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