Tree, understory vegetation and fuel data has been collected in permanent plots across the
HFQLG pilot project area both before and after treatment. In 2011 work with Timber Stand
Structure Monitoring (TSSM) data focused on developing more in-depth and comprehensive analysis of pre and post-treatment forest conditions in relation to several of the HFQLG
Monitoring Report Objectives. Work was done collaboratively between the HFQLG
Implementation Team, VMS Enterprise Unit and the Pacific Southwest Research Station (PSW).
Preliminary reports have been developed to address changes in large down logs, snags, canopy cover, large live (overstory) trees, average basal area, early seral foraging habitat and California spotted owl ( Strix occidentalis occidentalis ) habitat. These preliminary reports are in the process of being compiled and finalized for publication in a research paper. Completion and submittal of the research paper " Fuels reduction and group selection in Sierran Mixed-Conifer forest:
Monitoring short-term effects on environmental attributes" is scheduled for 2012.
Forest stand data collection continued in 2011, sampling a total of 4 units 1 year posttreatment (“post-1 year”) and 8 units 5 years post-treatment (“ post-5 year”). Currently a total of
304 TSSM data sets have been collected, including 170 pre-treatment units, 111 post-1 year units, and 23 post-5 year units. Year 2012 will be the final year for TSSM data collection.
Tentatively, 55 post-1 year and 52 post-5 year stands are scheduled for data collection in 2012.
This report presents a summary of analysis completed to date regarding changes in average forest stand basal area, quadratic mean diameter and understory vegetation 1 year after implementation of HFQLG silvicultural and fuels treatments.
Basal area and quadratic mean diameter are measures commonly used when determining forest stand density and describing habitat characteristics. These are important measures as they help indicate conditions such as the level of competition for growing space and the developmental stage of a stand. Basal area and quadratic mean diameter are defined below:
Basal Area - Basal area is the cross sectional area (in square feet) of a tree bole measured at 4.5 feet from ground level.
Quadratic Mean Diameter (QMD) - Quadratic mean diameter is the diameter (measured
4.5 feet from ground level) of the tree of average basal area.
Treatments under the HFQLG act are designed to meet multiple objectives including removing excessive live fuels (small understory and midstory trees), promoting stand health and maintaining or developing desirable habitat such as early seral foraging habitat or late seral habitat. Treatments resulted in a reduction of basal area and increase in quadratic mean diameter. Increases in quadratic mean diameter are due to primarily removing smaller trees and

retaining larger trees. Table 1 displays the average change in basal area and quadratic mean diameter in treatment stands grouped by ecological zone.
Results and Discussion
Treatments led to significant decreases in basal area in trees less than 24" diameter ( p <
0.001). This decrease averaged between 29 - 31 square feet of basal area or roughly 19% of average total basal area. There was no significant change in basal area of trees 24" diameter and larger, including the subgroup of trees 30" diameter and larger.
Table 1—Basal area and quadratic mean diameter (trees ≥ 5 inches diameter) pre- and post- treatment (1 year) by ecological zone; Plumas, Lassen and Tahoe (Sierraville Ranger District)
National Forests
Zone Basal area Quadratic mean diameter
East side
Transition
West side
All
Pre
135 (53)
253 (107)
177 (67)
159 (68) ft
2
/acre
Post
91 (34) a
142 (49)
132 (57)
111 (51)
***
***
***
***
Pre
11.9 (2.0)
12.7 (3.8)
13.3 (2.7)
12.5 (2.5) inches
Post
14.9 (2.9)
17.7 (5.8)
16.6 (4.3)
***
***
***
15.7 (3.4) a * p < 0.05,
** p < 0.01,
*** p <0.001; significance values for pre vs. post comparison
***
Trees 30" in diameter and larger are an important element in classifying late seral habitat under current management direction. There was high variation in basal area of large trees ( ≥ 30" diameter) among treatment units. Large trees on average accounted for 7% of total basal area or
12.8 square feet per acre prior to treatments. These values are probably low compared to historical conditions (North et al. 2007). For old-growth dependent species, management goals are to prevent decreases in large-tree density or basal area where it is low; promote the health and longevity of existing large trees; and promote the recruitment of future large overstory trees at sustainable levels. Reductions in basal area from the removal of small trees provide additional site resources to promote the development, health and survival of large trees. Additionally, silvicultural and fuels treatments remove undesirable live and dead fuels thereby increasing stand resiliency in the event of wildfire.
The monitoring data indicate that treatments succeeded in maintaining existing large tree basal area overall. The basal area of large trees had a small, statistically insignificant increase, from 12.8 to 14.5 sq ft/acre after treatment. This slight increase is most likely due to ingrowth of trees that were near 30" diameter prior to treatment.
Management interest in early seral forage is, by definition, confined to species that provide preferred food sources (e.g., leaves, seeds, and berries) to wildlife. The large majority of understory plant species in mixed conifer forest are consumed in some way, but there are nonpalatable, less-preferred, or otherwise noxious species in the study area such as bull thistle, chinquapin, cheatgrass and bracken fern. We classified each species as either palatable or nonpalatable in consultation with wildlife experts. Analyses were only done on palatable species.
Table 2 displays the average change in understory vegetative cover by life form grouped by ecological zone.

Results and Discussion
Treatments (including fuels reduction thinning and group selection) increased forage for early seral species, but the pattern of increase was contingent upon ecological zone and/or plant life form. Treatments more than doubled forb cover in eastside units. Graminoid cover increased significantly, by more than 50%, in both east side and west side units after treatment. There was a slight decrease in shrub cover in west side units after treatment, which was statistically significant ( p = 0.06).
Grasses and grass-like plants were highly responsive to treatment disturbance in both east side and west side forest. It is common for rhizomatous plants, with vegetative reproduction, to increase rapidly in extent after canopy-opening disturbance (Youngblood et al. 2006).
Shrub cover commonly decreases after mechanical or fire treatment (Bigelow and Manley
2010), and our data were consistent with that pattern in west side stands. Shrub cover in east side treatment units was not affected by treatment however. We conjecture that the most abundant shrubs in eastside forest are intolerant of shade and are therefore sensitive to the presence of overstory canopy, whereas west side forests may have shrubs that tolerate a wide range of light intensities (e.g., Symphoricarpos mollis ) and therefore would not display a strong relationship to canopy cover.
We tested to determine whether the change in understory cover was related to the change in overstory cover, but the lack of correlation suggested that response was due to the fact of having been disturbed, rather than the intensity of disturbance. Further analysis using five-year posttreatment surveys from 2012 will provide a better test of these relationships.
Table 2—Percent cover of forbs, graminoids, and shrubs (mean with standard deviation) before and after treatment according to ecological zone (east vs. west side) in Plumas, Lassen, and Tahoe (Sierraville ranger district) national forests
Zone
East side n Forb Graminoid Shrub
Pre Post Pre Post Pre Post per cent cover
1.8 (2.3) 4.3 (4.1)
*
4.4 (6.5) 7.0 (6.6)
**
12.5 (8.9) 12.2 (10.1)
Transition
West side
0 0.4 (0.6) 1.0 (2.2) 1.2 (2.7)
3.3 (7.0) 3.9 (5.5) 3.2 (7.1) 5.9 (6.9)
7.9 (16.1) 7.9 (11.0)
*
18.7 (15.8) 16.1 (13.0)
*
All 2.4 (4.9) 3.9 (4.7)
*
3.8 (6.6) 6.3 (6.7)
***
14.9 (13.0) 13.7 (11.6) b * p < 0.05,
** p < 0.01,
*** p <0.001; significance values for pre vs. post comparison
Literature Cited
Bigelow, S.W.; Manley, P.M. 2010.
Vegetation response to fuels management in the Lake
Tahoe Basin: . In: Long, J.W.; Stine, P., eds. Effects of Fuels Management in the Tahoe Basin: A
Scientific Literature Review. Davis, CA: Pacific Southwest Research Station and the Tahoe
Science Consortium: 42-83 p.
North, M.; Innes, J.; Zald, H. 2007.
Comparison of thinning and prescribed fire restoration treatments to Sierran mixed-conifer historic conditions. Canadian Journal of Forest Research. 37:
331-342.
Youngblood, A.; Metlen, K.; Coe, K. 2006.
Changes in stand structure and composition after restoration treatments in low elevation dry forests of northeastern Oregon. Forest Ecology and
Management. 234: 21.