wet–dry rhythms set the ecological cadence for
fire regimes.
13.3 Different Ecoregions, Different
Fire Regimes
Different ecoregions produce different fire
regimes (Bailey 2010). Several studies have
looked at variation in fire regimes at the
ecoregion scale. We will examine three of them.
13.3.1 Precolonial Fire Regimes (Vale)
Precolonial fire regimes for different vegetation
types in North America have been determined by
analyzing fire scars. In areas lacking trees, the
development of vegetation after recent fires plus
early journal accounts and diaries have been used
to make inferences about fire regimes. Thomas
Vale (1982) synthesized this information in his
book, Plants and People.
Vale analyzed “natural” vegetation types
based on ecoregions. He used two information
sources to characterize fire regimes: he extracted
relevant information from 45 published fire
regime studies, and he assessed species-specific
fire ecology for plants indicative of the areas
mapped. He found that fire regimes varied by
ecoregion (Fig. 13.1). In the northern coniferous
forest and woodland (boreal forest), for example,
infrequent large-magnitude fires carried the
flames in the canopy of the vegetation, killing
most of the forest. Such fires are called “crown
fires” because they burn in the upper foliage or
crown of the trees.
Other environments, such as the deciduous
forests of the east, probably had infrequent
crown or severe surface fires. These areas are
typically cool or wet and consist of vegetation
that inhibits the start or spread of fire.
In mountainous regions, fire frequency is
related to elevation. The lower-elevation forests
in the western United States had a regime of
frequent, small-magnitude, surface fires. Here,
the burning was restricted to the forest floor and
most mature trees survived. Ponderosa pine
forests are good examples of this kind of forest.
13.3.2 Fire Regime Types (The Nature
Conservancy)
The Nature Conservancy (2004), working in
cooperation with the World Wildlife Fund and
the International Union for Conservation of
Nature, has recently completed a global assessment of fire regime alteration on an ecoregional
basis. The assessment identified three broad fire
regime types (Fig. 13.2). The report reveals that,
among globally important ecoregions for conservation, 84 % of the area is at risk from altered fire
regimes. Almost half of priority conservation
ecoregions can be classified as “fire-dependent”
(shown in reddish brown).
In fire-dependent systems, fires are fundamental to sustaining native plants and animals. Many
of the world’s ecosystems—taiga forest, chaparral shrublands, savanna—have evolved with
fires. What characterizes all of these ecosystems
is resilience and recovery following exposure to
fires. In the case of chaparral, fire does not kill
most of the shrub layer; the shrubs sprout back
from root crowns.
Among all the ecoregions, 36 % are fire-sensitive; and for this ecoregion group frequent,
large and intense fires were, until recently, rare
events. In these systems, plants lack the
adaptations that would allow them to rapidly
rebound from fire. These areas are typically
cool or wet and consist of vegetation that inhibits
the start or spread of fire. Examples include the
tropical moist broadleaf forest and temperate
rainforests.
Another 18 % of ecoregions are classified as
fire-independent ecosystems. Here fires are
largely absent because of a lack of vegetation or
ignition sources, such as in Africa’s Namibian
Desert or in tundra ecosystems in the arctic.
According to The Nature Conservancy, fire
regimes are degraded in more than 80 % of
128
13 Use of Fire Regimes at the Ecoregion Scale
fire regimes.
13.3 Different Ecoregions, Different
Fire Regimes
Different ecoregions produce different fire
regimes (Bailey 2010). Several studies have
looked at variation in fire regimes at the
ecoregion scale. We will examine three of them.
13.3.1 Precolonial Fire Regimes (Vale)
Precolonial fire regimes for different vegetation
types in North America have been determined by
analyzing fire scars. In areas lacking trees, the
development of vegetation after recent fires plus
early journal accounts and diaries have been used
to make inferences about fire regimes. Thomas
Vale (1982) synthesized this information in his
book, Plants and People.
Vale analyzed “natural” vegetation types
based on ecoregions. He used two information
sources to characterize fire regimes: he extracted
relevant information from 45 published fire
regime studies, and he assessed species-specific
fire ecology for plants indicative of the areas
mapped. He found that fire regimes varied by
ecoregion (Fig. 13.1). In the northern coniferous
forest and woodland (boreal forest), for example,
infrequent large-magnitude fires carried the
flames in the canopy of the vegetation, killing
most of the forest. Such fires are called “crown
fires” because they burn in the upper foliage or
crown of the trees.
Other environments, such as the deciduous
forests of the east, probably had infrequent
crown or severe surface fires. These areas are
typically cool or wet and consist of vegetation
that inhibits the start or spread of fire.
In mountainous regions, fire frequency is
related to elevation. The lower-elevation forests
in the western United States had a regime of
frequent, small-magnitude, surface fires. Here,
the burning was restricted to the forest floor and
most mature trees survived. Ponderosa pine
forests are good examples of this kind of forest.
13.3.2 Fire Regime Types (The Nature
Conservancy)
The Nature Conservancy (2004), working in
cooperation with the World Wildlife Fund and
the International Union for Conservation of
Nature, has recently completed a global assessment of fire regime alteration on an ecoregional
basis. The assessment identified three broad fire
regime types (Fig. 13.2). The report reveals that,
among globally important ecoregions for conservation, 84 % of the area is at risk from altered fire
regimes. Almost half of priority conservation
ecoregions can be classified as “fire-dependent”
(shown in reddish brown).
In fire-dependent systems, fires are fundamental to sustaining native plants and animals. Many
of the world’s ecosystems—taiga forest, chaparral shrublands, savanna—have evolved with
fires. What characterizes all of these ecosystems
is resilience and recovery following exposure to
fires. In the case of chaparral, fire does not kill
most of the shrub layer; the shrubs sprout back
from root crowns.
Among all the ecoregions, 36 % are fire-sensitive; and for this ecoregion group frequent,
large and intense fires were, until recently, rare
events. In these systems, plants lack the
adaptations that would allow them to rapidly
rebound from fire. These areas are typically
cool or wet and consist of vegetation that inhibits
the start or spread of fire. Examples include the
tropical moist broadleaf forest and temperate
rainforests.
Another 18 % of ecoregions are classified as
fire-independent ecosystems. Here fires are
largely absent because of a lack of vegetation or
ignition sources, such as in Africa’s Namibian
Desert or in tundra ecosystems in the arctic.
According to The Nature Conservancy, fire
regimes are degraded in more than 80 % of
128
13 Use of Fire Regimes at the Ecoregion Scale