EEES4760/6760EEES4760/6760

Landscape EcologyLandscape EcologyJiquan chenJiquan chen

Feb. 25, 2009Feb. 25, 2009

1.1.FragmentationFragmentation

2.2.Island Biogeographic Theory (IBT)Island Biogeographic Theory (IBT)

1km

1km

50 m

81 ha

69 ha

59 ha

30 m

Case 7.2 (A) Degree of fragmentation of major river basins of the world

7.4 A fragmentation sequence

7.8 A constellation of separate habitat patches may be critical to the survival of individuals or populations

7.9 Many animals require a suite of different habitats or resources to meet life history needs

7.13 Roads can be significant barriers to the movement of small vertebrates and invertebrates

• Landscape structureLandscape structure• ·· Patch densityPatch density• ·· Patch sizePatch size• ·· Inter-patch distanceInter-patch distance• ·· ConnectivityConnectivity• ·· Boundary lengthBoundary length• ·· Interior/edge ratioInterior/edge ratio• ·· Maximum of core (interior forest)Maximum of core (interior forest)• ·· Total interiorTotal interior• ·· Stepping stonesStepping stones• ·· CorridorsCorridors

• SpeciesSpecies• ·· IsolationIsolation• ·· Number of generalistNumber of generalist• ·· Exotic speciesExotic species• ·· Nest predationNest predation• ·· Extinction rateExtinction rate• ·· Dispersal of interior speciesDispersal of interior species• ·· Large-home-range speciesLarge-home-range species• ·· Richness of interior speciesRichness of interior species

• OthersOthers• ·· Metapopulation dynamicsMetapopulation dynamics• ·· Genetic inbreedingGenetic inbreeding• ·· Size of disturbance patchesSize of disturbance patches• ·· Cumulative effects (rain, snow and Cumulative effects (rain, snow and

flooding effects)flooding effects)

EFFECTS OF FRAGMENTATIONEFFECTS OF FRAGMENTATION

The Checkerboard LandscapeThe Checkerboard LandscapePatterns of Patterns of clearcutting clearcutting development under development under various models(a-c) various models(a-c) Progression of Progression of clearcutting using clearcutting using the dispersed patch the dispersed patch model in which model in which areas are selected areas are selected for cutting so as to for cutting so as to be distributed be distributed regularly across the regularly across the landscape: shown landscape: shown are 25, 50, and 75% are 25, 50, and 75% cutover points. (e-cutover points. (e-f) Pattern of cutting f) Pattern of cutting at 50% point using at 50% point using single, four nucleus, single, four nucleus, and aggressive-and aggressive-parallel cutting parallel cutting systems. (Franklin systems. (Franklin & Forman 1987)& Forman 1987)

Susceptibility of Susceptibility of forests in the forests in the Douglas-fir region to Douglas-fir region to various damaging various damaging agent along a agent along a landscape cutting landscape cutting gradient as shown gradient as shown by the checkerboard by the checkerboard model model (Franklin & (Franklin & Forman 1987)Forman 1987)

Creating Creating Land Land MosaicsMosaics

An old-growth patch surrounded by a long rotation island that is cut in a An old-growth patch surrounded by a long rotation island that is cut in a programmed sequence such ( Harris 1984).programmed sequence such ( Harris 1984).

ConclusionsConclusions

•The number, size, and arrangement of the patches in a mosaic created by forest managers strongly influence the degree to which management objectives are fulfilled.

•Two recommendations are: (1) reduce the emphasis on dispersing small clearcut patches through the forest landscape, and (2) identify and reserve large patches of primeval forest in the landscape for maintenances of interior and amenity values.

•SLOSS debate

What do we want to know about fragmentation?What do we want to know about fragmentation?

• What are the relationships among patch area, shape, isolation, What are the relationships among patch area, shape, isolation, edge, the interaction of these factors, and various population and edge, the interaction of these factors, and various population and ecosystem? ecosystem?

• How do various landscape elements (e.g., corridors, linear How do various landscape elements (e.g., corridors, linear networks, and matrix) affect ecosystem processes and the networks, and matrix) affect ecosystem processes and the connectivity of populations in fragmented landscapes? connectivity of populations in fragmented landscapes?

• How do pattern-process linkages function in spatially and How do pattern-process linkages function in spatially and temporally dynamic landscapes across the range of spatial and temporally dynamic landscapes across the range of spatial and temporal scales? temporal scales?

• What levels of habitat loss and fragmentation does population What levels of habitat loss and fragmentation does population viability decline drastically? viability decline drastically?

• How long does it take population and ecosystem processes to How long does it take population and ecosystem processes to respond to physical changes in the landscape associated with respond to physical changes in the landscape associated with fragmentation? fragmentation?

Island Biogeographic Theory Island Biogeographic Theory 1. Early interest in habitat fragmentation arose from

island biogeographic theory (MacArthur & Wilson 1963 & 1967).

(MacArthur and Wilson, 1963)

19.4 – fish 198219.4 – fish 1982

(Preston, 1962; Nilsson et al. 1988)

19.3 – mammal 198919.3 – mammal 1989

The equilibrium The equilibrium model of island model of island

biogeography by biogeography by MacArthur and MacArthur and Wilson (1963)Wilson (1963)

Manipulative and Mensurative Manipulative and Mensurative ExperimentExperiment- Two Major Approaches- Two Major Approaches - -

• Manipulative experiment Manipulative experiment • Physically manipulates some attribute of the system in a Physically manipulates some attribute of the system in a

controlled manner, while holding all other attributes controlled manner, while holding all other attributes constant. constant.

• Mensurative experimentMensurative experiment• Simply observes or measures the system at different Simply observes or measures the system at different

locations or times locations or times • The treatment is the different conditions in space or The treatment is the different conditions in space or

time. time.

• Generally, manipulative experiments lead to stronger Generally, manipulative experiments lead to stronger inferences and therefore more reliable knowledge than inferences and therefore more reliable knowledge than mensurative experiments.mensurative experiments.

• An ideal manipulative experiment requires An ideal manipulative experiment requires

• The similarity among landscape minimizes the experimental The similarity among landscape minimizes the experimental errorerror

• The size of the landscape are functionally relevant to the The size of the landscape are functionally relevant to the process/organism(s) under considerationprocess/organism(s) under consideration

• Areal extent and configuration manipulation is needed to Areal extent and configuration manipulation is needed to assess independent and interactive of processes assess independent and interactive of processes

• Replication and randomReplication and random• Temporal and spatial controls (natural variability)Temporal and spatial controls (natural variability)• Observing the delayed effect Observing the delayed effect

Mensurative ExperimentMensurative Experiment• Can overcome some of the important limitations Can overcome some of the important limitations

• The practical and logistical difficulties of implementing The practical and logistical difficulties of implementing large-scale treatment large-scale treatment

• No practical limit to the spatial or temporal scale of the No practical limit to the spatial or temporal scale of the study system study system

• Flexibility in time lag effect Flexibility in time lag effect

• Still problems … Still problems … • Additional sources of variation associated with Additional sources of variation associated with

inconsistent and uncontrolled past perturbations inconsistent and uncontrolled past perturbations • Lack in pretreatment control – owing to substituting space Lack in pretreatment control – owing to substituting space

for time – inherent variability and autocorrelation for time – inherent variability and autocorrelation

• Landscape level studyLandscape level study• Isolation of a process Isolation of a process • Extinction threshold/ time lag/ synergisms Extinction threshold/ time lag/ synergisms

between habitat area and configuration between habitat area and configuration • Inequity in the organismal focus Inequity in the organismal focus

• Invertebrates, reptiles, and amphibians Invertebrates, reptiles, and amphibians • Replication / poorly controlled Replication / poorly controlled • Spatial information Spatial information

Lack in …Lack in …