Transcript Slide 1
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?