Sierra Nevada Research Center, Davis, CA Climate Change and California Forests Malcolm North Sierra Nevada Research Center, Davis, CA

Greatest changes are in nighttime minima Courtesy of Hugh Safford October May June Greatest changes are in nighttime minima Tahoe City 1875 m

California future climates: Precipitation (mm) Temperature (C) 2000 2020 2040 2060 2080 2100 400 800 1600 1200 10 14 12 16 20 18 Year Temp-HAD Temp-PCM Precip-HAD Precip-PCM HAD = Hadley Center 2 model: Very warm-wet future PCM = Parallel Climate Model: Warm-dry future California future climates: alternate scenarios Source: Electrical Power Research Institute 2003 60% of climate models predict increased ppt for California in general 23% predict decrease 17% predict no change Courtesy of Hugh Safford

Courtesy of Hugh Safford Expansion of C4 grassland Warming benefits broad-leaved spp at expense of needle-leaved Loss of habitat as warming drives veg-types higher Loss in shrubland due to increase in fire (= grassland) or higher ppt (= trees) Courtesy of Hugh Safford

Vegetation community responses Historic conditions, and predictions for 2100 based on the Hadley and PCM models Lenihan et al. 2003. Ecol Appl 12. Courtesy of Hugh Safford

ABCO PIPO QUKE PSME ABMA PIAL Species-specific responses: species will respond based on their own physiological response and their interactions with other species. Future communities will not look like current communities. Chaparral and gray pine Courtesy of Hugh Safford

Centennial-Scale Climate Trends Holocene MULTI-PROXY ANALYSIS Early Holocene 10500 to 7500 YBP Warming Mid-Holocene 7500 to 5000 YBP Warmest, Dry Post Mid- Holocene Transition 5000 to 3500 YBP Cooling, Wetter Neoglacial 3500 to 2600 YBP Cool, Wet Post-Neoglacial Drought 2600 to 1600 YBP Intense Drought Post-Drought Transition and Medieval Warm Period 1600 to 650 YBP Dry but Summer Wet Little Ice Age 650 to 150 YBP Cool Wet, Cool Dry Recent < 150 YBP Warm, wet From Tausch et al. 2004 Courtesy Connie Millar

Giant Sequoia Glacial: Interglacial Dynamics East Lk, 2863m, < 10kyr Kings Cyn, 1000m, 20kyr Central Valley, 54m, 26-22kyr Mono Lk, 1950m, 10-11.5kyr Current range, W Sierra, 1370-2200m Davis 1999a, Davis 1999b, Power 1998, Cole 1983

Past Climate Analogs: Mid Holocene: (3,000 B.C.-1,500 B.C.) Wetter period: Increase in fir and cedar, relative to pine and a decrease in oak Middle Warming Period (approx. 900-1200 A.D.): Rise in tree line but no significant vegetation shifts Early 20th Century (1880’s-1950): Warming (recovery from little Ice Age) and wet period Reconstruction or Pre-European Period (1800-1840) Very unusual period: end of the little Ice Age with cool, dry conditions

Historic Climate Naturally Fluctuated Plants track climate at each • Cyclically • Nested Time Scales - Millennial - Centennial - Decadal - Interannual • Rapid and Abrupt Transitions Plants track climate at each scale, but respond with unexpected lags and threshold behaviors Millar 2003

Southern California forests: interactions of multiple stressors CADE PIPO PIJE ABCO Sensitivity to air pollution (N and ozone) Susceptibility to insect/disease PILA Sensitivity to increased temperatures Sensitivity to water stress Sensitivity to fire (adult) Southern California forests: interactions of multiple stressors Who wins? Pollution Insects/disease Temps H2O stress Fire Courtesy of Hugh Safford

Before fire suppression (1865 on this graph), tree death and recruitment is pulsed by fire and El Nino events North et al. 2005

Oaks were especially sensitive to temperature; Oak species fluctuated from rare to widespread in W Sierra Anderson & Smith, 1994

20th Century Responses: Meadow Invasion Central High Sierra Nevada Studies Found increased colonization in diverse meadows with variable environmental, vegetative, & land-use histories

Mortality in the forest is now primarily driven by drought and beetles Tree density, from fire suppression contributes to drought stress The populations of some insects, including many bark beetles, are kept in check by cold over-wintering temperatures * * Mortality significantly higher than expected in high density and lower in low density *

What may happen to mixed-conifer understory herbs and shrubs with increasing nitrogen from air pollution, an increase or decrease in snowpack, and with and without fire? Hurteau and North. In press. No Burn Burn Snowpack: Nitrogen: None Addition Reduction Addition Reduction Control +S - S Burn only + S - S Addition + N + S + N - S+ N + S+ N - S+ N Herb biomass increased in shrub dominated communities when snow pack was reduced. Nitrogen additions unexpectedly increased herbaceous species richness. Fire was a more important factor in post-treatment species richness and cover than either snow pack addition or reduction.

What are the effects of different fuel treatments on forest carbon storage and emissions under modeled wildfire scenarios? Hurteau and North. In review.

Amount of carbon accumulated after 100 years without wildfire Hurteau and North. In review.

Amount of carbon released during prescribed burns over 100 years Hurteau and North. In review.

Amount of carbon accumulated after 100 years with a wildfire in 2010

Amount of carbon accumulated after 100 years with a wildfire in 2050 Hurteau and North. In review.

Treatment 2100 Live Tree tC Rx Fire tC Released 2040 Trees/ha The amount of carbon (tC/ha) stored in live trees and the total amount released over the model’s 100 year run for all prescribed burns (Rx) and for the 2050 wildfire. The 2100 carbon budget is the amount of carbon stored in live trees in 2100 minus the total released in all prescribed fires and the 2050 wildfire for each of the eight treatments. The 2040 trees/ha is each treatment’s stand density in the nearest time step before the 2050 wildfire. Treatment 2100 Live Tree tC Rx Fire tC Released 2040 Trees/ha 2050 Wildfire tC Released Total Released (tC/ha) 2100 Carbon Budget Control 200.5 NA 541 40.9 159.6 Burn 303.2 55.9 322 19.5 75.4 227.8 Understory Thin 240.6 479 25.9 214.7 Understory Thin + Burn 161.6 46.5 244 15.1 61.6 100.0 Restoration 244.3 241 24.0 220.3 Restoration + Burn 232.3 41.9 89 12.6 54.5 177.8 1865 268.7 215 16.9 251.8 1865 + Burn 277.4 27.3* 166 9.4 36.7 240.7

Hurteau and North. In review.

Conclusions: Forest communities are unlikely to simply move up in elevation or latitude Tree species will respond differently, making future forest compositions difficult to predict Snow pack reduction may benefit herbs, but fire is still the strongest influence on the understory Bark beetles may become a real problem in high density forests, particularly as winter and night time minimum temperatures rise A preliminary FVS model suggest fuels treatments producing a low-density stand structure dominated by large fire-resistant pines may best protect carbon sinks in wildfire prone forests