and diseases. Considering how each of these management activities can often interact synergistically with the other activities, it remains a wonder to me that this hasn't already happened. It may just be that a vision like this, to come to fruition, will require a collective societal decision that wildland management is worth an investment.

 

The Mattole River: good for many uses.

 

I'll be upfront: I stole the title of this post from my supervisor at UC Extension in Eureka, Yana Valachovic, who also took the pictures. She has talked about this subject several times to various audiences, and I think it's so interesting I wanted to post it.

Below are two pictures of the same California bay laurel (Umbellularia californica)  tree, one from a distance and one up close. Bay laurel (also called pepperwood, Oregon myrtlewood, or just plain bay) is the main transmitting host of Phytophthora ramorum. The pathogen produces loads of spores on the leaves of bay laurel, and the spores are then blown or splashed onto other trees. If those trees happen to be tanoaks, coast live oaks, Shreve oaks, California black oaks, or--maybe--canyon live oaks, they can be killed. (The bay laurels, meanwhile, remain completely unharmed.)

Because of this, some of the management activities aimed at controlling Sudden Oak Death focus on strategic removal of some bay laurels to reduce disease risks for particular important oaks and tanoaks. As part of our management experiments in the north coast, we decided to try cost-effective ways of killing large bay laurels. It's very expensive for crews to cut them down, remove the limbs, and burn the small limbs and foliage. So we decided to try girdling some trees to see how rapidly they would die in place. Even though the standing trunk and limbs would still be there, the foliage, which is the part of the tree that carries P. ramorum, would be gone.

To make a long story short: nothing doing. Those girdled bays are not interested in dying. The girdle on the tree below was made by one of the landowners with whom we are collaborating. And boy, did he ever girdle it! The "beaver cut" he made goes at least six inches deep into the sapwood.

The top picture gives you a good look at this beaver cut. But if you look at the bottom picture, you'll see that the tree is trying to heal itself.

 

  

 

The roughened area of bark-like tissue in the center of the trunk is an area where the tree is trying to grow a new "bridge" of cambial tissue over the girdled area to heal itself. The crown of this tree is still green and healthy-looking, over two years after it was girdled, despite the tree's inability to move food between crown and roots.

Obviously, bay laurels are amazingly resourceful trees! Maybe this is one reason why several ecologists have speculated that as tanoaks decline in coastal California because of the effects of Sudden Oak Death, bay laurels will increase in dominance in many areas.

One of the biggest problems in dealing with invasive, non-native species is that it is rarely possible to exterminate them once you've seen the mess they've made, and you often don't even know to be concerned until the problem is too large to deal with. Preventative actions to limit their introduction in the first place and aggressive actions to control early infestations seem to be the best course of action, but has its obvious limitations. How many of us know to floss regularly to prevent tooth decay but still end up with a root canal anyway?

One issue with preventative measures is measuring success. With a control effort, you can say "we had X and now it's gone." With a preventative measure, such as limiting importations or strictly regulating the movement of plant material, all you can say is "X didn't happen" and there are many questions then of whether "X" would have happened at all and whether your draconian measures did more harm than good in the meantime.

This exact topic came up at the SOD Science Symposium a couple of weeks ago, and it seems to come up with every new pest that grabs our attention. When will we stop reinventing the wheel on this topic? If stricter across-the-board regulations aren't the answer, how will we get all interested parties to agree which pests are important to stop, when, and how? Will there have to be another Sudden Oak Death - or Chestnut blight, or Dutch elm disease - to resonate with the nation as a whole?

 

chestnut blight

dutch elm disease