principles of landscape ecology140.126.122.189/upload/1071/b07305a201868204701.pdf · forman. 1996....

Challenges, Threats & Opportunities 1

Principles of Landscape Ecology

Learning OutcomesLearning Outcomes

n Learn terminology associated with landscape ecology principles—patches, buffers, fragmentation, corridors, edges, and matrixes

n Understand how landscape characteristics 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 Ecology Principles to Follow:

Source for Landscape Ecology Principles 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 Island Press.


Landscape EcologyLandscape Ecology

Landscapes are living systems with 3 broad characteristics: structure,

function, and changelandscape structure—spatial pattern or

arrangement of landscape elementslandscape function—movement and flows

of animals, plants, water, wind, materials and energy

landscape change—dynamics of spatial pattern 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

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imm

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tion

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extin

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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

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imm

igra

tion

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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 than smaller 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 forspecies movement. They also contain uncommon species where larg e 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 maintaining species richness. Where one patch contains a limited portion of the 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.

RecolonizationRecolonizationA 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 is curvilinear 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 interaction

When 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 BoundariesA 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 BoundariesA curvilinear “tiny-patch” boundary may provide ecological benefits such as less soil erosion and greater wildlife usage.

Edge Curvilinearity and Width Edge Curvilinearity and Width Curvilinearity 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 ShapeAn 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 OrientationA 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 Habitatfragmentation—breaking up larger, intact habitat

into 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 more habitats

attrition—disappearance of one or more habitat patches

Corridors and ConnectivityCorridors and ConnectivityContinued habitat loss and isolation requires

landscape connectivity

--wildlife movement corridors and stepping stones--corridors may function as barriers or filters to species movement

--stream or river systems are especially significant 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 to scale 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 ConnectivityA row of stepping stones or patches is intermediate between 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 fine particles 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 from the 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 AlternativesAlternate 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 SizeAs mesh size of a network decreases, probability of survival drops sharply for species that avoid or is inhibited by corridors.

Intersection EffectIntersection EffectAt 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 PatchA 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 ofexotic species, a nature reserve may be protected against damage by invaders using a buffer zone with strict controls on wildlife species.


Grain Size of MosaicsGrain Size of MosaicsA coarse-grained landscape containing fine-grained areas is optimum to provide for large patch ecological benefits.

Animal Perception of Scale and FragmentationAnimal Perception of Scale and FragmentationA finely-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 ScaleApplications 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 change in the environment depends on

where change occurs …

Human reactions to visual change in the environment depends on

where change occurs …

n Immediate foreground: up to 100m awayPeople see fine details (leaf, broken limbs)n Foreground: 100-800m awayGeneral shape and scale most importantn Middle ground: 800-6400m awayPatterns and topography dominate n Background: more than 6400m awayBlocks of color is main perception

Assessing visual qualityAssessing 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 landforms contribute to the landscape character?

n Do environmental elements change with the seasons? Special species blooms when ---e.g. raffelesia ?


Scenic Management Strategies Scenic 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 natural disturbance]

n Put signs up explaining reforestation of clearcuts

principles of landscape ecology140.126.122.189/upload/1071/b07305a201868204701.pdf · forman. 1996....

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