Differences in population structure require habitat-specific conservation strategies in the threatened steppe grassland plant Astragalus exscapus

Population structure of Laurus nobilis L. in Central Italian forests: evidence for its ongoing expansion

“…For this purpose, each plot was defined by the sum of individuals counted in the two subplots. Studies on population structures used proportions of each plant life stage in the clustering (Brys et al 2003;Kienberg and Becker 2017). Since mature trees were sampled in a different scale from juvenile individuals (the former within plots and the latter within subplots), we clustered population structures using only proportions of juveniles life stages of L. nobilis.…”

“…1 Maps showing a the distribution of L. nobilis in Italy obtained from (Filibeck 2006;Agrillo et al 2017) and b the distribution of the sampled sites in Central Italy. The black dots represent L. nobilis occurrences, the dashed square encloses the study area, and the red dots represent the sampled sites (color figure online) younger life stages (Hegland et al 2001;Brys et al 2003;Endels et al 2004;Kienberg and Becker 2017). A summarizing illustration of the three types of the population structures found in literature is reported in Fig.…”

“…Fig.2Main types of population structures according the proportions of individuals in each life stage of the plant. The figure was adapted according toBrys et al (2003),Endels et al (2004),Hegland et al (2001), andKienberg and Becker (2017) …”

Is a restricted niche the explanation for species vulnerability? Insights from a large field survey of Astragalus tragacantha L. (Fabaceae)

“…Theoretical models predict that any kind of stochasticity (demographic, genetic, environmental) will exponentially increase the extinction risk of small and isolated popultions (Ovaskainen and Meerson, 2010). Schurr et al (2019) At first glance, the low frequency of smallest and biggest individuals (4.3% and 3.3%), with most intermediate sizes individuals (Table 2), suggests a stable population type by comparison to the demography of Astragalus exscapus L., an endangered steppe grassland species (Kienberg and Becker, 2017). However, by contrast to A. exscapus, seedlings and plantlets were very rarely 16 / 27 observed during 15 years of a regular field survey (L. Affre pers.…”

“…Although population density is a good estimator of population viability, in long living perennial plants such as A. tragacantha it is recommended to use population structure, i.e. the distribution of age or size stage related to the age (Kienberg and Becker, 2017). We therefore base our analyses on total density and densities of different size stages of A. tragacantha.…”