Episodic Recruitment of Limber & Bristlecone Pines White Mountains, CA
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Episodic Recruitment of Limber & Bristlecone Pines White Mountains, CA Connie Millar, Bob Westfall, and Diane Delany USDA Forest Service Sierra Nevada Research Center Albany & Lee Vining, CA Special thanks to Mike Dettinger and Dan Cayan Abrupt Changes in Subalpine Forests 1. Colonization & Extirpation – Past 4000 yrs Limber Pine in Great Basin Ranges HT G OU R D Droughts Id’ed by other proxies: 600-800 ybp 1300-1400 ybp 1400-2100 ybp 2100-2700 ybp 2800-2900 ybp Correlate to pine retreat phases Mt Grant, Wassuk Range Millar, Westfall, King, in prep Abrupt Changes in Subalpine Forests 2. Shift in Treeline - Medieval Individual Spp Response – WhiteWing Mtn Deadwood Species, 3051 m NG I M R WA Whitebark Pine krumm W White Pine ↓ 250 m Lodgepole Pine ↓ 250 m Jeffrey Pine ↓ 500 m Mtn Hemlock ↓ 250 m Sugar Pine ↓ 600 m Medieval vs Present Ann ppt -24 mm Ann minT +3.2°C Ann maxT +2.3°C Millar, et al. 2006 Mixed Conifer Forest 800-1350 CE Abrupt Changes in Subalpine Forests 3. Habitat Conversion – 20th Century Colonization of Subalpine Meadows -PDO # Trees PDO/ PDSI Tmin Precip Millar, Westfall, et al. 2004 Abrupt Changes in Subalpine Forests 4. Change in Crown Form – 20th Century Development of Upright Stem “Flags” O -PD # Flags PDO/ PDSI Tmin Precip Millar, Westfall, et al. 2004 Abrupt Changes in Subalpine Forests 5. Habitat Conversion – 20th Century Colonization of Persistent Snowfields NG WARMI # Trees Tmin Millar, Westfall et al. 2004 Abrupt Changes in Subalpine Forests 6. Increase in Branch Growth – 20th Century MING R A W 1907 Vale & Vale. 1994 Branch Growth 1984 Tmin Millar, Westfall, et al. 2004 Abrupt Changes in Subalpine Forests 7. Increase in Forest Mortality – 20th Century & Dieback of Limber Pine Forests T H G ROU D NG I M R WA # Dead Trees Tmin/ Tmax Precip Millar et al., In press Climate Scenarios Context Treeline elevation incorporated into regional climate models; assume proportional rise with temperature Hayhoe et al. 2004 PNAS 101: 12422-12427 From: California Climate Change Center. 2006. Our Changing Climate; Assessing the Risks to California Recruitment of Subalpine Conifers - Are they colonizing beyond current range? - Where? When? Who? What conditions? Subalpine Species of Great Basin Ranges Limber Pine (P. flexilis) White Pine Range, NV Great Basin Bristlecone Pine (P. longaeva) Bristlecone Pine (BCP) & Limber Pine (LP), White Mtns, CA 1. Current treelines (m) Upper Lower Bristlecone pine 3400 3000 Limber pine 3250 3000 2. Dolomitic soils favor BCP & exclude LP LaMarche 1973 3. BCP treeline shifts with climate -- 150m above current treeline Research Questions: What is the nature of limber pine recruitment (<120 yrs) relative to: -- elevation (upper, mid, lower treeline) -- species (BCP vs LP ) -- soils & aspect -- vegetation structure upper mid lower FIELD METHODS -30m wide belt transects x 30 m plots -Tallied all live & dead trees & diameters -Aged all LP < 30 cm diameter Recruit Results low upper mid Plot Density LP by Age Class, 7 Sites - LP recruiting 100 m above current BCP upper treeline - 300 m above current LP treeline - Recruit pulse concentrated 1976-1991 - Dolomitic or non-dolomitic soils - Former forest (upper); meadow (mid); ravines (low) - Limber Pine recruit – all sites Climate Analyses - Methods Composite Climate Indices from Four Instrumental Stations Independence, CA; Mina, NV, temperature Independence, Tahoe, Yosemite NP, CA; Mina, CA, precipitation Period-of-Record: 1906 – 2005 Reanalysis Data From Kalnay et al., 1996; NOAA/ESRL; http://www.cdc.noaa.gov/ Climate and Recruit Simple Correlation Analysis Multiple Regression Analysis: Non-linear Least Squares Response-Surface Model (2nd Order) Recruitment-Climate Correlations Fit of overall model, R2 = 0.77 Temperature Annual Min Temp Annual MaxTemp Dec Max Temp Jan Max Temp May Min Temp June Min Temp June Max Temp Sept Min Temp r p 0.58 0.38 0.32 0.36 0.45 0.58 0.37 0.45 <0.001 <0.001 0.002 <0.001 <0.001 <0.001 <0.001 <0.001 Precipitation Annual Precip WY Precip Sept Precip Sept Precip -1yr …More recruit with warmer years, esp warmer springs & summers …More recruit with wetter autumns r p 0.08 NS 0.06 NS 0.15 0.17 0.28 <0.01 Interactions of Recruitment with Climate Ann min Temp x Recruit x (Ann Precip, July Precip, & Sept Precip 1-yr prior) July Precip log Recruit Annual Precip Blue curves = higher Tmin Red curves = lower Tmin 1-yr prior Sept Precip Life History Stages of Pines Cone Development (Masting) Seed Dissemination BCP 2-year development “Masting” 2-3 yrs Seed Germination LP Seedling Establishment Atmospheric Pressure – Reanalysis Data April to June 1-yr Prior June Recruit Yr Dec to Feb Prior Winter Aug to Oct Recruit Yr Aug-Oct 2 yrs Post Recruit Modeled LP recruitment 1910-2001 Linear & Spline Fits Annual Min Temp July to Oct Precip Limber Pine Recruit and the Atlantic Multidecadal Oscillation Limber Pine Recruit, all sites AMO – red line Summary 1. Treeline shift individualistic by species in White Mtns 2. LP recruit 300m above current LP and 100m above current BCP treelines 3. LP recruit below lower treeline in ravines 4. LP & BCP recruit into sage meadows at mid-elevation 5. Recruit episodic & complexly related to climate 6. LP recruit favored under warming temps, wet autumns 7. Overall elevation gain proportional to temp increase (1.95°C lapse; 2.0°C composite instrumental)
