55
Of course, fi re frequency and intensity are linked to climatic patterns and conditions
including rainfall amount and pattern as well as temperatures that are linked to
global phenomena (Swetnam and Betancourt 1990 ). In southwestern North America,
large fi res usually high elevation fi res occur after dry springs with smaller fi res
following wet springs with lower elevation semiarid grasslands probably following
the same pattern.
Evidence of past grassland fi res throughout the world is sparse, diffi cult to fi nd,
and not from the usual scientifi c sources. Some historical evidence for fi res in southwestern North America comes from newspaper reports, from the earliest travelers,
and from early settlers (Humphrey 1958 ; Inglis 1964 ; Bahre and Shelton 1993 ).
Although evidence concerning past fi res is tenuous, evidence suggests grasslands
require fi res, but some do not agree.
Encroachment of grasslands by woody legumes and other woody species caused
by man and his grazing animals has probably been going on in many parts of the
world for thousands of years. However, in southwestern North America, the process
has been only going on a relatively short time, probably for a few hundred years.
Apparently encroachment and changes in the composition and structure of arid and
semiarid low elevation grasslands in many parts of southwestern North America
seemed to have started after the beginning of large-scale cattle ranching and fi re
exclusion in the 1850s–1870s (Humphrey 1958 ; Bahre 1991 , 1995 ; Neff et al.
2008 ). Unfortunately, fi res in these low elevation communities today are rare
because of changes coupled to high intensity, continuous grazing that reduces the
amount of light, fl uffy fuel required for fi res. Today the presence of woody plants,
little fi ne fuel, and community fragmentation are causes of reduced fi re frequency
(Collins and Wallace 1990 ). Grass biomass and all fi re characteristics have declined
with the increase in density and size of woody plants in these communities.
Seedlings of woody plants found in grasslands are sensitive to fi re (McPherson
1995 ). Plant sensitivity is size dependent and mortality is mostly related to small
size. Small woody plants are killed by fi re and larger ones are top killed and some
will not re-sprout if top killed. Woody plants are susceptible to fi re mortality until
they are fairly large and have a thick bark. Additionally, if encroaching woody
plants do not produce seeds before the next fi re, or do not re-sprout after being top
killed by fi re, these encroached grasslands would remain relatively free of woody
plants. Fire-tolerant woody species would be top killed but suppressed by reoccurring fi res and remain in the grassland, but at a small size (Archer 1994 ). With a
reduction of the grassland fuel by herbivory, fi re frequencies would decrease and
approach zero, promoting encroachment, establishment, growth, and increased
woody legume and other woody plant cover and density.
Management of southwestern North American grasslands and grasslands
throughout the world is a diffi cult task. Encroachment of woody legumes and other
woody species will continue with fi re suppression. The goal of management of
these grasslands should be sustainability. That should include sustainable grass production that leads to sustainable animal production. That does not mean all grass
can be harvested by the animals. In order to maintain grasslands as grasslands, they
should be burned at reasonable intervals to suppress or remove the woody plants,
8 Management and Community Restoration
Of course, fi re frequency and intensity are linked to climatic patterns and conditions
including rainfall amount and pattern as well as temperatures that are linked to
global phenomena (Swetnam and Betancourt 1990 ). In southwestern North America,
large fi res usually high elevation fi res occur after dry springs with smaller fi res
following wet springs with lower elevation semiarid grasslands probably following
the same pattern.
Evidence of past grassland fi res throughout the world is sparse, diffi cult to fi nd,
and not from the usual scientifi c sources. Some historical evidence for fi res in southwestern North America comes from newspaper reports, from the earliest travelers,
and from early settlers (Humphrey 1958 ; Inglis 1964 ; Bahre and Shelton 1993 ).
Although evidence concerning past fi res is tenuous, evidence suggests grasslands
require fi res, but some do not agree.
Encroachment of grasslands by woody legumes and other woody species caused
by man and his grazing animals has probably been going on in many parts of the
world for thousands of years. However, in southwestern North America, the process
has been only going on a relatively short time, probably for a few hundred years.
Apparently encroachment and changes in the composition and structure of arid and
semiarid low elevation grasslands in many parts of southwestern North America
seemed to have started after the beginning of large-scale cattle ranching and fi re
exclusion in the 1850s–1870s (Humphrey 1958 ; Bahre 1991 , 1995 ; Neff et al.
2008 ). Unfortunately, fi res in these low elevation communities today are rare
because of changes coupled to high intensity, continuous grazing that reduces the
amount of light, fl uffy fuel required for fi res. Today the presence of woody plants,
little fi ne fuel, and community fragmentation are causes of reduced fi re frequency
(Collins and Wallace 1990 ). Grass biomass and all fi re characteristics have declined
with the increase in density and size of woody plants in these communities.
Seedlings of woody plants found in grasslands are sensitive to fi re (McPherson
1995 ). Plant sensitivity is size dependent and mortality is mostly related to small
size. Small woody plants are killed by fi re and larger ones are top killed and some
will not re-sprout if top killed. Woody plants are susceptible to fi re mortality until
they are fairly large and have a thick bark. Additionally, if encroaching woody
plants do not produce seeds before the next fi re, or do not re-sprout after being top
killed by fi re, these encroached grasslands would remain relatively free of woody
plants. Fire-tolerant woody species would be top killed but suppressed by reoccurring fi res and remain in the grassland, but at a small size (Archer 1994 ). With a
reduction of the grassland fuel by herbivory, fi re frequencies would decrease and
approach zero, promoting encroachment, establishment, growth, and increased
woody legume and other woody plant cover and density.
Management of southwestern North American grasslands and grasslands
throughout the world is a diffi cult task. Encroachment of woody legumes and other
woody species will continue with fi re suppression. The goal of management of
these grasslands should be sustainability. That should include sustainable grass production that leads to sustainable animal production. That does not mean all grass
can be harvested by the animals. In order to maintain grasslands as grasslands, they
should be burned at reasonable intervals to suppress or remove the woody plants,
8 Management and Community Restoration