Past, present, and future in the forests of the Sierra Nevada: variability in forest response to environmental change, and management strategies to promote ecosystem resilience Hugh Safford USDA Forest Service, Pacific Southwest Region University of California-Davis, Dept. of Environmental Science and Policy [email protected]707-562-8934
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Past, present, and future in the forests of the Sierra ... · –Climate change, wildfire, ... –
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Past, present, and future in the forests of the Sierra Nevada: variability in forest response to environmental change, and management strategies to promote ecosystem resilience
Hugh Safford USDA Forest Service, Pacific Southwest Region
University of California-Davis, Dept. of Environmental Science and Policy
Center of the problem is in lower elevation forests, but whitebark pine infection is
increasing
Jeffrey pine killed by fire in S. California, 6 yrs post-fire with no
regeneration: fire X temperature X drought X pine beetles
Loss of piñon pine near Topaz Lake, western Great Basin: invasive species
X fire X pine beetles
Interactions among stressors are creating threshold conditions on the fringes of the Sierra Nevada
Frequent anthropogenic fire reducing shrubland to grassland: fire X exotic
species X drought
Massive tree mortality in San Bernardino Mtns, early 2000s:
drought X pine beetles X air pollution
C L
I M
A T
E
Moser et al. 2009
The future: modeling projects continued warming and continued transition from snow to rain…
…as well as continued increases in fire activity…
State of California 2009
NRC 2011
Winter minimum temperature °C
High Suitability
Low Suitability
Current LTB
Future LTB
Modeling suggests that climatic warming will bring the Lake Tahoe Basin right into the center of
cheatgrass’ climatic niche by mid-century
…and range expansion of invasive species, pests, and diseases
Velo
z et al. 20
09
Cheatgrass • White pine blister
rust is spreading south
• Sudden oak death is spreading north (and predicted to move east)
• Golden spotted oak borer is spreading north…
• ?
Lenihan et al. 2008
0
5
10
15
20
25
30
35
Current
(1961-
1990)
GFDL-B1
(2071-
2100)
PCM-A2
(2071-
2100)
GFDL-A2
(2071-
2100)
% o
f la
nd
sc
ap
e
subalpine forest and
alpine
evergreen conifer forest
mixed evergreen forest
mixed evergreen
woodland
shrubland
grassland
arid lands
Much drier & much warmer
Same ppt. & warmer
Slightly drier & warmer
Together, these trends will likely lead to major changes in Sierra Nevada ecosystems
Increase in hardwood types, loss in conifer forest;
increase in grassland; major loss of subalpine forest
Summary II
• To this point, low and high elevation forests have experienced similar changes in temperatures and overall meteoric water input
• But rate and nature of forest change have been very different
- Much more relative change at low elevations (forest composition, density, fire frequency, fire severity, etc.)
- High elevation forests much closer to HRV
• Drivers of change - Fire suppression - Climate change (especially snow to rain ratios) - Invasive species, insects, disease
• The effects of all of these are expanding uphill over time…
Are there simple things we can do to increase forest resilience to these interacting
stressors?
General strategies
Reduce forest densities to reduce moisture stress and moderate threat of severe fire
• Strategic use of mechanical thinning and rx fire necessary in areas where human management has greatly changed forest structure (i.e., low elevation forest)…
• but very little of the ground is actually accessible and treatable, so major expansion of “wildland fire use” (WFU; use of wildfires under moderate burning conditions for resource benefit) is likely the only way to treat large areas
• WFU can most easily be implemented in and upwind of large wilderness areas, in higher elevation forests
Use the physical habitat template as a guide to the types and intensities of treatment
• Warm slopes should be thinned heavier than cool slopes (but not overthinned! Understory veg and seedlings need moderating effect of tree canopy)
• Maintain riparian corridors (but don’t ignore the fuels there!)
• Canyons and lower north-facing slopes will likely maintain cooler conditions and should be managed as microclimatic refugia
• Where fire activity is likely, don’t expect upper S and SW facing, windward slopes to sustain forest
General strategies
Expand genetic heterogeneity in the future forest, both within and among species
• Where planting is undertaken, select from a wider genetic pool (e.g., seeds from warmer, drier seed zones)
• Design planting so as to incorporate trials of seedlings of different provenance
• Be careful with assisted migration! Conduct full and open assessment of the likely consequences. High elevation forest trees are probably among the species least likely to cause problems though…
• Remember that the key life stage for successful recruitment is the juvenile stage! Models based on long-lived adult trees may not be as useful as we think
General strategies
Adopt an experimental approach to implementing management actions to respond to global change
• Let’s face it: we don’t know what is going to happen… • …but we do have some reasonable hypotheses • These should be turned into implementable
management actions, developed collaboratively, and tested on reasonably large landscapes
• Example: expand some forest thinning practices from low elevation forests to lower portions of red fir forest
• If we don’t monitor, we learn nothing, and the effort is wasted
• We will make mistakes, but human learning is experiential and mostly fed by unexpected outcomes
General strategies
Don’t give up on restoration!
• “Restoration” = static replication of snapshot photos of 1653: focus on restoring ecosystem processes that are necessary for sustainability with (ultimately) a minimum of human input
• Historical reference conditions may not be appropriate endpoints, but they will often be useful waypoints
• History is only source of information for processes and trends that happen over time-scales longer than the human life; focus should be on understanding mechanics of change
• Focus on restoration of ecological function: single-species and preservation-based strategies have higher probability of failure
• Humans are part of ecosystems and their numbers are increasing: they can’t be removed from the equation