Any American forester you ask will tell you that lichens do not harm trees, and that typically, they grow so slowly as to be imperceptible. I know, because I've asked quite a few of them. There are a couple of types of lichen however, that have gone wildly rampant in just the past three years, smothering branches and tree trunks. I've seen it on both the East and West Coast. These pictures are mostly from a walk yesterday with the Tewksbury Foot Bassets - at the end, there is video of the hunt, and some footage of amazing lichens from California earlier this fall.
So, whether these lichens actually harm trees, or simply thrive when a tree is already dying from other causes, I leave to the experts. But I can say definitively that, once this particular lichen appears, the tree is going to die soon - whether it is ten years old or one hundred. If ever some professional decides to investigate this trend, I'll eat my hat if it's not related to profound, probably irreversible, potentially life-threatening disruption of the nitrogen cycle...and as we all know by now, reactive N is an essential component of tropospheric ozone, the others being volatile organic compounds and ultra-violet radiation.
This may look like a perfectly fine specimen of a tree but a closer look at the branch over the heads of these bassetters shows an alarming amount of lichen and also broken branches, and no terminal [young tips that will form leaves in the spring] growth.
This lichen is proliferating on everything from yews to sycamores, beeches, maples, spruce, oaks and boxwood. Actually I can't think of a tree species I haven't seen it on.
It's even spreading like wildfire on wooden fences, rocks and roofs.
Whenever it appears on seemingly healthy branches, they swiftly transform to losing their bark, and then the tree dies.
This is a segment from the research:
"Biodiversity of plant communities is sensitive to N added by air pollution. Nitrogen-loving species are often favored and increase in prominence as ecosystem nitrogen availability increases. Forests and woodlands in many regions of the world show large changes in epiphytic lichen communities in response to chronic atmospheric nitrogen deposition. These lichen community impacts occur at nitrogen pollution thresholds as low as 3-6 kg/ha/yr."
The Table 3 list specifies: "Lichen community change from oligotrophic [Oligotrophs are characterized by slow growth, low rates of metabolism, and generally low population density] and to eutrophic species dominance" [fast-growing, nutrient enriched like this one, bigger than the branch it's on!]
"Adding nitrogen to forests whose growth is typically limited by its availability may appear desirable, possibly increasing forest growth and timber production, but it can also have adverse effects such as increased soil acidification, biodiversity impacts, predisposition to insect infestations, and effects on beneficial root fungi called mycorrhizae. As atmospheric nitrogen deposition onto forests and other
ecosystems increases, the enhanced availability of nitrogen can lead to chemical and biological changes collectively called 'nitrogen saturation.' As nitrogen deposition from air pollution accumulates in an ecosystem, a progression of effects can occur as levels of biologically available nitrogen increase."
From Table 1., Nitrogen Deposition:
Below is Figure 6, Lichen Based Critical Load Exceedance Map. Areas shown in red and orange received atmospheric nitrogen deposition at levels deleterious to communities of epiphytic (tree dwelling) lichens. This map shows that these effects occur in over half of the forested land area, including urban forests, of the continental U.S. Levels of certainty in the critical load exceedance estimates vary among ecoregions depending on the amount of available lichen community data.
Did you happen to see number 3., in the 3rd column?? INCREASED TREE MORTALITY
Amazingly, there is a webcam at Harvard Forest, and those trees, too, have the lichen. Here's what it looks like - all the reflective white is lichen.
As it happens my friend Susan went to Harvard Forest last week with her husband, Roger, pictured in the little museum.
They sent me these photos, depicting the condition of the woods.
The path is blocked by fallen trees, and others have split.
This is a rather dramatic way to die.
This pine tree has no needles.
Here is a terrific chart, ostensibly about how to set policy. Point B1 is the point of a "clearly identified, ecological threshold at which a tipping point occurs." That point is exactly where we are now. It's too damn bad hardly anybody realizes it, and it's especially too bad that nobody in authority has the courage to say it, loudly.
This is the bleak colors of the hills and fields, which used to be so beautiful, full of magnificent trees. Some of these cedars cling to a bit of green, but the red ones are never coming back. By the end of the winter they will all be quite as dead as the one in the lower left corner.
This tree is sort of average if you include the many that are now totally missing.
Absurdly, the dandelions have begun blooming again.