Safeguarding the rare woodland species Gagea spathacea: Understanding habitat requirements is not sufficient

A large proportion of temperate forest plant diversity is found in the herb layer.
However, for many of its species, little is known about their autecology, which
makes it difficult to assess potential threats and efficiently safeguard the diversity of understorey herbaceous communities. This also applies to Gagea
spathacea (Liliaceae), a globally rare spring geophyte, which mainly occurs in
deciduous forests of northern Central Europe. We investigated the causal relationships between population characteristics of G. spathacea and abiotic site
conditions across different forest communities in the center of its distributional
range. Leaf length (a surrogate of the species' vegetative propagation) was positively related to soil moisture and soil nitrogen. Consequently, mean leaf
length was highest in moist forest communities of the alliance Alno-Ulmion.
Moreover, mean variability in leaf length was lowest in those forests, indicating
a higher and more stable vegetative propagation via bulbils. We found no support for a significant relationship between leaf length and leaf density or
between leaf length and flower formation. Population density varied strongly
among forest sites, but was not related to soil moisture and hardly influenced by soil nitrogen. Our results suggest that soil water and nutrient supply play a
vital role in determining the species' vegetative propagation, whereas the duration of habitat continuity is most likely an important determinant of population size and density. Conservation strategies therefore require a better
understanding of the complex interrelationships between abiotic site conditions
and the historical context-dependency of habitats.