Long-Term Patterns of Vegetation Change Following Fire
1. Long-Term Patterns of
Vegetation Change
Following Fire
November 11, 2010
Roger D. Blew
INL Environmental Surveillance, Education
and Research Program
2. [photo of wildfire]
We have heard so much about the risks wildfire brings to western rangelands.
3. [photo of wildfire]
More and more, fire in sagebrush steppe leaves behind only cheatgrass and
other invasive, non-native species.
.
4. [Photo of wildfire]
In recent years it seems the risks increase
and the consequences of fire loom larger.
5. [Photo of wildfire]
As land managers feel the heat to reduce the risks and repair the
aftermath, a question that seems to have been forgotten is,
“How was this supposed to work?”
“What was supposed to happen after a fire?”
6. The INL is mostly good to excellent condition Wyoming big sagebrush and
bluebunch wheatgrass rangeland and provides and excellent opportunity to
address that question of “What was supposed to happen?”. This project was
initiated to address that question and to also assess the efficacy of artificially
seeding sagebrush onto a burn.
7.
8. These fires remove all aboveground plant material leaving
only charred remains behind…
9. …and often leaves the impression of total destruction
and devastation.
10. Two growing seasons
after fire. Quick
recovery of native
grasses and forbs,
with only limited
invasion by non-
natives.
This is the expected fire recovery on the INL Site
11. Our conclusion about short-term
natural recovery…
If there was a healthy plant
community before the fire…
There will be one after the fire.
12. Long-Term Recovery
• West and Yorks (2002) reported after
20 years no apparent trend toward a
community representative of the pre-
burn community.
– Little or no recovery of Wyoming big
sagebrush.
• Humphrey (1984) reported diversity
changed little up to 36 years after fire.
13. Long-Term Recovery
• Neele et al (2000) in Mountain big
sagebrush considered burns older than
37 years to be equivalent to unburned.
• Differences in vegetation between sites
were related to topography, fire
intensity, grazing pressure and post-fire
climate.
• No differences in forb cover associated
with time since fire.
14. Long-Term Recovery
• Colket (2003) reported on recovery of
Wyoming big sagebrush on a chrono-
sequence of fires up to 92 years old.
– Sagebrush density increased to similar to
nearby unburned plots at a time
approaching 92 years.
15. Goals and Objectives
• The goal of the study was to provide a
better understanding of the role of fire
in the vegetation dynamics of sagebrush
steppe communities.
– The primary objective was to examine long-
term changes in vegetation following fire
– A secondary objective was to consider
these changes in terms of models used to
guide management of sagebrush steppe
rangeland.
21. Species Richness
• No patterns suggesting
directional change in
species richness with time
since fire.
• For native perennial
functional groups, species
richness did not differ
significantly between burns
a few years old and those
nearly a century since fire.
22. Conclusions
• No evidence for recovery patterns that
would be directional, linear or
predictable for any functional group
• No evidence for serial replacement or
substantial increases or decreases in
the distribution or importance of
individual species across burn ages,
except big sagebrush.
23. Conclusions
• Densities of species or functional
groups were highly variable in plots
within burns of the same age, indicating
factors other than time since fire
influenced vegetation composition.
• No pattern of change in species
richness with time since fire
24. Models of Community Change
• Our results help to clarify the long-
term trajectory of plant community
change following fire.
– No directional change in species richness,
density or frequency of the native
perennial species, except big sagebrush.
– Big sagebrush increased in density and
frequency with time since fire.
25. Models of Community Change
• Response to fire in sagebrush steppe is
often characterized as secondary
succession.
• Our results suggests fire would be more
analogous to a disclimax or subclimax.
– Fire results in a relatively stable community
– Then slowly re-invaded by an overstory
dominant woody species.
26. Range Condition
Model
EXCELLENT
GOOD
FAIR
POOR
Classical Succession
Model
Annual Weeds
Bare Soil
Perennials Absent
I
Mustards
Annual Forbs
Artemisia present
II
ARTR and/or
BRTE/ POSE
dominant
III
IV ARTR >50% cover
PSSP <50% cover
V
ARTR <50% cover
PSSP >50% cover
Fire?
From Allen-Diaz and
Bartolome (1998)
• No appropriate
pathway for fire
• Only option is
IV to V
• This means fire
triggers a move
toward climax
rather than as a
disturbance
resetting
succession away
from climax as in
other Clementsian
models.
27. Models of Community Change
• Westoby et al. (1989) proposed State
and Transition Models to overcome the
limitations of the mono-climax
Clementsian-based range condition
models.
• S&T models describe recognizable and
relatively stable assemblages of species
and transitions triggered by natural
events or management actions.
28. Many of the reported
S&T models carry
over assumptions
from the
Clementsian, climax-
driven models that
limit their ability to
describe vegetation
change associated
with fire in high
quality sagebrush
steppe
S & T Models
Late Seral
Sagebrush Steppe
Depauperate Late
Seral Sagebrush
Steppe
Native Perennial
Grass Dominant
Invasive Annuals
Dominant
Legend
F– Fire
D – Drought
IG – Improper Grazing
PG – Proper Grazing
PH – Phenoxy Herbicide
VM – Vegetation Modification via
grazing systems, prescribed fire,
brushbeating or chaining.
IG
D
PG
PH
F
VM
IG
F
IG
29. Late Seral
Sagebrush Steppe
Depauperate Late
Seral Sagebrush
Steppe
Native Perennial
Grass Dominant
Invasive Annuals
Dominant
Legend
F– Fire
D – Drought
IG – Improper Grazing
PG – Proper Grazing
PH – Phenoxy Herbicide
VM – Vegetation Modification via
grazing systems, prescribed fire,
brushbeating or chaining.
IG
D
PG
PH
F
VM
IG
F
IG
• Many S&T models
show no transition
from “Late Seral” to
“Native Perennial
Grass” dominated
stages, as fire would
trigger.
• Other models show a
fire transition to
“Native Perennial
Grass” but only from
“Depauperate Late
Seral.”
• Still others show
“Depauperate Late
Seral doesn’t burn.
S & T Models
30. Some models do not allow
for a transition from
“Depauperate Late Seral”
to “Late Seral” except by
vegetation modification.
• Results of long-term studies
show this transition can
occur without vegetation
management (Anderson and
Inouye, 2001).
• Requires a lag phase of 2 to
3 decades, but similar
ecological processes (and
time) would be expected
following vegetation
management.
S & T Models
Late Seral
Sagebrush Steppe
Depauperate Late
Seral Sagebrush
Steppe
Native Perennial
Grass Dominant
Invasive Annuals
Dominant
Legend
F– Fire
D – Drought
IG – Improper Grazing
PG – Proper Grazing
PH – Phenoxy Herbicide
VM – Vegetation Modification via
grazing systems, prescribed fire,
brushbeating or chaining.
IG
D
PG
PH
F
VM
IG
F
IG
31. S & T Models
• Allen-Diaz and Bartolome (1998)
– “To date, published applications of the ST
model have used its adaptability to
describe processes of vegetation change
and response to management controls that
are disappointingly similar to those
described by the classic succession and
[range condition] models.”
32. Summary of Long-Term
Recovery Results
• No evidence of thresholds to community
types that might require management
action to correct.
• No evidence of B.tectorum or other
annual species dominating after fire.
• No apparent threshold preventing
return of big sagebrush following fire in
high quality sagebrush steppe.
33. Sagebrush
Native Perennial
Grass
Co-dominant
Re-sprouting Shrub
w/ Depleted
Native Perennial
Grass
Sagebrush Dominant
w/ Depleted
Native Perennial
Grass
Native Perennial
Grass Dominant w/
Re-sprouting Shrubs
Sagebrush Dominant
w/ Depleted
Native Perennial
Grass & w/
Invasive Annuals
Re-sprouting Shrub
w/ Depleted
Native Perennial
Grass & w/
Invasive Annuals
IG
D PG
IG
D PG
IG
D PG
IG
D PG
Sagebrush w/
Invasive Annuals
Dominant
Invasive Annuals
Dominant
Reference State
Indicators: Native perennial grass dominance or
co-dominance, minimal invasive annual species.
Feedbacks: High net annual productivity, C and N
pool growth, and seed production reinforce
dominance by native perennial grasses
At-risk Community Phases: Native perennial
herbaceous cover reduced and substantial
presence of invasive annual species.
Trigger: Improper grazing or extended drought
reduces vigor and depletes native perennial
grasses.
Alternative State
Indicators: Dominated by invasive annual species. Sagebrush
overstory may be present prior to fire.
Feedbacks: Frequent fire and improper livestock grazing reinforces
dominance by invasive annual species and inhibits recovery of native
perennial species.
Restoration Pathway: No fire and long time period
to support re-invasion by native perennials.
Threshold: Sufficient presence of invasive
annual grasses to spatially and temporally re-
distribute soil resources (ie. water and nutrients)
affecting competitive interactions with native
perennial species.
F
NF
IG
F – Fire
NF – No Fire
D - Drought
IG – Improper Grazing
PG – Prescribed Grazing
IG
D
F
NF
F
NF
F
NF
34. S & T Models
• Allen-Diaz and Bartolome (1998)
– “ST models offer the advantages of
general applicability but require detailed,
time- and site-specific data to fully exploit
their capabilities for description and
prediction.”
– States and transitions should be derived
quantitatively from long-term observations.
35. Management Implications
• Although fire is a rare but natural process in
sagebrush steppe, it is essential to recognize
burned areas can be part of the reference
state.
• S & T models that could be used to guide
management decisions should include all
potential states, transitions and thresholds.
• S & T models must not be constrained by
previous paradigms of vegetation community
dynamics or management.
36. Models of Community Change
• Important because they form the basis
for communicating our understanding of
how and why communities change
through time or in response to
disturbance.
• Important because they provide
guidance on available management
strategies.
37. “There is an increasing need for the
experimental study of succession. A
thorough understanding of successional
phenomena in forests, pastures,
abandoned fields, etc., is of the utmost
importance in pursuing the several lines
of industry concerned and in conserving
our national resources”
Weaver and Clements (1938)
38. Conclusions
If there was a healthy plant
community before the fire,
there will be one after the
fire.
40. Conclusions
In high quality sagebrush steppe
rangeland there appear to be no
thresholds preventing eventual
return to a community dominated
by sagebrush and native perennial
grass following fire.
![[photo of wildfire]
We have heard so much about the risks wildfire brings to western rangelands.](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)