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Gravel pits as habitat islands : floristic diversity and vegetation analysis

Bzdon G.

Polish Journal of Ecology

2008

Vol. 56, nr 2

239-250

Open-cut excavations formed as a result of exploitation of mineral deposits are the least studied ecological sites. Habitat heterogenity is reflected by remarkable floristic and phytocoenotic diversity. Being isolated by the surrounding vegetation of contrasting types - they can be considered as "habitat islands". Twenty excavations (area from 100 m[^2] to 2 ha) were selected - 10 located in cropland, 10 - in coniferous forest. The intensiveness of gravel pit exploitation was differentiated. Some of them were exploited, other ones were abandoned 10.30 years ago. The floristic records were taken during summer period in each pit and in near-by vegetation at the distance not larger than 200 m. As much as 280 species of vascular plants were found in 10 selected gravel pits surrounded by coniferous forest communities, which contained only 111 taxa. The flora of mid-field excavations was definitely richer that the flora of their surroundings. Sorensen.s similarity index (S[o]) for mid-forest gravel pits and their surroundings ranged between 27% and 40% while that for midfield gravel pits and their neighbourhood - from 15% to over 27%. The U Mann-Whitney test demonstrated that the number of species noted in selected gravel pits significantly differed from that in the surrounding. It was true for both (mid-forest Z = 3.70; P = 0.00021) and mid-field gravel pits (Z = 3.78; P = 0.00016). Native species were dominating in the flora of both mid-field and mid-forest excavations (77% and 82 % respectively). Hemicryptophytes were found to dominate (46%) over other groups of life forms in both types of gravel pits. A high contribution of terophytes - over 19% in mid-forest excavations and over 25% in mid-field ones is noteworthy. The results showed that gravel pits could play a role of enclaves for natural and semi-natural vegetation thus acting as local centres of floristic diversity in human modified monotonous agricultural or monospecies pine forest landscape.