Temporal and spatial variation in the demography of Gentiana pneumonanthe, a rare perennial herb

1 A total of 35 transition and elasticity matrices for the rare iteroparous herb Gentiana pneumonanthe was analysed for temporal and spatial variation. The data used were collected annually from 10 sites in six different populations on up to seven occasions in the period 1987-93. 2 In general, temporal variation was higher in transition matrices than in elasticities, while between-site variation was high for both transition and elasticity matrices. 3 The relative contributions of three life-history transitions, progression (or growth, G), recruitment from seed (fecundity, F) and survival (retrogression plus stasis, L) to the finite rate of increase, lambda, were also highly variable, between years within as well as between sites. The observed variation is very large in comparison with that previously observed either between or within other iteroparous herbs from open habitats, even showing some overlap with demographic patterns normally characteristic of woody plants. 4 A G-L-F ordination shows a long, narrow band across the entire diagram from matrices with a low elasticity for L and high elasticities for G and F at one end to matrices which have an elasticity of 1.00 for L on the other. 5 Correlations between the G-, L- and F-elasticities, lambda, and the vegetation cover suggest that the band in the ordination diagram represents a successional pathway in wet heathlands from invasive to regressive populations. Elasticity matrices from regularly mown hay meadows are characteristic of stable populations, but represent senile, regressive populations after mowing has ceased. 6 Relationships between lambda and the elasticities of G, L and F show that in matrices of stable or declining populations (lambda less than or equal to 1) survival is most important. In growing populations (lambda > 1) the contribution of progression and fecundity becomes larger, 7 Given their relatively large temporal and spatial variation, elasticities are useful in nature conservation and management only if the corresponding value of lambda is taken into account. 8 Significant positive correlations between transition probabilities of different life stages were observed. This phenomenon may increase the risk of extinction by environmental stochasticity.