I. Title Page
Title:
Identifying Spatially Explicit Reference Conditions for Forest
Landscapes in the Lake Tahoe Basin, USA
Subtheme this proposal is
responding to (choose only
one)
Principal Investigator:
Theme 2: Forest Management, Fuels Reductions, and Stream and
Meadow Restoration
Subtheme: Fires and Fuels (d)
Dr. Alan Taylor
The Pennsylvania State University
309 Walker Bldg
Phone: 814-865-1509
Fax: 814-863-7943
Email: aht1@psu.edu
Hugh Safford
USDA – Forest Service, Pacific Southwest Region
1323 Club Drive, Vallejo, CA 94592
Phone: 707-562-8934
Fax: 707-562-9050
Email: hughsafford@fs.fed.us
Carl Skinner
Pacific Southwest Research Station
3644 Avtech Parkway, Redding, CA 96002
Phone: 530-226-2554
Fax: 530-226-5091
Email: skinner@fs.fed.us
Sue Lavan
The Pennsylvania State University
248 Deike Bldg
Phone: 814-865-7650
Fax: 814-865-7809
Email: sal5@psu.edu
$ 197,348.00
$ 69,110.00
Co-Principal Investigators
Co-Principal Investigators
Grants Contact Person
Funding Requested:
Total Value of In-Kind and
Financial Contributions:
1
1
II. Narrative
Justification
Forest conditions at the time of Euro-American settlement (hereafter presettlement) are increasingly used as
a point of reference for ecologists and managers for characterizing the range of variability in ecological processes
and structures at a time when ecosystems were less affected by people (Kaufmann et al. 1994, Swanson et al. 1994;
Landres et al. 1999). During this period the clarity of Lake Tahoe was high and much of the Lake Tahoe Basin is
thought to have been covered by mature and old-growth forest cover (Manley et al. 2000). Reference conditions are
also used to identify restoration goals and restoration treatments for places where contemporary forest conditions are
outside their range of historic variability (e.g., Morgan et al. 1994, White and Walker 1997, Fule et al. 1997,
Swetnam et al. 1999, Moore et al. 1999). Presumably, managing forests for conditions similar to the reference are
consistent with maintaining high lake clarity and with reducing the risk of unexpected outcomes such as species
extinction compared to conditions created by Euro-American land use practices such as logging, grazing and fire
suppression management (Swanson et al. 1994, Landres et al. 1999, Moore et al. 1999). This ecosystem
management perspective has been embraced by a wide range of stakeholders in the Lake Tahoe Basin. The desired
future condition for public forest lands is conceived as being similar to those in the Euro-American period (i.e.,
Christopherson et al. 1996). Consequently, identifying reference conditions is a key step in the ecosystem
management-restoration planning process and it can be a particularly challenging task in forests that have been
highly altered by human activity (USFS 2004).
Forests in the Sierra Nevada in general and the Lake Tahoe basin in particular have been dramatically
altered by Euro-American land use practices (Vankat and Major 1978, McKelvey and Johnston 1992, SNEP 1996).
The demise of the presettlement forests in the Lake Tahoe Basin is well documented. Forests in large parts of the
basin were nearly clearcut between ca. 1860 and 1920 to meet demand for wood in the silver mines in Virginia City,
and areas served by rail from Truckee (Leiberg 1902, Strong 1984, Lindström 2000). Forest has re-established on
much of the cutover land, but the characteristics of these second growth forests differ markedly from presettlement
forest (Manley et al. 2000; Taylor 2004; Beaty and Taylor 2007a). These second- growth forests have more trees,
more basal area, and more pioneer species (e.g. lodgepole pine) that regenerate after severe disturbance than the
original forest (Taylor 2004). Fire was also a keystone disturbance agent in the presettlement forest environment that
regulated the structure of forest stands and forest landscapes, but fire is an extremely rare disturbance in the
contemporary forest (Taylor 2004; Taylor and Beaty 2005; Beaty and Taylor 2007b). Moroever, the quantity of
surface and aerial fuels in these highly altered forests is now much greater than in presettlement forest and this has
greatly increased the risk of stand-replacing fire (Weatherspoon et al. 1992; Manley et al. 2000). The risk of high
severity fire in the Lake Tahoe Basin poses a significant threat to water quality, life, property, and wildlife habitat in
the Lake Tahoe Basin (Murphy 2000; Manley et al. 2000). Reducing the risk of high-severity fire by treating fuels
and changing the structure of forests so they are resilient to fire and more similar to reference forests is a major
challenge for resource managers in the Lake Tahoe Basin (TRPA 2002), and in the Sierra Nevada (Christopherson et
al. 1996; Manley et al. 2000; USFS 2004).
A common approach for identifying reference conditions for ecosystem management and restoration of fire
resilient forests is to quantify presettlement forest conditions (i.e. forest structure and composition) and fire regimes
and compare them to those of the contemporary forest. Differences can be used to develop strategies and treatments
to increase resilience of forest stands or forested landscapes to fire (e.g. Weatherspoon and Skinner 1996;
Stephenson 1999; Agee and Skinner 2005). These differences have been used to design treatments to reduce surface
and canopy fuels, tree density, and basal area in small areas of forest in the Lake Tahoe Basin and in other fire-prone
forests in the west (e.g. Covington and Moore 1994). However, knowledge of reference conditions at the scale of
forested landscapes is lacking and this information is needed to plan and evaluate the ecological implications of fuel
treatments including the use of prescribed fire (Skinner and Chang 1996). For example, more intensive fuel
treatments may be appropriate on portions of landscapes (i.e. upper slope positions) (Taylor and Skinner 1998) that
historically burned at higher severity (Weatherspoon and Skinner 1996; Agee and Skinner 2005).
Background and Problem Statement
Research on fire regimes and forest structure in fire-prone forests in California before the onset of fire
suppression management demonstrate that there are important feedbacks between topographic setting, forest
structure and composition, and the frequency, severity, and spread of fire (van Wagtendonk 1995; Miller and Urban
2000; Taylor 2000a; Beaty and Taylor 2001; Bekker and Taylor 2001; Taylor and Skinner 1998, 2003). Thus,
reference conditions that are topographically distributed yield data on spatial variability in dominant ecosystem
elements that probably regulate landscape ecosystem structure and function. These spatially explicit studies indicate
that presettlement forest landscapes were more heterogeneous than the contemporary forest landscape and that
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spatial variability in fire regimes and forest structure were key components contributing to higher heterogeneity
(Vankat and Major 1978; Taylor and Skinner 1998, 2003; Beaty and Taylor 2001; Gruell 2001; Nagel and Taylor
2005). Much of this research was conducted in Wilderness or areas where evidence of the presettlement forest had
not been removed by burning or logging. Identifying reference conditions in highly altered forest ecosystems, where
evidence of the original forest was removed by 19th century logging as in the Lake Tahoe Basin is considerably more
challenging.
Reference conditions for forest structure and fire regimes in the Lake Tahoe Basin that could be used as
initial information to guide vegetatation and fuels management have been estimated for small areas of forest. For
example, Barbour et al. (2002) quantified the composition, density, and basal area of trees in 38 patches of old
growth forest scattered throughout the Lake Tahoe basin. Barbour et al. (2002) used the composition, density and
basal area of large live trees (>40 cm dbh) to describe the presettlement reference in four widespread forest types: 1)
Jeffrey pine forest; 2) mixed conifer forest; 3) white fir forest; and 4) red fir forest. A similar approach, with
additional detail on forest size and age structure and fire regimes, was used by Taylor (2000b) to quantify
presettlement reference conditions for scattered old-growth stands of mixed conifer forest on Lake Tahoe’s west
shore. Using an alternative approach, Taylor (2004) measured well-preserved cut tree stumps dating from the 19th
century to estimate reference conditions for forest structure in 20 forest stands on the east shore of Lake Tahoe. The
stumps yielded reference estimates for: 1) Jeffrey pine forest; 2) mixed conifer forest; 3) red fir forest; and 4)
lodgepole pine forest. Fire scars preserved in the cut stumps and in scattered live presettlement trees also provided
estimates of the return interval, extent, and season of fire during the presettlement period for Jeffrey pine and red fir
forests (Taylor 2004; Taylor and Beaty 2005; Scholl and Taylor 2006).
Although these studies provide useful information on presettlement conditions in small patches of oldgrowth forest they provide little insight into the spatial heterogeneity of the presettlement forest landscape in the
Lake Tahoe Basin. Research of reference forest conditions elsewhere in northern California indicate that
presettlement forest structure (i.e. density, basal area, tree size and age distributions), and fire regimes (i.e.
frequency, severity, extent) were strongly associated with topographic characteristics. For example, fire return
intervals and forest structure vary with slope aspect and elevation in lower (Jeffrey pine/mixed conifer) and upper
montane (red fir, lodgepole pine, mountain hemlock) forests (e.g. Taylor 2000a; Beaty and Taylor 2001; Bekker and
Taylor 2001). Similarly, evidence of high-severity fire (even-aged forest, montane chaparral) was concentrated on
steep upper slope positions (e.g. Taylor and Skinner 1998, 2003; Beaty and Taylor 2001; Nagel and Taylor 2005).
Research on mixed conifer forests on portions of a landscape that was never logged on the west shore of Lake Tahoe
also suggest that topography exerted strong control on presettlement fire regimes and forest structure (Beaty and
Taylor 2007b).
Goals and Research Objectives
The overall goal of this project is to develop a spatially explicit reconstruction of the presettlement forest
landscape conditions and associated fire regimes for the Lake Tahoe Basin that can be used by land managers in the
ecosystem restoration planning and implementation process. Work will be conducted in a 2000 ha forest in the
General Creek watershed that was not logged because of ownership (Lindström 2000) and includes a wide range of
forest types. This work contributes directly to research needs identified under Theme 3 (Forest Management
Activities: Implications for Ecosystem and Public Health). An understanding of the spatial variability in
presettlement forest characteristics is essential for understanding if and how planned stand-level activities
(mechanical fuel treatments, prescribed burning, etc.) scale up and contribute to restoration of functioning forest
landscapes (i.e. habitat, forest health, hydrologic condition, etc.). A mismatch between the cumulative effects of
stand level treatments in contemporary forests and spatial variability in presettlement vegetation patterns may fail to
achieve the goal of restoring fire resilient functioning landscapes. This research will build on previous work on
lower montane mixed conifer forests and fill critical gaps in knowledge on the spatial variability of presettlement
forest structure and fire regimes in the Lake Tahoe Basin.
The specific objectives of this project are to:
1) Identify the relationship between spatial variability in presettlement forest structure (composition, density,
basal area, size structure) and topographic variables in the lower and upper montane forest zones of the
Lake Tahoe Basin;
2) Identify the relationships between spatial variability in fire regimes (fire return interval, season of burn) and
topographic variables in the montane and upper montane zone in the Lake Tahoe Basin;
3
3) Develop a spatially explicit reconstruction that distributes and visually represents presettlement forest
structure, forest fuels, and fire regimes for lower and upper montane forests in the Lake Tahoe Basin.
Methods and Approach and Research Location
Presettlement forest structure
Data for presettlemement forest structure and topography will come mainly from th completed studies, and
additional fieldwork to fill critical data gaps. Plot and stand-level data on site characteristics and presettlement forest
structure will be obtained for the studies summarized in Taylor (2000a, 2004), Nagel and Taylor (2005), Barbour et
al. (2002), Scholl and Taylor (2006), and Beaty and Taylor (2007, in press). These studies provide information, in
varying detail, on the composition, size structure, and/or age structure of trees in forests that were never cut in the
Basin (except stump data in Taylor 2004). A preliminary assessment of these data indicate that further sampling of
uncut forest in the General Creek Watershed will be necessary to ensure a full representation of forest conditions
and topographic variables for reconstruction of forest conditions and model development.
Forest reference conditions (density, basal area, diameter) for the pre-fire suppression period will be
reconstructed for plots in uncut forest using dendroecological methods (cf. Fule et al. 1997). The reference date for
the forest reconstruction will be 1880. Few fires were recorded in fire scar samples in forests on the west or east
shore after 1880 (Taylor 2004; Nagel and Taylor 2005; Beaty and Taylor 2007a,b). Reconstructing forest conditions
for an earlier date would be less precise because woody material in the forest would have been consumed by later
fires.
Forest reference conditions in 1880 will be reconstructed using measurements of the contemporary forest
and the following procedure. First, stems of live trees that established after 1880 (i.e., stems ≤120 yrs old) will be
eliminated. Second, diameters of trees (stems >10 cm dbh) that were alive in 1880 will be identified by subtracting
radial growth since 1880 from each diameter measurement of a contemporary tree. Tree age and annual growth
increment will be determined from age-diameter regression equations for each species from increment cores already
collected in the plots (n >1000).
Trees that died since 1880 must also be included in the forest reference condition estimate if they
established before 1880. The date of death for snags and downed trees in the contemporary forest plots need to be
estimated using measurements of dbh and decay class, and estimates of decomposition rate (cf. Fule et al. 1997).
Once death dates for snags and downed trees are determined, the dbh of trees alive in 1880 but dead today can be
determined using tree death dates and average annual radial growth rates for each species from the age-diameter
regression equations. Standing dead trees, snags, and logs were measured and identified to species (if possible) in
all of the earlier studies, but they were not grouped into decay classes. Plots/stands will be relocated using GPS
coordinates of the plots and stands and the dead wood will be classified according to Maser et al. (1979). This
classification can be done rapidly but is important for determining tree death dates. Reconstructed forest
characteristics are underestimated by not including the standing dead, snag, and log components of forest structure
in estimates. The first use of this approach in California forests indicates that average presettlement forest density
and basal area are underestimated by 20% (plot range 0-85%) when these components are not included (Taylor and
Scholl 2006). Sensitivity analyses also indicate that estimates of presettlement tree density, basal area, and tree
diameter are not strongly influenced by variation in decomposition conditions used to estimate tree death date
(Taylor and Scholl 2006). Thus, the presettlement forest condition estimates are robust given the inherent limitations
of using dead trees and logs as evidence of the presettlement forest.
Presettlement fire regime data
Data on presettlemement fire regimes and topography will be compiled from the location of samples of
wood with cross-dated fire scars (n=156) in studies summarized in Taylor (2000a), Taylor and Beaty (2005), Nagel
and Taylor (2005), Scholl and Taylor (2006), Taylor and Beaty (2007a,b). These samples provide information on the
presettlement frequency, return interval, and season of fire in lower and upper montane forests. Samples are
distributed over a broad range of elevation on different slope aspects. A preliminary analysis of these data indicates
there is a strong relationship between topographic variables and presettlement fire frequency and fire severity. Fire is
more frequent at low versus high elevation and on south versus north-facing slopes. Fires were also more severe on
upper than lower slope positions, particularly on south facing slopes. Further sampling of higher elevation upper
montane forests will be necessary to develop a more complete data set for to identify the relationships between fire
regimes, forest characteristics and topography in the General Creek Watershed.
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Spatially explicit reconstruction of presettlement forest conditions
Presettlement forest structure
Groups of plots with similar presettlement forest structure and composition will be identified using cluster
analysis. First, a forest structure classification will be developed using the density of each tree species in 20 cm
size-classes using Ward's method, and relative Euclidean distance as a similarity measure (McCune and Meford
1999). Second, a species importance value classification will be developed by calculating the importance value for
each tree species in each plot as the sum of relative basal area, relative density, and relative frequency (range 0-300).
Species importance values will then also be grouped using Ward's method, and relative Euclidean distance. Ward's
method minimizes within- group variance relative to between-group variance (van Tongeren 1995). Next,
differences in topographic variables that control forest structure and composition among groups (i.e. elevation, slope
aspect, slope position, topographic conversion index, topographic relative moisture index, etc.) will be identified
using a distribution free Kruskal-Wallis H test (Sokal and Rohlf 1995).
Topographic variables which distinguish presettlement forest groups will be used for the spatially explicit
reconstruction of forest conditions. Distinguishing topographic variables will be identified using Classification and
Regression Trees (CART) (De’ath and Fabricius 2000). CART explains variation in the response variable (structural
groups or important value groups) by repeatedly splitting the data into progressively more homogenous groups
based on the explanatory variables. The final CART model of presettlement forest conditions, the importance of
different topographic variables in the model, and classification error will be assessed by: 1) the percentage of
correctly classified sites; 2) cross-validation (Test, V-fold); and 3) deviance of the terminal node (Gini measure).
The spatial location of a forest groups across the landscape will be determined by applying the CART
model to topographic variables in a GIS. A 4.0 ha grid will be will be established over the 10-m digital elevation
model of the Lake Tahoe Basin. Topographic variables (see example list above) within each grid cell will then be
used in the CART model to predict the forest group for each cell. The end result of this process is a map depicting
spatial variability in presettlement forest groups across the landscape.
A standard tool used by forest vegetation managers, the Forest Vegetation Simulator (FVS) (Dixon 2003)
will be used to characterize and depict presettlement forest conditions (size, height, canopy cover, crown size) in
each group. FVS uses lists of tree species and tree size (dbh) to calculate and visualize forest characteristics in plots;
the Stand Visualization System (SVS; McCaughley 2004) is used to visualize the forest structure modeled by FVS.
Tree lists for each presettlement forest group will be determined by calculating the and average (and range) tree list
for plots in each group. Stand characteristics for average minimum or maximum conditions can also be easily
calculated, thus providing quantitative data on the range of variability for each group at both the plot and landscape
scale. Figure 1 depicts average stand structure from FVS for a presettlement forest group in a mixed conifer forest in
Yosemite National Park as a demonstration of proof of concept.
The presettlement forest reconstruction will be represented on the landscape by integrating visualizations of
stand structure from FVS with the map of presettlement forest groups in the GIS. Stand visualizations will then be
distributed on the landscape using the Landscape Management System (LMS; http//lms.cfr.washinton.edu/) and
EnVision (http://forsys.cfr.washignton.edu/envision.html). EnVision creates landscape-scale visualizations, while
LMS organizes the input data and coordinates between SVS and EnVision. This procedure will be used to represent
the range of stand conditions (i.e. average, minimum, maximum, etc.) within forest group at the landscape scale by
using different inputs (i.e. mean of minimum or maximum values) into FVS for spatial representation in the GIS.
Figure 2 depicts average stand structure from FVS scaled to the landscape for six presettlement forest compositional
groups in a mixed conifer forest in Big Oak Flat in Yosemite National Park as a demonstration of proof of concept.
Both the contemporary and presettlement forest conditions are shown.
Presettlement fire regimes
A spatially explicit representation of fire frequency and season of burn will also be derived using CART
and topographic variables derived from the GIS. Relationships between forest type, and point fire return interval and
topographic variables will be developed using regression models. Best fit models will then be used with topographic
data in the GIS to depict spatial variability in presettlement fire frequency and season of burn. A similar CART
model for fire severity which is reflected in the spatial distribution of patches of young trees or montane chaparral
(Beaty and Taylor 2001, 2007a,b; Nagel and Taylor 2005) in the presettlement forest will be also be developed. The
final CART models for presettlement fire regime variables, the importance of different topographic variables in a
model, and classification error will be also be evaluated using the same measures as for the forest groups.
Presettlement fuels
5
Based on the original plot data and FVS runs, we will also generate the distribution of subcanopy fuels
(i.e., the tree component, including ladder fuel estimates) in the different compositional groups identified in the
CART analysis. This will allow a first-approximation of forest fuel characteristics and loadings in the reference
landscape. We will use the Fuel Characteristic Classification System (FCCS; Prichard et al. 2006) to characterize
average (and range of) surface and canopy fuels in each group and across the landscape using GIS. FCCS provides
much greater flexibility and detail than the standard surface fuel models, and allows for more explicit incorporation
of fuel complexity and geographic diversity in fuel structure. FCCS outputs the standard measures of surface fire
severity (flame length, spread rate, etc.), but also generates canopy torching, and dependent and independent crown
fire potentials, as well as available fuel loadings (Prichard et al. 2006). FCCS inputs for herbaceous and shrub fuel
layers will be based on (1) plot data from contemporary stands of analogous condition (where available; we foresee
using FIA, the R5 Ecology Plot database, Stand Exams, plots sampled for the TRPA Lake Tahoe Basin IKONOS
vegetation map, and plots sampled for the NRCS Lake Tahoe Basin soil survey – where necessary, we will fill data
gaps with our own plot sampling), and (2) presampled values available for different floristic and structural
conditions from the FCCS reference library and the Natural Fuels Photo Series
(http://www.fs.fed.us/pnw/fera/research/fuels/photo_series/) for western mixed conifer, red fir, and yellow pine
systems. Reference condition stands will be “burned” in FCCS under standard fire-weather conditions in order to
calculate reference conditions for surface and crown fire behavior, and fuel loadings. These “baseline conditions”
can be compared to current conditions to provide a quantitative fire severity-based metric (such as “condition class”)
for departure from reference conditions.
Strategy For Engaging Managers
Management professionals in the Lake Tahoe Basin will be engaged early and often in the course of this
project. At the beginning of the project we will meet with resource and fire and fuels managers at the USDA Forest
Service Lake Tahoe Basin Management Unit and the California (west shore parks) and Nevada (east shore parks)
state parks system to present our project objectives and the expected deliverables for the project. To inform and
engage additional fire and resource managers we will also meet with the Lake Tahoe Unified Steering Group For
Forest Assessment and Protection. This group includes representatives from a wide range of land management and
regulatory agencies, and local fire districts, concerned with fire and forest conditions in the Lake Tahoe Basin.
Additional meetings with detailed updates of progress and results relevant to fire, fuels, and resources management
will be scheduled at the beginning of the second year of work. Members of these groups will also receive the annual
and final reports. At the end of the project a workshop will be held (location to be determined, USFS, TRPA are
strong possibilities) on how to use the information for project planning and implementation and to ensure
interoperability with systems used by agencies. We expect that managers will be comfortable using our tools and
results. We specifically chose the FVS and FCCS modeling tools because they are widely used by forest managers
including those in fire and vegetation management.
III. Figures
Figure 1 Visualization of a presettlement forest group 5 at the stand scale in a Yosemite National Park mixed conifer
forest. The left is the reconstructed forest in 1899 and the right is the forest as it was measured in the field 2004.
6
Figure 2. depicts average stand structure from FVS scaled to the landscape for the six presettlement forest groups
(see Figure 1) in Yosemite National Park as a demonstration of proof of concept. Both the presettlement (left) and
contemporary forest landscape (right) are shown.
Deliverables/Products
1) Digital GIS data and maps of the presettlement forest landscape.
2) Presettlement forest compositional group summaries. These summaries will include information on stand
density, basal area, and tree diameter distributions and be provided in table (paper) and digital form (tree
lists). Digital form will permit managers to input these data for other uses in SVS, wildlife habitat relations
models, and other models that require information on initial vegetation cover (hydrology, surface run-off,
fire behavior, fire effects, etc.).
3) Presentations to managers (USFS, Nevada State Parks, California State Parks, TRPA, etc.) at interagency
meetings on project objectives and progress).
4) Interagency workshop with managers on how they can use the landscape reconstruction for planning and
project implementation.
5) Two annual reports and a final report.
6) Publication of results in peer reviewed journals. Target journals with subject matter appropriate for this
work include Ecological Applications, Landscape Ecology, and Forest Ecology and Management.
Milestones/Deliverables (revised July 2008)
Starting
Date
Ending
Date
Complete award agreement
Compile stand structure data
8/1/08
8/1/08
9/15/08
6/30/09
Meet with Basin stakeholder agencies (USFS, CA, NV State
Parks, Lake Tahoe Unified Steering Group For Forest
Assessment and Protection,)
Conduct 1st year field work and prepare summary report
7/1/09
7/1/09
8/15/09
8/31/09
9/1/09
6/1/10
4/1/10
6/1/10
7/1/10
6/1/10
7/31/10
8/31/10
9/1/10
12/31/10
1/1/11
4/1/11
6/30/11
7/31/11
4/1/11
8/31/11
9/30/11
Analyze presettlement stand structure and fire regimes from
field and tree core data for all studies using data from FIA, the
R5 Ecology Plot database, Stand Exams, plots sampled for the
TRPA Lake Tahoe Basin IKONOS vegetation map, and plots
sampled for the NRCS Lake Tahoe Basin soil survey
Annual progress report to PSW with simultaneous distribution to
agencies
Meet with Basin stakeholder agencies
Conduct 2nd yearfield work and prepare summary report
Integration of geospatial data sets and development of DFA and
CART models of presettlement forest structure
Develop spatially explicit representations of presettlement forest
landscapes within GIS and digital maps and representations of
conditions; write and submit publications
Basin workshop on using information
Submit final report and digital data of presettlement forest
landscape (maps and compositional group summaries)
Project completion date
1
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