Download Disturbance

Population and community-level consequences
of fragmentation
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•
•
•
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
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•
•
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
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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