Cost-efficient forest management for safeguarding Siberian flying squirrel (Pteromys volans) habitats in Central Finland

Figures & data

Figure 1. Location of the study area.

Table 1. Average stand characteristics of the study area in Jyväskylä.

Fertility	Number of stands	Area, ha	Area, %	Stand age, yrs (average, range)	Stand volume, m^3 ha^−1 (average, range)	Tree species distribution, % of the stand volume
						Pine	Spruce	Birch	Aspen
1	10	10.9	2.0	108 (44–149)	150 (68–246)	21	41	22	17
2	197	202.3	36.3	71 (0–141)	241 (0–490)	16	68	14	2
3	251	297.3	53.3	71 (0–151)	213 (0–402)	34	52	12	1
4	35	35.9	6.4	78 (0–155)	133 (0–288)	77	15	7	1
5	9	11	2.0	57(0–135)	66 (0–151)	94	2	4	0
6	2	0.8	0.1	58 (0–115)	51 (0–101)	100	0	0	0
All	504	558.1	100	72 (0–155)	214 (0–490)	29	57	13	2

Fertility improves with descending order: 1 presents the most fertile site type. Site fertility levels based on the Finnish site type classes from the most fertile (class 1) to the most barren, class 6 (Tonteri et al. 1990).

Table 2. Costs and maximum traversing distances for forests and other habitats used in Least Cost Path (LCP) analysis.

Class number	Habitat class name	Cost	Description
1	The most preferred habitat (nesting habitat)	1	Technical cost of 1 was assigned for the best habitat type to avoid Manhattan type of path shapes in resulting paths within class 1 stands
2	The most preferred habitat type in future	22	Maximum moving distance 7500 m
3	Movement habitat	32	Forests with average tree height >10 m, do not fulfill criteria for habitat types 1 or 2, maximum moving distance 5000 m
4	Movement barrier	2000	Forests with average tree height < 10 m, openings, fields, maximum moving distance 64 m, allows for additional 1000 m moving in movement habitat
5	Water	4000	All types of waters, maximum moving distance 32 m, allows for additional 1000 m moving in movement habitat
6	Roads	2000	Maximum moving distance 64 m, allows for additional 1000 m moving in movement habitat

LCP was calculated between every combination of two nesting habitats and the number of paths traversing through stands was used as a weight for stands in scenarios. The most preferred habitat type in future refers to stands with similar characteristics as in the most preferred stands but they probably fulfill the age and DBH of trees of class 1 criteria during the simulation period of 30 years. Maximum distances of movement barriers, waters and roads were adjusted such that they allowed for additional 1000 m movement in moving habitat.

Table 3. Forest management scenarios with stand characteristics, connectivity criteria and actions allowed.

Forest management scenario	Stands characteristics, connectivity and actions allowed
	Stand characteristics for nesting habitat	Actions	Criteria for connectivity	Actions
SG1	Not relevant^a	No restrictions	Not relevant^a	No restrictions
Forest management scenarios contributing SFS habitats, SG2−SG11
SG2	Large aspen^b [4]	No cuttings^c	No criteria	No restrictions
SG3	Large aspen and/or medium-sized aspen^d [19]	No cuttings	No criteria	No restrictions
SG4	Large aspen and/or medium-sized aspen and/or large birch^e [68]	No cuttings	No criteria	No restrictions
SG5	Large aspen [4]	No cuttings	Number of connections, NOC > 500 [29]	Only thinnings^f
SG6	Large aspen [4]	No cuttings	NOC > 500 or NOC > 200 [67]	Only thinnings
SG7	Large aspen [4]	No cuttings	NOC > 500, NOC > 200 or NOC > 50 [143]	Only thinnings
SG8	Large aspen and/or medium-sized aspen and/or large birch [68]	No cuttings	NOC > 500 [29]	Only thinnings
SG9	Large aspen and/or medium-sized aspen and/or large birch [68]	No cuttings	NOC > 500 or NOC > 200 [67]	Only thinnings
SG10	Large aspen and/or medium-sized aspen and/or large birch [68]	No cuttings	NOC > 500, NOC > 200 or NOC > 50 [143]	Only thinnings
SG11	Large aspen and/or medium-sized aspen and/or large birch [68]	No cuttings	NOC > 500, NOC > 200 or NOC > 50 [143]	No cuttings

Allowed cuttings are presented for each management scenario SG1–SG11. Calculated SFS indexes were applied both at the onset of simulations as well as at the end of the 30-yr simulations. Numbers in brackets indicate the number of individual stands with corresponding stand characteristics and connectivity criteria at the onset of the simulations, year 2021.

^a In SG1 each stand is managed according to silvicultural guidelines which currently ignore SFS habitats.

^b Large aspen indicates that in a stand there are aspen stems/trunks with minimum diameter exceeding 22 cm (at breast height).

^c No cuttings indicate that neither thinnings nor clear cuttings are allowed in such stands.

^d Medium-sized aspen corresponds to a diameter of < 20 cm for aspen.

^e Large birch requires a birch stem larger than 22 cm at breast height.

^f Only thinnings allowed in such stands, no clear cutting.

Figure 2. Overview of dataset, indexes, simulations, and optimization procedure to construct management scenarios. Applied software presented in blue font. ArcGIS Desktop 10.6.1 (ESRI 2018) was used in the spatial analyses and Motti Stand Simulator (Salminen et al. 2005; Hynynen et al. 2015) in the simulations. Further analyses were carried out with SAS (ver 9.4, X64_10PRO platform) and J (Lappi and Lempinen 2014) software.

Table 4. Stumpage prices and silvicultural costs (in real terms) applied in assessing the NPV for forest management scenarios SG1-SG11.

Stumpage prices	Sawlogs, € m^−3	Pulpwood, € m^−3	Energywood, € m^−3
First commercial thinning	Pine: 42.19 Spruce: 42.70 Birch: 37.00	12.70 14.72 12.23
Intermediate thinnings	50.99 50.69 41.85	15.88 19.38 15.10
Final cutting	60.38 60.30 49.44	18.76 23.73 18.18
All cuttings and tree species			Stems: 4.24 Crowns: 3.40 Stumps: 1.43
Silvicultural costs
Labour cost of planting Material costs of planting Seeding Mounding Disc trenching Patch scarification Early cleaning Precommercial thinning Clearing of a thinning area Ditch network maintenance Fertilization	0.16–0.20 €/seedling^a 0.19–0.24 €/ seedling^a 224.5 € ha^−1 355.5 € ha^−1 196.0 € ha^−1 313.9 € ha^−1 35 € hour^−1^b 35 € hour^−1 35 € hour^−1 185 € ha^−1 320 € ha^−1

^a Unit costs per seedling depends on tree species (planting density).

^b Unit cost per hour, total costs calculated with time consumption models resulting in € ha⁻¹.

Figure 3. Suitable SFS forests (dark colour) and corridors (lines) associated with management scenario SG1 (a) and SG11 (b) after a 30 year-period.

Table 5. Average stocking and volumes of birches and aspen and total number of connections associated with forest management scenarios.

Forest management scenario	Average stocking (of which birches and aspen volumes), m^3 ha^−1	Area of suitable SFS forests at the end of time horizon^b, hectares
SG1	196.4 (23.1 and 1.1)^a	87.2
SG2 SG3 SG4	197.8 (23.1 and 1.2) 202.7(23.3 and 1.4) 213.2 (24.2 and 1.4)	90.1 101.1 120.4
SG5 SG6 SG7	207.9 (23.9 and 1.2) 220.6 (25.6 and 1.2) 236.5 (27.0 and 1.5)	103.1 120.5 139.8
SG8 SG9 SG10	217.6 (24.7 and 1.4) 225.4 (25.8 and 1.4) 236.9 (27.0 and 1.5)	124.2 131.8 140.3
SG11	237.8 (27.4 and 1.6)	140.3

^a The first value, 23.1 represents the volume of birches, and the second, 1.1 of aspen, m³ ha⁻¹.

^b The end of the time horizon corresponds to year 30.

Figure 4. Net Present Values (NPV) associated with forest management scenarios SG1-SG11, when 2% and 4% interest rates applied.

Table 6. Cost of an additional hectare suitable for SFS, € ha⁻¹.

Forest management scenario	Cost with 2% interest rate, € ha−^1	Cost with 4% interest rate, € ha^−1
SG2	14 081	14 145
SG3	12 580	12 026
SG4	13 897	13 398
SG5	20 187	18 916
SG6	19 810	17 769
SG7	21 801	18 957
SG8	15 461	14 668
SG9	17 607	16 046
SG10	21 741	18 929
SG11	22 127	19 251

Interest rate 2% and 4%.

Table 7. Cost of an additional hectare suitable for SFS, € ha⁻¹ when adjusted cutting removals applied.

Forest management scenario	Cost with 2% interest rate, € ha^−1	Cost with 4% interest rate, € ha^−1	Area of suitable SFS forests at the end of time horizon, hectares
SG3adjusted	12 176	11 388	153.5
SG5adjusted	5 584	5 423	154.7
SG8adjusted	9 947	8 448	167.2
SG11adjusted	25 948	20 628	165.6

Interest rate 2% and 4%. Area of suitable SFS forests also depicted at the end of the time horizon, i.e. 30 years. For BAUadjusted the suitable SFS forests covered 149.1 hectares at year 30 (cf. Table 5: SG1 87.2 ha).

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