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Vasilopoulos G., Tsiripidis I. and Karagiannakidou V. 2007. Do abandoned tree plantations resemble natural riparian forests? A case study from northeast Greece. Bot. Helv. 117: 125 -142.The conversion of a riparian forest to plantations of fast-growing, exotic species (Populus canadensis, Robinia pseudoacacia) may alter the floristic composition and soil properties, which may prevent the regeneration of natural forests when plantations are abandoned. Along the Nestos River in northeast Greece, we investigated how former plantations differ from natural forests after at least 14 years of abandonment. We carried out 60 vegetation relevØs and took soil samples in each plot to determine soil texture and chemical properties. Relationships between the forest type (natural vs. abandoned plantations), the floristic composition of the understory and soil properties were analysed with classification (TWINSPAN) and ordination (DCA). There was a clear floristic differentiation between natural forest and abandoned plantations, especially those of Robinia pseudoacacia. The topsoil of abandoned plantations had a lower content of organic matter and nitrogen, and the tree layer was still dominated by the formerly planted species. However, there was a similar floristic gradient, related mainly to soil texture (sandy vs. loamy sediments), in both the natural forest and abandoned plantations. Thus, even though the establishment of natural riparian forest species in the former plantations was scanty, their present floristic composition sufficiently reflects the natural ecological gradient to serve as a basis for a management plan to restore the natural riparian forest.

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The establishment of a network of reserves is of fundamental importance to the loss of biodiversity. Seven different area selection methods for the establishment of a reserve network were applied in the present study: (a) 5% cut-off value of the grid cells with the highest species richness or conservation value, (b) complementarity analysis using as criteria species richness or conservation value or rarest species richness, and (c) mixed complementarity analysis using as criteria species richness or conservation value. These methods were applied in the orchid taxa of east Macedonia. The conservation values of taxa were estimated on the basis of regional rarity, broad-scale rarity, and species specialization. The spatial overlap between the resulting networks and the Natura 2000 network of the study area was assessed. Furthermore, the efficiency of the latter network to protect the orchid taxa of the study area was examined. Our results suggest that: (a) a multiscale estimation of rarity is necessary for the unbiased estimation of species conservation values; (b) species specialization adds valuable ecological information to the assessment of taxa conservation values; (c) complementarity and mixed complementarity analyses on species richness or conservation value safeguard all the taxa of the region; (d) complementarity analysis on the basis of the richness of the rarest species safeguards all the rarest taxa, but not the total number of the remaining taxa; (e) the 5% cut-off value on species richness or conservation value fails to protect all the taxa of the region, including a large number of the rarest taxa; and (f) the Natura 2000 network, despite its large coverage in the study area, fails to safeguard all the taxa, including some of the rarest.