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

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

3. 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

4. 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

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

6. 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

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

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

9. 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 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 ( )
Very unusual period: end of the little Ice Age with cool, dry conditions

10. 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

11. 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

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

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

14. 20th Century Responses: Meadow Invasion
Central High Sierra Nevada Studies
Found increased colonization in diverse meadows with variable environmental, vegetative, & land-use histories

15. 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 *

16. 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.

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

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

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

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

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

22. 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
Burn
277.4
27.3*
166
9.4
36.7
240.7

23. Hurteau and North. In review.

24. 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