The formerly continuous and widespread juniper (Juniperus communis L.) populations are currently divided into small and fragmented relics in numerous European countries. Additionally, many of these populations suffer from an absence of natural regeneration and consist predominantly of senescent individuals. In order to maintain juniper as a valuable element of the cultural landscape in Europe, I considered a restoration management to be indispensable. The goal of the present thesis is based on this consideration.
Using different DNA marker systems, I firstly tested various juniper populations on different spatial and temporal scales for potential imprints of habitat fragmentation. Afterwards my intention was to evaluate the analysed populations on the regional scale in terms of nature conservation and to develop a scientifically based conservation management plan, which should focus on planting activities.
In a Europe-wide study I used an AFLP marker approach to reconstruct aspects of the biogeographic history of juniper and to detect potential distinct genetic lineages. Those lineages are supposed to delineate geographic regions within which plant material can be interchanged. The genetic analysis revealed no distinct genetic lineages. Along with other scientific findings about juniper the results point to a glacial persistence of juniper in Central Europe. I suppose that during the last glacial period, this species managed to survive in several small and suitable habitats, which were probably diffusely scattered and permanently changing. Moreover, I hypothesise that recurrent fragmentation and founder events since the last glacial maximum (LGM) up until today are highly likely to have occurred in this species.
On a regional scale, i.e. in the Rhenish Uplands (RU) (West Germany), I used nSSR markers to gain insights into the genetic structure and variation of eight relict juniper populations. Such knowledge is necessary for planting activities in order to prevent negative effects in the respective populations. At the same time, I tested these populations for genetic imprints of the recent habitat fragmentation. The investigated nSSR loci in juniper were characterised within the scope of this thesis. A detailed validation of the newly developed nSSR markers is presented. In addition, I performed a case study by investigating the genetic diversity and differentiation of different pollen clouds, which have become reproductively effective in the filial generations (embryos). For this purpose a specific computer software was developed. Next, a palynological study was conducted to determine physical pollen flow distances of juniper pollen grains. In terms of plantings I assume that such data is relevant for the spatial organisation of already existing juniper individuals and the respective plant material. Considerably high levels of genetic diversity and an absence of recent genetic bottlenecks in all populations as well as an absence of an isolation- by-distance effect led me to the assumption that the current habitat fragmentation has not yet affected the genetic diversity in the investigated juniper populations. Instead, I postulate that the genetic diversity and differentiation have been ‘frozen’ since the recent fragmentation started. The genetic diversity of the filial generation is not reduced in comparison to the adult generation, although the palynological study points to locally restricted pollen flow distances.
After defining a ‘Leitbild’ for viable juniper populations based on widely accepted population ecological and genetic theories, I used the genetic results to evaluate the analysed populations of the RU in terms of nature conservation. The reasons why this evaluation was not satisfactory are discussed in detail. Further on, I commented critically on the evaluation criteria of the ‘Leitbild’ and their respective quality demands with regard to the life-history traits of juniper and its biogeographic history as presented within this thesis.
Based on the presented genetic results and on the apparent absence of natural regeneration in all populations it remains uncertain whether the current habitat fragmentation will affect the genetic diversity and structure of the eight populations deleteriously in the future. However, if juniper will not start with natural regeneration again, this will certainly lead to an extinction of the respective populations because without substitution, senescent individuals will gradually die off. Thus, in the distant future juniper will probably become extinct in areas where it does not regenerate naturally. Therefore, I developed a sustainable, demographically and genetically substantiated restoration management plan as a final outcome of this thesis. It is based on the genetic analysis presented here and on expert knowledge, and it includes guidelines and recommendations concerning the collection of plant material, its treatment in the greenhouse and plantings in the field.