HFQLG Soil Monitoring Data Review, 2009
Prepared by David Young, Zone Soil Scientist, Jan 2010
Review of Soil Conditions Before and After Treatment, 2001-2009 Data
This year 2009 soil monitoring data (25 units) was added to the data set analyzed for previous annual
monitoring reports, and re-analyzed for overall synthesis of status and trend. Only units with pre- and
post-treatment data were included in the analysis. A total of 77 units with pre- and post-treatment data
sampled between 2001 and 2009 are represented in the data shown in this summary. All of the 2009
data is from the Meadow Valley sale area, Mt. Hough RD. Overall results are not appreciably different
than previously reported; therefore detailed statistical analyses were not performed this year. When
more data from the revised 200-point monitoring methods becomes available the statistical analyses
will be revisited.
Table 1. Silvicultural Units Included in the Data Set.
2001-2008
Thinning Units
39
Group Selection Units
11
Mastication Units
2
Total
52
2009
12
13
0
25
Total
51
24
2
77
Soil Cover Conditions
Forest Plan soil quality standards generally require 50% effective soil cover to avoid soil erosion. Soil
cover can be duff, litter, large wood, vegetation or rock, all of which prevent bare soil from eroding.
Dominant soil cover conditions from pre- to post-treatment were compared. A large difference
between silvicultural methods was apparent, as previously reported. Figures 1 and 2 display grand
averages across all units. Thinning units on average have 80% effective soil cover post-activity; 7 of the
units (14%) have less than 70% cover, and only 1 unit (2%) has less than 50% cover.
Group Selection units have on average about 60% effective cover; 15 of the units (63%) have less than
70% cover; 7 of the units (29%) have less than 50% cover, with all but 1 of these in a single sale area
(PEG21, Eagle Lake RD). Duff is the most effective cover in preventing erosion, and is much more
reduced in group selection units. Mastication units both exceed 85% cover (not shown).
Overall, 90% of the units meet this standard, with the problem areas being predominantly group
selection units from a particular sale area.
Interpretation/Recommendations:
The soil cover standard of 50% is a general standard intended to indicate a potential hazard of erosion.
The standard itself is satisfied in 90% of units. While it is outside the scope of this monitoring to validate
standards, the standard itself should not be the sole consideration in erosion risk assessment: hazard X
consequences = risk. For erosion protection, the size and distribution of bare areas are more important
than overall percentage of the unit. Erosion hazard of bare areas varies by site-specific factors such as
soil type (erodibility), slope gradient, and topography; consequences of the hazard also vary by unit
configuration and proximity to streams.
Thinning Units - Pre & Post Soil Cover
80
70
PERCENT COVER
60
50
40
PRE
30
POST
20
10
0
duff
rock
veg
lwd
bare
DOMINANT SOIL COVER COMPONENT
Figure 1. Soil Cover Condition for Thinning Units.
Group Selection Units - Pre & Post Soil Cover
80
70
PERCENT COVER
60
50
40
PRE
30
POST
20
10
0
duff
rock
veg
lwd
DOMINANT SOIL COVER COMPONENT
Figure 2. Soil Cover Condition for Group Selection Units.
bare
Group selection units not meeting the standard do not necessarily pose high risks for erosion or
sediment delivery, as they are generally quite small and well buffered from streams in the landscape.
Conversely, units meeting the standard with 50-70% cover may have site-specific problems if much of
the bare area is concentrated in a small portion of the unit. While it is difficult to assess the level of risk
on the group select units for erosion, it is clear that these units are being impacted more than thinning
units and are not meeting the standard. It is recommended to work with the vegetation management
administration staff to try and work with the operators on these units to do less disturbance and leave
more ground cover.
Incorporating results from Stream Condition Inventory and Best Management Practices (BMP)
monitoring is appropriate to look into effectiveness of erosion control measures, such as soil cover. In
2007 and 2008, the SCI protocol was applied to 15 streams where pre-project data had been measured.
For all of these streams, none of the three fine sediment measures were significantly different when
compared with the pre-project data, indicating that project activities did not result in increased
sediment delivery. BMP effectiveness evaluations focus on whether or not project-generated sediment
is delivered to streams or whether channel banks are disturbed. In 2005 through 2009, 792 site-specific
BMP effectiveness evaluations were conducted to assess practices associated with stream course
protection, skid trails, landings and prescribed burns. Sixty-two of these 792 evaluations were rated as
ineffective, resulting in a 92% BMP effectiveness rating.
It is recommended that size and distribution of bare areas continue to be qualitatively evaluated and
described in notes during post-activity sampling efforts to identify problem areas needing attention. It is
also advisable that group selection units be evaluated with the FS Disturbed WEPP model to determine
on a more soil and site specific basis how much remaining cover is minimally required to avoid erosion
hazards; in some cases this may exceed 50%. The 50% cover standard is a fair coarse-filter indicator for
most units, but the modeling tools have been developed to easily evaluate these units more closely.
Soil Compaction
Soil compaction (loss of soil porosity) has been viewed as a major factor affecting soil productivity.
Compacted soil can have lower water infiltration rates, higher or lower water holding capacity
(depending on soil texture), and increases in soil strength that can restrict root growth. Soil compaction
from pre- to post-treatment was compared. Problems with analysis and interpretation of these data
have been discussed previously in 2007-2008 reports, and will not be repeated here. Sampling
methodology has been revised to address the problems, but not enough ‘new protocol’ data is available
to analyze in a meaningful manner. Therefore, data is presented below in previous fashion for reporting
trends.
Figure 3 shows grand averages across all units. Forest Plan soil quality standards generally require
detrimental compaction to occupy less than 15% of a unit. Overall, 52% of the units meet this standard
post-activity, including 45% of thinning units and 67% of group selection units. However, only 58% of
units overall met the standard pre-activity (53% of thinning units and 71% of group selection units).
Therefore, most of the detrimental compaction existed pre-activity. More pertinent to current
activities, there were 9 units (5 thinning, 4 group, 12%) that met the standard pre-treatment and
exceeded it post-treatment; the rest either exceeded the standard pre-treatment or met the standard
post-treatment (or both, which is why the percentages above do not appear to reconcile; this is one of
the apparent sampling problems already discussed in previous reports and addressed).
Variation in the data is large, indicating that some units exceed the standard by large margins, both pre
and post. Levels of compaction in group selection units are roughly half that of thinning units, which is
counter to expectations; the reason for this is apparently a non-normal and skewed data distribution
(figure 4), i.e. several thinning units with extreme levels of compaction are skewing the average upward.
Post-treatment compaction within units that were subsoiled versus not subsoiled is shown in figure 5.
On average there is no beneficial difference of treatment; in fact, 60% of subsoiled units exceed the
standard versus 40% of non-subsoiled units. However, analysis using unit averages does not tell us how
much more detrimental compaction treated units would have had without treatment, so generalizations
are difficult to infer.
Compaction - Averages Across Units
45
40
PERCENT OF UNIT
35
30
25
20
15
10
5
0
PRE
POST
Thinning
PRE
POST
Group Selection
PRE
POST
Mastication
Figure 3. Detrimental Compaction by Silvicultural Method (with standard deviations).
Post-Treatment Distribution of Compaction Level
12
Thinning
NUMBER OF UNITS
10
Group Selection
8
6
4
2
0
COMPACTION (%)
Figure 4. Post-Treatment Distribution of Detrimental Compaction.
Post-Treatment Compaction and Subsoiling
45
Not Subsoiled
40
Subsoiled
PERCENT OF UNIT
35
30
25
20
15
N = 30
N = 21
N = 13
10
N = 11
5
0
Thinning
Group Selection
Figure 5. Post-Treatment Detrimental Compaction With and Without Subsoiling.
Interpretation/Recommendations:
Recent research findings (Powers and others 2005) indicate that the effect of increased compaction on
total biomass productivity varies with soil type. Soil textures on units monitored in 2009 were classified
as “loamy,” a soil type which does not show significant changes in productivity when compacted.
Consequently, though some units do not meet the 15% standard for compaction, a decrease in soil
productivity (total biomass productivity) is not expected.
As stated above, there are known problems making pre-post comparisons with the compaction data
that make interpretation of the results questionable. These problems have already been addressed and
changes made to sampling methodology, but we do not yet have data for units pre- and post-treatment
using the revised protocols. Therefore, rather than focus upon overall results, it may be more important
to re-evaluate the units reported with very high levels of compaction (figure 4) to determine what is
different about those units, and if changes are needed with equipment operations for future activities.
It is also important to note that the overall change in compaction levels is not large, with only 9 units
going from meeting the standard pre operation and being over the standard post operation. Many
units that met the standard pre operation also met the standard post operation. This is indicating most
of the compaction sampled is legacy compaction.
It is apparent from the data that subsoiling is not being successful in reducing compaction to acceptable
levels, but it is unclear (analyzing unit averages alone) if this is because not enough mitigation is being
done, treatment is ineffective, or the legacy compaction is causing misleading results. It is
recommended to perform a more detailed per-unit data analysis with some of the subsoiled units, to
see how much of the unit is being subsoiled, compaction calls at those points, and how much overall
unit compaction is being mitigated. It is important to note that subsoiling is usually only done on main
skid trails and landings of the current operation. This type of treatment would only subsoil the most
recent compaction and may subsoil a small amount of legacy compaction depending on the level of reuse of old skid trails. Therefore, much of the compaction being sampled could be legacy compaction inbetween current mains skid trails. To evaluate subsoiling effectiveness the subsoiled areas should be
evaluated on their own merits apart from the rest of the unit. Cost and effectiveness of mitigation
treatments versus equipment limitations during harvest should be an explicit management
consideration, i.e. mitigation versus prevention of compaction. Presumably equipment is already
limited to designated skid trails; perhaps more intensive contract administration is needed to assure
adherence to these limitations.
Soil Displacement
Soil is considered displaced when either 2 inches of duff or 1/2 of the humus-enriched topsoil (A
horizon), is removed from an area 1 meter square or larger. Although forest Plan soil quality standards
and guidelines do not have a minimum area considered significant, or a permissible extent within units,
minimizing soil displacement is a management objective. Soil displacement was compared from pre- to
post-treatment. Figure 6 shows grand averages across all units. Thinning units average about 5%
displacement, with only 2 units (4%) barely exceeding 15%. Group selection units average about 10%
displacement, with 6 units (25%) exceeding 15% and 2 units just exceeding 20%. In the group selection
pre-data, the high variation is driven by 5 Meadow Valley units with displacement reported in the 3060% range; this would be very unusual for ‘normal’ timber operations, and indicates a high level of
displacement in the group selection units, as is also indicated with the soil cover results, or a possible
sampling problem with observer interpretation of what constitutes detrimental displacement (minimum
area) or both.
Displacement - Averages Across Units
45
40
PERCENT OF UNIT
35
30
25
20
15
10
5
0
PRE
POST
Thinning
PRE
POST
Group Selection
PRE
POST
Mastication
Figure 6. Detrimental Displacement by Silvicultural Method (with standard deviations).
With only 2 mastication units, data shows huge variation because the 2 units were very different- one
went from 0 to 8% pre to post, and the other 23 to 35% pre to post.
Interpretation/Recommendations:
While the displacement standard is difficult to apply on the ground, units exceeding 20% displacement
should be considered unusual for ‘normal’ timber operations. These units should be re-evaluated to
determine if modification of sampling methodology or changes with equipment operations during
activities are warranted. It is recommended to work with the vegetation management administration
staff to try and work with the operators on these units to do less displacement by trying to streamline
movement of equipment, i.e. less turning etc.
Down Woody Debris
Downed woody debris is described as large logs (at least 10 feet long and 20 inches diameter) in decay
classes 1-5. Forest Plan soil quality standards generally require 3 or more logs per acre to be left on the
ground post-treatment to help maintain long-term soil productivity, maintain soil moisture as well as for
wildlife purposes. Figures 9 and 10 show averages and unit statistics across all units. Thinning units as a
group meet the standard with 4 logs per acre post-activity. More specifically, 30 units (59%) have at
least 3 logs/ac, 15 units (29%) have 1-2 logs/ac, and 6 units (12%) have no large wood.
DOWN WOODY DEBRIS (logs/acre)
Downed Woody Debris
30
25
20
15
10
5
0
PRE
POST
Thinning
PRE
POST
Group Selection
PRE
POST
Mastication
Figure 9. Downed Woody Debris by Silvicultural Method (with standard deviations).
Group selection units as a group do not meet the standard with 1.2 logs per acre post-activity. More
specifically, 4 units (17%) have at least 3 logs/ac, 4 units (17%) have 1-2 logs/ac, and 16 units (67%) have
no large wood. However, half of the group selection units had no large wood prior to treatment, so
conditions were worsened by current activities in only 4 units. Of the 2 mastication units, 1 meets the
standard both pre- and post-treatment, 1 does not.
The data shows large variability, indicating that some units had copious amounts of large wood pretreatment. Overall, 35 units (69%) had 6 or more logs per acre (double the standard), and 23 units
(45%) had 10 or more. Of course, most of this wood would have been removed for fuel reduction
objectives. Post-treatment, 14 units (12 thinning +2 group, 27%) have 6+ logs per acre and 4 units (all
thinning, 8%) have 10+ logs per acre.
Downed Woody Debris
PERCENT OF UNITS
90
80
PRE
70
POST
60
50
40
30
20
10
0
No Down
Wood
3 or More
Logs per Acre
Thinning
No Down
Wood
3 or More
Logs per Acre
Group Selection
No Down
Wood
3 or More
Logs per Acre
Mastication
Figure 10. Downed Woody Debris, Unit Percentage Statistics.
Interpretation/Recommendations:
Soil quality standards are intended to be evaluated and applied on an individual unit basis. However,
large down woody debris is a highly variable metric across the landscape, for both natural and managed
stands. Obviously, if a unit has little or no wood prior to treatment, it cannot be expected to meet the
standard post-treatment. Therefore it should be expected, statistically and on the ground, that a
portion of units will not meet the standard. Further, the size of a unit can have a large bearing on the
result, as wood is distributed unevenly on the landscape; the smaller the unit, the greater chance of a
sample ‘missing’ any concentrations of wood. Group selection units are generally very small, so it is not
too surprising that many of them had little or no wood prior to treatment. It would probably be most
appropriate to analyze this standard based on groups of units, aggregated by sale area, watershed, or
aspect within larger HUC watersheds.
Soil Moisture
Soil moisture monitoring equipment was installed in 4 Meadow Valley thinning units and paired control
units (adjacent unharvested areas) in August 2009. Monitoring equipment captures moisture and
temperature data hourly around the clock, with sensors installed at 10, 20, 30, and 40 inches depth.
Data through late October has been downloaded, but has not yet been adequately analyzed for this
report. Figure 11 is just a preliminary example of soil moisture in two treated units with their paired
controls, showing the kind of data that will be available next year. Unit 3 shows a significant difference
between treated and untreated stands, unit 2 does not. The arrival of fall rain shows up discretely.
Soil Moisture at Two Meadow Valley Units
(Daily Noontime, 20" Depth)
60%
SOIL MOISTURE (% volume)
Unit 2 - untreated
50%
40%
Unit 2 - treated
Unit 3 - untreated
Unit 3 - treated
30%
20%
10%
0%
Figure 11. Autumn soil moisture status in two thinning units.
Trends of treated and untreated areas being wetter or dryer may change and reverse in different parts
of the growing season. Therefore, it is intended that these units will be monitored through the 2010
growing season (an entire wetting/drying cycle), and then the equipment will be moved to other
locations to gather similar data.