Thinleaf alder, Alnus incana ssp. tenuifolia, is a critical species in riparian areas of the central and southern Rocky Mountains in the United States. Observations in recent years indicate that branch dieback and mortality of alder are widespread and increasingly common. Some range and fisheries experts report that it first drew their attention about 10-12 years ago. Cytospora canker is associated with the damage in almost all cases, but that does not suffice as an explanation.
This summer we conducted a survey throughout the Colorado mountains as well as southern Wyoming and northern New Mexico. More details to come.
Among the potential root causes are:
1. Climate change may have stressed alder and increased susceptibility to Cytospora canker. This coul d include anthropogenic effects as well as population and distribution fluctuations associated with natural, long-term climatic variability.
2. An alder disease caused by a new species of Phytophthora, possibly introduced from Europe.
3. An alder disease caused by the alder phytoplasma, possibly introduced from Europe.
4. Introduction of a new species or form of Cytospora.
5. The population dynamics of alder are conceivably such that large numbers of dead and dying stems are part of the equilibrium condition.
White pine blister rust was just found in two places in the southeastern mountains of Colorado, about 300 miles from the nearest known occurrence of the disease. This is a huge leap in distribution, and differs from the usual slow spread.
Still in the process of devastating limber and whitebark pines in Wyoming, and southwestern white pine in the Sacramento Mountains of southern New Mexico, the pathogen has now appeared between those infested areas. It was found in the Sangre de Christo Mountains, in both the San Isabel National Forest and the Great Sand Dunes National Park, and in the Wet Mountains, also in the San Isabel N.F. There it threatens not only limber pine, the only host it was found on, but also Rocky Mountain bristlecone pine and southwestern white pine.
Two means are considered potentially responsible for this long-range dispersal. The feasibility of dispersal of spores over long distances in high-altitude winds is under study. California is considered a possible source for such spores in New Mexico and Colorado. Another mechanism is the transport of infected trees. White pines have become quite popular for lanscaping in mountain communities, and there is increased construction of new homes and subdivisions in private land bordering National Forests. Many, if not most of this demand is met through transplanting from the wild rather than growing the trees from seed in nurseries.
Slowly but relentlessly, this pathogen continues to move into uninfested areas. The devastation to high-elevation ecosystems is also slow but just as relentless and permanent.
When a fire is raging, and a record-breaking one at that, everything except safety seems to become a low priority compared to fire suppression efforts. However, during the Biscuit Fire, the largest in Oregon's history, complex and time-consuming measures to restrict the spread of Port-Orford-cedar root disease were carried out by a team of up to 7000 firefighters.
As related by Ellen Goheen, forest pathologist in the US Forest Service in Oregon, the rules put into place to restrict the invasion of new drainages by the devastating pathogen, Phytophthora lateralis, were never questioned by the firefighting organization. Helicopter bucket loads of water taken from infested areas was treated with bleach to kill the pathogen before application to the fire. Trucks, bulldozers and other vehicles were washed to remove mud each day before leaving infested areas. Local land managers were familiar with the measures to exclude the disease from uninfested areas, supported them, and incorporated them into fire suppression activities. Although temporary road closures for the same purpose are not always respected by the public, this has to be regarded as a stellar success in forest disease management efforts.
MgCl2 is becoming somewhat controversial in Colorado. It is increasingly used for both dust abatement on unpaved roads and as a winter de-icing agent on paved roads. As its use has increased, so have observations, reports and complaints of damage to roadside trees.
MgCl2 has long been used for dust abatement, but it is being used on an increasing number of roads. More recent is the increased, heavy usage as deicing agent. In Summit County, one truckload sufficed to treat the road system in a winter storm in the '70's, but today 20-30 trucks are needed, largely because of increased traffic and expectations. And the concentration of salt in the sand has gone up from 2% to 5%.
Strings of dead and dying trees along the sides of both paved and unpaved roads are becoming more common. Most often the damage is on the downhill side, suggesting that flow and soil transport are most important, but sometimes (and perhaps especially with lodgepole pine) trees rooted above the road may be affected and the damage may be one-sided, suggesting that salt in aerosol created by traffic may be an important transport mechanism.
In some areas, the public and towns are pressuring the Colorado Department of Transportation to acknowledge the problem and work toward solutions. We certainly need better information on this. The problem is obvious.
We put on a Hazard Tree Training recently. For the last part we have students inspect trees and rate them. While flagging trees to rate, I picked a small subalpine fir that looked perfect in every way as a "trick tree," i.e., one with no defects. Well, they proved me wrong!
The students looked things over much more closely than I had. Some of them were coring every tree just to be safe. Well it turned out this small, healthy fir was nearly hollow, at least in the first meter or so. While we were reviewing the trees later, someone spotted a small fruitbody at a twig stub. The twig stub couldn't have been 1 cm diameter, and the fruitbody was only about 1x2 cm. Then we spotted more fruitbodies on dead lower branches that were partly covered by litter.
I suspected Stereum sanguinolentum (the bleeding Stereum, so called because it may exude a reddish liquid if bruised while fresh and moist), and a microscopic look (together with George Chamuris's great book, The Non-Stipitate Stereoid Fungi of the Northeastern United States and Adjacent Canada) proved it. This interesting little fungus is sometimes a saprobe on fairly fresh dead wood, but is well know as a stem decayer of wounded balsam fir in eastern Canada. However, Boyce mentions a case of it causing root disease on some planted conifers in Idaho! This find was unique since the tree was apparently unwounded and decayed in the butt. All in all a very interesting find!
The last few weeks have been a real eye-opener with respect to Phellinus pini. In my four years in the Colorado area, I had only seen the stem decay fungus on Engelmann spruce (Picea engelmannii). However in the last two weeks I have seen it on lodgepole pine, subalpine fir, and Douglas-fir.
The new finds were outside my usual stomping grounds. I was up in the northwestern part of Wyoming, on the Shoshone National Forest between Yellowstone National Park and Cody, for cruiser training. There we were in a stand with a lot of defect and decay. In addition to fantastic punk knots on spruce, we found a lodgepole with small, obscure punk knots. We felled the tree and found mostly brown discoloration and very early stages of decay for about the first 15' of the stem. Nowhere was there more advanced decay. Only when I split a piece longitudinally could I find a few white pockets and zone lines that we typically see with Phellinus pini. Later we found a Douglas-fir with punk knots - the dead branches tended to pull out easily and had the golden-brown color of the mycelium on the rotted ends.
Then, last week in hazard training in Frisco, Colorado (near Breckenridge) we found several subalpine fir (Abies lasiocarpa) with the disease.
Of course the pathogen has a wide host range, but these are the first times I have personally seen it in anything but spruce. In both areas, the fungus was apparently most common on Engelmann spruce. In southern Colorado it appears to be more restricted to spruce and these other hosts must be rare.