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Population structure of a clonal endangered plant species Iris sibirica L. in different habitat conditions

Kostrakiewicz K.

Polish Journal of Ecology

2008

Vol. 56, nr 4

581-592

The investigations of structure of the genets and populations of Iris sibirica L. were carried out in the period 1999-2002. The studies were conducted in Molinietum caeruleae patches localized in Southern Poland. The patch labelled MW ("more wet") measured 5,600 m[^2] and was chracterised by presence of large depressions filled with stagnant water, concentrated chiefly in the central part of the site. In this locality species with a high competitive potential (like Phagmites australis Trin., Chamanerion angustifolium (L.) Scop., Epilobium hirsutum L., Filipendula ulmaria (L.) Maxim. and others) prevailed. The patch called LW ("less wet") measured 1,800 m[^2] and was characterised by small number of depressions scattered throughout the site. In this locality dominated the plants of minor competitive abilities (like Lathyrus pratensis L., Lotus corniculatus L. and others). The spatial pattern of populations was described on the basis of the locations of all ramet clusters in 100 m[^2] square plots. Each ramet cluster was attributed to a developmental stage. The differences in height of ramets between stages was estimated on the basis of lenght of the tallest leaf and generative shoot measured in all genets and ramet clusters in both populations (30 leaves and all generative shoots in 5 clusters of ramet at generative and senile stages and 4 - at fragmentation phase in both populations). In study year 2000 Iris sibirica population in LW locality was consisted of 26 ramet clusters and showed an aggregation structure, while population growing in MW site was consisted of 502 ramet clusters and presented the group-aggregation spatial structure constituted by groups of dozen or so ramet clusters, forming large aggregations. Both populations showed signs of senility in effect of absence of genets in prereproductive stages. In 2001 and 2002 the seedlings and juvenile genets appeared only in artificially made gaps. The genets in initial stage are much lower (about 40 %) than older ones and the ramet in MW locality reached greather height (6 to 23%) than in LW site. The evaluation of structure of populations taken as indicator of their vitality, show that the population from less wet locality was in better condition despite of low abundance. Domination of ramet cluster at generative stage and vicinity of plants with low competitive potential enables longer existence of Iris sibirica in occupied site. In more wet locality the I. sibirica population is worse equiped to survive. Advanced senility and the vicinity of plants with high competitive potential might inhibit the proliferation of I. sibirica ramet clusters, accelerate their fragmentation or even eliminate from occupied site.