Rescue program

Rescue and backup population

Backup population in Protected Landscape area Kokřínsko Máchův kraj

Outside of the rescue program, P. praelongus was outplanted into several revitalised pools in the PLA Kokořínsko: a pool above Harasov Pond (2001), a pool in the floodplain of the Liběchovka (2001), pools below Plešivec (2002), a backwater pool at Štampach (2003), the pool at Medonosy (2010), and a pool at Tupadly (2013). Long-term monitoring of the populations in Kokořínsko revealed that their condition depends on the succession stage of the pools. In most of pools with sufficient depth (0.5–1.2 m), the population density was highest in the 5th–7th year after outplanting. Then the population decreased to tens of shoots and further to individual shoots. In small and shallow pools (at Medonosy, possibly also at Tupadly), P. praelongus reached its maximum in the 3rd year, but then disappeared later, weakened by warmer water and outcompeted by competitively stronger species. The highest number of P. praelongus shoots (almost 3000) was recorded in nine pools below Plešivec, where it successfully grew in 2008. It had been surviving best in two big pools until fishermen started keeping grass carp there in 2013. The populations of P. praelongus in the big pools disappeared completely; a small number of plants exists in three small pools unreachable by the fish.

Also the population in the pool above Harasov Pond grew successfully; it reached almost 1400 shoots in 2007. Unfortunately, this pool was repeatedly influenced by flushes of nutrients during floods and the species gradually retreated to make place to species which thrive better in high trophic conditions (mainly Potamogeton natans and Calliergonella cuspidata). At present, the quantity of aquatic macrophytes in this pool is very small. The populations in two pools in the Liběchovka River floodplain disappeared for two reasons. In the big and shallow pool with clay sediment on the bottom, the water was excessively warmed and the plants, damaged by heat, were not able to compete against Typha latifolia. The population in the medium-sized pool was in good condition until 2010, but it retreated because of intensive spreading of Potamogeton natans and Calliergonella cuspidata. The population in the backwater pool at Štampach developed hopefully; the plants only suffered from heat in the shallow parts, but thrived well in the deepest central part of the waterbody. Yet reeds (mainly Typha sp., Phragmites australis) intensively overgrew the pool and filamentous algae of Chara sp. prevailed. A sparse P. praelongus population has survived in the central part of the pool. In the latest pools, founded in 2010 (the pool at Medonosy) and in 2013 (the pool at Tupadly), the conditions were not suitable for P. praelongus from the very beginning. The pool at Medonosy is situated in a reed bed and is being intensively overgrown by reeds, predominating aquatic plants (Ceratophyllum demersum, Potamogeton berchtoldii, Lemna trisulca), and filamentous algae (Chara sp.). The backwater pool at Štampach is shallow with a clay bottom. The plants suffer from heat and the pool is drying out.

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