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 Eleva tion Rang e (feet) Annu al Preci pitati on Arctic- Alpine Alpine Tundra 11, , "- 40" Hudsonian Spruce-Fir or Subalpine Conifer Forest 9, , "- 40" CanadianMixed Conifer Forest 8, "- 30" TransitionPonderosa Pine Forest "- 26" Upper Sonoran Pinyon-Juniper WoodlandPinyon-Juniper Woodland, Semi-Arid Grasslands, Semi-Arid Scrub Semi-Arid Grasslands "- 20" Lower Sonoran Mojave, Sonoran, or Chihuahuan Desert "- 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 km 2 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 diversity 2. Maintenance of production capacity of forests 3. Maintenance of soil and water resources 4. Maintenance of forest contribution to global carbon cycle 5. 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