Individual variation and the effects of weather, age and flowering history on survival and flowering of the long-lived perennial Gentiana pneumonanthe

Gentiana pneumonanthe, the marsh gentian, is a declining species in both Britain and Europe as a result of loss of its heathland habitat or inappropriate management of that which remains. We analysed long-term demographic data sets (1977 - 1991) from four populations of the plant to test the hypotheses that an individual plant's survival and its chances of flowering in any year are related to its age and performance in previous years, taking into account the climatic conditions that existed in those years. The results show that: 1) 'new' plants (2 yr old) had a higher mortality rate (mean = 20.8%) than 'young' (3 yr old) plants (mean = 5.0%), which in turn had a higher mortality than older, 'mature' (four or more year old) plants (mean = 3.8%); 2) 'new' plants had a higher mortality rate after either a growing season with below average rainfall or an above average winter rainfall; 3) mortality of 'mature' plants was independent of age, indicating no evidence of senescence; 4) 'mature' plants had a higher mortality rate after above average rainfall during the previous winter; 5) plants that have flowered within the previous two years are most likely to flower in the current year indicating high individual variation in flowering performance; 6) more plants flower and flowering plants produced more flowers in the two years following a warmer than average growing season. The above factors are related to current site management and the implications are discussed. Suggestions are given for changes in management of the sites where this rare plant occurs.