Contribuţii Botanice - 2009, XLIV: 83-91 Grădina Botanică “Alexandru Borza” Cluj-Napoca SMALL-SCALE STRUCTURE CHANGE IN PLANT ASSEMBLAGES ON ABANDONED GOLD MINING WASTE DUMPS (ROŞIA MONTANĂ, ROMANIA) Anamaria ROMAN 1,2 , Dan GAFTA 2 , Vasile CRISTEA 2 , Sergiu MIHUŢ 3 1 Institutul de Cercetări Biologice, str. Republicii, nr. 48, RO-400015 Cluj-Napoca, Romania 2 Universitatea Babeş-Bolyai, Facultatea de Biologie şi Geologie, Catedra de Taxonomie şi Ecologie, str. Republicii, nr. 42, RO-400015 Cluj-Napoca, Romania 3 CFMCB, str. Iancu de Hunedoara, nr. 12, RO-400696 Cluj-Napoca, Romania e-mail: popanamaria19@yahoo.com Abstract: We studied gold mining waste dumps in Roşia Montană (South-eastern Carpathians) that had similar environmental conditions and management histories but different ages due to successive cessation times of mining activities. A cronosequence for four waste dumps was included in the study: WD2, ~ 2 yrs old; WD20, 20– 25 yrs old; WD4, 38–45 yrs old; and WD60, ~ 60 yrs old. At each waste dump we recorded all vascular plant species within 5 randomly placed 1 m 2 quadrats. Our hypothesis is that these waste dumps represent distinct seral stages, in terms of total species richness, overall plant composition and relative number of species in various plant functional groups distinguished on the basis of pollen and seed dispersal mode, N-fixing and vegetative lateral spread. We analysed the difference in these parameters between waste dumps of different ages. Floristically, WD2 is well separated from WD20; WD20 is obscure but clearly different from WD40; and WD40 is well separated of WD60. One ruderal species (Tussilago farfara) and one dwarf shrub (Vaccinium vitis- idaea) are the best discriminators of WD2 and WD60, respectively. The total number of plant species increased steadily and significantly from WD2 to WD40 but declined on WD60. Significant changes in the relative number of species from each plant functional group were detected between at least two sites along the waste dump cronosequence. Whereas the relative richness of plant functional groups related to pollen/seed dispersal mode do not indicate a succession progress on WD60 as compared with the younger ones, the proportion of N-fixing species and the distribution of total species richness suggest a mid-successional stage associated with the oldest waste dump. This inconsistency may be a sampling effect (small number and size of quadrats) or the consequence of small, recent disturbances. Keywords: cronosequence, floristic dissimilarity, gold mining waste dumps, plant functional groups, seral stages, species richness, succession Introduction The intensive mining of gold has permanently affected the overlying ecosystems, the land-use potential, and the attractiveness of landscapes. Furthermore, mining leaves behind damage stretching over large areas. It is therefore an important task to understand the natural processes related to succession for cost-effective, successful restoration of such areas. The characterization of community responses to any given disturbance in terms of plant functional groups makes it possible to identify general trends in vegetation changes as well as comparison between communities of differing species composition with respect to specific processes [15, 16, 31]. Highly disturbed landscapes (e.g. mining areas, overgrazed areas, old- fields) with the same abiotic and biotic conditions (soil, potential vegetation, propagule sources, previous and present management activities), provide the opportunity to investigate the relative importance of plant functional groups along successional time. One of the general trends in succession is that species number increases from early to mid-successional stages and declines toward late-successional stages [2, 21]. The increase period is due to species accumulation during the colonization phase, whereas the decreasing part is the consequence of competitive exclusion.