2007 HFQLG SOIL MONITORING REPORT
Prepared by:
Randy Westmoreland, HFQLG Soil Monitoring Leader
& Colin Dillingham, HFQLG Monitoring Coordinator
Statistical analysis by Jim Baldwin, PSW Statistician,
February 1, 2008
This report summarizes soil monitoring data collected on the Lassen, Plumas and
Sierraville District of the Tahoe National Forests between 2001 and 2007 as a part of the
Herger - Feinstein Quincy Library Group (HFQLG) Forest Recovery Act Pilot Project.
In 2006 the analysis of the soil compaction data indicated that there was a need to
increase the precision of the data. Confidence intervals were too wide to make definitive
statements about the effect of management in some instances. In 2007, the soil
monitoring work focused on analysis of the cumulative pre-post monitoring data set and
testing two additional sampling protocols to see if the precision of the data could be
improved and make adjustments as needed.
The soil monitoring is required by the HFQLG EIS to answer the question:
Question 6) Do Activities meet Soil Quality Standards?
The soil quality standards and guidelines for soil in the HFQLG forests are found in the
Land and Resource Management Plan (Forest Plan) for each forest.
The definitions, thresholds and indicators in FSH 2509.18 - SOIL MANAGEMENT
HANDBOOK, R5 Supplement No. 2509.18-95-1 were utilized to provide a consistent
method to measure soil condition for this and past years. The 1995 handbook supplement
defines detrimental soil disturbance when the resulting condition exceeds the threshold
values. Recent science (Powers et.al. 2005) raises questions whether exceeding the
threshold value given in the FSH supplement for total soil porosity actually constitutes a
significant change in soil productivity for all soils in general. While the use of the
thresholds and definitions in the handbook supplement and forest plans provides a
consistent method to measure soil properties, the interpretation of the significance of the
monitoring findings needs to take in to account this recent science.
Whenever heavy ground based equipment is used to perform resource management
activities (such as DFPZ construction) the potential for adverse impacts to soil quality
exists. This includes compaction, disturbance and displacement of soil, or a loss of
ground cover and large woody debris. The individual forest plans set standards and
guidelines for compaction, ground cover, and large woody debris to keep these impacts
within acceptable limits in the context of the benefits accrued from managing the land.
Although not a part of the soil quality analysis standards, the HFQLG soil monitoring
includes recording the level of disturbance and displacement of soil. From 2001 to 2004
planned treatment units were sampled pre-treatment to document existing conditions.
Post-treatment monitoring of units began in 2004 and continued through 2007. After
evaluation of the pre-post unit pairs, it was determined that 40 thinning units, 11 group
selection units and 2 mastication units were available for analysis, bringing the total to 53
units available for pre-post analysis.
In 2007 soil monitoring work was focused on statistically reviewing all data collected to
date and testing two new sampling protocols. Two new pre-treatment units, one repeat
pre-treatment unit, and two repeat post treatment units were sampled in 2007 at a higher
intensity (200 points instead of 60 points) to test if the 200 point methodology would
increase statistical precision. See appendix 1 for a description of the methodology
discussion.
Harvest areas were sampled by transects; landing areas were excluded. Preliminary
statistical analyses were completed for all units with soil compaction data.
For details on sampling protocols for the 2006 and earlier data see the sampling
methodology in the HFQLG monitoring plan. Sampling protocols used in 2007 are
attached.
2001 - 2007 Data Review of Soil Conditions Before and After Treatment
Review of Data
The field data from all soil monitoring to date was entered into a spread sheet and was
recalculated. There were not significant changes in the calculated unit summaries (per
Jim Baldwin).
Overview
The review of monitoring data indicates that legacy compaction is commonplace. The
mean value for all units was 21%, which is statistically above the 15% threshold. Only
the Group select treatment showed a statistically significant increase in soil compaction.
Almost all (97.5%) of the thinning units met the recommended thresholds in the Forest
Plan soil quality standards for soil cover of at least 50%. Group selection units did not
meet soil cover standards in over half of the units. Evidence or observation of increased
soil erosion was minimal. Soil displacement was well within acceptable standards. The
percent area with soil disturbance increased compared to pre-treatment monitoring
especially in the group selection units, but appears to be acceptable within the normal
range of controlled logging activities. Large woody material decreased from levels
observed during pre-treatment monitoring. Standards and guidelines for retention of large
woody material, which recommend at least 3-5 large logs per acre as determined on a
project-by-project basis, were met in only 62% of the thinning units and 18% of group
selection units.
Figures 1 and 2. Bars represent 95% confidence intervals.
Pre Treatment versus Post Treatment Conditions
(Average of 11 Group Selection Units)
100
100.0%
Pre Treatment
Post Treatment
95.2%
80
67.5%
Percent
60
47.6%
40
36.4%
18.2%
20
18.0%
10.3%
5.55% 4.76%
0
Compaction
Displacement
Disturbance
Soil Cover
Met Soil
Quality Std
(50% Cover)
Soil Conditions
Pre Treatment versus Post Treatment Conditions
(Average of 40 Thinning Units)
100
100.0%
Pre Treatment
Post Treatment
89.8%
97.4%
77.7%
80
Percent
60
40
29.8%
25.0% 23.6%
20
16.9%
6.2%
4.04%
0
Compaction
Displacement
Disturbance
Soil Conditions
Soil Cover
Met Soil
Quality Std
(50% Cover)
Soil Porosity
Soil compaction (loss of soil porosity) has been viewed as a major factor affecting soil
productivity. Compacted soil has lower water infiltration rates, can have higher or lower
water holding capacity (depending on soil texture), and increases in soil strength that can
restrict root growth. Standards and Guidelines within the Forest Plans for the Lassen and
Tahoe National Forests limit detrimental soil compaction to no more than 15 percent of
an activity area excluding the transportation system. Standards and Guidelines within the
Plumas National Forest Plan allow no more than 15 percent of an activity area to be
dedicated to skid trail and landings. Activity areas are typically defined as harvest units.
Comparisons of the before and after treatment soil porosity status were made for 53 Units
for various types of treatments and subsoiled status. Table 1 includes the results of the
statistical analysis of the compaction data. Although the Group select treatment showed a
trend for increase in soil compaction, it was not statistically significant (P-value = 0.07).
Note that the variance in the data set is very large, and when all units are included in one
dataset, there is a normal distribution around no change (Figure 1).
Table 1. Mean percentages of tile-spade measurements that were determined to
exhibit soil compaction, the number of units (N), and the standard error of the
mean. Also presented is the summary of change in mean percentages of tile-spade
measurements that were determined to exhibit soil compaction along with the 95%
confidence intervals and the standard error of the mean difference for various types
of treatment and subsoiled status.
PostTreatment
Characteristic
Treatment
All
Group
Select
Compaction
Masticate
Mechanical
Thinning
Subsoiled
All
No
Yes
All
No
Yes
All
No
Yes
All
No
Yes
# of
units
53
25
28
11
1
10
2
2
0
40
22
18
Mean
22.3
24.9
19.9
18.2
33.3
16.7
17.5
17.5
23.6
25.2
21.7
Std.
Err.
2.3
4.1
2.4
3.7
3.7
9.2
9.2
2.9
4.6
3.1
PreTreatment
Mean
21.8
21.4
22.1
10.3
0.0
11.3
12.5
12.5
25.4
23.2
28.0
Std.
Err.
2.9
4.5
3.8
2.9
3.0
12.5
12.5
3.6
5.0
5.2
Mean
0.5
3.5
-2.2
7.9
33.3
5.3
5.0
5.0
-1.7
2.0
-6.3
Difference
Lower Upper
95%
95%
Std.
CL
CL
Err.
2.0
-3.4
4.5
2.8
-2.3
9.3
2.7
-7.7
3.4
3.9
-0.8
16.5
3.2
-2.0
12.7
3.3
-37.4
47.4
3.3
-37.4
47.4
2.3
-6.4
2.9
2.9
-3.9
8.0
3.5
-13.7
1.1
Pvalue
0.794
0.220
0.431
0.070
0.134
0.374
0.374
0.456
0.481
0.088
Note that the 95% confidence intervals for the mean characterize how well the mean of
units is estimated. Also, for example, the estimate of 23.6% for post-treatment
mechanical thinning units does not mean that all units were above the 15% threshold.
This is simply the estimate for the mean of a collection of units. A commonly used
significance level of 0.05 was used to denote statistical significance.
Density
0.000
0.005
0.010
0.015
0.020
0.025
0.030
Histogram of % Compaction Change
-40
-20
0
20
40
% Compaction Change
Figure 3. Frequency Distribution differences in pre-post compaction measurements
Explanation of findings and trends
The desired condition is that detrimental soil compaction is limited to no more than 15
percent of an activity area. Although the mean pre-existing compaction value is over
threshold (statistically significant; P = 0.04), the estimate does not indicate that all units
were above the 15% threshold. Note that there is a very wide prediction interval for the
amount of compaction for individual units. Further analysis of each individual unit was
completed to determine which units are statistically over the threshold.
Pre Post Sets
Group Select – 5 of 11 units (45%) have the sample mean over the threshold, but because
of the wide prediction interval, only 2 units (18%) are statistically over threshold (lower
limit of confidence interval is above 15% threshold).
Thinning – 28 of 40 units (70%) have the sample mean over the threshold, but because of
the wide prediction interval, only 17 units (43%) are statistically over threshold (lower
limit of confidence interval is above 15% threshold).
The comparison of pre- and post-sampling shows that the overall trend is no significant
change. The silvicultural prescription, the location of trees to be removed, the soil
moisture at time of harvest and the kinds of logging equipment used has changed from
the pre-treatment situation to the latest entry being monitored and is likely partially
responsible for any change in compaction. It is important to note that most units that
exceed the threshold post-treatment start with a significant amount of legacy compaction
from previous treatments. Even where current equipment operations are well controlled,
cumulative effects including legacy compaction may exceed the standard.
While the sample post-treatment mean amount of compaction is 2.2% less than the pretreatment mean for units that were subsoiled (which is expected if subsoiling acts as a
mitigation measure to reduce compaction), the decrease in compaction was not
statistically significant (P = 0.22). Prevention of compaction should be considered the
highest priority. Use subsoiling as a second best management choice where it is
appropriate based upon the area management objectives, the particular soil
characteristics, and other factors.
Significance of the Findings for Soil Porosity (Compaction)
Recent findings on compaction effects on total biomass productivity (soil productivity)
(Powers and others 2005) indicate that for soils with texture classes grouped into “sandy”
(coarse sandy loams or sandier) declines in total biomass productivity are not expected.
On soils grouped as “loamy”, compaction did not appear to significantly decrease or
increase total biomass productivity. On soils grouped as “clayey” (such as clay loams or
more clay), total biomass productivity declined when compacted.
Soils monitored for the pre-post comparisons can be characterized as being in either the
“sandy” or “loamy” soil texture groupings. Soil textures monitored in 2006 on 11 units
would be classed as “sandy” and soil textures on 2 units would be classed as “loamy”.
None were classified as “clayey”. The remaining 40 units in the sampling pool have been
classified with soil mapping information and are all in “sandy” or “loamy” soil texture
groupings. So in regard to overall significance, it appears that although some units do not
meet the 15% standard for compaction, a decrease in soil productivity (total biomass
productivity) would not be expected unless they occur on “clayey” soils. Additional
analysis will be completed.
There were some unexpected results in the compaction data. The monitoring data
appears to show a decrease in compaction on some units that were not subsoiled. Several
factors could contribute to these results:
•
Although GPS is used to locate post-treatment transects in the same approximate
location as the pre-treatment transects, the post-treatment transects are not in the
exact same locations. Sampling a different line across the landscape will result in
some random variation in results.
•
Compaction is a continuous variable. Still the protocol for compaction sampling
requires the crew to judge detrimental compaction based on soil structure and
other field properties, and to judge if it is above or below a threshold. A smaller
set of core samples is collected, taken to the laboratory for measurement, and used
to calibrate the sampling crew. Variation in samplers and their skills can lead to
some variability in results.
Legacy Compaction in Pre-treatment Unit Data Set.
In 2007 the results for compaction were analyzed to determine if a unit was statistically
above or below the threshold. Although the sample means of some units are over
threshold, when analyzed statistically, the lower end of the confidence interval is below
the 15% compaction threshold. Units that were over threshold after recent treatments had
high levels of compaction before treatments from past activities (legacy compaction)
Pre Treatment Units
Out of 163 pre treatment, 51 units (31%) have their mean compaction over the15%
threshold. Because of the wide prediction interval, only 31 units (19%) are statistically
over threshold (meaning that the lower limit of confidence interval is above 15%
threshold). The other 20 units with the mean over threshold have their 95% confidence
intervals both above and below the 15% threshold.
Other Soil Attributes (soil cover, down large wood, soil displacement, soil
disturbance)
Soil Ground Cover – Cover of duff & litter, vegetation, large woody debris or rock.
This is a composite of two recommended thresholds from the R5 soil quality analysis
standards: the effective soil cover (ESC) for erosion prevention and the organic matter
(OM) threshold for fine OM. The ESC standard is site specific and the OM standard
(regional threshold) is for a minimum of 50% fine OM, preferably undisturbed.
Large Woody Material – Down logs at least 20” in diameter and 10’ long. Standards
and Guidelines require 3 logs per acre after treatment
Soil Disturbance – Is there any indication of soil disturbance (e.g., loss of duff and litter
or evidence of past equipment operation). Although not a part of the soil quality
standards, this monitoring includes a metric for soil disturbance.
Soil Displacement – Soil has been moved from its original location, resulting in
loss of topsoil. Although not a part of the soil quality standards, this monitoring includes
a metric for soil displacement.
Ground Cover
An increased level of disturbance is reflected in the ground cover data where 7 out of 11
(64%) group selection units did not meet the 50% ground cover standard and guide. It is
worth noting that 2 of the 7 units had 48% cover and so were close to the standard and
guide.
Almost all thinning units (39 out of 40) exceeded the minimum standard and guide (50%
ground cover) for ground cover. 67.5% of the thinning units had 75% or more ground
cover with the highest recorded value being 94% cover.
Figure 4. Bars represent 95% confidence intervals.
Post Treatment Soil Ground Cover
100%
97.5%
Group Selects
Thinning Units
80%
Percent of units
67.5%
60%
40%
36.4%
20%
0.0%
0%
Met Soil Quality Std
(50% cover)
> 75% Soil Cover
Table 2. Mean percentages of soil ground cover, the number of units (N), and the
standard error of the mean. Also presented is the summary of change in mean
percent soil ground cover along with the 95% confidence intervals and the standard
error of the mean difference for various types of treatment and subsoiled status.
PostTreatment
Characteristic
Treatment
All
Group
Select
% Soil Cover
Masticate
Mechanical
Thinning
Subsoiled
All
No
Yes
All
No
Yes
All
No
Yes
All
No
Yes
# of
units
52
25
27
11
1
10
2
2
0
39
22
17
Mean
71.7
79.5
64.4
47.6
57.1
46.7
86.7
86.7
77.7
79.9
74.9
Std.
Err.
2.4
2.2
3.6
4.8
5.2
1.7
1.7
1.7
2.2
2.6
PreTreatment
Mean
91.1
90.0
92.0
95.2
90.5
95.7
91.7
91.7
89.9
89.9
89.9
Std.
Err.
1.0
1.5
1.3
1.3
1.3
8.3
8.3
1.2
1.7
1.7
Mean
-19.4
-10.5
-27.6
-47.6
-33.3
-49.0
-5.0
-5.0
-12.2
-9.9
-15.0
Difference
Lower Upper
95%
95%
Std.
Err.
CL
CL
2.6
-24.7
-14.1
2.2
-14.9
-6.0
4.1
-36.0
-19.2
5.4
-59.7
-35.5
5.8
-62.1
-35.9
6.7
-89.7
79.7
6.7
-89.7
79.7
1.6
-15.4
-8.9
2.1
-14.4
-5.5
2.4
-20.0
-10.0
Pvalue
0.000
0.000
0.000
0.000
0.000
0.590
0.590
0.000
0.000
0.000
A commonly used significance level of 0.05 was used to denote statistical significance.
Large Down Woody Material
Downed logs were also reduced more within group select units than the thinning units
with only 2 out of 11 units meeting the guideline of 3 logs per acre after treatment. 3 of
the 11 units (30%) had no logs pre treatment. 6 units (55%) went from meeting the
guideline to not meeting the guideline.
Of the 40 thinning units monitored, 6 units (15%) had no logs in the pre monitoring. 8
units (21%) were reduced from meeting the guideline to not meeting the guideline. 25
units (61.5%) met the guideline pre and post treatment. For informational purposes, an
additional 3 units had between 2.5 and 2.7 logs per acre, and almost met the guideline.
One unit (2%) went from not meeting the guideline to meeting the guideline post
treatment. In the 25 units that met the guideline the range in estimated number of logs
per acre was 3 to 12.
Figure 5. Bars represent 95% confidence intervals.
Post Treatment Large Down Woody Material
(Decomposition Classes 1-5)
100
Group Selects
Thinning Units
81.8%
Percent of units
80
61.5%
60
40
18.2%
20
12.8%
0
No Down Wood
(all classes)
3 or more logs/acre
(all classes)
Table 3. Mean percentages of units that met large down woody material guidelines,
the number of units (N), and the standard error of the mean. Also presented is the
summary of change in mean percentages of units that met large down woody
material guidelines along with the 95% confidence intervals and the standard error
of the mean difference for various types of treatment and subsoiled status.
PostTreatment
Characteristic
Treatment
All
% of Units
with > 3 Logs
per Acre
Group
Select
Masticate
Mechanical
Thinning
Subsoiled
All
No
Yes
All
No
Yes
All
No
Yes
All
No
Yes
# of
units
52
25
27
11
1
10
2
2
0
39
22
17
Mean
51.9
60.0
44.4
18.2
0.0
20.0
50.0
50.0
61.5
63.6
58.8
Std.
Err.
7.0
10.0
9.7
12.2
13.3
50.0
50.0
7.9
10.5
12.3
PreTreatment
Mean
80.8
88.0
74.1
72.7
100.0
70.0
50.0
50.0
84.6
90.9
76.5
Std.
Err.
5.5
6.6
8.6
14.1
15.3
50.0
50.0
5.9
6.3
10.6
Mean
-28.8
-28.0
-29.6
-54.5
-100.0
-50.0
0.0
0.0
-23.1
-27.3
-17.6
Std.
Err.
7.4
10.8
10.4
15.7
16.7
0.0
0.0
8.6
11.7
12.8
Difference
Lower Upper
95%
95%
CL
CL
-43.8
-13.9
-50.4
-5.6
-51.1
-8.2
-89.6
-19.5
-87.7
-12.3
0
0
0
0
-40.5
-5.7
-51.7
-2.9
-44.8
9.5
Pvalue
0.000
0.016
0.009
0.006
0.015
0.011
0.030
0.188
A commonly used significance level of 0.05 was used to denote statistical significance.
Soil Disturbance
In group select units (2 acres or less) soil disturbance is higher than in thinning units.
This is expected as the treatment (100% tree removal to create openings for regeneration)
is more intense than general thinning.
In thinning units soil disturbance for all monitored units is within expected range. The
expected range is between 30% and 60 % of a unit based on past observations and the
footprint monitoring (previous HFQLG monitoring that was done estimating the amount
of ground traveled to harvest a typical thinning unit using GPS to track skidding
operations).
Figure 6. Bars represent 95% confidence intervals.
Post Treatment Soil Disturbance
100
100.0%
Group Selects
Thinning Units
Percent of units
80
62.5%
60
40
35.0%
20
2.5%
0.0%
0.0%
0
None
1-25%
Percentage of Sample Points in a Unit That
Show Soil Disturbance
> 25%
Table 4. Mean percentages of measurements that were determined to exhibit soil
disturbance, the number of units (N), and the standard error of the mean. Also
presented is the summary of change in mean percentages of tile-spade
measurements that were determined to exhibit soil compaction along with the 95%
confidence intervals and the standard error of the mean difference for various types
of treatment and subsoiled status.
PostTreatment
Characteristic
Treatment
All
Group
Select
Disturbance
Masticate
Mechanical
Thinning
Subsoiled
All
No
Yes
All
No
Yes
All
No
Yes
All
No
Yes
# of
units
53
25
28
11
1
10
2
2
0
40
22
18
Mean
37.6
31.0
43.6
67.5
47.6
69.5
29.2
29.2
29.8
30.4
29.1
Std.
Err.
2.9
2.4
4.8
6.1
6.4
14.2
14.2
1.9
2.4
3.2
PreTreatment
Mean
17.4
12.2
22.0
18.0
9.5
18.9
14.9
14.9
17.3
12.1
23.8
Std.
Err.
2.5
2.6
4.0
4.4
4.7
14.9
14.9
3.1
2.8
5.7
Mean
20.2
18.8
21.5
49.5
38.1
50.6
14.3
14.3
12.5
18.4
5.4
Difference
Lower Upper
95%
95%
Std.
CL
CL
Err.
3.4
13.3
27.2
3.4
11.9
25.8
5.8
9.5
33.5
6.1
35.8
63.2
6.7
35.5
65.7
0.7
4.8
23.7
0.7
4.8
23.7
3.3
5.9
19.1
3.7
10.6
26.1
5.3
-5.9
16.6
Pvalue
0.000
0.000
0.001
0.000
0.000
0.033
0.033
0.000
0.000
0.328
A commonly used significance level of 0.05 was used to denote statistical significance.
Soil Displacement
Overall, the level of soil displacement measured post treatments was low. Soil
displacement from the HFQLG treatments does not appear to be a significant problem for
soil quality in either group selection units or thinning units.
Figure 7. Bars represent 95% confidence intervals.
Post Treatment Detrimental Soil Displacement
100
Group Selects
Thinning Units
80
65.0%
Percent of units
63.6%
60
40
27.5%
18.2%
20
18.2%
7.5%
0
None
1-10%
Percentage of Sample Points in a Unit with
Displaced Soil
> 10%
Table 4. Mean percentages of sample points determined to exhibit soil
displacement, the number of units (N), and the standard error of the mean. Also
presented is the summary of change in mean percentages of sample points
determined to exhibit soil displacement along with the 95% confidence intervals and
the standard error of the mean difference for various types of treatment and
subsoiled status.
PostTreatment
Characteristic
Treatment
All
Detrimental
Displacement
Group
Select
Masticate
Mechanical
Thinning
Subsoiled
All
No
Yes
All
No
Yes
All
No
Yes
All
No
Yes
# of
units
53
25
28
11
1
10
2
2
0
40
22
18
Mean
4.9
6.5
3.4
4.8
0.0
5.2
21.7
21.7
4.0
5.4
2.4
Std.
Err.
0.9
1.4
1.1
2.6
2.8
13.3
13.3
0.7
0.9
0.9
PreTreatment
Mean
6.4
6.1
6.7
5.5
0.0
6.1
11.7
11.7
6.4
5.9
7.0
Std.
Err.
1.0
1.5
1.4
2.5
2.7
11.7
11.7
1.1
1.5
1.8
Mean
-1.5
0.4
-3.2
-0.8
0.0
-0.9
10.0
10.0
-2.3
-0.5
-4.5
Difference
Lower Upper
95%
95%
Std.
CL
CL
Err.
1.3
-4.0
1.0
1.5
-2.6
3.4
2.0
-7.2
0.8
4.1
-9.9
8.3
4.5
-11.1
9.4
1.7
-11.2
31.2
1.7
-11.2
31.2
1.2
-4.7
0.1
1.5
-3.6
2.7
1.8
-8.3
-0.8
Pvalue
0.228
0.799
0.110
0.852
0.853
0.105
0.105
0.058
0.754
0.020
A commonly used significance level of 0.05 was used to denote statistical significance.
Mastication
Mastication is a mechanical method for reducing competing vegetation and thinning
small trees. Typically, a grinding head is mounted on the end of the boom of an
excavator. The excavator then travels through a unit masticating the competing brush and
small trees. The excavator exhibits low ground pressure and leaves a mulch of shredded
debris in its wake. The result is generally low soil disturbance and compaction to the soil
while leaving relatively high soil cover. Two units that had been masticated were
monitored in 2006.
Because the pre-treatment conditions of the two masticated units were drastically
different, the data are presented separately because the average values are not very
meaningful. Both units are pine plantations, but one unit showed no compaction,
displacement or disturbance prior to treatment. The other unit had high levels of legacy
compaction, displacement and disturbance prior to treatment; probably from prep work
when the unit was planted. Although the data for Waters Unit 8D appear to exceed
desirable conditions, this has not yet been evaluated statistically, but it is planned.
Waters 8D
Waters 8E
Before
After
Before
After
Compaction -
25%
27%
Compaction -
0%
8%
Displacement -
23%
35%
Displacement
0%
8%
Disturbance -
28%
43%
Disturbance -
0%
15%
Soil cover -
84%
85%
Soil cover -
100%
88%
Findings and trends
Applying statistical analysis to the data confirmed which units that could be determined
to be compacted beyond the standard and guide and informed the monitoring team of the
need to increase precision of the data set and amend the monitoring protocol. There is
evidence that treatment with ground based equipment in group selection units increased
the overall amount of compaction. This incremental increase is significant in that the pretreatment mean is below threshold and the post-treatment mean is above threshold. The
sample mean of compaction estimates increased in some individual thinning units, but as
a group, compaction did not statistically increase in thinning units. Analysis of the
current data set was that was collected with the older 21 (group selection) or 60 sample
point (thinning unit) methodology indicated a need for a 200 sample point methodology.
The older methodology generally precludes precise determination of compaction at the
individual unit level, so statements cannot be made if individual units went from slightly
below threshold to slightly above threshold.
In the group selection units, the standards and guides for ground cover and large downed
wood were not met more often than in thinning units. The treatment for group selection
units is to remove all trees from small, 2 acre or less, patches. This requires the
equipment to cover more of the ground than with a typical thinning operation.
Significance of the Findings for Soil Porosity (Compaction), Ground Cover and Large
Downed Logs.
The standards and guides for compaction (soil porosity) set limits on aerial extent of
compacted ground to maintain soil productivity. Recent findings on compaction effects
on total biomass productivity (soil productivity) (Powers and others 2005) indicate that
for soils with texture classes grouped into “sandy” (coarse sandy loams or sandier)
declines in total biomass productivity are not expected. On soils grouped as “loamy”,
compaction did not appear to significantly decrease or increase total biomass
productivity. On soils grouped as “clayey” (such as clay loams or more clay), total
biomass productivity declined when compacted.
Most surface soils monitored can be characterized as being in either the “sandy” or
“loamy” soil texture groupings. None were classified as “clayey”. Additional pretreatment monitoring was initiated in 2007 to evaluate finer textured soils and this focus
will be continued to better evaluate compaction where it is important. So in regard to
overall significance, it appears that although some units do not meet the 15% standard for
compaction, a decrease in soil productivity (total biomass productivity) would not be
expected unless they occur on “clayey” soils.
The reductions in ground cover and large down wood in group selection units may be an
issue. The reductions themselves may not decrease soil productivity as this is a short
term condition and both ground cover and large down wood would be expected to
increase within the first few years after treatment, especially ground cover. However, the
ground cover also effects the soil erosion potential. Effort should be taken to meet
ground cover standards and guides to protect soil from erosion and to protect water
quality.
There were some unexpected results in the monitoring data. The monitoring data appears
to show a decrease in compaction on some units that were not subsoiled and some of the
other data showed results that go down when they should go up. Several factors could
contribute to these results:
•
Although GPS is used to locate post-treatment transects in the same approximate
location as the pre-treatment transects, the post-treatment transects are not in the
exact same locations. Sampling a different line across the landscape will result in
some random variation in results.
•
Compaction is a continuous variable. Still the protocol for compaction sampling
requires the crew to judge detrimental compaction based on soil structure and
other field properties, and to judge if it is above or below a threshold. A smaller
set of core samples is collected, taken to the laboratory for measurement, and used
to calibrate the sampling crew. Variation in samplers and their skills can lead to
some variability in results.
•
There is variability in compaction along any transect line and repeated sampling 7
to 40 points along that transect will result in variability among overall compaction
estimates.
Adaptive Management Changes as a result of Monitoring
Finding: Analysis of the soil compaction data indicates that there is a need to increase the
precision of the data. Confidence intervals are too wide to make definitive statements
about the effect of management in some instances.
Management Response: Changes in the sampling protocol are being developed and were
implemented during the 2007 and planned for the 2008 evaluations.
Finding: Legacy compaction exists above threshold levels in both group selection and
thinning units and cumulative increased compaction effects are occurring in group select
units. However, negative effects on soil productivity are not expected for soils with
“sandy” or “loamy” soil texture classes. Subsoiling, although not appropriate in all
situations, may reduce compaction.
Management Response: Subsoiling is continuing to occur where appropriate. A review
of subsoiling was conducted by the Regional Soil Scientist in 2006 and recommendations
have been provided. Forest plan standards and guidelines may need to be amended to
allow for compaction for particular soil types where negative impacts to soil productivity
are not expected. Findings from the 10 year results of the Long Term Soil Productivity
Study and other studies will be used to revise the LRMP standards.
Finding: Increases in detrimental compaction are occurring in group selection units, and
possibly in some thinning units. Prevention and/or reduction of detrimental compaction
can be improved by using soil moisture objectives relative to equipment operations to
determine when equipment operations should be permitted.
Management Response: There have been increases in seasonal operation restrictions to
dry soil conditions when soil strength is high for soil textures dominated by loam or clay
particle sizes. Slash has been placed on skid trails during harvest operations in some
project areas in an effort to reduce compaction.
Finding: Post-treatment soil ground cover in group selection units did not meet LRMP
standards in 74% of the units.
Management Response: Discussions are being initiated between timber sale
administrators, soil scientists and forest leadership to improve ground cover results after
project implementation.
Finding: Post-treatment large down woody material standards were only met in 18% of
group selection units and 62% of thinning units.
Management Response: Discussions are being initiated between timber sale
administrators, soil scientists and forest leadership to increase the amount of large down
woody material after project implementation.
References
R. F. Powers et al. 2005; The North American long-term soil productivity experiment:
Findings from the first decade of research; Forest Ecology and Management 220 (2005)
31-50.
Appendix 1.
2007 Protocol Review
Protocol Testing
Two treated unit (post treatment) and three untreated units (pre treatment) were sampled
with two different protocols involving more intense sampling. One protocol used the
same tile spade protocol but increased the number of sample points per unit from 60 to
200. The other protocol used more of a stratified sampling technique to qualify the
transect line used for the 200 samples into disturbance categories and estimates of impact
were calculated from the stratification. Soil cores were done on every other point in the
200 sample protocol to check against the spade calls. Soil cores were also taken to
quantify the amount of compaction for each category within the stratified sampling
protocol.
Comparing 60-point and 200-point surveys
Original plans had approximately 3 transects of 20 survey points each. There was
concern that this level of sampling effort might not have enough precision for some levels
of the characteristics of soil compaction, soil displacement, disturbance, and downed
woody debris. To see if a total of 200 sampling points (over 5 transects) greatly
increased the precision five units were sampled at this increased intensity. We expect the
standard errors for all estimates to be reduced by approximately half with the increased
sampling intensity and that is generally what is observed.
Those units are named below and denoted by the name of the associated Excel
worksheet.
3 transects of 20 points
Project/Unit
Pre
Post
5 transects of 200 points
Pre
Wolf Ranch 67
Wolf Ranch 67PRE200
Slapjack 14A
Slapjack 14APRE200
Humbug 70
H70PRE
Post
H70_pre200
Leftover 160
LFT160Post
Leftover 160POST200
Red Clover 54
RC54POST
RC54_post200
Wolf Ranch and Slapjack have no other observations for which to compare at the less
intense sampling effort but those are still included in the summary below which gives the
estimated average (mean) and the estimated standard error (SE) as the measure of
precision.
Project
HUMBUG
LEFTOVER
RED CLOVER
SLAPJACK
WOLF RANCH
Unit
PrePost
70
PRE
160
54
POST
POST
Detrimental
Compaction
(%)
Detrimental
Displacement
(%)
Disturbance
(%)
Mean
SE
Mean
SE
Mean
SE
60
5.0
2.9
16.7
4.4
33.3
6.0
200
3.5
1.8
8.9
1.6
8.0
4.4
60
6.7
4.4
0.0
0.0
28.3
3.3
200
2.0
0.9
6.5
2.3
21.5
2.7
60
41.7
1.7
15.0
7.6
43.3
14.8
200
16.5
1.7
11.0
3.0
30.0
3.2
# of
Sample
Points
14A
PRE
200
0.7
0.7
0.0
0.0
0.0
0.0
67
PRE
200
19.0
5.3
3.5
2.3
11.8
4.5
Because the selection of the samples for both the 60-point surveys and 200-points
surveys consists of roughly equally-spaced samples along 3 or 5 transects, we do not
expect any differences in overall averages. We do expect the differences to be associated
with the precision of the averages. However, Red Clover 54 does appear to differ in the
averages for the 60-point and the 200-point surveys. The cause is unknown.
Below is a similar table to the above table but for the percentages for soil class.
Project
HUMBUG
LEFTOVER
RED CLOVER
SLAPJACK
WOLF RANCH
Unit
Pre/Post
70
PRE
160
54
POST
POST
# of
Sample
Points
C0
C2
C3
C4
C5
Mean
SE
Mean
SE
Mean
SE
Mean
SE
Mean
SE
60
70.0
5.0
0.0
0.0
6.7
4.4
21.7
8.3
1.7
1.7
200
75.7
1.8
8.1
1.6
4.1
0.4
11.5
2.2
0.6
0.6
60
60.0
7.6
10.0
2.9
5.0
5.0
21.7
1.7
3.3
1.7
200
74.5
4.1
5.0
1.8
3.5
1.7
16.0
2.3
1.0
0.6
60
66.7
7.3
1.7
1.7
0.0
0.0
31.7
8.8
0.0
0.0
200
62.5
3.6
1.0
1.0
10.0
1.8
25.0
2.9
1.5
0.6
14A
PRE
200
100.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
67
PRE
200
81.4
6.8
0.0
0.0
1.8
1.3
16.7
5.5
0.0
0.0
Finally, we have a table for the mean amount of logs (woody debris in all classes) per
acre. Note that no woody debris was recorded for Slapjack 14A and Wolf Ranch 67.
Project
HUMBUG
LEFTOVER
RED CLOVER
SLAPJACK
WOLF RANCH
Woody Debris
All classes
# of
(logs/acre)
Sample
Unit Pre/Post Points
Mean
SE
70
160
54
PRE
POST
POST
60
9.2
2.2
200
1.9
1.6
60
4.2
1.7
200
1.8
0.9
60
12.5
2.5
200
7.3
2.5
14A
PRE
200
-
-
67
PRE
200
-
-
Discussion of statistical analysis results
Tile Spade vs Core Analysis
There was good agreement of spade methodology and core methodology (90 and 88% of
the time the two methods agreed in the two units analyzed).
Core data in Humbug 70 has a high chance of some errors in the dataset due to the large
volume of rocks in the samples.
There was good representation of each disturbance class with 200 tile spade data points.
When Dave looked at the data with 100 tile spade data points, there was up to 10% error,
which indicates that we need to stick with 200 spade data points.
In Humbug 70 there was 88% overall spade agreement and most of the time the spade
and core data did not agree, the core data was near the threshold and the spade data was
N2 or Y3, indicating that it was near threshold. There were a few points with core data
indicating well over threshold and a N1 call by McComb – we all suspect that the core
data was off due to the high rock content (i.e. transect 1, point 49). Most of the sample
points that did not agree were cobble soil type, where soil core data is less likely to be
accurate.
Initial Statistical Comparison of 200 points vs 60 points
1. There seems to be no persistence of status at a point from pre to post measurements.
This is examined by calculating the standard error for the difference in proportions both
by assuming independence of points and using McNemar’s formula which accounts for
potential associations from the repeated measures at the same point. One almost always
ends up with nearly identical estimates of the standard error of the difference.
Attempting to measure the same point twice (pre and post) does not appear to reduce the
variability as hoped.
2. Using 200 points rather than 60 will reduce the standard errors of the estimates of pre,
post, and difference proportions by about 45%. (If you even went up to 240 points, the
standard errors would be just cut in half from that of 60 points.).
3. Since we are trying to detect a 5% change, the current method using 60 tile spade
sample size is simply inadequate unless the mean is far above or below threshold.
Standard error calculated from the Pilot data using a sample size of 200 appears to meet
our sampling objectives.
4. The analysis for clearcut units with only 21 tile-spade sample points shows a very high
standard error and consequently wide 95% confidence intervals (i.e. post-treatment data Red Clover 2-20 38% compaction +/- 21% and Red Clover 2-30 – 24% compaction +/18%). There was a good discussion on the need for 200 sample points in the group
selection units. Methodology using 200 sample points in these relatively small 1 – 2 acre
units may oversample the unit. Jim Baldwin had previously explained that with binomial
data, it doesn’t matter how large the unit is. It was discussed that we wouldn’t expect as
much variability in a small unit, so the number of sample points could possibly be
smaller. We decided that we would collect 200 sample points in one group selection unit,
analyze that unit, and make a decision on how many sample points we need to collect in
future group selection units.
The decision was to adopt the 200 tile spade point transect sampling method and continue
the statistical evaluation process. The 200 point method did appear to decrease the
standard error. Future analysis will determine if this increased the precision adequately
or not.