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

http://www.fws.gov/mountain-prairie/species/mammals/grizzly/

<20

0? >500

40-50 30-40 ?

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

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

Natural Landscapes are also heterogeneous

Why?

Natural Landscapes are also heterogeneous

Why?

Topography and climate

How Rain Shadows Formwet W sides, dry E sides

Olympics

Puget Trough

Cascades

Ellensburg

North BendPpt 100-200” Ppt 10-12”

Ppt 36”

Seattle

Ppt 100”

Ppt 10-12”

Rainshadows

PacificOcean

Air mass

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

Structural diagram for successional seresin Douglas-fir forests(Franklin and Spies 1991)

Natural succession

Structural diagram for successional seresin Douglas-fir forests(Franklin and Spies 1991)

Succession from different sources of disturbance: fire, cutting

Natural succession

• 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

Regional & landscape

scale patterns of forest

disturbance

Turner et al. 2001

from Turner, et al (2001)

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

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

• 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

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

• Stimulates new growth• Higher protein• Higher digestibility

• Attracts moose, elk, deer, and their predators (wolves) plus bears

Fire improves browse quality

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 fire-dependent species with serotinous cones

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

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

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