Roads, Fragmentation, and Edges Lecture 19 April 26, 2005
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Roads, Fragmentation, Roads, Fragmentation, and Edges and Edges Lecture 19 Lecture 19 April 26, 2005 April 26, 2005
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Roads, Fragmentation, and Edges Lecture 19 April 26, 2005. What is fragmentation?. Definitions various: Riitters 2002: `Fragmentation refers to the amount of [habitat] and its spatial pattern.' - PowerPoint PPT Presentation
Transcript of Roads, Fragmentation, and Edges Lecture 19 April 26, 2005
Roads, Fragmentation, and Roads, Fragmentation, and EdgesEdges
Lecture 19Lecture 19
April 26, 2005April 26, 2005
Definitions various:Riitters 2002: `Fragmentation refers to the amount of [habitat] and its spatial pattern.'
Noss & Cooperrider 1994: ‘Process by which habitats are increasingly subdivided into smaller units, resulting in their increased insularity as well as losses of total habitat area.’
What is fragmentation?What is fragmentation?
Cadiz Townshipsoutheastern WI
What Causes Fragmentation?RoadsClearcutsAgricultureHousing DevelopmentRecreationOther?
What are the effects?Edge effectsMany effects are highly cause dependent.
Alteration of the flow of information, energy, and matter…
What is fragmentation?What is fragmentation?
How does fragmentation relate to How does fragmentation relate to landscape ecology?landscape ecology?
TheLandscape
Energy
Information
Matter
Fragmentation
Energy: Decrease disturbance spread.Increase some localized disturbance severities.
Information: Decrease spread of native organisms? Increase spread of exotic organisms?
Matter: Increase the flow of water.
What is fragmentation?What is fragmentation?
1.0
0.6
0.4
0.00.0 1.0P
The probability that the neighbor is the same habitat.
Proportion of habitat
Habitat Patch
Transitional
Perforated
Edge
Adapted from:Riitters, K., Wickham, J., Coulston, J. 2000 Ecology and Society 4(2) [online]
Interior
What is fragmentation?What is fragmentation?Highly sensitive to scale! b, c, d, e = 81 km 2, 729 km 2, 6561 km 2 , and 59049 km 2
Riitters, K., Wickham, J., Coulston, J. 2004 Ecology and Society 9(2): 13 [online]
EDGES = Transition areas where rates or magnitude of ecological transfers (energy, materials, nutrients) change abruptly in relation to transfers within patches (T. Hayes, adapted from Wiens et al., 1985).
EDGE EFFECTS = Interactions between two adjacent ecosystems separated by abrupt a transition area.
Edge EffectsEdge Effects
Dr. Thomas D. HayesWind River ExperimentForest, Washington.
Edge EffectsEdge Effects
TheLandscape
Energy
Information
Matter
Edges
Energy: SunlightWind
Information: Barrier to seed dispersal
Matter: Barrier to precipitation
Generally applies to any cause of fragmentation
that creates sharp boundaries.
Total edge lengthEdge densityEdge contrastEdge persistenceVarious combinations of above
Floristic or typecontrast
Structuralcontrast
How do we measure edge?How do we measure edge?Metrics of edge intensityMetrics of edge intensity
Contrast
How do we measure edge?How do we measure edge?Metrics of edge intensityMetrics of edge intensity
versus
Greater total length Greater persistence
RoadsRoads
RoadsRoads
15-20% of US impacted1% of US = road corridor6.2 million km10% in Nt’l Forests1% of roads are interstate
highways
Trends: • Road density increasing slowly.• Vehicle Miles Traveled
increasing rapidly.
from Richard T.T. Forman.
Roads: Critical Roads: Critical ConsiderationsConsiderations
Key variables: road width and symmetry road usage intensityconnectivity of road network surface typeage of the road
Key feature: Permanence!
from Richard T.T. Forman.
Direct Effects of RoadsDirect Effects of Roads
TheLandscape
Energy
Information
Matter
Roads
Energy: Decrease disturbance spread.
Information: Road kill.Decrease spread of native organisms. Increase spread of exotic organisms.
Matter: Increase the volume and velocity of water flow.Increase inputs of NOX, O3.
Indirect Effects of RoadsIndirect Effects of Roads
TheLandscape
Energy
Information
Matter
Roads
IndirectFacilitation ofHuman Activity
Roads increase fragmentation.Loss of interior habitat.Roads are networks that facilitate human activity.Roads increase the size and efficiency of human vectors of landscape change.
landscapepattern
Roads
Roads: a critical source Roads: a critical source of fragmentationof fragmentation
Riitters, K., Wickham, J., Coulston, J. 2004 Ecology and Society 9(2): 13 [online]
Fragmentation due to ClearcutsFragmentation due to Clearcuts
Fragmentation due to ClearcutsFragmentation due to Clearcuts
landscapepattern
Clearcuts
Clearcuts are less permanent. However, they require large roads networks.Clearcuts are perhaps more ambiguous than roads. Clearcuts may benefit some native species. Depending on disturbance frequency, may not increase exotic species.
Fragmentation due to ClearcutsFragmentation due to Clearcuts
Franklin & Forman 1987Landscape Ecology 1: 5-18
Fragmentation due Fragmentation due to Clearcutsto Clearcuts
Susceptibility of forests in the Douglas-fir region to variousdamaging agents
Landscape area gradient created by checkerboard cutting.
Franklin & Forman 1987Landscape Ecology 1: 5-18 P
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0 25 50 75 100Cutover area in landscape
Fragmentation due Fragmentation due to Clearcutsto Clearcuts
Changes in biotic characteristics of a Douglas-fir forest landscape along a cutting gradient.
(A) Diversity of species dependent on a forest interior environment. (B) Total species diversity in the landscape within cutover areas of the landscape. (C) Total game populations in the landscape.
Franklin & Forman 1987Landscape Ecology 1: 5-18
0 25 50 75 100Cutover area in landscapeCheckerboard model
Example:Example:Edge effects due to clearcutsEdge effects due to clearcuts
Dr. Thomas D. HayesWind River ExperimentForest, Washington.
Dr. Thomas D. HayesWind River ExperimentForest, Washington.
Measured climate in three edge environments: clearcut, near-edge, and far-edge
Diurnal surface temperatures are extremely variable in the three environments, due both to higher daily maximums and lower minimums, relative to interior forest in all seasons of the year.
During the growing season, forest-floor moisture is reduced up to 75 m into forest from edge.
In late winter and early spring, snow retention is reduced in the far-edge, relative to the other 3 forest environments.
Effects of Edges: MicroclimateEffects of Edges: Microclimate
Dr. Thomas D. HayesWind River ExperimentForest, Washington.
Litter fall is reduced up to 60 m into forest fragments more than 2 decades following edge creation.
Different measures of litter decomposition rates all show lower rates starting at 15-30 m and extending up to 90 m inside forest fragments.
Effects of Edges: Organic MatterEffects of Edges: Organic Matter
Source: Dr. Thomas D. HayesWind River ExperimentForest, Washington.
Other Causes of FragmentationOther Causes of Fragmentation
More permanent than clearcuts. Not readily detected with remote sensing.Serves as ‘effective fragmentation’ to many organisms, e.g. wolves.
Development - notably seasonal housing.
Recreation (‘Wreck-reation’)
Other Causes of FragmentationOther Causes of Fragmentation
Dams fragment riparian ecosystems
Photo credit:PacifiCorp Holdings, Inc.
Mitigation of FragmentationMitigation of Fragmentation
Mitigation of FragmentationMitigation of Fragmentation
Banff, Canada
Reconnect the landscape:Overpasses and UnderpassesZoning for corridorsCorridor restoration (next lecture)
Mitigation of FragmentationMitigation of Fragmentation
Removal of Barriers - small scale restorationRoad RemovalDam Removal
WI has been the leader1000s of dams removed
Breaching and removal of the Shopiere Dam, Turtle Creek, Wisconsin. Photo courtesy of
Wisconsin Department of Natural Resources.
Metrics of Landscape Metrics of Landscape Configuration Relevant toConfiguration Relevant toRoads and FragmentationRoads and Fragmentation
Core areaNumber of core areasMean core areaVariation in core areaCore
Area
Edge effectdistance
Less core area
More core area
Fragmentation MetricsFragmentation Metrics
Sample Metrics:ConnectancePatch cohesion indexTraversability index
Connectivity
Refers to functional connections between patches.
The “functional connection” depends onthe process or organism of interest.
May be based on:• Strict adjacency or a threshold
distance• A decreasing function of distance• A distance function weighted for
resistance – the least-cost path between patches
Fragmentation MetricsFragmentation Metrics
Isolation/proximityMean nearest neighbor distanceIndex of Proximity
Low isolation/high proximity High isolation/low proximity
Fragmentation MetricsFragmentation Metrics
DispersionNearest Neighbor Relative Variance IndexNearest Neighbor Index of Dispersion
Fragmentation MetricsFragmentation Metrics
High Dispersion
Low Dispersion
ContagionContagion indexLacunarity
Low contagion High contagion
Fragmentation MetricsFragmentation Metrics
