The Species Reintroduction Programme at the
Berlin-Dahlem Botanic Garden

Isolde Hagemann

Palmengarten der Stadt Frankfurt am Main
Siesmayerstraße 61
D-60323 Frankfurt, Germany


The protection of the living space of all plant species is not something which in the near future can actually become a reality. Attempts must be made to prevent the extinction of threatened species and populations by preserving them in cultivation. The reintroduction programme at the Berlin-Dahlem Botanic Garden includes annual species, perennials in wet habitats, perennials from dry areas and annuals from agricultural locations. The programme will be enlarged to conserve threatened plants in the surrounding County of Brandenburg.


Species protection has been a new focus of emphasis in botanic gardens in recent years. One important part of this task in such gardens has been caring for species threatened world-wide which have been located and actively cultivated and documented, following their appearance on search lists published by Botanic Gardens Conservation International.

Another important activity is participating in the conservation of local flora, as formulated in the 1975 Resolution of the Conference in Kew concerning "The functions of living plant collections in conservation and conservation oriented research and public education."

Because of the concern raised by news of the ongoing destruction of tropical rain forests, and the resulting loss of many, in some cases unknown, species, a conservation programme for purely locally endangered species may seem insufficient or misplaced. However, it is important to retain the diversity still present in nearly every location, whether distant or close at hand (Ebel & Rauschert 1982, Ern 1980, Fessler 1980). Also, the information gathered during reintroduction programmes in the vicinity of botanic gardens is necessary in order to correctly evaluate the effectiveness of such efforts, which could lead to their eventual use in other more remote parts of the world.

Introduction Criteria

The requirements for reintroduction projects are strict. They include the following basic principles:

In agreement with the Berlin city department responsible for environmental protection and green belt maintenance, some 20 extremely endangered species were chosen in 1987 to be multiplied in the Berlin Botanic Garden and to be prepared for later reintroduction (Hagemann & Bley 1991; Hagemann, Vogt & Hömberg 1991). These were plants on the endangered species, or "Red" list of West Berlin in 1987.

Following this decision, our respective scientists and gardeners responsible for species conservation accepted the new assignment. As enough seeds, or in some exceptional cases other plant parts, of the remaining populations were collected, multiplication in the Berlin-Dahlem Botanic Garden began in earnest. Where possible, cultivation was preferably done from seeds so as to retain genetic variability. This was not always feasible, so that sometimes multiplication was first performed with slips and later continued by means of the resulting seeds harvested. In preparation for reintroducion, plant growth during garden cultivation was studied and the results documented.

At the same time, sites for the reintroductions were selected from various potential locations. Obtaining approval from the respective government agencies proved essential in carrying out the programme with a minimum of friction. For example, permission was applied for at the Berlin environmental protection agency when the locations were in the territory where it had jurisdiction. Sometimes a soil analysis at problematic sites had to be obtained from a recognized laboratory to determine the location's suitability. This was mainly limited to the pH value of the upper soil layer and the availability of certain nutrients. Holes were drilled to locate the depth of the water table and in connection with this, an attempt was made to find the causes of the dying out of the species, so as to eliminate, or at least reduce their impact. As a result, certain procedures were sometimes instituted, for example: the suppression of stronger competing species by regular mowing.

In addition, other factors were considered, such as the number of individuals per site, arranging the plants in bed-like rows or planting groups among existing vegetation, directly seeding the area rather than transplanting, and the availability of "safe sites" for the offspring of self-seeding plants after the specimens initially introduced became established. All of these considerations showed that different strategies were necessary for each species and each location. Occasionally a reintroduction failed and then was tried again using a different method. Here our experience showed that, when feasible, as many different ways as possible of reintroducing a species should be attempted simultaneously, in order to compare the effectiveness of each technique directly, since only in this case were temperature and precipitation the same for all methods.

Of great importance in assuring a good rate of growth is selecting the right time to reintroduce the plants. Young specimens should be in the stage of rapid growth; plants which are too old have poor chances. Older individuals should be divided, or new seedlings started. The importance of choosing the right time for planting out is not to be underestimated. In our experience late spring and late summer worked best. The plants must have enough time in late summer to form new roots before temperatures drop sharply, causing root growth to be put on hold. On the other hand, the time that seedlings remain in cultivation in the botanic garden should be held to a minimum to keep the danger of hortification as low as possible.

In our case, the care of reintroduced plants was in the hands of graduate students, who took up the projects as part of research for their doctoral theses. With financial assistance from the department of city management, development and environmental protection, they documented the results of the reintroductions in regular reports and assisted with the necessary caretaking (watering, marking the test locations, studying the plant societies and population biology, supervising the plants and their care, and so on). Special documentation forms were designed for the species to standardize the collection of data.


Now I would like to explain our methodology and the problems arising in the reintroduction of the following four groups of plants:

Annual species

Alyssum alyssoides is ranked in category 1 of the Berlin 1991 endangered species list. It is a winter annual which thrives in Sedo-Scleranthetali societies on nutrient-poor, sandy soil with low water-holding capability. Only a few individuals inhabiting just one location could be found in Berlin. Firstly, plants were raised in the Botanic Garden from seeds collected at the original location, and then seeds taken from a rich harvest in the Garden were sown directly at the site to reinforce the existing population. After this attempt completely failed, seeds were propagated in Jiffypots in the garden, and then in July of 1991 groups of 7-9 seedlings in each pot were planted out in their pots, after they had reached about 5 cm in size, for a total of some 450 plants.

Fig.1 Euphorbia palustris with receptacles to catch the elusive seeds.

Of this number, 30% reached seeding stage, which must be viewed as a success in the case of an annual species. In the fall (autumn) of 1991 there were a large number of seedlings and young plants. In spring 1992 another 400 Jiffypot-propagated individuals were planted in three neighboring sites. Although these were given just two waterings per week, the plants in partly shaded places or in full sun, but with moisture-holding soil, survived the unusually hot summer, while those in sunny, sandy locations died. The sand there had reached temperatures of 60°C.

Appropriate to the seasonal relationships of annual winter species, once again direct sowing in the natural location was tried this past summer (1991) on neighboring sites and precisely marked to obtain further insight and to test the chances of success using this method. It appears to be highly important to try various reintroduction procedures with each species. The sum of our experience to date allows us to conclude that the attempts to strengthen the population of Alyssum alyssoides in its relict location in Berlin can be considered successful.

The pumping out of water and resultant lowering of the water table is responsible for the decline of species in wet areas. Without removing this cause it is not possible to expect a successful reintroduction of species in such places to last over the long-term, as can be shown by various examples where our efforts proved futile. Because an increase in the water table within Berlin's city limits cannot presently be expected, substitute habitats for these species were sought, which gave rise to long discussions over the acceptability of this method. However, because no better alternative presently offered itself, substitute locations were accepted as the best solution available. For some species artificially created biotopes were selected, such as small lakes resulting from the quarrying of sand and gravel, whose banks were planted with native species of the surrounding area; or areas located near the relict habitat were chosen that were comparable from the standpoint of conditions and plant sociology. The results up to now have been good to very good. We agree that resorting to substitute habitats for reintroduction is justified only in extreme emergencies and at best should represent only a temporary solution until conditions in the original location can be restored. Furthermore, detailed documentation of all the various measures taken is highly important.

Perennials in wet habitats

Euphorbia palustris serves as a good example of a perennial in wet habitats. It grows in wet meadows (Filipendulion) and also exists in river bank associations (Convolvuletum). Euphorbia palustris was added to category one on Berlin's "Red" list and now belongs to those species receiving special safeguarding under the German Species Protection Law of 1989.

Fig.2 Euphorbia palustris multiplied in the garden for reintroduction.

Three plants had been taken from the relict location in 1985, and were first multiplied by slips in the botanic gardens. In 1990 and 1991 plants from cuttings were reintroduced, which were well developed but produced a relatively small number of fruits. It is possible that pollinators were lacking at the substitute site chosen.

Collecting seeds in the botanic garden first became possible after we designed special receptacles to catch the elusive seeds (see Fig 1).

They were planted in the garden with the objective of propagating a number of young plants (see Fig 2). Following this, hundreds of seedlings could be grown, of which 200 were planted out for the first time in 1992 on two substitute sites.

They grew well and have already flowered and borne fruits this year. Documenting the self-seeding of these plants will be impossible, however, due to the companion vegetation. Therefore, keeping track of the development of the populations will have to be limited in the following years to counting the number of flowering specimens.

Perennials from dry areas

The sites of several species growing in dry grassland habitats on nutrient-poor soil were so damaged that some species, such as Silene chlorantha, S. otites and Veronica spicata were elevated in 1991 to category one on Berlin's "Red" list and accepted into the species conservation programme at the Botanic Garden. For Silene chlorantha it is possible that the site in the Heiligensee Baumbergen is its furthermost westerly location. The nutrient-poor, dry grassland terrain in these hills with southwest Asian steppe plant elements is a special feature of Berlin but also has significance over a much broader region.

These sites were extensively damaged, primarily by military exercises. Already in 1987 seeds were collected there from the small surviving populations of Silene chlorantha and Veronica spicata. These were cultivated and multiplied in the botanic garden, and despite military manoeuvres, individual plants were added to the original habitats to strengthen the sites' remaining populations. Only after military activity was restricted to one part of the area in 1989 and the site was declared a nature preserve, could larger numbers of specimens be reintroduced. In the fall (autumn) of 1990, 150 individuals of Silene chlorantha were transplanted from the garden to the direct vicinity of the remnant population.

Fig. 3 Silene otites, multiplied in the garden for reintroduction.

The choice of individual places to which to transplant this species proved easy, since gaps in the remaining vegetation supplied enough space. By the summer of 1991, 75 seedlings from self-seeding plants were already established. Some 5000 fruits, each with an average of 80-100 seeds, were counted on the reintroduced plants. One could then conclude that the seed available in the soil had been substantially increased. A further 65 individuals were planted in the fall (autumn) of 1991; 100 more in the fall of 1992. Areas planted on the upper edges of pits or ditches lightly shaded by aspens proved to be the most successful.

Obviously, seeds falling out of the capsules onto the steeply sloping sides free of competing species found especially good conditions, as indicated by the number of rosettes propagated by means of self-seeding plants which added up to about 200.

Development of plantings at the Baumbergen site shows a high rate of progression through self-seeding, indicating the plant to be on the way to permanent re-establishment. This development will be documented in the years to come and, should it be necessary, further plantings added to bolster it.

The Silene chlorantha planted in the garden shows a similar high rate of self-seeding.

Just a few metres away from the remaining Silene chlorantha were the few surviving individuals of Veronica spicata (Borowy 1993). Seeds were also collected from this population and multiplied in the botanic garden for reintroduction.

One hundred seedlings were reintroduced in 1992 for the first time. Watering them twice a week proved sufficient to allow nearly all of them to survive the unusually hot summer, and they have already flowered and produced fruits, more than meeting all our expectations.

In September innovation shoots had been formed with which the plant will pass the winter. To evaluate how well the new plants took root, a few were dug up and examined. This revealed that a richly divided root system with especially numerous, flat-spreading roots had developed.

Fig.4 Silene otites at its site of origin, a year after reintroduction.

In the fall of 1992 a further 150 individuals were planted out. Because of the many gaps in existing vegetation, good conditions should predominate for the young offspring at the original site.

It is interesting to observe the different leaf arrangements that appear to be closely related to growing conditions. The rosette leaves above the soil have petioles and are relatively spread apart, while those on the flowering shoots have no petioles and are much smaller. The latter can curl up into boat-like shapes in very hot weather. Anatomical analyses could surely provide information about the dissimilar constructions of the rosettes and stem leaves. Perhaps the different seasonal growing conditions, dry summer months and wet fall are reflected in the leaf structures.

Similarly to Silene chlorantha, we had good results in the case of a reintroduction of 200 specimens of Silene otites, which had been reduced to just a few individuals at a location on the Windmuhlenberg, a hill in the western part of the city (see Figs 3 and 4).

There we could eliminate the causes threatening extinction, (accumulating dog faeces and heaps of garden waste), by having it designated as an environmental preserve and erecting a fence.

Another 10 species have meanwhile been added to the ongoing reintroduction programme at the Botanic Garden, and are presently being multiplied for later transplanting to their natural habitats.

Starting two years ago, one of our graduate students began to do research on the cultivation of threatened species in the Garden, so that the results could be compared with observations at the relict or substitute sites following future reintroductions.

Annual species from agricultural locations

Annual crop weeds which have largely disappeared in agricultural areas following the use of herbicides and fertilizers, must also be considered endangered in certain regions.

Our program involves Arnoseris minima and Hypochoeris glabra (Borowy 1993), which thrive in sandy fields containing few nutrients, but whose remaining populations are reduced to about 20 individuals.

The cultivation of these species in the botanic garden has been conducted in a manner similar to conditions found in their natural setting. This meant that small areas were prepared similar to agricultural fields and sown with grain crops.

Seeds were collected from the remnant populations and propagated in Jiffypots. Four weeks later the sprouted clusters were transplanted between the rows of grain. In the last two years of garden cultivation of both species we harvested so many fruits that the reintroduction can begin next year.

To assure survival in the original locations it is necessary either to allow part of the farmland to lie fallow, or to cultivate strips around the edges of fields non-intensively, that is, without fertilizers or herbicides. Farmers in Germany receive financial compensation for their loss of profit when they participate in this type of edge-strip cultivation. It is called the "Ackerrandstreifen Programm."

Reinforcement of the populations within the framework of the edge-strip cultivation program will be attempted next year by increasing the occurrence of Arnoseris minima and Hypochoeris glabra through direct sowing and by reintroductions of Jiffypot seedlings.

The measures taken to strengthen Berlin's endangered species populations have had varying degrees of success. Because the habitats supporting moisture-loving species in Berlin have been affected, and the chances for long-term survival following attempted reintroductions must still be regarded as poor, plantings in substitute locations are preferable because they have progressed well up to now. In contrast, the establishment and self-seeding of reintroduced species preferring a dry habitat has proven very successful in their original sites, giving them good chances of survival in the long run. However, a thorough evaluation of the success of these reintroductions will first be possible after 5-10 years.

In every successful case the plants were transplanted to the site with their root balls or in Jiffypots. So far, we have had only poor results with the direct sowing method of reintroduction. Recently, additional species from the area surrounding the city, and from the County of Brandenburg in which Berlin is located, have been brought into the programme, have been propagated and are being multiplied for future reintroductions.

Informing the visitor

An important aspect of the task is informing the garden visitor about these projects. Therefore, we have started providing information about individual species examples in the format of a series entitled, "Endangered Plant Species".

This coming year we will also experiment with placing placards describing our programme at a reintroduction site within the City, so that the attention of passers-by can be drawn to the problem of threatened native species and the efforts being made to save them.