Karsiborska Kępa

The site consists of 3 islands in the Świna River Delta (OSO) with Karsiborska Kępa being the most important area used by the population of Acrocephalus paludicola. On Karsiborska Kępa there is a private nature reserve belonging to the beneficiary. The two other small islands are leased by the beneficiary from the local community (representing state treasury). The total area of the site is over 300 ha. A formerly large suitable breeding area for Acrocephalus paludicola is now decreased to about 60 ha.

The extensive grazing on Karsiborska Kepa has created and preserved a halophytic plant community (rush-meadow), a type of habitat which is rare in the rest of Poland. Among several communities is Juncetum Gerardi atlantico-balticum maritime, Junco-Samoletum Valerandii and Puccinellio-Spergularietum salinae. Some of these assemblages are threatened by overgrowing of reedbeds Phragmites communis. The communities of the island are half-natural meadows, mostly consisting of about ten different species of grasses. The banks are overgrown by rush communities (Phragmitetea, mostly by Scirpo-Phragmitetum).

Karsiborska Kepa island is surrounded by a dam protecting it from floods. Within the dam most of the ground is rough coastal grazing saltmarsh over mineral soil and the rest is pasture succeeding to Phragmites communis where the soil is more organic. Karsiborska Kepa island has a well developed network of dykes and canals. The area is flat but it is covered by many small to medium pools and swampy spots that may stay flooded the whole year.

Karsiborska Kepa holds a high diversity of breeding and passage wetland birds: waders, geese and ducks. Especially noteworthy is an internationally important population of the globally threatened Acrocephalus paludicola. The area is also important for breeding waterfowl and wintering Anser spp. Several species of raptors use the site for feeding.

Karsiborska Kepa holds the second largest number of Acrocephalus paludicola breeding territories in the Pomeranian population. The results of the 2006 Acrocephalus paludicola survey show that it holds over 20 vocalizing males of the total Pomeranian population (Germany and Poland) of 80 vocalizing males. On the national and the EU level, the site maintains 0.5% of Acrocephalus paludicola population respectively, but it is a crucial site for the conservation of genetic diversity of the Acrocephalus paludicola, holding 25% of the total population of the genetically distinct and sharply declining Pomeranian population of the species.

The site has very good potential for restoration of Acrocephalus paludicola habitats, and in the future it could serve as the main dispersion centre for Acrocephalus paludicola to other restored breeding sites in Pomerania.