Taxonomic resources are essential for the effective management of invasive plants because biosecurity strategies, legislation dealing with invasive species, quarantine, weed surveillance and monitoring all depend on accurate and rapid identification of non-native taxa, and incorrect identifications can impede ecological studies. On the other hand, biological invasions have provided important tests of basic theories about species concepts. Modern taxonomy therefore needs to integrate both classical and new concepts and approaches to improve the accuracy of species identification and further refine taxonomic classification at the level of populations and genotypes in the field and laboratory.

lnstitute oj Applied Ecology CS-281 63 Kostelec nad Èerný/ni lesy, Czechoslovakia JIØÍ LIŠKA Botanical Institute, Czechoslovak Academy oj Scie/lces CS-252 43 Prùhonice, Czechoslovakia AB,5TRACT The population or Sibba/dia lelra/ldra, a cushion plant, on thc scrcc slape at 3800 m a.s.l. in thc Pamiro-Alai Mountains consists or isolatcd individuals with positivcly ske\Ved size distribution. Direct competition among isolated individuals is improbable. The dirrerences in cushion size are due mainly to the age or individuals and the local síle quality. Linear relationship between the growth in height or a cushion and its latcral growth \Vas round. Frost injuries are more extensive in the small cushions, bul the proportion or arrlicted plants is greater in the large ones. Slightly contagious spatial pattern resulting rrom the environmental heterogeneity was detccted. Seventeen specics were observed to invade the cushions. Total biomass or intruding species is highly correlated with the cushion volume as \Vel I as with biomass. Species diversity increases with cushion area. A 10g-linear relationship between the number or invading species and cushion area \Vas round. Both the number and cover or the species occurring outside or the Sibba/dia letrandra cushions are negatively correlated with the cover or Sibba/dia tetrandra. The spatial pattern or Sibba/dia populations dirrers considcrably bet\Vcen the study plot on a flat site and lhal on the screc slape. On thc flat sitc, Sibba/dia rorms a carpet consisting or individuals which cannot bc clearly distinguishcd rrom cach othcr. Thcrc also, thc numbcr and covcr or the othcr species incrcases, and the most succcssrul spccics are those \Vhich are capable or colonizing Sibba/dia cushions.

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