Growth and yield models for forest stands on drained peatland sites in southern Finland

Forest Ecology and Management 107 Ž1998. 1–17

Growth and yield models for forest stands on drained peatland sites in southern Finland Hans Gustav Gustavsen a

a,)

, Riitta Heinonen b, Eero Paavilainen b, Antti Reinikainen

b

Finnish Forest Research Institute, Joensuu Research Station, P.O. Box 68, FIN-80101 Joensuu, Finland b Finnish Forest Research Institute, Vantaa, P.O. Box 18, FIN-01301 Vantaa, Finland Accepted 15 October 1997

Abstract Linear regression functions are presented for predicting the volume increment and yield of peatland stands on sites drained for forestry in southern Finland. The data were collected from 329 permanent sample plots measured over a 70-yr period. Site was incorporated into the functions by means of four post-drainage classes ŽI–IV.. These site classes were derived from the functional relationships between the post-drainage yield Žtotal yield minus initial stand volume. at a reference time of 40 yr since drainage within the 21 vegetational site types represented in the data. The growth and yield functions were derived separately for each yield class. Stand volume, stem number, age since drainage, effective temperature sum, peat depth, and ditch spacing were used as predictors in the growth and yield functions. A site classification table, based on stand dominant height, drainage age, and initial volume, is presented for determining the yield class when applying the functions. Yield class can also be determined from the vegetational site types widely used in Finland. The reliability of the forecasts primarily depends on the quality of the data used in deriving the functions and on the input data in an application situation. Care should be taken when applying the functions to long-term simulations of future post-drainage growth and yield, where the growth and yield functions can be applied together. q 1998 Elsevier Science B.V. Keywords: Peatland forest; Post-drainage stand development; Total stand yield; Simulation; Site productivity; Site classification

1. Introduction The tree-specific and stand-specific models for predicting growth and yield that have been developed in Finland are mainly for forest stands growing on mineral soils Že.g., Vuokila, 1965; Koivisto, 1970; Gustavsen, 1977; Nyyssonen and Mielikainen, 1978; ¨ ¨ Vuokila and Valiaho, 1980.. Many of these models ¨

)

Corresponding author. Tel.: q35-813-2514000; fax: q35813-2514111; e-mail: [email protected].

have also been applied to drained peatland forest despite the differences in stand structure, hydrology, and nutrient conditions between upland and peatland sites. The total area of forest stands on drained peatland sites in Finland is 5.96 million ha, which represents more than 20% of the area of productive forest land. There is, therefore, an obvious need for growth and yield models specifically developed for forest stands growing on drained peatland. Much of the international knowledge about improved forest growth on peatlands after drainage is based on results from the Nordic countries and Rus-

0378-1127r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. PII S 0 3 7 8 - 1 1 2 7 Ž 9 7 . 0 0 3 2 4 - 1

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H.G. GustaÕsen et al.r Forest Ecology and Management 107 (1998) 1–17

sia. The drainage activity in countries such as the USA and Canada is much younger, and the few studies so far reported are restricted to single shortterm experiments ŽHanell, 1988; Sundstrom, ˚ ¨ 1992.. Although much research has been conducted in peatland forestry, there are still relatively few productivity investigations based on statistical models that give the post-drainage increment or yield in absolute Ž1988. has develcubic metres per unit area. Hanell ˚ oped increment and yield functions for forest stands growing on drained peatlands throughout Sweden. No specific increment and yield functions for peatland stands have been developed in Norway, where peatland forest stands belonging to productive forest land are classified on the basis of upland site index classes ŽH40. and vegetation types by Thurmann-Moe Ž1963.. The major papers concerning growth models for drained forest in Russia are those published by Knize et al. Ž1981., Knize and Dekatov Ž1990., Pakhutchij Ž1991. and Krasilnikov et al. Ž1992.. Peatland investigations in North America have concentrated on black spruce Ž Picea mariana ŽMill... stands, e.g., Stanek Ž1968., Perala Ž1971., Payandeh Ž1973., Paivanen and Wells Ž1978., Sundstrom ¨ ¨ ¨ and Jeglum Ž1992. and Sundstrom ¨ Ž1992.. Growth and yield studies on forest established on drained peatlands are numerous in Finland Že.g., Multamaki, ¨ 1923; Lukkala, 1927; Heikurainen, 1959; Huikari et al., 1967;Seppala, ¨ ¨ 1969; Keltikangas et al., 1986; Penttila, ¨ 1989.. In addition, studies based on the results provided by the national forest inventories ŽPaavilainen and Tiihonen, 1984, 1985, 1988; Gustavsen and Paivanen, 1986; Mattila and Penttila, ¨ ¨ ¨ 1987. give a reliable picture of the development of forest stands on drained and undrained peatlands in Finland in general. Nevertheless, many of the investigations lack mathematical functions derived from statistical analyses that could be used for estimating stand increment on drained peatlands. Increment regression models or simulation models for drainage peatland have been presented by Saramaki ¨ Ž1977., Laine and Starr Ž1979., Ojansuu et Ž al. 1991., Miina et al. Ž1991., Miina Ž1996., Niemisto¨ Ž1991., Hokka ¨ ¨ et al. Ž1995.. Stand increment for virgin forested mires in Finland have been Ž1986.. The presented by Gustavsen and Paivanen ¨ ¨ single-tree growth models of Ojansuu et al. Ž1991.

for drained and undrained peatlands have been developed for predicting growth in large forest areas for use in the long-term forestry planning program, MELA ŽSiitonen, 1983.. The validation of these functions indicated an average bias of 1.1 m3 hay1 5 yry1 Žoverestimation. in the predicted 5-yr increment estimates Žroot mean square error s 39%. for virgin and drained pine and spruce mires. The lack of mathematical–statistical growth and yield functions for general use in Finland gave rise to the present study. The existing models are too few and limited, and have not been evaluated as tools for forest management uses. Some of the functions are restricted with respect to geographical area, tree species, and site, or have been developed for studying the influence of growth factors and not for the estimation of future growth. The main purpose of this study was therefore to improve the possibility of

Fig. 1. Location of the study areas; the numbering is according to Table 1.

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estimating increment and yield of a stand after drainage by developing alternative regression functions for predicting the absolute volume increment and yield in stands on drained peatland sites in southern Finland. The functions are intended for use in both practical forest management planning and in forest yield and economic research, such as estimation of the short- and long-term post-drainage increment and yield, and total stand yield for the entire life of the stand. 2. Materials and methods 2.1. Sample plot data The study was conducted using a network of permanent sample plots located in stands on drained

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mires, considered suitable for practical forest drainage ŽHeikurainen, 1980., throughout southern Finland. The sample plots were established between 1911 and 1982 by the Finnish Forest Research Institute. Data from 329 of the plots located in 26 study areas ŽFig. 1, Table 1. have been subjectively selected for this study. The stands have been remeasured from 2 to 9 times at varying time intervals Ž2–17 yr. after drainage; most of the remeasurements were done at 5–10-yr intervals Žon average 7 yr.. The size of the plots varies between 0.10 and 0.25 ha and their location in relation to the ditches was subjectively chosen ŽFig. 2.. The tree species composition of the original virgin mire stands was typical of similar stands in southern Finland ŽHeikurainen, 1971; Gustavsen and Paivanen, ¨ ¨ 1986., i.e., Scots pine Ž Pinus silÕestris L.. domi-

Table 1 Summary of the permanent plot data utilized in this study Study area

Bromarv, Solbole ¨ Teijo Tuusula, Ruotsinkyla¨ Pernaja Lapinjarvi ¨ Kymi Karjala Ylane, ¨ Leijansuo Forssa Ylane, ¨ Paroninsuo Ylane, ¨ Tapiola Vanaja Sippola Kauttua Eurajoki Padasjoki Mantyharju ¨ Niinisalo Vilppula Haadetjarvi ¨¨ ¨ Tohmajarvi ¨ Karstula Tervo Viitasaari Kajaani Muhos Total

Location N

E

deg

min

deg

min

60 60 60 60 60 60 60 60 60 60 60 60 60 61 61 61 61 61 62 62 62 62 63 63 64 64

02 15 22 31 37 36 51 47 45 49 57 57 50 06 18 24 25 51 04 02 15 56 06 10 16 50

23 22 25 26 26 26 22 22 23 22 22 24 27 22 21 25 25 22 24 22 30 24 26 26 27 26

03 23 00 02 10 54 06 18 41 16 26 26 02 11 45 03 23 25 29 44 22 25 48 03 58 06

Temperature sum d.d.

Number of original mire types

Number of sample plots Žstands.

Number of measured growth periods

1300–1350 1350 1300–1350 1300–1350 1350–1400 1300–1350 1300–1350 1300–1350 1350 1300–1350 1300–1350 1300–1350 1350–1400 1250–1300 1250–1300 1300–1350 1350–1400 1200–1250 1200–1250 1200–1250 1200–1250 1150–1200 1250–1300 1200 1100–1150 1050–1100

7 1 13 1 12 3 2 8 2 2 1 1 3 2 5 12 1 7 12 4 5 7 3 4 1 9 128

11 1 57 1 23 3 6 22 3 3 1 1 4 6 13 26 1 15 38 6 20 22 3 5 3 35 329

33 2 216 1 56 6 10 55 6 4 2 1 14 12 41 112 2 66 215 7 44 99 6 11 3 84 1108

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Fig. 2. Example of the location of a sample plot Žplot 5. in a ditch system Žspacing is 50 m..

nated stands Ž196 plots., Norway spruce Ž Picea abies ŽL.. Karst.. dominated stands Ž43 plots., downy birch Ž Betula pubescens, Ehrh.. dominated stands Ž54 plots. and mixed stands Ž36 plots. of the above species, with occasional mixtures of other hardwood genera Ž Alnus, Salix, Sorbus, etc... The studied forest stands have been thinned Žon average 2–3 low thinnings. and drained without any fertilizations. The thinnings after drainage have decreased the structural diversity of the original virgin mire stands; the un-

even age and tree-size structure, usually remain for the duration of the first tree generation after drainage ŽHokka ¨ ¨ and Laine, 1988; Uuttera et al., 1996.. However, in our studied forest stands the repeated selective cuttings after drainage have made the stand structure much more even-aged Žhomogenous.. The growth and yield functions derived in this study are based on the repeated measurements of all 329 plots, i.e., on 1108 growth-period observations. The data for only the most recent growth period on each plot, i.e., 329 observations, were used separately to characterize the long-term post-drainage situation of the stands and to examine the reliability of the final growth and yield functions Žsee Section 2.4.. 2.2. Measurements and calculations The following environmental variables were measured at the time of drainage: peat-layer thickness,

Table 2 Original site types and sample plot characteristics Žmeans, standard deviations. Mire site type a

Number of sample plots

Spruce hardwood mires LhK 8 RhK 25 RhSK 3 MK 27 VSK 18 KgK 16 PK 8 PsK 10 Pine fens and bogs VLR 2 RhSR 18 VSR 40 KgR 12 PsR 7 KR 9 LkSR 28 IR 51 TR 12 RaR 6 Open fens RhSN VSN LkN a

9 9 11

Number of growth periods

Age of drainage Žyr.

Ditch spacing Žm.

Peat depth Žm.

Initial volume Žm3 hay1 .

47 92 5 95 57 50 16 42

42 " 17 44 " 17 22 " 10 42 " 20 37 " 12 34 " 16 39 " 16 44 " 17

92 " 10 77 " 23 54 " 11 76 " 25 75 " 21 89 " 14 78 " 22 74 " 18

0.41 " 0.46 1.32 " 1.18 0.73 " 0.38 1.25 " 0.73 1.03 " 1.02 0.19 " 0.08 1.84 " 1.69 1.65 " 1.81

39.1 " 37.9 20.0 " 30.7 21.7 " 37.5 49.8 " 42.8 12.2 " 10.2 54.6 " 35.3 23.6 " 34.3 5.0 " 6.3

14 58 130 32 30 29 105 184 54 11

69 " 0 33 " 22 42 " 18 24 " 8 57 " 10 45 " 13 38 " 12 40 " 15 44 " 3 25 " 18

99 " 0 61 " 23 76 " 25 83 " 20 74 " 34 39 " 33 70 " 23 69 " 28 63 " 26 53 " 24

0.90 " 0.14 0.71 " 0.30 0.79 " 0.81 0.15 " 0.10 1.61 " 1.82 1.50 " 1.12 1.37 " 1.25 1.88 " 1.36 0.91 " 0.36 2.35 " 0.55

5.0 " 0.0 5.7 " 4.1 11.2 " 19.7 56.6 " 29.6 15.0 " 16.1 25.3 " 28.5 27.2 " 24.9 26.2 " 29.8 13.2 " 8.2 5.8 " 4.9

13 29 15

33 " 4 52 " 12 36 " 1

73 " 14 67 " 18 54 " 4

1.62 " 1.00 1.17 " 0.42 4.03 " 1.65

0.0 " 0.0 0.1 " 0.3 0.0 " 0.0

See Appendix A for list of symbols.

H.G. GustaÕsen et al.r Forest Ecology and Management 107 (1998) 1–17

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Table 3 Yield classes and sample plot characteristics Žmeans, standard deviations. Yield class Žmire site types1 .

Number of sample plots

Number of growth periods

Age of drainage Žyr.

Ditch spacing Žm.

Peat depth Žm.

I ŽLhK, VLR. II ŽRhK, RhSK, MK, KgK, VSK, RhSN. III ŽPK, PsK, RhSR, VSR, LkSR, PsR, KR, KgR, VSN. IV ŽIR, TR, RaR, LkN.

10 98 141 80

61 312 471 264

47 " 19 39 " 16 40 " 17 39 " 14

93 " 09 77 " 22 70 " 25 65 " 26

0.51 " 0.46 1.07 " 0.97 1.07 " 1.13 2.06 " 1.53

a

See Table 2.

ditch spacing, effective temperature sum Žthreshold temperature of q58C. and original site type. During the long period covered by the study there have naturally been some methodical changes in the measurement and calculation procedures. Most of the changes have concerned the selection of sample trees on the plots and the stem-volume estimation. The variables measured on the sample and tally trees have, however, always been the same. All the trees on each plot were numbered and the diameter at breast height Ž d . measured in two directions Žat right angles to each other. in mm. Sample trees were selected Ždescribed below. and their diameter measured at a height of 6 m Ž d 6.0 ., or at 3 m in the case of trees less than 8 m Ž d 3.0 .. Their height Ž h. in m and bark thickness Ž b . in mm were also measured. Measurements carried out prior to 1948 were made according to the procedure described by Ilvessalo Ž1932., pp. 17–19. From 10 to 18 sample trees belonging to the dominant and lower canopy classes were subjectively selected. The stem volume of the sample trees Žincluding those felled during thinning. were determined by stem section volume measurements. Total stand volume was then calculated from the average volume and stem number in each diameter class. In the period 1948–1973, about 25–30 standing sample trees were measured per plot. The sampling design was the same as during the previous prior period. The stem volume, however, was estimated using the volume tables Ždbh, height, taper class. developed by Ilvessalo Ž1947.. Total stand volume was estimated on the basis of the stem volumes estimated from the tables and the number of stems in each diameter class. During the period of 1973–1979 the same number of sample trees as during 1948–1973 were objectively selected by relascope. The total stand volume was calculated on

the basis of the basal area value and the mean unit volume of the relascope sample trees ŽKuusela, 1960, 1966, pp. 11–14.. Since 1979, sample trees were selected systematically and the stand characteristics computed using KPL, a computer program developed by Heinonen Ž1994.. The total stand volume was calculated on basis of volume characteristics of the sample trees, computed from the stem volume and taper curve functions developed by Laasasenaho Ž1982.. The following data for each plot were extracted from the data for each of the four time-periods described above and combined into a single file: tree species composition, time since drainage, the period in years since the last measurement, total volume, mean annual volume increment during the period, total yield, dominant height Žnot always available. per species and stand, and the stand volume at the time of drainage. These data were used to calculate

Fig. 3. Example of the grouping of data into post-drainage yield classes ŽI–IV. Žpost-drainage at Tdr s 40 yr. with the aid of yield models Žcurves. Ž Ynv s f ŽTdr ...

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Table 4 Data on yield classes and stands, from the most recent measurement Yield class Žmire site type1 .

Total yield Žm3 hay1 .

I ŽLhK, VLR. II ŽRhK, RhSK, MK, KgK, VSK, RhSN. III ŽPK, PsK, RhSR, VSR, LkSR, PsR, KR, KgR, VSN. IV ŽIR, TR, Rar, LkN.

411.1 " 69.4 260.7 " 31.2 10.9 " 8.5 7.4 " 3.1 23.0 " 1.0 899 " 460 21 238.9 " 113.5 159.8 " 79.2 5.4 " 2.4 5.5 " 2.5 16.4 " 4.5 2916 " 2786 20

a

Stand volume Žm3 hay1 .

Mean postdrainage yield Žm3 hay1 yry1 .

Current growth Žm3 hay1 yry1 .

Dominant Stem height number Žm. Žhay1 .

Tree species% pine spruce hardwood

Initial volume Žm3 hay1 .

29 39

50 41

32.3 " 36.4 30.6 " 36.6

198.9 " 111.3 148.7 " 85.4

5.5 " 2.6 5.3 " 2.6 14.2 " 4.1 3394 " 2949 62

8

30

18.2 " 25.2

136.1 " 84.0

2.9 " 1.7 4.3 " 3.1 11.2 " 4.0 2180 " 2256 97

0

3

19.1 " 26.0

112.2 " 73.4

See Table 2.

the 5-yr volume increment sum Ž Iv5 . on the basis of the mean annual volume increment value for every growth period Žirregular.. The period increment was calculated as the difference in volume at the end of two successive measurements. In addition to the current total yield Ž Yv ., i.e., the sum yield in both the pre- and post-drainage periods of the stand up to the last measurement, the post-drainage yield Ž Ynv . was also calculated as the difference between the total

yield and stand volume at the time of drainage Ž Yv y V0 .. The mean annual post-drainage yield Žincrement. was calculated as the post-drainage yield divided by the number of years since drainage ŽTdr .. The changes in the method for calculating stem volume have probably led to small relatively insignificant bias in the period stand increment for about 150 observations Žin all 1108. calculated as the difference between two stand volumes based on dif-

Fig. 4. The mean annual post-drainage yield on mire site types in relation to the site quality index of Heikurainen and Seppala ¨ ¨ Ž1973.. The yield Ž y . expressed under bark. The index Ž x . describes the productivity after drainage according to temperature sum of 1250 d.d.

H.G. GustaÕsen et al.r Forest Ecology and Management 107 (1998) 1–17

ferent stem volume calculation methods Žcf. Laasasenaho, 1982.. These small systematic errors are, however, outweighed by the advantage of having such an extensive long-term material, where the increment values covering most of the observation period in this study, were calculated using the same method.

Table 5 The mean values of dominant height Ž Hdom . in post-drainage yield classes ŽI–IV. of drained peatland forest stands in Southern Finland Tdr V0 0–20, m3 hay1 I

2.3. Vegetational site type classification The virgin mire site type was determined before ditching or very soon after Ž0–3 yr. in the case of 85% of the sample plots. In the remaining cases, the classification was done later and often with the help of old vegetation data or drainage plan documents. The original classification was made using a contemporary version of Cajander Ž1913. classification ŽCajander, 1914; Lukkala, 1929, 1939; Lukkala and Kotilainen, 1945; Heikurainen and Huikari, 1960.. For this study, all the site type names were adapted to the mire site types and nomenclature presented by Heikurainen and Pakarinen Ž1982. ŽTables 2 and 3, see Appendix A.. This was also in agreement with that of Laine and Vasander Ž1990.. Operational site groupings can be formed on the basis of the original mire site types. Those referred here are the site types according to Huikari Ž1952, 1974. and the predicted peatland forest type according to Laine Ž1989..

Fig. 5. The average post-drainage yield Ž Ynv . development as a function Ž2–5. of years since drainage ŽTdr . within site classes ŽI–IV., based on post-drainage yield at Tdr s 40 yr.

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II

Hd o m , m 10 14.0 12.9 20 16.5 14.3 30 18.2 15.3 40 19.6 16.0 50 21.4 16.8

) 40

21–40

III

IV

I

II

III

IV

I

II

III

IV

11.2 12.5 13.4 14.2 14.8

9.9 10.4 10.6 11.0 11.2

15.4 18.0 19.8 21.4 23.4

14.0 15.6 16.7 17.4 18.3

12.2 13.6 14.6 15.4 16.1

10.8 11.3 11.5 12.0 12.2

16.0 18.7 20.7 22.3 24.3

14.6 16.2 17.4 18.1 19.0

12.7 14.2 15.1 16.0 16.7

11.2 11.7 12.0 12.5 12.7

Site classification model ŽEq. Ž6.. based on stand volume at the time of drainage Ž V0 ., current dominant height Ž Hdom ., drainage age ŽTdr . and post-drainage yield Ž Ynv ..

2.4. Modelling The construction of regression functions for the prediction of volume increment and yield was initiated with graphical and numerical correlation and preliminary linear regression analyses to select a good combination of variables for the final functions. The following model Ž1. was used in all the regression analyses, except for one case Žsee Fig. 4.: ln y s ln a q b 1 P ln x 1 q b 2 P ln x 2 q . . . qbn P ln x n Ž 1. where y is the future 5-yr volume increment Ž I v5 ., or post-drainage yield Ž Ynv ., or actual total yield Ž Yv ., x 1 , x 2 , . . . , x n are stand and environmental variables, and a, b 1 , b 2 , . . . ,bn are the parameters to be estimated. Preliminary examinations, performed separately for the original site types and for the two operational site type groups Žsee Section 2.3., showed that the most important regressors were stand volume Ž V ., initial volume Ž V0 ., stem number Ž N ., dominant height Ž Hdom ., years since drainage ŽTdr ., temperature sum ŽTS ., thickness of peat layer ŽTP ., ditch spacing Ž S K . and the original site type Žsee Appendix A.. The analysis of the data showed a high variation in growth and yield within a single site mire type. The mean differences in growth and yield between the mire site types and also between the operational vegetational groupings were small, but

H.G. GustaÕsen et al.r Forest Ecology and Management 107 (1998) 1–17

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statistically significant in the overall testing. However, the risk of making major errors in estimation of the site variable would therefore arise if many small site classes were applied in practice. Due to the results the site quality was expressed using only four post-drainage yield classes: - 150, 150–199, 200–249, ) 249 m3 hay1 . The basis for the site classification system was the post-drainage yield Ž Ynv . at 40 yr after drainage ŽFig. 3.. The use of 50 m3 hay1 Ž Ynv . as the class interval in classification Žequivalent to 80 m3 hay1 in total yield Yv s Ynv q V0 . was based on the mean standard deviation of the total yield in the data Ž85 m3 hay1 . Žaverage pre-drainage yield was 30 m3 hay1 s V0 ., and on the average difference between the sites in existing Finnish growth and yield tables for upland forest stands ŽIlvessalo and Ilvessalo, 1975; Vuokila and Valiaho, 1980.. The classification of the data ¨ according to the values of Ynv at Tdr s 40 yr was begun by deriving a regression function for each of the 21 mire site types. The function Ž Ynv s Ž Yv y V0 . s f ŽTdr .. described the relationship between the post-drainage yield Ž Ynv . and the time since drainage ŽTdr . for all stands classified as the same original

mire site type at the time of establishment of the permanent plots. On the basis of these functions, 21 post-drainage yield curves were plotted against drainage age, and the yield class was then determined for each stand at the time Tdr s 40 yr Žan example in Fig. 3.. Stands belonging to the same original site type were not split between the yield classes, despite considerable intra site type variation in yield and growth. However, this procedure ensured that the longer term post-drainage development data of each stand automatically affected the estimation of the parameters in the regression functions, based on the 5-yr remeasurement observations. The final growth and yield functions were then derived separately from these observations in each of the four post-drainage yield classes. Statistically, there were shortcomings in the data for applying linear regression; in presupposed normality and continuity in the distribution of the variables and in the statements of constant variance and linearity. The use of logarithmic transformations of the variables corrected for some of these discrepancies. The possible influence of the autocorrelation in the dependent variables caused by the longitudinal data was exam-

Table 6 Functions for predicting stand volume increment Ž I v5 . on drained peatland sites in Southern Finland Dependent variable ln I v5 Variable

Post-drainage yield class and function I, 7 Coefficient

Intercept ln V P ln N P lnŽTdr q 1. ln V ln N lnŽTdr q 1. TS TP SK

3.7791 0.0030

y0.0052 sy s 0.2941 sf s 0.2867 R 2 % s 15.3 S.E.% s 29.3 PRESSs 10.969 Q 2 PRESSs 0.012 RMSEs 11.7% n s 61

II, 8 t-value 11.9 1.8

III, 9

IV, 10

Coefficient

t-value

Coefficient

t-value

Coefficient

t-value

y1.7749

y4.0

y1.2682

y3.2

y8.2926

y7.9

0.1977 0.2317 0.1515 0.0017 y0.0096

7.1 8.6 6.3 6.2 y4.2

0.2248 0.1666 0.2024 0.0013

9.7 5.8 8.0 5.2

0.3606 0.4932 0.1777 0.0044 y0.0130

7.2 9.7 3.5 6.4 y3.0

y2.2 sy s 0.4899 sf s 0.3720 R 2 % s 43.3 S.E.% s 38.5 PRESSs 44.994 Q 2 PRESSs 0.397 RMSEs 11.0% n s 312

sy s 0.6427 sf s 0.4374 R 2 % s 54.1 S.E.% s 45.9 PRESSs 103.520 Q 2 PRESSs 0.467 RMSEs 14.8% n s 471

sy s 0.9346 sf s 0.6735 R 2 % s 49.1 S.E.% s 75.8 PRESSs 176.879 Q 2 PRESSs 0.230 RMSEs 31.0% n s 264

H.G. GustaÕsen et al.r Forest Ecology and Management 107 (1998) 1–17

ined by separate analyses of subsets of data Žonly the last observation from each stand-cross sectional data., and the effect of collinarity between regressors was examined by ridge regression technique in the final variable selection. Using also a critical strategy, i.e., minimising the number of predictors, ensuring a high number of observations for estimation of each functions Žyield class I being an exception., helped to correct for discrepancies and to attain satisfactory models. Systematic errors in the growth and yield estimates were examined using one-, two- and threeway residual tables covering the whole range of the predictors and regressors in question.The differences among the equations describing the post- drainage yield in each site class were examined by analysis of variance Ž F-test., and the predictive ability of the growth and yield models were tested with cross validation Že.g., Weisberg, 1985, pp. 228–230.. Four cross validation sections for each yield class data

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were made Žcf. Palmborg and Nordgren, 1996. and Predictive Sum of Squares ŽPRESS., the explained variation of the cross-validation ŽQ 2 PRESS. and average prediction error ŽRMSE. were calculated. 3. Results 3.1. The stands Stand volume at the time of drainage Ž V0 . varied from 0 to 57 m3 hay1 , depending on the mire site type ŽTable 2.. These volumes are, in general, smaller than those reported by Heikurainen Ž1971. and GusŽ1986. for similar virgin mires. tavsen and Paivanen ¨ ¨ The highest stand volumes at the time of drainage were associated with mesotrophic spruce swamp ŽMK, KgK. sites and oligotrophic pine forest ŽKgR. sites. The volumes for the most fertile sites ŽLhK, RhK and VLR. and the Carex globularis spruce

Fig. 6. Residuals Žln y y ln yˆ . in the volume increment equations 7, 8, 9, 10 ŽTable 6. according to predicted volume increment ln y, ˆ ln y s observed increment.

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swamps ŽPsK. were unexpectedly low. There was a depression of initial volumes in fenlike types that was not observable after the classification of data into yield classes ŽTable 3.. The stand volume Ž V . of the growing stock from the most recent measurement ŽTable 4. was 80% or more of the total yield on poor, pine-dominated sites, but only about 60% for the more fertile, hardwoodmixed sites. The stand volume was strongly correlated with the stand dominant height Ž Hdom . Ž r s q0.81. and with the post-drainage yield Ž Ynv . Ž r s q0.80.. The dominant height was again strongly correlated with the post-drainage yield Ž r s q0.77., and therefore clearly related to the post-drainage yield classes ŽTable 4.. Total yield Ž Yv . of the site at the time of the last measurement was affected by the number of years since drainage and stand volume at the time of drainage. The mean annual post-drainage yield Žs Ynv rTdr . is therefore a better basis for comparing the post-drainage productivity of different sites, and was well correlated with the pine bog and fen ŽVLR–RaR. sites and for those that were originally treeless fens ŽRhSN–LkN.. For the spruce– hardwood swamps, this relationship was irregular; low yield was associated with the most fertile sites ŽRhK and RhSK. and high yield with the oligotrophic PK sites. The mean annual post-drainage yield of the site types correlated strongly Ž r s q0.73.

with the site quality index as presented by Heikurainen and Seppala ¨ ¨ Ž1973. and Heikurainen Ž1973, 1980. ŽFig. 4.. The current annual volume increment calculated for the last measured period represents a different period of time compared to the time since drainage of the stands. It thus varied more irregularly than the mean annual post-drainage yield and was weakly related to the fertility of the site types The range was 1.8–7.5 m3 hay1 yry1 , depending on the site type, but the growth of most of the site types Ž90%. was in excess of 4 m3 hay1 yry1 . Other variables, such as tree species composition, were related to stem number. The sharpest difference in species composition occurred in the yield classes ŽTable 4.: class I was hardwood-dominated; in class II birch and spruce amounted to 80% with pine accounting for the remaining 20%; in class III the percentage of conifers was 79% and the poorest yield class IV was strongly dominated by pine Ž97%.. 3.2. Post-drainage yield (site) classification The curves in Fig. 5 describe the average development of the post-drainage yield Ž Ynv . as a function Ž2–5. of the drainage age ŽTdr . within each of the four classes ŽI–IV. used as basic site variables in the final growth and yield functions ŽSection 3.3..

Table 7 Functions for estimating current total yield Ž Yv . Žsum of all growth and removals in the pre- and post-drainage period. in stands on drained peatland sites in southern Finland Dependent variable ln Yv Variable

Yield class and function I, 11

Intercept ln V lnŽTdr q 1. ln N

II, 12

III, 13

IV, 14

Coefficient

t-value

Coefficient

t-value

Coefficient

t-value

Coefficient

t-value

1.4035 0.8854 0.1698 y0.1233 sy s 0.7889 sf s 0.2502 R 2 % s 90.4 S.E.% s 25.4 PRESSs 23.362 Q 2 PRESSs 0.385 RMSEs 11.8% n s 61

2.5 12.9 4.0 y2.4

1.6369 0.8754 0.1373 y0.1330 sy s 1.0017 sf s 0.3352 R 2 % s 90.0 S.E.% s 32.7 PRESSs 38.722 Q 2 PRESSs 0.876 RMSEs 7.5% n s 312

7.0 37.2 6.8 y5.8

1.5700 0.8049 0.1498 y0.1069 sy s 1.1403 sf s 0.3252 R 2 % s 91.9 S.E.% s 33.4 PRESSs 56.205 Q 2 PRESSs 0.908 RMSEs 8.0% n s 471

8.2 47.3 8.0 y5.0

1.1410 0.8421 0.1502 y0.0979 sy s 0.9511 sf s 0.3216 R 2 % s 88.7 S.E.% s 33.0 PRESSs 44.391 Q 2 PRESSs 0.813 RMSEs 10.3% n s 264

5.7 36.7 6.2 y4.3

H.G. GustaÕsen et al.r Forest Ecology and Management 107 (1998) 1–17

Post-drainage yield class I: ln Ynv s y0.1442 q 1.5958ln Ž Tdr q 1 . , R 2 % s 91.6, sf s 0.3858

Ž 2.

II: ln Ynv s y0.0563 q 1.4243ln Ž Tdr q 1 . , R 2 % s 81.9, sf s 0.6106

Ž 3.

III: ln Ynv s y0.4420 q 1.4526ln Ž Tdr q 1 . , R 2 % s 80.6, sf s 0.6304

Ž 4.

IV: ln Ynv s y0.2280 q 1.2330ln Ž Tdr q 1 . , R 2 % s 63.6, sf s 0.7036

Ž 5.

The continuous by class effect used to test the homogenity of slopes, was statistically significant Ž F s 5.349, p s 0.001. for Eqs. Ž2. – Ž5.; the respect to time ŽlnŽTdr q 1.. is different in the levels of the post-drainage yield classes Žcf. the curves in Fig. 5.. The four yield classes can be expressed in the following absolute terms of average stand productivity as the mean annual post-drainage yield over the time period of 40 yr since drainage Ž Ynv 40 yry1 .: yield class I s 8.7 m3 hay1 yry1 , II s 5.6, III s 4.3, IV s

11

2.5. The post-drainage yield cannot be directly measured in the field and has to be determined indirectly using measurable variables, prior to the prediction of growth and yield. A yield classification model ŽTable 5. for stands growing on drained peatlands in southern Finland was therefore derived from the pooled data Ž926 observations., where the yield class can be determined on the basis of stand dominant height Ž Hdom ., initial volume Ž V0 . and drainage age ŽTdr .. Table 5 was derived from the following relationship ŽEq. Ž6.. between the dominant height and the drainage age, the initial volume and the post-drainage yield Ž Ynv .: ln Hdom s 1.7407 q 0.0777ln V0 q 0.4656ln Ž Ynv rTdr . , R 2 % s 59.6, sf s 0.3220

Ž 6.

3.3. Growth and total yield functions The main results in the study are the four functions 7–10 in Table 6 for predicting future 5-yr

Fig. 7. Residuals Žln y y ln yˆ . in the total yield equations 11, 12, 13, 14 ŽTable 7. according to estimated total yield ln y, ˆ ln y s observed yield.

12

H.G. GustaÕsen et al.r Forest Ecology and Management 107 (1998) 1–17

Fig. 8. Predicted 5-yr volume increment Ž I v5 . as a function of stand volume Ž V . and years since drainage ŽTdr . in post-drainage classes I–IV Žequations 7–10 in Table 6.. The other predictors are standardized to mean value: Eq. 7: N s 3786, S K s 93, Eq. 8: N s 3908, TS s 1266, TP s 9, Eq. 9: N s 3912, TS s 1230, Eq. 10: N s 3011, TS s 1263, T P s 15.3.

volume increment Ž I v5 . of stands growing on drained peatlands in southern Finland. Examples of the residuals of the growth functions in the basic data are given in Fig. 6. Four additional functions 11–14 for estimating actual total yield Ž Yv . at the beginning of the future 5-yr period Žtime of measurement. are presented in Table 7 and the residuals in Fig. 7. Actual total yield comprises all summarized growth and removal of the stand in both pre- and postdrainage periods up to the time of measurement. The functions are logical with respect to variables. In the growth functions, describing the change in stand and site caused by the drainage, were needed environmental variables in addition to stand characteristics. The enviromental variables were not necessary Žno significance. for estimating the total yield Žhaving a more static character., because of the logical strong correlation to stand criteria. Examples of predicted volume increment according to the functions 7–10 are presented in Fig. 8. In short- and long-term

predictions of future yields the growth and yield functions can be used in combination; i.e., the yield functions Ž11–14. give the initial yield estimates in the simulation and the additional future stand development Žyield. can be predicted using the growth functions Ž7–10..

4. Discussion 4.1. Reliability At the moment, the data used in this study are the best available long-term permanent sample plot material in Finland. It is unique with respect to age and covers a wide range of drained mire forest stands ŽTable 2. in southern and central Finland, and also includes comprehensive information about the original mire sites and stand characteristics at the time of drainage. Statistically, however, there are shortcom-

H.G. GustaÕsen et al.r Forest Ecology and Management 107 (1998) 1–17

ings in the data for deriving linear regression functions ŽSection 2.4.; e.g., the presence of collinearity in the data caused problems in variable selection and weakened the reliability of the parameters in the functions. The significance tests Ž t-values. of the individual parameters in the functions may therefore be uncertain; the functions are intended for making predictions and not for studying separately the effects of individual predictors on growth and yield. No clear changes, however, were observed in the estimated coefficients and test values after examination using ridge regression analysis and cross sectional data. No clear systematic errors were found in the functions ŽFigs. 6 and 7.. There may, however, be some bias in the predictions when applying the growth functions in practice owing to the lighter than normal thinnings that were performed on the sample plots. The main volume increment functions may lead to considerable Žrandom. errors ŽS.E.%. in the prediction of growth for individual stands; errors varied from 29 to 45% in yield classes I–III and was as high as 76% in class IV ŽTable 6.. The average growth prediction errors ŽRMSE. according to the cross validation of the basic data, varied from 11 to 31%, and indicated that the errors of single predictions will decrease when a large number of predictions are made for several stands in forestry planning inventories. It must be concluded, that all the growth and yield functions in the four site classes do not give results with the same reliability; e.g., the cross validation showed no or poor predictive ability ŽQ 2 PRESS. for growth equations of yield class I and IV. However, compared to the errors in predicted volume increment estimates from the single-tree growth models of Ojansuu et al. Ž1991. ŽRMSEs 39%. for drained and undrained peatland forests, the functions seemed to have an acceptable accuracy for predicting future growth. The relative errors in the growth estimates are of the same order of magnitude as for the functions derived for virgin peatland stands ŽGustavsen and Paivanen, 1986., and are about 10 to 20% higher ¨ ¨ than those for upland stands Že.g., Nyyssonen and ¨ Mielikainen, 1978.. Due to the variation of pristine ¨ mires the forest types of drained peatlands are ecologically more heterogenous than upland forest types Že.g., Laine, 1989; Paavilainen and Paivanen, 1995.. ¨ ¨

13

Therefore the mean values for volume, dominant height, tree age, etc., do not describe the real growth and yield status in peatland stands as well as they do in the case of upland forests. The structure of the studied forest stands were rather homogenous with respect to tree size structure, and therefore one single dominant height classification model was adjusted to the whole data neglecting the fact that site index models should be principally species-specific. Recently, however, Gustavsen Ž1996. has showed that only small systematic errors were connected to the use of one site index model for both spruce-, birchand pine-dominated stands and mixed stands on drained peatland. However, from a theoretical point of view separate models would be more reliable and correct. The potential effects of the long-term stand development of trends in forest productivity according to calendar time and changes in average tree age were not possible to de-correlate in this study. On the other hand it must be pointed out that in Finland no studies have indicated an overall trend of increasing forest productivity as in some other European countries Žcf. Spiecker et al., 1996.. 4.2. Growth and yield comparisons Direct comparison between the results from this study and those from other investigations are difficult to make because of differences in site-classification systems. In Finland, the classification of pristine mires is based on site ecological principle ŽEurola et al., 1984., and the type of variation is explained by nutritional and hydrological variables. Hydrological differences between sites radically decrease after drainage and the type series of drained peatland forest is determined by nutritional fertility ŽPaavilainen and Paivanen, 1995.. ¨ ¨ The most relevant study for evaluating the postdrainage results obtained in this study is that of Ž1988. in Sweden. The mean annual postHanell ˚ drainage volume increments ŽMAI. for the tall and low herb type, Žspruce q hardwoods., bilberry– horsetail type, Žspruce q hardwoods., tall sedge type Žpine. and low sedge type, Žpine. Ž9.8, 8.4, 3.4 and 2.2 m3 hay1 yry1 . in climatic conditions Žtemperature sum s 1300 d.d.. according to Table 10 of Ž1988., correspond very well to the average Hanell ˚

14

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post-drainage productivity of yield classes I–IV in this study. The annual volume increments for virgin mire sites ŽGustavsen and Paivanen, 1986. are clearly ¨ ¨ below the values obtained for stands established on drained peatland sites. The comparison to some site type-yield studies ŽHeikurainen, 1959; Keltikangas et al., 1986; Paavilainen and Tiihonen, 1988. showed that features characteristic of the present data ŽTable 4. are the high mean volumes in yield class IV Ždwarf-shrub pine bog ŽIR. V s 125 m3 hay1 . and the high percentage of hardwoods in class II Žherb-rich spruce– hardwood swamps ŽRhK. 70%..

Appendix A. Symbols and abbreviations

Tree: b d d 3.0 d 6.0 h Stand: Hdom Iv5 N V V0 Yv

Ynv

bark thickness at breast height, mm diameter at breast height Ždbh., cm, including bark diameter at 3 m height, Žfor sample trees shorter than 8 m., cm, including bark diameter at 6 m height, cm, including bark height, m dominant height Žmean height of 100 thickest trees hay1 ., m volume increment during the future 5-yr period, m3 hay1 5 yry1 , including bark number of stems per hectare volume, m3 hay1 , including bark initial volume at the time of drainage, m3 hay1 , including bark current total yield, Žsum of the yields in pre- and post-drainage periods., m3 hay1 , including bark current post-drainage yield, m3 hay1 , including bark: Yv y V0

EnÕironment: TS effective temperature sum Žthreshold temperature of q58C., d.d. TP thickness of peatlayer, m Ždm in the functions.

Tdr SK

years since drainage, yr ditch spacing, m

Site classifications: Mire site types Žsee Heikurainen and Pakarinen, 1982. and their correspondence with the site classes 1–6 of Huikari Ž1952, 1974., the peatland forest types Žtkg. of Laine Ž1989. and the post-drainage yield classes ŽI–IV. in this study. Spruce–hardwood swamps: LhK eutrophic spruce–hardwood swamp; 1; Rhtgk; I RhK herb-rich Ž mesotrophic . spruce – hardwood swamp; 2; Rhtkg; II RhSK herb-rich Ž mesotrophic . spruce – hardwood fen; 2; Rhtkg; II MK Vaccinium myrtillus Žmeso-oligotrophic. spruce swamp; 3; MtkgŽI.; II VSK tall-sedge Žmeso-oligotrophic. spruce– hardwood fen; 3; MtkgŽII.; II KgK paludified Vaccinium myrtillus Žoligomesotrophic. spruce forest; 3; MtkgŽI.; II PK Vaccinium Õitis-idaea Žoligotrophic. spruce swamp; 4; PtkgŽI.; III PsK Carex globularis Žoligotrophic. spruce swamp; 4; PtkgŽI.; III Pine fens and bogs: VLR eutrophic pine fen; 1; MtkgŽII.; I RhSR herb-rich Žmesotrophic. pine fen; 2; MtkgŽII.; III VSR tall-sedge Žmeso-oligotrophic. pine fen; 3; PtkgŽII.; III KgR paludified Žoligotrophic. pine forest; 4; PtkgŽI.; III PsR Carex globularis Žoligotrophic. pine swamp; 4; PtkgŽI.; III KR spruce–pine Žoligotrophic. swamp; 4; PtkgŽI.; III LkSR low-sedge Žoligotrophic. pine fen; 4; Vatkg; III IR dwarf-shrub Žombrotrophic. pine bog; 5; Vatkg; IV TR cottongrass Žombrotrophic. pine bog; 5; Vatkg; IV

H.G. GustaÕsen et al.r Forest Ecology and Management 107 (1998) 1–17

RaR

Sphagnum fuscum Žombrotrophic. pine bog; 6; Jatkg; IV ¨ Open fens and bogs: RhSN herb-rich Žmesotrophic. sedge fen; 2; MtkgŽII.; II VSN tall-sedge Žmeso-oligotrophic. fen; 3; PtkgŽII.; III LkN low-sedge Žombro-oligotrophic. fen; 5; Jatkg; IV ŽVa s dwarf-shrubs, Ja¨ s ¨ Cladina-lichens. Others: R2% degree of determination Ž R s multiple correlation coefficient. sy original standard deviation of the dependent variable sf residual standard deviation Žstandard deviation of the dependent variation about the function. S.E.% relative standard error of the estimate: 2 100 P e s f y 1 y observed values of the dependent variable yˆ calculated values of the dependent variable yˆ mean value of calculated y-values by the models y mean value of observed y-values PRESS predictive sum of squares: ÝŽ y y yˆ . 2 2 Q PRESS explained variation of the cross-validation: Ž1-PRESSrSStotal . SS total sum of squares of the deviation of the observed y-values from the mean: ÝŽ y y y.2 RMSE relative average prediction error:

(

ln n

natural logarithm number of observations.

References Cajander, A.K., 1913. Studien uber die Moore Finnlands. Acta ¨ Forestalia Fennica 2 Ž2., 1–208.

15

Cajander, A.K., 1914. Metsahallinnon suonkuivaustoissa ¨ ¨ ¨ kaytetyt ¨ suotyypit. Metsatilasto XVII. Metsahallitus, 10 pp. ¨ ¨ Eurola, S., Hicks, S., Kaakinen, E., 1984. Key to Finnish mire types. In: Moore, P. ŽEd.., European Mires, Academic Press, London, pp. 11–117. Gustavsen, H.G., 1977. Valtakunnalliset kuutiokasvuyhtalot. ¨ ¨ Abstract: Finnish volume increment functions. Folia Forestalia 331, 1–37. Gustavsen, H.G., 1996. Site index model approach for drained peatland forest stands. Suo 47 Ž2., 37–46. Gustavsen, H.G., Paivanen, J., 1986. Luonnontilaisten soiden ¨ ¨ puustot kasvullisella metsamaalla 1950-luvun alussa. Sum¨ mary: tree stands on virgin forested mires in the early 1950’s in Finland. Folia Forestalia 673, 1–27. Hanell, B., 1988. Postdrainage forest productivity of peatlands in ˚ Sweden. Can. J. For. Res. 18 Ž11., 1443–1456. Heikurainen, L., 1959. Tutkimus metsaojitusalueiden tilasta ja ¨ puustosta. Referat: uber Flachen und ¨ waldbaulich entwasserte ¨ ¨ ihre Waldbestande in Finnland. Acta Forestalia Fennica 78 Ž4., ¨ 1–279. Heikurainen, L., 1971. Virgin peatland forests in Finland. Acta Agralia Fennica 123, 1–26. Heikurainen, L., 1973. Soiden metsankasvatuskelpoisuuden ¨ laskentamenetelma. ¨ Summary: a method for calculation of the suitability of peatlands for forest drainage. Acta Forestalia Fennica 131, 1–35. Heikurainen, L., 1980. Metsaojituksen alkeet. Gaudeamus, Laut¨ takyla, ¨ 284 pp. Heikurainen, L., Huikari, O., 1960. Kaytannon ¨ ¨ ¨ suotyypit ja niiden metsaojituskelpoisuus. Keskusmetsaseura Tapio. Helsinki, 40 ¨ ¨ pp. Heikurainen, L., Pakarinen, P., 1982. Mire vegetation and site types. Peatlands and their Utilization in Finland. Finnish Peatland Society, pp. 14–23. Heikurainen, L., Seppala, ¨ ¨ K., 1973. Ojitusalueiden puuston kasvun jatkumisesta ja alueellisuudesta. Summary: regionality and continuity of stand growth in old forest drainage areas. Acta Forestalia Fennica 132, 1–36. Heinonen, J., 1994. Koealojen puu-ja puustotunnusten laskentaohjelma KPL. Kayttoohje. Summary: computer programme ¨ ¨ package for computing stand and single tree characteristics from sample plot measurements. Metsantutkimuslaitoksen ¨ tiedonantoja, 504, pp. 1-80. Hokka, ¨ ¨ H., Laine, J., 1988. Suopuustojen rakenteen kehitys ojituksen jalkeen. Summary: postdrainage development of structural ¨ characteristics in peatland forest stands. Silva Fennica 22 Ž1., 45–65. Hokka, tila ¨ ¨ H., Penttila, ¨ T., Siipola, M., 1995. Metsaojitusalueiden ¨ ja puuston kehitys yksityismailla kolmen metsalautakunnan ¨ alueella. Folia Forestalia 1, 21–33. Huikari, O., 1952. Suotyypin maaritys maa-ja metsataloudellista ¨¨ ¨ kayttoarvoa silmalla ¨ ¨ ¨ ¨ pitaen. ¨ Summary: on the determination of mire types, especially considering their drainage value for agriculture and forestry. Silva Fennica 75, 1–22. Huikari, O., 1974. Site quality estimation of forest land. Proc. of the Int. Symp. of Forest Drainage, 2–6 September, 1974, Sodankyla-Oulu, Finland, pp. 15–25. ¨

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Huikari, O., Aitolahti, M., Metsanheimo, U., Veijalainen, P., ¨ 1967. Puuston kasvumahdollisuuksista ojitetuilla soilla Pohjois-Suomessa. Summary: on the potential tree growth on drained peatlands in northern Finland. Communicationes Instituti Forestalis Fenniae 64 Ž5., 1–51. Ilvessalo, Y., 1932. Establishment and measurement of permanent plots in Finland. Communicationes Forestalis Fenniae 17 Ž2., 1–28. Ilvessalo, Y., 1947. Pystypuiden kuutioimistaulukot. Summary: volume tables for standing trees. Communicationes Forestalis Fenniae 34 Ž4., 1–149. Ilvessalo, Y., Ilvessalo, M., 1975. Suomen metsatyypit metsikoiden ¨ ¨ luontaisen kehitys-ja puuntuottokyvyn valossa. Summary: The forest types of Finland in the light of natural development and yield capacity of forest stands. Acta Forestalia Fennica 144, 1–101. Keltikangas, M., Laine, J., Puttonen, P., Seppala, ¨ ¨ K., 1986. Vuosina 1930–1978 metsaojitetut suot: Ojitusalueiden inventoin¨ nin tuloksia. Summary: peatlands drained for forestry during 1930–1978: results from field surveys on drained areas. Acta Forestalia Fennica 193, 1–94. Knize, A.A., Dekatov, N.N., 1990. Peculiarities of coniferous wood stands after drainage. Experimental and mathematical modelling in studying biogeocoenoses of forests and peatlands Žin Russian., ISBN 5-02-004627-2. Moscow: Nauka, pp. 77– 90. Knize, A.A., Pirogov, N.A., Belobrova, N.I., Morozov, V.V., Filippov, G.V., 1981. Modelling growth of drained pine mires. Methodical guide for practical foresters Žin Russian.. Leningrad Forest Research Institute, 44 pp. Koivisto, P., 1970. Regionality of forest growth in Finland. Seloste: metsan ¨ kasvun alueellisuus Suomessa. Communicationes Instituti Forestalis Fenniae 72 Ž2., 1–76. Krasilnikov, N.A., Knize, A.A., Sabo, E.D., 1992. Determination of efficiency of forest peatland drainage in European Russia Žin Russian.. St. Petersburg Forest Research Institute, 63 pp. Kuusela, K., 1960. Volume and increment calculations of sample plot determined with the relascope. Acta Forestalia Fennica 71, 1–20. Kuusela, K., 1966. A basal area mean tree method in forest inventory. Seloste: Pohjapinta-alakeskipuumenetelma¨ metsien inventoinnissa. Communicationes Instituti Forestalis Fenniae 61 Ž2., 1–32. Laasasenaho, J., 1982. Taper curve and volume functions for pine, spruce and birch. Communicationes Instituti Forestalis Fenniae 108, 1–74. Laine, J., 1989. Metsaojitettujen soiden luokittelu. Summary: clas¨ sification of peatlands drained for forestry. Suo 40 Ž1., 37–51. Laine, J., Starr, M.R., 1979. An analysis of the post-drainage stand increment in relation to the peatland site type classification in Finland. Proc. Int. Symp. Classification of Peat and Peatlands, Hyytiala, ¨ ¨ Finland. International Peat Society, Helsinki, pp. 147–159. Laine, J., Vasander, H., 1990. Suotyypit. Kirjayhtyma. ¨ Helsinki, 80 pp. Lukkala, O.J., 1927. Tutkimuksia soiden metsataloudellisesta oji¨ tuskelpoisuudesta erityisesti kuivatuksen tehokkuutta

silmallapitaen. Referat: untersuchungen uber die wald¨ ¨ ¨ ¨ wirtschaftliche Entwasserungsfahigkeit der Moore. Communi¨ ¨ cationes Instituti Forestalis Fenniae 15 Ž1., 1–278. Lukkala, O.J., 1929. Soiden ojituskelpoisuuden maaraaminen. ¨¨ ¨¨ Keskusmetsaseura Tapio. Helsinki, 20 pp. ¨ Lukkala, O .J., 1939. Soiden m etsaojituskelpoisuus. ¨ Keskusmetsaseura Tapio, Helsinki, 48 pp. ¨ Lukkala, O.J., Kotilainen, M.J., 1945. Soiden ojituskelpoisuus. Keskusmetsaseura Tapio, Helsinki, 56 pp. ¨ Mattila, E., Penttila, ¨ T., 1987. Lapin ja Koillis-Suomen metsalautakuntien suometsat ¨ ¨ vuosina 1952–1984. Summary: peatland forests of Lappi and Koillis-Suomi forestry board districts, North Finland, 1951–1984. Folia Forestalia 703, 1–49. Miina, J., 1996. Management of Scots pine stands on drained peatland: a model approach. DSc ŽAgric. and For.. thesis. University of Joensuu, Faculty of Forestry, 72 pp. Miina, J., Kolstrom, ¨ T., Pukkala, T., 1991. An application of spatial growth model of Scots pine on drained peatland. For. Ecol. Manage. 41, 265–277. Multamaki, ¨ S.E., 1923. Tutkimuksia ojitettujen soiden metsan ¨ kasvusta. Referat: untersuchungen uber das Waldwachstum ¨ entwasserter Torfboden. Acta Forestalia Fennica 27 Ž1., 1–121. ¨ ¨ Niemisto, ¨ P., 1991. Hieskoivikoiden kasvatustiheys ja harvennusmallit Pohjois-Suomen turvemailla. Summary: growing density and thinning models for Betula pubescens stands on peatlands in northern Finland. Folia Forestalia 782, 1–36. Nyyssonen, A., Mielikainen, K., 1978. Metsikon ¨ ¨ ¨ kasvun arviointi. Summary: estimation of stand increment. Acta Forestalia Fennica 163, 1–40. Ojansuu, R., Hynynen, J., Koivunen, J., Luoma, P., 1991. LuonŽMELA.-Metsa2000-versio. nonprosessit metsalaskelmassa ¨ ¨ Metsantutkimuslaitoksen tiedonantoja, 385, pp. 1-59. ¨ Paavilainen, E., Paivanen, J., 1995. Peatland Forestry. Ecology ¨ ¨ and Principles. Ecological Studies 111. Springer-Verlag, Heidelberg, 248 pp. Paavilainen, E., Tiihonen, P., 1984. Etela-ja Keski-Suomen ¨ suometsat ¨ vuosina 1951–1981. Summary: peatland forests in southern and central Finland in 1951–1981. Folia Forestalia 580, 1–20. Paavilainen, E., Tiihonen, P., 1985. Keski-ja Pohjois-Pohjamaan seka¨ Kainuun suometsat ¨ vuosina 1951–1983. Summary: peatland forests in Keski-Pohjanmaa, Kainuu and Pohjois-Pohjanmaa in 1951–1983. Folia Forestalia 617, 1–19. Paavilainen, E., Tiihonen, P., 1988. Suomen suometsat ¨ vuosina 1951–1984. Summary: peatland forests in Finland in 1951– 1984. Folia Forestalia 714, 1–29. Paivanen, J., Wells, E.D., 1978. Guidelines for development of ¨ ¨ peatland drainage systems for forestry in Newfoundland. Department of Environment, Canadian Forestry Service, St. Johns, Newfoundland, Information Report N-X-156, pp. 1–44. Pakhutchij, V.V., 1991. Productivity factors of stands on drained forest soils in the European Northeast Žin Russian.. Institute of Biology of Komi scientific centre, Ural Division, Russian Academy of Science, Syktycvkar, 100 pp. Palmborg, C., Nordgren, A., 1996. Partitioning the variation of microbial measurements in forest soils into heavy metal and

H.G. GustaÕsen et al.r Forest Ecology and Management 107 (1998) 1–17 substrate quality dependent parts by use of near infrared spectroscopy and multivariate statistics. Soil Biol. Biochem. 28 Ž6., 711–720. Payandeh, B., 1973. Analysis of forest drainage experiment in nothern Ontario: I. Growth analysis. Can. J. For. Res. 3 Ž3., 387–398. Penttila, ¨ T., 1989. Growth response of peatland stands to drainage in northern Finland. In: Jeglum, J.K., Overend, R.P. ŽEds.., Proc. of Symposium ‘89’ Peat and Peatlands Diversification and Innovation, Vol. 1. Peatland Forestry, Quebec City, Quebec, Canada, pp. 70–77. Perala, D.A., 1971. Growth and yield of black spruce on organic soils in Minnesota. USDA Forest Service, Research Paper NC-56, pp. 1–16. Saramaki, ¨ J., 1977. Ojitettujen turvemaiden hieskoivikoiden kehitys Kainuussa ja Pohjanmaalla. Summary: development of White birch Ž Betula pubescens ehrh.. stands on drained peatlands in nothern central Finland. Communicationes Instituti Forestalis Fenniae 91 Ž2., 1–59. Seppala, kasvun kehitys ojitetuilla ¨ ¨ K., 1969. Kuusen ja mannyn ¨ turvemailla. Summary: post-drainage growth rate of Norway spruce and Scots pine on peat. Acta Forestalis Fennica 93, 1–89. Siitonen, M., 1983. A long term forestry planning system based on data from Finnish national forest inventory. Forest inventory for improved management. Proceedings of the IUFRO subject group 4.02 meeting in Finland, Sept. 5–9, 1983. Helsingin yliopiston metsanarvioimistieteen laitoksen tiedo¨ nantoja, 17, pp. 195–207.

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Spiecker, H., Mielikainen, K., Kohl, ¨ ¨ M., Skovsgaard, J. ŽEds.., 1996. Growth Trends in European Forests. European Forest Institute Research Report No. 5, Springer-Verlag, 372 pp. Stanek, W., 1968. A forest drainage experiment in nothern Ontario. Pulp Pap. Mag. Can. 69 Ž18., 58–62. Sundstrom, ¨ E., 1992. Five-year growth response in drained and fertilized black spruce peatlands: I. Permanent growth plot analysis. Forestry Canada, Ontario region. NEST Technical Report TR-02, Information Report, O-X-417, pp. 1–19. Sundstrom, ¨ E., Jeglum, J.K., 1992. Five-year growth response in drained and fertilized black spruce peatlands: II. Stem analysis. NEST Technical Report TR-03, Information Report O-X420. Thurmann-Moe, P., 1963. Klima og skoggrofting. Norsk Skog¨ bruk 9, 273–278. Uuttera, J., Maltamo, M., Hotanen, J.-P., 1996. Stand structure of undrained and drained peatland forests in central Finland. Suo 47 Ž4., 125–135. Vuokila, Y., 1965. Functions for variable density yield tables of pine based on temporary sample plots. Seloste: Tilapaiskoea¨ loihin perustuvat yhtalot kasvu-ja tuotostaulukoita ¨ ¨ mannyn ¨ varten. Communicationes Instituti Forestalis Fenniae 60 Ž4., 1–86. Vuokila, Y., Valiaho, H., 1980. Viljeltyjen havumetsikoiden kas¨ ¨ vatusmallit. Summary: growth and yield models for conifer cultures in Finland. Communicationes Instituti Forestalis Fenniae 99 Ž2., 1–48. Weisberg, S., 1985. Applied Linear Regression, 2nd edn. Wiley, Chichester, 324 pp.