Lecture 9 Landscape Ecology

7/27/2019 Lecture 9 Landscape Ecology

http://slidepdf.com/reader/full/lecture-9-landscape-ecology 1/21hallenges, Threats & Opportunities

Principles of

Landscape Ecology

Learning OutcomesLearning Outcomes

n Learn terminology associated withlandscape ecology principles—patches,

buffers, fragmentation, corridors, edges,

and matrixes

n Understand how landscapecharacteristics and patterns influence

the distribution and survivability of

species

n Be able to apply principles to project

design and land use planning

Source for Landscape EcologyPrinciples to Follow:

Source for Landscape EcologyPrinciples to Follow:

Dramstad, W.E., Olson, J.D., and R.T.

Forman. 1996. Landscape Ecology

Principles in Landscape Architecture and Land-Use Planning . Washington,

DC: Harvard University and IslandPress.



Landscape EcologyLandscape EcologyLandscapes are living systems with

3 broad characteristics: structure,function, and change

landscape structure —spatial pattern orarrangement of landscape elements

landscape function —movement and flowsof animals, plants, water, wind,materials and energy

landscape change —dynamics of spatialpattern and function over time

Landscape ElementsLandscape Elementsn Patches —differentiated by size,

number, and location; e.g., large or

small, round or elongated, few or numerous, dispersed or clustered

n Corridors —attributes are narrow or

wide, straight or curvy, continuous or

disconnected .

n Matrix —attributes are single or subdivided, variegated or homogenous,

continuous or perforated

High

Low

R a t e o f i m m i g r a t i o n

o r e x t i n c t i o n

Equilibrium number

Immigration and extinction rates

Number of species on island

(a)

© 2004 Brooks/Cole – Thomson Learning

Theory of

island

biogeography

(a.k.a. species

equilibrium

model)– number

of species is

determined by

balance

between species

immigration

rate and

species

extinction rate

High

Low

R a t e o f i m m i g r a t i o n

o r e x t i n c t i o n

Small island

Effect of island size

Number of species on island

(b)

Large island

© 2004 Brooks/Cole – Thomson Learning

With time,

larger

islands have

larger

equilibrium

number of

species thansmaller

islands



PatchesPatches

Edge Habitat and SpeciesEdge Habitat and SpeciesDividing a large patch into two smaller ones

creates additional edge habitat leading to greater

number of edge species

Interior Habitat and SpeciesInterior Habitat and SpeciesDividing large patch into two smaller ones

removes interior habitat reducing population

sizes and number of interior species

A larger patch has larger population size for a

given species than smaller patch, making it less

likely that the species will go locally extinct

Local Extinction ProbabilityLocal Extinction Probability



ExtinctionExtinctionProbability of species becoming locally extinct is

greater if a patch is small or of low habitat quality

A large patch is likely to have more habitats

present and therefore contain a greater number

of species

Habitat DiversityHabitat Diversity

Barrier to DisturbanceBarrier to DisturbanceDividing large patch into two smaller ones

creates barrier to spread of some disturbances

Large Patch BenefitsLarge Patch BenefitsLarge patches of natural vegetation (e.g., forest) protect aquifers and

interconnected stream networks, sustain viable populations of interior species, provide core habitat and escape cover for large-home-range

vertebrates and permit near natural disturbance regimes



Small Patch BenefitsSmall Patch BenefitsSmall patches provide different and supplemental ecological benefits.

When they interrupt extensive matrix, act as stepping stones for

species movement. They also contain uncommon species where large

patches are absent or are unsuitable for a species..

Habitat LossHabitat LossRemoving a patch causes habitat loss, reducing

population size of a species dependent on that

habitat type leading to fewer species

Metapopulation DynamicsMetapopulation DynamicsRemoval of patch reduces size of metapopulation (interacting

subdivided population) increasing the probability of local, withi n-

patch extinctions, slowing down recolonization, and reducing

stability of metapopulation

Number of Large PatchesNumber of Large PatchesWhere one large patch contains almost all the species for that patch

type, two large patches may be considered minimum for mainta ining

species richness. Where one patch contains a limited portion ofthe

species pool, up to four or five large patches are probably required.



Grouped Patches as HabitatGrouped Patches as HabitatSome generalist species can survive in a number

of nearby smaller patches, although individually

inadequate, are together suitable.

ExtinctionExtinctionProbability of species going locally extinct is greater in

isolated patch. Isolation is a function of both distance and

characteristics of the matrix habitat.

RecolonizationRecolonization A patch located close to other patches or the “mainland” will have

higher chance of being re-colonized within a time interval than more

isolated patch.



Patch Selection for ConservationPatch Selection for ConservationSelection of patches for conservation should be based on 1)

contribution to overall system (relation to other links or patches) and 2)

unusual or distinctive characteristics (rare, threatened, or endemic

species).

Edges and BoundariesEdges and Boundaries

edge or boundary—outer portion of patch where

environment differs from interior of patch

--whether a boundary or edge iscurvilinear or straight influences the flow of

nutrients, water, energy, and species along or

across it.

--boundaries may be ‘political’ or ‘administrative’ (artificial)

--human development influences

interaction between human-made and natural

habitats

Edge Structural DiversityEdge Structural DiversityVegetative edges with high structural diversity, vertically,

or horizontally, are richer in edge animal species.

Edge WidthEdge WidthEdge width differs around a patch with wider edges on on sides

facing predominant wind direction and solar exposure.



Florida

Administrative and natural

ecological boundary interaction

Administrative and natural

ecological boundary interactionWhen administrative boundary of protected area doesn’t coincide

with ecological boundary, the area between boundaries often

becomes distinctive and may act as buffer, reducing influence oninterior of protected area.

Edge as FilterEdge as FilterPatch edges normally act as filters that dampen the

influence of the surroundings on the patch interior.



Edge AbruptnessEdge AbruptnessIncreased edge abruptness increases movement along

an edge whereas less edge abruptness favors movement

along an edge.

Example of Edge AbruptnessExample of Edge Abruptness

Natural and Human EdgesNatural and Human EdgesMost natural edges are curvilinear and complex, whereas

humans tend to make straight, simple, and hard edges.



Straight and Curvilinear BoundariesStraight and Curvilinear Boundaries A straight boundary tends to have more species

movement along it while a more complex boundary is

likely to have movement across it.

Hard and Soft BoundariesHard and Soft Boundaries A curvilinear “tiny-patch” boundary may provide

ecological benefits such as less soil erosion and greater

wildlife usage.

Edge Curvilinearity and WidthEdge Curvilinearity and WidthCurvilinearity and edge width determine the total amount

of edge habitat within a landscape.



Coves and LobesCoves and LobesCoves and lobes along an edge provide greater habitat

diversity than a straight edge encouraging higher species

diversity.

Edge and Interior SpeciesEdge and Interior SpeciesMore convoluted patches have a higher proportion of

edge habitat, slightly increasing the number of edge

species, but sharply decreasing interior species.

Interaction with SurroundingsInteraction with SurroundingsThe more convoluted the shape of a patch, the more

interaction (both positive or negative) between the patch

and the surrounding matrix.

Ecologically ‘Optimum’ Patch ShapeEcologically ‘Optimum’ Patch Shape An ecologically optimum patch provides several ecological benefits

an is generally “spaceship shaped” with rounded core plus curvilinear

boundaries and fingers for species dispersal.



Shape and OrientationShape and Orientation A patch oriented with its long axis parallel to the dispersal

route will have lower probability of being recolonized.

Loss and Isolation of HabitatLoss and Isolation of Habitat

fragmentation—breaking up larger, intact habitatinto smaller dispersed patches

dissection—splitting an intact habitat into two

patches separated by a corridor

perforation—creating holes within essentially

intact habitat

shrinkage—decrease in size of one or morehabitats

attrition—disappearance of one or more habitat

patches

Corridors and ConnectivityCorridors and Connectivity

Continued habitat loss and isolation requireslandscape connectivity

--wildlife movement corridors and stepping

stones

--corridors may function as barriers or filters to

species movement

--stream or river systems are especiallysignificant corridors in landscapes



Controls on Corridor FunctionsControls on Corridor FunctionsWidth and connectivity control the 5 major functions of

corridors: habitat, conduit, filter, source, and sink.

Corridor Gap EffectivenssCorridor Gap EffectivenssEffect of corridor gap depends on length of gap relative toscale of species movement and contrast between corridor

and gap.

Structural vs. Floristic SimilarityStructural vs. Floristic SimilaritySimilarity in vegetation structure and floristics(plant species)

between corridors and patches is preferable but similarity in structure

alone may be adequate for interior species movement.

Stepping Stone ConnectivityStepping Stone Connectivity A row of stepping stones or patches is intermediatebetween a corridor and no corridor in providing for interior

species movement.



Distance Between Stepping StonesDistance Between Stepping StonesFor highly visual species, the effective distance for

movement between stepping stones is the ability to see

each successive stepping stone.

Stepping Stone LossStepping Stone LossLoss of one small patch functioning as stepping stone for movement inhibits movement and increases patch

isolation.

Cluster of Stepping StonesCluster of Stepping StonesThe optimal spatial arrangement of a cluster of stepping stones

between large patches provides alternate or redundant routes whi le

maintaining linear orientation between large patches.

Roads and “trough” CorridorsRoads and “trough” CorridorsRoad, railroad, powerline, and trail corridors tend to be connected,

relatively straight, and subject to regular human disturbance. Act as:

1) barriers that subdivide populations of species into metapopultions;

2) conduits for disturbance tolerant species; 3) sources of erosion,

sedimentation, exotic species and human effects on matrix.



Wind Erosion and ControlWind Erosion and ControlModest winds reduce soil fertility by removing and blowing fineparticles long distances. Wind erosion control reduces field size in

the preponderant wind direction and maintains vegetation, furrows, or

soil clods in spots susceptible to vortices.

Stream Corridor and Dissolved SubstancesStream Corridor and Dissolved SubstancesDissolved substances (nitrogen, phosphorus, toxins) entering

vegetated stream corridor are controlled from entering the channel

and reducing water quality by friction, root absorption, clay, and soil

organic matter. Wide corridors of dense natural vegetation are most

effective.

Corridor Width for Main StreamCorridor Width for Main StreamTo maintain natural processes, maintain interior upland habitat on

both sides wide enough to control dissolved substance inputs fromthe matrix; also provides conduit for upland interior species and

habitat for floodplain species displaced by flooding or lateral channel

migration.

Corridor Width for a RiverCorridor Width for a RiverTo maintain natural processes, maintain upland habitat on both sides as a

conduit for upland interior species displaces by lateral channel migration. A

“ladder pattern” of large patches crossing the floodplain provides a hydrologic

sponge, traps sediment, provides organic soil matter for aquatic food chain,

logs for fish, and habitats for rare floodplain species.



Connectivity of a Stream CorridorConnectivity of a Stream CorridorWidth and length of vegetated stream corridors interact to deter mine

stream processes. A continuous stream corridor, without major g aps,

is essential to maintain cool water temperature and high oxygen

content required by certain fish species.

Landscape MosaicsLandscape Mosaicsecological health of landscape measured by

connectivity of natural systems.

mosaics reflect the pattern and scale of

landscapes.

corridors interconnect to form networks.

Networks exhibit connectivity, circuitry, and

mesh size.

Spatial scale is perspective from which landscape

is analyzed--ranges from fine scale (zoomed

in) to broad scale (zoomed out)

Network Connectivity and CircuitryNetwork Connectivity and CircuitryConnectivity (degree to which all nodes are connected) combined

with circuitry (degree to which alternate routes are present) indicates

how simple or complex a network is and provides index of

effectiveness of linkages for species movement.

Loops and AlternativesLoops and Alternatives Alternate loops or routes in a network reduce negative effects of

gaps, disturbances, predators, and hunters within corridors.



Corridor Density and Mesh SizeCorridor Density and Mesh Size As mesh size of a network decreases, probability of

survival drops sharply for species that avoid or is inhibited

by corridors.

Intersection EffectIntersection Effect At intersection of natural vegetation corridors, commonly

a few interior species are present and species richness is

higher than elsewhere in network.

Species in a Small Connected PatchSpecies in a Small Connected Patch A small patch or node connected to a network of corridors

is likely to have more species and lower rate of local

extinction than equal sized isolated patch.

Dispersal and Small Connected PatchDispersal and Small Connected PatchSmall patches or nodes along a network provide effective

habitat for individuals to pause and/or breed, resulting in

higher survival rate for dispersing individuals.



Loss of Total vs. Interior HabitatLoss of Total vs. Interior HabitatFragmentation decreases total amount of a habitat type,

but proportionally causes much greater loss of interior

habitat.

Fractal PatchesFractal PatchesFractal configuration is natural reaction to transition, with

isolated patches reacting similarly to disturbance as a

group.

Suburbanization, Exotics, and Protected AreasSuburbanization, Exotics, and Protected AreasIn landscapes undergoing urbanization and consequent invasion of

exotic species, a nature reserve may be protected against damageby

invaders using a buffer zone with strict controls on wildlife species.



Grain Size of MosaicsGrain Size of Mosaics A coarse-grained landscape containing fine-grained areas

is optimum to provide for large patch ecological benefits.

Animal Perception of Scale and Fragmentation Animal Perception of Scale and Fragmentation A fine ly-fragmented habitat is normally perceived as continuous

habitat by wide ranging species whereas coarsely fragmented habi tat

is discontinuous to all species except the most wide-ranging animals.

Specialists and GeneralistsSpecialists and GeneralistsSpecialist species are more likely to be negatively affected by fine-

scale fragmenation than are generalist species of similar size.



Mosaic Patterns for Multihabitat SpeciesMosaic Patterns for Multihabitat SpeciesMultihabitat species are favored by 1) “convergency points” where

three or more habitats converge, 2) “adjacencies” where different

combinations of habitats adjoin, and 3) habitat “interspersion” where

habitats are scattered rather than aggregated.

Applications Vary by Scale Applications Vary by Scalen Macro or regional scale

--regional wildlife conservation park or

forest reserve

--forest plan

--new suburban development project

n Meso or landscape scale

--new roads or powerline corridors

n Micro or site scale

--smaller logging concession

Human reactions to visual changein the environment depends on

where change occurs …

Human reactions to visual changein the environment depends on

where change occurs …

n Immediate foreground: up to 100m away

People see fine details (leaf, broken limbs)

n Foreground: 100-800m away

General shape and scale most importantn Middle ground: 800-6400m away

Patterns and topography dominate

n Background: more than 6400m away

Blocks of color is main perception

Assessing visual quality Assessing visual quality

n What types of trees grow in area?

n Age, maturity and density?

n What shape, colors and tecture do trees and

vegetation create?

n Are there water features that draw

attention?

n How do rock outcrops and landformscontribute to the landscape character?

n Do environmental elements change with the

seasons? Special species blooms when ---

e.g. raffelesia?


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Scenic Management StrategiesScenic Management Strategies

n Buffer zones along roads “viewshed”

n Do not harvest at top of ridges

n Natural appearing clearings with edges

and curves [could be fire or naturaldisturbance]

n Put signs up explaining reforestation of

clearcuts

Lecture 9 Landscape Ecology

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