Patrick Endels

Temporal changes (1986-1999) in populations of primrose (Primula vulgaris Huds.) in an agricultural landscape and implications for conservation

In Belgium, Primula vulgaris is a rare and declining species. Its fate is bound up with the ever-changing agricultural landscape in northwestern Belgium and analysis of historical data showed a shrinking distribution area during the last decades. Contrary to the situation in England and France,most of the populations are situated in small landscape elements in the agricultural landscape and not in woodland. The population size distribution is skewed to very small populations ( <10 individuals) with few younger life stages in small populations,higher proportions of older adults and unequal flower morph numbers. The changes in several population traits during a 13-year interval are correlated with initial population status,indicating that small populations tend to be more prone to extinction than larger ones. Small remnant woodland patches may be seen as ‘safe sites’: in this environment population sizes were more or less stable during the 13-year period whereas populations in ditches around arable fields were particularly susceptible to decline. Under current conditions,the long term survival of the species in small landscape elements is highly critical unless land use practices change drastically in the near future. The minimum viable populations concept and management of small landscape elements are discussed. # 2002 Elsevier Science Ltd. All rights reserved.

Changes in pin-thrum ratios in populations of the heterostyle Primula vulgaris HUDS.: Does imbalance affect population persistence ?

Summary The heterostyle Primula vulgaris is a rare and declining species in Northern Belgium; its presence is restricted to a limited number of small landscape elements in a matrix of intensively managed agricultural land. In 1986 and 1999 we recorded numbers of pin-thrum flower morphs in respectively 34 and 89 populations. No structural imbalance in flower morph numbers was found, but imbalances were significantly larger in small populations. Moreover, relative imbalance also increased between 1986 and 1999. Population persistence however, was not correlated with morph imbalance: changes in population size between the two survey periods did not depend on initial flower morph imbalance. Results are compared with other heterostyly-related population research in Primula species and the relative importance of deterministic and stochastic processes for population persistence are discussed. To conclude, the introduction of missing morphs into relic populations with only pin or thrum plants is suggested to reduce pollinator-limited seed set.

Rapid response to habitat restoration by the perennial Primula veris as revealed by demographic monitoring

The demography of Primula veris, a typical species of the species-rich Mesobromion grasslands, was investigated at two contrasting habitats in Eastern Belgium. Both a forested site and a clear-cut parcel were part of formerly larger calcareous grassland areas. By monitoring the demographic response of the target species, this study attempts to clarify the differences in fecundity, growth and survival between a restored and degraded calcareous grassland site. A study of plant traits showed a decrease in number of flowers, inflorescence stalks and plant size under a closing tree canopy. We surveyed individuals in permanent plots between 1999 and 2001. At the forested site, a first sign of decline included lower proportions of flowering individuals and afterwards an increase in mortality was found. Alternatively, removing canopy resulted in an immediate flowering response and both increased growth and seedling recruitment the year after. At both sites, survival rates strongly depended on the initial state, location and year. Projection matrix analysis revealed large differences in modelled population growth rates between sites and years. Under closing canopy the species showed only slow population decline, but the decrease was larger in the last survey year when higher mortality affected the number of reproductive individuals. Transitions between stages with the highest impact on population growth rate were identified by elasticity analysis. If calcareous grassland is forested, survival of reproductive adults is predicted to be very important for conservation of P. veris populations. However, seedling recruitment needs to be raised to guarantee long-term persistence of the populations. On the other hand, clear-felling of a site for restoration of species-rich calcareous grasslands may result in a rapid recovery of certain species.

Impact of management and habitat on demographic traits of Primula vulgaris in an agricultural landscape

Abstract Question: Is demographic performance of Primula vulgaris correlated with habitat characteristics of the small landscape elements in which it occurs? Can we use this species as an indicator for species-rich semi-natural habitats? Location: Flanders, Belgium. Methods: To capture differences in demographic traits and habitat characteristics, both within and between populations, a two-level survey was carried out. Population size and structure of 89 P. vulgaris populations in different types of small landscape elements was recorded in 1999. At plot level, densities of different life stages were determined and these were related to edaphic conditions and vegetation structure and composition. Results: Three different population types were distinguished: (1) dynamic populations, characterized by seedling and juvenile proportions, (2) normal populations with relatively more adults, but with considerable numbers of seedlings and juveniles and (3) senescent populations, mainly consisting of adults. Senescent populations were significantly smaller than populations with a dynamic demographic structure. At plot level, comparison of demographic characteristics between different management regimes revealed that recruitment rates and total plant density of P. vulgaris were highest in plots that received a regime that included mowing and clearing of ditch banks whereas densities were lower along forest edges. For these plots, it was shown that nutrient levels were higher. Densities of adults as well as juvenile and seedling densities were negatively correlated with vegetation height. Conclusions: Local disturbance and heterogeneity may mask the relationship between unfavourable conditions and demographic characteristics at population level, but it is clear that in small populations recruitment needs to be lifted to guarantee its persistence. Performance of P. vulgaris in small landscape elements can be a first indication of plant species diversity in small landscape elements. Nomenclature: Lambinon et al. (1998).