Fire and Savannas

Oct 14, 2010

What is a savanna?

• Scattered trees and sometimes shrubs

• Dense herbaceous understory

• Often an “ecotone”

What is an ecotone?

• TTYP – What kinds of environmental factors or disturbances could create an ecotone?

Savannas throughout the world• Cerrado• Serengeti• Madagascar

savannas• Australian eucalyptus

savannas• Indian savannas

North American Savannas• Prairie/forest transition

zone temperate savannas– Oak/mesquite in south– Oak with some hickory in

central– Oak to aspen in north

• Oak savannas in CA and S.W.

• W & S.W. Ponderosa pine• S.E. Pine savannas

Midwestern oak savannas

• Ecotonal between prairie and oak/hickory forest

• Scattered oak (hickory?) trees

• Understory with prairie and forest components

• Different terms:– Oak barrens, oak

openings, oak grove

Shifts in the savanna ecotone

• Savanna distribution has changed over time

• What factors influenced the distribution of savanna?

• Topography• Moisture• Fire• Grazing

• Humans• Climate• Soils

TTYP: Shifts in the savanna ecotone

• Topography and• Landscape features

(e.g. streams)• Moisture• Fire• Grazing• Humans• Climate• Soils

How do these factors influence the distribution of prairie, savanna, and woodland?

Over what time periods?

Are any of these inter-related? How?

Shifts in the savanna ecotone

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• • • • •

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Shifts in the savanna ecotone

• Flatter topography (L) • Less soil moisture / drier climate (L/M) • Far from rivers and streams (L/M) • Sandier soils (L)• More frequent fires (S)• More humans if starting fires (less humans

if suppressing fires) (S/M/L)• More grazing

• Topography: broken, more ridges, slopes (L)

• More soil moisture (M)• Closer to rivers and streams (L/M)• More clayey-loamy soils (L)• Less frequent fires (S)

• More humans if suppressing fires (less humans, if no supp.)

• Less grazing

Savanna tree species• Bur oak

– Thick corky bark, deep roots– Most fire-resistant oak– Adventitious buds along branch resprout

• Black oak– Top-killed, but resprouts with vigor

• White oak– Moderate fire resistance, good resprouter

• Red oak– Not very fire resistant– Low sprouting capacity when top-killed– Mostly on steep north slopes

Savanna shrub species

• Gray dogwood, hazelnut, smooth sumac• Clone-formers• Burned to the ground by fire

Savanna ground layer

• Herbaceous species• Fuel for fire• Gradient of light environments = high diversity• Species with different light requirements:

– Full sun– Full shade– Light shade– Moderate sun– Blend of shade and sun (“true savanna species”):

http://oaksavannas.org/savanna-forbs.html#Pruka