Vegetations of abandoned open-pit bauxite mines reclaimed with austrian pine – a nature conservation assessment

Abstract

Coenological studies of the herb-layer vegetation in abandoned open-pit bauxite mines reclaimed with Austrian pine (Pinus nigra) were executed in Gerecse Mts. (Nagyegyháza) and Bakony Mts. (Sáska and Szőc). The three Austrian pine stands represented different ages (Szőc: 6 years; Nagyegyháza 15 years; Sáska 20 years), thus, they were regarded a successional chronosequence. By pointing 10 m by 10 m quadrats, percentage cover of herb-layer species, the cover of Austrian pine as well as the species number, cover and Shannon-diversity of herb-layer vegetation were determined concerning each quadrat and sample area. We studied the effect of pine cover on species number, diversity and cover of herb-layer vegetation. Based on species-cover values, group distributions of social behaviour types, Raunkiaer life-forms and phytosociological groups (BORHIDI 1993) were calculated for characterizing the vegetation of the study sites. Group distributions were statistically compared by performing homogeneity tests. The quasi-mean naturalness value of the vegetation was calculated for each sampling site, regarding to the group distribution of social behaviour types and the naturalness values of con- stituting species. We examined the differences and similarities between the vegetation of the studied reclaimed mines and the vegetation of (1) the potential climax association (Cotino–Quercetum pubescentis) of the area, and (2) vegetation of young forest stands developed through regenerative succession in a similar habitat and during comparable time-span to that of the reclaimed mine sites, but without any effect of Austrian pine.
Great differences were shown among the vegetations developed in the study areas. These differences were reflected in the dominant species and the Shannon-diversity as well as in the significant differences found among the distributions of the examined plant-trait spectra. Disturbance-tolerant species (chiefly Calamagrostis epigeios and Solidago gigantea) were dominant in the herb-layer of the youngest pine stand (Szőc), became subdominant in the middle-aged plantation (Nagyegyháza) and represented low cover ratio in the oldest stand (Sáska). In parallel with the descending cover of disturbance-tolerant species, cover ratio of the natural flora’s species gradually increased, resulting in the higher diversity and naturalness value of the vegetation. The increasing canopy cover of Austrian pine reduced the species number and total cover of the herb layer, but did not have any affect on Shannon-diversity. We observed the disappearance of several plant species from the high pine-cover quadrats. The flora of the reclaimed mines differed significantly from both the potential vegetation type of the areas and from the associations developed through regenerative succession followed the clear-cutting of oak forests. The vegetation of the reclaimed bauxite mines had lower naturalness: the relative abundance of disturbance-tolerant and indifferent species (mainly of the indigenous and alien ruderal competitors) was higher, but the ratio of the natural broad-leaved forest species (mainly of the specialists) was smaller than in the potential vegetation. Similar differences were observable in case of the flora of the bauxite mines was compared with the same-age stage of regenerative succession of sessile oak – Turkey oak forests. Both the supplantation of weeds and the spreading of natural competitors were slower under the pine canopy; geophytes of oak forests and protected species were absent even from the herb layer of the oldest Austrian pine stand. Lack of the appropriate propagule sources in the reclaimed areas are probably contributed to the unfavourable influence of Austrian pine exerting on the regenerative succession. In the reclamation areas, the early restoration of the native flora should be aimed instead of maintaining the alien pine plantations.