Endangered plant species in Berlin's modified ecosystems
The Hans-Baluschek-Park near Schöneberger Südgelände in Berlin. Photo: Greg Planchuelo
Endangered plant species in Berlin's modified ecosystems
Author: Esther Felgentreff, TU Berlin
It is well known that cities have a wide variety of habitats and are home to many plant species. Species threatened with extinction also occur in cities. The first thing that comes to mind when thinking about this is probably places that are as „natural“ as possible, spots that – at least in comparison – still seem quite untouched. But is that true at all? Do endangered species really only occur in these so-called remnant habitats?
What has actually not yet been studied on a large scale is the extent to which altered urban ecosystems can be important habitats for endangered plant species. This is something that Greg Planchuelo has been working on in recent years as part of his doctoral thesis at the Technical University of Berlin in the Department of Plant Ecology and Ecosystem Science, and he has provided some exciting insights.
Following the concept of ecosystem novelty, habitats can be divided into three categories according to the degree of human intervention: largely unaltered remnant habitats; hybrid ecosystems that have already been altered from their historical state, but can still return to it; and novel ecosystems that have been intensively altered and cannot return to their historical state.
Conservation efforts in cities have traditionally focused on remnant habitats. However, in urban areas in particular, these make up only a small percentage of the land area: there are many more hybrid and novel ecosystems.
Greg Planchuelo therefore wanted to take a closer look at the role of different ecosystems in the occurrence of endangered plant species in Berlin. To do this, he formulated three research questions: (1) To what extent do urban ecosystems with varying degrees of ecological novelty harbor endangered plant species?
(2) To what extent are populations of endangered plant species dependent on remnant habitats, i.e., is there a spatial relationship?
(3) And what factors drive the survival of populations of endangered plant species?
To answer these questions, he mainly used three data sets from Berlin: First, a long-term monitoring dataset with the location of more than 1700 populations of endangered plant species. Second, a biotope map in which the many ecosystems of Berlin were precisely categorized into nine biotope classes (for example, forests, grasslands, water areas, sealed surfaces, etc.). And thirdly, an ecological novelty map showing the degree of ecological novelty of more than 7500 biotope types. 77% of Berlin’s area was assigned to the novel category, 16% hybrid, and only 7% were remnant habitats.
To answer the first question – to what extent urban ecosystems with different degrees of ecological novelty harbor endangered plant species – the dataset with the location of populations of endangered plants was spatially combined with the ecological novelty map. The surprising result: novel ecosystems have the most populations of endangered species. Remnant habitats, however, have the highest density of populations, so significantly more populations occur there per km2 than in novel or hybrid ecosystems.
He also found that a quarter of all species were found in all 3 „novelty categories,“ but nearly half of all species occur in only one of the three categories. It can be concluded that each novelty category has its own specific species composition – and thus all ecosystems in all three categories are important for the conservation of endangered plant species.
This indicates that not only do remnant habitats provide homes for endangered plant species, but that novel and hybrid ecosystems play at least as important a role in this regard. Especially in the case of novel ecosystems, this arguably represents quite a paradigm shift: who would have thought, for example, that grassland areas such as the Tempelhofer Feld or spontaneously vegetated wastelands could support significant populations of endangered plant species?
One of the conclusions that emerges from Greg Planchuelo’s work is thus: not only remnant habitats are worth protecting, but also hybrid and novel ecosystems, and these should therefore be considered in conservation approaches.
For the second question – is there a spatial link between endangered plant species and remnant habitats? – spatial dependance analyses were performed between the location of populations of endangered plants and the location of remnant ecosystems. It was found that populations of endangered plants tend to cluster in close proximity to remnant habitats. Nonetheless, populations in novel ecosystems do not follow this rule and thus are not spatially dependent on remnant ecosystems. In turn, it can be theorized that there is no direct species exchange between remnant and novel ecosystems, and that any exchange between the two has to happen through hybrid ecosystems, that could be acting as “stepping stones”. Thus, all three categories are interconnected indirectly, where remnant ecosystems act as a source of these species into the city through a source-sink dynamic and where independent meta-communities exist in novel ecosystems. Various factors, for example the mode of dispersal of a plant, play a role in the exchange between habitats.
For question 3 – factors influencing the survival of endangered species – he used data on the survival of the populations of endangered species over an average period of 7.6 years. It was found that only 65 % of the populations originally mapped had survived. A statistical model was then used to examine factors that might have influenced survival. One factor that significantly reduces the likelihood of survival is a high percentage of sealed area near the population. A positive effect is a short distance to the nearest remnant habitat, which confirms the results from the second question. Furthermore, differences between different habitat types could be found – surprisingly, the survival rate was lowest in forests. Since Berlin’s forests are under protection, this is alarming. In contrast, survival rates were highest in anthropogenic biotopes such as green spaces and built-up areas, although the lowest species numbers were found in these areas. This could be explained by the fact that species in these places are already well adapted to urban conditions. Thus, it could be promising to (re)introduce selected species to grasslands. Grasslands had the second highest number of populations and an intermediate survival rate. Interventions with regional seeds could support populations here.
In terms of plant species characteristics, species requiring high soil moisture were found to be at high risk of extinction – A consequence of Berlin’s dry soils combined with several summers of drought.
Overall, the studies probably showed above all the great potential of urban habitats – even away from historical remnant habitats – for endangered plant species.
Planchuelo, G., von Der Lippe, M., & Kowarik, I. (2019). Untangling the role of urban ecosystems as habitats for endangered plant species. Landscape and Urban Planning, 189, 320-334.
Planchuelo, G., Kowarik, I., & von der Lippe, M. (2020). Endangered plants in novel urban ecosystems are filtered by strategy type and dispersal syndrome, not by spatial dependence on natural remnants.
Planchuelo, G., Kowarik, I., & von der Lippe, M. (2020). Plant traits, biotopes and urbanization dynamics explain the survival of endangered urban plant populations. Journal of Applied Ecology, 57(8), 1581-1592.