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

• 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

Varner et al., 2005

• 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

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).

• 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

Causes of Mortality

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 decisionshttp://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

Bellwood 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.

Complexity in restoration outcomes

Suding et al., 2004

• Species responses

• Trophic interactions

• Reduced connectivity

• Climate change

Explanations for resistance

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?