On Friday, the San Francisco Chronicle published a story about Sudden Oak Death and the spread of P. ramorum in waterways. It mentioned that ten streams, ditches, or ponds in six states have now been found infested with P. ramorum. Many of these are states that are officially considered uninfested because the pathogen has not been found in the forest environment. In all these cases, the pathogen has been linked to nearby nurseries that have at one time or another carried infested ornamental plants.

The article points out that the most mysterious case is right here in Humboldt County. Two streams in McKinleyville, north of Arcata, are infested with P. ramorum. Although both streams run through heavily developed residential neighborhoods, we from UC Cooperative Extension have teamed up with Humboldt County Ag Department and Redwood National Park personnel to try to find the source of the spores in the stream by walking as much of the streambanks as possible to find symptomatic plants--and so far, we have found nothing in two seasons of looking.

Near both streams, there is very little host material for P. ramorum to infect. There are very few ornamental hosts and almost no bay or tanoak. The bright side may be that this paucity of host material means little chance of the pathogen's escaping the stream and spreading further. Another positive is that at the point where P. ramorum has been recovered in each stream, the waterways empty into the ocean in short order.

Although a nearby nursery in McKinleyville has had infected plants at various times in the past, there is no definite link between the nursery and the streams--the streams are too far away for water from the nursery to easily make its way to the streams--unlike in other states, where it's obvious how infested runoff exited each nursery and made its way to each nearby waterway.
 
The mysterious cases of persistent spores in these streams highlight the troubling difficulty of definitively ridding infested nurseries and forests of P. ramorum.



Monitoring Rock Creek in Del Norte County for Phytophthora ramorum using rhododendron leaf baits.

A couple of months ago, I was on a large ranch near Boonville in Mendocino County, walking back from a plot where we have been counting and measuring trees killed by P. ramorum. As I came out of the drainage where most of the dead trees were, I was suddenly walking through a white oak woodland.

Here the trees were statelier, they were widely spaced, and everything felt drier. Besides the white oaks, huge bay laurels shaded the leaf litter and flowering plants in the understory. I looked down and saw this:

This is Lithophragma, aka the "woodland star." It was waving in the breeze, so I didn't get a very clear picture. I'm a sucker for all those delicate-looking flowers with complicated petals so often found in oak woodlands. Here's another one, Silene:

One of the interesting things about our oak woodlands is the variety to be found among them, even in just the northern part of the state. In Humboldt County, many of our coastal ridges and "bald hills" are crowned by open stands of white oaks. Driving past Laytonville in Mendocino County, one passes majestic stands of long-limbed valley oaks. Along Highway 20 from Lake into Colusa County, blue oak savanna with golden grass and plenty of other oak species carpets the tall rolling hills. On the way into the Bay Area from the north, the driver can't miss the coast live oaks lining the ridges near the road, heavy branches dipping down to the ground. In all these habitats, oaks have evolved to take advantage of relatively little water and thin soils, factors that make these places dicey, at best, for Douglas-fir or other conifer survival.

But Douglas-firs will try to survive there if they can get a foothold. In the eras of Native American use and European settlement, fires were either started or allowed to burn through many of these woodlands to maintain their open character. This kept conifers out. But beginning in the twentieth century, fires were kept out, and the conifers started to come in.

In the north coast, we are losing many oak woodlands and historically open prairie areas to Douglas-fir encroachment--and also to encroachment by some hardwood species that like the increased shade, such as bay laurel.

Interestingly, in many of these places it's easy to tell that the Douglas-firs don't really like it there. Here's a picture of one of the sites where we have installed some experimental silvicultural treatments to try to limit slow the spread of P. ramorum. It's an old prairie that has been under Douglas-fir invasion for a very long time. Note the crowded conditions and sickly-looking conifers. The Douglas-firs here are suffering from heavy infestations of two root diseases, Phaeolus schweinitzii (the velvet-top fungus) and Armillaria.

Bay laurel, though, is not as particular as Douglas-fir. If it can get established,it can grow surprisingly well even in places that seem as though they should be too dry. And in an area where P. ramorum has also become established, it will find the bay laurel--the tree is like a P. ramorum magnet.

Mountain biking through China Camp State Park a few days ago, I was struck by all of the different signs of change in the forest around me. First, I rode through the area that recently burned along the southeast corner of the park. The air still smells of charcoal and the ground is black, but I know that come winter and spring, new green shoots will burst forth, adding to the mosiac of plants and habitats in the grassland. All along that trail, I saw another sign of change - the seasonal coloring of everyone's favorite plant, poison oak. At least the deepening red of the leaves makes the dreaded plant more visible and easier to avoid.

Further along the trail, I moved out of the warm sun of the oak woodlands and into damp and shaded canyons, dim under the canopies of redwood and bay trees. Here the change was not only marked by the shift in temperature and tree species but also by the amount of Sudden Oak Death mortality visible. Immediately upon entering one such spot, I saw a full tanoak canopy down on the hillside next to the trail, leaves brown and dry. While I had seen plenty of dead and dying coast live oaks along other, earlier parts of the trail, the sense of mortality was somehow greater here.

The overall change that Sudden Oak Death will bring to this forest, and other simliar forests in California and Oregon, is still largely unknown. Over the past decade, we've seen the trees go and mourned their immediate loss - but once those skeletel reminders are gone, will we recognize the changes that have occured in these woods?

Finally, a note on changes on a personal level. Due to the financial constraints currently affecting the state and the UC system, my fellow blogger Nicole Palkovsky will no longer be working on Sudden Oak Death outreach. We wish Nicole the best and look forward to a time we can work with her again. Chris Lee and I will continue to post to this blog on a regular basis and welcome your input as well. That said, I'm off for a couple weeks of vacation, so keep Chris busy with your comments and thoughts in the meantime, and I'll be writing here again in August.