Roads, Fragmentation, and Edges Lecture 19 April 26, 2005

1. Roads, Fragmentation, and EdgesLecture 19April 26, 2005

2. What is fragmentation? 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.’ Cadiz Township southeastern WI

3. What is fragmentation? What Causes Fragmentation? Roads Clearcuts Agriculture Housing Development Recreation Other? What are the effects? Edge effects Many effects are highly cause dependent. Alteration of the flow of information, energy, and matter…

4. How does fragmentation relate to landscape ecology? Fragmentation Energy The Landscape Information Matter 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.

5. 1.0 Perforated Edge 0.6 Transitional Proportion of habitat 0.4 Habitat Patch 0.0 0.0 1.0 P The probability that the neighbor is the same habitat. What is fragmentation? Adapted from: Riitters, K., Wickham, J., Coulston, J. 2000 Ecology and Society 4(2) [online] Interior

6. 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]

7. Edge Effects 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. Dr. Thomas D. Hayes Wind River Experiment Forest, Washington.

8. Edge Effects Edges Energy The Landscape Information Matter Generally applies to any cause of fragmentation that creates sharp boundaries. Energy: Sunlight Wind Information: Barrier to seed dispersal Matter: Barrier to precipitation

9. How do we measure edge?Metrics of edge intensity Total edge length Edge density Edge contrast Edge persistence Various combinations of above Contrast Floristic or type contrast Structural contrast

10. How do we measure edge?Metrics of edge intensity Greater total length Greater persistence versus

11. Roads

12. Roads • 15-20% of US impacted • 1% of US = road corridor • 6.2 million km • 10% in Nt’l Forests • 1% of roads are interstate highways • Trends: • Road density increasing slowly. • Vehicle Miles Traveled increasing rapidly. • from Richard T.T. Forman.

13. Roads: Critical Considerations Key variables: road width and symmetry road usage intensity connectivity of road network surface type age of the road Key feature: Permanence! from Richard T.T. Forman.

14. Direct Effects of Roads Roads Energy The Landscape Information Matter 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.

15. Indirect Effects of Roads Roads Energy Indirect Facilitation of Human Activity The Landscape Information Matter 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. landscape pattern Roads

16. Roads: a critical source of fragmentation Riitters, K., Wickham, J., Coulston, J. 2004 Ecology and Society 9(2): 13 [online]

17. Fragmentation due to Clearcuts

18. Fragmentation due to Clearcuts landscape pattern 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.

19. Fragmentation due to Clearcuts Franklin & Forman 1987 Landscape Ecology 1: 5-18

20. Fragmentation due to Clearcuts Susceptibility of forests in the Douglas-fir region to various damaging agents Landscape area gradient created by checkerboard cutting. Potential for windthrow in residual forest patches. Potential for wildfire ignition and spread. Franklin & Forman 1987 Landscape Ecology 1: 5-18 0 25 50 75 100 Cutover area in landscape

21. Fragmentation due to 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 1987 Landscape Ecology 1: 5-18 0 25 50 75 100 Cutover area in landscape Checkerboard model

22. Example:Edge effects due to clearcuts Dr. Thomas D. Hayes Wind River Experiment Forest, Washington.

23. Effects of Edges: Microclimate Dr. Thomas D. Hayes Wind River Experiment Forest, 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.

24. Dr. Thomas D. Hayes Wind River Experiment Forest, Washington.

25. Effects of Edges: Organic Matter • 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. Source: Dr. Thomas D. Hayes Wind River Experiment Forest, Washington.

26. Other Causes of Fragmentation Development - notably seasonal housing. Recreation (‘Wreck-reation’) More permanent than clearcuts. Not readily detected with remote sensing. Serves as ‘effective fragmentation’ to many organisms, e.g. wolves.

27. Other Causes of Fragmentation Dams fragment riparian ecosystems Photo credit: PacifiCorp Holdings, Inc.

28. Mitigation of Fragmentation

29. Mitigation of Fragmentation Banff, Canada Reconnect the landscape: Overpasses and Underpasses Zoning for corridors Corridor restoration (next lecture)

30. Mitigation of Fragmentation • Removal of Barriers - small scale restoration • Road Removal • Dam Removal • WI has been the leader • 1000s of dams removed Breaching and removal of the Shopiere Dam, Turtle Creek, Wisconsin. Photo courtesy of Wisconsin Department of Natural Resources.

31. Metrics of Landscape Configuration Relevant toRoads and Fragmentation

32. Fragmentation Metrics Core area Number of core areas Mean core area Variation in core area Core Area Edge effect distance Less core area More core area

33. Fragmentation Metrics • Connectivity • Refers to functional connections between patches. • The “functional connection” depends on • the 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 Sample Metrics: Connectance Patch cohesion index Traversability index

34. Fragmentation Metrics Isolation/proximity Mean nearest neighbor distance Index of Proximity High isolation/low proximity Low isolation/high proximity

35. Fragmentation Metrics Dispersion Nearest Neighbor Relative Variance Index Nearest Neighbor Index of Dispersion High Dispersion Low Dispersion

36. Fragmentation Metrics Contagion Contagion index Lacunarity Low contagion High contagion