On the Problem of Flora Formation in Industrially Disturbed Land Areas

Key words: flora, industrially disturbed lands, taiga zone.

A major part of the global population already lives amid so called technogenic landscapes, in which industrial waste dumps and other types of disturbed land areas have a special place with regard to deleteri ous effects on the natural environment and human health. In Sverdlovsk oblast, they concentrate in the vicinities of all large cities and most other populated areas, covering more than 63 300 ha of land (Chaikina and Ob’edkova, 2003). Such territories are initially devoid of the soil and plant cover, and their ecologi cally specific substrate lacks the pool of seeds and other viable diaspores. Hence, the establishment of plants in them starts from point zero.

Studies on specific features of flora formation in such areas are of theoretical and practical significance for their biological recultivation and restoration of biological diversity. Problems concerning specific fea tures and patterns of these processes in industrial waste dumps have been considered in recent decades in many countries (Burda, 1991; Rostanski and Wozniak, 2000; Tokhtar’ et al., 2003; Tokhtar’ and Kharkhota, 2004). Intensive studies on bioecological characteristics of corresponding floras are performed in Ukraine (Bashuts’ka, 2002; Zhukov et al.; 2004, Yaroshchuk et al., 2007).

The purpose of this study was to reveal consistent trends in the restoration of floristic diversity in indus trially disturbed lands using the example of such areas in the taiga zone.

The objects studies in Sverdlovsk oblast were as fol lows: spoil banks of open cut bauxite mines near the city of Severouralsk (below, designated L 1); the southern spoil bank of the Veselovskoe lignite mine near the city of Karpinsk (L 2); refuse dumps of the foundry sand pit in the village of Basyanovskii (L 3); ash dumps of district power plant (DPP) in the city of Verkhnii Tagil (L 4); spoil banks of the Estyuninskii open cut iron ore mine near the city of Nizhnii Tagil (L 5); spoil banks of coal mines near the village of Bulanash (L 6); spoil and tailing dumps of dressing plants at the Bazhenovskoe serpentine asbestos mine, the city of Asbest (L 7); spoil and tailing dumps of the Pervouralsk titanomagnetite ore mine, the city of Per vouralsk (L 8); and spoil banks of Bilimbaevskoe flux ing limestone mine, the village of Bilimbai (L 9).

In Chelyabinsk oblast, studies were performed on spoil banks of Cheremshanskoe nickel ore mine near the city of Verkhnii Ufalei (L 10). The rock composi tion of the above dumps was briefly described previ ously (Chibrik, 2007).

The flora of these sites was characterized on the basis of geobotanical releves compiled for plots with different aged phytocenoses by conventional methods (Korchagin, 1964) and the results of additional route surveys. The age of sites was estimated from mine sur veying data. On the whole, 15–30 releves were made for each site. The initial floristic lists were published previously (Chibrik and El’kin, 1991).

Substrates of the sites are poor in nutrients, stony, and contain no soil (therefore, no plant diaspores). Therefore, the formation of their vegetation in the course of spontaneous overgrowing follows the pattern of primary succession as determined by Shennikov (1964). The age of the sites is young to medium, with the vegetation including serial phytocenoses up to 25– 30 years of age.

The species richness of individual local floras ranges from 57 to 149 in dependence on ecotope diver sity, which is minimum on the Estyuninskii spoil bank (L 5) and maximum on the ash dump of Verkhnii Tagil DPP (L 4), where herbaceous communities develop along with forest communities. The lowest fluctua tions of species composition (from 75 to 88 species) are characteristic of five sites with typical forest com munities.

Data on the bioecological structure of floras in industrially disturbed sites of the forest zone are shown in the table. Mesophytes dominate in all plant com munities, with their proportion ranging from 59.7% on spoil banks of coal mines in Bulanash (L 6) to 84% on those of the Pervouralsk titanomagnetite ore mine (L 8). The total proportion of mesophytes and xer omesophytes varies from 76 to 91% of the total species number. An analysis of life forms according to Raun kiaer’s scheme provides evidence for the prevalence of hemicryptophytes and considerable role of geophytes, with phanerophytes being dominant. Spoil banks of Bulanash coal mines (L 6) are an exception, since only herbaceous communities develop on them. With respect to the mode of fruit and seed dispersal, structural rearrangements in the floras involve three groups: autochores + barochores, zoochores, and hemianemochores + anemochores. In the floristic composition of communities following the forest pat tern of development, the proportion of zoochores reaches 27.9% (spoil banks of Severouralsk bauxite mines, L 1). In sites where only herbaceous commu nities develop (spoil banks of Bulanash coal mines, L 6) or such communities prevail (ash dumps of Verkhnii Tagil DPP, L 4), this proportion decreases to 14.5 and 17.5%, respectively. All floras contain a considerable proportion of anemochorous and hemianemochorous species, which decreases as the tree layer develops and crown closure increases. It should be noted in this context that dominants and the majority of species in the tree layer are anemochores. Forest communities with tree crown closure of about 0.4–0.8 grown on spoil banks of Basyanovskii sand pit (L 3), Estyunin skii iron ore mine (L 5), and asbestos mine (L 7) and contain 29.4–32.0% of species with the anemo chorous type of seed dispersal. The proportion of such species increases in communities where the degree of crown closure is lower (no more than 0.5) and reaches a peak of 49.4% in the flora of coal mine spoil banks, where only herbaceous plants can grow because of unfavorable ecological conditions (cone shaped mounds, stony substrate with acid pH, poor nutrient supply, etc.).

In terms of landscape–zonal classification, three prevailing groups can be distinguished: ruderal, forest, and meadow species (see table). The proportion of ruderal species depends on the degree of plant com munity development, decreasing in medium aged communities. Other relevant factors are the pattern of vegetation in surrounding areas and properties of the sub strate. Thus, Severouralsk (L 1), Yuzhnoe Veselovskoe (L 2), Basyanovskii (L 3), and Estyuninskii (L 5) spoil banks are surrounded by forest, and the propor tion of ruderal species is small even in communities formed in their “youngest” areas. A relatively high percentage of meadow species is due to incomplete canopy closure and large glades at forest margins, as well as to a major contribution to plant communities at early stages of their formation.

Analyzing local floras, we calculated the grades of species constancy as the sum of constancy classes in plant communities of all sites studied in the taiga zone. The constancy class of a species in each site was deter mined from the percentage of cenoses in which the species was recorded relative to the total number of cenoses described in the site (Shennikov, 1964): class I, 1–10%; class II, 1–20%; class III, 21–30%; …; class X, 91–100%. Thus, a species described in more than 91% geobotanical releves (i.e., sampling plots) was assigned the highest constancy class X. The high est possible grade of species constancy in the taiga zone was 100, indicating that the species had con stancy class X in all ten sites studied within this zone. The grades of species dominance were calculated in the same way.

The constancy grade characterizes the activity of species expansion to technogenic landscapes (Yurtsev, 1982; Didukh, 1982). Among 260 species described in industrially disturbed sites of the taiga zone, high con stancy grades (>50) were assigned to 13 species: trees Pinus sylvestris L. (66), Betula pendulaRoth (59), and Salix capreaL. (59) and herbaceous plants Chamaen erion angustifolium(L.) Scop (81), Tussilago farfaraL. (79),Achillea millefoliumL. (70), Trifolium pratenseL. (63), Taraxacum officinaleWigg. (62), Poa pratensisL. (59), Amoria repens(L.) C. Presl (56), Cirsium setosum (Willd.) Bess. (52), Festuca rubraL. (52), and De schampsia cespitosa(L.) Beauv (50). Many of them dominate in developing phytocenoses with respect to coverage and abundance. The above species comprise the core of floristic complex in the sites studied. Bioecological parameters of these species show that most of them are perennials (88.1% of the total species list). However, an important phytocenotic role at early stages of plant cover development in lifeless technogenic ecotopes is played by annuals and bienni als, which dominate in abundance and biomass in some sites. Mesophytes account for 71.5% of the spe cies list and are represented by different life forms (according to Raunkiaer): hemicryptophytes prevail (31%), with the total proportion of these species together with herbaceous chamaephytes and the inter mediate group of geophytes–hemicryptophytes reaching 64.3%; phanerophytes account for 16.7% (being dominant by other parameters); and the pro portion of therophytes and therophytes–hemicrypto phytes (annual and biennial) is only 11.9%. In terms of landscape–zonal classification, meadow and forest species prevail (35.7 and 23.9%), but proportions of ruderal and meadow–ruderal species are also consid erable (19.0 and 14.2%, respectively). The results of aerographic (ecogeographic) analysis confirm the prevalence of boreal species (85.7%; together with polyzonal species, 95.2%) among latitude groups and of Eurasian (52.4%) and circumpolar species (23.8%) among longitude groups.

A comparative analysis of these results and published data (Chibrik and Kravchenko, 1990; Bashuts’ka, 2002; Tokhtar’ and Kharkhota, 2004) provides evidence a zonal trend in the establishment of vegetation in techno genic barrens: new phytocenoses develop so as to approach the pattern of natural vegetation surround ing the technogenic ecosystem. This applies not only to the forest zone of the Urals but also to other natural zones, including the forest–steppes of the Urals and Ukraine. An additional argument in favor of this con clusion comes from floristic lists of herbaceous vegeta tion on spoil banks of some Ural iron ore mines, on substrates with a high content of stones and unfavor able ecological conditions (Chaikina and Ob’edkova, 2003): depending on the site, these lists range from 10 to 66 species.

Thus, against the background of general zonal trend in the formation of local flora, conditions char acteristic of a given technogenic site have a major, often decisive effect on this process. Therefore, analy sis of the structure of local floras can be used for esti mating the potential of disturbed land areas for biolog ical recultivation.