DISPERSAL SPECTRA OF 3 PLANT HABITATS WITH SIMILAR PHYSIOGNOMY IN MESIC AND ARID ZONES

The dispersal spectra of three different habitats are characterized by the properties of diaspores and mother plants influencing dispersal d istances. Additionally, the predominant dispersal agents and dispersal effects are considered. The studied areas are a stand of annuals in a small Wadi in the Wadi Araba (Jordan), a disturbed dry grassland on s andy soil in Berlin, and a limestone grassland in northern Hessen (Ger many). The vegetation of the three habitats is more or less open and n ot stratified. The habitat conditions differ in their climate (arid an d temperate) and in the manner and intensity of disturbance (wind, wat er, human impact). Despite a similar physiognomy of the vegetation, th e dispersal spectra of the three plant communities differ remarkably. The spectra reflect the habitat conditions, especially the prevailing dispersal agents. In Central European habitats telechory is more frequ ent than in the arid stand of annuals. At the arid site, characters ap parently hindering dispersal (antitelechorous characters) and those wh ich have no influence on dispersability (atelechorous characters) are frequent.Irrespective of the climate, high frequencies of polychory ar e correlated with disturbance by biotic or abiotic impacts. In polycho rous species in the mesic habitats, two telechorous characters are oft en combined while in the arid habitat telechorous and atelechorous cha racters are mostly correlated with antitelechorous characters. The spe ctra of the diaspore weights at the disturbed sites are similar in bot h climates. A striking difference is the lack of extremely light diasp ores in the desert habitat. Though the vegetation is nearly unstratifi ed, anemochorous diaspores tend to be exposed higher than average on b oth sites.