Forest fragmentation reduces habitat area and increases isolation. It progresses from habitat loss to perforation to further reduction in patch sizes. Graph theoretic approaches can assess connectivity through representation of patches as nodes and dispersal corridors as links. For tree canopy in Prince George's County, MD, all patches are connected at 2,300 feet. Top patches providing intra-patch, flux, and connector connectivity are identified. Protecting these high ranking patches preserves around 35-47% of connectivity based on different graph metrics.

1. Forest Fragmentation:
The State of Our Forests
and Prospects for
Conservation
Maile C. Neel

2. Taryn Sudol Nikolaus Anderson
Sustainable
Development and Norton-Brown
Conservation Herbarium
Program
Thanks to Prince George’s County for access to tree canopy and Green Infrastructure data

4. The Three R’s : Representation, Redundancy and Resilience
The 3 R’s rest on of the premise that
biodiversity conservation is about space –
space in which species go about the activities
that allow them to shelter, feed and breed.
Shaffer and Stein (2000) Our Precious Heritage

5. Three R’s : Representation, Redundancy and Resilience
Represent sites that support species or processes of interest
Include redundant sites to protect against catastrophic loss
Choose sites that are resilient to disturbance
Large
Well connected to other sites

6. Photos from Buzzle

7. Fragmentation includes both habitat loss and isolation
Extensive continuous habitat
Increasing
Habitat
Loss Reduced extent
See incision into habitat
Increased edge effects
Perforation
Additional reduction in area
Yet more reduction in area
More patches
Isolation of small, remnant patches

8. Increasing
Amount of
Aggregation
Increasing Amount of Habitat
Neel et al. 2004, Landscape Ecology

16. You Are 146,171 acres total
Here 28,055 patches
Mean Patch Size: 5.3 acres
Median Patch Size: 0.3 acres
Largest Patch: 6,690 acres
47% of land area in
the county

17. 20000
15000
Number of Patches
10000
5000
0
1 10 50 100 500 1000 3000 >5000
Patch Area (Acres)

18. National Land Cover Data Set Classification
Developed
Forested
Agriculture
Miles
0 1.75 3.5 7 10.5

20. Examples of tree
canopy in
developed areas

22. 106,063 acres total
9,818 patches
Mean Patch Size: 10.8 acres
Median Patch Size: 0.26 acres
Largest Patch: 3,971 acres
Green Infrastructure
Tree Canopy in GI
Miles
0 1.75 3.5 7 10.5

23. 7000
6000
5000
Number of Patches
4000
3,456 patches are ≥1 acre
3000
2000
1000
0
1 10 50 100 500 1000 3000 >5000
Patch Area (Acres)

25. Only 1,006 patches have
any habitat farther than
180 feet from an edge.

27. Graph Theoretic Approaches to Connectivity Assessment
Links
Patches
Components:
All individual patches
(nodes)
&
Patches joined by links
(edges)
•Number of Components at a particular distance
•Distance at which all nodes form one component
•Number of nodes in the largest component

28. Three Sources of Connectivity
Area Within Continuous Patches Intra-Patch
D
A C
B
Size
Movement Between Patches that are Either a Source or Destination Flux
D
A C
B
Size of A and C and number of links
Movement Through Stepping Stone Patches Connector
D
A C
B Number of links and size of A and C

29. Integral Index of Connectivity - IIC
area
number of links
area of the landscape
A D
C
B
nlAC=2
Equivalent Connectivity (ECIIC) – the area of one continuous habitat
patch that has the same value of IIC as the observed landscape.

30. Graph Theoretic Approaches to Connectivity Assessment
1) How large and extensive
are networks of patches
that would be accessible
to an organism that could
disperse a specified
distance?
2) At what distances is the
network most sensitive to
changes in different
aspects of connectivity?
3) How do individual patches
contribute to different
aspects of connectivity?
Miles
0 0.45 0.9 1.8 2.7

31. 106,063 acres total
9,818 patches
Only patches ≥ 1 acre
104,249 acres total
3,456 patches
Green Infrastructure
Tree Canopy in GI
Miles
0 1.75 3.5 7 10.5

32. 2000
Number of Components
1500
1000
2300 ft - all patches form a connected network
500
0
0 2000 4000 6000 8000
Distance (feet)

33. Components at 200 feet
309 patches are
N=851 in the largest
component
Miles
0 1.75 3.5 7 10.5
3,456 original patches

34. Components at 300 feet
1,945 patches are
N=409
in the largest
component
Miles
0 1.75 3.5 7 10.5
3,456 original patches

35. Components at 500 feet
2,284 patches are
N=179
in the largest
component
Miles
0 1.75 3.5 7 10.5
3,456 original patches

36. 45000
ECIIC (Acres)
35000
When all patches are first
connected, ECIIC= 38,657 acres
25000
15000
Total Acres: 104,249
0 2000 4000 6000 8000
Distance (feet)

37. Patch Importance and Network Sensitivity
Sequentially remove each
patch
Recalculate all network
statistics
Change in the network
values without a patch
indicates its importance to
connectivity
Sum of changes across all
patches indicates network
sensitivity
Changes can be assessed as
Total IIC
Intra-patch
Flux
Connector

38. 2
Sum of varIIC acres 
0e+00 1e+09 2e+09 3e+09 4e+09 5e+09
0
2000
4000
6000
Total IIC
8000

39. 2
Sum of varIIC acres 
0e+00 1e+09 2e+09 3e+09 4e+09 5e+09
0
2000
4000
6000
Total IIC
Within Patch
8000

40. 2
Sum of varIIC acres 
0e+00 1e+09 2e+09 3e+09 4e+09 5e+09
0
2000
4000
6000
Flux
Total IIC
Within Patch
8000

41. 2
Sum of varIIC acres 
0e+00 1e+09 2e+09 3e+09 4e+09 5e+09
0
2000
4000
6000
Flux
Total IIC
Connector
Within Patch
8000

42. 2
Sum of varIIC acres 
0e+00 1e+09 2e+09 3e+09 4e+09 5e+09
0
500
1000
1500
Flux
Total IIC
2000
Connector
Within Patch

43. Components
200 feet 300 feet
Miles Miles
0 1.75 3.5 7 10.5 0 1.75 3.5 7 10.5
N=851 N=409

44. Top ten ranked patches
for intra-patch
connectivity
Miles
0 1.75 3.5 7 10.5
300 foot distance

45. Top ten ranked patches
for flux connectivity
Miles
0 1.75 3.5 7 10.5
300 foot distance

46. Top ten ranked patches
for connector function
~12% loss in ECIIC value
18% loss in ECIIC value
21% loss in ECIIC value
Miles
0 1.75 3.5 7 10.5
300 foot distance

48. 34,233 acres total
3,160 patches
32% of all canopy in Green
Infrastructure is protected

49. Intra-Patch Connectivity
45% protected
2 patches missing altogether

50. Flux Connectivity
35% protected
3 patches missing altogether

51. Connector Patches
47% protected
6 patches missing altogether