Transcript Disturbance
Population and community-level consequences of fragmentation • • • • interrupts ecological patterns and processes reduced habitat patch area edge effect increased patch isolation – decreased successful movement (immigration and emigration) – increased likelihood of local extinction Processes operating between fragments • dispersal – increasing fragmentation decreasing colonization rates – leads to decreasing # of species within patch – increasing risk of local extinction of species within patch Processes operating between fragments • dispersal • matrix – disturbed/converted habitat surrounding fragments – potential roles? matrix Persistence of populations • In which directions would you predict net movement of individuals? • Which populations are more likely to persist? why? Disappear? • What are the factors most important in determining a population’s likelihood to persist? • Which populations, if they disappear, are most likely to be recolonized? Grizzly bear • 50,000 historic estimate • Persecution and habitat changes == about 1,200 wild grizzlies remain in lower 48 Grizzly bear ecosystems 40-50 30-40 ? <20 0? >500 http://www.fws.gov/mountain-prairie/species/mammals/grizzly/ Y2Y Yukon to Yellowstone Conservation Initiative • Goal: maintain and sustain region to allow wilderness, wildlife, native plants, and natural processes to function as an interconnected web of life • Partnerships of NGOs, businesses, foundations, concerned citizens, scientists • Based on science • Balance area needs Cascade Land Conservancy In conjunction with members of communities, work toward largescale conservation • Habitat Lands • Farmland • Working Forests • Parks, Trails and Open Spaces • Shorelines and Estuaries Natural Landscapes are also heterogeneous Why? Natural Landscapes are also heterogeneous Why? Topography and climate How Rain Shadows Form wet W sides, dry E sides Rainshadows Air mass Pacific Ocean Ppt 100-200” Cascades Olympics Ellensburg Puget Trough Ppt 10-12” Seattle North Bend Ppt 36” Ppt 100” Ppt 10-12” Generalized Forest Zones of the Washington Cascades Cross-section of Cascades WEST EAST Alpine Alpine Spruce-fir Mountain hemlock Douglas-fir Pacific silver fir Ponderosa pine Western hemlock Shrub-steppe Natural succession Structural diagram for successional seres in Douglas-fir forests (Franklin and Spies 1991) Natural succession Structural diagram for successional seres in Douglas-fir forests (Franklin and Spies 1991) Succession from different sources of disturbance: fire, cutting Natural Disturbances • Disturbance: an event that causes a change to resource availability, substrate, or the physical environment – • Fire, wind storm, insect outbreak, floods Disturbance regime: spatial and temporal dynamics of disturbances over a longer time period – Defined by frequency, intensity, severity, size Regional & landscape scale patterns of forest disturbance from Turner, et al (2001) Turner et al. 2001 Patch Dynamics: over space and time, disturbances create a mosaic of patches of various sizes, shapes, and successional stages across an area from Turner, et al (2001) Role of Fire Habitat diversity: • landscape mosaics • uneven-aged stands (in most cases) • dead and dying trees Nutrient release Leads to a greater diversity of wildlife Landscape mosaic created by the 1988 Yellowstone fires Ecological Legacies • • • Remain after disturbance Influence ecological effects of disturbance and patterns of succession Snags, logs, roots, seeds Scrub Oak: Survive fires only by resprouting Wildlife Responses to Fire Serotinous Cones • Sealed by resin • Opened by fire • A new generation grows (ex Jack Pine) Winners and Losers • • • • • Disturbances change habitat naturally Some wildlife increase = “winners” Some wildlife decrease = “losers” Some generalists show little change Disturbance is not “good” or “bad” for all wildlife How Did Fire Affect PNW Forests? Historical Fire Regimes • High Severity – Infrequent (100+ yrs) and stand-replacing • Mixed Severity – Less frequent (25-75 yrs) and a mix of severities • Low Severity – Frequent (5-15 yrs) but low intensity Fire improves browse quality • Stimulates new growth • Higher protein • Higher digestibility • Attracts moose, elk, deer, and their predators (wolves) plus bears Pyrophilic Insects Barbeque Beetle • Infrared sensors on abdomen to detect fire from a distance • With predators and sticky tree resin gone after fire, good conditions for mating Xenomelanophila miranda beetle • Mate on charred trees soon after fire Black-backed Woodpecker • Nearly restricted in its habitat distribution to standing dead forests created by stand-replacement fires • Feed on larvae of the black fire beetle Longleaf Pine of the Southeast • Fire-dependent ecosystems • Historically, surface fires every 3-5 years – Ignited by lightning and Native Americans • Now maintained by prescribed burning Red-cockaded Woodpecker • Endangered (SE) • Requires large, live longleaf pine trees • Longleaf is a fire-adapted species Lives in large LIVE longleaf pine • Drills holes around the cavity • Resin flows – defense against snakes • Longleaf pine type one of most endangered forest types in world – 99% gone Prescribed burning used to maintain Longleaf Pine savanna There is no ecological equivalent to fire Kirtland’s Warbler • Endangered species • In danger of extinction until an out-of-control fire triggered a population revival • Nests in young Jack Pine, a firedependent species with serotinous cones Wildlife Management • Stand-replacement fires may be necessary for longterm maintenance of many pyrophilic wildlife populations • Such fires are controversial due to human safety Wildlife Management • Salvage cutting may reduce the suitability of burnedforest habitat by removing the most important element-standing: fire-killed trees needed for foraging and nesting (ecological legacies) • Prescribed burning becoming more accepted as a tool to reduce fuel loads Landscape Alterations Can Profoundly Affect Natural Ecological Systems High Urbanization Persistence of Change Low Agriculture Effect of Fragmentation Timber Harvest High Low Similarity of Alteration to Natural Habitat