Physical Evidence used to Establish
Reference Conditions for the
Southwest Jemez CFLR Project
In order to set goals that underlie restoration treatments, it is
essential to know as much as possible about past forest
conditions, especially the “reference conditions” that existed
before forest structure and function were altered by the
disruption of the frequent fire regime as extensive settlement
influenced the environment.
The “reference conditions” were not unchanging through
time, but were sustained across what has been called a
“natural range of variability” (Falk1990; Landres et al. 1999).
The evidence data that we obtain is not just a point in time
reference, but a representation of a range of healthy
sustainable conditions that existed for hundreds of years.
These conditions enabled the “evolutionary environment” of
Southwestern conifer trees – an environment in which tree
species, plants and animals evolved and adapted under a
frequent fire ecological process.
Restoring conditions similar to those of the natural range of
variability is more than trying to return to the past; rather, it is
a good way to assure the long-term health of these forests into
the future.
One way to determine reference conditions is to collect
evidence data from physical remains of old trees. Trees
present before the disruption of the frequent fire regime, that
historically regulated the ecological function of these forests,
are an obvious source of information about forest structure at
an earlier time. While many of the trees standing at that time
have either died naturally or been harvested, their remains
generally persist for many decades in the arid climate of
the Southwest. Searching for and identifying these
remains can establish some of the most accurate records of
past forest structure and composition.
This report documents the types of physical evidence that
was utilized to establish the HRV, or historic stand
densities, that were associated with the frequent fire
regimes that shaped the ecological processes of these
forests prior to the on set of expanded settlement activities
that disrupted the frequent fire regime. For the Southwest
Jemez project we determined 1880 as the date when
frequent fire was disrupted.
To gather reference information, we randomly located one
acre plots (209’X209’) within the sample areas. We then
located and tallied all the historic evidence within the plot
(stumps, logs, snags and live trees that were determined to
be in place 132 years ago). We recorded tree species, but
we did not map tree locations within the plot; instead, we
made observations about historic tree arrangement. We
also made notes on existing stand conditions but did not
collect quantitative data on basal area, trees per acre, tree
age, etc. We did collect quantitative data related to species
composition and tree densities (TPA).
This photo shows two pieces of evidence that we
incorporated into our data to assess reference
conditions; downed logs and cut stumps
representing trees that were known to have been in
existence in 1880.
Downed logs. Especially where fire has been absent,
fallen trees can persist for decades on the forest floor.
Applying a common understanding of tree decaying
concepts, it is possible to identify those trees that were
present at the time of the frequent fire regime, in this case
1880 (based on fire history studies done for the area).
Even where fires occurred evidence of downed trees were
seldom completely eliminated.
The dense wood of the tree roots and lower bowl will last for
decades and provide a reliable source to re-establish historic
structure.
Stumps. Most of the Southwest’s large ponderosa pine and
Douglas Fir trees were cut during the nineteenth and
twentieth centuries, but in most instances their stumps still
persist. Again data indicating diameter, cross-dating tree
rings, and applying tree decay factors can establish trees
existence at a time prior to the alteration of frequent fire.
In addition to determining if a stump qualifies as a tree
that was in existence at the time period of interest, we
also identify the tree species and look at the historic
spatial patterns. In this photo one can see a single stump
in the foreground and several evidences in the far ground
that were part of a tree group (arrows).
It is possible to find evidence of old tree bark in the soil
(arrow) that indicates the diameter of the tree. Where fire
or other impacts have left only the core portion of the tree
stump it is necessary to look at decay factors to verify that
the stump in question meets the criteria to be counted.
Even when fire impacts the evidence it is rare that all
of the stump is destroyed. As in this case both sides of
the stump remain. Even when the interior portion has
been consumed by fire.
Information obtained at a stump, where fire or other
elements have not impacted the evidence, can be applied to
other evidence in the area. Here the center core of the
stump remains along with an exterior portion of the stump
and the root system, making it easy to “size” this stump
and determine it should be included in the HRV tally. By
utilizing this information it was possible to evaluate a near
by stump where only the center core was present and
conclude that it too should be counted.
Another example of a cut tree stump that can be located
and utilized as evidence of the historic forest structure,
including tree density, species composition, size and
structural pattern on the landscape.
Live trees. Trees that were shown to have been in
place at the time period being evaluated (in the case of
the SW Jemez project we used trees that were >132
years old), were also identified and tallied as part of the
historic tree structure.
Snags. In addition to stumps, logs and live trees we
also evaluated snags (arrow), and based on size
appropriateness and decay factors included them in the
historic tree structure.
As with tree stumps, snags can with stand
certain elements of fire and continue to
provide reference information for long
periods of time.
This photo shows snags (blue arrows), down logs
(orange arrows) and live trees (red arrow), that would be
included in the determination of the historic structure.
We also evaluated adjacent areas where the historic frequent
fire regime structure had not been impacted by logging.
This photo was taken at the Monument Canyon Research
Natural Area where no historic tree harvest occurred. This
area was treated (tree removal) to maintain most of the
historic structure. However, not all of the remaining trees
in the photo are historic frequent fire regime trees. But this
Research Natural Area provides an excellent opportunity to
evaluate historic tree conditions. It also provides evidence
of how frequent fire regulated stand structure and density.
We also looked at areas, outside of our sample plots, that
we encountered in the field, where groups of live presettlement (pre 1880) trees remained mostly intact
(arrows), to evaluate historic tree patterns.
By looking for and documenting historical
tree evidence it is possible to gain an
understanding of the tree pattern, structure
and composition that existed when
frequent fire influenced the forest. That
information can then be compared to
existing conditions to evaluate the
restoration needs of the forest.