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FO — Forestation (Skovrejsning)

Summary

Conversion of agricultural land to forest. A permanent land-use change. The land stops receiving N fertilizer, and tree uptake and soil processes dramatically reduce N leaching. FO has both N and P co-benefits.

Eligibility / Potential area

PotV(i,"FO") = (1 − lav(i)) × Countcy(i) × IniPotV(i) / 5
Low-lying fields (lav(i) fraction) are excluded — afforestation is only applicable on "high" (non-waterlogged) land. Driven by data from FO_YES.inc and FO_NO.inc (which define where forestation is/is not allowed).

N Effect

NEffM(i,"FO") = prodeff(i) − 8   [where prodeff(i) = leaching(i)]
The effect is the field's N leaching minus an 8 kg N/ha/yr background loss that persists even under forest (from atmospheric deposition and legacy soil N). Effect is field-specific, driven by leaching(i).

P Effect

FO has P effects through both erosion and macropore pathways: 

P_Effects_erosion(i,"FO")   = erosion_field(i) × (PotV(i,"FO") / IniPotV(i))
P_Effects_macropore(i,"FO") = macropore_field(i) × 0.35 × (PotV(i,"FO") / IniPotV(i))
Effects are scaled to the fraction of the field with FO potential (since only the non-low-lying part can be forested).

Cost

CostM(i,"FO"):
  livestock ≥ 0.8:  prodcost(i) − Adj_Ann_Jordv_2pro(i) + 200  DKK/ha/yr
  livestock < 0.8:  prodcost(i) − Adj_Ann_Jordv_2pro(i)          DKK/ha/yr
Adj_Ann_Jordv_2pro(i) is an annuitized land value subsidy payment that farmers receive for afforestation. This reduces the net cost relative to simple opportunity cost.

Retention type

TR (Total retention) — N reduction from FO passes through the full (1 − TotRet(i)/100) landscape retention before reaching the coast.

Mutual exclusions

  • Member of lr1(j) (full land retirement) — contributes to me(i) at weight 1
  • Via mutexc5, mutexc6: excludes lm and bz measures
  • Cannot be combined with IBZ (mutexc17)
  • VP2 FO on same field blocks further FO selection

Data sources

  • Forest potential: FO_YES.inc, FO_NO.inc
  • Land value annuity: Adj_Ann_Jordv_2pro.inc
  • Leaching (→ N effect): leaching.inc
  • P effects, cost structure, N effect formula: hard-coded in TargetEcon 2026.gms

Catalog source

DCA Rapport nr. 174 (Eriksen et al., 2020): "Virkemidler til reduktion af kvælstofbelastningen af vandmiljøet", Chapter "Skovrejsning" (p. 152–164).

N effect confirmed: Annual N leaching from afforested agricultural land averages 8 kg N/ha/yr over an entire rotation (range 5–15 kg N/ha). Reference leaching from agricultural land: 61 kg N/ha/yr (2020 catalog baseline). Therefore the N reduction = 61 − 8 = 53 kg N/ha/yr. This matches the model formula NEffM(i,"FO") = prodeff(i) − 8 exactly (using field-specific leaching in place of the national average of 61 kg N/ha).

Updated (2025): Rolighed et al. (2025) confirms the same 8 kg N/ha residual leaching, but applies the updated 2021 baseline (58 kg N/ha on omdrift) → national FO N effect becomes 50 kg N/ha nationally. The per-field formula prodeff(i) − 8 remains unchanged. See DCA_diff_effekt_2025.md for 108-catchment differentiated FO values (not currently used in differentiation_effects.inc but available for VP4).

Confidence level: ** (somewhat uncertain — data from ~10 Danish afforestation sites; long-term dynamics still being monitored)

Dynamics: N leaching peaks in years 0–5 (from soil disturbance), drops to near zero at years 5–20 (tree uptake phase), then rises again to ~8 kg N/ha as trees mature and N deposition exceeds tree uptake. The model's formula captures the long-run average.

Budget cost from catalog: 22 DKK/kg N (sandy soil) to 56 DKK/kg N (clay soil); welfare economic: 28–72 DKK/kg N.

Economic breakdown (Tabel 3, p. 162): At 3% discount rate, the annuity from timber production is approximately +37 DKK/ha/yr (nearly neutral — explaining why Adj_Ann_Jordv_2pro can be close to or equal to prodcost on marginal land). At 4% discount rate, this annuity becomes −470 DKK/ha/yr (a cost).

Adj_Ann_Jordv_2pro(i) resolved: This is the annuitized income from the forest grant scheme (Norwegian: annuitet ved skovdyrkning, based on Lundhede 2020 / Meilby et al. 2014). It represents the expected timber revenue discounted over the rotation period. The parameter varies by region and soil type.

Side effects noted in catalog: - Pesticider: positive (afforested land uses no pesticides) - Nature/biodiversity: positive - Phosphorus: positive (reduces erosion losses; see P catalog SR379 for details) - Climate: strongly positive (12 t CO₂/ha/yr carbon sequestration average; range 4–21 t CO₂/ha/yr)

Notes & open questions

  1. Adj_Ann_Jordv_2pro(i) — ✅ Confirmed: annuitized timber income from skovrejsning grant scheme (Lundhede 2020).
  2. FO is in report1(j) (TR measures minus FO is a separate reporting category) — why is FO excluded from report1? Possibly because it is a permanent land-use change treated differently from other TR measures.
  3. Tripartite agreement mandates ≥28,000 ha of new afforestation (Afforestation_eq).

Scenario appearances

To be filled as scenarios are documented.

  • WL — companion permanent measure (NR vs FO's TR retention; different hydrology)
  • LRh — related high-land retirement measure
  • SA — temporary vs permanent conversion; same TR retention type
  • EC — energy crops (alternative permanent/long-term conversion)
  • Retention types — FO uses TR (total retention)
  • P loss pathways — FO reduces erosion + macropore P
  • Cost concepts — livestock surcharge; Adj_Ann_Jordv_2pro subsidy reduces net cost
  • DCA differentiation effects — per-catchment FO values available (not yet in model)
  • Tripartite Agreement — FO floor: ≥28,000 ha