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Trees and Lichens
Name: Keith Wyner
Status: educator
Age: 50s
Location: N/A
Country: N/A
Date: 2001-2002
Question:
Trees on the north coast of California are dying. The
bearded lichen seems to be one of the culprits. In checking with the
department of forestry and others, there seems to be a myth that lichens
are a healthy sign of the forest. One of the scientists with, "Ask A
Scientist", also answered the same to an inquiry about trees in Louisiana
dying. Lichen break off and land on healthy trees. The lichen become
entrenched in the bark layer of the tree, and kill off the tree when the
lichen covers the branches, leaves, and bark. I have been pulling it off
healthy trees in my yard. The forests are dying before our eyes. In this
case, the scientists are "barking" up the wrong tree when they say
lichen, and especially the bearded lichen, is harmless and is a sign of a
healthy forest. Simple scientific observations prove the opposite. Is it
related to the sudden oak death? Though it favors firs, it will go after
almost anything it lands on. Why is it killing the trees and where can I
get more "accurate" information on the subject or discuss/chat with
someone who might be know more about it? The destructive bearded lichen
seems to coexist with another flat lichen. What is the scientific name
for the bearded lichen and what is the scientific name of the other flat
lichen it always seems to be with on the dying branches. Is the bearded
lichen part of the Bryoria genus?
Replies:
Tree decline is often not a simple cause and effect relationship but
sometimes a complex web of interacting factors, i.e., tree decline concept:
predisposing, inciting, and contributing factors.
The following might be helpful:
http://www.r5.fs.fed.us/fpm/fh_94-95/provm262.htm
http://cemarin.ucdavis.edu/ecology.html
"Sudden Oak Death (SOD) is best understood in the larger context of the
role of tree disease in the forest. The organisms involved in the disease,
including the pathogen Phytophthora ramorum, as well as associated
secondary insects and fungi, must also be understood as interacting
components of the forest ecosystem."
http://www.aces.edu/department/ipm/lichens.htm
"Lichens, generally, are not considered plant pathogens. Only a few cases
of parasitic activity by lichens have been reported. The fungal partner of
one lichen was suspected of killing twigs and small branches of elm by
infecting the cork cambium, which is found just below the bark. This
suspected pathogenic activity was never proven. Lichenized forms
(Strigula spp.) of the green alga Cephaleuros are plant
pathogens. Strigula is the causal agent of algal leaf spot of camellia,
southern magnolia, and other shrubs and trees in the Deep South. Although
southern magnolia and camellia are most common hosts, this disease has also
been reported on honey suckle, live oak, mahonia, maple, privet, sumac,
sweet gum, and wax myrtle. On leaves of southern magnolia, the lichen
Strigula appears as numerous small grey-white crusty spots. Spotting of
the leaves may be unsightly, but this disease is not a threat to tree
health. Lichens can cause other plant problems. Folicose and fruiticose
lichens on leaves may shade foliage, but shading may slow as the host plant
grows. A thick covering of lichens on a twig or branch may interfere with
gas exchange of host tissues, causing their further decline or death."
Anthony R. Brach, Ph.D.
This is not my area of expertise; however, I do know that the University of
California, Riverside and University of California, Davis both have
excellent botany and plant pathology departments. You might contact them or
the U. S. Forestry Service. Those contacts should be able to answer your
inquiry.
Vince Calder
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Update: June 2012
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