1

Fig. 1. Study regions and presence of productive (annual growth greater than 1 m3 ha–1 yr–1) drained peatland forests classified by fertility class. Administrative boundaries from the National Land Survey of Finland, 4/2024. Peatland fertility map: Geological Survey of Finland (GTK) (2024) open license CC BY 4.0, including GTK’s data of peatland fertility levels in Finland 1.0/2023, imported from the Hakku service on July 31, 2024.

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Fig. 2. Study procedure. First, the representative forest attribute data were derived from the Finnish Forest Centre (FFC) inventory plots for 20 forest stands, as shown in the table. Details of the allometric roadmap processed by the MOTTI simulator can be found in Laurén et al. (2021), section 2.3.8. Three ditch depth scenarios were simulated for all study sites. SUSI calculates daily hydrological and biogeochemical fluxes of the ecosystem, which are derived into economic and environmental indicators and their trade-offs.

Table 1. Total area, area of productive (annual growth greater than 1 m3 ha–1 yr–1) peatland forests and mean volume of productive peatland forests of different site fertility classes (SFC) in different regions. SFCs were classified according to Vasander and Laine (2008). Data derived from the NFI computing service (Natural Resources Institute Finland 2023).
Region SFC Abbreviation Total area
[ha] 		Productive forests
[ha] 		Mean volume
[m3 ha–1]
Southern Finland (SF) Herb-rich heath Rhtkg 151 255 145 041 177
Vaccinium myrtillus Mtkg 313 263 299 173 168
V. vitis-idaea Ptkg 204 703 194 034 135
Dwarf shrub Vtkg 121 811 95 130 95
Central Finland (CF) Herb-rich heath Rhtkg 149 554 139 549 153
V. myrtillus Mtkg 445 609 415 501 146
V. vitis-idaea Ptkg 521 154 467 359 122
Dwarf shrub Vtkg 371 867 243 159 83
North Ostrobothnia–Kainuu (NOB–K) Herb-rich heath Rhtkg 106 670 80 914 116
V. myrtillus Mtkg 372 538 264 537 130
V. vitis-idaea Ptkg 669 930 401 992 107
Dwarf shrub Vtkg 378 863 157 673 71
Lapland Herb-rich heath Rhtkg 63 870 45 495 90
V. myrtillus Mtkg 121 036 80 652 119
V. vitis-idaea Ptkg 369 941 197 602 81
Dwarf shrub Vtkg 213 000 45 371 52
Table 2. Forest attributes representing average forest characteristics in different regions and site fertility classes (SFC), calculated from Finnish Forest Centre inventory plots (FFC 2023). SF = Southern Finland, CF = Central Finland, NOB–K = North Ostrobothnia–Kainuu, N = number of stems, BA = basal area, Dg = basal area-weighted mean diameter, Hg = basal area-weighted mean height, Hdom = dominant height, VOL = stem volume. SFCs were classified according to Vasander and Laine (2008). The * indicates the extended range of selection by stand volume due to lack of similar field plots.
Region SFC and dominant tree species FFC plots N
[ha–1] 		BA
[m2 ha–1] 		Dg
[cm] 		Hg
[m] 		Hdom
[m] 		VOL
[m3 ha–1]
SF Rhtkg (spruce) 6 1073 22.6 20.3 16.4 19.2 178
Mtkg (spruce) 14 851 20.2 21.3 17.4 19.7 169
Mtkg (pine) 16 932 19.8 22.0 17.9 20.2 168
Ptkg (pine) 44 915 16.8 20.2 16.6 18.6 134
Vtkg (pine) 11 1156 15.1 15.0 12.3 14.4 94
CF Rhtkg (spruce) 4 903 21.1 21.8 15.3 17.9 149
Mtkg (spruce) 21 1111 19.2 18.9 15.6 18.4 144
Mtkg (pine) 13 1391 20.5 17.3 14.7 17.4 147
Ptkg (pine) 78 872 16.1 18.9 15.6 17.7 122
Vtkg (pine) 34 1015 13.6 15.7 12.2 14.3 84
NOB–K Rhtkg (spruce) 5 1420 20.0 18.1 12.7 15.4 120
Mtkg (spruce) 7 1328 19.1 17.9 14.1 17.0 130
Mtkg (pine) 41 1296 19.0 17.2 14.1 16.4 132
Ptkg (pine) 44 1131 16.0 16.4 13.3 15.5 106
Vtkg (pine) 18 1266 12.9 13.9 10.8 12.8 71
Lapland Rhtkg (spruce) 3* 1637 20.6 16.5 11.4 13.8 113
Mtkg (spruce) 3* 1824 19.3 16.2 12.7 15.6 118
Mtkg (pine) 15 1904 20.2 14.6 11.6 14.0 119
Ptkg (pine) 5 2224 16.4 12.3 9.5 12.3 81
Vtkg (pine) 3* 2083 12.4 10.6 8.2 10.2 55
Table 3. Annual and midsummer (July–August) weather statistics in our study regions. SF = Southern Finland, CF = Central Finland, NOB–K = North Ostrobothnia–Kainuu.
SF CF NOB–K Lapland
Annual mean temperature (°C) min. 3.2 1.7 1.0 –0.7
mean 5.1 3.8 2.9 1.5
max. 6.8 5.4 4.5 2.8
July–August mean temperature (°C) min. 14.5 13.4 13.1 12.5
mean 16.3 15.2 15.0 14.5
max. 18.7 17.6 17.1 16.9
Annual rainfall (mm) min. 434 441 406 387
mean 644 663 621 539
max. 814 857 786 754
July–August rainfall (mm) min. 69 30 34 26
mean 148 170 168 130
max. 288 276 303 239
Annual solar radiation (MJ m–2) min. 3053 2933 2887 2613
mean 3409 3200 3145 2895
max. 3659 3583 3475 3107
July–August solar radiation (MJ m–2) min. 925 866 825 781
mean 1034 998 980 901
max. 1181 1209 1151 1081
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Fig. 3. Annual and midsummer (July–August) temperature, precipitation, and solar radiation during the 20-year simulation period in our study regions. SF = Southern Finland, CF = Central Finland, NOB–K = North Ostrobothnia–Kainuu.

Table 4. Average water table below the soil surface during the growing season (May–October) in different regions, site fertility classes (SFC) and scenarios: NO_DNM = no ditch network maintenance, DNM60 = reduced ditch depth of 60 cm, DNM90 = conventional ditch depth of 90 cm. SF = Southern Finland, CF = Central Finland, NOB–K = North Ostrobothnia–Kainuu. SFCs were classified according to Vasander and Laine (2008).
Region SFC NO_DNM [m] DNM_60 [m] DNM_90 [m]
SF Rhtkg –0.47 –0.55 –0.73
SF Mtkg (spruce) –0.49 –0.66 –0.95
SF Mtkg (pine) –0.43 –0.75 –1.09
SF Ptkg –0.35 –0.57 –0.89
SF Vtkg –0.26 –0.41 –0.67
CF Rhtkg –0.38 –0.51 –0.72
CF Mtkg (spruce) –0.34 –0.41 –0.53
CF Mtkg (pine) –0.32 –0.51 –0.80
CF Ptkg –0.27 –0.37 –0.54
CF Vtkg –0.19 –0.27 –0.41
NOB–K Rhtkg –0.30 –0.35 –0.45
NOB–K Mtkg (spruce) –0.28 –0.31 –0.39
NOB–K Mtkg (pine) –0.25 –0.39 –0.62
NOB–K Ptkg –0.22 –0.29 –0.41
NOB–K Vtkg –0.14 –0.20 –0.30
Lapland Rhtkg –0.26 –0.34 –0.49
Lapland Mtkg (spruce) –0.25 –0.30 –0.40
Lapland Mtkg (pine) –0.23 –0.34 –0.52
Lapland Ptkg –0.20 –0.27 –0.36
Lapland Vtkg –0.14 –0.21 –0.31
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Fig. 4. Tree volume development, variation of the average growing season (May–October) water table below the soil surface, and annual water runoff and evapotranspiration during the 20-year simulation period in four example sites: a spruce-dominated herb-rich heath forest (Rhtkg) in southern Finland (SF), a spruce-dominated Vaccinium myrtillus-type peatland forest (Mtkg) and a pine-dominated V. vitis-idaea-type peatland forest (Ptkg) in central Finland (CF), and a nutrient-poor dwarf-shrub peatland forest (Vatkg) in the North Ostrobothnia–Kainuu region (NOB–K). Scenarios: NO_DNM = no ditch network maintenance, DNM_60 = reduced ditch depth of 60 cm, NDM_90 = conventional ditch depth of 90 cm.

Table 5. Average forest volume growth in different regions, site fertility classes (SFC) and scenarios: NO_DNM = no ditch network maintenance, DNM60 = reduced ditch depth of 60 cm, DNM90 = conventional ditch depth of 90 cm. The net present value of ditch network maintenance (NPVDNM) in scenarios DNM_60 and DNM_90 was calculated using discount rates of 2%, 3% and 4%. NPVDNM was not calculated for scenarios with a negative volume growth response to DNM. SF = Southern Finland, CF = Central Finland, NOB–K = North Ostrobothnia–Kainuu. SFCs were classified according to Vasander and Laine (2008).
Region SFC Volume growth
[m3 ha–1 yr–1] 		NPVDNM
[€ ha–1] (2%) 		NPVDNM
[€ ha–1] (3%) 		NPVDNM
[€ ha–1] (4%)
NO_DNM DNM_60 DNM_90 DNM_60 DNM_90 DNM_60 DNM_90 DNM_60 DNM_90
SF Rhtkg 8.7 8.9 8.1 –94 € –133 € –164 €
SF Mtkg (spruce) 10.3 10.0 8.7
SF Mtkg (pine) 6.9 6.5 6.0
SF Ptkg 7.7 8.2 7.5 205 € 113 € 38 €
SF Vtkg 5.3 6.1 6.2 338 € 366 € 223 € 246 € 129 € 148 €
CF Rhtkg 7.6 8.2 7.6 169 € 83 € 14 €
CF Mtkg (spruce) 7.9 8.8 8.8 489 € 544 € 347 € 392 € 231 € 268 €
CF Mtkg (pine) 6.1 6.6 6.3 258 € –31 € 157 € –81 € 74 € –122 €
CF Ptkg 5.9 7.0 7.3 648 € 882 € 477 € 670 € 338 € 497 €
CF Vtkg 3.6 4.8 5.6 572 € 1124 € 415 € 869 € 287 € 661 €
NOB–K Rhtkg 5.5 6.3 6.3 433 € 529 € 301 € 380 € 193 € 258 €
NOB–K Mtkg (spruce) 6.0 6.9 7.1 460 € 658 € 323 € 486 € 211 € 345 €
NOB–K Mtkg (pine) 5.7 6.6 6.7 500 € 558 € 356 € 404 € 238 € 278 €
NOB–K Ptkg 4.8 5.8 6.2 491 € 811 € 349 € 612 € 232 € 449 €
NOB–K Vtkg 2.5 3.4 4.1 297 € 775 € 189 € 582 € 101 € 425 €
Lapland Rhtkg 4.1 4.8 4.8 298 € 293 € 190 € 185 € 101 € 98 €
Lapland Mtkg (spruce) 3.9 4.7 4.9 263 € 417 € 161 € 288 € 78 € 182 €
Lapland Mtkg (pine) 3.6 4.3 4.6 184 € 351 € 96 € 233 € 24 € 137 €
Lapland Ptkg 2.9 3.6 3.9 86 € 234 € 15 € 137 € –42 € 58 €
Lapland Vtkg 1.5 2.2 2.7 –5 € 191 € –60 € 102 € –104 € 29 €
Table 6. Average annual soil and ecosystem (soil + biomass) CO2-equivalent greenhouse gas (GHG) balances in different regions, site fertility classes (SFC) and scenarios: NO_DNM = no ditch network maintenance, DNM60 = reduced ditch depth of 60 cm, DNM90 = conventional ditch depth of 90 cm. A negative value indicates a loss of carbon in soil or biomass (carbon source), and a positive value indicates an addition of carbon storage in forest ecosystem (carbon sink). Trade-offs between net present value (NPV) and increased soil GHG emissions (TO NPV GHG) were calculated using a discount rate of 3%. SF = Southern Finland, CF = Central Finland, NOB–K = North Ostrobothnia–Kainuu. SFCs were classified according to Vasander and Laine (2008).
Region SFC Soil GHG balance
[kg ha–1 yr–1] 		TO NPV GHG
(3%) 		Ecosystem GHG balance
[kg ha–1 yr–1]
NO_DNM DNM_60 DNM_90 DNM_60 DNM_90 NO_DNM DNM_60 DNM_90
SF Rhtkg –6860 –8220 –10 570 2120 1030 –2150
SF Mtkg (spruce) –6530 –8850 –12 070 3980 1410 –3100
SF Mtkg (pine) –5720 –9610 –13 230 1340 –2950 –7130
SF Ptkg –4260 –6880 –10 840 2 € 3750 1650 –2980
SF Vtkg –2910 –5200 –8470 5 € 2 € 2670 1800 –1380
CF Rhtkg –5600 –7350 –10 070 2 € 2420 1370 –1990
CF Mtkg (spruce) –4450 –5440 –7280 17 € 7 € 3650 3580 1840
CF Mtkg (pine) –3980 –6110 –9640 4 € 2270 720 –3090
CF Ptkg –3160 –4690 –7040 16 € 9 € 3050 2680 680
CF Vtkg –1830 –3240 –5220 15 € 13 € 1830 1720 520
NOB–K Rhtkg –3830 –4770 –6450 16 € 7 € 2380 2310 760
NOB–K Mtkg (spruce) –3020 –3750 –5080 22 € 12 € 3560 3790 2750
NOB–K Mtkg (pine) –3360 –5270 –8230 9 € 4 € 2550 1640 –1210
NOB–K Ptkg –2110 –3410 –5160 13 € 10 € 2990 2750 1520
NOB–K Vtkg –1010 –2280 –3820 7 € 10 € 1550 1240 520
Lapland Rhtkg –2800 –4110 –6200 7 € 3 € 2110 1640 –400
Lapland Mtkg (spruce) –1840 –2850 –4320 8 € 6 € 2640 2520 1330
Lapland Mtkg (pine) –2300 –4070 –6400 3 € 3 € 1620 600 –1420
Lapland Ptkg –1220 –2530 –3960 1 € 2 € 1970 1510 420
Lapland Vtkg –670 –2090 –3650   2 € 1080 410 –580
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Fig. 5. Annual CO2 and CH4 emissions, and CO2-equivalent soil and ecosystem (soil + biomass) greenhouse gas (GHG) balance during the 20-year simulation period in four example sites (see Fig. 4).

Table 7. Average annual nitrogen (N) and phosphorus (P) export in different regions, site fertility classes (SFC) and scenarios: NO_DNM = no ditch network maintenance, DNM60 = reduced ditch depth of 60 cm, DNM90 = conventional ditch depth of 90 cm. SF = Southern Finland, CF = Central Finland, NOB–K = North Ostrobothnia–Kainuu. SFCs were classified according to Vasander and Laine (2008).
Region SFC N export
[kg ha–1 yr–1] 		P export
[kg ha–1 yr–1]
NO_DNM DNM_60 DNM_90 NO_DNM DNM_60 DNM_90
SF Rhtkg 4.95 6.53 8.94 1.05 1.20 1.48
SF Mtkg (spruce) 3.48 4.45 7.05 0.67 0.70 1.00
SF Mtkg (pine) 2.09 5.36 10.39 0.40 0.90 1.50
SF Ptkg 1.79 2.32 4.37 0.22 0.26 0.45
SF Vtkg 1.25 1.96 3.07 0.13 0.19 0.30
CF Rhtkg 3.59 4.87 7.46 0.87 0.97 1.24
CF Mtkg (spruce) 2.04 2.39 3.67 0.52 0.58 0.71
CF Mtkg (pine) 1.92 2.42 4.44 0.38 0.41 0.73
CF Ptkg 1.17 1.63 2.47 0.17 0.21 0.27
CF Vtkg 0.65 0.92 1.62 0.06 0.09 0.15
NOB–K Rhtkg 1.77 2.50 4.27 0.64 0.75 0.93
NOB–K Mtkg (spruce) 1.10 1.32 2.34 0.35 0.43 0.55
NOB–K Mtkg (pine) 1.37 1.75 3.28 0.29 0.31 0.50
NOB–K Ptkg 0.62 1.11 1.89 0.10 0.15 0.22
NOB–K Vtkg 0.15 0.49 1.05 0.01 0.04 0.09
Lapland Rhtkg 1.38 2.20 3.93 0.50 0.62 0.77
Lapland Mtkg (spruce) 0.78 1.16 2.07 0.25 0.35 0.47
Lapland Mtkg (pine) 1.07 1.54 2.24 0.32 0.30 0.35
Lapland Ptkg 0.30 0.80 1.44 0.05 0.12 0.19
Lapland Vtkg 0.08 0.48 1.06 0.01 0.04 0.10