GEOG 311 Midterm 2

physical components of an urban ecosystem

urban atmosphere

urban biosphere

urban hydrosphere

urban pedo and lithosphere

built system

human controlled habitats

support certain uses (gardens, playing fields)

support aesthetics (parks)

support functional objectives (noise barriers)

vacant areas with no human management

develop habits that are colonized naturally

results in contrasting communities

why do cities have a larger diversity of species

diversity of microhabitats, introduced species, and different levels of management

wetlands and aquatic environments

important for many organisms but are usually considered undesirable for development and may be drained to reduce insect harassment

species composition

cities have introduced species either intentionally ior inadvertantly

intentional introduced species

decorative landscaping, horticulture, display

inadvertently introduced species

seeds, plants, insects, rodents, diseases

how alien species are introduced

railway lines and truck terminals, airports, garden centres, ports, individuals

impacts and consequences of introduced species

• they can replace native species but at the same time increase biodiversity of the ecosystem

• can be resistant, fast growing, and adaptive BUT can be a nuisance for construction and green space management

• urban habitats are unique and can be regionally of high value for conservation of endangered species

disturbance

a discrete event in time that disrupts an ecosystem

colonization

the ability of species to establish and survive as plants or seeds, or re-colonize by dispersal through wind, water, animals, and humans

dispersal

can be greatly enhanced in a city because of large flows of people, vehicles, soil import, manure, mulches, swapping seeds, and cuttings

succession

describes the gradual replacement of species through time, usually after a disturbance

succession without human intervention

bare soil → herbs → shrubs → woodland

succession in cities

best recognized on disturbed sites

initial colonizing species are distinct as they flourish in disturbed soils, aka weeds

effects of urban vegetation on ecosystem components

• cooling through shading and transpiration

• delays and reduces storm-water run off

• litter fall increases soil formation, roots increase soil porosity

• positive effects on air quality and noise propagation

• provides habitats for animals and food for urban wildlife

urban wildlife

changing city context favours colonizing species over long-term resident species

drastic loss of already otherwise rare or endangered species

indigenous species lost to competition with invaders, crowded out, or due to stress

main stresses for urban wildlife

human disturbances

loss of habitat, food, resources

noise, light, traffic

pollution, toxins, disease

main benefits for urban wildlife

milder climate (UHI)

indoor spaces, urban vegetation

abundant food from waste, human supplements

fewer predators

urban impacts on wildlife

• destruction/alteration of habitat

• creation of new habitat

• supplementary food supplies

• extinction of some species

• introduction of new species

• some adaptation

Urban avoiders

species that are sensitive to changes in habitat and generally disappear during urban development

species that are having a large home range are mostly affected by increasing fragmentation during urbanization

ex: grizzly/black bear, cougar, elk

urban adapters

species that are adaptable and thrive on urban resources

usually ‘edge’ or early successional native species that can also use urban resources

ex: raccoon, coyote, crows

urban exploiters

species that exploit the urban environment with a close relationship with humans, rely heavily on human subsidies

ex: cockroaches, brown rat, house sparrow, pigeon

urban mammals

urban species have a smaller home range than rural counterpart

human control driven by fear

ex: grey squirrel, mice, hedgehog, fox, oppossum, skunk

urban birds

usually considered attractive, hence tolerated

diversity increases in city centers but suburban areas as rich as country sides

inner cities are rich in abundance but few species, primarily cliff divers

urban insects

constant import of insects in food, furniture, on plants, and animals

dead wood in construction materials and building, bridges, and fences are breeding sites

ex: flies, roaches, silver fish, weevils, termites, beatles

conservation of urban habitats - species specific

protection of regionally/globally rare plants and animals that found a niche in urban ecosystems to maintain biodiversity

conservation of urban habitats - habitat specific

protection of endangered habitats due to urbanization to maintain ecosystem functions and refufe

island biogeography applied to cities

in city remnant ‘islands’ of vegetation and animals with their diversity is related to

• size of area

• connections with other sites

patch

a relatively homogenous area that differs from its surroundings

corridor

an area of habitat connecting patches

matrix

the ‘background ecological system’ within which patches and corridors are set

in urban areas the matrix is usually the built environment

mosaic

the pattern of patches, corridors, and matrix that form an urban landscape in it’s entirity

network

an interconnected system of corridors

connectivity

a measure of the closeness, links, and degree of spatial continuity of a corridor and network of patches

arrangement and size of habitat

the arrangement and size of a habitat is crucial

fragmentation is very negative and linear

linking green space is vital - especially true for larger animals

Earthquake liquefaction

during an earthquake some water saturated materials may loose their strength and transform into a fluid losing ability to support infrastructure

landslide risk

in Metro Vancouver, along the north shore mountains and also the shorelines and riverbanks are most at risk

linked to orography (slope steepness) and subsurface materials

recent volcanic deposits most at risk

bearing capacity and subsidence

bearing strength of the ground must be larger or equal to pressure imposed by a building/structure

groundwater table

the ancient lake bed is a variable mixture of clay and volcanic soil

as the ground water table sinks, the surface sinks unevenly

challenges with subsurface materials

engineers should know the bearing strength at least to a depth of 2W

strength should be spatially uniform

situation on slopes more complicated, as bearing pressure is not symmetric

coastal erosion and lost settlements

coastal cities are prone to marine erosion and flooding

coastal erosion limits the expansion of settlements

coastal settlements are further threatened by increased sea level due to climate change

why are hazardous areas often areas of intense and rapid urbanization?

low lying coastal areas

volcanic soils are fertile

floodplains and deltas are fertile and flat

faults in rocks can trap and transport water

ecosystem services of urban soils

soils are the interface between biosphere, hydrosphere, atmosphere

important components of strategies to promote sustainable urban development

what do urban soils provide

habitat

regulator services

resources

urban soils

usually takes 1000s of years to form a fully developed soil profile

can be destroyed by bulldozers in minutes or by erosion in a season

impacts on soil after construction

stripping

mixing

importation

compaction

land consumption

productive soils are removed or paved over otherwise degraded as urban expansion progresses

properties of urban soils

great vertical and spatial variability

modified soil structure leading to compaction

presencce of anthropogenic materials and contaminants

interrupted nutrient cycling and modified soil organism activity

presence of surface crust on bare soil

restriction aeration and restricted water drainage

modified soil temperature regimes

formation of ‘rubble’ soils

decaying bricks, mortar, litter, pollutants, form soil

the amount of this parent material is huge in cities

technosols

soils that contain at least 20% anthropogenic materials in the top 1m

have lots of carbonates and alkalinity

soil formation pathways in urban environments

humus enrichment

carbonate enrichment

water-logging

reductomorphic processes as a result of anaerobic conditions

soil erosion in cities

removal of cover during construction is the most damaging phase

compaction hastens runoff and therefore erosion, leads to gullying and rapid losses in storms

erosion also takes nutrients from soils and deposits them in aquatic systems

soil moisture changes

‘water proofing’ of surface and groundwater pumping cause desiccation of urban soils

over watering causes leaching nutrients and minerals, fertilizer/biocide down wash, landslides, waste of water

problems with earth system processes: cold climates

permanently frozen ground

overlaying active layer require special types of construction and foundations for buildings and infrastructure

problems with earth system processes: arid climates

water supply problems, wind erosion, flash floods

possibility of salt weathering of building materials and foundations

problems with earth system processes: tropical climates

rapid weathering and decomposition of building materials

deep and uneven weathering of most rocks in tectonically stable areas

frequent rain events causing rapid water erosion of exposed ground surfaces

surface warming underneath cities

surface warming due to urbanization modifies the temperature of the ground so that near the surface, ground temperatures are increased