I. Title Page
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Drought stress and bark beetle outbreaks in the future forest:
Extending an existing model to inform climate change
adaptation
1c) Impact of climate change on ecological communities and the
evaluation of adaptation strategies
Robert M. Scheller
Environmental Science and Management Department
Portland State University
P.O. Box 751, Portland, OR 97207
Phone: (503) 725 – 2497
Fax: (503) 725-9040
Email: rmschell@pdx.edu
E. Louise Loudermilk
Environmental Science and Management Department
Portland State University
P.O. Box 751, Portland, OR 97207
Phone: (503) 725 - 2364
Fax: (503) 725-9040
Email: e.louise.loudermilk@pdx.edu
Matthew Hurteau
School of Forest Resources
Pennsylvania State University
306 Forest Resources Building, University Park, PA, 16802
Phone: 814-865-7554
Email: matthew.hurteau@psu.edu
Peter Weisberg
Department of Natural Resources and Environmental Science
University of Nevada-Reno
1664 N. Virginia St., Mail Stop 186, Reno, NV 89577
Phone: 775-784-7573
Email: pweisberg@cabnr.unr.edu
Carl Skinner
USDA Forest Service
Pacific Southwest Research Station
3644 Avtech Parkway, Redding, CA 96002
Phone: 530-226-2554
Email: cskinner@fs.fed.us
Nicole Braman
College of Liberal Arts & Sciences
Portland State University
P.O.Box 751, Portland, Or 97207
Phone: 503-725-8947
Fax: 503-725-4233
Email: bramann@pdx.edu
$ 159,765
$
Abstract
Managing forested landscapes in the context of a changing climate presents new and multifaceted
challenges. Maintaining ecological integrity while future disturbance regimes are altered will require an integrated
assessment of critically relevant processes. These include forest nutrient cycling, succession, multiple disturbances,
and management regime. Successful forest management will require information about the projected impacts of
climate on forest communities, disturbance feedbacks, as well as the effectiveness of mitigation strategies for
reducing these effects. We propose to evaluate how climate change and associated drought induced stress will affect
forest productivity and mortality as well as alter susceptibility to bark beetle outbreaks across the forested landscape
of the Lake Tahoe Basin. Furthermore, we will evaluate the effectiveness of forest treatment options for mitigating
mortality from drought stress and bark beetles. This research will be an extension of our current SNPLMA funded
project (P049) which is assessing the impacts of climate change and forest treatment options on wildfire and above
and belowground forest carbon dynamics. The proposed research will leverage the spatial data, model
parameterization, and analysis conducted to date for P049, while incorporating drought-impact growth estimates
from site-level data collected from another SNPLMA funded project (P029). Our project will demonstrate how
climate impacts multiple natural disturbances that regulate long-term forest productivity, resilience, and overall
forest health. Results will enable managers to assess various forest mitigation strategies for adapting to a changing
climate.
Justification
Lake Tahoe Basin (LTB) managers are faced with managing a forest disturbed by multiple and interacting
forces (climate, insects, drought, wildfire) that are highly dynamic across space and time. Climate change is of
particular concern because of the overarching impacts on Basin wide processes, such as forest productivity (Battles
et al. 2008), resilience (Millar et al. 2007), carbon (C) sequestration potential (Hurteau and Brooks 2011), fire and
insect risk (Coops and Waring 2011), amongst others (e.g., water quality).
Throughout the western U.S., increasing temperature and decreasing precipitation have been identified as
the root cause of increasing tree mortality (van Mantgem et al. 2009). Climate projections for California however,
suggest little change in annual total precipitation, although temperatures are expected to continue increasing (Cayan
et al. 2008). Increasing temperature amplifies drought stress in plants because of the direct effects on
evapotranspiration rates (Seager et al. 2007). In the dominant Sierra mixed-conifer forest species, future climate is
projected to decrease productivity and increase mortality (Battles et al. 2008). Large-scale droughts are already
occurring in some systems. In southwestern piñon-juniper woodlands, prolonged water stress has increased
susceptibility to other disturbance agents and large mortality events (Breshears et al. 2009). A 5-fold increase in
drought related mortality is expected to occur in southwestern U.S. forests by the end of the century (Adams et al.
2009).
Across the U.S., more than 70 million acres of forested land are at risk of mortality from 26 different
insects and diseases (US Department of Agriculture 2004). Bark beetles (e.g., Dendroctonus spp., Ips spp., Scolytus
spp.) in particular, have been an especially important factor contributing to tree mortality in the U.S. (Fettig et al.
2007). The link between bark beetle outbreaks and drought is significant (Dobbertin et al. 2007; Guarín and Taylor
2005). This is especially true in areas that have been fire suppressed and have high tree densities; the stress of
resource competition from surrounding trees coupled with warm temperatures creates a suitable environment for
beetle infestation (Parker et al. 2006), notwithstanding improved conditions for longer or multiple insect life cycles
and dispersal capacity (Hicke et al. 2006).
Beetle outbreaks are expected to increase in the near future due to prolonged dry seasons and increased
drought stress caused by climate change. It is projected that bark beetle infestation risk will increase by 2.5-5 times
in western forests by the end of the 21st century (Gan 2004; Hicke et al. 2006). The coniferous forests of the
western U.S. have already experienced unprecedented levels (> 20 million ha annually, including pathogens, (Dale
et al. 2001)) of bark beetle infestations driven by the compounding factors of fire suppression, high tree density,
increasing temperatures, and extended drought (Fettig et al. 2007; Hicke et al. 2006). This is also evident in the
LTB where an extended drought period (1986-1992) caused landscape-level drought and bark beetle driven
mortality patterns, damaging >260,000 m2 tree basal area (Macomber and Woodcock 1994).
The excessive fuel accumulation resulting from nearly a century of fire suppression (Stephens and Ruth
2005) and several decades of climate warming (Westerling et al. 2006) has also caused increasingly greater area
burned in U.S. National Forests. The amount of U.S. forest lands affected by wildfires and phytophagous insects are
similar and often overlap in area (Hicke et al. 2006). The overlap is due to the feedbacks associated with tree stress
and fuel loading. Even if trees survive a fire, they are stressed and become more susceptible to beetle infestation.
An area not recently burned may still experience bark beetle attack (e.g., from drought stress) and will subsequently
increase dead fuel loading in outbreak areas (Parker et al. 2006). Where prescribed burning is applied and fire
intensities are lowered, trees may be fire-stressed and may therefore become prone to subsequent bark beetle
invasion. Specific to the LTB, Bradley and Tueller (2001) found that bole charring, duff consumption, and crown
scorch were significant predictors of beetle attack after a prescribed burn and over 24% of the trees were infested in
prescribed burn plots.
With increasing temperatures in the west, these multifaceted tree stressors weaken individual tree resistance
and reduce overall forest resilience to drought, bark beetles, and wildfires. As a consequence, LTB forests may be
more vulnerable to rapid change than previously assumed, with the potential for a climate regime shift to nonanalogue vegetation (Hurteau and Brooks 2011). For example, if a Jeffrey pine stand experiences drought, the
resulting mortality and stress may trigger subsequent insect outbreaks and/or provide more fuel for wildfire. If a
large, contiguous area is similarly affected, Jeffrey pine seed rain will diminish and, if the drought continues,
germination and establishment will be reduced. The result would be a large area dominated by chaparral and shrubs
with substantially lower embodied C and reduced ability to continue to uptake C. Furthermore, if conditions
conducive to subsequent fire occur more frequently, establishment of tree regeneration may be further limited
because of the increase in fire-induced mortality (McGinnis et al. 2010). Forest resilience can however, be
maintained and even enhanced through active management that reduces resource competition and that limits insect
mortality and the risk of high-intensity wildfire (Fettig et al. 2007).
Although climate, drought, and insects are external factors that LTB managers cannot directly control, it is
nonetheless important to understand the inherent processes and projected effects on the forest. This knowledge
provides the foundation for developing strategic adaptive planning, especially related to invasive field applications,
such as forest thinning. In addition to reducing fire risk, forest thinning has the potential to reduce drought stress
and bark beetle susceptibility (Fettig et al. 2007). Research and extension (Donaldson and Seybold 1998b) has
suggested ‘integrated pest management’ techniques to mitigate bark beetle infestation, including thinning and
sanitation methods. These techniques are geared towards maintaining the health of un-infested trees and the
removal of infested ones. The effectiveness of these techniques has not been tested in the Lake Tahoe Basin (but see
Bradley and Tueller 2001), especially in a climate change context. Understanding the long-term effectiveness of
various thinning strategies is most feasibly done using a modeling approach, given the difficulty of designing and
maintaining long-term field experiments that incorporate multiple disturbance types and inherent feedbacks among
disturbances, succession, forest insects and pathogens, and climate change. This proposed project aims to use an
existing modeling framework (developed for P049) of forest landscape processes (wildfires, climate change,
succession, fuel treatments) to include mortality from drought and bark beetles. More specifically, for our current
project (P049), we are evaluating a suite of fuel treatment scenarios to assess treatment effectiveness for reducing
wildfire C emissions and maximizing total landscape C storage. Our proposed project would extend this by a)
integrating the effects of drought and insects into our estimates of C dynamics and shifting species distributions over
the next 100 years, and b) by examining fuel treatment effectiveness for also reducing tree mortality from drought
and insects.
Our current project (P049) and this proposal directly fit the needs identified in the Forest Health theme
and subtheme (1c). While our current project is focused on projecting forest response and C emissions due to
climate change and changing wildfire regimes; this proposed research will broaden the scope to encompass a
multitude of climate sensitive drivers of forest productivity and mortality. We will expand our modeling framework
to ultimately establish the potential range of key climate conditions relevant to drought stress and bark beetle
outbreaks. Our overall approach is shown in Fig. 1. Our existing modeling framework (P049) and tree-ring data
collected as part of another project (P029) will further calibrate modeled forest productivity with site-specific data.
We will be able to identify which forest types and species in the Basin are most vulnerable to climatic changes (e.g.,
drought) and improve our projections of future species distributions. Fuel treatment options are used in the current
project to manage for wildfire risk. These treatment strategies will be evaluated to assess increased tolerance to bark
beetle outbreaks in relation to drought, especially in host-specific areas (e.g., Pinus jeffreyi, Abies concolor). We
will assess the effectiveness of treatments in conserving the ecological integrity of the LTB forests as a whole and
within specific communities (e.g., mixed conifer). Furthermore, all of our team members have been a part of
SNPLMA (and non-SNPLMA) projects in the LTB management area. We have a combined knowledge of the
basin’s forests, ranging from field studies to landscape modeling. We have worked directly with LTB managers on
model development, particularly in guiding our objectives and fuel treatment scenario design. Our project will
demonstrate the climate-driven impacts on multiple natural disturbances that drive long-term forest productivity,
resilience, and management for overall forest health.
Background and Problem Statement
Climate change is occurring in the LTB, with projected effects ranging from changes in water quality
(Coats et al. 2006; Coats et al. 2010) to reduced forest growth and C sequestration potential (Fig. 2, (Loudermilk et
al. in preparation)). Climate change effects on landscape wide drought and beetle activity in the LTB are imminent
and may come to drive tree mortality patterns. Thirty percent of the conifers in the LTB were killed by bark beetles
during an extended drought that occurred between 1986 and 1992. Some areas had concentrated mortality rates as
high as 80%. The intersection with the Wildland Urban Interface increased fire risk (i.e., higher dead fuel loads) and
reduced the forest’s aesthetic quality (Donaldson and Seybold 1998a; Donaldson and Seybold 1998b; Macomber
and Woodcock 1994). Drought stress alone causes regional scale mortality across the Sierra Nevada landscape; and
is also projected to increase due to the temperature sensitivity of soil moisture (Battles et al. 2008; Guarín and
Taylor 2005; Seager et al. 2007). There is also risk of a long-term shift in forest community composition due to
climate-reduced resilience accentuated by insect and drought mortality (Millar et al. 2007).
Understanding the potential of compounding and complex factors that climate may pose on the LTB
forested system can help guide long-term management planning. The potential feedbacks with drought, wildfire,
bark beetle outbreaks, and climate change over a long temporal scale (e.g., over many decades) and across large
spatial scales (> 10,000 ha) requires a robust modeling approach. Our proposed landscape modeling approach
provides the framework necessary to implement components that influence the forest at an ecosystem scale and
evaluate scenarios to assess mitigation strategies or other impacts on the forest (e.g., climate emissions scenarios).
Projections from our current SNPLMA project (P049), suggest continued above and belowground C sequestration
across the LTB (Fig. 2). Climate under both low and high emission scenarios will however, reduce forest
productivity (biomass growth) resulting in reduced C storage potential in both live and dead C pools, as compared to
projections using current climatic conditions (Fig. 2).
Successful forecasting of drought effects on growth requires a site specific long-term data set that
establishes the relationship between drought stress (reduced soil moisture) and growth; these data are available from
across the LTB (i.e., tree-ring growth data, P029) and will be used in the proposed research. We have already
established the relationship between annual growth, drought stress, and competition in Sierra mixed-conifer forest
(Hurteau et al. 2007) and have gathered the data required to quantify the relationship between drought stress and
annual growth for mixed-conifer species in the LTB as part of P029.
Mitigation strategies, such as fuel treatments are a necessity in western U.S. forests, where a course of ‘no
action’ is not without consequence. The clear relationship of tree density and drought stress to bark beetle
susceptibility (as well as fire risk) drives the management motivation to implement extensive fuel treatments in the
LTB (Fettig et al. 2007). In our current model, we are developing multiple fuel treatment scenarios to assess their
effectiveness in reducing fire severity and spread as well as examine changes in forest structure and C dynamics.
Problem Statement:
Effective forest management requires a better understanding of a) the potential for amplified drought and
beetle induced mortality, b) the interactions among climate-driven processes (wildfire, drought, beetle outbreaks,
forest succession), c) the effects of current and future management activities (i.e., forest treatments) on the severity
of drought and insect mortality, d) additional management alternatives for maintaining resilience and flexibility
given the large uncertainty about the future of the LTB. A landscape-scale approach is critical to addressing these
issues – the LTB is a tightly linked system and projections beyond the next decade require an integrated, landscapescale approach. For example, an assessment of the long-term implications of management on drought and bark
beetle occurrence and associated levels of tree mortality requires consideration of landscape heterogeneity and
outbreak patterns. Our proposed approach will enable us to estimate how forest community composition, the
distribution of tree species, and forest C will change in the coming decades. We will provide a comprehensive
outlook into climate change effects on multiple forest processes, disturbances, and forest response to these complex
interactions.
Goals, Objectives, and Hypotheses
Our primary objective is to evaluate climate change effects associated with drought stress (reduced forest
productivity, increased mortality) and bark beetle outbreaks across the forested landscape of the Lake Tahoe Basin.
Furthermore, we will evaluate forest treatment options for mitigating mortality from drought stress and bark beetle
outbreaks and their effectiveness (Fig. 1). This research will be an extension of our current SNPLMA project
(P049) which is assessing the impacts of climate change on wildfire and above and belowground forest C dynamics
and examines fuel treatments options. The proposed research will leverage the spatial data, model parameterization,
and analysis conducted to date for P049, while incorporating drought-impact growth estimates from site-level data
collected from another project (P029). Our modeling approach will demonstrate the climate-driven impacts on
multiple natural disturbances that drive long-term forest productivity, resilience, and overall forest health, while
enabling managers to assess various mitigation strategies for adapting to a changing climate.
Based on these objectives, we will test the following hypotheses using projections from our simulation
modeling:
1) Drought stress reduces aboveground growth and net C sequestration. Climate change will increase drought
stress through reduced soil moisture.
2) Drought stress caused by a changing climate will increase tree mortality and alter community composition.
3) Expected increases in bark beetle outbreaks in coming decades due to drought stress will also increase tree
mortality and alter community composition.
4) Overall forest C will continue to be sequestered, regardless of emissions scenario (see Fig. 2 preliminary
results), although at a slower rate than current-day climate due to the coupled impacts of temperature and
precipitation changes, extended drought, wildfires, and beetle outbreaks.
5) Fuel treatments that decrease forest density will reduce drought stress, therefore mitigating the potential for bark
beetle infestation. This will in turn reduce the risk of large or sudden forest community changes.
6) The effectiveness of fuel treatments in maintaining forest resilience will increase under future climate
conditions due to increased intersections between wildfires, bark beetle infestation, and treatments.
Study area:
Approach, Methodology, and Location
Our study area comprises approximately 208,800 acres of forested land in the Lake Tahoe Basin (LTB).
The climate is Mediterranean with a summer drought period. Vegetation is dominated by a mixed conifer forest of
Jeffrey pine (Pinus jeffryi), lodgepole pine (P. contorta), sugar pine (P. lambertii), white fir (Abies concolor), and
red fir (A. magnifica). Today’s forests have substantially departed from historic conditions and are overly dense with
small trees and extraordinary accumulations of fuels (Beaty and Taylor 2008). Forest treatment prescriptions in the
LTB are based primarily on Sierra Nevada-wide management directions to reduce surface and ladder fuels in order
to modify fire intensity and limit the potential for crown fire spread. From an ecological perspective, these
treatments also provide a means to reduce resource competition between trees (hence, improve forest vigor) and
reduce susceptibility to drought stress and insects.
Sampling Design & Available data:
We will use our current modeling framework (developed for P049) and will implement existing datasets
and literature values on drought and insects to further develop the model, requiring no new field data collection.
The current model has incorporated a multitude of datasets, including 1) Forest Inventory Analysis (FIA) and Forest
Service (e.g., GIS clearinghouse) data from the region to estimate forest structure and composition, Basin wildfire
regime data, as well as fuel treatment implementation, b) eddy flux tower data to calibrate monthly net ecosystem
exchange and net primary productivity, and c) projected climate emission data (temperature, precipitation, wind
speed) from Basin estimates (Coats et al. 2010). Tree-ring data collected across the Basin (described below, P029)
provides the link between drought stress and reduced tree growth at the LTB (Hurteau et al. 2007), which will be
critical for further model calibration. Overall tree morality will be calibrated using an existing empirical dataset, for
example; FIA data, literature estimates (e.g., (Macomber and Woodcock 1994)) , and forthcoming tree mortality
maps from the LTB for each year from 1985 to 2010 (ongoing Lake Tahoe License Plate Program project, “Tree
Health within the Lake Tahoe Basin: Interactions with Fuel Management Treatments”, PIs R. Nowak and P.
Weisberg).
The project will not require any additional processing of projected climate change; the downscaling of the
projected emissions climate data (A2, B1 scenarios) is complete and implemented into the existing modeling
framework. These climate data will be used to drive drought and insect projections (Drought and Insect extension,
discussed below) necessary for this project.
Tree Ring Analysis:
Tree growth is a function of climatic influences, age-related growth patterns, and disturbance (Fritts and
Swetnam 1989). Annual growth increment coupled with allometric equations to estimate woody biomass can be
used to estimate Aboveground Net Primary Productivity – ANPP (Jenkins et al. 2003) . Thus, embodied in an
annual tree-ring record is the result of how these different factors have influenced tree-level ANPP. Given the longlived nature of trees, tree-ring records provide an opportunity to reconstruct ANPP as a function of known climatic
conditions.
To quantify estimates of site-level ANPP, we will leverage tree-ring data collected as part of another
current project (P029). These data include measured cores from 301 trees, representing 5 species from 52 plot
locations around the LTB. Cores were prepared using standard dendrochronological techniques and cross-dated
(Stokes and Smiley 1968). Cross-dating was statistically validated using the COFECHA program (Grissino-Mayer
2001). To determine if local LTB climate patterns correspond with regional climate patterns, we will use a nested
calibration approach previously used by North et al. (2005a) and Hurteau et al. (2007). This approach utilizes
climate records from local weather stations to calculate standardized water-year totals for comparison with three
widely cited El Niño - La Niña sources ((Kiladis and Diaz 1989; Smith and Sardeshmukh 2000), NOAA Climate
Prediction Center, http://www.cpc.ncep.noaa.gov). In previous work conducted with Co-PI Hurteau (Hurteau et al.
2007; North et al. 2005b), standardized water-years that were one standard deviation above or below the mean were
correlated with El Niño and La Niña events, respectively. Given the focus on drought stress, we will isolate treering measurements in average climate and La Niña years to develop a standardized drought-impact growth
relationship by species, while considering the association with the Pacific Decadal Oscillation (Trouet and Taylor
2010). This relationship will be used to validate our ANPP-climate relationship.
Current model:
We are currently simulating forest C dynamics, disturbance, and succession using the LANDIS-II forest
landscape model (Scheller et al. 2007) in the LTB. LANDIS-II simulates succession and disturbance in a
framework that emphasizes interactions among ecosystem processes and disturbances. Successful application and
sensitivity testing has been conducted for succession, insect, fire, wind, dispersal, and harvesting (e.g., (Scheller et
al. 2011b; Sturtevant et al. 2004; Sturtevant et al. 2009)) and used extensively in climate change research (e.g., (Xu
et al. 2011)).
The Century Succession extension for LANDIS-II simulates the regeneration and growth of trees and
shrubs, detrital C and nitrogen(N) dynamics, soil C and N dynamics, and heterotrophic respiration (Scheller et al.
2011b). The growth of trees and shrubs is determined by unique species attributes (shade tolerance, C allocation,
C:N ratios for foliar, wood, root biomass, lignin, etc.), edaphic properties, and available N. Century extension
parameterization from our current research in the LTB is complete (Loudermilk et al. in preparation). Fuel
treatment boundaries and vegetation type data have been developed. Aboveground biomass and ANPP have been
calibrated against the available literature (e.g.,(Campbell et al. 2009)) and will be further refined using the tree ring
analysis outlined above.
Wildfire is currently modeled using the Dynamic Fire and Fuel System extension (Sturtevant et al. 2009),
which simulates mixed severity fires dependent upon fuels, weather conditions (from weather station data or climate
projections), slope and topography. Modeled wildfires have been calibrated to current fire regimes, fuel
characteristics, and climate conditions. The fire regime under a changing climate is mechanistically simulated
through altered fire weather conditions, such that fire effects are an emergent property of climate change.
Simulating Beetle Infestations:
Beetle events will be modeled using the Biological Disturbance Agent (BDA) extension for LANDIS-II
(Sturtevant et al. 2004), which simulates the spread of insects as a function of insect host preferences, outbreak
frequency and dispersal distances. The extension simulates tree mortality, and insect host specificity and host and
non-host response. Multiple insects can be simulated and the insect extension will interact with the fire extension,
since defoliation and mortality due to insect damage can cause higher fuel loads (in the short term), increasing fire
spread and severity. Furthermore, fire occurrence can increase suseptibility to beetle attack. We will modify the
BDA to interact with the Drought extension (discussed below) such that spread and severity are amplified by
drought stress. These interactions will be verified (via a sensitivity analysis) to historic patterns of outbreaks as
compared to local estimates of the Palmer Drought Severity Index (Guarín and Taylor 2005).
Outbreak frequency and duration will be empirically derived from known outbreaks in the LTB (e.g.,
(Bradley and Tueller 2001)). Simulated outbreak size and mortality (%, biomass) will be calibrated using maps of
bark beetle caused tree mortality previously developed for the LTB (e.g., (Macomber and Woodcock 1994)),
alongside regional disturbance maps (e.g., Aerial Detection Survey of the USDA Forest Service) and FIA mortality
estimates. Although this extension will be developed for the local genera of bark beetles (Dendroctonus spp., Ips
spp., Scolytus spp.), host specificity will include impacts from the Jeffrey pine beetle (Dendroctonus jeffreyi) and the
pine engraver beetle (Scolytus centralis) on Jeffrey pine (Pinus jeffreyi) and fir species (Abies spp.), respectively
(Donaldson and Seybold 1998a). The Biological Disturbance Agent extension will provide estimates of % mortality
and dead biomass by species due to bark beetle infestation.
Simulating Drought Stress and Mortality:
Drought effects will be modeled using the Drought Disturbance extension for LANDIS-II (Gustafson and
Sturtevant, in review). This extension simulates mortality and reduced establishment due to drought stress. Drought
sensitivity is species and maturity class specific: i.e., seedlings respond differently to drought than mature trees do.
Drought frequency and duration will be parameterized with regional records of historic drought (e.g., (Benson et al.
2002)) , especially those linked with species and age-specific tree mortality (e.g., (Battles et al. 2008; Guarín and
Taylor 2005; van Mantgem et al. 2009). Drought caused mortality will be calibrated using literature estimates
derived from the Sierra Nevada (e.g., (Guarín and Taylor 2005; van Mantgem and Stephenson 2007)). The Drought
Disturbance extension will provide estimates of % mortality and dead biomass due specifically to drought.
Drought stress effects on tree growth are modeled in the Century extension of LANDIS-II (described
above), while drought related mortality and effects on establishment will be modeled through the Drought
Disturbance extension. Our tree-ring analysis will aid in linking drought and reduced growth and provide unique
validation opportunity for scaling site to landscape level ANPP estimates.
Climate change, drought stress, and beetle outbreaks will be integrative in the model. Our downscaled
climate projections (from P049) will be used to estimate drought years (Gustafson and Sturtevant, in review).
Within the Century extension, we can estimate overall drought reductions to growth. These data will be combined
to generate an overall drought stress index. The drought stress index will feed into the BDA, increasing site-scale
susceptibility to outbreaks. We will calibrate this link using historic drought and outbreak data (e.g., (Benson et al.
2002; Macomber and Woodcock 1994), tree-ring analysis).
Forest Fuel Treatment Assessment:
Forest fuel treatments are being modeled using the Biomass Harvest extension for LANDIS-II (Radeloff et
al. 2006). Fuel treatments will be modeled identically to our current project, but with the goal to assess the
resiliency of the forest to drought stress and beetle outbreaks across our various fuel treatment scenarios. Our
current fuel treatments scenarios were developed from communication with LTB forest managers, in association
with a recent manager’s workshop in May 2011. Essentially, a range of rotation lengths (e.g., 15, 30 years) and
target areas (e.g., defensible space) are implemented across three fuel treatment scenarios and two treatment stand
selection approaches (e.g., fire risk, forest health). This provides a range of treatment strategies to be tested
alongside varying climate scenarios.
Analysis of Model Outputs:
In accordance with the current project (P049), multiple simulations will be implemented using a Monte
Carlo framework (Yang et al. 2008) to account for the stochastic nature of simulated climate and wildfires. Model
projections will be analyzed to determine coupled drought stress and bark beetle impacts on forest mortality under
varying climate conditions (e.g., current climate vs. A2 emissions scenario). This includes providing time-series
maps of biomass loss associated with each mortality driver (e.g., mortality from beetle attack) on specific tree
species. We will also employ a factorial design (climate scenarios x fuel treatment scenarios) to test our hypotheses;
we will determine how each scenario combination (using a three way ANOVA) contributes to mortality from
climate driven drought stress and bark beetle outbreaks. ANPP validation analysis (i.e., tree-ring data vs. LANDISII simulations) will provide results estimating the degree of uncertainty between empirical site-level growth and
simulated patterns in response to drought.
Relationship of the research to previous and current relevant research
The proposed research will directly build upon the expertise and dataset developed for the SNPLMA
funded project, Management options for reducing wildfire risk and maximizing C storage under future
climate changes, ignition patterns, and forest treatments (P049). We will utilize the same suite of modeling
tools and the spatial datasets necessary to execute P049, in which PI (Scheller) and Co-PIs (Loudermilk, Weisberg)
are associated. We have conducted workshops with forest managers to determine likely and potential fuel
treatments over the near term. The research will also build upon parallel research being conducted in the New
Jersey pine barrens that is evaluating the effects of climate change, wildfire, and insect outbreaks on forest C
dynamics ((Scheller et al. 2011a; Scheller et al. in preparation; Scheller et al. 2008) funded by the Forest Health
Monitoring program of the USFS). In addition, Co-PIs Scheller and Weisberg are conducting research on the effects
of drought and climate change on forests in northern Nevada (funded by USGS). The proposed research will also
leverage data collected as part of the SNPLMA funded project, Modeling the influence of management actions on
fire risk and spread under future climatic conditions (P029). As part of this project, Co-PI Hurteau established
stand structure plots and collected tree-rings across the mixed-conifer zone of the LTB. These tree-ring data have
already been prepared and measured, allowing for substantial cost-savings in this proposed project. We have
already utilized projected climate data from a completed SNPLMA project at the LTB (P030, (Coats et al. 2010)).
Co-PI Weisberg has completed a related LANDIS-II modeling project (SNPLMA grant 05-CR-11051900-012) that
examined the influences of fire and harvesting regimes on nitrogen and phosphorus cycling in the context of the
LTB’s particular history of pre-settlement fire, settlement-era logging, subsequent fire exclusion, and recent fuels
management activities. Weisberg has an ongoing project funded by the Lake Tahoe License Plate Program that uses
satellite remote sensing to quantify and map the relationship between forest density, fuel treatments and forest
mortality over the 1984 – 2011 period. Results from this study will be used to calibrate overall mortality levels
simulated by the Biological Disturbance Agent and Drought Disturbance extensions of LANDIS-II. This project also
builds upon other studies from the LTB, specifically on tree mortality patterns and impacts from disturbances (e.g.,
(Bradley and Tueller 2001; Macomber and Woodcock 1994)).
Strategy for engaging with managers and obtaining permits
Our current project (P049) has given us extensive experience engaging managers through both meetings
and workshops. We have successfully engaged managers during the 2010 SNPLMA Symposium on Forest
Management Decision Support Tools, effectively putting C emissions on their ‘radar’. In addition, a fuel treatments
workshop in May 2011 successfully solicited fuel treatment data from managers and engaged them in scenario
generation that has improved and refined our futures scenarios. Numerous managers have expressed interest in
having a complete picture of disturbances and C dynamics on the landscape.
We will extend these prior successes through continued engagement with the SNPLMA science groups and
through continued interactions with managers. Due to our short time frame (1 year), we anticipate presenting at one
additional SNPLMA management and science meeting and conducting a final workshop that will summarize our
final results with comprehensive results incorporating all aspects of both projects. No permits are required for this
project.
Description of deliverables/products
The extension of our research will provide spatial and temporal data on the coupled ecological effects of
climate and various disturbance regimes, with specific outputs of mortality (%, biomass) by species and residual
forest composition and structure. This includes estimates of varying wildfire regime and C dynamics (above and
belowground), as promised with the current project. We will provide local managers with a time series of Basin
wide mortality risk maps and species risk maps, specifically developed from mortality patterns and frequencies
associated with drought and beetle disturbance. These will illustrate the projected ecological impacts associated
with climate change and varying fuel treatment strategies. Our modeling results will enable us to inform managers
of the ecological outcomes that may result from implementing various fuel treatment strategies, and will ultimately
guide future goals of reducing climate induced drought stress and bark beetle response and overall forest health.
Publications: We anticipate at least 2 peer-reviewed publications and associated presentations at regional or
international meetings. Topics will include:
1) Future forest vulnerability of climate induced drought stress and bark beetle outbreaks in the LTB
2) Significance of fuel treatment strategies for maintaining long-term forest resilience in a changing climate
within the LTB
Schedule of Major Milestones and Deliverables
The proposed project is scheduled to begin in October 2012 and run for 1 year (through September 2013)
Milestone/Deliverable
Progress Reports
Start Date
End Date
Description
Submit brief progress report to Tahoe Science Program
coordinator by the 1st of July, October, January, and April.
October 2012
Beginning immediately, Co-PI
(Loudermilk) will conduct the
LANDIS-II modeling at Portland
State University (full time)
December 2012
Collect & analyze data related to
beetle damage, tree response to
drought, including GIS analysis
of tree mortality maps
February 2013
Tree-ring data analysis to
establish link with LANDIS
Project initiation
October 2012
Data compilation & analysis
(GIS, empirical)
October 2012
ANPP analysis
January2013
Drought modeling
January 2013
March 2013
Beetle modeling
March 2013
May 2013
LANDIS-II Modeling
January 2013
May 2013
Comprehensive LANDIS-II
Modeling (link w/ P049)
June 2013
August 2013
Forest C, landscape
composition maps
July 2013
July 2013
Final Workshop at LTB
August 2013
August 2013
Annual Accomplishment
Report
Journal Articles
September 2013
September 2013
July 2013
September 2013
Calibrate drought extension with
empirical data, literature values
(mortality) & ANPP calibration
w/tree-ring data
Calibrate BDA extension with
empirical data, literature values
Parameterize the LANDIS-II
model for the Lake Tahoe Basin
to simulate drought stress and
beetle outbreaks
Model and analyze forest & C
dynamics impacted by climate
change, fire, fuel treatments,
drought stress and bark beetles
Time-series maps of C and forest
composition, age-structure will be
prepared & summarized
Results will be presented and
reviewed with managers
Prepare annual summary of
accomplishments
At least 2 scientific articles will
be submitted to peer reviewed
journals
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Figures
Climate
Fire
Drought
Mitigation:
Fuel Treatments
Forest
Community
& Carbon
Forest
Productivity
& Mortality
Bark Beetles
Fig. 1. Proposed research schematic: Climate induced stressors on forest productivity and mortality,
including feedbacks with bark beetles. Mitigation through fuel treatments are expected to reduce the
potential for drought stress, reduce fire risk, and subsequent bark beetle infestation.
Fig. 2. Projected C dynamics across the Lake Tahoe Basin. These graphs represent mean C (g C m-2)
across the forested landscape and standard error bars across three replicate model simulations. Live C:
above and below ground live C components of the vegetation (bole, leaves, roots); Soil Organic C (SOC):
C stored in the soil; Aboveground Net Primary Productivity (ANPP): a measure of forest growth
represented as C uptake; Detrital C: C stored in dead plant material (leaf litter, coarse woody debris, dead
fine and coarse roots). Base climate: Current climate used throughout simulation; B1 & A2: Projected
climate emissions scenarios. Note the difference in scale of the y-axis between graphs.