THE AUGUST 2003 COTTONWOOD BURN FIELD SURVEY
Howard Horowitz
Abstract
Conifer-shrub growth interactions were systematically measured on ten sites identified as “high priority” herbicide treatment areas on the 1994 Cottonwood Burn, in the Sierraville District of Tahoe National Forest. The conifers are primarily Ponderosa pine and Jeffrey pine; some stands were planted, while others were dependent on natural regeneration. The principal shrub species, Ceanothus velutinus, is the principal target of the herbicide proposal, and greenleaf manzanita is a secondary target species.
Trees and shrubs were measured on one-hundredth acre plots that were studied in linear transects that ran across the proposed treatment sites. Overall, 183 plots were examined on ten sites. Within each plot, conifer-shrub growth information was recorded, including height, leader, whorl and diameter measurements for up to two crop trees per plot. The location of each crop tree with regard to brush species is noted – it may be growing within a ceanothus thicket, or it may be growing on the edge of ceanothus, or it may be growing in a patch of open ground.
The measured growth data was statistically analyzed by Becky Parker to evaluate the relationships between conifer stocking and growth and ceanothus height and density.
Total conifer stocking was not significantly related to either the height or the density of ceanothus. Crop tree diameter was significantly greater where ceanothus is present on plots than where it is absent, and diameter is significantly greater for trees growing at the edge of ceanothus than for trees growing inside of ceanothus. Diameter differences between the outside and edge positions, and the outside and inside positions, are not statistically significant. Crop tree height is significantly greater on plots with ceanothus present than on plots where it is absent, although height differences were not significant between the inside, edge, and outside locations. Crop tree leader growth is significantly greater on plots with ceanothus present than on plots where it is absent, and the edge has a greater mean leader growth than either the inside or outside position. As with diameter, only the difference between edge versus inside positions is statistically significant. Crop tree cumulative whorl growth is also significantly greater in the presence of ceanothus than in its absence, although there were no statistically significant differences between inside, edge, or outside positions.
The survey reveals that the presence of ceanothus is not negatively impacting either the survival or the growth of conifers on these Cottonwood sites. To the contrary, ceanothus has a positive association with conifer growth on these sites, as measured in terms of diameter, height, leaders, and cumulative whorl growth.
Introduction
Thousands of acres of conifer plantations are treated annually for “release” from ceanothus and other shrub species. Yet systematic measurements of conifer-brush growth interactions are almost non-existent on operational release project sites. Instead, forest managers have tended to rely on abstract assertions of “competition for sunlight, moisture, and nutrients” to assert the need for herbicide treatment wherever brush has a substantial presence. The word “release” is an imprecise term in forest management, with meanings that range from the prevention of conifer mortality to the maintenance of optimum conifer growth rates. Further imprecision comes from the use of the same word “release” to describe both the spray treatment and its intended effect. When the forester plans to “release” one thousand acres, it becomes very easy to simply assume that accomplishing the treatment (herbicide spraying) will by definition accomplish the desired effect (accelerating conifer growth). Since systematic measurements of conifer-shrub growth are not taken across these operational sites, no system exists to examine whether the prescribed “release” treatment is producing a measurable “release” effect.
In the absence of such evaluation, the effectiveness of “release” treatment is assumed, regardless of whether it is real.
The Groundwork survey system for evaluating conifer-shrub growth interaction was developed in 1978 by a team that included Gregory Prull, Howard Horowitz, Laura Weeks, John Cloud, Robert Rydell, and other experienced forest workers. It was used to evaluate proposed herbicide treatment sites in the Lowell District of the Willamette National Forest, where over 2,000 acres had been prioritized as needing release treatment from Ceanothus velutinus. Subsequently, this survey system was utilized to evaluate growth interactions in Roseburg BLM, Eugene BLM, and Siskiyou National Forest.
I incorporated the field data from these surveys into my EPA testimony at the 2,4,5-T Cancellation Hearings in Washington DC, and Gregory Prull and I presented oral and written testimony to the House Subcommittee on Forests in 1980 and 1981. The field surveys were incorporated into my doctoral dissertation Conifer-Shrub Growth Interactions on Proposed Brush Control Sites in the Western Oregon Cascades (University of Oregon, 1982). I was an invited participant in the Forest Service workshop The Role of the Genus Ceanothus in Western Forest Ecosystems, which took place in Corvallis in November 1982, and resulted in USFS Gen Tech Report #182 (1985).
I first became aware of the Cottonwood herbicide proposal after getting contacted by local residents in June 1999, and participated in the July 13, 1999 field tour conducted by the Tahoe National Forest. The similarities between the issues raised by this proposed release project and those discussed in my dissertation and in the Groundwork field surveys were remarkable. Since then I have been a contributor to both the E.A. public comment process, and to the court case that followed. In August 2003 I spent 8 days on the Cottonwood Burn with citizen volunteers from the Forest Interest Group, measuring conifer and shrub growth on a representative sample of proposed herbicide release sites. After several days of training and practice, we took measurements on 183 plots in linear transects that run through 10 sites listed as “high priority” for release from ceanothus.
Each of the plots is marked with flagging tape, and is located by GPS position as well, to facilitate revisiting if necessary for future growth measurements or for independent verification.
Survey Methodology: What Information is Needed for Accurate Site Evaluation?
The Forest Service data for the Cottonwood Burn is inadequate because it does not record critical information that would allow more precise examination of the ecological interactions on a site-by-site basis. The Sierraville District states that it records the height growth of conifers and brush, and also brush density, which is their primary criterion for treatment prioritization. That allows several questions about each site to be accurately answered: 1) what is the density and distribution of brush on each unit? and 2) Is the conifer stocking adequate for plantation success? Where are the understocked and overstocked areas on each site located? This is necessary information, but it is not sufficient to identify the need for release treatment. If operational field surveys record only tree height, brush height, and brush density, we cannot obtain a clear picture of what is really going on, because the information lacks precision about species interaction. In the absence of good growth measurements, subjective opinions based on “years of experience”, or abstractions such as “competition for moisture”, cannot be objectively tested on operational forestry sites.
The Groundwork survey records additional information on the field survey plots: the height, diameter, leader growth, and 3 years of whorl growth of each crop tree. Most importantly, within each sampled plot, the location of each crop tree relative to brush species is recorded (inside, edge, or open-grown), as well as its vertical relation to adjacent shrubs (dominant, codominant, or overtopped).
This growth information is recorded only for crop trees. They are selected on the basis of form, vigor, and spacing, just as they would be selected by a precommercial thinner. (On overstocked stands, the excess trees will need to be thinned out in the near future.) Recording and analyzing the crop tree growth and location data allows the following questions to be answered with site-specific accuracy:
1) How are crop conifer diameter growth, height growth, leader growth, and cumulative whorl growth affected by the presence and density of brush species?
2) How are conifer diameter, height, leader, and cumulative whorl growth affected by crop tree location with regard to brush species? How do trees growing along the edge of brush species compare with trees growing in the open, or trees growing inside the brush canopy?
3) What percentage of the crop trees are overtopped by brush? How much more slowly are these overtopped trees growing? What percentage of the crop trees are dominant?
4) Has annual conifer growth been increasing or decreasing in recent years?
Other observations, such as animal browse or yellowing needles, or microsite conditions such as rocky ground or severe compaction, are noted on a plot-by-plot basis. The impacts of these conditions on crop tree growth can then be evaluated with greater confidence than can be done without field data. Other variables that were recorded on each plot, such as slope and aspect, may independently exert influence on conifer growth. If the plot data is recorded, then these influences can all subsequently evaluated by statistical analysis.
Modification in the Groundwork Protocol for the Cottonwood Survey
The only significant modification in the Groundwork methodology, as it was applied to the August 2003 Cottonwood Field Survey, involved the pattern of plot transects.
Previously, plots were taken on uniform grid patterns that completely encompassed each management unit at a density of at least one plot per acre. The advantage of this very thorough site coverage is that it allows the pinpointing of problem areas within the larger management units. However, the Cottonwood Burn herbicide proposal involves such an enormous area (over 20,000 acres) that a small crew of volunteers could not possibly measure the conifer-shrub growth on more than a fraction of the project.
We decided to sample as many of the proposed high priority sites as we could, rather than taking plots in grid patterns that would encompass every acre of each management unit chosen for growth measurement. Therefore, surveyors took plots in linear transects that crossed through the middle of each site. The plot centers on each linear transect were spaced 100 feet apart; intervening distances were paced with compasses and tape measures, and each plot’s GPS coordinates were recorded. On several occasions, the surveyors decided to end a plot line, because the transects were entering into large areas with absolutely no brush, although the maps indicated that we were still in proposed treatment areas. When that happened, the surveyors would change direction, and begin another compass-line transect into an area that did contain brush species. The transect maps are included in the back of this report.
The August 2003 survey was necessarily limited to a modest series of transects that cross through a 10-site sample of this very huge proposal, but it already provides far more accurate and detailed conifer and shrub growth information than anything the DEIS provides. If the Forest Service chose to upgrade its site evaluation methods to incorporate additional conifer-shrub growth data, they would have a much clearer picture of the regenerating Cottonwood Burn. Field personnel could be readily taught to perform the stand exams, or they could be contracted out to bidders from the private sector, as many other stand exams are. The site-specific data would rapidly accumulate to allow the development of meaningful local growth projections, as contrasted to the nonsensical projections constructed in the spurious “reference stand” methodology described in Section d-4 of the Cottonwood DEIS. Although good stand exams are somewhat slower and therefore costlier than simple stocking/density surveys, they would save an enormous amount of money in the long run, and would result in better forest management. (The district could have thoroughly surveyed every acre of the Cottonwood Burn for a small fraction of the cost of the Cottonwood DEIS, for example).
Conclusions:
I taught a small dedicated group of citizen volunteers how to take the Groundwork-style plots, because that information would help to promote a better understanding of the conifer-brush growth interactions in the Cottonwood Burn. Some of these citizen volunteers were themselves very knowledgeable about botany and field science, so it was a productive learning experience all around.
Since the field work was completed last August, I have had nothing to do with the analysis of the Cottonwood Burn growth data, and have never met Becky Parker, the statistician that FIG hired to perform the data analysis. However, the results of her analysis confirm what is apparent from walking extensively across these proposed herbicide treatment sites: there is much microsite variability, but overall the burn is regenerating into a floristically diverse and healthy early-successional forest. Although thickets of ceanothus are widely present in some portions of the burn, they are mostly well-stocked with young conifers. Most of the crop conifers are now well-established, and are emerging above the brush.
Becky Parker’s statistical analysis of the Cottonwood Burn Recovery field data speaks for itself, and is included in this report. I will only summarize its highlights here:
1) Total conifer stocking was not significantly related to either ceanothus height or ceanothus density. That is, the density of conifer stocking is not dependent on either the presence or absence of ceanothus. Plots that were taken in dense ceanothus patches did not have, overall, either fewer conifers or more conifers than plots taken in largely open areas.
2) Crop tree growth was significantly greater on plots where ceanothus was present than on plots were ceanothus was absent. This was confirmed for all measures of crop conifer growth: diameter growth, height growth, leader growth, and cumulative whorl growth.
There are many ways to try to explain or interpret these results, although I hesitate to place too much credence in any particular explanation. They could be related to the many beneficial impacts that ceanothus is capable of providing to the sites where it grows, although the one-sided Cottonwood DEIS largely ignores the literature that discusses these beneficial effects. The benefits of ceanothus are substantial and long-term, and include symbiotic nitrogen-fixation, the production of nutrient rich litter that decomposes to improve soil texture and fertility, the amelioration of harsh sites by moderation of heat stress, rhizosphere associations with beneficial soil organisms that fight conifer pathogens, the provision of valuable browse for wildlife, and others. A very different interpretation could be that ceanothus may tend to occupy the better sites to begin with, and therefore the conifer perform better there too. Rather than argue about theoretical explanations (as the Forest Service does when they insist that “competition” or “moisture stress” is threatening the survival and growth of the trees, I suggest that the measurements speak for themselves.
3) Conifers growing in the “edge” location had slightly greater diameter, height, and leader growth than conifers growing in either the “inside” or the “outside” location. The edge location’s growth advantage was statistically significant in some comparisons, and not statistically significant in others. Again, I am more confident simply reporting the results than in trying to provide a definitive explanation of the reasons for the result. However, this result is consistent with Groundwork surveys performed 25 years ago in the Willamette National Forest and in Roseburg BLM. In each case, the mean growth of the “edge” trees was slightly greater than either the “inside” trees or the “outside” trees.
In conclusion, the conifer-growth interactions that were measured on these plots contradict the DEIS contention that Ceanothus velutinus is threatening the survival and growth of the young conifer trees. To proceed with the DEIS preferred alternative, in the absence of any objective evidence of need, would subject the area ecosystem to a massive dose of toxic contamination for no beneficial purpose.