ESRM 450Wildlife Ecology and Conservation

ECOLOGICAL DISTURBANCE

Concepts, Approaches, and Applications

Parameters of Disturbance Regimes

From White (n.d.)

The Disease Spiral

From Manion (1991)

Yellowstone Fires of 1988

A shift in biological and management perspectives

What are the effects of fire size and pattern?

Fire disturbance is an inherent process in forest ecosystems

An example from PNW forests

From Agee (1993)

Low severity fire regimes

High severity fire regimes

Landscapes with moderate severity fire regimes often have complex spatial patterns

Southern Cascade Range, Oregon

Wind disturbance

Wind disturbance in the Pacific Northwest

Cyclonic winds are associated with tropical storms intensified by the jetstream. Significant events are recorded every ~20 years.

1921 windstorm on the Olympic Peninsula

Wind and forest harvest

Wind and forest harvest

From Kimmins (1999)

Insects

Low vigor trees are at greatest risk

Tree Mortality

Mountain Pine Beetle

Shaded areas show locations where trees were killed. Intensity of damage is variable and not all trees in shaded areas are dead. www.fs.fed.us/r6/nr/fid/data.shtml

= Host Type

1980 - 2004

Pacific Northwest Region, Natural Resources,

Forest Health Protection

Pinus spp.

Mountain Pine Beetle outbreaks (1959-2002)

Courtesy of Mike Bradley, Canfor Corporation

Dying Pinus edulis Jemez Mts., October 2002

Jemez Mts., May 2004

Interactions among disturbance agents

Cascade Range, Oregon

From Gara et al. (1985)

Fire, mountain pine beetles, and fungi

Fire effects on forest landscapes

From Swanson (1981)

Causes and rates of tree mortality vary with stand age (Douglas-fir, PNW)

Regen. Full veg. Closed Mature Old cover canopy forest forest

Stand age (yr) 0 – 5 5 – 20 20 – 100 100 – 200 > 200

Mortality rate Very high High High to mod. Mod. to low Mod. to low

Mortality Phys. stress, Competition Competition Pathogens Windcauses herbivory phys. stress pathogens wind pathogens

pathogens pathogens wind competition physiol. disorders

herbivory

From Swanson (1981)

Fire regimes• What is a “fire regime”?

– Frequency and severity– Seasonality, vegetation, controls

(climate, fuels, ignition sources)

• Fire frequency– Point fire return interval– Composite fire interval– Fire cycle/rotation

• Fire severity (low, mixed, high) x

y

0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.2

0.4

0.6

0.8

1.0

Baker & Kipfmueller (2001)

Fire regime properties

Properties Drivers

Temporal distribution Climate/weather Vegetation/fuels Topography/landform

Frequency or fire interval (mean and variance)

Duration

Seasonality

Ignition availability and flammability

Drought or days w/o rain

Drought or days w/o rain

Vegetation recovery / fuel buildup

Consumption stages

Greenup and leaf fall

Interaction of fire size with fuel availability

Interaction of topography with fire spread

Spatial distribution

Extent (mean and variance)

Pattern (patch size, aggregation, contagion)

Intensity and severity (mean and variance)

Fire spread driven by weather

From orographic atmospheric instability to apparent chance

Micro-climate/weather from topography and fuels

Vegetation/fuels connectivity

Vegetation/fuels connectivity

Vegetation/fuel density and configuration

Topographic barriers to fire spread

Topographic barriers to fire spread

Slope/aspect interact with weather

Low-severity fire in ponderosa pine and other dry forest ecosystems

Pinus ponderosa

Pinus contorta

High severity, but lots of geographic variation.

High-severity fire regimes are associated with more serotinous cones.

Serotinous cones

Non-serotinous cones

N. Snell – California Academy of Sciences

At treeline, rare patchy fires

Whitebark pine (Rocky Mountains)

Sagebrush fires can be mixed to high severity

Clint Wright

Chaparral fires are associated with synoptic weather (Santa Ana winds) and human ignitions.

Climatic change and controls on fire

FuelsFuels

ClimateClimate

TopographyTopography

Temperature increasesTemperature increases

ENSO?

• Fire frequency• Fire severity• Fire area burned• Air quality

Climate-limited or fuel-limited?

• Different fuel types respond differently to climate.

• Two mechanisms: drying of fuels and production of fuels.

• Drying happens seasonally, whereas production affects fire on scales from years to decades.

Managing fire regimes in the context of climatic change and other stresses

Examples from forests of Western North America

Mixed conifer(Sierra Nevada, southern California)

Ozone and particulate pollution Fire exclusion high stand densities Extended warm period insects Ponderosa pine, Jeffrey pine, white fir die Fuels accumulate severe fires Exotic plants increase where fires do occur.

Global warming

Bark beetles and defoliators

Ponderosa and Jeffrey pine

mortality

Fuel accumulation

Large severe fires

Changes in species composition (including exotics)

Sierra Nevada mixed conifer

Fire exclusion

High stand densities

OzoneHigher temperatures &

more severe and extended droughts

Lodgepole pine

Extended warm period, insects, pines die, fuels accumulate, sets up for large fires.

Global warming

Higher temperatures & more severe and extended droughts

Bark beetles and defoliators

Lodgepole pine mortality

Fuel accumulation

Large severe fires

Changes in species composition (including exotics)

Interior lodgepole pine

Stand-replacing fire regime

Extensive mature cohorts (70-80 yrs)

Salvage logging

•Multiple disturbances

•Fire and insects are modifying different regions (so far).

•Direct effects of global warming = melting of permafrost.

Stand-replacing fire

Stand-replacing beetles

Stand replacing fire + global warming

Stand replacing insect kill + global warming

Ecosystem changeEcosystem change

White spruce

Paper birch

Black spruce

Southcentral forests (non-maritime)/Interior forests on permafrost-free soils

Interior forests on permafrost soils

Ice-rich lowlands (deciduous forests)

Upland coniferous forests

Higher temperatures

Beetles

Large fires

Species conversion

More deciduous forest

Thermokarst ponds

Wetlands, fens, and bogs

Coniferous and deciduous forest

?

More stand-replacing fires

Fuel accumulation

Permafrost degradation

Global warming

Managing fire and fuels is mostly a sociocultural challenge

Federal fire suppression cost in 2002 = $1.6 billion (~$500 per ha burned)

Current conditions Target (historical) conditions

Objective: Reduce crown fire hazard

Guiding scientific question

How can fuel treatments be designed to modify fire hazard and potential fire behavior?

Burning

Thinning

Scientific principles of fuel treatment:Modifying forest structure

• Raise canopy base height

• Reduce canopy bulk density

• Reduce canopy continuity

AND reduce surface fuels

Principle #1 – Canopy base height

Dense stand with understory

-------- Canopy base height < 2 m

Treated stand after thinning from below

-------- Canopy base height > 6 m

Principle #2 – Canopy bulk density

Dense stand with understory

Canopy BD > 0.30 kg m-3

Treated stand after thinning from below

Canopy BD < 0.10 kg m-3

Principle #3 – Canopy continuity

Dense stand with understory

Treated stand after thinning from below

Surface fuels must be treated following removal of trees

Analysis of stand development assists treatment scheduling

2003 2010 2015 2020

No treatment

Thinning

Effective fuel treatment programs must consider large landscapes

Many constraints to effective fuel treatments

Need lots of tree removal

Lack of markets for small wood

EIS, EA and other review

Litigation

Risk of escaped fire

Scheduling (~20-year cycle)

Toward science-based firemanagement and policy

Develop guidelines that quantify the effects of fuel treatments on fire behavior

Integrate scientific information and human values(ecological + cultural restoration)

Develop a rational economic approach

Educate the public on living with fire

Principles of fire-resilient forestsObjective Effect Advantage Concerns

Reduce surface fuels

Reduces potential flame length

Fire control easier, less torching

Low surface disturbance

Increase canopy base height

Requires longer flame length to begin torching

Less torching Opens understory, may allow surface wind to increase

Decrease crown density

Makes independent crown fire less probable

Reduces crown fire potential

Surface wind may increase, surface fuels may be drier

Retain larger trees

Thicker bark, taller crowns, higher canopy base height

Increases survivability of trees

Removing smaller trees is economically less profitable

Adapted from Agee (2002)

How do forest harvest practices compare to natural disturbance processes?

Standard thinning

How do forest harvest practices compare to natural disturbance processes?

Variable density thinning

How do forest harvest practices compare to natural disturbance processes?

Clearcut

How do forest harvest practices compare to natural disturbance processes?

Multiple clearcuts