2008 HFQLG SOIL MONITORING REPORT
This report summarizes soil monitoring data collected on the Plumas National Forest and
Sierraville District of the Tahoe National Forest in 2008 as a part of the Herger Feinstein Quincy Library Group (HFQLG) Forest Recovery Act Pilot Project.
In response to the statistical analysis of previous soil monitoring data conducted in 2007,
this year all units monitored had 200 sample points, as opposed to the 60 sample points in
thinning units and 21 sample points in group selection units as done previously.
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 displacement of soil.
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. The Tahoe standard and guides
allows for more than 15 % of an activity area if long term soil productivity is not
impaired as assessed by the soil specialist. 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.
In the 2008 field season eight units were monitored after treatment. Comparisons of the
before and after treatment soil porosity status were made for these eight units for various
types of treatments.
Pre Post Sets
The comparison of pre and post data continues to be somewhat problematic as the data
shows unexpected results such as the amount of compaction decreasing with ground
based treatments. Four of the eight units exhibited an increase in compaction, while four
saw a decrease in compaction. The decreases in compaction could be attributed to various
reasons. Meadow Valley 17a went from 2% to 1% compaction. This is minor and could
be a sampling error. The decrease in soil compaction in Meadow Valley 477 (a group
selection unit) from 24% to 17% could be influenced from increasing the number of
sample points from 21 to 200. The increased sample size samples the ground more
intensely and is assumed to be more accurate due to less influence from each sample
point. Decreases in soil compaction for Beak 86 and Bits 15 post-treatment are likely to
be from the way the pre-treatment sampler (Ford) and the post-treatment sampler
(McComb) determined soil compaction in rocky soil. Ford determined that if rocks were
pushed together at the soil surface and he couldn’t get the spade into the soil the site was
compacted. On the other hand, McComb observed that in these situations the rocks are
absorbing the pressure of machinery traveling over the soil surface and the soil between
thee rocks is not compacted. The large amount of coarse fragments in these soils prevents
obtaining a good core sample to quantitatively determine soil bulk density.
Two of the eight units monitored were over the 15% threshold for compaction (Meadow
Valley 477 and Beak 86). Both of these units were over threshold pre-treatment. This
continues to be consistent with previous monitoring results in that most units that exceed
the threshold post-treatment start with a significant amount of legacy compaction from
previous treatments.
The comparison of pre- and post-sampling continue to indicate that the overall trend
seems to be that harvest operations can add some compaction to the treated area. The
amount of compaction added is influenced by the silvicultural prescription, the location
of trees to be removed, the soil type, the soil moisture at time of harvest and the kinds of
logging equipment used. This year’s data also continues to indicate that the incremental
increase of one thinning or group selection treatment does not by itself exceed the
standards and guides. The highest increase this year was in the Meadow Valley 389
group selection unit which went from 0% compacted pre-treatment to 13% compacted
post-treatment. This is still below the 15% threshold.
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.
Soil textures monitored in 2008 on all eight units would be classed as “loamy”. None
were classified as “clayey”. 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.
Other Soil Attributes (soil cover, down large wood, soil displacement
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 ranges from 40-70%.
The OM standard (regional threshold) is for a minimum of 50% fine OM, preferably
undisturbed.
All eight units met R5 Soil quality standards for Effective Soil Cover. Only one unit
(Meadow Valley 389) failed to meet the 50% standard for fine organic matter with 45%.
Large Woody Material – Down logs at least 20” in diameter and 10’ long. Standards
and Guidelines require three logs per acre after treatment
Three of the eight units met the standard of at least three logs per acre. Six of the units
showed an increase in large woody material. The other two stayed the same.
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.
The level of soil displacement measured post treatment was low. All eight units had less
than 10% displacement with most units showing only a slight increase post-treatment.
Meadow Valley 17a went from 20% displacement pre-treatment to 4% post-treatment.
The reason for this is not clear.
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.