Differences in Forest Stand Structure Between Forest Ownership Groups in Central Finland

Journal of Environmental Management (1997) 51, 145–167

Differences in Forest Stand Structure Between Forest Ownership Groups in Central Finland Matti Maltamo∗, Janne Uuttera† and Kullervo Kuusela† ∗The University of Joensuu, Faculty of Forestry, P.O. Box 111, FIN-80101 Joensuu and †The European Forest Institute, Torikatu 34, FIN-80100 Joensuu Received 18 August 1996; accepted 5 July 1997

This study investigates the differences in the stand structure of forests on mineral soils between different forest ownership groups in five forestry districts in central Finland. The study area includes the forestry districts of: KeskiSuomi, Pohjois-Karjala, Pohjois-Savo, Etela¨-Pohjanmaa and Keski-Pohjanmaa. The study is based on the sample plot tree data from the 8th National Forest Inventory of Finland (NFI). The comparisons between the ownership groups were made according to forest site types and stages of stand development. The stand structure variables used were: the range of tree diameter distribution, the number of tree storeys and the number of tree species. The number of tree storeys was estimated from the diameter distribution using non-parametric kernel smoothing. The differences between the forest ownership groups were considerable. On moist heaths the forests in private ownership had a greater number of tree storeys and greater diameter range compared to those forests owned by forest industrial companies or by the state. On the dryish and dry heaths similar differences occurred in the number of tree species. Information on the state of forests based on large-scale inventory data is a valuable tool for the development of forest management, regional forest management planning and even large-scale ecological planning. In the future, variables, such as those presented and compared in this study, could also be used for monitoring the state of forest management and for forest product certification.  1997 Academic Press Limited

Keywords: diameter distribution, forest management planning, habitat diversity, National Forest Inventory, silviculture.

1. Introduction In Finland the forest industry is the most important industrial sector. It is based almost totally on domestic raw material. At the present there are about 200 000 km2 of production forest land, which is 66% of the total land area (Metsa¨ntutkimuslaitos, 1996). Two-thirds of the production forests are on mineral soils and the rest on peatlands (Metsa¨ntutkimuslaitos, 1996). The ownership of forests in Finland is divided between 0301–4797/97/100145+23 $25.00/0/ev970140

 1997 Academic Press Limited

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Forest structure in central Finland

private forest owners (54·2 % of the production forest area), forest industrial companies (7·7%), the state (33·4%), municipalities, the church, and different kinds of public and private communities (all together 4·7%). During the last decades the share of the privately owned forests has further been divided into forests owned by farmers and forests owned by private forest owners other than farmers. The share of the latter has increased rapidly during the past three decades. In former decades forest management planning has focused on wood production. However, forestry throughout Europe is experiencing a period of major restructuring. The Ministerial Conference on the Protection of Forests in Europe held in Helsinki 1993 defined the principle of sustainable forest management to be the maintenance of productivity as well as the biodiversity of forests when utilizing forests (Ministerial Conference of the Protection of Forests in Europe, 1993a; 1993b). Following the resolutions of the Helsinki Conference, a list of indicators for monitoring the sustainability of forestry practices within Europe was published in 1994. From this tentative list every country has to prepare a list tailored to their own needs. The Finnish list of indicators for sustainable forest management was published in 1995 by the Ministry of agriculture and forestry (Maa- ja metsa¨talousministerio¨, 1995b). This set of indicators includes 165 variables depicting six main criteria for sustainable forest management. By monitoring these main criteria Finnish forestry aims to maintain the level of wood production and production of non-wood products, and also to preserve forest biodiversity. Due to international agreements and views on the treatment and utilization of forests, forestry in Finland has undergone great changes in the recent past. This has been caused by the changing needs for benefits gained from forests expressed by forest owners and other citizens (e.g. Kangas and Niemela¨inen, 1996) and new guidelines of forest policy (Palo and Hellstro¨m, 1994). The management and utilization of commercially exploited forests has become increasingly multi-objective in nature. In multiobjective forestry, wood production is seen only as one of the several target parameters, together with other aspects such as conservation of biodiversity and the natural beauty of the landscape (Kangas and Kuusipalo, 1993; Pukkala and Kangas, 1993). In response to international agreements the sustainability of forest utilization has to be monitored. Indicators used for monitoring the changes in forest biodiversity and the pressures on biodiversity in Finland (Maa- ja metsa¨talousministerio¨, 1995b), as well as the new Forest Law of Finland (Maa- ja metsa¨talousministerio¨, 1995a), emphasizes the need to take account of valuable habitats and key-biotopes when planning forest management. A forest key-biotope is a valuable habitat or environment, where the existence of one or several threatened species is possible (Aapala et al., 1994). Most of these habitats derive their nature conservation value from the physical conditions supported by the vegetation community on the site or on its surroundings (for example springs, streams, small ponds, very fertile forest lands and mires, rocky forests and precipices) (Soininen, 1996), and these habitats tend to be quite stable. However, within the field of forest biodiversity conservation it is now considered that the goal of maintaining the overall diversity (i.e. a-, b- and c-diversity, cf. Haila and Kouki, 1994) cannot be achieved in conservation areas only (e.g. Margules et al., 1988, Virkkala et al., 1994). In addition to preservation of the a-diversity within a certain habitat type (for example maintaining the vegetation structure of key-biotopes), the maintenance of overall forest diversity requires systematic operations in production forests. In order to maintain the a- and b- diversity of stand structure variables, the natural variation of the vegetation structure under different physical conditions has to be maintained at

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every stage of the vegetation succession (cf. Uuttera and Maltamo, 1995). In the future, with the help of geographic information systems (GIS) and ecological knowledge on species requirements on landscape pattern, landscape ecological forest planning can be used for preserving c-diversity of habitats. The recently formulated instructions for forest management of the Forest and Park Service of Finland and organizations of private forest owners, the Forestry Centre Districts, have noted these components of forest structural diversity (Metsa¨hallitus, 1993; Metsa¨keskus Tapio, 1994). When planning future activities for the preservation of forest structural diversity, it is essential to have basic information about the differences in forest structure between different ownership categories. The special forest ownership structure in Finland (54·2% of the production forest area owned by private forest owners and a great number of small forest holdings) makes the support of forest management and planning even more crucial. Even though the changes in forest management during the 1990s does not yet show very clearly in today’s forests, there may have been earlier differences between ownership groups in the intensity of silvicultural methods and in objectives of forest management. Management applying less intensive forestry practices has been characteristic of the privately owned forests, especially in those owned by farmers. Investigations on forest structural diversity using large-scale forest inventory data can help decision makers to define forest categories, where to place emphasis in management to ensure the desired variation of forest structure. In future, this kind of basic information may play an important role in internationally approved national forest product certification systems, which are planned to ensure sustainability of forest management with regard to biodiversity preservation. The objective of this study is to investigate the structural differences between the forests of different ownership categories. The comparisons between forest ownership categories are made within the stages of forest succession and physical conditions of mineral soil sites. 2. Material and methods The study area includes the forestry districts of Etela¨-Pohjanmaa, Keski-Pohjanmaa, Keski-Suomi, Pohjois-Savo and Pohjois-Karjala (Figure 1). In these forestry districts the abiotic growth conditions are relatively similar (Cajander, 1949; Kalela, 1961), but there are some differences in the amount of precipitation, topography and soil texture. The study area is located around the border of the southern- and middle-boreal vegetation zone (Figure 1). The proportions of the forests owned by different ownership groups are divided quite equally within the test areas (Table 1), especially in the forestry districts of Keski-Suomi and Pohjois-Karjala (Metsa¨ntutkimuslaitos, 1996). The study material consists of the forest measurements of the 8th National Forest Inventory of Finland (NFI). In this study only the sample plots located on mineral soils (peatlands excluded) were considered. The sample plots were located according to the NFI sampling framework on the sides of a half-square, each half-square including 21 sample plots (e.g. Metsa¨ntutkimuslaitos, 1989). The distance between sample plots is 200 m and the distance between the half-squares is 7 km in an east–west-direction and 8 km in a north–south-direction (Figure 2). In NFI the tree data is measured with relascope principle (Bitterlich, 1984). The relascope factor by which the sampled trees were chosen was 2 km2 ha−1. The sample plots were regarded as stands in calculations even though there may be situations where a few plots were located in same stand due to sampling framework.

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Forest structure in central Finland

Keski-Pohjanmaa

Pohjois-Savo

Pohjois-Karjala

Etelä-Pohjanmaa

Keski-Suomi

Helsinki Figure 1. The locations of the study areas (forestry centre districts) in Finland. The border of the southernand middle-boreal vegetation zone and capital of Finland are also presented.

T 1. The proportions of the forest land area in different ownership groups (%) (Metsa¨ntutkimuslaitos, 1996). Forest ownership groups: Farm=private farmers, Private=private forest owners other than farmers, Company=forest industrial companies, State=the state, Others=municipalities, the church, and different kinds of public and private communities District

Farm

Private

Company

State

Others

Pohjois-Karjala Pohjois-Savo Keski-Suomi Etela¨-Pohjanmaa Keski-Pohjanmaa

30·6 34·9 30·8 49·8 40·6

24·2 37·9 36·0 37·7 34·6

21·9 16·7 19·9 2·1 3·2

20·4 5·6 9·2 4·2 14·9

3·0 4·9 4·0 6·2 6·6

The study material was divided into the ownership groups, site fertility (bonitet) and the development stage of the stand. The ownership category ‘‘Others’’ used in the inventory, which included forests owned by several different groups (i.e. municipalities, church, public and private communities, etc.), had relatively few observations and was

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7 km N 8 km 0

400

800 m

Figure 2. Sampling design of the 8th National Forest Inventory of Finland (NFI) (Metsa¨ntutkimuslaitos, 1989).

removed from the data. The forest ownership groups of (1) private farmers, (2) other private forest owners, (3) forest industrial companies, and (4) the state, were compared. With regards to site fertility the data were divided according to the Cajanderian forest site types (Cajander, 1926), which was applied for different tree species compositions. The essential idea of the Cajanderian system is that all stands with identical floristic composition and ecological characteristics of the ground vegetation belong to the same forest site type. From these forest site types groves (Oxalis-Mayanthemum-type) and grovelike heaths (Oxalis-Myrtillus-type) were combined, as well as dryish (Vacciniumtype) and dry heaths (Calluna-type). Moist heaths (Myrtillus-type) formed their own category. Forests of more fertile sites are usually dominated by Norway spruce (Picea abies Karst.) or by birch, i.e. Silver birch (Betula pendula Roth.) or Pubescent birch (B. pubescens Ehrh). Forest of poorer site fertility are dominated by Scots pine (Pinus sylvestris L.). In addition to these tree species, many deciduous tree species, such as Alder (Alnus incana Moench, Willd.) and Aspen (Populus tremula L.), may exist as a secondary tree species. Very poor heaths (Cladonia-type,) and rocky and sandy forest lands were excluded from the original data due to small number of observations. To keep the number of categories in comparisons reasonable, the development stages of the stands were also combined. The seedling and sapling stands were treated as one category as well as the young and middle-aged forests. Mature forests formed their own category. In the mature forests category the proportions of old forests (age [140 years) were investigated separately across different ownership groups and forestry centre districts. The recently established regeneration areas, shelterwood stands and clear-cut areas including only seed parent trees, were also removed from the data due to a small amount of growing stock in these stands. In addition those forests where wood production is restricted due to conservation were also excluded. The number of these stands was small, only 22 plots were located in natural parks and 46 in different camping areas and other kinds of parks. The study considered the same stand structure variables as the studies of Uuttera and Maltamo (1995) and Uuttera et al. (1997). The age and basal area of the stand were used to define in more detail the development stage. Information on the existing tree species, the range of the tree diameters at breast height (cm) and number of the tree storeys within the sample plot were used to define the stand structure.

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Forest structure in central Finland

Due to lack of information for tree height, tree diameters were used to separate tree storeys. To modify the sampled trees so as to better represent the whole forest stock, the diameter distribution was smoothed to a continuous form. First, the diameter distribution weighted by the basal area, was transformed to represent the number of stems per hectare (e.g. Kuusela, 1966). Secondly, a non-parametric kernel-estimate was fitted to the modified diameter distribution. When using non-parametric methods in estimation there is no presumption of the form of the distribution, instead the form is determined from the original data itself (Silverman, 1986). This fact makes the nonparametric estimation methods very flexible. The kernel-estimate is calculated with the formula:

A B

x−Xi 1 1 ;K f(x)= nh i=1 h

(1)

where, n=stem number per hectare, h=smoothing parameter, K=kernel function, x=sample from density function, Xi=observed diameter of sample tree i. Normal distribution was chosen to be the form of the single kernel. The final kernelestimate is the sum of these kernels. The value of the smoothing parameter h was determined to be 2 according to former studies (Uuttera and Maltamo, 1995; Uuttera et al., 1996; 1997). From the smoothed kernel-estimate the number of tree storeys was determined using objective rule. If the peak in the smoothed diameter distribution was recognized, the peak was determined as a tree storey with the rule: DIST [0·5 Dformerpeak

(2)

where, DIST=Dpeak−Dformerpeak, Dpeak=the diameter class, in which the peak was found in the smoothed diameter distribution, Dformerpeak=diameter class, in which the former tree storey was determined. Equation 2 states the greater the diameter class, the greater the relative distance of the diameter distribution peaks must be in order to be defined as a new tree storey. The value of the window parameter h itself restricts the tree storeys from existing very close to one another. The differences in mean values of the forest stand structure variables, i.e. diameter range, the number of tree storeys and the number of tree species, were tested statistically between different ownership groups within forestry centre districts. Statistical tests were made if the data category had more than 15 observations. Statistical comparisons between forestry centre districts were not made because there are small differences in abiotic growth conditions in an east–west direction within the test areas. However, regional variation in the averages of the stand structure

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variables was investigated by calculating relative proportions of sample plots by forestry centre districts, which have the average values greater than the corresponding mean values of the whole study area. Data categories were included in this comparison if they had at least 15 observations. 3. Results The relative proportion of stands in different categories compared, divided by soil fertility and stand development stage, were similar enough amongst the different ownership groups and, in most cases, had enough observations to justify comparisons (Table 2). In addition, the age and the basal area of the stands for the different categories proved to be comparable (Table 2). The age of the state-owned mature forests was systematically greater in comparison to the other ownership groups (Table 2). This increases the values of the stand structure variables, the number of tree storeys and the diameter range. For groves and grovelike heaths the low number of observations in state-owned forests restricted the statistical significance tests for the stand development stages of seedling and sapling stands and mature forests (Table 3). The results support the presumption that stand structure variation is greater on soils of higher fertility (Table 2). The differences between the ownership groups in groves and grovelike heaths are small regardless of their respective forest management history. However, on these fertile soils forests owned by forest industrial companies had lower mean values of stand structure variables compared to other forest ownership groups (Table 2). These differences were statistically significant in seedling and sapling stands and in young and middle-aged stands (Table 3). The greatest differences occurred on moist heaths in the young and middle-aged forests (Table 2). This category also has the greatest number of observations for all ownership categories. All of the compared stand structure variables in privately owned forests have greater mean values than those in forests owned by forest industrial companies (Table 2) and these differences are statistically significant (Table 3). The differences between privately and state-owned forests are most noticeable in the number of tree storeys and diameter range, while the difference in the number of tree species proved to be statistically insignificant (Tables 2 and 3). However, the diameter range in state-owned mature forests on moist heaths is greater than in any other ownership group and this difference is statistically significant. This is the only case where stateowned forests have statistically greater values than privately owned forests. On dryish and dry heaths the mean values of the stand structure variables were lower in forests owned by forest industrial companies in comparison to those forests owned by private forest owners (Table 2). The differences proved to be statistically significant in seedling and sapling stands in relation to the number of tree storeys and the diameter range. In young and middle-aged forests all the stand structure variables of forests owned by forest industrial companies have significantly lower values in comparison to privately owned forests (Table 3). The number of tree species in young and middle-aged forests owned by the state is also significantly lower than that of privately owned forests (Table 3). When the stand structure variables are investigated according to forestry centre districts, differences between ownership groups in the forestry centre district KeskiSuomi become very clear (Tables 4 and 5). An equal share of forested land between the ownership groups in Keski-Suomi also makes tests of statistical significance feasible in most of the soil fertility categories and stand development stages. Significant

2+3

4+5

2+3

4+5

6

2+3

4+5

6

6

Groves

Groves

Groves

Moist heaths

Moist heaths

Moist heath

Dry heaths

Dry heaths

Dry heaths

Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State

Development stage

Fertility

Owner 161 159 17 7 798 764 106 34 276 186 25 6 215 234 76 43 1386 1272 499 275 586 498 170 146 177 175 100 61 653 655 472 450 156 151 62 89

N 5·2 5·7 5·6 7·4 40·9 37·1 34·8 33·0 82·9 80·5 81·9 98·8 5·5 5·2 6·6 7·0 45·9 44·8 35·1 37·1 93·8 90·6 91·1 116·4 7·3 7·5 7·4 7·9 39·4 37·8 29·3 36·6 102·0 102·2 101·3 114·6

Age 8·5 9·4 5·9 8·0 21·6 21·2 21·5 17·9 26·0 27·3 28·2 31·0 5·6 5·5 5·8 4·5 20·0 19·9 18·4 18·1 24·2 24·0 24·5 26·3 5·9 5·0 4·9 5·3 15·0 14·4 13·7 13·9 19·0 19·2 18·4 18·6

Basal area 1·32 1·32 1·06 1·43 1·96 1·88 1·75 1·68 2·27 2·27 2·12 2·83 1·14 1·13 1·07 1·12 1·85 1·79 1·62 1·64 2·12 2·15 2·11 2·23 1·11 1·13 1·05 1·10 1·49 1·51 1·43 1·48 1·73 1·78 1·68 1·76

Tree storeys 1·73 1·78 1·29 2·14 2·29 2·26 2·26 2·44 2·44 2·60 2·36 2·67 1·40 1·36 1·32 1·35 2·17 2·22 2·07 2·12 2·45 2·40 2·26 2·52 1·23 1·26 1·18 1·18 1·57 1·54 1·36 1·39 1·70 1·83 1·76 1·69

Tree species 8·1 7·7 4·1 8·3 21·1 19·7 18·2 16·2 29·3 28·8 30·7 34·7 4·2 4·0 3·5 3·6 17·8 17·4 14·2 15·0 24·5 24·8 24·9 26·7 4·4 4·0 2·7 4·4 11·9 12·0 10·4 11·4 18·0 18·1 18·5 19·1

Diameter range

T 2. The averages of the stand structure variable values in the whole study area divided by ownership group, site fertility and stand development stages. For explanations of the forest ownership groups see Table 1. Stand development stages: 2+3=seedling and sapling stands, 4+5=young and middle-aged forests, 6=mature forests 152 Forest structure in central Finland

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T 3. Comparison of the statistical differences of the averages of the stand structure variables (t-test) within the whole study area. Comparisons are made according to site fertility and forest ownership groups· Forest ownership groups: I=private farmers, II=private forest owners other than farmers, III=forest industrial companies, IV=the state. For the explanations of the development stages see Table 2. Statistical significance: ∗∗∗=P(T
Development I vs. stage II

GROVES Tree storeys Tree species Diameter range GROVES Tree storeys Tree species Diameter range GROVES Tree storeys Tree species Diameter range MOIST HEATHS Tree storeys Tree species Diameter range MOIST HEATHS Tree storeys Tree species Diameter range MOIST HEATHS Tree storeys Tree species Diameter range DRY HEATHS Tree storeys Tree species Diameter range DRY HEATHS Tree storeys Tree species Diameter range DRY HEATHS Tree storeys Tree species Diameter range

2+3

4+5

I vs. III

I vs. IV

II vs. III

II vs. IV

III vs. IV

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2+3

4+5

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2+3

4+5

6

differences in stand structure variables exist between private forest owners in seedling and sapling stands and young and middle-aged stands (Tables 4 and 5). On moist heaths the differences in mean values of stand structure variables between privately owned forests and forests owned by forest industrial companies and the state are clear

2+3

4+5

6

2+3

4+5

6

2+3

4+5

6

Groves

Groves

Groves

Moist heaths

Moist heaths

Moist heaths

Dry heaths

Dry heaths

Dry heaths

Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State

Development stage N

Fertility

Owner 27 35 5 3 156 192 43 12 68 46 16 4 67 71 19 7 256 327 172 64 131 137 47 21 42 55 36 10 112 154 145 97 28 39 20 16

Age 5·3 6·5 5·0 9·0 43·1 39·3 40·3 20·3 82·0 81·3 83·2 87·3 5·6 4·5 6·9 6·7 41·7 41·8 35·8 36·8 93·5 88·2 94·5 97·1 7·8 6·9 7·3 9·2 34·1 31·7 27·3 34·3 98·5 97·5 99·3 110·2

Basal area 9·3 8·0 5·6 8·7 23·0 23·4 21·9 18·8 24·5 27·3 28·3 22·5 6·1 5·4 4·1 2·9 20·4 20·0 18·1 17·6 25·1 23·4 24·7 23·9 6·4 4·8 5·4 9·4 16·1 14·8 13·6 15·4 19·9 18·9 16·4 19·1

Tree storeys 1·48 1·14 1·00 1·67 2·08 1·87 1·79 1·67 2·13 2·13 2·06 2·75 1·16 1·07 1·11 1·0 1·79 1·76 1·59 1·63 2·14 2·05 1·92 1·52 1·07 1·09 1·00 1·20 1·52 1·44 1·42 1·44 1·68 1·72 1·35 1·69

Tree species 2·19 1·60 1·20 2·67 2·35 2·25 2·14 2·33 2·37 2·57 1·94 2·50 1·40 1·37 1·21 1·00 2·12 2·17 2·06 1·98 2·47 2·28 2·19 2·29 1·40 1·18 1·19 1·70 1·74 1·56 1·37 1·41 1·86 1·69 1·45 1·94

Diameter range 13·1 4·9 4·6 13·3 23·0 20·7 20·0 12·0 27·6 27·6 30·6 31·5 4·7 3·6 3·8 0·3 17·5 17·0 14·1 13·9 26·1 24·5 23·3 18·8 4·6 3·0 1·9 10·2 12·1 11·7 10·4 11·0 18·9 17·6 15·1 17·8

T 4. The averages of the stand structure variable values in the forestry centre district of Keski-Suomi divided by ownership group, site fertility and stand development stages. For explanations of the code variables see Tables 1 and 2 154 Forest structure in central Finland

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T 5. Comparison of the statistical differences of the averages of the stand structure variables (t-test) within the forestry centre district of Keski-Suomi. Comparisons are made according to site fertility and forest ownership groups. For explanations of the code variables see Tables 2 and 3 Compared ownership groups Forest site fertility/ Stand structure variable GROVES Tree storeys Tree species Diameter range GROVES Tree storeys Tree species Diameter range GROVES Tree storeys Tree species Diameter range MOIST HEATHS Tree storeys Tree species Diameter range MOIST HEATHS Tree storeys Tree species Diameter range MOIST HEATHS Tree storeys Tree species Diameter range DRY HEATHS Tree storeys Tree species Diameter range DRY HEATHS Tree storeys Tree species Diameter range DRY HEATHS Tree storeys Tree species Diameter range

Development I vs. stage II 2+3

4+5

I vs. III

I vs. IV

II vs. III

II vs. IV

III vs. IV

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2+3

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4+5

6

in the young, middle-aged and mature forests (Tables 4 and 5). On moist heaths differences occur in the number of tree storeys and the diameter range, while on the dryish and dry heaths corresponding differences occur in the number of tree species. These differences in the number of tree species disappear when the stand develops to the mature forest succession stage (Tables 4 and 5). The division of forest land between the different forest ownership groups is most

156

Forest structure in central Finland

even in the forestry centre district of Pohjois-Karjala (Tables 6 and 7). The results for the sapling stands on groves and grovelike heaths for private forest owners here proved to be quite the opposite in comparison to those of the forestry centre district of KeskiSuomi. In middle-aged forests on moist heaths, the results were, however, similar to the forestry district of Keski-Suomi. However, the differences in stand structure variables between privately owned forests and forests owned by forest industrial companies and the state are even greater and can also be seen in the number of tree species (Table 6). On the contrary, when we compare young and middle-aged forests on dryish and dry heaths the differences between forest ownership groups are smaller compared to those in Keski-Suomi (Tables 4 and 6). However, the differences in the number of tree storeys and the number of tree species proved to be statistically significant between private forest owners and forest industrial companies (Table 7). In the forestry centre district of Pohjois-Karjala, within the mature forests on the moist heaths, the stand structure variables were greatest in forests owned by the state in comparison to the other forest ownership groups (Table 6). The differences in diameter range were statistically significant (Table 7). The average age of the forests in this category was also the greatest in the state owned forests (126 years, Table 6), including the oldest sampled forest (245 years). This explains, to a large extent, the differences in diameter range. Also on dryish and dry heaths the sampled state owned mature forests were, on average, older than the forests in other forest ownership groups (Table 6), but there is no corresponding statistically significant differences in stand structure variables compared to moist heaths (Table 7). In the forestry centre district of Pohjois-Savo statistically significant differences occurred mostly in young and middle-aged forests on moist heaths (Tables 8 and 9). The proportion of the state owned forests was very low and the statistical tests between other ownership groups could be made for only two categories (Table 9). In the forestry centre district of Pohjois-Savo the distribution of forest soil fertility was clearly weighted by the more fertile soils, in comparison to the other forestry districts. In the forestry centre district of Keski-Pohjanmaa the results followed the trend of the overall results: statistically significant differences in stand structure between privately owned forests and forests owned by the state occurred on moist heaths in young and middle-aged forests. These differences occurred for all stand structure variables (Tables 10 and 11). On the dryish and dry heaths the difference in the number of tree species between young and middle-aged forests owned by private forest owners and the state was even clearer than in the other forestry centre districts under examination (Table 7 and 12). The proportion of forests owned by forest industrial companies was so low that statistical tests between this and other forest ownership groups could not be carried out. In the forestry centre district of Etela¨-Pohjanmaa the differences in stand structure variables between different forest ownership groups occurred in the number of tree species on dryish and dry heaths, while on moist heaths there were no clear differences (Tables 12 and 13). In the other categories the differences in stand structure variables between ownership groups were small. As with the forestry centre district of KeskiPohjanmaa, in the forestry centre district of Etela¨-Pohjanmaa the proportion of forests owned by forest industrial companies was low. When considering regional variation between forestry centre districts, in most cases, the mean values of stand structure variables in the forestry centre districts of PohjoisKarjala and Pohjois-Savo were greater, and for the other test areas lower than the values of the whole study area (Table 14). One exception was that of the ownership

2+3

4+5

6

2+3

4+5

6

2+3

4+5

6

Groves

Groves

Groves

Moist heaths

Moist heaths

Moist heaths

Dry heaths

Dry heaths

Dry heaths

Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State

Development stage

Fertility

Owner 51 43 4 3 201 145 27 9 50 27 5 2 35 35 21 24 304 253 193 118 142 94 72 85 21 22 41 25 126 103 194 225 25 18 20 48

N 5·6 6·1 3·8 8·3 36·0 31·9 29·3 32·0 76·9 78·6 79·0 110·0 6·2 4·9 6·5 8·0 44·7 46·5 34·7 34·5 88·9 88·1 90·2 125·7 6·6 8·3 7·6 6·6 35·0 39·5 32·1 37·0 95·0 102·9 111·3 116·8

Age 6·5 10·0 7·5 8·7 20·1 20·6 19·0 18·4 26·0 25·5 30·0 21·0 6·5 5·1 6·7 6·0 20·4 19·7 17·7 17·5 25·4 24·4 23·7 27·6 4·6 5·1 4·1 3·8 15·4 14·9 12·9 13·3 21·4 18·3 19·2 17·5

Basal area 1·20 1·47 1·00 1·33 1·91 1·87 1·67 1·44 2·40 2·44 2·40 2·50 1·29 1·17 1·05 1·19 1·88 1·87 1·59 1·67 2·25 2·22 2·21 2·39 1·14 1·09 1·07 1·04 1·56 1·55 1·42 1·51 1·84 2·00 1·65 1·90

Tree storeys 1·59 1·72 1·25 1·67 2·27 2·34 2·19 2·44 2·78 2·59 4·00 2·00 1·66 1·29 1·33 1·57 2·18 2·14 1·92 2·16 2·56 2·47 2·35 2·56 1·00 1·09 1·10 1·08 1·49 1·43 1·33 1·39 1·60 2·17 2·15 1·63

Tree species 5·0 9·7 4·8 6·0 20·3 19·4 16·2 14·8 31·2 30·4 32·4 22·0 6·3 3·5 3·5 6·1 18·6 18·6 13·7 15·0 26·0 24·9 25·6 28·7 3·4 4·0 2·8 1·6 12·5 12·7 10·0 11·4 19·0 22·2 18·9 20·5

Diameter range

T 6. The averages of the stand structure variable values in the forestry centre district of Pohjois-Karjala divided by ownership group, site fertility and stand development stage. For explanations of the code variables see Tables 1 and 2 M. Maltamo et al. 157

158

Forest structure in central Finland

T 7. Comparison of the statistical differences of the averages of the stand structure variables (t-test) within the forestry centre district of Pohjois-Karjala. Comparisons are made according to site fertility and forest ownership groups. For explanations of the code variables see Tables 2 and 3 Compared ownership groups Forest site fertility/ Stand structure variable GROVES Tree storeys Tree species Diameter range GROVES Tree storeys Tree species Diameter range GROVES Tree storeys Tree species Diameter range MOIST HEATHS Tree storeys Tree species Diameter range MOIST HEATHS Tree storeys Tree species Diameter range MOIST HEATHS Tree storeys Tree species Diameter range DRY HEATHS Tree storeys Tree species Diameter range DRY HEATHS Tree storeys Tree species Diameter range DRY HEATHS Tree storeys Tree species Diameter range

Development I vs. stage II 2+3

I vs. III

I vs. IV

II vs. III

II vs. IV

III vs. IV

∗∗— — ∗∗—

4+5 — — —

— — ∗

— — —

6 — — — 2+3 — ∗ —

∗ ∗ —

— — —

— — —

— — —

— — —

— — —

∗∗∗ ∗∗ ∗∗∗

∗∗ — ∗∗∗

∗∗∗ ∗∗ ∗∗∗

∗∗ — ∗∗∗

— ∗— —

— — —

— — —

— — ∗—

— — —

— — ∗∗—

— — ∗—

— — —

— ∗— —

— — —

— — —

— — ∗

— — —

— — —

∗ ∗ ∗∗∗

— — —

∗ — ∗∗

— — —

— — ∗—

— ∗— —

— ∗— —

— — —

— — —

— ∗ —

— ∗ —

4+5

6

2+3

4+5

6

group private farmers in the forestry centre district of Keski-Suomi, where the proportion of the average exceeding values was close to that of forestry centre districts PohjoisKarjala and Pohjois-Savo. A great proportion of forests owned by industrial companies in the forestry centre district of Etela¨-Pohjanmaa consisted of only one fertility class and stand development stage. Finally, the proportion of the old forests (age [140 years) in different ownership

2+3

4+5

6

2+3

4+5

6

2+3

4+5

6

Groves

Groves

Groves

Moist heaths

Moist heaths

Moist heaths

Dry heaths

Dry heaths

Dry heaths

Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State

Development stage

Fertility

Owner 77 76 8 0 337 340 36 6 132 99 4 1 59 74 35 4 283 296 119 34 133 148 47 10 13 20 18 4 55 83 109 32 17 27 18 8101·0

N

41·7 36·1 32·4 34·6 83·1 80·5 80·3 74·0 4·5 5·1 6·5 4·8 44·8 41·2 33·9 40·4 90·2 91·4 89·5 99·4 6·2 6·9 7·4 5·5 33·7 32·4 27·2 27·0 105·2 101·1 93·3 22·8

5·0 5·0 7·0

Age

21·9 20·4 22·9 12·8 26·8 27·7 25·5 30·0 4·2 5·8 6·2 5·0 20·3 19·6 19·8 21·6 24·0 24·9 26·0 25·2 5·2 4·6 5·3 5·0 14·9 15·6 15·0 13·8 19·1 20·2 18·8 1·63

9·5 9·9 5·3

Basal area

1·95 1·93 1·78 2·00 2·30 2·29 2·00 2·00 1·07 1·18 1·03 1·25 1·89 1·81 1·68 1·76 2·13 2·15 2·23 2·50 1·15 1·10 1·06 1·00 1·49 1·55 1·42 1·31 1·94 1·93 2·00 1·63

1·34 1·33 1·13

Tree storeys

2·26 2·22 2·47 2·00 2·42 2·67 2·00 3·00 1·25 1·38 1·37 1·75 2·10 2·23 2·29 2·47 2·42 2·42 2·26 2·50 1·31 1·30 1·28 1·00 1·51 1·64 1·43 1·5 1·82 2·07 1·56 18·5

1·65 1·91 1·38

Tree species

21·3 19·8 17·6 20·4 30·1 29·3 29·0 43·0 2·9 4·6 3·0 4·8 18·2 17·8 14·6 18·4 24·7 25·6 26·0 26·7 7·4 3·5 3·4 3·5 11·8 12·5 10·9 11·7 22·1 19·8 21·6

8·1 8·0 3·5

Diameter range

T 8. The averages of the stand structure variable values in the forestry centre district of Pohjois-Savo divided by ownership group, site fertility and stand development stage. For explanations of the code variables see Tables 1 and 2 M. Maltamo et al. 159

160

Forest structure in central Finland

T 9. Comparison of the statistical differences of the averages of the stand structure variables (t-test) within the forestry centre district of Pohjois-Savo. Comparisons are made according to site fertility and forest ownership groups. For explanations of the code variables see Tables 2 and 3 Compared ownership groups Forest site fertility/ Stand structure variable GROVES Tree storeys Tree species Diameter range GROVES Tree storeys Tree species Diameter range GROVES Tree storeys Tree species Diameter range MOIST HEATHS Tree storeys Tree species Diameter range MOIST HEATHS Tree storeys Tree species Diameter range MOIST HEATHS Tree storeys Tree species Diameter range DRY HEATHS Tree storeys Tree species Diameter range DRY HEATHS Tree storeys Tree species Diameter range DRY HEATHS Tree storeys Tree species Diameter range

Development I vs. stage II

I vs. III

II vs. IV

II vs. III

III vs. IV

IV

— — —

— — ∗—

∗ — —

— — —

2+3 — ∗— — 4+5 — — ∗

— — ∗

— — —

∗— — —

— — —

∗∗ — —

— ∗— —

∗∗ ∗— ∗∗∗

— — —

— — —

6 — — — 2+3

4+5

— ∗— —

∗ — ∗∗∗

6 — — —

2+3 — — — 4+5 — — —

— — —

— — —

— — —

— — —

— ∗ —

6 — ∗ —

groups and in different forestry centre districts was calculated (Table 15). In all five forestry centre districts under examination, the greatest proportion of old forests was in the state owned forests. Even so, this proportion was only notable in the forestry centre district of Pohjois-Karjala. In other forestry centre districts the proportions of old forests included only a few sample plots.

2+3

4+5

6

2+3

4+5

6

2+3

4+5

6

Groves

Groves

Groves

Moist heaths

Moist heaths

Moist heaths

Dry heaths

Dry heaths

Dry heaths

Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm rivate Company State Farm Private Company State

Development stage

Fertility

Owner 2 3 0 1 0 29 0 4 3 6 0 0 20 22 1 10 228 163 6 41 52 42 0 28 6 27 1 18 149 135 5 71 26 10 2 17

N

24·4 5·9 5·0 6·0 5·7 15·2 13·3 10·8 13·5 17·0 27·0 29·0 19·2

107·3 7·2 7·9 8·0 9·3 46·7 40·1 23·0 41·4 104·7 111·5 96·0 118·9

22·0 20·7 32·0

44·3 69·3 86·7

5·7 5·0 8·0 2·4 19·2 20·1 23·3 15·7 23·5 23·6

4·0 23·3 19·1

0·0 40·1 41·2

4·8 6·4 8·0 6·4 47·2 48·7 45·0 37·4 103·0 97·0

6·7 4·7

Basal area

2·0 4·3

Age

2·21 1·14 1·11 1·00 1·17 1·45 1·57 1·80 1·51 1·69 2·30 3·00 1·53

1·10 1·09 2·00 1·00 1·84 1·83 2·17 1·51 2·06 2·26

2·00 2·67 2·50

1·00 1·80 1·66

1·67 1·00

Tree storeys

2·57 1·19 1·30 2·00 1·11 1·66 1·58 1·20 1·38 1·42 2·20 3·50 1·65

1·35 1·27 1·00 1·00 2·31 2·36 2·67 2·02 2·46 2·71

3·50 2·67 2·00

2·00 2·27 2·34

2·33 1·00

Tree species

26·4 4·6 3·9 5·0 6·1 12·5 12·0 9·8 12·0 17·6 22·2 31·5 16·6

3·6 3·3 12·0 0·5 16·9 17·7 22·0 13·1 22·3 25·4

20·5 31·7 30·5

0·0 19·0 16·0

13·7 1·7

Diameter range

T 10. The averages of the stand structure variable values in the forestry centre district of Keski-Pohjanmaa divided by ownership group, site fertility and stand development stage. For explanations of the code variables see Tables 1 and 2 M. Maltamo et al. 161

162

Forest structure in central Finland

T 11. Comparison of the statistical differences of the averages of the stand structure variables (t-test) within the forestry centre district of Keski-Pohjanmaa. Comparisons are made according to site fertility and forest ownership groups. For explanations of the code variables see Tables 2 and 3 Compared ownership groups Forest site fertility/ Stand structure variable GROVES Tree storeys Tree species Diameter range MOIST HEATHS Tree storeys Tree species Diameter range MOIST HEATHS Tree storeys Tree species Diameter range MOIST HEATHS Tree storeys Tree species Diameter range DRY HEATHS Tree storeys Tree species Diameter range DRY HEATHS Tree storeys Tree species Diameter range DRY HEATHS Tree storeys Tree species Diameter range

Development I vs. stage II

I vs. III

I vs. IV

II vs. III

II vs. IV

III vs. IV

4+5 — — — 2+3 — — — 4+5 — — —

∗∗ ∗ ∗∗

∗∗ ∗ ∗∗

— — —

— — ∗—

— — —

— — —

— — —

— — —

— — —

— ∗∗ —

— ∗ —

6

2+3

4+5

6 — — —

4. Discussion The results of this study are based on the tree data of the 8th Finnish National Forest Inventory (NFI), which was conducted in the late 1980s and early 1990s. These data therefore illustrate the effect of the earlier forest management regimes on the forest structure at the time of the NFI sampling; they do not reveal the effects caused by the changes in forest management instructions and forest management that have been applied in the 1990s. Due to the sampling method used (relascope sampling), the description of the forest stand structure of seedling and sapling stands, which reflect most rapidly the effects of new management, is not very reliable. The small differences in stand structure variables in seedling and sapling stands between forest ownership groups may be partly due to the greater sampling error of small trees compared to that of large trees (Vuokila, 1959). Private forest owners seem to grow their forests on average at higher density within

2+3

4+5

6

2+3

4+5

6

2+3

4+5

6

Groves

Groves

Groves

Moist heaths

Moist heaths

Moist heaths

Dry heaths

Dry heaths

Dry heaths

Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State Farm Private Company State

Development stage

Fertility

Owner 3 2 0 0 74 58 0 3 23 8 0 0 34 32 0 1 315 233 9 18 128 77 0 2 65 51 4 4 211 180 18 25 65 57 3 0

N

5·8 5·8 4·0 19·6 20·2 16·4 21·8 22·7 23·2 32·0 6·0 5·5 5·0 3·5 14·1 14·0 15·6 15·0 18·3 17·9 12·0

4·0 50·5 48·9 41·7 47·5 99·5 92·7 137·5 7·6 7·9 7·0 8·3 41·0 42·9 30·7 41·6 104·6 104·2 77·3

16·7 26·4 24·0

63·3 99·2 77·5

6·6 6·4

20·6 21·1

12·7 5·0

Basal area

46·5 46·7

6·7 7·5

Age

2·00 1·11 1·20 1·25 1·00 1·45 1·48 1·44 1·44 1·67 1·60 1·00

1·00 1·84 1·70 1·33 1·56 1·99 2·17

1·12 1·13

1·67 2·22 2·00

1·93 1·78

1·33 1·50

Tree storeys

2·50 1·20 1·39 1·25 1·00 1·48 1·50 1·17 1·28 1·75 1·65 1·00

1·00 2·19 2·26 2·33 1·94 2·32 2·34

1·38 1·44

2·67 2·00 2·38

2·31 2·26

1·67 2·50

Tree species

32·5 3·9 5·5 3·8 1·3 11·0 11·7 12·0 11·2 16·3 15·7 8·0

1·0 17·8 16·1 13·8 17·0 22·1 23·5

3·5 4·4

28·3 24·7 23·8

18·9 18·4

7·7 7·5

Diameter range

T 12. The averages of the stand structure variable values in the forestry centre district of Etela¨-Pohjanmaa divided by ownership group, site fertility and stand development stage. For explanations of the code variables see Tables 1 and 2 M. Maltamo et al. 163

164

Forest structure in central Finland

T 13. Comparison of the statistical differences of the averages of the stand structure variables (t-test) within the forestry centre district of Etela¨-Pohjanmaa. Comparisons are made according to site fertility and forest ownership groups· For explanations of the code variables see Tables 2 and 3 Compared ownership groups Forest site fertility/ Stand structure variable GROVES Tree storeys Tree species Diameter range MOIST HEATHS Tree storeys Tree species Diameter range MOIST HEATHS Tree storeys Tree species Diameter range MOIST HEATHS Tree storeys Tree species Diameter range DRY HEATHS Tree storeys Tree species Diameter range DRY HEATHS Tree storeys Tree species Diameter range DRY HEATHS Tree storeys Tree species Diameter range

Development I vs. stage II

I vs. III

I vs. IV

II vs. III

II vs. IV

III vs. IV

4+5 — — — 2+3 — — — 4+5

6

∗∗ — ∗

— — —

— ∗ —

∗— — —

2+3 — ∗— — 4+5 — — —

— ∗∗ —

— ∗ —

— ∗∗ —

— ∗ —

— — —

6 — — —

T 14. The relative proportion (%) of data categories having the greater averages of the stand structure variable values than corresponding value of the whole study area. Results are presented by forestry centre districts for the whole forestry centre district and by ownership groups. (All= all ownership groups together, for the explanations of the other forest ownership group codes see Table 1) Forestry centre district District

All

Farm

Private

Company

State

Pohjois-Karjala Pohjois-Savo Keski-Suomi Etela¨-Pohjanmaa Keski-Pohjanmaa

60·2 72·4 33·0 26·0 38·3

66·7 50·0 65·3 13·6 33·3

61·5 85·2 11·1 36·8 52·9

42·1 71·4 30·4 66·7 —

68·8 100·0 16·7 20·0 25·0

M. Maltamo et al.

165

T 15. The relative proportion (%) of the old forests (age [140 years) in different ownership groups. Results are divided by forestry centre districts. For the explanations of the forest ownership group codes see Table 1 Forestry centre district District Pohjois-Karjala Pohjois-Savo Keski-Suomi Keski-Pohjanmaa Etela¨-Pohjanmaa

Farm

Private

Company

State

0·4 0·3 0·1 0·9 0·9

0·5 0·2 0·3 0·9 1·1

1·1 0·2 0·2 0 0

7·5 0·9 1·8 1·8 1·4

the young age categories compared to that of forests owned by the state or the forest industrial companies. The increasing effect of stand density on stand structural variation can be seen in the stages of young and middle-aged forests. The application of management regimes is often more homogenous in forest industrial company and state owned forests compared to forests owned by private forest owners. Private forest owners’ preference for the preservation of secondary tree species to fill the possible gaps in growing space of a stand increases further structural variation. The differences in the mean values of stand structural variables between privately owned forests and forests owned by the state or forest industrial companies in mature forests are relatively small, except in state forests on moist heaths in the forestry centre district of Keski-Suomi. The present mature forests have been regenerated naturally and have been managed intensively only during last decades and are still partly unmanaged regardless of the ownership group. However, when the present middleaged forests become mature forests, this work suggests that more differences in the forest structure between the ownership groups will develop. On the very fertile soils the differences in the stand structure variables between forest ownership groups within forestry centre districts can not be compared due to the low number of observations. However, across the data as a whole the differences in the mean values of stand structure variables between private forest owners and forest industrial companies are clear in sapling stands. In the later successional stages these differences vanish. It has been stated that on the most fertile forest sites even the artificial regeneration method, including soil preparation and cleaning of the sapling stand, does not, in the long run, affect the stand structure (Uuttera and Maltamo, 1995). This is the opposite phenomenon to that found in moist and dry heaths, where artificial regeneration causes lower mean values of the stand structural variables (Uuttera and Maltamo, 1995). On moist heaths, management affects the stand structure because the natural regeneration of new seedlings and the separation of the tree storeys, caused by competition between tree individuals, is not as quick as on more fertile sites. On the other hand, moist heaths still provide living conditions for several tree species, and forest management does not necessarily affect the number of existing tree species. There is, furthermore, evidence that a mixture of broad-leaved tree species in conifer dominated stand increases the stem wood production of a stand (Mielika¨inen, 1985). Therefore, the goal of practical forest management has been the maintenance of the deciduous tree species mixture on moist heaths. On dryish and dry heaths the natural variation of the stand structure is low. This

166

Forest structure in central Finland

is explained by the stronger biological competitiveness of pine in comparison with other tree species. The natural secondary tree species regenerated in the seedling stage cannot regenerate naturally in subsequent successional stages, even if their existence were a desirable management object. Therefore, changes in the stand structure caused by forest management in the sapling stage are quite permanent. The regional variation between forestry centre districts followed the east-west gradient, being greater in the eastern parts although there were some exceptions. Based on the study material, it is difficult to say if there has been some regional differences in the management of the forests between forestry centre districts or if the differences are caused by the different climatic-edaphic conditions. In general it seems that the mean values of stand structure variables are smaller in the production forests of Finland in comparison to those of the Ladenso Forest Inventory Area, the Republic of Karelia, Russian Federation (Uuttera et al., 1996). The Ladenso Inventory Area is located across the border of south-eastern part of Pohjois-Karjala and there are relatively similar abiotic growth conditions compared to those in the test areas of this study but the management of the forests has been much less intensive than in Finland. However, in comparison with this study the classification of site fertility and stand development stages were slightly different in the study of Uuttera et al. 1996. It seems though, that the greatest differences in stand structure variables caused by forest management exist in young and middle-aged forests. However, it may be that these differences have already been created by the more intensive management of the sapling stands in Finland compared to Russian Federation (Uuttera and Maltamo, 1995). Large-scale information on forest structure is a valuable tool for the development of forest management, regional forest management planning and even large-scale ecological planning. From the point of view of the habitat diversity of a forest area, it should be noted that those stands of smaller structural diversity represent different habitats than those of great structural diversity. They have, for example, different micro-climate, different root competition for nutrients and water between trees and other plants, different water and decomposition regimes, and different plant and animal communities (e.g. Huston, 1994). However, the maximization of the structural variation of the stand should not be the goal of forest management, but the natural within stand variation under different physical conditions and stand successional stages should be maintained. The results of this study indicate that small-scaled silviculture and variation in the silvicultural methods applied under the different physical conditions of the stand lead to more diverse stand structure. On the other hand, small scale management applied in small forest holdings may lead to greater forest fragmentation on landscape level. The management target of a desirable biologically diverse forest should be based on the scientific, empirically confirmed knowledge of the components of the overall diversity. Therefore, the results of this study should be considered as a vital, but first step in acquiring the information on all the components of overall diversity at landscape level connected with economically profitable production of wood and other benefits. At the stand level, variables, such as those presented and compared in this study, could be used in the future for monitoring the state of forest management with regard to biodiversity preservation and also for forest product certification. The authors thank Dr Jyrki Kangas, Professor Pekka Niemela¨, Professor Jukka Salo and Dr Jussi Sarama¨ki for their valuable comments on the manuscript. We also thank the Finnish Forest Research Institute, especially Mr Arto Ahola, for providing the material of this study.

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