Halloween seems an appropriate time to highlight a national
horror story. Although this post looks at it
through the prism of Idaho, sadly the tale is unfolding in many places
throughout the U.S. West.
We start the tale innocently enough: comparing the number of
standing trees per acre on forest land across Idaho. But first, a bit of background. In USFS nomenclature “forest land” is the broadest classification of land with trees growing on it, including lands that have at least 10 percent forest cover; timberland refers to forest land that surpasses a productivity threshold and is not legislatively reserved from being actively managed.
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According to the USFS's Forest Inventory and Analysis ("FIA") unit,
there are nearly 21.5 million acres of forest land across the state. Eighty percent of the forest land in the state is
managed by the federal government, with the vast majority (76 percent of the
state’s forest land) managed by the United States Forest Service (“USFS” or
“NFS”). The State of Idaho manages six
percent of the forest land in Idaho with the remaining 14 percent managed by
private land owners. These lands are
interspersed with one another across the state.
With that is background, let’s plunge ahead with our tale. For the three primary forest managers/owners
in Idaho, the USFS, the State of Idaho (“IDL”, for Idaho Department of Lands),
and private land owners, the average forest land acre carries roughly the same
number of live trees (122 per acre for USFS, 119 per acre for IDL, and 108 per
acre for private). However, the number
of standing dead trees per acre on the USFS (43) is roughly double the number
of standing dead trees per acre on State (20) and Private lands (14). Why would this be? Remember, the USFS doesn’t represent an isolated
pocket of property but rather is by far the most significant land manager in
terms of geography within the state.
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IDL and private land is generally more actively managed, including
higher harvest activity, than forest land managed by the USFS. For instance, as can be seen in the graph
below, although USFS managed lands represent 76 percent of all forest land, it
currently accounts for less than 15 percent of the annual timber harvest in the
state. On the other hand, the state,
comprising six percent of the forest land acreage, accounts for nearly 30
percent of the harvest. In the case of
private land owners, 60 percent of the annual harvest is sourced from their
acreage, representing 14 percent of the forest land in the state.
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To further examine the link between active management and
tree mortality, the next chart focuses on USFS land only. As can be seen there are 10 columns in all,
comprising five sets of two columns each.
Each set of two columns shows the number of living trees and the number
of standing dead trees per acre.
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The far right set of two columns on the chart above corresponds
to the USFS graph shown in the prior trees per acre by ownership chart. The other four sets of two columns segregate USFS
forest land into four different categories.
The first two sets look at more productive forest land while the second two sets of columns look at
less productive forest lands. The more
productive forest land area is further sub-divided between acres that are not
reserved, i.e. that are open to active management, and acres that are reserved,
or legislatively withdrawn from any active management occurring on them. Designated wilderness areas are an example,
the most common in fact, of acreage that is reserved from active
management. Similarly, the less
productive acres are sub-divided between not reserved and reserved.
Several patterns emerge when the data is analyzed in this
way. First, the more productive lands
carry more lives trees per acre than less productive lands. Second, the ratio of the number of dead trees
per acre compared to the number of live trees per acres is higher on less
productive lands. But, third, and most
important here, is regardless of productivity, there are more dead trees per
acre on lands where no active management is possible. Fourth, on the most productive areas that
are open to be actively managed, the number of standing dead trees per acre is
still nearly double that seen on IDL and private ownership. Thus, on the USFS even acres where ostensibly active
management can be practiced, not enough is being done and trees are dying.
Beyond, the charts and numbers, the reality is all too obvious
to anyone who looks at Idaho’s national forests. Suppression of fire and significant reduction
harvesting, both for regeneration and thinning, have allowed forest managed by
the USFS to become overcrowded and old.
In the relatively dry climates of the Inland West, the old, overcrowded
conditions weaken trees, making them more susceptible to insects, disease, and
death.
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Trees per acre are one thing and seem bad enough but when
the number of dead trees per acre are multiplied across the size of the USFS
holdings in the state the magnitude of the losses becomes even more sobering. The next chart compares the volume represented
in standing dead trees on the USFS compared to volume in live trees on other
ownerships in Idaho. As can be seen, the
volume represented in the standing dead trees on USFS timberland (not reserved
and productive lands) exceeds the live volume on any other single ownership
class in the state. Total standing dead
volume on all USFS forest land is nearly equal to the total live volume on all
other ownerships combined in the state.
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For those concerned about global climate change and green
house gases, there is an additional element of this carnage that is often
overlooked. As is well known, trees grow
by utilizing atmospheric elements, including carbon dioxide, other nutrients from the soil, sunlight energy, and water. One result of this growth process is a reduction in carbon dioxide, fixing carbon within the tree's cellular structure and producing oxygen as a by-product When a tree dies and begins a slow process of decay, the fixed carbon within the tree is released. However, this process will take a long time
in the dry Inland West so a significant amount of carbon remains ‘stored’ in
the dead trunk for an extended period of time.
However, no new tree can take its place while it stands, and so that
portion of the forest is no longer in effect exchanging carbon dioxide for oxygen as it
once did while carbon that had been stored within the tree during decades of growth slowly leaks away.
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But standing dead trees and standing dead volume speaks to
what has been --- not what is happening.
The chart below begins to look at what is happening now, not what has
been. It compares the volume in trees
that die annually to the volume of trees harvested annually by ownership.
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The first two stacked columns on the chart compare mortality
on non-reserved forest land acres – acres that are open to active management –
to 2012’s harvest. Each column is
sub-divided by ownership to depict the contribution of each ownership category
to the state total. The comparison is
made on non-reserved acres because those are the only acres on which active
management, including timber harvest, can occur. The last column on the chart depicts the
annual mortality occurring on forest land acreage reserved from active
management.
Total mortality, on both non-reserved and reserved forest
land, is nearly 4 times the amount of volume being harvested annually
state-wide. The annual mortality on the
USFS acres that are open to active management is over 18 times the volume of
the annual harvest from those same acres.
Finally, the annual mortality on the 3.8 million acres of reserved –
Wilderness – acres in the state exceeds the annual harvest on the 16.4 million
acres of forest land in the state open to active management across all
ownerships. In a word, the Idaho
Wilderness is being slaughtered.
The chart below shows net annual growth and annual harvest
on Idaho forest lands. The ratio of net annual growth to annual harvest ("growth/drain ratio") is a common, sometimes overused, metric used to test harvest intensity. Net annual growth is the amount of growth occurring in a year minus the amount of annual mortality. As can be readily
seen, not only does state-wide net annual growth exceed
state-wide harvest, the net annual growth on each ownership exceeds the annual
harvest for each individual ownership class in the state. Notably, the "growth/drain" on private ownerships (1.33) exceeds the same ratios on USFS (1.17) and
IDL (1.12).
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Looking at those results on the USFS one might be tempted to
conclude harvest levels could be increased only slightly before harvest exceeds
net annual growth, prompting forest inventory to fall. However, this is one example where the growth-drain ratio alone doesn't provide an adequate picture of forest conditions; in this case, the high level of mortality
distorting what is occurring on USFS lands.
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The chart above separates the components of net annual growth apart and
further separates them by non-reserved (i.e. open to active management) and
reserved forest lands for each ownership class.
As can be seen on this chart, on most ownerships annual mortality is a fairly
small relative to annual growth (16 percent on IDL and private forest land in
Idaho). Unfortunately, this is not the
case for the USFS. On USFS non-reserved
forest lands annual mortality is a whopping 76 percent of annual growth. However, on reserved forest land the picture
is even more dire; annual mortality is 206 percent of annual growth. Idaho’s spectacular wilderness and
back-country areas are slowly dying.
Dying by starvation, dying by thirst, dying by strangulation. Combining the non-reserved and reserved
acreage results in a slightly positive net annual growth where annual growth
exceeds annual mortality by four percent.
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Will Zombie Trees overrun the national forests in
Idaho? And remember, Idaho is simply a
snapshot of the dynamic underway in many public forest lands across the U.S.
West. As bad as it is, unfortunately,
the story does not end with a moonscape of standing dead trees. Ultimately a lightning strike will cremate
the standing and tilting remains of zombie trees, polluting expansive air
sheds, further ravaging wildlife habitat, exposing streams and rivers to
significant sediment loads and reduced shade, and sometimes sterilizing soils for a
generation.
While popular science and belief stretch to
accommodate and explain such ravages as part of the “natural order”, the fuel
loads fanning today’s wildfires are not natural and the results rarely
orderly. Yes, thankfully there is a kind
of rejuvenation in the aftermath of wildfire’s annihilation. But in light of the destruction it seems the
question is could such rejuvenation be achieved in a manner with less apocalyptic
fury and lower societal cost.
Earthquakes, hurricanes, and pestilence are all natural as well. Yet, we try to operate in a manner to
mitigate their damaging effects on society, not amplify them. As a society will we find the will to halt
the advancing scourge of zombie trees?
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