2026-03-19

Achieving 30×30 requires radical land transformation

Achieving 30×30 in highly cultivated nations requires radical land transformation

The Global Mandate

  • The Kunming–Montreal Global Biodiversity Framework calls for protecting 30% of land and sea by 2030
  • In countries with large intact ecosystems, this often means designation of existing nature

The Local Reality (Denmark)

  • Denmark is ~60% cultivated
  • The 30% target cannot be met through existing nature alone
  • It requires active transformation of agricultural land into new ecosystems

Modeling the tension between intrinsic biodiversity and instrumental climate utility Mixed-Integer Linear Programming (MILP)

Nature for Nature (w = 0)

Intrinsic value

  • Optimization target:
    Potential species richness, phylogenetic diversity, and rarity

  • Goal:
    Maximizing the complexity and intrinsic value of biological assemblages across nature types

Nature for Society (w = 1.4)

Instrumental value

  • Optimization target:
    Potential carbon sequestration (above- and below-ground) and avoided emissions

  • Goal:
    Maximizing climate mitigation utility through afforestation and peatland rewetting

Nature types

Current map

How to plan future landscapes

\[ \text{maximize CI} = \color{#d7191c}{W_B \times \text{Biodiversity}} + \color{#7b3294}{W_C \times \text{Carbon}} + \color{#2c7bb6}{W_Q \times \text{Contiguity}} \]

  • Biodiversity
    • Species richness
    • Phylogenetic diversity
    • Rarity
  • Carbon
    • Aboveground carbon sequestration
    • Belowground carbon sequestration
    • Avoided emissions through rewetting of carbon-rich soils
  • Contiguity
    • Rewards adjacent restored cells of the same nature type
    • Promotes larger and more cohesive habitat patches
  • pareto edge design
    • Biodiversity weight fixed at 1
    • Carbon weight varies from 0 to 1.4
    • Contiguity included in all runs

What constrains the optimization?

Optimization constraints
The same national targets are imposed across all weights and planning contexts
Component Requirement
Eligible land Only agricultural cells can be converted
Decision rule Each selected cell can be assigned at most one of 8 nature types
Area target Total converted area constrained to meet the national 30% protected area target
Representation At least 5% of selected area in each of the 8 nature types
Rewetting At least 70,000 ha rewetted
High-carbon soils At least 80% of rewetted area must occur on soils with >6% carbon
Forest expansion At least 100,000 ha of new forest
Locked land Cultivated protected land must be converted; permanent grasslands may only become open nature

Free vs constrained: where can the model choose?

Paretto edge

% not endangered

% critically endangered

Beta diversity Jaccard

Beta diversity Sørensen

Edge cases

That gives a nice top-bottom comparison.

Elbow members: national

Elbow members: East Jutland closeup

Habitat composition

Exploring the solutions

Area composition by weight
Comparison of key Pareto solutions under free and constrained optimisation
Interpretation
Free
Constrained
Forest Open Dry Wet Forest Open Dry Wet
0.0 Nature for Nature 29.6% 70.4% 47.8% 52.2% 25.9% 74.1% 44.5% 55.5%
0.1 Elbow in both 70.5% 29.5% 56.4% 43.6% 62.8% 37.2% 58.9% 41.1%
0.2 Elbow in both 74.1% 25.9% 62.4% 37.6% 66.4% 33.6% 63.7% 36.3%
0.3 Elbow in Free only 74.9% 25.1% 67.6% 32.4% 67.4% 32.6% 66.5% 33.5%
0.4 Elbow in Free only 75.1% 24.9% 71.6% 28.4% 68.0% 32.0% 68.0% 32.0%
1.4 Nature for Society 77.4% 22.6% 77.4% 22.6% 70.5% 29.5% 70.5% 29.5%

Robustness map slide: dominant recommended land use where agreement is high

Consensus

value count Percentage Area Coverage cumsum
100 84206 27.01 3368.24 7.84 7.84
83 10059 3.23 402.36 0.94 8.78
67 96432 30.94 3857.28 8.98 17.76
50 28782 9.23 1151.28 2.68 20.44
33 72855 23.37 2914.20 6.78 27.22
17 19375 6.22 775.00 1.80 29.03