Population and community-level consequences of fragmentation
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Transcript of Population and community-level consequences of fragmentation
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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
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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
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Processes operating between fragments
• dispersal• matrix
– disturbed/converted habitat surrounding fragments– potential roles?
matrix
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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?
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Grizzly bear
• 50,000 historic estimate• Persecution and habitat
changes == about 1,200 wild grizzlies remain in lower 48
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Grizzly bear ecosystems
http://www.fws.gov/mountain-prairie/species/mammals/grizzly/
<20
0? >500
40-50 30-40 ?
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Y2YYukon 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
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Cascade Land Conservancy
In conjunction with members of communities, work toward large-scale conservation
• Habitat Lands• Farmland• Working Forests• Parks, Trails and Open Spaces• Shorelines and Estuaries
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Natural Landscapes are also heterogeneous
Why?
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Natural Landscapes are also heterogeneous
Why?
Topography and climate
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How Rain Shadows Formwet W sides, dry E sides
OlympicsPuget Trough
CascadesEllensburg
North BendPpt 100-200” Ppt 10-12”
Ppt 36”
Seattle
Ppt 100”
Ppt 10-12”
Rainshadows
PacificOcean
Air mass
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Generalized Forest Zones of the Washington Cascades
Cross-section of Cascades
Western hemlock
Pacific silver fir
Mountain hemlock
Alpine
Alpine
Spruce-fir
Douglas-fir
Ponderosa pine
Shrub-steppe
WEST EAST
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Structural diagram for successional seresin Douglas-fir forests(Franklin and Spies 1991)
Natural succession
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Structural diagram for successional seresin Douglas-fir forests(Franklin and Spies 1991)
Succession from different sources of disturbance: fire, cutting
Natural succession
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• 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
Natural Disturbances
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Regional & landscape
scale patterns of forest
disturbance
Turner et al. 2001
from Turner, et al (2001)
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from 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
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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
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Landscape mosaic created by the 1988 Yellowstone fires
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• Remain after disturbance• Influence ecological effects of disturbance and patterns of
succession• Snags, logs, roots, seeds
Ecological Legacies
Scrub Oak: Survive fires only by resprouting
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Wildlife Responses to Fire
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Serotinous Cones
• Sealed by resin• Opened by fire• A new generation grows
(ex Jack Pine)
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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
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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
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• Stimulates new growth• Higher protein• Higher digestibility
• Attracts moose, elk, deer, and their predators (wolves) plus bears
Fire improves browse quality
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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
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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
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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
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Red-cockaded Woodpecker
• Endangered (SE)• Requires large, live
longleaf pine trees• Longleaf is a fire-adapted
species
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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
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Prescribed burning used to maintain Longleaf Pine savanna
There is no ecological equivalent to fire
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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 fire-dependent species with serotinous cones
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Wildlife Management
• Stand-replacement fires may be necessary for long-term maintenance of many pyrophilic wildlife populations
• Such fires are controversial due to human safety
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Wildlife Management• Salvage cutting may reduce the suitability of burned-
forest 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
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Persistenceof
Change
Similarity of Alteration to Natural HabitatHigh Low
Low
High
Agriculture
TimberHarvest
Urbanization
High
Low
Effect ofFragmentation
Landscape Alterations Can Profoundly Affect Natural Ecological Systems