Refuge Notebook
Peninsula Clarion Article
Dated
20 July 2001
Did Beetle-kill forests burn in the past?
by Ed Berg
We
have a lot of dead beetle-killed spruce forest on the Peninsula, and we have had
two scary fires in these forests in recent years. The 1996 Crooked Creek fire
northeast of Ninilchik spread quite rapidly with a strong wind and covered 17,510
acres in a remote area. The 1998 Hutler Road fire east of Homer could have burned
up many homes, but fortunately homeowners generally had prepared good defensible
spaces, and quick response by the firefighters prevented a major disaster.
If
however we look further back into the past, can we see evidence of beetle-killed
forests burning? This question has puzzled me for several years, and I am tentatively
prepared to argue that over the last two hundred years, we have at this point
no evidence of fires in beetle-kill. We have looked at tree-rings in 17 stands
on the Peninsula, from Kachemak Bay to the Swanson River oilfield northeast of
Kenai. We see evidence of bark beetle outbreaks over the whole in the Homer area
Peninsula in the 1810s 1820s, and regional outbreaks on the
southern Peninsula in the 1870s-1880s, and the northern Peninsula
in the 1970s. We also see evidence of local outbreaks at various other times,
such as the Mystery Hills in the early 1980s. In none of these sites do
we see any evidence of a stand-replacing fire after a beetle outbreak.
There
are two areas that would seem to be particularly good candidates to find evidence
of fire after beetle kill: the Tustumena benchlands and the forests south of Deep
Creek to the Anchor River. The Tustumena benchlands experienced a series of burns,
dating at 1871, 1891, and 1910 reburn, according to trapper Andrew Berg who lived
in the Tustumena Lake area from the 1890s until his death in 1939. The tree-rings
show that the central and southern Peninsula forests near the coast experienced
heavy beetle kill in the 1870s, so the timing is right for the 1871 benchlands
fire.
Up on the benchlands one can still find a lot of dead and partially
burned wood in certain areas, which probably escaped the 1910 reburn of the earlier
burned areas. On two trips we have examined a lot of this wood for beetle scars,
but have never found any sign of them. In the Homer area, however, we have found
old (unburned) snags, which died in 1884 with good beetle scars. (We look for
the maternal galleries, which are 3-4 inches long and a quarter inch wide, lying
parallel with the axis of the tree. These can be quite visible on old barkless
wood.) The absence of evidence, of course, proves nothing, but is possible that
benchlands escaped the 1870s beetle infestation because of the higher elevation
(above 1000 feet) and cooler environment.
The second area for a possible
beetle kill-and-fire connection is the broad forested zone from Ninilchik to Anchor
Point. This forest is predominantly continuous white spruce with not much hardwood.
It has experienced 90-100% mortality of the mature spruce, and has been heavily
logged in recent years. Last month we looked in detail at an uncut stand on East
Road, southeast of Ninilchik, which is being considered for a prescribed burn
next year by the Alaska Division of Forestry. This stand is representative of
the area, but it is only one sample of a large area and our results must be considered
tentative.
This stand had a somewhat "even-aged" mature look,
where the largest trees are about the same size, i.e., 15-20 inches in diameter
in this case. Even-aged stands are typically formed after a fire; the largest
trees are all about the same age and were recruited within 10 years or so after
the fire. Appearances can be deceiving, however, and we were definitely fooled
by this one. The largest trees dated from the late 1700s to the 1850s,
indicating that they only appeared to be of similar age but really were not. Furthermore,
we found no burned wood in the stand, which one would expect from a 19th century
burn. We took Pulaskis and opened up old moss-covered logs on the ground, hoping
to find charcoal (or beetle scars) on these logs as evidence of fire, but only
found thoroughly rotten wood. These unburned rotten logs indicate that at least
one generation of trees has come and gone on this site before the present generation
of trees.
We did find locally abundant charcoal-covered wood in the soil,
especially among exposed roots in throw mounds of blown-over birch trees in an
adjacent logged area. This charcoal shows that the stand did burn at some point
within the 8000 years that spruce forests have been on the Peninsula. We are getting
a radiocarbon date on this charcoal, but we expect that it will show that the
stand has not burned for at least 400-500 years.
In the tree-rings from
this site we can see a growth release in the 1880s, which is typical of
our southern Peninsula sites, and we can say with reasonable certainty that this
forest was thinned by the bark beetles during the regional outbreak of the 1870s.
So once again, we see that a forest that did not burn after a beetle outbreak.
To
sum up, in the Tustumena benchlands we had a fire in 1871, but apparently no beetle-kill,
whereas in the Ninilchik East Road site we had beetles but no fire afterward.
The East Road site is thus typical of the 16 stands, which we have previously
studied, which show beetle outbreaks at various times but no evidence of fire.
Should
a homeowner draw consolation from these studies? Unfortunately, no. The climate
is warmer and drier today. Basically, it is drought, not beetle kill that creates
the real fire hazard. A drought-stressed live spruce next to your house is every
bit as flammable as a beetle-killed spruce. We have had an unbroken run of warm
summers since 1987, which has increased evapotranspiration and caused a regional
drying of the landscape. This drying can be seen in falling water tables in wetlands
and closed-basin lakes. Dead or live, our spruce trees burn just fine when they
are dry. Residents in the 1996 Big Lake fire no doubt remember how that fire burned
so destructively in well-dried black spruce that was quite alive and had no beetle-kill
in it.
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Ed Berg has
been the ecologist at the Kenai National Wildlife Refuge since 1993. Previous
Refuge Notebook columns can be viewed on the Web at http://kenai.fws.gov.
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