Proposal: Tahoe Research Supported by SNPLMA Round 10
I. Title Page Hemispherical image of conifer­encroached aspen stand, South Lake Tahoe, CA. July 2009. Title: Proposal to Conduct Research in Support of the Lake Tahoe Restoration Act and the Lake Tahoe Environmental Improvement Program
Stocking Guidelines for Aspen Restoration Stocking Guidelines for Aspen Restoration Subtheme this proposal is responding to Principal Investigator and Receiving Institution Forest Health Subtheme 1b: Modeling and decision support tools for multi‐objective forest management Dr. John‐Pascal Berrill, Assistant Professor Department of Forestry and Wildland Resources Humboldt State University 1 Harpst Street, Arcata, CA 95521‐8299 Phone: (707) 826‐4220; Fax: (707) 826‐5634 Email: pberrill@humboldt.edu Co‐Principal Investigator Dr. Christa M. Dagley, Research Associate Department of Forestry and Wildland Resources Humboldt State University 1 Harpst Street, Arcata, CA 95521‐8299 Phone: (707) 826‐1220; Fax: (707) 826‐5634 Email: christadagley@gmail.com Agency Collaborator Victor Lyon, Aspen Community Restoration Project Manager USDA Forest Service, Lake Tahoe Basin Management Unit 35 College Drive, South Lake Tahoe, CA 96150 Phone: (530) 543‐2749; Fax: (530) 543‐2693 Email: vlyon@fs.fed.us Grants Contact Person Julie Davy, Interim Director Sponsored Programs Foundation, Humboldt State University 1 Harpst Street, Arcata, CA 95521‐8299 Phone: (707) 826‐4189 or (707) 826‐5203; Fax: (707) 826‐4783 Email: jms49@humboldt.edu Funding requested: $ 143,437 Total cost share (financial and $ 43,249 (23.2% of total project cost) in‐kind contributions): 1
Proposal: Tahoe Research Supported by SNPLMA Round 10
II. Proposal Narrative a. Project abstract Quaking aspen forest communities in the Lake Tahoe Basin are being encroached and out‐competed by conifers that impact aspen vigor and stifle natural regeneration. Removal of conifers has been advocated, and is being tested around the Tahoe Basin. However, little is known about stocking and treatment persistence: specifically, how much growing space must we provide aspen trees and their root sucker regeneration for vigorous growth to be sustained until the next restorative thinning? The proposed research will provide aspen stand data and a decision support system for Tahoe Basin land managers involved in aspen restoration. The project will quickly generate interim stocking guidelines for restorative thinning treatments in aspen stands, followed by a rigorous analysis of growth, regeneration, and thinning response in aspen stands. The analysis culminates in development of a transparent, user‐friendly stocking assessment model that will support management decision making for restoration treatment design and scheduling of future treatments. b. Justification statement The proposed research project directly addresses subthemes 1b: “Modeling and decision support tools for multi‐objective forest management” and 2b: “Special status species and communities and priority invasive species” by providing results of data analysis and a decision support system for land managers involved in aspen (Populus tremuloides) restoration throughout the Lake Tahoe Basin. Aspen stands in the Tahoe Basin currently cover ~2,500 acres; sixty‐four percent of these aspen stands are currently at moderate, high, or highest risk of loss (EIP Project #10029: Aspen Community Spatial Distribution and Condition Assessment; Aspen Community Mapping and Condition Assessment Project, March 2007). Quaking aspen is considered a keystone species and one of the few broad‐leaved hardwood trees in many western forests (Shepperd et. al. 2006). Issues such as providing wildlife habitat, aesthetics, water quality, natural firebreaks, and sustaining ecological processes are driving the interest in restoring aspen stands. The proposed project will quickly generate interim stocking guidelines that could be applied as early as summer 2010 to support the design of thinning prescriptions for upcoming restorative treatments in aspen stands. Next, predictive models of growth, regeneration, and thinning response in aspen stands will be developed using existing and new data. The analysis culminates in development of a spreadsheet‐based stocking assessment model that will support project‐level management decision making to improve aspen forest health. This field data‐intensive project is also designed to detect any unintended consequences of restorative treatments and allow for rigorous analysis of such sporadic phenomena as windthrow or sunscalding by collecting a large sample of pre‐ and post‐treatment data. We have a one‐time‐only opportunity to capture detailed forest data in conifer‐
encroached aspen stands prior to implementation of restoration treatments throughout the Tahoe Basin (i.e., recording pre‐treatment baseline conditions that likely influence post‐treatment response, treatment impacts, and treatment effectiveness). c. Concise background and problem statement Quaking aspen communities in the Lake Tahoe Basin are being encroached by conifers. Aspen is classified as a ‘shade intolerant’ pioneer species that depends on high light levels to regenerate and maintain vigor (Perala 1990). Conversely, the majority of conifers encroaching aspen stands throughout the Tahoe Basin are moderately (lodgepole pine) to highly (red fir, white fir) tolerant of shade. Their tolerance of shade allows the conifers to grow under the shade of aspen tree crowns, and eventually overtop the relatively short‐lived aspen stems (Shepperd et al. 2006). Associated with shade tolerance is the ability of a tree species to withstand crowding and maintain vigor. Shade tolerant species can withstand greater crowding than intolerant species such as aspen (Smith and Smith 2005). Shade tolerant species retain live branches and foliage under partial shade, whereas the live crown base of intolerant trees quickly retreats upward as lower branches become shaded under crowded conditions. Loss of live crown leads to loss of vigor, with an associated decline in pest and disease resistance. In a clonal species such as aspen that regenerates mainly by vegetative root suckers, loss of crown volume and vigor among existing stems will lessen carbohydrate storage within root systems (DeByle and Winokur 1985). Entire aspen clones with depleted energy reserves could succumb to major disturbances or changes in 2
Proposal: Tahoe Research Supported by SNPLMA Round 10
climate (Rehfeldt et al. 2009). Removal of conifers encroaching aspen stands has been advocated and is being practiced in the Tahoe Basin (EIP Project #10080: Aspen Community Restoration Projects). However, there is an urgent need for aspen stocking guidelines to support design of thinning treatment prescriptions. For example, thinning in heavily encroached stands may liberate enough growing space for large aspen stems in the overstory to regain vigor, but may not reduce tree stocking to a level where aspen root suckers have sufficient growing space to maintain vigor until the next scheduled thinning treatment. Alternatively, vigorous aspen regeneration may not be the main objective of restoration in stands where larger aspen stems are still thrifty. Clearly one prescription will not suit all aspen stands in the Tahoe Basin or the goals of the land owner/manager, highlighting urgent need for stocking guidelines and a flexible stocking assessment model to support decision making for multiple objectives across the diverse array of aspen stand structures in the Tahoe Basin. Stand density index (SDI) is a widely‐used metric of relative “crowding” in forest stands. It is easily calculated using the number of trees per acre and their quadratic mean diameter at breast height (dbh). Stands with many small trees could be experiencing the same level of “crowding” (i.e., same SDI) as stands with fewer larger trees. Values for SDI of each tree species in a mixed stand (e.g., aspen‐conifer) or different age classes in a multiaged stand (e.g., aspen suckers and overstory trees) can be summed to give whole stand SDI (Long and Daniel 1990; Woodall et al. 2005; Shepperd 2007). Stand SDI cannot exceed a given upper level – once all available growing space is occupied – and this upper limit can differ widely between tree species of different shade tolerance. For example, the shade‐tolerant red fir has an upper limit of SDI = 2470 (metric units, Reineke 1933) whereas lodgepole pine has an upper limit of SDI = 1705 (Long 1985). Theoretically, trees in a mixed lodgepole pine‐red fir stand would grow until SDI > 1705 when lodgepole pine would be outcompeted by red fir that tolerates a higher level of crowding. Long (1985) proposed guidelines for stand density management based on SDI expressed as a percentage of the upper limit of SDI, where: 25% = onset of competition; 35% = lower limit of full site occupancy; and 60% = lower limit of self thinning. Once SDI exceeds 60% of the maximum, stands enter the “zone of imminent mortality” (Long 1985). The upper limit of SDI and the zone of imminent mortality are yet to be established for aspen stands in the Tahoe Basin, but are certainly lower than SDI limits for encroaching red and white fir, and would help guide managers interested in relieving crowding in conifer‐encroached aspen stands. Preliminary analysis of Tahoe Basin aspen data gathered in summer 2009 has indicated that competition‐
induced aspen mortality is already occurring within these stands, and that restoration thinning restricted to the removal of smaller conifers (e.g., < 35 cm dbh) may not reduce stand SDI enough to preclude self thinning nor allocate enough growing space for aspen regeneration to maintain vigor (Figure 1). Diameter limits for thinning (e.g., only cut conifers < 35 cm dbh) are easily communicable to stakeholders and contractors, but do not explicitly consider stocking and growing space needs of the existing aspen trees or future regeneration in different stand structures and conditions. Managers need an objective means of evaluating different aspen‐conifer stocking and composition scenarios in terms of post‐treatment growth and vigor, and treatment persistence forecasts in planning and budgeting for future thinning treatments (Figure 2). d. Goals, objectives, and hypotheses to be tested The main goal of our project is to provide managers with stocking thresholds for pure and mixed aspen stands and a decision‐support system (DSS) that generates stocking guidelines for restoring aspen stands in the Tahoe Basin. Specifically, our objectives are to: 1. Evaluate the effectiveness of recent and planned aspen restoration thinning treatments by simulation, and compare against a range of simulated alternate treatments. [completed 2010] 2. Characterize pre‐treatment “baseline” conditions and analyze regeneration patterns. [completed 2011] 3. Assess residual stand health and damage resulting from restoration treatments. [completed 2012] 4. Quantify relations between post‐treatment overstory stocking and regeneration (aspen and conifer). Develop predictive models for probability of regeneration occurrence and regeneration growth rate. 3
Proposal: Tahoe Research Supported by SNPLMA Round 10
[completed 2013] 5. Develop a stocking assessment model that predicts growth and vigor of overstory and understory aspen, old ‘legacy’ conifer, and encroaching young conifer in any combination resulting from restoration thinning treatments. [completed 2013] Hypotheses include: [analysis method in italics] 1. a. Aspen Community Restoration Project hand thinning treatments removing conifers up to a size limit of 45 cm dbh reduce stand density (in terms of stand density index; SDI) to a level where aspen overstory trees can regain vigor, but not down to a level where aspen sucker regeneration is released from overstory competition and can maintain vigor. [filter pre­treatment data by tree size to simulate various thinning intensities, calculate SDI, compare to published data for biological maximum in pure and encroached aspen stands around U.S.] b. South Shore Fuels Reduction and Healthy Forest Restoration Project hand thinning treatments using a dbh limit of 35 cm do not reduce stand SDI below the “zone of imminent mortality” for aspen; neither residual aspen overstory or aspen suckers are sufficiently released from competition to resume growth. [filter pre­treatment data by tree size, comparison against max. SDI] c. Mechanical thinning treatments applied by the Aspen Community Restoration Project and the South Shore Fuels Reduction and Healthy Forest Restoration Project aim to remove larger conifers, whereby reducing SDI to a level where aspen overstory trees can regain vigor and existing suckers are released from imminent competition‐induced mortality. [filter pre­treatment data by tree size, comparison against max. SDI] 2. a. Probability of occurrence and abundance of existing understory aspen suckers and conifer seedlings is directly related to different parameters including: density of neighboring overstory trees (basal area, SDI); predicted light and leaf area index (from hemispherical photo analysis); distance from overstory trees of same species (seed fall/suckering); microsite topography from Lidar‐based terrain data (hollow, flat, hillslope, raised ground); elevation above stream channel (depth of water table) and/or distance from channel. [multivariate analyses: logistic regression; multiple linear regression] b. Geographic location (Northeast, Northwest, or South shores of the Tahoe Basin) does not significantly affect relationships between regeneration and site/stand factors listed above (2.a.). [dummy variable in logistic regression; multivariate discriminant analysis] 3. a. Residual stand assessment reveals that mechanical restoration treatments result in more basal scarring and damage to aspen suckers than hand thinning [Kruskall­Wallis rank­sum tests]. b. The area of bare mineral soil left exposed after restoration treatments is greatest following mechanical displacement of cut conifers and lowest under hand thinning with manual burn pile construction. [binomial proportions test]. c. Incidence of windthrow and sun scalding of residual aspen trees increases with thinning intensity and level of pre‐treatment crowding (SDI). [logistic regression] 4. a. Post‐treatment aspen suckering occurrence is related to distance from residual aspen stems while conifer germination occurrence is related to distance from mature conifers, microsite topography, and distance from stream, [multivariate logistic regression] and greater following mechanical treatments due to greater root and soil disturbance. [dummy variable in logistic regression] b. Post‐treatment regeneration abundance is related to factors listed above (4.a). [log­linear regression] c. Post‐treatment height growth of aspen sucker regeneration is a function of light, best described by a sigmoidal curve with a “saturating” relationship of maximal growth as understory light approaches 100% of above canopy light (full sun). Conifer regeneration growth proceeds at lower light levels due to greater shade tolerance (Figure 3). [non­linear mixed­effects regression] d. Understory light predicted from hemispherical photo analysis is strongly correlated with SDI of 4
Proposal: Tahoe Research Supported by SNPLMA Round 10
neighboring overstory trees; the relationship is significantly affected by species composition (red fir and white fir trees cast more shade than pine or aspen of equivalent size). [ANCOVA, multiple linear regression] e. Data for dbh growth of aspen and conifers obtained from retrospective analysis of increment cores correlate with SDI of neighboring stand (from variable‐radius prism plot); overstory SDI and species composition are significant explanatory variables in growth models for overstory and understory aspen and encroaching understory conifer (i.e., aspen sucker growth ceases as stand SDI approaches “zone of imminent mortality”. [non­linear mixed­effects regression models] 5. a. Aspen and conifer dbh growth model predictions, combined with density (trees per hectare) and average tree size of overstory aspen and conifer, give change in SDI over time for separate stand components: aspen overstory, aspen sucker regeneration, lodgepole pine, and fir (red, white) overstory and understory trees. [models developed above applied in combination] b. Being related to stand density (SDI), aspen overstory tree vigor is predictable across a range of stocking and species composition scenarios (e.g., thinning treatment scenarios specified by managers based on pre‐
treatment stand conditions and thinning prescriptions under consideration). [spreadsheet­based stocking assessment model] c. Being related to overstory SDI and species composition, the vigor of aspen regeneration is predictable across a range of overstory stocking and species composition scenarios (e.g., thinning treatment scenarios specified by managers). [spreadsheet­based stocking assessment model] e. Approach, methodology and location of research Urgent need for preliminary stocking guidelines – based on the best available information – will be addressed by summarizing available SDI data and relevant published information to estimate the approximate ‘biological maximum’ stand density for pure aspen and aspen‐conifer stands around the U.S. Pre‐treatment data that we collected from four 1‐ha (~2.5 ac) plots located in Tahoe Basin aspen stands in summer 2009 will receive ‘virtual thinning’ (i.e., thinned by removing tree records from datasets) and SDI will be calculated for these virtual post‐treatment stands thinned at various intensities (e.g., cutting to varying diameter limits; Figure 1). This preliminary analysis will be made available to managers within one month of the grant being awarded. We expect that this vital information will prompt managers to alter restoration treatment prescriptions for summer 2010, specifically by thinning stands down below the recommended preliminary ‘threshold level’ of growing space needed for aspen trees and new suckers to regain or maintain vigor. The preliminary stocking guideline analysis can only be regarded as indicative, and will be augmented using data collected from aspen stands around the Tahoe Basin. First, we propose to expand our 2009 pre‐
treatment dataset collected in four aspen stands on the Southern (3 plots) and Northwestern (1 plot) sides of the Tahoe Basin by establishing five new plots in summer 2010 to obtain wider and more balanced sampling coverage around the Tahoe Basin (i.e., three plots in the South, three plots in the West/Northwest, and three plots in the East/Northeast, giving a total of nine 1‐ha permanent sample plots). Information gathered in these large plots includes tree and stand density data, regeneration data, and hemispherical canopy imagery before and after thinning. Multivariate analysis of pre‐treatment regeneration patterns will guide sample design and stratification in the second part of the proposed research based on environmental variables influencing regeneration. In this second part, we will collect increment cores to obtain growth rate data for aspen trees, aspen regeneration, encroaching conifers, and ‘legacy conifers’ within thinned and unthinned aspen stands around the Tahoe Basin. Third, we will re‐measure and assess the permanent 1‐ha plots after thinning to characterize relationships between understory light obtained from hemispherical photo analysis, overstory tree stocking, and aspen and conifer regeneration abundance and vigor. When applied in combination (in a spreadsheet format), these data and predictive models form the basis of a user‐friendly stocking assessment model that will support restoration treatment prescription design and forecasting of treatment persistence (i.e., the time taken for stands to return to crowded conditions after thinning) (Figure 2). Details of our proposed approach, methodology, and research locations are as follows: We will establish additional one‐hectare permanent plots in five stands scheduled for restoration treatment in 2010. In collaboration with Victor Lyon (USFS) we have identified sample stands located on the 5
Proposal: Tahoe Research Supported by SNPLMA Round 10
West/Northwest and East/Northeast shores of the Tahoe Basin, including Blackwood and Secret Harbor Creek. Potential sample stands identified by David Catalano (NDOW) include North Canyon and Tunnel Creek. Repeating the sampling methods from summer 2009, plot corners will be permanently demarcated with rebar and PVC and their locations recorded with GPS. Detailed pre‐treatment conditions will be assessed as follows: thousands of established aspen and conifer trees will be measured and their locations mapped (e.g., 1 ha plot x 5 sites x 400 trees/ha = 2000 trees). The tree measurements will give data for stand density (basal area, trees per hectare), tree species composition, stand and canopy structure, and spatial pattern. Tree stem location maps and environmental data (topography, stream channel location) will give distance to watercourse, elevation above stream channel, and microsite characteristics for individual trees in each plot. The pre‐treatment stem location maps will be used to re‐visit each tree during the first post‐treatment assessment, coding each tree record as healthy, cut, or damaged. Instances of damage to residual aspen trees or regeneration will be coded (e.g., scarred, crown damage, leaning) with repeat inspections tracking any change in health over time during annual post‐treatment aspen condition assessments (e.g., windthrow, crown dieback, stem infections, sun scalding; DeByle and Winokur 1985). The four 1‐ha plots established in 2009 each gave between 279 and 578 tree records (~1600 tree records total) including 58‐186 tree records for aspen >10 cm dbh in each plot (530 aspen tree records total). A very large sample size will be needed for rigorous logistic regression analyses of the probability of sun scald or windthrow occurrence, or any unforeseen consequences of thinning on residual aspen trees. The increment core sampling for retrospective analysis and modeling of tree growth will also be spread around the Tahoe Basin, allowing for analysis of growth differences between sample sites (e.g., elevation, effect of rain shadow on East side, volcanic soils in North, etc.) and development of widely‐applicable growth models. Sampling will include pure and conifer‐encroached aspen stands (e.g., Fountain Place) and aspen stands thinned >7 years before coring that will give several years of post‐treatment growth response data (North Canyon, Sugar Pine Point, Cathedral). A stratified sampling approach will give increment core data for both overstory and understory trees of each species growing in a range of conditions (from relatively open through to crowded), giving a ‘matrix’ of data representing possible growing conditions for non‐linear regression modeling. Hundreds of increment cores will be collected, mounted on core boards, and measured manually or scanned and analyzed for ring width using WinDendro® software. Stand density around each tree cored will be quickly assessed using a basal area prism giving number of trees and basal area by species, which together give SDI (anticipated main explanatory variable in growth models; strongly correlated with alternate explanatory variable to be tested: leaf area index). A more definitive analysis of growth can be undertaken in future after re‐measurement of our permanent plots (e.g., after 10‐20 years), but the proposed retrospective growth modeling methodology represents an economical, efficient short‐term solution to an urgent problem: how long will vigorous aspen sucker growth be sustained under any proposed thinning treatment scenario? Pre‐treatment regeneration counts will be assessed in a systematic grid of subplots (>10% subsample of main plot area) and will allow us to separate pre‐ and post‐treatment regeneration, and analyze patterns of regeneration as they relate to various ecological and environmental variables. Regenerating aspen and conifer will be tagged and measured repeatedly, giving initial survival/height growth in response to treatment. Hemispherical canopy photos taken at the center of each regeneration subplot before and after thinning will be processed to obtain estimates of canopy leaf area and understory light for each regeneration subplot (Figure 4). Proportion of subplot ground area disturbed by thinning (i.e., exposed mineral soil, accumulated debris) will be recorded. The nine 1‐ha permanent plots will collectively contain a total of approximately 240 regeneration subplots (n=107 existing subplots, and proposed n≈130 new subplots), giving a large enough sample size (n >200) for rigorous multivariate regression analyses of understory light and regeneration. The regression models used to test our hypotheses will ultimately be applied as predictive equations. Each equation will have a specific function within the stocking assessment spreadsheet. For example, the model user will specify number of trees of each species before and after thinning, and their sizes, and any site factors (e.g., elevation, aspect) found to significantly influence regeneration or growth. User‐specified overstory stocking after thinning will enter overstory growth models for each species. Predicted overstory growth – in terms of SDI – will also enter the regeneration growth models, reducing predicted regeneration growth rates 6
Proposal: Tahoe Research Supported by SNPLMA Round 10
due to increasing overstory competition over time. Additional models for windthrow or sun scald risk – if applicable ‐ will be linked to overstory stocking, warning the model user of excessive thinning intensity. Changes in average tree vigor (as a percentage of maximum growth potential) for aspen regeneration and overstory trees will be graphed over time under each user‐defined management scenario. Finally, we will use the stocking assessment model to develop comprehensive stocking guidelines for aspen restoration by simulation. The model will be used repeatedly to model a variety of thinning treatments applied to a range of aspen‐conifer combinations. f. Relationship of the research to previous and current relevant research, monitoring, and/or environmental improvement efforts The Principal Investigator (Dr. Berrill) and Co‐PI (Dr. Dagley) are currently collaborating with Victor Lyon (Project Leader, Aspen Community Restoration Project) and Duncan Leao (Forester‐Vegetation Planner, South Shore Fuels Reduction and Healthy Forest Restoration Project), and have completed comprehensive pre‐treatment assessments of four aspen stands scheduled for conifer removal treatments. The proposed research has been designed to build on preliminary findings from our initial analysis of stand data gathered in summer 2009 (Berrill and Dagley, unpublished data) and published data for aspen stands outside the Tahoe Basin (e.g., Woodall et al. 2005). The stocking assessment model will be constructed by introducing equations and parameters for aspen into an existing spreadsheet model framework developed for multiaged redwood‐
Douglas‐fir stands in California by the Principal Investigator (Berrill and O’Hara 2007, 2009). Stocking assessment models have been developed for several other species. Their development has been advocated for Sierra Nevada forest types (North et al. 2009). However, these models do not consider time between thinning treatments. Our approach will add growth models to the basic stocking assessment model framework, allowing managers to predict treatment persistence. The Principal Investigator has significant experience in growth model development using small, difficult datasets. If our analysis reveals that regeneration patterns are predictable, we will also add regeneration models for conifer seedlings and aspen suckers. The Principal Investigator and Co‐PI both have experience in sampling, multivariate analysis, and modeling of regeneration patterns (Section VII: Curriculum vitae). Pre‐treatment regeneration count data collected in 2009 within Tahoe Basin aspen stands (n = 107 subplots giving ~12% sample of ground area in four 1‐ha permanent plots) suggested that aspen regeneration was not lacking in these heavily conifer‐
encroached stands. We counted 2964‐3967 aspen suckers per hectare (1200‐1606 aspen suckers per acre) in the four plots. This represents further evidence that the crucial question is: how much growing space must we provide this aspen regeneration for it to grow vigorously and move up into the canopy (to replace senescing aspen trees)? Tree growth will be assessed in aspen stands throughout the Tahoe Basin, with the stand selection process guided by Victor Lyon (Project Leader, Aspen Community Restoration Project). Growth and response to thinning will also be assessed in aspen stands thinned earlier this decade under the direct supervision of David Catalano (Wildlife Biologist III, Nevada Department of Wildlife) and Tamara Sasaki (Resource Ecologist, California State Parks). Of particular importance is the collection of pre‐treatment “baseline” data from additional aspen stands scheduled for thinning around the Tahoe Basin. The proposed research is timed to coincide with significant restoration activities being undertaken by federal and state agencies. g. Strategy for engaging with managers and obtaining permits Throughout the project we will work with managers involved in aspen restoration around the Lake Tahoe Basin. We have obtained advice, positive feedback, and permission to sample aspen stands from aspen restoration project managers: Victor Lyon (Project Leader, Aspen Community Restoration Project), Duncan Leao (Forester‐Vegetation Planner, South Shore Fuels Reduction and Healthy Forest Restoration Project), Dave Marlow (Management Analyst III, Nevada Division of State Lands), David Catalano (Wildlife Biologist III, Nevada Department of Wildlife) and ‐ pending the Agency granting an official research permit ‐ Tamara Sasaki (Resource Ecologist, California State Parks). Our highest priority will be the rapid and widespread dissemination of results from the preliminary stand density analysis, with clear discussion of the implications for management. It is imperative that we release 7
Proposal: Tahoe Research Supported by SNPLMA Round 10
this information before restoration treatments are implemented in summer 2010, as it has the potential to increase effectiveness of some thinning prescriptions. We will contact the agency collaborators named above and request that they distribute our findings to any other land managers involved in aspen management and restoration in the Tahoe Basin. This expanded network of aspen managers will be kept updated on progress throughout the project as results become available. A public presentation and roundtable meeting in Year 3 will be followed by a workshop for land managers. The workshop will include a tutorial session for application of the stocking assessment model, and distribution of the CD‐Rom and user guide for the spreadsheet model. A descriptive color pamphlet summarizing key findings, and containing photos and contact information, will be printed and distributed at the public meeting. Extra copies will be provided to workshop participants, to distribute and make available to visitors of their offices. h. Description of deliverables/products and plan for how data and products will be reviewed and made available to end users This study will produce:  Preliminary stocking guidelines for aspen restoration thinning treatments [Year 1];  Predictive models for probability of regeneration occurrence and growth rate of aspen and encroaching conifers;  User‐friendly stocking assessment model that predicts growth and vigor of overstory and understory aspen, old ‘legacy’ conifer, and encroaching young conifer in any combination resulting from restoration thinning treatments (spreadsheet model on CD‐Rom and user guide);  Comprehensive stocking guidelines for aspen restoration thinning treatments [Year 3]. In addition, we will generate:  Quarterly reports of progress and study findings;  Final report written specifically for Tahoe Basin managers summarizing data and presenting key findings;  Pamphlet for the public summarizing key findings;  Two scientific papers submitted to peer‐reviewed journals: (1) “Patterns of regeneration, growth, and thinning response in conifer‐encroached aspen stands” Canadian Journal of Forest Research and (2) “Simulated response to thinning and treatment persistence in conifer‐encroached aspen stands” Western Journal of Applied Forestry;  Two conference presentations: proposals for oral and/or poster presentations will be submitted to the Tahoe Basin Science Conference, the Northwest Chapter of the Society for Ecological Restoration (SER), meetings in the PSW, and/or the Ecological Society of America annual meetings. Products of this research will be:  Reviewed internally by agency collaborators and Humboldt State University faculty;  Posted online under a new “Aspen Restoration” link on the Tahoe Integrated Information Management System (TIIMS) website (summary data, reports, powerpoint presentations, stocking assessment model). Finally, in an accessible Tahoe Basin location (e.g., LTBMU Headquarters, South Lake Tahoe) we will:  Host a public presentation of findings and facilitate a roundtable discussion;  Host a workshop for land managers, including hands‐on tutorial for stocking assessment model. 8
Proposal: Tahoe Research Supported by SNPLMA Round 10
III. Schedule of major milestones/deliverables Major milestones and deliverables are listed in the following project schedule (deliverables shown in bold). Milestone/Deliverables Start Date End Date Description Preliminary stocking guidelines May 2010 Jun 2010 Synthesis of existing data sets to determine maximum SDI and develop stocking guidelines Site selection Jun 2010 Jun 2010 Organize site visits with agency managers to assess suitability Install permanent sample plots Jun 2010 Aug 2010 Install 1‐ha plots at each study site and complete pre‐treatment measurements; perform post‐
treatment measurements for thinned sites Data entry, summary, process images, analysis Aug 2010 Mar 2011 Complete pre‐treatment stand summaries, process pre‐treatment hemispherical photos, analyze regeneration patterns Design sampling scheme Apr 2011 May 2011 Design sampling protocols for retrospective growth analysis Site selection Jun 2011 Jun 2011 Choose additional sites for retrospective growth analysis Collect post‐treatment measurements and increment cores Jun 2011 Aug 2011 Residual stand assessments following restoration treatments; increment cores for retrospective growth analysis Measure increment cores, analyze growth data Aug 2011 Dec 2011 Analysis of growth rates from ring width measurements: geographic patterns, species differences Growth model development Jan 2012 May 2012 Fit models to growth data; construct stocking assessment model spreadsheet Collect post‐treatment data, process images Jun 2012 Aug 2012 Assess regeneration, health; process post‐
treatment hemispherical photos Data entry and analysis Aug 2012 Dec 2012 Multivariate analysis of regeneration patterns; add regeneration “ingrowth” component to stocking assessment model Stocking assessment model Dec 2012 Jan 2013 Develop and implement final models in spreadsheet, simulate different treatments Quarterly progress reports Jul 2010 Apr 2013 Submit progress reports to Tahoe Science Program coordinator by the 1st of July, October, January, and April, and summary of annual accomplishments in January Scientific manuscripts Jan 2013 May 2013 Prepare and submit manuscripts to peer‐
reviewed journals Final report, public meeting, and workshop May 2013 May 2013 Submit final report, host public meeting and workshop for managers 9
Proposal: Tahoe Research Supported by SNPLMA Round 10
IV. Literature cited Berrill, J‐P.; O’Hara, K.L. 2007. Patterns of leaf area and growth efficiency in young even‐aged and multiaged coast redwood stands. Can. J. For. Res. 37(3): 617‐626. Berrill, J‐P.; O’Hara, K.L. 2009. Simulating multiaged coast redwood stand development: Interactions between regeneration, structure, and productivity. West. J. Appl. For. 24(1): 24‐32. DeByle, N.V.; Winokur, R.P. 1985. Aspen: ecology and management in the western United States. Gen. Tech. Rep. RM‐119, U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. Fort Collins, CO. Long, J.N. 1985. A practical approach to density management. For. Chron. 61: 23‐27. Long, J.N.; Daniel, T.W. 1990. Assessment of growing stock in uneven‐aged stands. West. J. Appl. For. 5: 93–96. North, M.; Stine, P.; O'Hara, K.; Zielinski, W.; Stephens, S. 2009. An ecosystem management strategy for Sierran mixed‐conifer forests. Gen. Tech. Rep. PSW‐GTR‐220. U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. Albany, CA. Perala, D.A. 1990. Populus tremuloides. pp. 555‐569. In: (Burns, R.M. and B.H. Honkala, tech. coords.) Silvics of North America: 2, Hardwoods. Agriculture Handbook 654. U.S. Department of Agriculture, Forest Service. Washington D.C. Rehfeldt, G.E.; Ferguson, D.E.; Crookston, N.L. 2009. Aspen, climate, and sudden decline in western USA. For. Ecol. Manage. 258: 2353‐2364. Reineke, L.H. 1933. Perfecting a stand‐density index for even‐aged stands. J. Agric. Res. 46: 627–638. Shepperd, W.D. 2007. SDI‐Flex: a new technique of allocating growing stock for developing treatment prescriptions in uneven‐aged forest stands. pp. 171‐180. In: (Powers, R.F., tech. editor) Restoring fire‐
adapted ecosystems: proceedings of the 2005 national silviculture workshop. Gen. Tech. Rep. PSW‐GTR‐
203. U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. Albany, CA. Shepperd, W.D.; Rogers, P.C.; Burton, D.; Bartos, D. 2006. Ecology, biodiversity, management, and restoration of aspen in the Sierra Nevada. Gen. Tech. Rep. RMRS‐GTR‐178, U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. Fort Collins, CO. Smith, A.E.; Smith, F.W. 2005. Twenty‐year change in aspen dominance in pure aspen and mixed aspen/conifer stands on the Uncompahgre Plateau, Colorado, USA. For. Ecol. Manage. 213:338‐348. Woodall, C.W.; Miles, P.D.; Vissage, J.S. 2005. Determining maximum stand density index in mixed species stands for strategic‐scale stocking assessments. For. Ecol. Manage. 216: 367‐377.
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Proposal: Tahoe Research Supported by SNPLMA Round 10
V. Figures Figure 1: Diameter distribution data for aspen‐conifer stand at Christmas Valley, South Lake Tahoe. Shown above are pre‐treatment data from 1‐ha permanent plot. Shown below is same stand after simulated “virtual thinning” removing all conifers below 35 cm dbh (14 inches dbh) from the dataset. Removal of hundreds of smaller conifers gave only minor reduction in stand density index (SDI), suggesting that very little relief from crowding would be achieved under this restorative thinning prescription. Note: the 1‐ha plot included areas of stream channel and open rocky areas; SDI was much higher in heavily encroached parts of the plot. 11
Proposal: Tahoe Research Supported by SNPLMA Round 10
Figure 2: Conceptual diagram of aspen‐conifer stand SDI before and after thinning 50% of encroaching conifer stocking. Note: decline in aspen overstory and lack of aspen regeneration before thinning in crowded stand; as trees in the thinned stand grow larger, more shade is cast on aspen regeneration and it loses vigor, and eventually dies; later, larger aspen lose vigor as stand SDI enters the “zone of imminent mortality” (Long 1985) for aspen; conifer growth proceeds at higher SDI than aspen (Woodall et al. 2005). Figure 3: Conceptual diagram of conifer and aspen growth rates in different understory light environments. Growth expressed relative to maximum possible growth rate. Percent above canopy light approaches zero in full shade and 100% in full sun. Theoretical data based in part on DeByle and Winokur (1985). 12
Proposal: Tahoe Research Supported by SNPLMA Round 10
Figure 4: Schematic diagram of 1‐ha (100 x 100 m) permanent sample plot in riparian aspen stand with conifer encroachment. Pre‐treatment data include tree locations and size attributes, counts of regeneration in subplots, and hemispherical canopy photography. Anticipated post‐treatment data include records of trees cut/damaged, repeat hemispherical photos, and regeneration recruitment and growth. 13