The Trail Companion

     ...continued.

      So far the disease has only been seen in wildlands, not in street trees or in yards [where it appears near homes it has always been in trees that are functionally part of adjacent open space]. There are other diseases that also occasionally kill trees, particularly those that have been stressed through injury, compacted soils, overwatering, air pollution, etc, but the causitive organism for the oak mortality syndrome has not been identified as occurring except in wildlands so far. Wildlands with much human use, like China Camp State Park on the shore of the Bay in Marin County, does seem to be a possible correlation, however.
      It is difficult to make any recommendations yet. The main ones are: don't move infected wood to new areas, and don't move mud from the vicinity of infected trees to new areas. Dead wood should be allowed to dry out.
      It has been shown that the disease comes first, then the insects, so insecticides are not considered promising for control.
      New understandings are expected to be coming along in the coming weeks and months, since we now have a much better idea what we are dealing with and it is being studied intensively by many people.
      Some arborists present at the meeting said they are seeing a marked increase also in wetwood infections -- another disease, caused by bacteria. Part of the problem is that we have so many very old oaks, not so many middle-aged or young ones. Old oaks seem to be more vulnerable to disease.
      I thought it was a great idea to bring in an expert on the pine pitch canker disease containment problem, Richard Hawley of Greenspace The Cambria Land Trust, though it is caused by a totally different organism in different ways, the lessons learned are worthwhile. He brought a great publication "Programs for Capturing, Handling, Utilizing, and Disposing of Infected Pine Material in San Luis Obispo County". One little tidbit I picked up from his discussion is the problem of pallets. Packing materials are typically built crudely of unfinished wood, and sometimes still have the bark on them -- and thus are a probable vector for spreading disease from continent to continent, sort of the botanical equivalent of ballast water, which has brought so many foreign organisms to San Francisco Bay that an estimated 80%+ of the biomass of the Bay consists of introduced organisms.
      All three panelists gave us some historical perspective on other tree declines, of which there have been many in the last 100 years, most notably the loss of the American Chestnut, which began in 1904 and was complete by the 1950s. The first slide was a very old photograph of American Chestnuts -- so big their trunks looked like old growth redwoods -- the trees grew to 10' in diameter and over 100' tall, and over about 45 years all were at least top-killed in their extensive native range, where they were once a dominant tree, with huge ecological effects. In North America in this century there have been significant declines of oaks, maples, birches, ashes, sweetgums, beeches ... also in trouble in recent decades the Monterey pines, some Colorado pines, aspens and dogwoods. Western Australia suffered a particularly serious decline of Eucalyptus, involving many species with very high mortality, turning some forested areas into grassland.

Jeffrey A. Caldwell
Garden Habitat Network

Jeffrey A. Caldwell, along with Andreas Reimann are preparing an initiative to establish a garden habitat network to preserve and restore biodiversity in our inhabited landscape - the California Garden Habitat network. If interested, contact Andreas at jareimann@ucdavis.edu or 530-754-9478.


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