Transcript Simulated effects of prescribed burning on the population

NMFWA Annual
Meeting
14 March 2012
Atlanta, GA
Courtesy Beth Evans
Wade A. Wall ERDC-CERL
Janet B. Gray Fort Bragg Endangered
Species Branch
Matthew G. Hohmann ERDC-CERL
Historical (1500
A.D) estimates: 1-3
years
 Fire suppression,
buildup of fuel
loads
 Prescribed fire ~ 20
years (red
cockaded
woodpecker
 Benefits: wildfire
reduction, improved
habitat, species
management

Reduced
competition
 Increased
survivorship
 Increased
productivity
 Increased flowering
 Increased
germination
 Reduced seed
predation



50% of rare plant
species in FL
exhibited positive
responses
(Slapcinsky et al.
2010)
• 9 of 18 no
response
Climatic uniqueness
of Florida?
• Fire history
centerforplantconservation.org
 Determine
effects of
fire on study species
• Identify “optimal” fire
return interval
• Model population
dynamics
 Interpret
results in
light of the climatic
history of the
Sandhills region.

Astragalus michauxii
• Sandhills milkvetch
• “Pea swales”
• xeric sandhill scrub
• Fort Bragg, Gordon

Pyxidanthera brevifolia
• Sandhills pyxie moss
• xeric sandhill scrub
• Fort Bragg, Dix

Both species SAR, FSC
 A. michauxii
• Surveyed 87 pops.
• Tagged all identified
individuals 2007
• Measured
survivorship, growth,
reproduction 20072010
 stem height
 Counted viable seeds in
400 fruits
 P. brevifolia
• Selected 24 pops. (out
of 277 total pops.)
• Tagged 1000
individuals
• Measured
survivorship, growth,
reproduction 20082010
 Major, minor axis
 Estimated percent
coverage
 Fruit production
 Generalized
t+1
linear models to
analyze
survivorship,
growth, and
reproduction.
 Matrix
modeling to
project
population
growth through
time
t
small large
N
small 0.3 0.15
25
large 0.2
50
0.8
N
(7.5+7.5) =
15
(5+40) = 45
=
Short-term effect of fire on
mortality: A. michauxii
Short-term effect of fire on
mortality: P. brevifolia
Fire reduces fruit production in A.
michauxii
Fire reduces fruit production in P.
brevifolia
Regeneration following fire size is dependent in A.
michauxii
Regeneration following fire is size dependent in P.
brevifolia
Projected population growth rate lower under annual
burning

Vegetation differences
during last ice age
• Spruce forest
• Exposed soil, reduced
biomass
 Lower competition
 Adapted to colder
environment?

Fire replaced climate as
limiting factor
• Necessary for competition
removal
• A. michauxii and P.
brevifolia may not be as
adapted to fire as other
species.
rst.gsfc.nasa.gov

Short term consequences
of fire
• Increases mortality
• Decreases seed production
• No increase in seedling
recruitment
• Slow regrowth?

Long term consequences
of fire
• Reduction of competition,
woody growth
• Necessary for long term
population persistence
 “Caught between a rock and a
hard place”
 Current fire return interval
adequate
Distribution of Astragalus michauxii and
Pyxidanthera brevifolia across Fort Bragg
Military Reservation
 Rare
taxa may have
different responses to
fire
• Different histories
 Lack
of information
on many plant
species in firedependent
ecosystems
 412
plant SAR
• ~318 dependent on or
influenced by fire
• Few have been studied
Fort Bragg Military Installation
Fort Bragg Endangered Species Branch
ERDC-CERL
North Carolina State University