Widespread increase of tree mortality rates in the western United States

Transcription

1 Widespread increase of tree mortality rates in the western United States VAN MANTGEM, PHILLIP J. (1), STEPHENSON, NATHAN L. (1), BYRNE, JOHN C. (2), DANIELS, LORI D. (3), FRANKLIN, JERRY F. (4), FULÉ, PETER Z. (5), HARMON, MARK E. (6), SMITH, JEREMY M. (7), TAYLOR, ALAN H. (8), VEBLEN, THOMAS T. (7) (1) USGS, Sequoia and Kings Canyon Field Station, Generals Highway, Three Rivers, CA 93271, (2) Rocky Mountain Research Station, 1221 South Main Street, Moscow, ID 83843, (3) Department of Geography, University of British Columbia, West Mall, Vancouver, British Columbia V6T IZ2, (4) College of Forest Resources, Box , University of Washington, Seattle, WA 98195, (5) School of Forestry and Ecological Restoration Institute, Northern Arizona University, Box 15018, Flagstaff AZ 86011, (6) Department of Forest Science, 210 Richardson Hall, Oregon State University, Corvallis, OR 97331, (7) Department of Geography, Campus Box 260, University of Colorado, Boulder, CO 80309, (8) Department of Geography, The Pennsylvania State University, University Park, PA U.S. Department of the Interior U.S. Geological Survey

2 The Western Mountain Initiative

3 Climatic change is here, NOW. IPCC / Mann, Bradley, & Hughes Basagic and Fountain 2005

4 What does this mean for forests in the western United States? Background mortality rates are increasing in old growth forests across the western United States. Increasing mortality rates appear to be related to external causes.

5 A growing body of evidence suggests that environment (particularly climate) affects forest demographic rates Large-scale die-off Background mortality Credit: USFS

6 A growing body of evidence suggests that environment (particularly climate) affects forest demographic rates Large-scale die-off Background mortality (1) subtle, slow, neglected (2)... but important! Credit: USFS

7 Tropical forests are changing RAINFOR plot network Increasing recruitment and mortality rates (Phillips et al. 2004) Increasing stand biomass (Körner et al. 2004) Changes in species composition (increasing liana densities) (Phillips et al. 2002, Laurence et al. 2004) Credit: O. Phillips Credit: Y. Malhi

8 Could similar changes be occurring in temperate forests?

9 Forest mortality across western North America

10 Criteria (76 plots) undisturbed old-growth forests fates of individual trees at least three complete censuses over 10 years 100 sampled trees per plot plot area 0.25 ha

11 Mortality rate (% yr -1 ) P<0.0001, n= Year

12 A widespread trend? regional differences elevational differences size differences taxonomic differences

13 1 2 5 Forest mortality across western North America

14 1 PNW Coastal Forests w. red cedar, w. hemlock, sitka spruce n = 10 plots, 6 ha, > 1,800 trees Trend: Increasing P = 0.03 Mortality rate (% yr -1 ) PNW Coastal Year

15 2 Cascades douglas fir, w. red cedar, w. hemlock n = 37 plots, 44 ha, > 17,000 trees Trend: Increasing P < Mortality rate (% yr -1 ) Cascades Year Credit: USFS

16 Swain Mt, CA red fir, white fir n = 2 plots, 1.5 ha, > 1000 trees Trend: Increasing P < Mortality rate (% yr -1 ) Swain Mountain, CA Year

17 Sierra Nevada white fir, incense cedar, sugar pine, etc. n = 18 plots, 20 ha, > trees Trend: Increasing P = Mortality rate (% yr -1 ) Sierra Nevada Year

18 5 Priest River, ID grand fir, w. hemlock, w. red cedar n = 1 plot, 1 ha, > 500 trees Trend: Increasing P = Priest River Mortality rate (% yr -1 ) Year Credit: D. Powell

19 Colorado Rocky Mountains lodgepole pine, subalpine fir, engel. spruce n = 7 plots, 10 ha, > 10,000 trees Trend: Increasing P < Mortality rate (% yr -1 ) Colorado Year

20 Mortality rate (% yr -1 ) 2.0 Fort Valley, AZ Fort Valley, AZ ponderosa pine n = 1 plot, 16 ha, > 3000 trees Trend: Increasing P < Year 7

21 1 Mortality rate (% yr -1 ) , P<0.03, n=10 2, P<0.0001, n=37 3, P<0.12, n= , P<0.0001, n=18 5, P<0.06, n=1 6, P<0.001, n=7 7, P<0.02, n= Year

22 1 5 A widespread trend? regional differences elevational differences 2 taxonomic differences size differences

23 Recruitment rates

24 Recruitment rates Mortality rate (% yr -1 ) 2.0 1, P<0.03, n=10 2, P<0.0001, n=37 3, P<0.12, n= , P<0.0001, n=18 5, P<0.06, n=1 6, P<0.001, n=7 7, P<0.02, n= Year Recruitment rate (% yr -1 ) , P=0.14, n=37 3, P=0.63, n=2 4, P=0.44, n=18 5, P=0.40, n= Year

25 Elevational differences? Credit: A. Caprio

26 Elevational differences? Forest turnover (% yr -1 ) y = x r 2 = 0.49, P < Elevation (m) Stephenson and van Mantgem (2005) Credit: A. Caprio

27 Elevational differences? Mortality rate (% yr -1 ) <1000 m, P<0.0001, n= m, P<0.0001, n=20 >2000 m, P<0.0001, n= Year Credit: A. Caprio

28 Tree size differences? Credit: NPS

29 Tree size differences? Mortality rate (% yr -1 ) <15 cm, P<0.0001, n= cm, P<0.0001, n=76 >40 cm, P<0.0001, n= Year Credit: NPS

30 Taxonomic groups Credit: NPS

31 Taxonomic groups 2.0 Abies, P<0.0001, n=62 Pinus, P<0.0001, n=37 Tsuga, P<0.0001, n=47 Other species, P=0.0002, n=64 Mortality rate (% yr -1 ) Year Credit: NPS

32 What does this mean for forests in the western United States? Background mortality rates are increasing in old growth forests across the western United States. Increasing mortality rates appear to be related to external causes.

33 Trends in stand density & basal area Increased mortality from self-thinning? Density (stems ha -1 ) Density, P<0.001 Basal Area, P< Basal Area (m 2 ha -1 ) Year

34 Density dependence?

35 Density dependence?

36 Density dependence? Probability of mortality Average radial growth (mm yr-1)

37 Fire regime Credit: E. Knapp

38 Fire regime Mortality rate (% yr -1 ) <25 yrs, P<0.0001, n= yrs, P<0.0001, n=31 >250 yrs, P<0.0001, n= Year Credit: E. Knapp

39 Climatic trends Average Temp.( o C) Relationship to mortality trend Ave. temperature: P = Deficit (mm) Climatic water deficit: P = Water Year

40 What does this mean for forests in the western United States? Background mortality rates are increasing in old growth forests across the western United States. Increasing mortality rates appear to be related to external causes.

41 Hemingway on long-term research There are some things which cannot be learned quickly, and time...must be paid heavily for their acquiring. -- Ernest Hemingway Hemingway was a jerk. -- Harold Robbins

42 Die-back event of piñon pine in the Southwest October 2002 May 2004 Photo credit: C. Allen

43 Die-back event of piñon pine in the Southwest Die-back occurred in the context of increasing temperatures coupled with a reduction in precipitation -- leading to stronger drought response than in the past! Annual precipitation (mm) Annual temperature ( o C) Breshears et al. 2005

44 Stressed trees are more susceptible to fire van Mantgem et al. 2003

45 What does this mean for forests in the western United States? Current NPS natural resources policy: -- When possible, restore and maintain naturallyfunctioning ecosystems. -- When this is not possible, maintain the closest approximation of the natural condition.

46 What does this mean for forests in the western United States? Current NPS natural resources policy: -- When possible, restore and maintain naturallyfunctioning ecosystems. -- When this is not possible, maintain the closest approximation of the natural condition.

47

48 Early vs. late mortality trends Mortality rate (% yr -1 ) Fraser Exp. Forest Fort Valley Exp. Forest P=0.29 P=0.18 P=0.025 P= Year Credit: E. Knapp

49 Changes in western North America Hydrologic changes Barnett et al., 2008

50 Glacier retreat Changes in the Sierra Nevada Repeat photography at ~100 years reveal that all ten of the glaciers surveyed have experienced a reduction in ice volume and surface extent Basagic and Fountain 2005

51 Changes in the Sierra Nevada Range shifts The Yosemite Grinnell Resurvey Up 2000 elevation Piñon mouse Ground Squirrels Alpine Chipmunk Pika (Patton and Chow 2005) 17 historically new bird species now at 10,000 many from lower elev. some breeding (Rush 2005)

52 Tree-ring isotope analysis

53 Mortality rates are increasing in the Sierra Nevada Thick black line, predicted trend Annual mortality rate Year Annual increase = 3% yr -1, P = van Mantgem & Stephenson 2007

54 Causation: The Importance of Annual Resolution Data Stress mortality (standing dead: insects, fungi, or no symptoms) Annual mortality rate Stress mortality β D = 0.005, s.e. = 0.001, P = Average mortality rate Water deficit, 3 yr. running average Water deficit (mm yr -1 ) Related to water deficit Year van Mantgem & Stephenson 2007