Smooth Bark Helps To Protects Trees From Pine Beetle Attacks
Dec. 23, 2013
Scott Ferrenberg
According to a new CU-Boulder study, trees with smoother bark are better at
repelling attacks by mountain pine beetles, which have difficulty gripping the
slippery surface, says researcher Scott Farrenberg.
CUT 1 “It’s really a simple thing – that the bark doesn’t have enough texture
for an insect to grip a tree and for that reason alone. With very little to grab
onto the beetles just fall off the tree.” (:11)
The current mountain pine beetle epidemic has spread across 3.4 million acres
in Colorado since the outbreak was first detected in 1996.
Ferrenberg says the findings may help land managers make decisions about
which trees to cull and which to keep in order to best protect forested
properties against pine beetle infestation.
CUT 2 “What we envision is that a forest manager or even a private
landowner could easily measure these traits. It’s as simple as understanding
the proportional coverage of bark types on a tree. (:10) And by using those to
decide which trees are more susceptible and which are most resistant to bark
beetle we can make intelligent decision about which trees we should cut to
thin the landscape and help to manage bark beetles by reducing the number
of trees that can support their populations.” (:25)
Ferrenberg, who led the study, says he first began to suspect that bark texture
might affect the survival of trees while he and colleague Jeffry Mitton, a
professor of ecology and evolutionary biology, were walking through a stand
of high-elevation limber pines.
CUT 3 “We noticed that the smooth bark trees were not dying at the same
rate as the trees with rough bark. That inspired us to look into the reasons
behind it. (:11) And we discovered not only that this pattern held up under a
large cross section of the landscape but that there was a historical precedence
of ecologists hypothesizing that smooth bark could be a defense against
insects It just so happens that nobody tested it.” (:25)
To prove their visual findings, Ferrenberg says he and Mitton conducted a
simple but effective test to see if smooth bark truly affected a beetle’s ability
to attack pine trees. They did this by capturing pine beetles in flight and then
placing them on trees with smooth bark and on trees with rough bark and
simply watching.
CUT 4 “We found out pretty quickly that they could not hang on to the
smooth bark. Every beetle in our trial fell off the tree in about a minute and
they rarely fell off the rough bark. We only found one beetle out of all the
ones we tested that actually fell from a rough bark tree.” (:14)
They also made another finding, says Ferrenberg. He says smooth bark trees
tend to be younger giving them two big advantages in defending against
pine beetle attacks.
CUT 5 “They have a lot of smooth bark to prevent bark beetle attacks from
the outright and they also tend to have a lot of defenses inside the tree. (210)
225 - The man defense of a pine against pine beetle is the resin that you
would see on the stem after a beetle attack. And that comes from a system of
resin ducts that are found vertically and horizontally in the tree. (:19) And it
turns out that trees that can resist bark beetle attacks always have
significantly greater numbers of these resin ducts. That tends to be true of
trees that are growing faster and trees that are younger. (:31)
Ferrenberg says it’s is very important to recognize that what has been learned
from this study is that tree defenses play a vital role in bark beetle
populations even when they are at epidemic levels.
CUT 6 “And that’s something that we have really not spent a lot of time
thinking about in the past. So I think that’s really neat from the perspective of
a manager because it means there’s really no point in time when it’s not
worth considering tree defensives. (:12) Even if the epidemics have been
rolling across the landscape for a long time there’s still something that we can
do for those areas that haven’t been attacked. We can make more intelligent
and focused decisions using traits that are easy to measure.” (:22)
-CU-