This is part one of a series on forest health.
Driving or walking through local pine forests it’s difficult not
to notice that some of the trees are now either bare of needles or
their needles have turned a rusty red instead of the deep green
people are used to. While some of the trees died because of
drought, lightning or root-disturbing activities, many have been
killed by bark beetles.
All these dead trees have people worried about increased forest
fuel load, which could allow forest fires to become Hayman-like
wildfires. Others are worried about how the forest looks and how
that will affect the tourist and outdoor recreation
trades.
The worry may be a premature. A study released last month by
scientists at Colorado State Forest Service, Colorado State
University, the University of Colorado and the University of Idaho
suggests even extensive beetle kill is normal and the number of
dead trees may not increase forest fire danger.
There is a bark beetle for nearly every kind of coniferous tree
but the ones most likely to cause problems in Teller County are the
Mountain Pine beetle and the Ips beetle. Colorado has been hit hard
by beetle infestations in last few years but Arizona and New Mexico
have been hit even harder. Beetles have killed hundreds of millions
of trees throughout the southwest.
Bark beetle kill trees in two ways – by girdling the tree with
its egg and feeding chambers and by spreading a deadly blue fungus.
These beetles are native to the area and they and the trees have a
long history together.
According to the study, beetles ordinarily are present in low
numbers at all times, killing a few weak trees here and there, but
in some years the insect population increases rapidly and kills
large numbers of trees. These outbreaks are a natural occurrence
and they don’t happen often.
“Typically decades pass before another outbreak affects a
forest,” the report states.
In the last few years the infestation has been especially heavy
as many trees are already stressed by drought and are unable to
fight off a beetle attack.
The last few decades also have seen warmer summer and winter
conditions. Warm summers accelerate insect growth and reproduction
and mild winters allow more of the beetle larvae to survive to
breed again in the spring.
Climate change may also be the reason that, for the first time
on record, beetles are killing trees in large numbers at elevations
above 9,000 feet. The report took a cautious turn when it came to
why this may be happening and whether it is a natural
phenomenon.
It states: “It is difficult to know if the current insect
activity at high elevations is truly unprecedented, given the lack
of data on precise spatial patterns of prehistoric
outbreaks.”
The report adds, however, that given the warmer high elevation
temperatures the extent of beetle kill above 9,000 feet isn’t
surprising.
The first half of the report covers the beetle kill and factors
that may be involved in the current cycle of infestation. It also
explains the ecology of the various kinds of pine forests,
including spruce, fir and lodgepole, and their bark beetles, along
with the dangers associated with beetle kill.
Answering a question about how much beetle infestations will add
to fire risk, the report takes a cautious approach.
It states: “Based on current knowledge, the assumed link between
insect outbreaks and subsequent forest fire is not well-supported,
and may in fact be incorrect or so small an effect as to be
inconsequential for many or most of the forests in
Colorado.”
It adds that more research is necessary to be confident of that
position.
As for whether large numbers of dead trees caused by beetle
infestation are a sign of an unhealthy forest, the report says the
term “forest health” is ambiguous and the presence of large numbers
of dead trees and beetles in themselves may not be signs that the
forest ecology as a whole is unhealthy. It acknowledges that dead
trees are unappealing to look at.
The second half of the report covers what forest managers should
do about beetles. It lists six options and then explains why they
will or won’t work.
The first option is spraying with insecticide, something it
explains may be a good solution for saving important individual
trees but won’t work for the entire forest.
Option two is preventing or controlling outbreaks through forest
management. Here again, this may work for small forests but
probably not for larger forests. The report stresses that
prevention and control programs, including removal of old or
unhealthy trees and forest thinning, have to be done on a regular
basis. Also, once a heavy outbreak has started, forest management
probably won’t be able to stop it. Finally, forest management can’t
control the climate, which is a major factor in
outbreaks.
Options three, four ands five are related. Three calls for
removing dead trees to reduce wildfire risk. Four calls for
salvaging dead trees to improve forest health and five calls for
salvaging the insect-killed trees for their economic value. Salvage
has to be done quickly before timber quality deteriorates, and
there may be too many dead trees over too large an area for this to
be possible, the report states.
Option six is the one that has brought the most controversy from
forest managers – no treatment. It states: “Natural ecological
processes generally lead to development of new forests after insect
outbreaks, so a ‘no treatment’ option can be a form of responsible
forest management.”
A future article will take up this option and why it and the
report is considered controversial.