Urban Ecology and Forest Ecosystems in Urbanizing Areas

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Urban Ecology and Forest Ecosystems in
Urbanizing Areas

• Lin Robinson
• Graduate Student
• College of Forest Resources
• linrobin_at_u.washington.edu

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What Is Urban Ecology?

• The interactions between humans and ecological
  processes in urbanizing areas.
• Humans dominate and/or impact most of earths
  ecosystems. pristine ecosystems are
  difficult/impossible to find, depending on you
  perspective.
• Human Ecosystem
• Actions Changes

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Why is the Study of Urban Ecology Important?

• Populations of urban areas are increasing
  worldwide
• The footprint of urban areas are increasing
  faster than population growth
• Chicago from 1950-1990 population increased by
  38, land area covered increased by 124
• Cleveland population increased by 21, but land
  area increased by 112 Source Marzluff et al.
  2001

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Population is Increasing Locally

• In King County, population has increased by 44,
  from 1.2 to 1.7 million over past 25 years
• The number of households has increased by 72,
  from 400,000 to 680,000 during same time
  period

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What is Sprawl?

• Sprawl is a form of urbanization distinguished
  by leapfrog patterns of development, commercial
  strips, low density, separated land uses,
  automobile dependency, and a minimum of public
  open space. -Oliver Gillham

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Urban to Wildland Gradient
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Urban to Wildland Gradient

• General Gradient
• Urban to Suburban to Rural to Exurban to
  Wildland
• But not always!
• e.g. Suburban to Exurban
• Polycentric development (urbanization spreads
  from several Urban centers)

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Definitions

• URBAN Buildings cover majority of land
  high-density SFH, MFH, commerce industry
  present
• SUBURBAN Moderate to high-density SFH MFH,
  basic services, light industry scattered
  throughout
• RURAL sparsely settled lands with low-density
  SFH on large lots in matrix of agricultural
  lands.
• EXURBAN Similar to Rural, but matrix consists
  of more natural vegetation
• WILDLAND Unsettled lands with occasional
  dwellings.

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What are the Results of Sprawl?

• Leapfrog development and eventual infilling
• Land conversion to other uses
• Environmental impacts
• Loss of forest and agricultural lands
• Loss of wetlands
• Loss and conversion of fish wildlife habitat
• Impacts to air and water quality, including
  groundwater recharge

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What Happens to Forests in Urbanizing Areas?

• Loss of forest habitats some types disappear
• Fragmentation and isolation of forest habitats
• Fragmentation the process of reducing size
• and connectivity of stands that compose a
  forest Source Agee in Rochelle et al. 1999
• Fragments may be very different from surrounding
  matrix

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What Happens to Forests in Urbanizing Areas?

• Increased edge results in changes in
  microclimate, predation, invasion by exotic
  species
• Loss of interior habitat, but increase in
  edge habitat
• Decrease in patch size shape connectivity
  also important
• Changes in species composition and forest
  structure increase in exotic (non-native)
  species

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Habitat Loss Fragmentation
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Klahanie Forest Fragments
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Open Closed Edges
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Extent of Edge Effects Vary
South/west exposure Prevailing wind direction
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Abrupt, open edges can become less open over time
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Edges in Exurban Areas
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Corridors and habitat continuity
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• Relationship of edge and interior habitat
• Assume edge effects extend 200m into forest (x
  200m)
• Patch would need to be 1.25 ha before there was
  any interior habitat at all
• Levenson (1976) found patch size of 2.3 ha needed
  for interior habitat in field studies

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Human Impacts to Forest Fragments

• Most human impacts occur within 82m of edge, but
  some extend as much as 130m (Matlack 1993).
• Clearing trampling of understory
• Loss of forest structure and biodiversity
• Dumping of garbage yard waste
• Lawn extensions
• Invasion by exotic (non-native) species
• Predation by pets (house cats)

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Fragmentation Impacts Wildlife Populations!!

• Fragmentation leads to increased edge, decrease
  in patch size, loss of interior habitat, and
  changes in forest structure composition.
• Wildlife impacts
• Direct loss of habitat loss of core habitat
• Habitat isolation disturbs migration breeding
• Smaller patch size results in decreased food
  supply and increased competition
• Loss of complexity affects breeding nest
  predation

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Some Wildlife Populations Increase

• Generalist species those that can survive in
  harsh edge habitats may actually increase
• Deer, beavers, geese, foxes, coyotes, opossums,
  raccoons
• Numbers of non-native bird species often increase
• Many times, these are not the species that
  inhabit interior forest habitat.

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Many Wildlife Populations Decrease

• Species that require interior forest habitats and
  native species often decrease in population size
  and diversity.
• Interior and ground-nesting birds decrease
• Cavity nesting birds decrease

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Cavity nesting birds in urban forests versus
managed forests
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Why Is This Important?

• Biodiversity issues
• Loss of some native plant animal species
• Proliferation of a less-diverse population of
  generalist edge species
• Loss of endangered species critical habitats
• Proliferation of exotic (non-native) species
• Spread of weeds landscape plantings

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Local Impacts
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(Draft)
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(Draft)
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(Draft)
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(Draft)
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Summary

• Increasing human populations in urban areas
  results in habitat loss conversion of forest
  lands other natural habitats to more urban
  uses.
• Sprawl results in fragmentation and isolation of
  the remaining forest habitats, smaller patch
  size, increased edge, and changes in forest
  composition structure.
• Wildlife populations change. Generalist/edge
  species often increase while species requiring
  interior habitat usually decrease.

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Recommended Reading

• Gillham, O. 2002. The Limitless City A Primer on
  the Urban SprawlDebate. Island Press.
• Schwartz, M. W. (ed). 1997. Conservation in
  Highly Fragmented Landscapes. Chapman Hall.
• Rochelle, J.A. et al. 1999. Forest
  Fragmentation Wildlife and Management
  Implications. Kononklijke Brill NV, The
  Netherlands.
• Marzluff, J.M. et al. (eds). 2001. Avian Ecology
  and Conservation in an Urbanizing World. Kluwer
  Academic Publishers.
• Peck, S. 1998. Planning for Biodiversity
  Issues and Examples. Island Press.

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Poetry and Ecologists

• Experts on corridors tried,
• To ignore the Freudian side,
• But anatomy prevailed,
• The consensus was hailed,
• That is neither too long or too wide!
• -Michael Soule

• There was a young critter named ess,
• Through a corridor had to progress,
• A barrier stopped it,
• A predator copped it,
• And that was one critter the less. -Noela
  Marr Cyril Hembrow