Agenda, March 25

• Weekly meteorologist

• Tests handed back- reviewed

• Fire Ecology lecture

• Lunch/ break

• Fire effects lab at ACMF

Ecology of Fire- Plants

Sequoiadendron giganteum; fire scar in California’s Yosemite National Park

Outline of Lecture

• Fire ecology in context

• Organizational hierarchies

• Communities adapted to fire regimes

• Plant responses to fire

• Woody plant mortality

Fire Ecology in the Context of Scientific Disciplines

• Ecology: The study of the interrelationships between organisms, and between organisms and their environment.

• Disturbance Ecology: The study of relatively discrete events in time/space that alter organisms, communities, or ecosystems and/or change resource availability or the physical environment (e.g. floods, volcanoes, mining, grazing…)

• Of the above disturbance types, what is fire most similar to?

• How does fire ecology differ from other types of disturbance ecology?

What Distinguishes Fire Ecology?

Ice Flow:•Impacts living organisms•Impacts physical environment•Any impact on future occurrence of ice flows?

Fire:•Impacts living organisms•Impacts physical environment•Is INFLUENCED and DICTATED by the biota, by living organisms•Its impact influences the nature of subsequent fires feedback loop

VS.

What Does Fire Ecology Entail?

The main factors that are addressed in fire ecology:

• Fire dependence or fire-related traits of plants and animals

• Fire history

• Fire regimes

• Fire effects on soils, water, plant species, animal species, from individuals to populations, communities, and ecosystems.

From Individuals to Ecosystems

• As fire influences biota and biota influences fire behavior and effects on both biotic and abiotic resources, the ecology of fire can be described for these feedbacks at multiple organizational levels

• How fire ecology is interpreted depends on the organizational level of interest– Ecosystems (fire with plants, fauna, water, soils,

energy and nutrient cycling)– Communities (fire with plants, fauna and their

interactions)– Populations (fire with a given plant, fauna species)– Individuals (fire with individual)

Organizational Hierarchies within Ecology and Fire Ecology

• Ecosystem: Characterized by fire disturbance regimes– Intensity, frequency, extent,

season, severity, synergism

• Community: Fire regimes, & interspecies/ interpopulation competition for resources– As above, and fire-related

population traits which dictate one species’ survival over another’s

– Example: Understory oaks vs. overstory pines

Oak/palmetto understory, slash pine overstory

Organizational Hierarchies, cont.

• Population: Fire regimes, interspecies and intraspecies competition for resources, – Age & size distribution, density, and health of population, and

implications for what fire-related traits are in effect– Example: a group of high-density monotypic Rky. Mt. lodgepole pine are

high-severity fire-adapted population when mature

Age distribution of Douglas-fir Density of Rky Mt. lodgepole pine stand

Organizational Hierarchies, cont.• Individual (autecology): Fire regimes, inter/intra

competition, and individual degree of fire adaptation– Age, size, and stature of individual, and its associated

fire-related traits– Example: Grass-stage vs. sapling longleaf pine

Why “fire-related trait” and not “adaptation”?

• “Adaptation” implies that fire was the primary selective force resulting in a particular trait; often this is not easily tested or proven– Example 1: Self-pruning in many Pinus species

increases overall photosynthetic efficiency, also protects the canopy from crown scorch.

– Example 2: Giant sequoia seeds need bare mineral soil– is this an adaptation to fire or flooding?

– Example 3: Eucalyptus species are highly volatile– is this selected for by herbivory or fire?

Why “fire-related trait” and not “adaptation”, cont.

• All fires are not created equal. One fire may select for a given species with a given trait, while another does the opposite. – Example 1: High-intensity fires with long flame lengths can

scorch and kill adult ponderosa pines, while low-intensity fires reduce competition and increase nutrient availability (fire type and intensity)

– Example 2: Soil-stored hard-coated seeds of manzanita species (Arctostaphylos) break dormancy only if fires are hot enough and if seeds are still viable (fire frequency, type, and residence time)

– Example 3: Annual winter burns in SE US pine flatwoods benefit sprouting species with high carbohydrate reserves, such as saw palmetto (fire seasonality)

“Fire dependent” communities?• Fire’s influence is most commonly observed and interpreted

at the community level

• Particular communities can be said to be “fire-adapted” or “fire dependent”, if the absence of fire significantly changes community structure, function, and composition, and if the presence of fire perpetuates the survival and sustenance of multiple populations therein.

• In many cases, changes in one attribute of a fire regime can alter community composition, structure, and/or function.

• Communities which are considered fire-dependent are typically dependant on particular fire regimes.

Communities (forests, shrublands, grasslands) are affected by fire differently; each community is influenced by a particular fire regime

(fire type, frequency, seasonality, area, severity, intensity).

Frequent fire No fire

Longleaf pine forestsSoutheastern USFire < 5 yearsLow intensity, understory, spring or summer

Boreal forestsN. LatitudesFire > 100 yearsHigh intensity, crown, Summer, large areas

Tropical rainforest23o N and SFire > 1000 years, smallMixed severity when it happens (high moistures)

Florida’s Fire-Dependent Ecosystems

• The Florida Natural Areas Inventory lists 23 terrestrial, 19 wetland communities in Florida: 16 of these are considered FIRE DEPENDENT– will change significantly if fire regime is altered

• Most important aspect of fire regime: frequency, which often determines type, severity, and intensity of fires

• Examples:

– Sandhill FRI 1-7 yrs

– Dry & Wet Prairie FRI 1-7 yrs

– Mesic Flatwoods FRI 3-7 yrs in N. FL, 1-7 in SFL

– Scrubby Flatwoods FRI 8-25 yrs

– Swamp FRI 8-100+ yrs

– Scrub FRI 26-100+ yrs

Florida Ecosystems• Fire Maintained

– Flatwoods– High pine / Sandhill– Scrub– Sawgrass prairies– Cypress swamps– Other grasslands– Freshwater marshes– Salt marshes

Florida Ecosystems

• Fire Influenced

– Upland hardwoods– Swamp forests– Dunes– Subtropical forests– Mangroves

If Fire Regimes are Altered, Communities Change via 4 Major

Mechanisms

1. Death of older individuals of a given species, partnered with lack of replacement by offspring, and subsequent replacement by other species– Example: Giant sequoia (Sequoiadendron

giganteum) of Sierra Nevada Mts.

Giant Sequoia Fire Ecology

Cones are serotinous & seeds require bare mineral soil & plenty of sunlight to germinate & grow

Sequoias are fire, insect, and decay resistant, but shallow rooting makes them vulnerable to windthrow

• Without fire, sequoia won’t reproduce: other conifers occupy the understory and can eventually replace sequoias (changing community ecology)• What aspect(s) of the fire regime has been impacted by fire suppression in giant sequoia groves?Ponderosa pine under sequoia

Mechanisms of change if community fire regimes are altered

1. Death of older individuals of a given species, partnered with lack of replacement by offspring, and subsequent replacement by other species– Example: Giant sequoia of Sierra Nevada Mts.

requires mineral soil and has serotinous cones

2. Active replacement by other species that would normally be killed in fires- they invade slowly but effectively outcompete existing vegetation– Example: Pine encroachment into grassy meadows

where fires have been suppressed

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3.The fire environment changes: microclimate, substrate availability, growing space, site quality

4.Fuel properties change after introduction of new plants, changing fire behavior– Moisture content of plant tissue– Chemical composition of plant tissue– Fuel loading– Fuel continuity– Fuel packing ratio– Seasonal availability of fuels

Mechanisms of change if community fire regimes are altered

From Communities to Populations to Individuals

What are the traits of individual plants that allow them to survive and perpetuate their species in fire’s presence?

Plant Traits Impacting Response to Fire

• Flower & seed production stimulated• Seed germination stimulated (seed or soil

conditions)• Rapid growth & development (longleaf pine)• Thick bark (pines, mature hardwoods)• Adventitious buds (gallberry, pond pine)• Root/basal meristem sprouting (oaks, grasses)

• Serotinous cones (sand pine)

Individual Plant Responses (fire-related traits) to Fire

• Classification of fire responses (Rowe, 1983)1. Invaders (well-dispersed weedy species with short-

lived seeds

2. Evaders (species with long-lived seeds stored in the soil or in the canopy

3. Avoiders (shade-tolerant species with slow recolonization rates- usually killed by fire)

4. Resisters (adults can withstand fires, otherwise intolerant of fire)

5. Endurers (sprouters)

•Cogongrass invades southeastern pine forests that typically have grass understories.• Cogongrass is much taller (up to 4 ft) than native grasses, increasing fuel loading and promoting fire• Resulting fires are more intense than those occurring in typical pine stands mortality of even (fire resistant) longleaf pine = alteration of the natural fire regime

InvadersInvaders

Cogongrass (Imperata cylindrica)

Invader: Melalueca quinquenervia

• A fire promoter • Melalueca invades wetland areas of S. Florida• Has very flammable vegetation due to volatiles• Fires in Melalueca stands are intense, often developing crown fires.

Avoiders• White fir (Abies concolor)

•Shade-tolerant

•Colonizes under canopy of fire-tolerant species in mixed-conifer or pine forests, primarily

•Low crowns encourage torching during fires, young trees act as ladder fuels into adult crowns

•Relatively thin-barked and resinous

•Shallow roots susceptible to soil heating

White fir sapling

Avoider: Chinese tallow tree (Sapium sebiferum)

• A fire suppressor• Invades grasslands and shrublands in the eastern U.S.• Produces leaf litter that is high in moisture content that decreases flammability of surface fuels• Shades out grasses and shrubs

Resisters• Ponderosa pine (Pinus ponderosa), longleaf and slash pine

– Thick, corky insulative bark– Self-pruning at maturity

– Occurs in open stands

– High foliar moisture– Susceptible to fire

when young – Fire regime is low

intensity, frequent surface fire

Endurers = Sprouters• Saw palmetto (Serenoa repens)

– Flammable foliage– Rhizomes store carbohydrates for immediate post-fire

sprouting response– Outcompetes obligate seeders– Can also reproduce via seeds

Evaders• Manzanita (Arctostaphylos glauca): Chaparral fire regime is

high-severity, high-intensity, low frequency (50-100+ yrs.), crown fire type– Obligate post-fire seeder, hard seed coat cracked– Increased seed production at older ages– High intensity fire kills endurers (sprouting competition)

Adult manzanita Young manzanita “stand”

Manzanita seedlings

Post-fire manzanita mortality and regeneration

When mortality DOES occur, how and why does it happen?

• Mortality is time & temperature dependent

• Can be delayed

• Resistance to heat– high when dormant and

moisture low– low in early summer– varies by species

Foliage mortality

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Temperature F

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Fire-Caused Plant Mortality• Fuel characteristics affect lethal heating

– Heat disperses in open stands– High fuel loads increase heat

release– High fuel moisture content

decreases heat– Litter and duff accumulations

increase heating at base of stem (esp. around old trees)

• Burn prescriptions also affect heat loads– Frequent fires reduce fuel loads– Ignition pattern– Season of burn

Woody Plant Mortality- foliage• Crown scorch (dead foliage)

– increases as air temperature increases

• Crown mortality affected by:– stand & shrub density

– fuel concentrations at the base of trees

– bud dormancy & heat resistance

– foliar moisture content

– presence of flammable compounds

• Crown consumption = crown mortality (nearly always)

Woody Plant Mortality- cambium

• Stem & cambium mortality affected by:– bark thickness, moisture & heat

resistance– stem diameter & degree of heat

girdling– heat received during all stages of

combustion

• Damage to tree stems managed by:– controlling fire intensity & flame length– reducing duff & litter consumption

• Shrub stems usually killed

Woody Plant Mortality- roots

• Root mortality affected by:– depth of lateral and feeding roots– moisture content of duff/litter and surface soils– duration of fire heating

• Damage to roots managed by:– knowing where roots are located– regulating duff & litter consumption by burning at

specified moisture contents