Presentation on theme: "Physical Evidence used to Establish Reference Conditions for the Southwest Jemez CFLR Project In order to set goals that underlie restoration treatments,"— Presentation transcript:
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 pre- settlement (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.