pre- and post-fire treatment influences on forest dynamics
TRANSCRIPT
Pre- and post-fire treatment
influences on forest dynamics
Rob York
Richard Harris
Joe McBride
An extremely
simple model…
…and a very simple model
Oliver and Larson 1996 Stand Dynamics
A very simple model….
…and a simple model
2 forest ecologists walk into a bar…
Pre-fire treatments
• Prescribed burns
• Thinning
• Regeneration harvests
• Planting
• Vegetation control
“Exogenous” Processes
• Climate change
• Exotic species invasions
Structure
Composition
“Endogenous” Processes
• Self thinning
• Site changes in microclimate
Fire Behavior
Soils
Snags
Resource
availability
Exotic species
Regeneration
Release
Factors of forest dynamicsPost-fire (pre-fire) treatments
• Salvage, planting, etc.
Guessing snag dynamics
Snag
density
Simulating snag dynamics
0 100 200
Simulation year
Vanderwel et al. 2009 CJFR
Observing snag dynamics
1 burn = net loss of snags2nd burn = little change in
net snag density
From Bagne et al. 2008, For. Ecol. Manage.
(Sierra National Forest)
(prescribed surface fires)
Snag dynamics: concluding points
• Snags (and other
structures) come and go
in pulses that coincide
with disturbances
• Fires can cause net
increases or decreases
in snag density
• Large snags come from
large trees
Simulations are necessary, but not sufficient
Regeneration dynamics following high-
severity fireTraditional expectation:
• Mainly “Initial Floristics” some “Relay Floristics”
• Progression toward tree-dominance
?
Response in Klamath-Siskiyous• 8 high-severity fires, structure measured 9-19 years post-fire
• Conifer density ranged over three orders of magnitude: 80-80,000 tph
• All colonization patterns found: immediate response, delayed pulse, constant, chronically absent
• Heavy shrub cover, but in general, enough conifers to foresee a stand developing (albeit slowly)
917 seedlings / ha
Model compliance?
•Initial Floristics dominant
• Trees predicted to dominate,
but with tons of “noise”
Shatford et al. 2007 J. of Forestry
Response in Lake Tahoe Basin
Russell and McBride 1998 Madrono
• Four stand-replacing fires: 1890’s, 1937, 1978, 1987
• Time until “recruitment” (seedlings reaching breast height)
• 1890’s fire: 30 years; 13% shrub cover after 100 years
• 1937 fire: 17 years; 88% shrub cover after 60 years
• 1978: 20 years and counting; 76% shrub cover
• 1987: 11 years and counting; 87% shrub cover
Model compliance?
•Initial floristics dominant
• Both tree and shrub
dominance outcomes
~
Response in Peninsular Range• 4 years after high-severity fire (Cedar Fire), “extirpation of mixed conifer forest”
• Predict a shift in vegetation type to shrub/hardwood dominance
• Lack of seed source is at least one important factor
Model compliance?
•Initial floristics?
• Stand-destroying fire?
Goforth and Minnich 2008
Regeneration dynamics following high-
severity fire - ConclusionsHigh variability is the rule, but some patterns:
• Initial Floristics
• Shrub dominance phase is common, length of persistence is not (decades to centuries)
• Seed source is very important, but hard to predict long-range dispersal ( > 200m)
?
Regeneration dynamics following
low-severity pre-fire treatments• Three recent studies looking at regen response to thinning and
Rx burning
• Common result:
• No treatment = increase in white fir and incense cedar
• Substrate + canopy disturbance = new cohort
• Seed production and weather following
treatment is critical (it’s mostly luck…)
• Need longer-term monitoring of recruitment rates
Moghaddas et al. 2008; Zald et al. 2008; vanMantgem et al. 2006
Image: York
Pictorial case studies of post-fire treatment
interactions with vegetation dynamics
• Star and Gap Fires, 2001
• Fountain Fire, 1992
Star Fire – Salvage, plant, herbicide
Forest dynamics = f(salvage retention level, species planted, type of herbicide)
• Objective = quickly get conifer tree dominance, rapid growth, big trees
Star Fire – Salvage, plant, leave
Stand dynamics = f(seed bank in soil, propagule pressure, species planted, planting conditions)
• Objective = shrub habitat, “slow boat” to conifer dominance
Forest dynamics = f(proximity to seed source, climate in first decade)
• Objective = Snag habitat (short term pulse), extended period of shrub habitat
Star fire – no treatment
Gap fire- salvage, plant, herbicide
Gap fire – salvage, plant, leave
Gap fire – plant, leave
Gap fire – no treatment
Fountain fire – Salvage/planted v.
no treatment
Guess which is which
2 outcome bookends after 40 years:
No post-fire treatments Post-fire treatments
Pre-fire treatments
• Prescribed burns
• Thinning
• Regeneration harvests
• Planting
• Vegetation control
“Exogenous” Processes
• Climate change
• Exotic species invasions
“Endogenous” Processes
• Self thinning
• Competition
• Site changes in microclimate
Fire Behavior
CONCLUSION:
MASSIVE variability from
local conditions
LARGE uncertainties
Soils
Snags
Resource
availability
Exotic species
Regeneration
Release
Structure
Composition
Dealing with uncertainty
• Locally informed decisions
• Active Adaptive Management
Walters and Holling 1978
Lawler et al. 2010 Frontiers in Ecol. Env.
Plan projects with existing objectives
Inference
Adjust management
Management experiment
(learning by doing)
Uncertainty, multiple
hypotheses
Monitoring
