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Transcript
Disturbance regimes in restoration ecology:
novel effects and ecological complexity
Sarah Marcinko
November 11, 2005
Outline
• Disturbance dependence
• Re-establishing disturbance regimes:
longleaf pine savannas and the
Everglades
• Restoration resistance
• Alternative states, positive feedbacks,
and uncertainty
• Discussion
Disturbance dependence
“Ecologically, fires, floods, droughts, storms
and disease outbreaks regulate population
size and species diversity across a range of
spatial and temporal scales. Over evolutionary
time, organisms also evolve traits that enable
them to survive, exploit and even depend on
disturbances.”
Lytle & Poff, 2004
Restoration nuances
• Timing, seasonality
• Frequency, intensity, duration (historic
range of variability)
• Disturbance effects vary among
species
• Scale dependence
Varner et al., 2005
• 97% loss of landscape
• Only ~50% of remnants
frequently burned
• Significant changes in forest
structure and composition
• Decline in understory cover
and richness
• Accumulation of surface
fuels and organic matter
Novel effects
“The most common approach to restoration of
long-unburned southern pine communities has
been the reinitiation of historical fire regimes
with prescribed fire” (p 537).
• Significant canopy mortality, especially among
large pines
– 91% FNA following small wildfire
– 75 -100% EAFB, but variable
• Smaller, fire susceptible species had high
survival rates
Causes of Mortality
• Direct effects
– Stem/root damage
– Canopy scorch
– Vascular damage
• Indirect effects
– Physiological
stress
– Pests/pathogens
Causes of Mortality
• Direct effects
– Stem/root damage
– Canopy scorch
– Vascular damage
• Indirect effects
– Physiological
stress
– Pests/pathogens
Florida Everglades
• Comprehensive Everglades Restoration
Plan: “Getting the water right”
(Lockwood et al., 2003)
• Fire regime largely ignored and fire
frequency altered due to water
management decisions
http://www.evergladesplan.org/facts_info/science_maps.cfm
• Complex interactions between fire and
water affect species conservation
Interactions between fire and water
Lockwood et al., 2003
Fire, water, and conservation
constraints
•Ground nesting species
susceptible to both fires and
floods
•Too much water  adults
fail to breed
•Fire  habitat lost
•Breeding activity peaks
during fire season and low
water flows
Restoration resistance
Suding et al., 2004
A graphic model depicting transitions
between ecosystem states. ‘Healthy’
resilient coral dominated reefs become
progressively more vulnerable owing to
fishing pressure, pollution, disease and
coral bleaching. The dotted lines illustrate
the loss of resilience that becomes evident
when reefs fail to recover from disturbance
and slide into less desirable states.
Bellwood et al., 2004
Complexity in restoration outcomes
Suding et al., 2004
Explanations for resistance
•
•
•
•
Species responses
Trophic interactions
Reduced connectivity
Climate change
Discussion
• Restoring pattern or process? How to prioritize?
• Scale of observation. If we were to examine these
systems over longer time periods (assuming
uninterrupted restoration efforts), would we see the
recovery of these systems to a former, desired state?
How do we proceed in restoration in light of this?
• How are the presence of alternative dynamic regimes
determined and how can we filter out confounding
factors?
• How do we restore ecosystem dynamics if historic
range of variability is unknown?