Gusev, A.P. Primary succession on phosphogypsum Dumps (Gomel Chemical Plant, Belarus) / A.P. Gusev // Russian Journal of Ecology. – 2006. - Vol. 37. - No. 3. - PP. 210-212
ISSN 1067-4136, Russian Journal of Ecology, 2006, Vol. 37, No. 3, pp. 210–212. © Pleiades Publishing, Inc., 2006.
Original Russian Text © A.P. Gusev, 2006, published in Ekologiya, 2006, No. 3, pp. 232–235.
The purpose of this study was to analyze primary succession in vegetation growing on a toxic technogenic substrate (phosphogypsum) and, in particular, to describe the species composition and ecological structure of plant cover at different stages of succession, to study soil-forming processes on phosphogypsum dumps, and to reveal the factors determining the rate ofplant establishment on them.
Field studies involved a geobotanical survey in10х10-m test plots (10 plots per stage) and an analysis ofsoil–litter macrofauna (samples from the litter horizon,50х50 cm) and soil formation (pits 1 m deep). Takinginto consideration topographic features of the dumpsite,studies were performed in three areas: near dumps,in the lower one-third of dump slope, and the upperparts of dumps (5–10 m above the ground level andhigher).
To study succession in the dumpsite, we constructedan ecological-genetic series including plots on dumpsof different ages: up to 15 years (stage 1), 15–30 years(stage 2), and more than 30 years (stage 3).
The establishment of the dumpsite resulted in completedestruction of original ecosystems and the localbiota in general, producing a kind of biological vacuum,and gave rise to abiogenic migration in whichwater and air flows play the dominant role. The processof colonization of the phosphogypsum substrate is temporallyand spatially nonuniform, because differentsites differ in the degree of their suitability for plantsand animals. For example, the pioneer groups of plantsappear first of all in the sites where the erosion andslope processes are less active and moisture and heatsupply are sufficient.
Let us discuss the results of studies on successionseries in the dumpsite.
Bare sites ofstage 1are affected by water erosionaccounted for by temporary streams. This is manifestedin the presence of erosional forms of microrelief: washouts,alluvial fans of destroyed material, etc. Plant speciessettling in moist places enriched with fine earthdevelop from seeds coming from neighboring ecosystems.This stage is characterized by a poorly developedplant cover, the absence of litter, a low species diversity,and poor natural regeneration of tree and shrub species.The pioneer group is represented by only two herbaceousplant species, reed grassCalamagrostisepigeios(L.) Roth and fireweedChamaenerionangustifolium(L.)Scop. Total coverage is less than 5%. The herbaceouslayer as such is absent, local plant growth isobserved in depressions of microrelief. Natural regenerationis observed in tree species (BetulapendulaRothandPopulustremulaL.), which populate phosphogypsumsimultaneously with fireweed. Birch dominates innatural regeneration, accounting for 80% of the totalnumber of young tree plants. Most of them are less than1 m high. On the slope, vegetation grows only in thelower part (1/10) and is developed even more poorly.
Atstage 2, coverage of the herbaceous layerincreases twofold, the density of young trees increasesby a factor of 2.7, and a thin litter layer appears inplaces. Plant cover of the sites adjacent to dumps is stilldominated by fireweed and reed grass, but new speciesappear:BromustectorumL.,CrepistectorumL., andRumexcrispusL.The density of young tree growth on the slopes variesfrom 100 to 5000 ind./ha (more than 90% of treesare lower than 1 m). Herbaceous plants are distributednonuniformly, forming patches that ascend almost tothe top of the dump.
Atstage 3, a thin tree and shrub layer with coverageof up to 20% is formed. The herbaceous layer in thesites adjacent to dumps has 70% coverage and is dominatedbyC. epigeos, Ch. angustifolium, C. tectorum,B. tectorum, andTanacetumvulgareL. Along withthem,Artemisia vulgarisL., AchilleamillefoliumL.,andTussilagofarfaraL. occur. Water erosion is almostabsent at this stage of succession. Open spots of phosphogypsumaccount for less than 20% of the area.
On the slopes, the density of young tree growth mayreach 4000–5000 ind./ha, with birch being dominant(50–70%). The diversity of tree and shrub vegetationincreases by a factor of 1.3, compared to stage 2. Theherbaceous layer has 30–90% coverage and almostcompletely prevents manifestations of water erosion.Dominant species are the same as in sites near dumps.Birch–willow shrubs 2–3 m high with a density of up to100 ind./ha occur on the upper part of the dumps. Theproportion of dead standing plants among them is 15–20%. The herbaceous layer on the upper part of tailingshas coverage of up to 30%.
Thus, the study of succession in the dumpsite of theGomel Chemical Plant provided a basis for the followingconclusions:
(1) Regeneration ecosystems adapted to an aggressivetechnogenic environment are formed in the dumpsite.
(2) An ecosystem with a fragmentary tree–shrublayer, a continuous herbaceous layer, a litter horizon,and an animal population (a complex of invertebrates)is formed on the dumps within 20–30 years.
(3) Succession proceeds at the highest rate at thebase of dumps, where conditions are relatively favorable(a small thickness of phosphogypsum crust and theoptimal level of the water table).
(4) Reed grass, fireweed, and birch, which dominatein the vegetation of dumps, are the species mostadapted to ecological conditions existing on the phosphogypsumsubstrate (a high illumination level combinedwith high mineralization and low pH of water).
