Habitat network — Task

Implementation: Habitat network (Recipe - QGIS).

Habitat network is the Task of finding which habitat patches are connected to each other — closer than a chosen connection distance — and which are isolated. Connected patches form clusters; the largest cluster is the landscape’s main network. Patches outside it are the candidates for regulation and restoration.

Used in examples: Habitat network at Ledreborg (Example).

Task Schema (tool-agnostic)

1. Start from the habitat patches — the nature content layer.
2. Choose the connection distance (decision point) — the largest gap a species can cross between patches.
3. Grow each patch by half the distance (Operator: dilation) — two patches up to the full distance apart then touch.
4. Join everything that touches (Operator: dissolve).
5. Make each separate piece one cluster (Operator: explode), and give each cluster an id.
6. Give each patch its cluster’s id (Operator: attribute transfer by location, see Aggregation).
7. Measure each cluster (Operator: aggregate per cluster) — number of patches and total habitat area per cluster.
8. Classify the patches (decision point) — main network (the largest cluster), smaller clusters, isolated patches (alone in their cluster).

Output: the patches with a cluster id, the number of patches and the habitat area of their cluster, and a class: main network, smaller cluster or isolated.

Epistemic Choices to record

• Connection distance: the decisive choice. At Ledreborg 50 m gives 357 clusters and leaves 63 % of the habitat area outside the main network; 100 m gives 129 clusters and 13 %; 200 m gives 22 clusters and 8 %. Base it on the species or species group in question, and show at least two distances.
• Straight-line gaps: a 100 m gap across a field and a 100 m gap across a road are treated alike.
• What “main network” means: the cluster with the most habitat area. A different measure (most patches, most woodland) can pick another cluster.
• Corridors count as habitat: hedges and streams connect patches. Run the Task once without them to see how much of the network they hold together.