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Background: Greece has two island archipelagos, the Aegean and the Ionian, which host a rich array of plants and wildlife, particularly endemic and threatened plant species. Despite the long history of island biogeographic studies in the Aegean, similar studies in the Ionian remain limited, with the two island archipelagos rarely being compared. Results: The Aegean and Ionian archipelagos share many features, especially regarding total plant diversity, but exhibit different patterns of endemism. For instance, when considering similarly sized islands, those in the Ionian host as many as, if not more, species compared to the Aegean. In contrast, the Ionian Islands are poor in endemics (particularly narrow range endemics, such as single island or regional endemics) and threatened taxa, compared to the Aegean Islands. In the Ionian, endemics only persist on the largest islands, and form a very small proportion of the species pool, compared to the Aegean archipelago. Conclusions: The lack of endemism might be attributed to the more recent separation of the Ionian Islands from the mainland and the shorter distance separating them from the mainland. In addition, the Ionian Islands receive higher levels of precipitation and are typically covered by denser and higher vegetation than the Aegean Islands. These conditions favour greater total species richness, but tend to lead to higher numbers of common species compared to threatened and endemic taxa. This study demonstrates that both isolation and precipitation serve as biodiversity drivers, influencing plant species diversity and endemism patterns, of the two Greek archipelagos. [ABSTRACT FROM AUTHOR]

We investigated the potential contribution of the persistent soil seed bank in post-disturbance restoration of the herb layer in a long-term overgrazed, mixed oak forest (NW Greece). We examined the impacts of grazing on plant richness and density in the soil seed bank in regard to the different dispersal and life strategy types of the herb layer taxa. Soil seed bank was qualitatively and quantitatively analyzed and contrasting plant guilds were defined according to life strategy type and dispersal mode. Soil seed bank differences between a) the upper and lower soil layers and b) plant functional guild pairs (ruderals vs. non ruderals, including typical forest taxa, and physically- vs. animal-dispersed plants) were statistically tested in overgrazed and sporadically grazed plots. Moreover, correlations in soil seed bank species dominance between overgrazed and sporadically grazed plots were examined by Spearman's Rank correlation. The majority of seeds were found in the upper (0-5 cm) soil layer. Seed density in the deeper (5-10 cm) soil layer was rather poor and did not differ significantly between overgrazed and sporadically grazed plots. In the upper soil layer, both seed density and plant species richness were significantly lower in the overgrazed plots. Overgrazing reduced both species richness and seed density of non-ruderal species in general and typical forest herbs in particular, while it did not affect ruderal species richness and density. Plant species richness and seed density of animal-dispersed taxa were reduced by overgrazing while physically-dispersed species were not affected; it is therefore concluded that large herds of grazers fenced in relatively small areas cannot act as efficient dispersal vectors of the former species. Our findings suggest that, upon cessation of grazing, the soil seed bank is rather inadequate to restore the herb layer of overgrazed forest sites. [ABSTRACT FROM AUTHOR]