Assessing the Impact of Land Cover Spatial Resolution on Forest Fragmentation Modeling James D. Hurd and Daniel L. Civco

Center for Land use Education And Research (CLEAR) Department of Natural Resources Management & Engineering The University of Connecticut U-4087, Room 308, 1376 Storrs Road Storrs, CT 06269-4087

Outline

• The Forest Fragmentation Model • Application to land cover of different

spatial resolutions

• Concluding remarks

Forest Fragmentation Modeling

Forest Fragmentation Model

Background Developed by Riitters et al.

(2000) to assess global forest fragmentation from 1 km land cover data.

Adapted for use on Landsat derived land cover

information (30-meter spatial resolution).

Categorizes forest pixels into 6 types:

• Core forest • Perforated forest • Edge forest • Transition forest • Patch forest • Undetermined forest

Forest Fragmentation Model

How It Works Based on Image Convolution.

Uses a roving analysis window of fixed size to determine vales of Pf (amount) and Pff (adjacency).

9x9 Analysis Window Forest Pixel Non-Forest Pixel

Forest Fragmentation Model

How It Works

9x9 Analysis Window Pf = 57 forest pixels 81 total pixels = 0.70

Forest Pixel Non-Forest Pixel Pf = proportion of forest pixels in analysis window.

Forest Fragmentation Model

How It Works

9x9 Analysis Window Pf = 57 forest pixels 81 total pixels = 0.70

Forest Pixel Non-Forest Pixel Pff = 86 pixel pairs, 119 pixel pairs, both forest at least one forest = 0.72

144 pixel pairs in a 9x9 window

(72 vertical, 72 horizontal) Pff = how connected are those forest pixels.

Forest Fragmentation Model

How It Works

• Core forest, Pf = 1.0 • Perforated forest, Pf > 0.6 and Pf – Pff > 0 • Edge forest, Pf > 0.6 and Pf – Pff < 0 • Transition forest, Pf < 0.6 and >0.4 • Patch forest, Pf < 0.4 • Undetermined forest, Pf > 0.6

and Pf = Pff

(Riitters et al ., 2000)

Forest Fragmentation Model

Definitions Core Forest

- all surrounding grid cells are forest.

Perforated Forest

such as would occur around a small clearing or house lot.

- the interior edge of a forest tract

Edge Forest

as would occur along a large agricultural field or urban area.

- the exterior edge of a forest tract such

Transitional Forest

grid cells are forest.

- about half of the surrounding

Patch Forest

are forest.

- less than 40% of surrounding grid cells

Forest Fragmentation Model

How It Works

Forest Pixel Non-Forest Pixel

Pf = 0.70

Forest Fragmentation Model

How It Works Pf - Pff = 0.70-0.72 = -0.02

Pf = 0.70

Forest Pixel Non-Forest Pixel

EDGE FOREST

Forest Fragmentation Model

Analysis Window Sizes Analysis windows of different sizes can be applied.

9x9 27x27 81x81

As analysis window size increases, the amount of core forest decreases.

Forest Fragmentation Model

Three Related Items to Consider 1. Spatial resolution of input land cover.

2. Width of desired edge (i.e. how far from a non forested feature do you need to be before you are in core forest?).

3. What analysis window size will you use?

Core Forest to Non-forest

n x n pixel analysis window, where minimum pixel distance = 1 + [( n n is odd – 1) / 2] Minimum distance = minimum pixel distance * pixel resolution

A core forest pixel will be at least the minimum distance from a non-forest pixel (pixel center to pixel center).

Core Forest to Non-forest

9x9 analysis window = 1 + [(9 - 1) / 2] = 5 pixels For 30 m pixels = 5 x 30 = 150 m (pixel centers) (5 x 30) – 30 = 120m (pixel edges)

5 pixels (150 m) No longer core forest

Forest Fragmentation Model

Three Related Items to Consider 1. Spatial resolution of input land cover.

2. Width of desired edge (i.e. how far from a non forested feature do you need to be before you are in core forest?).

3. What analysis window size will you use?

Application to Land Cover of Different Spatial Resolutions

Using Analysis Windows of Same Pixel Dimensions

Land Cover

1 - meter 5 - meter 10 - meter 30 - meter Larger spatial resolution created by degrading the 1-meter spatial resolution land cover

Forest Fragmentation Result 5 x 5 Analysis Window

1 - meter 5 - meter 10 - meter 30 - meter

Forest Fragmentation Result 15 x 15 Analysis Window

1 - meter 5 - meter 10 - meter 30 - meter

Forest Fragmentation Result 27 x 27 Analysis Window

1 - meter 5 - meter 10 - meter 30 - meter

Forest Fragmentation Result 81 x 81 Analysis Window

1 - meter 5 - meter 10 - meter 30 - meter

Application to Land Cover of Different Spatial Resolutions

Using Analysis Windows of Same Areal Extent

Land Cover

1 - meter 5 - meter 10 - meter 30 - meter Larger spatial resolution created by degrading the 1-meter spatial resolution land cover

Forest Fragmentation Result

1 - meter 271x271 5 - meter 55x55 10 - meter 27x27 30 - meter 9x9

Analysis Window Area =

approx. 7.3 hectares

transition, 8.60

patch, 0.46

developed, 20.35

non-forest, 2.57

water, 0.93

interior, 11.67

perforated, 0.34

edge, 55.09

1 – meter, 271x271 transition, 8.67

patch, 0.39

developed, 20.50

non-forest, 2.64

water, 0.94

interior, 10.91

edge, 46.43

perforated, 9.51

10 – meter, 27x27 transition, 8.57

patch, 0.46

developed, 20.34

edge, 53.50

5 – meter, 55x55 Transition, 9.46

non-forest, 2.60

water, 0.91

interior, 11.80

perforated, 1.82

Patch, 0.76

Developed, 21.46

Edge, 12.38

Non-forest, 2.54

Water, 2.48

Core, 14.03

Perforated, 36.89

30 – meter, 9x9

30 – meter Land Cover 9x9 Analysis Window

9x9 Analysis Window Pf = 0.765

Pff = 0.744

Pf - Pff = 0.021

PERFORATED FOREST

10 – meter Land Cover 27x27 Analysis Window

27x27 Analysis Window Pf = 0.844

Pff = 0.916

Pf - Pff = -0.072

EDGE FOREST

5 – meter Land Cover 55x55 Analysis Window

55x55 Analysis Window Pf = 0.848

Pff = 0.966

Pf - Pff = -0.118

EDGE FOREST

1 – meter Land Cover 271x271 Analysis Window

271x271 Analysis Window Pf = 0.847

Pff = 0.983

Pf - Pff = -0.136

EDGE FOREST

Edge/Perforated Definition

• Core forest, Pf = 1.0 • Perforated forest, Pf > 0.6 and Pf – Pff > 0 • Edge forest, Pf > 0.6 and Pf – Pff < 0 • Transition forest, Pf < 0.6 and >0.4 • Patch forest, Pf < 0.4 • Undetermined forest, Pf > 0.6

and Pf = Pff

Altering Definition of Edge/Perforated

9x9 Analysis Window applied to 30-meter spatial resolution land cover

Land Cover 9x9 Analysis Window

Altering Definition of Edge/Perforated

Results of Forest Frag. Model using a 27x27 Analysis Window on 10m Land Cover Riitters Original Definitions Perforated Pf – Pff > 0 Edge Pf – Pff < 0

NOT SO GOOD

Altered Definitions Perforated Pf – Pff > -0.05

Edge Pf – Pff < -0.05

BETTER

Altered Definitions Perforated Pf – Pff > -0.1

Edge Pf – Pff < -0.1

MORE LIKE 30m 9x9 FF RESULTS

Altering Definition of Edge/Perforated

Results of Forest Frag. Model using a 55x55 Analysis Window on 5m Land Cover Riitters Original Definitions Perforated Pf – Pff > 0 Edge Pf – Pff < 0

NOT SO GOOD

Altered Definitions Perforated Pf – Pff > -0.05

Edge Pf – Pff < -0.05

BETTER

Altered Definitions Perforated Pf – Pff > -0.11

Edge Pf – Pff < -0.11

MORE LIKE 30m 9x9 FF RESULTS

Altering Definition of Edge/Perforated

Results of Forest Frag. Model using a 271x271 Analysis Window on 1m Land Cover Riitters Original Definitions Perforated Pf – Pff > 0 Edge Pf – Pff < 0

NOT SO GOOD

Altered Definitions Perforated Pf – Pff > -0.1

Edge Pf – Pff < -0.1

BETTER

Altered Definitions Perforated Pf – Pff > -0.15

Edge Pf – Pff < -0.15

MORE LIKE 30m 9x9 FF RESULTS

Transition, 1.34

Edge, 5.43

Patch, 2.06

Developed, 17.68

Non-forest, 0.00

Water, 4.33

Perforated, 42.99

Core, 26.16

1 – meter, Pf – Pff threshold = -0.16

Transition, 1.45

Edge, 6.20

Patch, 2.11

Developed, 17.78

Non-forest, 0.00

Water, 4.18

Perforated, 42.89

Core, 25.39

Edge, 6.29

Transition, 1.36

Patch, 2.07

Developed, 17.50

Non-forest, 0.00

Water, 4.38

Perforated, 41.87

Core, 26.53

5 – meter, Pf – Pff threshold = -0.11

Edge, 6.79

Transition, 1.71

Patch, 1.90

Developed, 17.65

Non-forest, 0.00

Water, 4.19

Perforated, 35.56

Core, 32.19

Class Edge Bias Curve

Class Edge Bias = 0.0488 * ln(r) - 0.1601

where r = land cover spatial resolution

CLEAR Website clear.uconn.edu

CLEAR Website

http://clear.uconn.edu/projects/landscape/forestfrag/ff_tool.htm

Downloadable Tool for ESRI ArcGIS 9.2

Concluding Remarks

Concluding Remarks

When applying Forest Fragmentation model, three items to consider:

- land cover spatial resolution - desired width of edge/perforation - analysis window size

The spatial resolution (and landscape pattern) of the land cover impacts the result of the model:

- it may be desirable to alter the definition of edge and perforated.

Ultimately the results are only an approximation, but:

- provide a powerful visual impact - allow for the quantification of forest fragmentation.

Assessing the Impact of Land Cover Spatial Resolution on Forest Fragmentation Modeling

[email protected]

Center for Land use Education And Research (CLEAR) Department of Natural Resources Management & Engineering The University of Connecticut U-4087, Room 308, 1376 Storrs Road Storrs, CT 06269-4087