Impact of Climate Change on Western Forests
Mortality and Distribution Changes
Western Forests and Woodlands
Cobb, 2007, EESI
Western Forests and Woodlands
Woodlands=open stands of trees spaced far enough apart so that their canopies do not touch
Aerial view of Pinyon-Juniper Woodland in Central New Mexico Pinyon-Juniper Woodland in
Central New Mexico
Predicted Changes to Terrestrial Ecosystems as a result of Climate Change (IPCC 2007)
Warm temperatures, in the long-run, will strain water resources producing drought-induced stress and broad-scale die-offs of vegetation
Beginning trends are already being observed
Mortality is wide-spread throughout Western Forests
Observed & Predicted Changes to Terrestrial Ecosystems as a result of Climate Change (IPCC 2007)
Pinyon-Juniper Woodland
Juniper-Savanna Woodland
Alpine Tundra
Ponderosa Pine Forest
Spruce-fir
Mixed Conifer Forest
Merriam's Life Zones 1891
Modern Vegetation Zones
ElevationRange (feet)
AnnualPrecipitation
Arctic-Alpine
Alpine Tundra
11,500-12,700
35"-40"
Hudsonian Spruce-Fir or Subalpine Conifer Forest
9,500-11,500
30"-40"
Canadian Mixed Conifer Forest8,000-9500
25"-30"
Transition Ponderosa Pine Forest6000-8500
18"-26"
Upper Sonoran
Pinyon-Juniper Woodland, Semi-Arid Grasslands, Semi-Arid Scrub
3500-6500
10"-20"
Lower Sonoran
Mojave, Sonoran, or Chihuahuan Desert
100-3500
3"-12"
Reduction in available habitat for alpine and arctic species
Ecotone shifts
Cobb, 2007, EESI
Ecotone=zone of transition between two plant communities
In Northern New Mexico, the ecotone between pinyon-juniper woodland & Ponderosa pine forest is moving to higher elevation
Pinyon Mortality
Mortality extends across an area of 12,000 km2 in the
Southwest
Breshears et al. 2005, PNAS
NOTE:
P-J is now Juniper Savanna
Upward movement of biomes
Extent of Pinyon Mortality
Cobb, 2007, EESI
Mortality due to high temperatures combined with drought
Cobb, 2007, EESI
Causes of Pinyon Mortality
Three primary causes: Temperature Drought Insect Infestation
(bark beetle) In most trees, the
bark beetle was the ultimate cause of death
Trees weakened by global change-type drought are susceptible
Bark beetles populations are greater due to warmer winters
Cobb, 2007, EESI
Effect of temperature on pinyon pine growth
Summer temperatures reduce growth in pinyon pines. Indicating the influence of temperature as well as drought in pinyon mortality.
Newberry, 2009
Mechanisms of mortality
Tree mortality due to high temperatures can happen in three ways
1. Carbon starvation
2. Cavitation
3. Insect infestation (i.e., bark beetle) The first two are direct consequences of
environmental (abiotic) changes The third one is due to a biotic agent More recently, forest mortality due to high
temperatures alone (1& 2) are being observed throughout Western forests
Projected shifts in piñon distribution
Cole & Ironside, in prep.
So why do we care about tree mortality? Looking at effects the P-J
ecosystem…. Pinyon jays will lose their home Loss of an important food source for
humans and animals (pine nuts) Loss of understory plants
What else will happen? Increased soil erosion Increased soil temperature and
evaporation Increase fuel load for fires Forests become source not sink for
carbon dioxide
Forest-Climate Connection: Carbon Cycle
Cunningham/Cunningham 2002 text
Why the up and down pattern?
Annual fluctuations reflect differences in photosynthesis and respiration between summer and winter
Draft criteria for Sustainable Forests
1. Conservation of biological diversity2. Maintenance of production capacity of
forests3. Maintenance of soil and water resources4. Maintenance of forest contribution to global
carbon cycle5. Maintenance and enhancement of long-term
socioeconomic benefits to meet the needs of legal, institutional, and economic framework for forest conservation and management
Source: Data from USFS, 2002