Repatriation & reintroduction

 

Selection of potential localities and planting

One of the goals of the rescue programme was establishing several (3–6) new populations of P. praelongus in areas of its former occurrence (the Orlice, Ploučnice, Labe basins). Not only flood plains, but also oxbows, parts of rivers with slow stream, revitalized ponds and sandy lakes were considered. Apart from botanic assessment (especially concerning aquatic plants and littoral vegetation), basic water parameters were measured (pH, electrical conductivity). Also water transparency was measured with a Secchi desk. Optimal are localities with these parameters: water transparency more than 0.5 m (ideally 1m – indicated by presence of submerse macrophytes), pH 7–9 (neutral to mildly basic) and el. conductivity 110–410µS·m-1. Water should not be eutrophicated and muddy (danger of sedimentation on plants). It was also important to assess the shadow intensity and presence of competitively stronger species, expanding littoral species, or herbivore fish and ducks. If a locality fulfilled these requirements, discussion with owners and tenants about possibility of reintroduction of P. praelongus started. After their approval, P.praelongus was planted into the bottom sediment. Some of the reintroductions were not successful; other localities were then chosen following the same rules. A regular monitoring concerning size and vitality of populations of P. praelongus and other macrophytes started in the localities with successful reintroduction.

 

Reinforcing of the population in the TPA

Reinforcing of this population with plants from the rescue culture was only executed when the population was not vigorous enough (after sludge-removal or repeated nibbling by ducks). When the population flourished, no outplanting was done. The first reinforcement was carried out in 2005, when the conditions in the locality had stabilized after a partial sludge-removal. Another reinforcement was done in 2008, when new stems were planted to both shores of the oxbow. The source for outplantings in 2005 and 2008 was the rescue culture in IB, CAS, Třeboň. A replanting was done in 2011 and 2012, when some of the vital stems from the right side of the oxbow were replanted to the left side. About 10 stems were taken, which did not endanger the right-side population of about 1000 stems, and it helped to establish a new population on left shore. On the whole, about 70 stems were outplanted. The latest attempts to outplant stems from IB, CAS, Třeboň were done in 2015 and 2016 to reinforce the population devastated by duck-nibbling.

 

Reintroductions into potential localities

In the frame of the rescue programme, about 50 localities have been assessed concerning possible reintroductions. At first, localities in the outskirts of Hradec Králové were selected (mainly in the Orlice floodplain), then localities in the Ploučnice River basin in Českolipsko region were considered, where historical data about P. praelongus occurrence are known. These historical localities are not suitable for reintroduction today (they are usually used for fish breeding) and thus they were not chosen. Although a big attention was paid to selection of potential localities, the result was not positive. Most of the localities are absolutely unacceptable for reintroductions. Some of them were excluded immediately after first assessment, other were excluded thanks to unsuccessful outplanting. Failure of outplanting could be caused by a low number of outplanted stems, small size of plants and their low adaptability to new environment, but also by improper time of plantation. It is hard to predict weather development and time of higher water level or floods which damage plants with undeveloped root system. Plants carried out by the stream have a very low possibility to take roots in a proper locality. Yet this possibility exists, as it happened in the case of the new occurrence of P. praelongus near the bridge across the Orlice River at Slezké Předměstí suburb, discovered in 2007. This locality is situated in the lower water course of the Orlice River and this discovery was preceded by outplanting of P. praelongus into the TPA in 2005. Only two of the realized outplantings were successful – in the Kašparovo jezero lake in the Orlice floodplain near Slezké Předměstí suburb in Hradec Králové, and in the Ploučnice oxbow by Heřmaničky in Českolipsko region. These populations have still been observed.

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