BOTANY WITH BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

XIII. PLANT INDICATORS OF SURFACE WATERS

Periodically flooded depressions

Closed depressions with a variable hydrological regime are characteristic of subarid steppe and semi-desert conditions. An indicator of fluctuating moisture is the ecological compatibility within a single plant community of moderately moist species—such as true bedstraw (Galium verum) and British inula (Inula britannica)—alongside excessively moist meadow species like lakeshore bulrush (Schoenoplectus lacustris) and flowering rush (Butomus umbellatus). This coexistence results from soil waterlogging during one part of the vegetation period, followed by soil drying and a deep drop in groundwater levels during another. Direct indicators of the hydrological regime of limans and depressions are plants confined to soils with increased moisture. The presence of mesohygrophytic vegetation in steppe and semi-desert depressions points to areas of temporary surface Water concentration. The more hygrophytic the vegetation, the longer the duration of flooding in that area. Negative indicators of soil waterlogging are xerophytes, such as sheep's fescue (Festuca sulcata) and Lerch's wormwood (Artemisia lercheana).

There is a close relationship between plant communities and the duration of flooding in limans and depressions. In one of the limans of the Tselinograd Region [81], a sedge-rush community located in the central part of the liman is flooded by melted snow in spring for 67 days, with a water depth reaching 67 cm. Couch grass-beckmania communities are flooded for 58 days at a depth of 59 cm, and couch grass-brome-foxtail communities for 50 days with a water depth of up to 38 cm. Surrounding communities occupy gentle slopes and are flooded for shorter periods: couch grass-reedgrass-brome-forb communities for 24 days, and forb-grass communities for 22 days. Meadow-steppe communities situated along the edges of depressions are flooded for a short period not every year. In normal years, forb-couch grass-fescue and couch grass-fescue-wormwood communities remain unflooded.

In semi-desert limans, the frequency of flooding is of greater significance than its duration [83]. In the limans of the Trans-Volga region, the bottom—flooded annually or four years out of five—is populated by such hygrophytes as common reed (Phragmites communis), lakeshore bulrush (Scirpus lacustris), and slender sedge (Carex acuta). The zone of four- to three-fold flooding is traced by phytocenoses comprising sedges (slender sedge (Carex acuta), Gerard's rush (Juncus gerardii)) and grasses (creeping couch grass (Elytrigia repens), slough grass (Beckmania eruciformis)).

When flooding decreases to three or two times in a five-year period, grass-sedge communities predominate: creeping couch grass (Elytrigia repens), sweet vernal grass (Hierochloe odorata), and drooping sedge (Carex nutans). The peripheries of limans, flooded once every five years, are occupied by grass communities dominated by meadow foxtail (Alopecurus pratensis), creeping couch grass (Elytrigia repens), and crested wheatgrass (Agropyrum pectinatum). Along the BOUNDARIES OF THE flooded area stretches a ring of halophytes—warty orache (Atriplex verrucifera) and Montpellier camphorwort (Camphorosma monspeliaca)—beyond which wormwood-grass semi-deserts are situated.

Vegetation can directly indicate not only the flooded areas, but also the boundaries of periodic inundation. A significant portion of floating PLANT AND ANIMAL debris, as well as silt, is deposited along the flood boundaries. Soils characterized by high humus content and large amounts of nitrogen form here, As a result of which the flood limits are marked by dense thickets of nitrophilic plants, predominantly annual weeds. Some plants (such as tamarisk, camel thorn, and sea clubrush) sometimes regenerate abundantly along the flood boundaries, serving as clear markers.