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Succession occurs on a large part of German salt marshes following abandonment or reduction of grazing. Its speed and effect on the biodiversity of salt marshes has been discussed in the literature. Permanent plot studies show site-dependent differences in successional outcome. If grazing is to be continued, there is uncertainty about the stocking rates that are optimal for the conservation of plant diversity. We present an eight year permanent plot study with different grazing treatments on a high salt marsh at the marsh island of Hallig Langeness, Germany, which is enclosed by a summer dike. The study site is owned by WWF. Successional outcomes on the permanent plots depend on grazing intensity and depth of the groundwater table which is correlated with soil salinity. Intermediate stocking rates support a mixture of halophytes and glycophytes, the relative proportion of which depends on the depth of the groundwater table. Cattle grazing at stocking rates of 0.6 livestock units per ha were found to be optimal for plant diversity conservation. At sites with deeper groundwater tables and no grazing, dominant Elymus spp. stands develop and diversity is strongly reduced. If the groundwater table is high, succession following grazing abandonment is retarded and small halophytes prevail. [ABSTRACT FROM AUTHOR]

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Using the activitation method ( n,2 n) excitation-functions were measured forFe,Ge,Se,Rb,Sr,Y,Mo, andHg in the neutron-energy region 13-18 MeV. The results are checked for consistency by means of a systematic of ( n, 2 n) cross-sections as a function of the nuclear neutron excess ( N-Z)/A. Furthermore the data are compared with results from the statistical nuclear reactions theory which were calculated using optical model absorption cross-sections and the Fermi-gas-model formula for the nuclear level density. In the case ofHg the influence of preequilibrium nucleon emission was taken into account. [ABSTRACT FROM AUTHOR]