Saw sedge is a very important peatforming plant and also a rare and protected component of the Polish flora. More rare still is community Cladietum marisci (Allorge 1922) Zobr. 1935. It has been adopted as priority type of habitat of the Directive Natura 2000 and in the ecological network EECONET. This monograph regards the different aspects of ecology of this species, including habitat and geological conditions, the current resources of Lublin macroregion and the methods of its effective protection. The main objectives presented herein are: 1. determination the habitat conditions of saw sedge and the communities with Cladium, particulary the hydrological conditions, 2. examination the geological conditions, study of the influence of the different habitat factors (especially the changes of water level and burning) on the changes of species composition of communities with Cladium mariscus, 3. analysis of the rate and the causes of extinction of saw sedge in the macroregion, 4. examination of the current distribution and the valorization of localities, 5. review of the efficiency of the methods of saw sedge protection. The studies show the dependence of the occurrence of saw sedge on the depth of chalk undersoil. The studies show also high sensitivity of saw sedge to changes of the hydrologic conditions. Especially the cumulation of two factors: the water level decrease below the peat level connected with the periodical drying of habitat and the repeated fires of saw sedge bulrushes leads to the gradual depletion of Cladium mariscus and its replacement by meadow communities. The hydrological conditions determine the development of different variants of the community Cladietum marisci. Within the study area, there have been found four variants (in order from the most moist) of association of Cladietum marisci: C. m. with Carex elata, C. m. typicum, C. m. moss-grown variant and C. m. with Molinia caerulea. Three variants (without the last one) are in the dynamic balance, and the changes between them have fluctuating character depending on moisture and fires. The occurrence was found of saw sedge as an additional species in seven other plant associations: Phragmitetum australis, Caricetum davallianae, Caricetum buxbaumii, Caricetum elatae, Caricetum lasiocarpae, Molinietum caeruleae and in the community Schoenus ferrugineus. On the study area saw sadge grows upon only the marshy soils of fens and peat-muck soils. But on peat-muck soils Cladium mariscus backs out gradually, losing in competition mainly with Molinia caerulea. Then, prolonged upward movement of water level (more than 20 cm measured in summer period) also causes backing out of Cladium and the transformation of saw sedge community into other communities like: Phragmitetum communis, Caricetum elatae or Caricetum lasiocarpae. It has been ascertained that fires at high water level do not affect saw sedge rushes. The method of Cladium mariscus study on sample areas proposed in this paper has been positively verified. The highest biomass of above-ground shoots on 1 m² has been noted in the community Cladietum marisci typicum. The highest shoots density has been noted in the moss variant of Cladietum marisci. Then the highest generative and vegetative shoots of saw sedge have been discovered in the variant of Cladietum marisci with Carex elata. There has been noted an occurrence of saw sedge at 27 localities in the macroregion. But 96.6% of the population resources is concentrated on only four calcareous marshes near Chełm (2-15 km north-east from the town). The current total area of saw sedge rushes in the territory of the mac-roregion amounts to 779.4 ha. Over the last 50 years the area occupied by saw sedge has decreased by about 782.5 ha or by 50% of the former acreage. The greatest loss (100% or near 100%) has been noted in such localities as: Łąki Pomiary, Krowie Bagno, Rudolfin-Czerniejów and Bagno Łopata. The best form of protection of saw sedge is large area protection. The most valuable localities of saw sedge are protected as nature reserves. 21 other places of saw sedge occurrence have been reported for protection as ecological uses. But due to their small area and the low stability of the habitat conditions in such places saw sedge is still threatened. The most important for effective preservation of saw sedge is keeping the proper water regime and effective fire-fighting protection. In spite of the big resources of Cladium mariscus in the macroregion it has been proposed to include it in the list of threatened plants in the region, with category VU (vurnerable).