Climate Change Effects on Tree Growth, Vegetation Distributions and Fire

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Agnes Eaton
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1 Climate Change Effects on Tree Growth, Vegetation Distributions and Fire Crystal Raymond David Peterson USFS Pacific Northwest Research Station Jeremy Littell Climate Impacts Group University of WA April 8, 2011 Bellingham, WA

2 Climate Change effects on Forest Vegetation tree regeneration, growth, productivity, and mortality species biogeography and forest composition disturbance rates and severity (wind, fire, insects, pathogens) Interactions between disturbances

3 Water Balance Deficit The difference between atmospheric demand for water and the water available to satisfy that demand. slide courtesy of: J. Littell

4 Water balance and forest effects As deficit increases: tree growth and regeneration become more limited in water limited systems tree vulnerability increases fuel moisture declines, so fire activity (spread, severity, area, frequency) likely increases in forested systems slide courtesy of: J. Littell

5 Climate and tree regeneration Regeneration increases when the effects of limiting factors are reduced: Snowpack Growing season length Soil moisture in summer

6 Climatic variability and tree growth warm cold

7 Climatic change and tree growth Subalpine forests Mid elevation forests Dry low elevation forests Wet low elevation forests growth increase growth depends on precipitation large growth decrease growth increase or decrease

8 Species Distributions: What can we learn from the past? Abundance and distribution of tree species change individualistically in response to climate change. Are warm periods of the past an analog for the future? 9000 ~ 5000 years ago 900 ~ 700 years ago But current rate of warming is unprecedented no analogue climates are likely

9 Modeled Vegetation Distributions Historical (Rogers and Neilson 2010) MC1 vegetation type Subalpine Forest Maritime Conifer Forest Temperate Conifer Forest Regional examples subalpine fir, lodgepole pine, mountain hemlock, whitebark pine Douglas-fir, western hemlock, sitka spruce, Pacific silver fir Ponderosa pine, Douglas-fir, Lodgepole pine, grand fir, western juniper

10 wet, warm (A2) wet, hot (A2) dry, hot (A2) (Rogers and Neilson 2009)

11 Projecting future area burned in the PNW Use the relationships between annual area burned and climatic variables in the 20 th century to project area burned with future climate scenarios. Climate variables: 1. precipitation 2. summer temperature 3. water balance deficit Scale: 1. PNW Region 2. subregions Littell et al. 2010

12 Projections of future area burned for the PNW Historical average: 425,000 acres 2020s: 0.8 million 2040s: 1.1 million 2080s: 2.0 million Probability of a yr >> 2 million acres: Historical: 5% 2020s: 5% (1 in 20) 2040s: 17% (~1 in 6) 2080s: 47% (~1 in 2) *Best model (tie): summer precip + summer temp OR summer water balance deficit Littell et al. 2010

13 Future area burned in ecosections 2020s 2040s 2080s 2020s 2040s 2080s Western Cascades: 8-fold increase Eastern Cascades: 2-fold increase Littell et al. 2010

14 Pre-settlement large fires in the western Cascades Tree age data from Douglas-fir points to large fire ~1308: large fire or series of fires swept western Washington and burned at least half of the Olympic Peninsula ~1701: fires burned about 1 million acres on the Olympic peninsula and 3 10 million in western Washington Henderson, J. A., D. H. Peter, R. D. Lesher, and D. C. Shaw Forested Plant Associations of the Olympic National Forest. USDA Forest Service, Pacific Northwest Region. R6-ECOL-TP p.

15 Slide: Don McKenzie, USFS Tripod Complex Fire 2006 Highest-severity patches had mountain pine beetle

16 Climate Change Adaptation Options for Forest Management in the Pacific Northwest

17 1. Reconsider thinning prescriptions to: reduce inter-tree competition increase tree growth and vigor reduce fire hazard

18 2. Increase resilience at large spatial scales by increasing landscape diversity.

19 3. Maintain biological diversity Identify populations and species sensitive to increased disturbance Experiment with species and genotypes Develop gene conservation programs Maintain a tree seed inventory with high quality seed for a range of species

20 3. Control exotic species Implement early detection and rapid response Monitor post-disturbance conditions under which exotics may be better competitors in a warmer climate

21 4. Plan for post-disturbance response Anticipate extreme events through scenario planning Increase capacity to restore forests after disturbance Incorporate responses to disturbances in planning documentation

22 Questions

23 Changes in vegetation distributions dry, hot wet, hot wet, warm Subalpine Forest Maritime Conifer Forest Temperate Shrubland absolute area subalpine fir, lodgepole pine, mountain hemlock, whitebark pine Douglas-fir, western hemlock, sitka spruce, Pacific silver fir big sagebrush- bluebunch wheat grass, big sagebrish-idaho fescue

24 Changes in vegetation distributions dry, hot wet, hot wet, warm Temperate Conifer Forest Temperate conifer woodland Temperate Grassland Subtropical mixed forest absolute area ponderosa pine, Douglas-fir, lodgepole pine, grand fir ponderosa pine western juniper woodland bluebunch wheat grass, Idaho fescue Douglas-fir Madrone Tanoak

Will climate changedisturbance. interactions perturb northern Rocky Mountain ecosystems past the point of no return?

Photo: Craig Allen, USGS Will climate changedisturbance interactions perturb northern Rocky Mountain ecosystems past the point of no return? Rachel Loehman Research Landscape Ecologist USGS Alaska Science