Biscutella laevigata L. - ein postglaziales botanisches Relikt in Mitteldeutschland: Populationsstruktur und Interaktionen

Abstract

Faulhaber, M., Partzsch, M.: Biscutella laevigata L. - a post-glacial botanical relict in Central Germany:
population structure and plant-plant interaction. - Hercynia N. F. 51 (2018): 58 – 79.

The xerothermic grasslands in the landscape of porphyry outcrops were formed under sheep grazing
over centuries and developed a high biodiversity. In 1990 the traditional land use has been abandoned
due to economical reasons with the consequences of expansion of grass species such as Festuca rupicola
and the loss of dicotyledonous species. The glacial relict Biscutella laevigata ssp. gracilis is an
indicator of historical old grasslands and strongly endangered and protected by law. In order to answer
the following questions 1) how vital are the remaining populations of the dicot in the landscape of porphyry outcrops near Halle (Saxony-Anhalt) and is there a correlation between fitness and population
size and 2) how endangered is the dicot by increasing grass density. We investigated 1) the vitality and
fitness of the populations in the field and 2) the behavior of the dicot in stands with different densities
of the grass F. rupicola. We calculated the population sizes of the dicot and measured a set of vegetative
(above-ground biomass, number and length of leaves, SLA, extent and height of rosettes) and generative traits (generative biomass, number and length of flower-/fruit stems, number and weight of diaspores,
seed germination). In a garden experiment, where a set of environmental factors keeps constant, the
plant-plant interactions between B. laevigata and F. rupicola were investigated. In order to determine
interspecific and intraspecific interactions, we conducted monocultures (B9, F9) and mixtures (B3F6,
B6F3) each with nine individuals per pot and 12 replications.
Five of the populations of B. laevigata still documented in 1993 and 2003 were also found in 2013, but
two populations were lost due to grass expansion. Generally, population sizes were very low, between
11 und 152 individuals. There was a significant negative correlation between population size and biomass
of the surrounding vegetation. This shows that the species develops poorly in habitats with closed
vegetation cover. Leaf length, SLA and height of rosettes showed positive relationship, but number and
length of flower-/fruit stem showed negative relationship with population size, but without significance.
Seed size and seed weight showed a positive trend with population size. Number of fruits and germination
did not show some relationship.
The interaction experiment showed that performance of B. laevigata ssp. gracilis is reduced under interspecific
competition with F. rupicola, and F. rupicola performed worst under intraspecific competition.
In order to counteract the expansion of highly competitive grasses like F. rupicola and the decline of rare
endangered species like B. laevigata ssp. gracilis, the traditional grazing should be reintroduced. Moreover,
through trampling and biomass removal, herbivores create gaps that serve as important regeneration
niches for other plant species and positively promote biodiversity.