1 Introduction

Naturalists have always been intrigued by the ability of life to sustain conditions inhospitable to humans. Both scientific and popular literature contains numerous descriptions of biota living ‘on the edge’—in deserts, on barren soil of polar islands, under Antarctic ice, in deep waters, and in many other more or less unusual conditions. However, all these habitats exist for millennia, and living beings had sufficient time to evolve biochemical, morphological and behavioural adaptations allowing to live and even flourish in these ‘extreme environments’. More astonishing is the diversity of life persisting in industrial barrens—extreme habitats that appeared as a by-product of human activities only about a century ago.

The creation of metal-contaminated, phytotoxic land by atmospheric smelter effluents Footnote 1 has occurred in many parts of the world (Vangronsveld et al. 1995; Winterhalder 2000) and attracted agitated public attention: “Bushes shrank and vanished. Grasses died away. Blighted land replaced the forest. All around us dead hills, red, raw, ribbed by erosion, stood stark in the sunshine. Hardly two miles from dense woodland we were in the midst of a moonscape on earth. ... We were in the southeast corner of Tennessee, in the Ducktown Desert of the Copper Basin” (Teale 1951).

Unfortunately, industrial barrens are studied much less than other ‘extreme habitats’: the scientists were only called to evaluate the damage (e.g. Haywood 1910; Euler 1939; Dean and Swain 1944) or develop rehabilitation measures (e.g. Carter et al. 1977; Pommerening 1977; Winterhalder 2000). Importantly, information on several industrial barrens is reported only in publications describing reclamation measures (e.g. Pancholy et al. 1975; Sopper 1989; Vangronsveld et al. 1995, 1996; Kelley and Tate 1998; Winterhalder 2000). Even the researchers exploring pollution effects on plant communities tend to select the most polluted sites outside industrial barrens, because these habitats seem not comparable with less disturbed sites (e.g. Banásová et al. 1987). Therefore the first goal of our review is to introduce industrial barrens to a wide range of scientists, showing that these easy-to-reach habitats offer an excellent opportunity for a variety of ‘basic’ ecological and evolutionary studies. From a scientific perspective, unusual anthropogenic ecosystems of denuded barrenland with lifeless lakes can be considered opportunistic macrocosms (unique laboratories) for integrated research on the effects of harsh environmental conditions on ecosystem structure and functions (Nriagu et al. 1998).

Not every strong polluter is surrounded by industrial barrens. Their development seems only possible under specific combination of landscape characteristics, human activities, and co-occurring stressors; however, to our knowledge, no attempt was made to explore this problem by means of comparative analysis. The second goal of our review is therefore to find out both similarities and dissimilarities among the industrial barrens that exist (or did exist) across the Globe and on this basis identify the factors and conditions that are necessary and sufficient for environmental deterioration to reach its nearly final point (not the final point, because some life is always present in industrial barrens).

The barren landscape presents itself not only to ecologists interested in the complex effects of manmade disturbance on ecosystems, but also to those involved with the determination of public policy related to environmental pollution (Anand et al. 2003). It is only rarely appreciated that severely contaminated sites and other post-industrial landscapes may support regionally rare and endangered species (Johnson et al. 1978; Eyre and Luff 1995). Furthermore, industrial barrens clearly show the results of ‘gross negligence’ typical for early stages of industrial development, and their exploration can serve to ecological education of people. Therefore our third goal is to briefly describe the diversity of life in industrial barrens and call for conservation measures.

Last but not least, we aimed at identification of knowledge gaps that require immediate attention of international scientific community, because most of existing industrial barrens may disappear rather soon due to strict emission control and rehabilitation measures. On the other hand, the serious concern is the potential for developing nations to repeat the environmental mistakes made by the developed world (Padgett and Kee 2004). The knowledge on mechanisms behind the development of industrial barrens may help to prevent habitat deterioration in developing countries, especially in South-Eastern Asia where industrial emissions are predicted to increase drastically (Fowler et al. 1999).

2 Terminology

To our knowledge, no attempt was made to unify the terminology associated with description of the habitats severely disturbed by aerial emissions; terminology used by different researchers is summarised in Table 1. McCall et al. (1995, p. 847) defined ‘barrens’ adjacent to Sudbury smelters as landscapes “characterised by bare and sparsely vegetated land, severely eroded and blackened hilltops and acidic (pH < 4.0) and metal contaminated soils”. Later on, McCall et al. (1995, p. 849) introduced a 5% vegetation cover to delineate barrens by using aerial photographs; Eränen and Kozlov (2006) used 10% cover to define industrial barrens. However, these absolute values may appear misleading in landscapes with naturally low vegetation cover, like deserts.

Table 1 Documented occurrence of industrial barrens and dying forests on a barren soil (alphabetical order, by location)
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In this paper we classify as industrial barrens the bleak open landscapes evolved around the point sources of industrial pollution due to deposition of airborne pollutants, with small patches of vegetation (cover usually reduced to 10% or less relative to control) surrounded by bare land with illuvial horizon or even the rock exposed due to intensive soil erosion (relict soil cover usually less than 20%) (Figs. 1–3).

Fig. 1
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Sudbury, non-reclaimed industrial barren (2001)

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Fig. 2
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Nikel, industrial barren developed from Scots pine forest (2000)

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Fig. 3
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Zapolyarnyy, industrial barren developed from birch woodland on a bog (2000)

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Industrial barrens are usually surrounded by strongly modified ecosystems (Figs. 4–6) that have a potential to turn into industrial barrens under some circumstances (see below). In Sudbury, these habitats where “conifers are generally absent and the forest consists of a near monoculture of stunted and coppiced white birch (Betula papyrifera)” were defined as ‘semi-barren’ area (McCall et al. 1995, p. 847) or described as ‘savannah woodland’ (Courtin 1994). Similar habitats existing around Monchegorsk and Nikel were termed ‘birch transitional community’ (Kozlov 2001, 2002) or ‘birch woodlands’ (Kozlov et al. 2001); some Russian authors (e.g. Stepanov and Chernenkova 1989) used an expression ‘forests with dead field layer vegetation’ for secondary birch regrowth near the Karabash smelter (Fig. 6).

Fig. 4
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Revda, erosion of bare soils (2002)

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Fig. 5
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Krompachy, secondary forest on bare ground behind the smelter (2001)

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Fig. 6
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Karabash, secondary birch forest on bare ground (2002)

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3 Documented occurrence of industrial barrens

3.1 Responsible industries

We were able to obtain some information on 36 industrial barrens worldwide (Table 1). Nearly all of them (33 of 36) have developed in the impact zones of non-ferrous smelters and refineries, primarily those of copper-, nickel-, zinc- and lead-producing factories. The notable exceptions are the iron sintering plant in Wawa, Canada and the magnesite plants in Satka (Russia) and Lubenik (Slovakia). Industrial barrens are frequently associated with the historical smelting sites: 12 of them occur around industries that started operations in 18–19th centuries (Table 1). The most recent installation that caused development of industrial barrens is Ventanas smelter in Quinteros, Chile (operated since 1964).

Intriguingly, industrial barrens have not been observed around aluminium factories, which emit (or have emitted in the past) large amounts of phytotoxic compounds, primarily fluorine. Only Gilbert (1975, p. 120) mentioned that “very small areas of exposed rocky ground were at the denuding stage with eroding soils sparsely colonised by annuals” around two of three aluminium smelters in Norway. Recently, even the most exposed sites near the Bratsk aluminium factory in Siberia are covered by damaged and dwarfed forest with dense field layer vegetation (pers. obs.). Similarly, environmental impact of power plants, even the largest ones that emit more sulphur dioxide than some of smelters surrounded by barren lands (Pearce 1994), is not strong enough to cause development of industrial barrens.

In general, industrial barrens represent a relatively rare phenomenon: they were recorded around approximately 10% of point polluters which impact on biota was scientifically documented (by 2003, we retrieved the published information on biotic effects of 233 polluters: Kozlov and Zvereva 2003).

3.2 Geographical distribution and vegetation zones

Nearly a half of identified 36 industrial barrens, including those at incipient stages of development (Table 1), occur in North America, with nine localities in USA and five in Canada. Russia houses 10 industrial barrens, three of which are located in the Kola Peninsula and six in Southern Ural region. The only industrial barrens in the Southern hemisphere are reported from Chile and Tasmania. Industrial barrens have not been described from the tropics, and it can only be guessed whether this reflects geographical distribution of smelting activities, shortage of information or higher resistance of tropical ecosystems to extreme deposition of aerial pollutants.

Most of industrial barrens (27 of 36) occur in forested areas, where they generally replace coniferous or mixed forests. Barrens around Legnica, Poland, and Maatheide, Belgium, evolved from arable lands that were earlier covered by broadleaved forests. Similarly, smelter in Banská Štiavnica was earlier surrounded by oak-hornbeam forest. Industrial barrens near Zapolyarnyy, Norilsk and Yellowknife developed at the northern tree limit from sparse sub-tundra forests, birch woodlands and shrubby tundras. Barrens near Quinteros, Superior and in the Miami-Globe area are surrounded by shrubby grasslands and desert, while barrens at Mednogorsk developed from steppes.

3.3 Landscapes

Majority (27 of 36) of industrial barrens occur in the mountainous or hilly areas. However, since ore deposits are often associated with mountains, additional data are necessary to test the hypothesis that mountain landscapes are especially prone to severe disturbance caused by smelter fumes. Industrial barrens in relatively flat regions, like at Legnica in Poland, Harjavalta and Ykspihlaja in Finland, and at Maatheide in Belgium, seems less extensive, possibly due to less intensive soil erosion on planes.

Development of industrial barrens in mountain landscape can be enhanced by local meteorology. Fumes emitted by the lead and zinc smelter at Trail drifted north and south along the relatively narrow, mountain-bordered valley that constitutes a natural channel for the smelter gases (Archibold 1978; Quinn 1989). The prevailing north-westerly winds carry emissions of Palmerton smelter directly toward Blue Mountain, resulting in higher concentrations of pollutants than would be the case in level terrain (Jordan 1975). Similarly, predominance of meridional winds in surroundings of Monchegorsk caused development of extensive industrial barrens to both North and South of the nickel–copper smelter (Doncheva 1978; Kryuchkov 1993); at the same time, nearly undamaged Scots pine (Pinus sylvestris L.) forest still occurs some 5 km East of the smelter (pers. obs.).

Mountains can not only channel aerial emissions but also ‘trap’ the smoke, greatly enhancing vegetation exposure and the resulting damage. For example, the Copper Basin, comprising 3,300 ha, is surrounded by a rim of mountains (Wolt and Lietzke 1982). The Summer Valley near the Anaconda smelter “resembled a bowl, rimmed on three sides by the main range of the Rocky Mountains... During the winter months, and occasionally in the summer, an inversion often placed a lid over the valley and trapped the city’s smoke...” (MacMillan 2000, p. 25). Inversion conditions occur frequently near the Kellogg smelter in the fall (Ragaini et al. 1977); similarly, local contamination by nickel–copper smelters at Nikel and Monchegorsk is exacerbated by frequent temperature inversions (Kryuchkov and Makarova 1989).

3.4 Topography

Topography has an important effect on spatial pattern of both vegetation decline and recovery (Easmond 1971; Usui and Suzuki 1973; Gilbert 1975). In Sudbury, the line of vegetation discontinuity usually followed elevation contour lines (McCall et al. 1995). Exposed hilltops were particularly prone to fumigation damage in the past (James and Courtin 1985), and are now very slow to recover (McCall et al. 1995). Hilltops in Sudbury remain bare for decades after emission decline, and their sparse soils are still subject to erosion (Dudka et al. 1995). In industrial barrens near Monchegorsk vegetation damage was lower, and vegetation cover and species richness were higher in the bottom of the valley, near the small stream, compared with slopes that were only some 50–80 m above (Kozlov 1997).

4 Development of industrial barrens

4.1 Effects of pollutants

The largest air pollution problems in industrial barrens are episodic, with high ambient concentrations lasting a few hours to two days (Sivertsen et al. 1994). Near the smelters in the Kola Peninsula these episodes in 1980s occurred during 3–5% of days in winter and 1–2% in summer (Baklanov and Sivertsen 1994). During episodes, hourly concentrations of SO2 reached 1200 μg m−3 near Monchegorsk (Baklanov and Rodyushkina 1993), 2500 μg m−3 near Nikel (Sivertsen et al. 1994), and 14,800 μg m−3 near Norilsk (Savchenko 1998). During the summer of 1994, monthly average concentrations of SO2 in industrial barrens near Monchegorsk were 150–270 μg m−3 (Zvereva and Kozlov 2005, and unpublished). These values should be regarded intolerable for local forests, because the proposed SO2 critical levels estimated by different methods range 5–15 μg m−3 as a growing season mean (Manninen and Huttunen 1997).

Although acute damage by sulphur dioxide, the main phytotoxic component of smelter fumes, definitely contributed to vegetation decline (e.g. Haywood 1910; Euler 1939; Makhnev et al. 1990), the importance of this damage for the development of industrial barrens remains unclear. Extreme levels of sulphur dioxide, especially near the roastbeds, killed adjacent forests during relatively short time (Hedgcock 1912; Dean and Swain 1944; Gordon and Gorham 1963; Kryuchkov 1993; Hutchinson and Symington 1997). However, absence of industrial barrens around power plants and aluminium smelters hints that development of this kind of landscape is impossible without severe soil contamination by heavy metals (see Sect. 5.1). In particular, near Anaconda smelter, percent bare ground positively correlated with both concentrations of hazardous substances in soil and soil phytotoxicity revealed by laboratory experiments, thus suggesting the leading role of soil contamination in loss of vegetation in the field (Galbraith et al. 1995).

4.2 Accompanying disturbances

Smelting industry was usually preceded by or accompanied with other human-induced disturbances, which share the responsibility for the development of industrial barrens. In many historical smelter sites (e.g. Kellogg, Sudbury, Copper Basin, Queenstown, Ashio) deforestation was primarily due to harvesting for mine timber and fuel (Usui and Suzuki 1973; Hansen and Mitchell 1978; Winterhalder 2000). Shortage of fuel for smelters in the Copper Basin was noticed as early as in 1861; by 1878, about 130 km2 had been stripped of vegetation (Anonymous 2005b). Some 3,262,000 m3 of wood were consumed for roasting in Sudbury between 1890 and 1930 (Allum and Dreisinger 1987). Similarly, over 3 million tonnes of timber were cut down around Queenstown between 1896 and 1923 (Anonymous 2005a).

When commercial forests started to die due to pollution impact, the very first reaction of the foresters was to cut down the damaged stands in order to prevent losses of timber. This practice was widely applied in Central and Northern Europe (e.g. Gilbert 1975) until at least the mid-1970s, when it became obvious that the cost of harvested timber is minor in relation to the costs of rehabilitation measures required after clearcutting. In spite of this knowledge, some local regulations (existing, for example, in Russia) still require immediate felling of pollution-damaged forest in order to make use of the timber (Kozlov 2004). Alternatively, dead trees can be removed to make the landscape more ‘attractive’ visually; in spite of advice of the local scientists, this selective logging was conducted in spring of 2006 near the Monchegorsk smelter (pers. obs.). However, the polluted forest never become completely dead, and even the dead trees maintain some climatic and biotic stability in the contaminated habitats, in particular by ameliorating microclimate (Wołk 1977) and preventing soil erosion. The old clearcuts under severe pollution impact near both Monchegorsk and Nikel have been rapidly transformed to industrial barrens, while some vegetation in the adjacent uncut areas is still alive (Kozlov 2004).

Industries build in 1920–1940s did not require so much of timber as a fuel. Still forests were cut for building purposes, e.g. around Monchegorsk. Initial deforestation around Norilsk, Siberia, was caused by quite peculiar reasons: since prisoners were used extensively for the construction of the Norilsk industry, a buffer of 3–4 km in width was cut around each of prison camps (Kharuk 2000). Importantly, logging causes soil disturbance that may facilitate erosion.

Forests with unusually open canopies, like one observed near Palmerton smelter in 1970s (Jordan 1975), or forest with stunted trees and dead or nearly dead ground layer vegetation, recently existing e.g. near Krompachy, Harjavalta, Ykspihlaja, Revda and Karabash smelters (pers. obs.), seem to represent a transitional stage between forests and industrial barrens. For example, field layer vegetation cover near Harjavalta is ca. 5%, while cover of Scots pine remains as high as 44% (Salemaa et al. 2001). This kind of forest may gradually turn to industrial barrens; however, it is likely that most, if not all, industrial barrens evolved following a fire that destroyed remnants of forest or shrubby vegetation. In semi-barren and barren sites near both Monchegorsk and Nikel we have observed several highly localised fires that consumed woody debris and destroyed most of remaining vegetation, leading to the extension of the barren area. We suppose that dying forests around the smelters listed above will immediately turn into industrial barrens following a fire, because a natural post-fire regeneration is hampered by soil toxicity and altered microclimate (Jordan 1975; Hansen and Mitchell 1978; Vajda and Venäläinen 2005). The detrimental role of occasional forest fires was considered the primary reason of forest deterioration around Bell Bay aluminium smelter in Australia, mostly due to disruption of nutrient cycles and alteration of soil moisture regime (Mitchell 1982).

Both logging and forest damage by fumes from smelting and roasting increased the amount of woody debris in the impacted areas, making them especially vulnerable to occasional fires. Unusually large amount of woody debris is clearly seen on photographs taken in the vicinity of several smelters (Figs. 1–3). In Sudbury, not only sparks from wood-burning locomotives of the Canadian Pacific Railway started the fires, but also prospectors often burned the remaining vegetation and duff to reveal the bedrock below (Winterhalder et al. 2001). In Palmerton, hillside vegetation behind zinc plant was originally destroyed by fire (Pommerening 1977). In the Copper Basin, in times of dry weather, almost daily fires swept the earth bare of vegetation (Teale 1951). The degradation of the Copper Basin landscape may have been further exacerbated by lowland farmers, who trucked cattle into the Basin for free grazing, and regularly burned the land to encourage growth of a sparse pasture (Clay 1983).

4.3 Hampering of natural recovery

All catastrophic events that destroy vegetation, like fires or avalanches, are always followed by natural recovery that, sooner or later, results in restoration of about the same vegetation community. The extant plants growing in industrial barrens may sustain extreme pollution loads and produce viable seeds, sometimes even in larger amounts than in unpolluted sites (Zvereva and Kozlov 2001, 2005; Kozlov and Zvereva 2004). These seeds preserved in the soil seedbank remain viable for decades (Komulainen et al. 1994); still natural regeneration is absent or nearly absent in industrial barrens (Jordan 1975; Kozlov and Haukioja 1999; Rigina and Kozlov 2000). This is most likely due to high concentrations of heavy metals in uppermost soil layers (Table 2) that stunted radicle growth of many plant species (Stavrova 1990; Zeid 2001). Although seeds of several native plant species were capable of germinating in soils of industrial barrens at both Sudbury and Monchegorsk, root growth was so inhibited that seedlings quickly dried off and died completely (Winterhalder et al. 2001; Kozlov 2005). Persistence of some plants in industrial barrens may be transient, being explained not only by higher resistance of the survivors, but also by past phenotypic acclimatisation of mature plants to gradual increase in pollution (Kozlov 2005), and the extent of industrial barrens increases as plants age and die (Zverev and Kozlov, unpublished).

Table 2 Chemistry of humus layer or uppermost soil horizon in industrial barrens
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Additional problems for vegetation recovery may be imposed by slow decomposition of litter. This was in particular noticed around the Palmerton smelter, where a considerable portion of the area is covered with a layer of undecomposed tree bark (Sopper 1989) or by thick (6–16 cm) litter (Jordan 1975). Similarly, leaf litter is the major problem of semi-barren communities in Sudbury, because it hinders the establishment of understorey species by seeds (Winterhalder 2000).

4.4 Soil erosion

The soil of developing industrial barrens, having lost its protective vegetation cover, suffers from extensive erosion (Figs. 4, 5). Sparsely vegetated sites near Anaconda smelter are mostly devoid of topsoil (Marty 2000); soil erosion is especially severe on steep slopes (Redente and Richards 1997). The topsoil, and sometimes even the subsoil, have been lost in Ducktown (Seigworth 1943), Queenstown (Anonymous 2005a), Monchegorsk (Kryuchkov 1993), Nikel (Fig. 2), Zapolyarnyy (Fig. 3), Palmerton (Jordan 1975), Karabash (Stepanov and Chernenkova 1989), Ashio (Usui and Suzuki 1973) and several other sites. Even after emission decline, soil is still exposed to water erosion by runoff, summer desiccation, wind erosion and frost heaving (Hazlett et al. 1983; Dudka et al. 1995; McCall et al. 1995; Vangronsveld et al. 1995).

In contrast to dying forests with large amount of litter, erosion of bare ground is exacerbated by the intense frost-heaving and needle ice formation that resulted once the insulating leaf litter was gone (Winterhalder et al. 2001). As the result, soils of industrial barrens around Sudbury (Fig. 1), Monchegorsk, Nikel (Fig. 2), Palmerton, Karabash, and some other polluters have a stony covering (Sopper 1989; Winterhalder 2000; pers. obs.). These eroded lands are unlikely to revegetate naturally (Jordan 1975), and transformation of forests into industrial barrens has sometimes been claimed to be irreversible (Tsvetkov 1991), at least on the time scale of the human life span. In particular, the natural revegetation had not occurred in industrial barrens adjacent to Palmerton smelter for at least 50 years (Sopper 1989). Heavily contaminated sites at Maatheide in Belgium remained bare some 20 years following the closure of zinc smelter (Vangronsveld et al. 1995). Similarly, no regrowth appeared until 2006 in industrial barrens surrounding the Monchegorsk smelter (pers. obs.), although emissions of both sulphur dioxide and heavy metals drastically declined in early 1990s.

4.5 Positive feedbacks

In many cases initial (partly pollution-induced) forest disturbance causes secondary effects (like increased snow evaporation, followed by soil freezing and plant damage) that may enhance further disturbance in a positive feedback fashion (Kozlov 2001, 2002). Forest decline results in higher wind speed (see Sect. 5.3) that may enhance environmental stress via changes in snowpack structure. A thin and compact snow layer explains the lower soil temperatures recorded in industrial barrens during the wintertime (Kozlov and Haukioja 1997) that in combination with a pollution-induced decrease in cold-hardiness of conifers (Sutinen et al. 1996) increases the probability of death of extant trees from freezing injury. Importantly, climatic effects of deforestation may hamper recovery of vegetation even in absence of pollution (Arsenault and Payette 1997; Vajda and Venäläinen 2005).

Extant plants in industrial barrens facilitate deterioration of soil quality in their own root-inhabited areas: plant foliage traps contaminants, which then enter the soil (with either rainfall or plant litter) immediately under a plant. As the result, copper concentration in organic soil under Empetrum nigrum L. patches near Harjavalta smelter (49,000 μg g−1) was much higher than in surrounding barren soils (Uhlig et al. 2001). Similarly, in industrial barrens near Monchegorsk mean concentrations of plant-available nickel and copper in topsoil were higher under dwarf shrub patches than in bare areas (Zvereva and Kozlov 2005, and unpublished), and concentrations of several pollutants were higher under extant trees than in between-tree gaps (Lukina and Nikonov 1996).

Loss of biodiversity and creation of monoculture on semi-barren areas, such as birch woodlands near Sudbury and Monchegorsk, can increase population densities of pests and pathogens (see Sects. 6.1–6.3) which damage or even kill the remaining vegetation, thus contributing to the expansion of industrial barrens. In particular, bronze birch borer (Agrilus anxius Gory) killed 60–90% of birch stems near Sudbury by 1990s (Courtin 1994). Death of chestnut from diseases was reported in the impact zone of the Palmerton smelter (Jordan 1975), although it remains unclear whether this disease was facilitated by forest damage by smelter fumes. Forest pests were reported to accelerate dieback of the remaining trees near the polluters at Satka (Kulagin 1964) and Murgul (Acatay 1968).

Due to these positive feedbacks, industrial barrens may be to a certain extent resilient to external impacts, including both emission decline and restoration efforts. By using Monchegorsk smelter as an example, Tarko et al. (1995) predicted extension of the zone of biotic damage during several years following complete ceasing of emissions. In agreement with this prediction, gradual decline of mountain birch populations in industrial barrens surrounding the Monchegorsk smelter continued at least until 2006, some 10–15 year after drastic emission decline (pers. obs.). This kind of resilience is best described by the ‘alternative state’ models of ecosystems that consider abrupt shifts between two or more ecosystem states and incorporate system thresholds and feedbacks (Suding et al. 2004).

4.6 Time frame

Development of industrial barrens may proceed rather fast: although the copper smelter in Queenstown was built in 1895 only, the combination of timber felling, the sulphur fumes and the heavy rainfall in the area (which washed away the top soil) ensured that already by 1900 the whole valley around Queenstown looked like a desert (Anonymous 2005a). Appearance of industrial barrens near Quinteros was first observed some 10 years after the Ventanas smelter started its operations (R. Ginocchio, pers. comm.) But in most of the documented situations, development of industrial barrens takes 20–35 years; this time span was reported for Sudbury, Trail, Monchegorsk, Ducktown, Anaconda and Palmerton smelters (Table 1).

5 Environmental conditions in industrial barrens

5.1 Soil toxicity

Soils of industrial barrens contain huge amounts of toxic pollutants deposited from aerial emissions. In all documented cases (Table 2), the concentration of at least one pollutant in decomposed litter or in uppermost soil layer exceeded 1,000 μg g−1 (i.e. 1 g of pollutant per 1 kg of soil), or at least approached this value (Wawa). The highest concentrations of pollutants exceeded 10,000 μg g−1, with an absolute maximum of 135,000 μg g−1 of zinc near the Palmerton smelter (Buchauer 1973). These concentrations are much higher than the toxicity limits; however, the large (but highly variable—Table 2) fraction of metals is deposited in insoluble forms, such as oxides, and is therefore not readily available for plants and animals (Kozlov et al. 2000a). In spite of that, total rather than bio-available levels of pollutants are reported in most of studies (Table 2), although soil toxicity can not be judged from these total levels which therefore are only of limited value for ecotoxicology.

Since majority of heavy metals accumulated in soils are in non-soluble forms, their complete leaching from upper soil horizons will take centuries, e.g. 160–270 years for nickel and 100–200 years for copper accumulated in industrial barrens around Monchegorsk (Barcan 2002). It is estimated that mobilisation of metals stored in soils can sustain the high concentrations of copper and nickel in many lakes of the Sudbury basin for well over 1000 years (Nriagu et al. 1998).

Although soil acidification is often mentioned among principal reasons of vegetation damage or even decline, soils of industrial barrens are not always more acidic than soils of surrounding landscapes (Table 2). In some situations, the pattern may be even opposite: soils near Palmerton smelter are less acidic than in the background region, perhaps because of zinc oxide deposition (Jordan 1975). Similarly, soil pH near Vantanas smelter was 6.2 compared with 4.8 in background sites (Ginocchio 2000). Finally, soils around the magnesite plant at Satka are extremely alkaline (pH = 9), and development of industrial barrens was due to formation of thick (up to 10 cm!) cement crust preventing most of plants to grow (Kulagin 1964).

5.2 Soil nutritional quality

Although it is widely accepted that soil acidification promotes nutrient leaching from upper soil horizons, the data on soil nutritional quality are available only for some industrial barrens (Table 2). In particular, exchangeable Ca, Mg and K near Harjavalta smelter are reduced by a factor of 3–5 compared to more distant sites (Mälkönen et al. 1999). Nitrogen near Monchegorsk is reduced by a factor of 10 or more (Lukina and Nikonov 1999). The loss of base cations from the organic layer close to the smelter is primarily due to displacement by copper and nickel (Derome and Lindroos 1998). Since fertilisation generally improved plant performance in industrial barrens (Winterhalder 2000), it is believed that nutritional deficiency is one of the factors adversely affecting plant life in these habitats. Recently, soil nutritional quality was demonstrated to be the leading factor influencing abundance and diversity of microorganism populations in Sudbury pollution gradient (Anand et al. 2003).

5.3 Microclimate

Disappearance of vegetation, especially of trees, strongly modifies the climate of industrial barrens. Although this problem is investigated insufficiently, it seems that the most important changes are imposed by altered temperature and wind regime. Even at early stages of pollution-induced forest deterioration air and soil temperatures during the growth season may substantially increase, leading to an increased water loss from upper soil layers (Wołk 1977). Air temperatures in industrial barrens near Ducktown in summer were 1–2° C higher and in winter 0.3–1°C lower than in surrounding undisturbed (forested) sites (Hepting 1971). Similarly, air temperatures in barren sites at Monchegorsk were 1–2° C lower in cool periods (under +7° C) and 1–2° C higher in warm periods compared to undisturbed forests some 20–30 km apart (Kozlov and Haukioja 1997). Daily fluctuations in temperatures of barren soils are much higher than in undisturbed sites where the heat exchange is buffered by vegetation (Hursch 1948; Wołk 1977; Kozlov and Haukioja 1997; Winterhalder 2000). The lack of leaf litter results in enhanced frost action, imposing additional stress on plants (Sahi 1983). Barren soils are overheated in summer (e.g. average soil temperature in barren sites at Ducktown were increased by 11°C; Hepting 1971), and this overheating is accompanied by fast loss of soil moisture (Hursch 1948; Teale 1951; Freedman and Hutchinson 1980; Courtin 1994; Kozlov and Haukioja 1997; Marty 2000; Winterhalder 2000); all these factors obviously influence plant performance. Lower amount of precipitation was reported from Ducktown (Hepting 1971) but not found at Monchegorsk (pers. obs.). Importantly, drought may enhance toxicity of some contaminants, e.g. zinc (Jordan 1975).

Wind speed, measured in industrial barrens adjacent to the copper smelter at Ducktown, was increased by a factor 5–15 (Hepting 1971), while around the nickel–copper smelter at Monchegorsk it was two to three times as high as in nearly unpolluted forests (Kozlov 2002). High winds and subsequent particle movement that can sand blast, bury, and defoliate plants, were reported to impose additional stress on heavily contaminated sites near both Anaconda and Monchegorsk smelters (Marty 2000; Kozlov 2001).

Along with the direct impact of wind on plant performance, higher wind speed is responsible for thin snow layer (about one-third of that in unpolluted forests) in industrial barrens around the Monchegorsk smelter (Kozlov 2001) which, in turn, results in lower soil temperatures during the winter time (Kozlovand Haukioja 1997). Both these factors increase exposure of plants to frost damage. Soil freezing (in autumn) occurred in industrial barrens near Monchegorsk 10–11 weeks earlier and soil thawing (in spring) 3–4 weeks earlier than in unpolluted forests (Kozlov and Haukioja 1997). Furthermore, a lower accumulation of snow in industrial barrens, in combination with higher wind speed, may expose plants to additional drought stress. However, snow cover in industrial barrens near Nikel has about the same depth as in unpolluted forests (Ratkin 1999), and therefore the generality of the effects discovered near Monchegorsk remains unknown.

6 Life in industrial barrens

6.1 Biodiversity

General loss of biodiversity with the replacement of undisturbed habitats by industrial barrens seems indisputable (e.g. Jordan 1975; Kleinert 1988; Courtin 1994; Koponen and Niemelä 1995; Cicák et al. 1999); however, the magnitude of this effect had only rarely been documented. In the ‘total kill’ area around Wawa the ground flora declined to 0 to 1 species per 40 m2 from about 20–40 species in unpolluted sites (Gordon and Gorham 1963). Similarly, grass communities at Garfield contained 1–5 species per 50 m2 plot, compared to 7–22 species at most distant sites (Eastmond 1971). Near the Anaconda smelter, plant species richness in 1992–1994 was about one-third of control (Marty 2000). The number of plant species (observed in five 1-m2 plots) on 10–50 m from the edge of the O’Donnell roast bed (Sudbury, Canada) 66 years after its closure ranged 5–7, compared to 25–31 species at the distances 150–300 m of it (Hutchinson and Symington 1997). In Miami, Arizona, grasses, forbs, and small shrubs were entirely absent at the site proximate to the coppee smelter, whereas the cover of large shrubs had not been affected (Dawson and Nash 1980). The total floristic diversity near the Quinteros smelter was 17 species compared to 42 species in control sites (Ginocchio 2000).

In industrial barrens near Monchegorsk the number of vascular plant species ranged 0–25% of the number recorded in unpolluted (control) sites if censuses were made by using small plots (1–25 m2). However, if larger plots (100–10,000 m2) were surveyed, the decrease in species richness was around one-third, suggesting that pollution effects were expressed in decline of population densities rather than in selective removal of certain species (Kozlov et al. 1998, and unpublished).

Samples of moths and butterflies, as well as human-biting flies, collected in industrial barrens near Monchegorsk showed nearly the same diversity as samples from primary forests, although abundance of most species was drastically declined (Kozlov 1997; Kozlov et al. 2005a). Maximum species richness of ants in the Monchegorsk pollution gradient in 1993 was discovered in industrial barrens, whereas in 1994 it peaked in birch transitional communities surrounding the barren area (Kozlov 1997). This result is in line with findings by Koponen and Niemelä (1995) who reported higher species richness of ants in a barren site near the Harjavalta smelter than at more distant and less disturbed sites. Species richness of ground beetles (Carabidae) near the Lubenik magnesite plant was reduced to approximately one-third of observed in an unpolluted site (Kleinert 1988); however, rarefaction analysis shows that this difference was mostly due to differences in abundance, and actual species loss was much smaller, about 30% (Kozlov, unpubl.).

Some of insect species clearly prefer barrens to undisturbed habitats. In course of bait-trapping along the Monchegorsk pollution gradient, all the specimens of Polia conspicua (B.-H.), a mountain tundra noctuid moth, were collected between the external border of the industrial barrens and the smelter (Kozlov et al. 1996). Moreover, viable population of an extremely rare moth, Sesia bembeciformis (Hb.), the species considered extinct in Finland (Rassi et al. 1985), was discovered in an industrial barren south of Monchegorsk (Kozlov 1997). The buprestid beetle Melanopila formaneki (Jakobson) was for the first time discovered in Finland when studying Scots pines in a semi-barren site near the Harjavalta smelter (Heliövaara et al. 1990); the same site is also inhabited by several spiders which are missed from unpolluted forests (Koponen and Niemelä 1993). Industrial barrens may favour some life forms at the expense of others: for example, barrens near Lubenik magnesite plant were dominated by smaller ground beetles (Carabidae) with diurnal activity, whereas larger species with nocturnal activity were mostly associated with unpolluted habitats (Kleinert 1988).

In industrial barrens near Monchegorsk species richness of birds was reduced to approximately one third relative to unpolluted sites (Gilyazov 1993; Kozlov et al. 2005b). Near the magnesite factory in Lubenik the reduction in both species richness and abundance of breeding species seem even more pronounced (Cicák et al. 1999), although direct comparison is difficult due to different size of study plots. Among small mammals, only large-toothed redback vole (Clethrionomus rufocanus Sund.) and root vole (Microtus oeconomus Pall.) were captured near Monchegorsk, whereas six species were recorded in undisturbed forests (Kozlov et al. 2005b). Winter censusing of large mammals in industrial barrens revealed tracks of two species, mountain hare (Lepus timidus L.) and red fox (Vulpes vulpes L.), compared with eight species in unpolluted areas (Kozlov et al. 2005b).

To conclude, species richness of plants and animals in industrial barrens in an average comprises one-third to one-half of the observed in surrounding undisturbed habitats. However, diversity of some groups is not affected, and some species occurring in industrial barrens are not found in undisturbed habitats.

6.2 Population density and structure

Microbiota of degraded soils had been shown to lose its resilience to disturbance and become no longer able to perform normal processes of cycling nutrients, assimilating organic residues and maintaining soil structure. As the result, in industrial barrens near Harjavalta accumulated mass loss of Scots pine needle and fine roots was ca. 80% of observed in unpolluted site (McEnroe and Helmisaari 2001), whereas near Sudbury decomposition of birch leaves was reduced to ca. 40% of the control level (Johnson and Hale 2004). This retarded decomposition results in particular in formation of thick matt of litter under extant plants (pers. obs.); this litter seems to mitigate adverse climatic effects on field layer vegetation (Zvereva and Kozlov 2007), but it can also hamper seedling establishment (Jordan 1975).

Although abundance of most species in industrial barrens is extremely low (e.g. Gilyazov 1993; Kozlov 1997; Salemaa et al. 2001; Vorobeichik 2003, 2004; Kozlov et al. 2005a, b), some plants and animals flourish in these habitats. In particular this concern some willow species that are much more abundant in barren sites than in unpolluted forests. Increase in willow density, along with decline of pressure from natural enemies, favours several insect herbivores. Willow-feeding leaf beetle, Chrysomela lapponica L., generally not abundant through its distribution range, in some years reached extremely high densities in industrial barrens near both Monchegorsk and Nikel (Zvereva et al. 2002). Also its specialised parasites, scuttle fly Megaselia opacicornis Schmitz and tachinid fly Cleonice nitidiuscula (Zett.), earlier known from a few specimens only, are abundant in industrial barrens near both Monchegorsk and Nickel (Richter and Zvereva 1996; Zvereva and Kozlov 2000a; Disney et al. 2001). Similarly, densities of birch- and willow-feeding leafrollers, along with some Eriocrania leaf-miners, in industrial barrens near both Monchegorsk and Nikel are on an average much higher than in unpolluted forests (Kozlov 1997, Zvereva and Kozlov 2006). The higher mean and peak densities of Eriocrania observed in industrial barrens are explained by disturbance of density-dependent feedback with parasitoids (Zvereva and Kozlov 2006).

Population structure of both plants and animals is considerably changed in industrial barrens. Populations of some woody species (mountain birch and willows in Monchegorsk, white birch in Sudbury) become more continuos due to elimination of pollution-sensitive competitors, while ground layer vegetation is highly fragmented (Zvereva and Kozlov 2004, 2007). In Sudbury, the dimension of patches of ‘micro-deserts’ and ‘micro-oases’ varies typically between 5 m and 15 m (Courtin 1994). In Monchegorsk, patches of ground layer vegetation are usually smaller, ranging 0.2–2 m in dimension, with barren gaps reaching as much as 20–50 m (pers. obs.). Absence of natural regeneration causes strong shift in age structure of plant populations. The average site-specific age of randomly collected individuals of Empetrum nigrum ssp. hermaphroditum (Lange ex Hagerup) Böcher in industrial barrens near Monchegorsk and Nikel was 34–38 years, compared with 17–28 years in undisturbed forests (V. Zverev and M. Kozlov, unpublished).

Populations of some insects, like leafmining Eriocrania, in industrial barrens became more aggregated than in unpolluted forests, possibly because strong winds force ovipositing females of these tiny moths to walk along a birch twig rather than take a risk of flying to another birch tree (Kozlov 2003; Zvereva and Kozlov 2006).

6.3 Growth form of woody plants

The trees which managed to survive in industrial barrens generally demonstrate bush-like or even creeping growth forms (Kryuchkov 1993; Kozlov and Haukioja 1995; Rigina and Kozlov 2000). In the most polluted barren sites near Monchegorsk height of mountain birches was in an average nearly 10 times lower than in healthy forests (Kozlov 2001). Similarly, proportion of the low-stature spruces with abnormalities in crown architecture (dead upper canopies but extensive growth of creeping lowest twigs) increased when approaching the smelter (Kozlov 2001, and unpubl.). The bush-like growth forms were also observed in Scots pine and aspen (Populus tremula L.) surviving in industrial barrens near both Monchegorsk and Nikel (Kozlov et al. 1999, unpubl.). Two willow species (Salix borealis (Fries.) Nasar. and S. caprea L.) in industrial barrens have more epiciormic shoots than in unpolluted forests (Zvereva and Kozlov 2001). The most plausible explanation of all these changes in growth form is the damage of apical (supranival) twigs by wind-driven snow abrasion (Arsenault and Payette 1997), which may be enhanced by pollutants (Alexeyev 1990). Therefore the negative correlations between snow depth and vertical growth of mountain birch, as well as between snow depth and proportion of spruces with abnormal crown architecture, may reflect causal link between these phenomena (Kozlov 2001). An increased light availability (due to forest decline) may also have contributed to higher branching and formation of bush-like crowns in woody plants surviving in barren sites (Zvereva and Kozlov 2001).

6.4 Changes in interactions between organisms

In industrial barrens interactions between organisms may differ from those in unpolluted forests. For example, development of delayed inducible resistance (decrease in plant quality next year after intensive damage), one of the important negative feedbacks regulating population dynamics of herbivores, in boreal willow, Salix borealis is disturbed in barren sites (Zvereva and Kozlov 2000b). At the same time, winter and spring bud damage, caused by harsh environmental conditions in barrens, may improve willow quality for herbivores (Zvereva and Kozlov 2000c). These changes in host plant–herbivore interactions favour herbivore outbreaks (see Sect. 4.5). Importantly, compensatory responses of boreal willow to herbivore damage are reduced in industrial barrens (Zvereva and Kozlov 2001), thus damaged plants recover slower than in undisturbed habitats.

Plant–plant interactions, which are mostly competitive in favourable habitats, tend to become positive in stressful environments (Brooker and Callaghan 1998). In industrial barrens, where competition among plants is low due to decreased density, the role of facilitation increases. Near Ventanas smelter in Chile shrubs imposed nursery effect on ground layer vegetation, which lead to better plant recruitment under shrub canopies (Ginocchio et al. 2004). Dwarf shrubs grew and reproduced better under birch canopies compared to between tree gaps in barrens near Monchegosk, whereas in undisturbed habitats the effects of trees were negative (Zvereva and Kozlov 2004). These effects may be explained by alleviation of harsh environmental conditions by trees (Zvereva and Kozlov 2007).

6.5 Adaptation to life in industrial barrens

Heavy metal tolerance of plants has been studied extensively and provides a well-documented example of rapid evolutionary adaptation (Bradshaw and McNeilly 1981; Macnair 1997). Several grass species, including Agrostis scabra Willd., Deschampsia caespitosa (L.) Beauv., Agrostis gigantea Roth. and Poa compressa L., colonising Sudbury’s metal-contaminated soils, may have developed local metal-tolerant populations (Winterhalder 2000, and references therein). Although pollution tolerance in populations of long-lived trees has been detected less frequently than in populations of grasses and herbs, recently it had been demonstrated that long-lasting pollution impact increased pollution resistance of mountain birch in industrial barrens near both Monchegorsk and Nikel (Kozlov 2005; Eränen 2006), possibly by elimination of sensitive genotypes (survival selection) from the affected populations. Similarly, we discovered that resistance of non-specific esterases (enzymes degrading various xenobiotics) to heavy metals was higher in populations of leaf beetle, C. lapponica, from heavily contaminated barren sites (Zvereva et al. 2003). It should be stressed that metal-tolerant populations of plants and animals developed near point polluters represent unique genetic resource that will be lost (overcompeted) with restoration of natural communities following pollution decline.

Some changes in feeding behaviour of herbivorous insects may also be regarded as adaptations to life in the barren landscape. In particular, feeding niche breadth of the leaf beetle, C. lapponica, decreased with increase in pollution: in industrial barrens this species concentrated on the boreal willow that assures the best survival of larvae, whereas in surrounding forests it feeds on other willow species as well (Zvereva et al. 1995). Indirect data suggest that in industrial barrens some other herbivores may also prefer other host plants than in undisturbed forests. In particular, larval density of autumnal moth, Epirrita autumnata Bkh., measured on birches (most preferred host plant), strongly declined in industrial barrens near Monchegorsk (Ruohomäki et al. 1996). At the same time, the number of moths attracted by pheromone traps did not decline; the moths collected in industrial barrens were metal-contaminated and thus presumably of local origin (pers. obs.). These data suggest that larvae of autumnal moth near Monchegorsk have been feeding on plants other than mountain birch.

7 Significance of industrial barrens

7.1 Industrial barrens as refugia of rare and endangered species and populations

The sites of biological significance within severely degraded environments may not be as rare as is commonly thought, and assumption that physically or chemically hostile environments are incapable of attaining biological diversity is far from being true (Johnson et al. 1978). Industrial barrens are rather heterogeneous (Kozlov 1997; Uhlig et al. 2001; Ginocchio et al. 2004), with a range of different substrate types that favour different species. Therefore, in spite of the general loss of biodiversity, these habitats can develop a great richness of unusual and interesting plants and animals, including regionally rare and endangered species (Johnson et al. 1978; Heliövaara et al. 1990; Eyre and Luff 1995; Spalding and Haes 1995; also see above), and the overall site diversity can be high even when each patch is relatively poor. Furthermore, several plant species of low competitive ability benefit from fragmentation of the continuous ‘carpet’ of vegetation. Invertebrates in industrial barrens may escape from strong enemy pressure, and this ‘enemy-free space’ phenomenon may explain high abundance of some species that are usually depressed in less disturbed habitats (Zvereva and Kozlov 2000a, 2006).

7.2 Conservation of industrial barrens for science, education, and tourism

Although industrial barrens are usually seen as a by-product of human activities that deserves rehabilitation only, and the suggestion to conserve these severely modified landscapes is frequently perceived as a joke, their importance for science, education, and even sightseeing had been sometimes appreciated (Winterhalder 2000). However, conservation of industrial barrens is in line with conservation of historical industrial landscapes which form a part of the World Heritage (UNESCO 2006). Detailed investigation should be conducted prior ‘re-greening’ or rehabilitation of these unusual habitats. Non-selective reclamation works could be destructive to conservation interests, and losses associated with habitat reclamation may easily overcome the benefits gained. In particular, local metal-tolerant populations of plants and animals will definitely be lost.

Prospect of reforestation, that started a more than half of century ago (Seigworth 1943), has created some interest in preserving part of the Copper Basin landscape in its denuded and eroded state for historical purposes (Quinn 1988). Recently, a 200 ha exemplary plot of ‘desert’ remains as part of the display at the Ducktown Museum (Anonymous 2005c). Also a part of Sudbury industrial barrens (about 600 ha surrounding Alice and Baby lakes just behind the abandoned Coniston smelter) is identified in the city reclamation plan as an ‘industrial reserve’. Fortunately or unfortunately, the intention to preserve the extreme level of landscape damage nearly failed: due to natural recovery following pollution decline some 35 years ago the non-reclaimed area is now difficult to distinguish from reclaimed territories (K. Winterhalder and J. Gunn, pers. comm.). Still natural succession on derelict lands may produce unexpected communities of considerable scientific interest (Box 1993). Students and faculty of Laurentian University and other high schools often come to Sudbury to see the ‘past and present’ of the barren landscape. Industrial barrens at Monchegorsk are frequently visited for ‘scientific sightseeing’, especially by the researchers from the neighbouring Finland (Ruotsalainen and Markkola 2004); at least once they served a target of an international environmental field course.

As far as we know, only Queenstown had advertised the barren landscapes as tourist attractions. “By any measure Queenstown is one of the wonders of the world. It is a profound reminder of humanity’s capacity to destroy and pollute and, in that sense, it deserves to be seen by everyone” (Anonymous 2005a). This attitude, supported by local government, prevented reforestation of the hills around Queenstown, although some locals believe that the rainforest, which characterises the area, should be encouraged to regrow. Industrial barrens around Monchegorsk, although neither advertised nor conserved, still attract attention of foreign tourists: quite frequently, buses travelling to/from Murmansk, stop in the barren site for photographing the landscape.

8 Conclusion

8.1 Past and future of industrial barrens

Comparative analysis of the existing data demonstrated that industrial barrens have developed due to combined impact of different stressors, among which soil contamination by heavy metals, clearcutting and fires played the leading role. The combined effects are critical, as either stress alone would have caused much less damage (Jordan 1975). Pollution, accompanied by other human-induced disturbances (primarily clearcutting), damages and gradually kills the vegetation; this process is usually concluded by a fire, facilitated by unusually large amount of woody debris accumulated in severely damaged communities. Since vegetation recovery is hampered by soil toxicity due to extreme contamination by heavy metals, soils remain bare for a long time and suffer from extensive wind and water erosion exacerbated by the intense frost-heaving. The destructive processes are enhanced by both disturbance of negative feedbacks regulating e.g. relationships between plants, herbivores, and their natural enemies, and development of positive feedbacks, e.g. increase in climatic severity due to initial vegetation damage enhances decline of the remaining vegetation.

The most extensive industrial barrens appeared before 1970s; some of them have already been (partially) reclaimed or are recovering following closure of polluters (14 of 36 documented situations; Table 1) or rapid emission decline. Natural recovery of the existing barren sites may take long time; the example of Sudbury suggests that some 20 years after pollution decline may be sufficient to initiate this process. On the other hand, human-assisted recovery may proceed much faster (Vangronsveld et al. 1995, 1996; Winterhalder 2000). However, non-selective reclamation works could be destructive to conservation interests, and the care should be taken to preserve at least some of the unusual post-industrial habitats.

8.2 Industrial barrens as unintentional experiments

Links between pollution-oriented environmental studies (‘applied ecology’) and development of ecological theories (‘basic ecology’) are surprisingly weak (Ormerod et al. 1999). Researchers addressing basic ecological problems only rarely use the results of ‘unintentional pollution experiments’ (Lee 1998). However, industrial barrens offer unique opportunities for conducting ‘basic’ ecological research, in particular for testing some theories (assumed to be general) in an evolutionary novel stressful environment (Kozlov and Zvereva 2003; Vorobeichik 2004).

Studies in industrial barrens contributed to the development of the theories on plant growth, compensatory ability and reproductive strategies in stressful environment (Zvereva and Kozlov 2001, 2005), as well as to understanding of the role of host plant quality in regulating population dynamics of herbivores in ‘enemy free space’ (Zvereva et al. 1997). Exploration of plant–plant interactions in industrial barrens demonstrated that shift from competition to facilitation occurs not only in natural stress gradients, that were used to construct the predictive model (Brooker and Callaghan 1998), but also in human-induced stress gradients (Zvereva and Kozlov 2004, 2007). Importantly, results of ‘basic’ research on plant–plant facilitation are now suggested for practical application in phytostabilisation of heavily contaminated areas (Frérot et al. 2006).

Although net primary production had not been measured in any of industrial barrens, drastic decline in vegetation cover, along with reported retardation in plant growth (e.g. Kryuchkov 1993; Nöjd et al. 1996), suggest that productivity of plant communities declined by a factor of 10–100. Thus, industrial barrens are unique ecosystems capable to maintain relatively high diversity at very low productivity level, and their exploration is likely to contribute to the long-lasting debate (Hector and Schmid 1999; Tilman 1999) on the relationship between diversity, stability and productivity.

8.3 Management of polluted habitats

Recently, most industrial barrens show some signs of natural recovery due to emission decline or closure of responsible polluters; some of them have been or are being successfully revegetated. The latter strategy is in particular justified by the urgent need to prevent dispersion of metals to surrounding areas (e.g. Vandronsveld et al. 1995); it has a strong priority in densely populated sites, like Central Europe, in spite of high scientific and sometimes public interest to unusual post-industrial habitats.

Reclamation strategies used in industrial barrens vary from natural attenuation to extensive (and expensive) revegetation programs. Literature on this problem is rather extensive and had been repeatedly reviewed during the past years (Kozlov et al. 2000b; Winterhalder 2000; Adriano et al. 2004; Kozlov 2004); therefore we provide only a short summary of most relevant findings.

The reduction of emissions is a critical requirement for any reclamation programs. However, until measures to reduce air pollution are fully realised, efforts should be devoted to improving the vitality and maintaining the stability of affected ecosystems. The experience gathered to date suggests that the pollution-induced decline of forests can be slowed down and perhaps even reversed at most stages of degradation. In the case of continuing pollution, its effects can be mitigated to prevent further damage.

Restoration of terrestrial ecosystems after the reduction of emissions is based on the suggestion that some successional stages are not essential and can be bypassed by proper intervention. Thus, in practical terms, the rehabilitation of forests damaged by pollution is an attempt to partially substitute time with money. However, small-scale, short-term experiments still dominate over practical applications. Thus it is reasonably well known how to initiate the early stages of rehabilitation, but there are substantial uncertainties over the longer-term effects (e.g. Eränen and Kozlov 2006). The latter especially concern possible side-effects and ecological risks which may result from human intervention, such as increased leaching of toxic substances and/or nutrients. To reduce these risks, a careful analysis of the need for chemical treatments such as liming or fertilising should be carried out for each specified area. We suggest that whenever possible a ‘minimal intervention’ approach aimed at promoting natural succession should be used instead of ‘re-greening’ or an artificial re-creation of the desired ecosystem.