Final Report. Ecosystem response to aspen restoration (P091)

Transcription

1 Final Report SNPLMA Round 12 Science Ecosystem response to aspen restoration (P091) Investigators: John Pascal Berrill & Christa Dagley, Humboldt State University Agency Collaborators: Stephanie Coppeto, Kyle Jacobson & Shana Gross, USFS Mark Enders, NDOW Roland Shaw, NDOF Tamara Sasaki & Silver Hartman, CA State Parks Summary of Major Accomplishments We studied response of Lake Tahoe Basin aspen forest ecosystems to restoration thinning and subsequent burning of the piles of cut conifer wood within each forest. Outreach and dissemination over project period : Published peer reviewed journal article in Sept issue of Ecological Restoration entitled Predicting Treatment Longevity after Successive Conifer Removals in Sierra Nevada Aspen Restoration by J P Berrill, C.M. Dagley, and S.A. Coppeto We were invited speak at the Tahoe Science Conference held at UNR Reno, September 21 13, Our presentation was entitled Aspen Restoration in a Changing Climate We gave a presentation at the Aspen Ecology and Restoration Management Workshop, October 28 29, South Lake Tahoe, California. Our presentation was entitled Vegetation response to restoration thinning and slash pile burning in aspen Published peer reviewed journal article in Forest Research: Open Access in 2014, entitled Regeneration and recruitment correlate with stand density and composition in long unburned aspen stands undergoing succession to conifer in the Sierra Nevada, USA by J P. Berrill and C.M. Dagley. Summer field work and data analysis activities: Repeatedly re assessing vegetation and aspen trees surrounding burn piles at four aspen forest research sites around Lake Tahoe, specifically:

2 o Aspen and conifer seedling regeneration tallies and understory vegetation cover assessments in quadrats surrounding burned piles in the long term monitoring plot at each site. o Each aspen tree within 30ft of a burned pile was re inspected for health status, and inspected for signs of burning effects such as crown scorch. Re measuring aspen regeneration at multiple sites; unplanned extra work prompted by discovery that growth of young aspen was highly variable between years and possibly impacted by drought years. Collecting additional data at end of 2015 growing season gave one more year of data representing another drier than average year. These data have been analyzed and the resulting draft manuscript is being finalized. Re measuring understory vegetation and tree growth through repeat measures at multiple sites has been completed for the project period, and we continue to seek funding to continue with regular monitoring and re measurement of the permanent plots around Lake Tahoe. Aspen increment cores have been processed and measured for annual growth ring width, with climate treatment growth analysis in progress by HSU graduate student as part of their MS thesis research. A fifth pile burn site has been added through collaboration with CA State Parks, which will enhance sample sizes and strengthen the resultant analysis of data, but has delayed the final analysis as we await repeat assessment data for this extra site. Narrative The science project entitled Ecosystem response to aspen restoration led by Humboldt State University researchers Dr. John Pascal Berrill and Dr. Christa Dagley involved studying how the different parts of aspen forests respond to restoration treatments being implemented by land management agencies around the Lake Tahoe Basin. We studied response of the aspen ecosystem to removal of encroaching conifers and burning of cut conifer wood in piles. In particular, we studied response of aspen trees, the regeneration of new aspen and invading conifers, and changes in the herbaceous vegetation layer which is a hotspot of biodiversity in healthy aspen forests but gets shaded out by conifers and may be at risk of replacement by invasive plants. Cut conifers piled for burning were burned at four research sites around the Lake Tahoe Basin. At each site, piles were burned inside 2.5 acre long term monitoring plots (after studying conditions before burning). Each summer after pile burning we re assessed the vegetation and trees at Blackwood Creek (USFS) and Ward creek (USFS) on west shore, and at North Canyon (NDOW) and Secret Harbor Creek (USFS) on the eastern shore of Lake Tahoe. 2

3 The latest site at Emerald Bay was burned in winter 2015/16, assessed in summer 2016, and will be re assessed in summer 2017 by CA State Parks in collaboration with HSU. Photo Conifers had invaded this area at Secret Harbor Creek, outcompeted the aspen trees (dead, behind burned pile), and shaded out all the herbaceous vegetation that we expect to find in healthy aspen ecosystems. By repeatedly re assessing vegetation in and around burned piles, and vegetation throughout the entire 2.5 ac monitoring plot, we are learning what types of vegetation return and how long that takes. At the beginning of the study, we asked agency forest managers to have their contractors vary the size of piles of cut conifer wood throughout thinned stands to enable us to study the effects of pile size and other burning effects on aspen stands around Lake Tahoe. Each pile was measured for width and height, mapped for location, and its contents described by species and particle sizes. The analysis will test for the effects of these factors on ecosystem responses to the burning. Shown below is how understory vegetation cover (in terms of percent of available ground area not including rocks, tree stems, and coarse woody debris covered by understory vegetation) changed over time immediately adjacent to a burned pile, and within the footprint of burned pile, at Ward Creek (WA38). 3

4 Photo HSU students Ethan Hammett and David Perry counting tree regeneration and assessing herbaceous vegetation cover re occupying ground area exposed by burning of cut conifer wood in burn pile at WA 38 Ward Creek, USFS. Figure: Recovery of understory vegetation cover in and around burn pile. Percent cover of vegetation increases over time immediately adjacent to a burned pile, and within the footprint of burned pile, at Ward Creek (WA38). 4

5 Additional study piles are dry and ready for burning on USFS lands at Christmas Valley. But access to this remote, roadless area is difficult which to date has prevented prescribed fire crews from mobilizing enough resources to safely burn these piles. Data analysis of growth rates among young aspen suckers regenerating after thinning indicated that more data were needed, due to large variations in growth among young aspen (exacerbated by top breakage from snow, browsing, and other disturbances), so we collected growth data for another two growing seasons (2014 & 2015) and re analyzed the expanded dataset (Manuscript in prep.). One of our most interesting field observations were that young aspen growth could be negligible one year, then massive the next year, or vice versa, which suggested that we don t yet understand what is driving growth in the understory of aspen forests after conifer removal and pile burn treatments followed by years of drought. Preliminary analysis of aspen growth rings shows major fluctuations in growth between years (see graph below). This analysis includes increment core data for aspen tree diameter growth at multiple sites around the Lake Tahoe Basin. Figure: Aspen growth rings, detrended to show whether annual growth was above or belowaverage each year. Fluctuations were more pronounced in the understory. 5

6 Upcoming Plans Inevitable delays in pile burning and the addition of a new site meant that we postponed our final analysis of pile burn effects beyond the end of the project period. We will analyze all the collected pile burning data to develop pile building/burning recommendations for forest managers. We prioritized and completed the analysis and modeling of young aspen growth including the extra data collected in 2014 and 2015 to help inform managers of expected growth rates after different treatments. The dendrochronological study of aspen growth and climate is expected to be completed by the graduate student at HSU over the next 6 12 months. Another priority for research is to understand the rate of conifer encroachment (i.e., succession to conifer ), so that we can anticipate future invasions and be prepared to allocate sufficient resources to address the problem. We are currently examining growth rates of conifer trees and have initiated a new collaboration with USFS LTBMU to study conifer seedling regeneration growth rates around the Lake Tahoe Basin, to better understand treatment persistence, sometimes called treatment longevity ; the time taken for thinned stands to grow back to the same level of crowding as before treatment, i.e., how long the treatment really lasts. This will help managers anticipate need for, prioritize and schedule future conifer thinning treatments around the Lake Tahoe Basin. Photo conifer seedlings regenerating within recently thinned aspen stand at Cold Creek, South Lake Tahoe, CA. The process of encroachment or succession from aspen to conifer represents an ongoing challenge for forest managers in the LTBMU. 6

7 Priorities for Future Research Continued study of the impacts of pile burning of cut conifer wood inside aspen stands is a high priority. If possible, we will seek additional funding to assess pile burning responses at Christmas Valley if weather permits and the necessary resources are available to safely conduct the burning operation. In future, this will yield valuable independent data to validate and improve the geographic scope of models we will soon develop using pile burn data collected at our five sites where pile burning has been undertaken. We will also seek funding to continue with repeat assessments at all of the pile burn monitoring sites to get a longer time series of data on changes in trees and vegetation after thinning and pile burning restoration treatments. Re measurement of tree growth and regeneration throughout our thinned and unthinned monitoring plots, and assessment of tree health status at regular intervals is warranted. These nine long term permanent monitoring sites located around the Lake Tahoe Basin are designed to be assessed repeatedly into the future, generating valuable data for monitoring and analysis of response to successive treatments and change over time. These data will support adaptive management and allow us to test and refine the aspen stocking assessment model (SNPLMA Round 10 Science project) which allows managers to simulate different restoration thinning treatments in aspen stands and observe the modeled growth response over time. We have started a climate adaptation and genetic conservation project for aspen around the Lake Tahoe Basin. We are testing response of different aspen clones (genotypes) to assisted migration the deliberate movement of a genotype to a new location and climate. Our initial efforts will help us refine propagation and methods for establishment of more field tests. This is a repeat of a large experiment we have established in coast redwood, which is now starting to yield data and results on growth and moisture stress of different genotypes collected from different locations and climates that have undergone assisted migration. These field test sites also serve as lifeboat archives of genetic diversity in case some individual aspen stands or clones succumb to conifer succession or some other catastrophic disturbance. 7

8 Research Products derived from our SNPLMA Science Round 10 & 12 Projects Berrill, J P. ; Dagley, C.M.; Coppeto, S.A.; Gross, S.E. (in prep.). Curtailing Succession: Removing Conifers Enhances Understory Light and Growth of Young Aspen in Mixed Stands around Lake Tahoe, California and Nevada, USA.. Berrill, J P. ; Dagley, C.M.; Coppeto, S.A Predicting Treatment Longevity after Successive Conifer Removals in Sierra Nevada Aspen Restoration. Ecological Restoration 34(3): Berrill, J P.; Dagley, C.M Aspen restoration in a changing climate. Presentation at the Tahoe Science Conference. September 21 23, Reno, Nevada. Berrill, J P.; Dagley, C.M Regeneration and recruitment correlate with stand density and composition in long unburned aspen stands undergoing succession to conifer in the Sierra Nevada, USA. Forest Research: Open Access. Berrill, J P.; Dagley, C.M Vegetation response to restoration thinning and slash pile burning in aspen. Presentation at the Aspen Ecology and Restoration Management Workshop, South Lake Tahoe, California. October 28 29, Berrill, J P.; Dagley, C.M Stocking Guidelines for Aspen Restoration: Predicting Treatment Persistence after Successive Conifer Removals. SNPLMA Round 10 Science Project P051 Final Report. 18p. Dagley, C.M.; Berrill, J P.; Coppeto, S.; Jacobson, K Effects of slash pile burning after restoring conifer encroached aspen: interim pile building guidelines for aspen injury risk reduction. USDA Forest Service, Lake Tahoe Basin Management Unit Monitoring Report, December p. Berrill, J P.; Dagley, C.M Geographic patterns and stand variables influencing growth and vigor of Populus tremuloides in the Sierra Nevada (USA). ISRN Forestry Vol. 2012, ID: , 1 9. Berrill, J P.; Dagley, C.M Integrating research with monitoring objectives in forest restoration Keynote address at The North Coast Forest Restoration Cooperative Annual Meeting, Arcata, California. November 14, Berrill, J P.; Dagley, C.M Aspen growth and vigor around the Lake Tahoe Basin: effects of crowding and conifer antagonism. Presentation at the Tahoe Science Conference, Incline Village, Nevada. May 22 24, Berrill, J P.; Dagley, C.M Stocking guidelines for aspen restoration. Presentation at the Decision Support System Conference, Tahoe Science Consortium, Incline Village, Nevada. November 3 5, Dagley, C.M.; Berrill, J P A monitoring strategy for riparian forest restoration. Poster presentation at the 5th Biennial Lake Tahoe Basin Science Conference; Measuring Success of Ecosystem Restoration in Lake Tahoe Basin. Incline Village, NV. March Berrill, J P.; Dagley, C.M Preliminary stocking guidelines for aspen restoration in the LTBMU: Comparing thinning prescription diameter limits. Report prepared for Lake Tahoe Basin aspen forest managers. 23p. Berrill, J P.; Dagley, C.M.; Lyon, V Monitoring Aspen Restoration Treatments in the LTBMU: Methodology and Pre treatment Data Summary. Final Report: LTBMU Aspen Monitoring Project 20p. 8