Download - Graphes paysagers- Xavier Girardet

Xavier Girardet

Laboratoire ThéMA UMR 6049

UBFC / CNRS

Besançon

Modél i sat ion des réseaux

écologiques en écologie

du paysage :

l es graphes paysagers

Séminaire Atelier 8 /

ISIG, « Graphes et

réseaux en géographie »

De la mise sous cloche.. …aux réseaux écologiques

20001900 2010


L’émergence d’une discipline

20001900 2010

1970 1980 1990


L’émergence d’une discipline

Les graphes paysagers

20001900 2010

1970 1980 1990

2001 2006 2008 2012

From landscape structures to landscape networks

Artistic movement: focus on the nature

Protection of aesthetics landscape

1. De la mise sous cloche.. …aux réseaux écologiques


Protection of spectacular landscape



Protection of flora and fauna

In 1995, Germany had

5,314 nature reserves



Protection of flora and fauna



Networks of ecosystems



Ecological networks



- Ecological networks- Landscape connectivity

Structural connectivity Functional connectivity

Landscape networks


What is landscape ecology ?

LandscapeEcology

Broad Extents

K. McGarigal

2. L’émergence d’une discipline

What is landscape ecology ?

3 fundamental principles

1. The effect of spatial heterogeneity on ecological processes

2. The role of humans

3. A broad spatial scale: the landscape


The effect of spatial heterogeneity on ecological processes

MacArthur & Wilson (1967): The Theory of Island Biogeography



Forman & Godron (1986) : Landscape mosaic model



Metapopulation models: the first step to landscape connectivity


The role of humans

Forman (1995): Landscape fragmentation


A broad spatial scale: the landscape

Delcourt & Delcourt (1988) and Allen & Starr (1988):The hierarchical theory. Space and time are linked !


What is a landscape graph ?

Function

Reality

Model

3. Les graphes paysagers

3. Landscape graphs : origins

3. Landscape graphs : the sequel

3. Landscape graphs : the prequel

3. Intégration dans les scenarios de gestion et d’aménagement

Construction des graphes paysagers

Construction

des graphes

paysagers

Graph construction: identification of habitat patches and links

Landscape map

Suitable elements Barrier elementsOptimal habitat

Friction for speciesmovements

Minimum patch area

LANDSCAPE GRAPH


Mapping landscape

Input data

Landscape map in raster format

Categories defined accordingto a species/landscaperelation

Usually: cost value (friction) for each landscape category


Defining habitat patches

Patches = graph nodes

o Minimum patch area

o Connexity

o Capacity





o Connexity

4-connexity 8-connexity

Cell adjacent to the orange one

Focal cell

1

3

4-connexity=> 3 patches

8-connexity=> 1 patch

2 1

1

1





o Connexity

o Capacity

capacity = intrinsic quality of the patch as an indicator of its demographic potential

Function of the isotropicneighbourhood

Area of the habitat patch

Suitable elements Unfavourable elementsHabitat patches

Function of the anisotropicneighbourhood


Defining links

Voronoipolygon


Defining links

Topology- Complete- Planar

Direction

Distance- Euclidean distance- Least-cost distance

Threshold


Defining links

Topology- Planar- Complete

Direction

Distance- Euclidean distance- Least-cost distance

Threshold


Defining links

Land-use categories Function Cost

1 Ponds Habitat 1

2 Water Suitable 10

3 Built-up areas and infrastructures Unfavourable 1000

4 Forests Suitable 10

5 Wetlands Suitable 10

6 Croplands Unfavourable 1000

7 Grasslands Suitable 10

8 TGV line Unfavourable 2000


Defining links

Graph threshold

only links shorter than the threshold distance are kept.

(maximum dispersal distance of a given species)


Computing connectivity metrics

Several levels:

localcomponentglobal

Many metrics in graph theory…Rayfield B, Fortin MJ, Fall A, 2011. Connectivity for conservation: a framework to classify network measures. Ecology 92: 847-858.



Sum of capacity of patches connected to the patch i

i

… weighted according to the minimum distance to the focal patch

=> indicator of the potential dispersion from/to the patch i

Similar to the degree index

i i



Sum of the shortest paths through the focal patch i.

i

weighted both by the capacity of the twoend patches and by the distance betweenthem.

=> frequency of use of the patch i
