Natural forest remnants and transport infrastructure ...

Ecological Bulletins 51: 149–162, 2004

Natural forest remnants and transport infrastructure – does history matter for biodiversity conservation planning? Per Angelstam, Grzegorz Mikusiński and Jonas Fridman

Angelstam, P., Mikusiński, G. and Fridman, J. 2004. Natural forest remnants and transport infrastructure – does history matter for biodiversity conservation planning? – Ecol. Bull. 51: 149–162. To access Sweden’s wood resources during the past 150 yr, waterways for timber log driving were prepared and the networks of railroads and roads were developed. We related this human footprint to today’s amount of dead wood and protected natural forest remnants. The accumulated transport infrastructure over time was used as a surrogate measurement of past harvesting intensity in 25 × 25 km grid cells within two study areas in northern boreal forest (Norrbotten and Västerbotten) and one area in southern boreal and hemiboreal forest (central Sweden). The accessibility of the landscape was estimated as the length per grid cell of roads in northern Sweden and railroads in central Sweden, calculated at 50-yr intervals since 1850. Because terrain ruggedness affected the development of log driving on waterways in a given area, we used a 50 × 50 m digital elevation model to calculate the mean slope within grid cells as an estimate of inaccessibility. We found negative relationships between the amount of dead wood and transport infrastructure (accessibility) in all three study areas. The proportions of variation in dead wood explained by the indices of accessibility and inaccessibility in Norrbotten and Västerbotten were 18 and 28%, respectively. For central Sweden, the total amount of variation explained was only 9%. The average amount of dead wood was lower in central Sweden (2.1 m3 ha–1) than in Västerbotten (3.7 m3 ha–1) and Norrbotten (4.0 m3 ha–1). For the area of natural forest remnants, significant relationships were found in northern but not in central Sweden. A total of 41% (Norrbotten) and 54% (Västerbotten) of the variation in today’s amount of protected forest remnants were explained by the indices of accessibility and inaccessibility. We interpret differences in amount of dead wood and protected forests among regions as a consequence of anthropogenic impacts on local landscapes having occurred before the advent of the modern transport infrastructure. We also stress the need to be aware of the degree of deviation from natural conditions in present landscapes when formulating regional conservation goals. P. Angelstam ([email protected]), School for Forest Engineers, Fac. of Forest Sciences, Swedish Univ. of Agricultural Sciences, SE-739 21 Skinnskatteberg, Sweden and Dept of Natural Sciences, Centre for Landscape Ecology, Örebro Univ., SE-701 82 Örebro, Sweden. – G. Mikusi Mikusiński, Dept of Natural Sciences, Örebro Univ., SE-701 82 Örebro, Sweden. – J. Fridman, Dept of Forest Resource Management and Geomatics, Swedish Univ. of Agricultural Sciences, SE-901 83 Umeå, Sweden.

Copyright © ECOLOGICAL BULLETINS, 2004

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An issue of paramount importance in sustainable forest management is how to strike the balance between the use of renewable resources and the maintenance of biological diversity (Hunter 1999, Lindenmayer and Franklin 2002). Analyses of the life-history traits of endangered species show that they require habitat components that are commonly found only in naturally dynamic forests (e.g. Berg et al. 1994). Such components include large trees, old trees, a diverse tree species composition and different types of dead wood, often concentrated in remnants of naturally dynamic forests (e.g. Peterken 1996). Due to a lowered mean age of the forests and more intensive forest management, loss of dead wood is one of the most general consequences of intensified forest management (Siitonen 2001). Similarly, protected or remotely located forests usually represent the last remnants of near-natural forest (Angelstam and Andersson 2001, Yaroshenko et al. 2001, Aksenov et al. 2002, Götmark and Thorell 2003). Dead wood of different forms constitutes 20–25% of the total number of species in boreal forests (Siitonen 2001). Several studies have documented the amount of dead wood in forests with different histories (Sippola et al. 1998, Fridman and Walheim 2000, Siitonen 2001, Stokland 2001, Jonsson and Kruys 2001, Nilsson et al. 2002, Angelstam and Dönz-Breuss 2004, Shorohova and Tetioukhin 2004). In naturally dynamic old boreal forests the amount of dead wood is 60–90 m3 ha–1 (Siitonen 2001). A general pattern is that ca 30% of the total biomass consists of dead wood of different kinds including standing and lying trees of different size and decay stages (Nilsson et al. 2002). In forests recently subjected to stand scale disturbances, such as fire and wind, the proportion of dead wood is considerably larger. By contrast, in forests with a long management history, such as in central Sweden and Scotland, the amount of dead wood is considerably lower (ca 2 m3 ha–1; Fridman and Walheim 2000, Angelstam and Dönz-Breuss 2004). This means that the reduction of dead wood in managed landscapes compared with natural forests can be estimated as being > 95%. Siitonen (2001) argues that such a decline should lead to more than a 50% reduction of species, however, without considering possible effects of fragmentation and lack of temporal continuity. Since dead wood is a complex natural element that consists of many different traits including tree species, size, decay stage and exposition to light and moisture (e.g. Similä et al. 2003), the amount of specific combinations of these traits has declined even more. Sweden is a good example of an area that has gradually been altered by forest utilisation that started early in the centre of economic development and reached the periphery in relatively recent time. Forests of different types are the dominating natural potential vegetation below the tree line in Scandinavia (Mayer 1984). Clearing of forests started several thousand years ago in southern and coastal Sweden (e.g. Angelstam 1997). The first local industrial use of

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forest products were for the production of glass (Nordström et al. 1989), potash and tar (Borgegård 1973) as well as iron and steel (Furuskog 1924, Arpi 1951, 1959, Attman 1986). For a long time, from the 17th to the 20th century, this entailed an extensive local exploitation of the forests in Sweden (Wieslander 1936, Arpi 1959, Nordström et al. 1989). Before the middle of the 19th century large areas with near-natural forests subject to only local non-industrial use still existed in the remote upland and northern parts of Sweden (Niklasson and Granström 2000). In the middle of the 19th century, a fundamental transformation began in society, as well as in the forest landscape (Carlgren 1926, Heckscher 1935–49, Arpi 1959, Schön 2000). Industrialisation received an impetus, agriculture was intensified, and new areas were colonised in northern Sweden (Mörner 1982). Forests acquired a trade value and became a commodity to an extent never previously suspected. Until ca 1830–1840 the timber export from Sweden was modest, but then it increased exponentially (Mattson and Stridsberg 1981). The liberal economy led to a great increase of world trade. Starting in 1849 this resulted in a growth in number of sawmills along the whole Bothnian coast and an exploitation of the primeval forest in the inland areas of northern Sweden (e.g. Carlgren 1926, Bunte et al. 1982). Between 1850 and 1900, Sweden’s export of sawn timber had shown a tenfold increase and the annual harvests had reached close to 20 million m3. This historical development was clearly dependent on, and associated with, the growth of the transport infrastructure (Nilsson 1990). The first waterways were developed by building canals and by preparing rivers for log driving (Andersson 1907, Nordquist 1959, Törnlund and Östlund 2002). Other types of infrastructure, such as railroads and roads, were then built for long-distance transportation of wood (e.g. Hjelmström 1959, Qviström 2003). Two types of effects of infrastructure on biodiversity may be distinguished: primary and secondary (Seiler 2003). Primary effects include traffic accidents, noise, and changes in dispersal and movement capabilities of organisms (Forman et al. 2003). Secondary effects of infrastructure include human settlement and resource exploitation, land use changes and intensification, as well as industrial development (Carlgren 1926, Hoppe 1945, Friberg 1951, Lassila 1972, Mörner 1982, Qviström 2003, Williams 2003, Forman et al. 2003). The development of the transport infrastructure thus provides a commonly used surrogate measurement of the impact of economic development on forests worldwide (Yaroshenko et al. 2001, Aksenov et al. 2002, Williams 2003). The intensification of forest landscape use enabled by infrastructure development has had profound negative effects on forest biodiversity (Gärdenfors 2000). In managed landscapes dead wood and remnants of natural ecosystems provide qualities of high importance for biodiversity, both

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of which are negatively affected by macroeconomic factors (e.g. Skontoft and Solem 2001). For example, using National Forest Inventory data Fridman and Walheim (2000) reported at a coarse spatial scale clear dead wood distribution patterns in Sweden being clearly related to the history of forest use. The average amount of dead wood on managed productive forest land was 6 m3 ha–1, but with considerable variation among different forest regions. Approximately 25% of the total amount of dead wood consisted of snags and 75% of logs. Similarly, natural forest remnants are confined to the periphery of economic development (Yaroshenko et al. 2001). Protected areas devoted to nature protection are usually natural or semi-natural remnants of previously naturally dynamic landscapes. The degree of naturalness of these remnants may vary, but their rescue effect for forest biodiversity has been documented (Uotila et al. 2002). The regional distribution of protected areas in Sweden is clearly linked to the history of economic development. The majority of such areas are found in the northern part of the country, particularly on land being least productive (Nilsson and Götmark 1992, Fridman 2000). On the contrary, highly productive areas have been intensively managed for a long time, and as a result the amount of set-aside areas is low (Angelstam and Andersson 2001, Angelstam et al. 2003a). Such differences in the present amount of dead wood and natural forest remnants need to be considered when formulating regional conservation goals (e.g. Angelstam and Bergman 2004). The aim of this paper is to explore the idea that relative differences in the development of the transport infrastructure can be used as a measurement of the human footprint on structural elements of forest biodiversity. Specifically, we relate the accumulated transport infrastructure to the amount of dead wood and area of protected land at the landscape scale in three Swedish regions. The underlying hypothesis is that improved land accessibility, which enables forest resource extraction, leads to a decrease in the amount of natural forest remnants at the stand and landscape scale.

Historical background and methods for analysis During the past 150 yr, Swedish boreal and hemiboreal forests have provided vital raw material for use first in the iron industry, and later the forest industry (e.g. Furuskog 1924, Bladh 1995, Östlund and Zackrisson 2000). To meet the objective of this study, spatially explicit data representing local landscapes within a region were needed. While the amount of dead wood and protected forest areas are monitored for the whole of Sweden (see Fridman and Walheim 2000, Angelstam and Andersson 2001), detailed descriptions of the development of the infrastructure used for industrial forestry are more limited.


Inaccessibility: hindering log driving Large-scale industrial logging for export was a consequence of the arrival of the industrial revolution to Sweden. This development can be viewed as a “frontier” of logging of forests limited by the contemporary transport infrastructure (Andersson 1960, Mörner 1982, Bunte et al. 1982, Björklund 1984, Bladh 1995). Different means of long-distance transportation were used in different phases throughout the history of industrial forest use (Heckscher 1907, Andersson 1960, Nilsson 1990). Initially log driving on rivers was essential in both northern and upland central Sweden (e.g. Törnlund and Östlund 2002). The use of local log driving was practised during the 17th and 18th centuries in the Swedish mining districts even before the breakthrough of the forest export industry (Winberg 1944, Andersson 1960, Bladh 1995). However, from the middle of the 19th century log driving became a crucial link for the timber industry because natural watercourses allowed for long distance transportation at a low cost (Heckscher 1907, Hellström 1917, Nordquist 1959, Törnlund and Östlund 2002). We assumed that the early transport infrastructure, consisting mainly of waterways for log driving, was related to the average altitude, altitudinal range and topography. A more “rugged” landscape is relatively more inaccessible for the development of log driving. Using a 50 × 50 m digital elevation model (DEM), the index of topographic brokenness expressed as mean slope in degrees between each point in the DEM was calculated for each grid cell (Williams and Gallant 2000) and was used as a measure of inaccessibility in the context of log driving.

Accessibility: the development of transport infrastructure The development of railroads was essential for the transportation of wood products from inland areas to the coast in central Sweden where large rivers are much less common than in northern Sweden (Andersson 1907, Hellstrand 1980). In 1829 Gustaf af Uhr made the first proposal to build railways by connecting the canal systems between lake Vättern and lake Hjälmaren in Sweden (Anon. 1956). The interest for improved communications grew in the 1830s and 1840s. Inspired by the successful establishment of railroads in other parts of Europe, Adolf Eugene von Rosen proposed in 1845 a state railroad network from Stockholm to Göteborg, Ystad and Gävle. The proposal was turned down but meanwhile local narrowgage railways were built to connect waterways in regions with heavy industry around 1850. However, the first statesupported normal-gage railway was completed from Nora to Ervalla north of Örebro in 1856 and then the railroad network expanded with the advent of the industrial revolution (Jonasson 1950). This railroad network was the main

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transport infrastructure for export that enabled intensification of forest use, especially in the eastern part of central Sweden (Hellstrand 1980). Jonasson (1950) summarised the growth of the state railroad network from 1846 to 1946. In addition we used the information from 1990 (Castenson 1992). The road infrastructure played an increasing role from the mid-20th century (Nilsson 1990, Törnlund and Östlund 2002). For Norrbotten, Hoppe (1945) published maps of the road network expansion in that county up until 1940, and for Västerbotten, Lassila (1972) did the same until 1970. In short, we thus assumed that railroads (in central Sweden) and roads (in Norrbotten and Västerbotten) were factors increasing accessibility to the wood resources. All spatial analyses on the development of infrastructure were made in ArcView 3.2a (Anon. 2000). The maps published in Hoppe (1945), Jonasson (1950) and Lassila (1972) and were digitised and used in combination with the information from 1990 provided in Castensson (1992). To quantify the accumulated impact of transport infrastructure, the length of public roads and railroads was summed for the four points in time for each 25 × 25 km cell (Table 1). Some 25 × 25 km grid cells had part of their area outside the limits of the areas for which we had information about the transport infrastructure. This was due to the fact that the areas with information about infrastructure were delineated by natural (e.g. coast-line) and administrative (i.e. county and national borders) limits rather than according to the grid network. If the part of a cell located inside those limits was < 500 km2 (500/625 = 80%), that grid cell was excluded.

ventory (Ranneby et al. 1987) for each 25 × 25 km grid cell. These data cover both standing and lying dead wood. For the landscape scale we used a GIS database from the Swedish Environmental Protection Agency describing protected areas with high conservation value forest in Sweden. The database included the protected areas as of May 2000, i.e. excluding the areas designated in the government decision of 6 July, 2000. For each 25 × 25 km grid cell we estimated the total area of protected areas.

Statistical analyses To compare the amount of natural forest remnants at different scales (i.e. amounts of dead wood and protected areas) and proxies describing the contemporary transport infrastructure making forests accessible and terrain ruggedness, we expressed all data as mean values for each 25 × 25 km grid cell. The analyses are presented for the counties of Norrbotten (105 grid cells; ca 65000 km2) and Västerbotten (76 grid cells; ca 48000 km2) in the northern boreal forest, and central Sweden (230 grid cells; ca 144000 km2) in the southern boreal and hemiboreal forest (Fig. 1). First, we used correlation analysis to explore the relationships among all four variables (i.e. dead wood, protected areas, accessibility, and inaccessibility). Then, multiple linear regression analysis was applied to examine the relationships between accessibility and inaccessibility on the one hand, and natural forest remnants on the other.

Results Accesssibility and inaccessibility

Natural forest remnants As a measurement of a natural forest remnant at the stand scale, we used data about the average volume of dead wood collected 1995–1999 by the Swedish National Forest In-

The sums of public roads in Norrbotten and Västerbotten and of railroads in central Sweden for the four points in time are shown in Fig. 1. After a rapid development of railroads during ca 100 yr, which started in the industrial

Table 1. Summary of data sources and year of orgin used to quantify the development of the transport infrastructure concerning roads in northern Sweden (Norrbotten and Västerbotten) and railroads in central Sweden. Time

ca 1850

ca 1900

ca 1950

ca 2000

Norrbotten (Hoppe 1945, Castenson 1992)

1860

1900

1940

1990

Västerbotten (Lassila 1972, Castenson 1992)

mean of 1810/1910

1910

1950

1990

Central Sweden (Jonasson 1950, Castenson 1992)

1856

1896

1946

1990

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Fig. 1. Map of Sweden showing the accumulated amount of transport infrastructure in 25 × 25 km grid cells. The data refer to the road network from the beginning of the 19th century to 1990 in the counties of Norrbotten and Västerbotten, as well as to the railroad network in central Sweden from 1856 to 1990 (see also Table 1).

centres associated with the iron and wood industry in central Sweden, the expansion halted in the mid 20th century. In fact, the importance of the railroad network has declined in the past 50 yr both in total length (Fig. 2) and spatial extent. By contrast, the development of the road network development in northern Sweden followed a clear pattern of gradual expansion from the coast toward the mountains that covered all time intervals in the study. The accessibility expressed as the accumulated density of transport infrastructure (Fig. 2) and the inaccessibility of the landscape expressed as the mean slope (Fig. 3) varied considerably among the three regions (Table 2). The accumulated road density in Västerbotten was twice as high as

in Norrbotten. The degree of inaccessibility (i.e. topographic ruggedness) was much higher in the two northern regions than in central Sweden.

Amount of dead wood and protected areas There was considerable variation in the amount of dead wood and protected areas among the three regions in Sweden (Figs 4, 5). In general, today’s mean amount of dead wood is lower in central Sweden (2.1 m3 ha–1) than in Västerbotten (3.7 m3 ha–1) and Norrbotten (4.0 m3 ha–1) (Table 2). Similarly the average protected area was 10% in

Fig. 2. The historic development of the transport infrastructure in the form of public roads (Norrbotten, Västerbotten) and railroads (central Sweden).


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Fig. 3. Mean slope in degrees within 25 × 25 km grid cells in the three study areas in Sweden.

Västerbotten and 14% in Norrbotten, but only 1.2% in central Sweden (Table 2).

Transport infrastructure and natural forest remnants We found negative correlations between the amount of dead wood in the managed landscape and accessibility due to the development of the transport infrastructure from the middle of the 19th century to present time in all three study areas (Table 3). The relationships were, however, much stronger in Norrbotten and Västerbotten than in central Sweden (Fig. 6). Regarding inaccessibility, Västerbotten showed a clearer relationship than both Norrbotten and central Sweden (Table 3, Fig. 6). For the proportion of protected areas, negative correlations were found in Norrbotten and Västerbotten but no correlation at all was found in central Sweden (Table 3). It should also be noted that the proportion of protected areas in central Sweden was as low as in areas with high accessibility in Norrbotten and Västerbotten (Fig. 7). Note that with increasing accessibility the occurrence of high amounts of dead wood and protected areas declined (Figs 6, 7). Using multiple regression analysis we found that for the amount of dead wood, accessibility entered first in the models for both Norrbotten and Västerbotten (Table 4). The total variation explained by accessibility and inaccessibility put together was 18 and 28%, respectively. For central Sweden, accessibility entered first but the total amount of variation explained was only 9%. When using both pre-

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dictor variables to explain the proportion of protected areas, accessibility entered first in Norrbotten and inaccessibility first in Västerbotten (Table 5). Altogether 41% (Norrbotten) and 54% (Västerbotten) of the variation in today’s amount of protected areas was explained by these two variables. In central Sweden no significant fit was obtained using those two variables.

Discussion The impact of macroeconomic development on forests The aim of this interdisciplinary study was to explore the idea that the development of transport infrastructure can be used as an indicator of the complex macroeconomic history, and be linked to the resulting human footprint on structural elements once found in the naturally dynamic landscape. The negative relationships between the amount of dead wood and proportion of protected area in local landscapes one the one hand, and the development of the transport infrastructure from the middle of the 19th century to present time on the other, supports this idea. Similarly, Skonhoft and Solem (2001) reported a clear relationship between macroeconomic development and the decline in the amount of wilderness areas in Norway from almost 50 to < 10% during the 20th century. Hence, in northern Europe, large intact forest areas are now mainly found in remote parts of Russia (Yaroshenko et al. 2001).


Table 2. Amount of dead wood, proportion of protected areas, accumulated density of transport infrastructure (accessibility) and topographic steepness (inaccessibility) in central Sweden and Västerbotten and Norrbotten (mean ± SE). Transport infrastructure is expressed as roads in Norbotten and Västerbotten, while the corresponding figures for central Sweden refer to railroads. Variable

Norrbotten (n = 105)

Västerbotten (n = 76)

Central Sweden (n = 230)

Dead wood (m3 ha–1)

4.0 ± 0.2 median = 3.7 range: 0–11.3

3.7 ± 0.3 median = 3.3 range: 0.9–13.3

2.1 ± 0.1 median = 1.8 range: 0–12.4

Protected area (ha km–2)

14.2 ± 2.2 median = 2.72 range: 0–88.9

10.3 ± 2.5 median = 0.31 range: 0–91.15

1.2 ± 0.1 median = 0.53 range: 0–13.2

Accessibility – Infrastructure density (m km–2)

254 ± 17 median = 229 range: 0–910

428 ± 29 median = 379 range: 38.6–1102

136 ± 6 median = 139 range: 0–445

Inaccessibility – Topographic steepness (degrees)

2.96 ± 0.09 median = 2.90 range: 1.37–7.72

3.53 ± 0.16 median = 3.16 range: 1.38–8.38

1.28 ± 0.05 median = 1.12 range: 0.03–3.48

To validate the general pattern, a closer examination of the regional differences in the amount of different types of dead wood and natural forest remnants is needed. In this study we used the average total volume of dead wood at the stand scale as a response variable. As shown by Fridman and Walheim (2000), the differences in the total amount of dead wood among regions are solely due to differences in the amount of logs on the ground. The amount of snags showed no clear regional pattern, thus indicating that logs

on the ground is the relevant indicator of macroeconomic development. There were clear differences in the amount of dead wood between northern Sweden and central Sweden. The average amount of dead wood in central Sweden was half of that found in Västerbotten and Norrbotten in the north. We interpret this difference as a consequence of a longer forest utilisation history in the south with strong effects on forests that occurred before the advent of the modern transport infrastructure. The iron industry in the

Fig. 4. Amount of dead wood within 25 × 25 km grid cells in the three study areas in Sweden.


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Fig. 5. The amount of protected areas within 25 × 25 km grid cells in the three study areas in Sweden.

Bergslagen area in central Sweden is an important example of a heavier footprint on the forests in the south than in the north. In fact, the shortage of forest had become severe around the mines already by the 18th century (Wieslander 1936). The consumption of charcoal peaked during the end of the 19th century, and in 1885 it was estimated that 20–25% of the cut timber volume was used in making fuel for the iron industry in central Sweden (Arpi 1959). The spatial difference observed among regions for biodiversity indicators (Rametsteiner and Mayer 2004) such as dead wood (e.g. Siitonen 2001) and near-natural forest areas (e.g. Angelstam and Andersson 2001, Yaroshenko et al. 2001) has a corresponding temporal aspect. This is evi-

dent when examining differences in the amount of dead wood and the amount of remaining intact areas within a region over time. For example Linder and Östlund (1998) showed that the amount of dead standing trees declined gradually from ca 12 to < 1 m3 ha–1 during the period ca 1890–1960. Summarising, the general use of forest resources has developed in several more or less distinct steps linked to the effectiveness of timber extraction (Mattson and Stridsberg 1981, Angelstam and Arnold 1993, Drushka 2003, Williams 2003, Angelstam et al. 2004a). The first steps could be described as a pristine forest with most natural structures and processes being intact. Humans are part of the

Table 3. Correlation matrices for the four variables used in the study (p 500 m from a forest road. This means


Table 4. Results from multiple linear regression analyses of the current volume of dead wood against the accumulated amounts transportation infrastructures in northern Sweden (Norrbotten and Västerbotten, road network) and in central Sweden (railroad network) as a measure of accessibility, and topographic steepness as an indicator of inaccessibility. Study area

Accessibility

Inaccessibility

Norrbotten n = 105

β = –0.40 r2 = 0.18 p =