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the totality of plant communities (phytocoenoses) that are present in response to changes of the principal environmental factor or factors. The main ecological factors may include moistening or salinization of the soil, the content of humus or mineral nutrients in the soil, and differing grassland and bottomland regimes. The sere is most often associated with changes in the moisture content or salinity of the soil or with simultaneous changes in both these factors.
The sere that best reflects changes in the soil moisture content is best observed on slopes in the floodplains of rivers. The soil at the bottom of the slopes usually has a higher moisture content than the soil at the top, with the result that the phytocoenoses of the lower portions contain plants that are more hygrophilous. Moreover, changes in the moisture content are usually accompanied by changes in a number of other factors (temperature, humus content in the soil), although the moisture content remains the principal ecological factor. Seres that are associated with simultaneous changes in both the salinity and moisture content of the soil may be observed along the shores of salt lakes and when the bottoms of such lakes become overgrown with vegetation as they dry out. Seres are also clearly manifested on the gently sloping shores of freshwater lakes that are in the process of bog formation.
A. M. BYLOVA