pre- and post-fire treatment influences on forest dynamics

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

the end.

ryork@berkeley.edu

www.foreststeward.com