The Schwäbische Alb or Swabian Alb in southern Germany is one of three locations in Germany where, since 2008, huge numbers of scientists have been exploring the relationship between species diversity, land use and their role for ecosystems processes. The German Research Foundation (DFG) is funding these huge open-air laboratories, also known as biodiversity exploratories, from 2006 to 2017.
As the name suggests, exploratories have a more exploratory than descriptive nature. Each of the three open-air laboratories is equipped with a scientific infrastructure and consists of a variety of precisely measured study areas with control and experimental plots and a database. This database is continuously updated with data on the environment, climate, plants and animal diversity and ecosystems processes.
Entomologists, botanists, bat experts and soil ecologists are working hard to understand the complex mechanisms of nature. At a meeting that recently took place at the Haupt- and Landesgestüt Marbach (state-owned stud farm) in the centre of the Swabian Alb Biosphere Reserve, scientists provided information on recent findings to land users such as foresters, shepherds, farmers and nature conservationists.
Each of the three biodiversity exploratories comprises at least 500 square kilometres with around 100 standardised field plots covering manifold management types and intensities in grassland and forests. Forest areas range from intensively used pole wood plantations to uncultivated beech forests with an old stock of trees. Livestock grazing, cutting and fertilisation determine the intensity of land use. At the lower end of the land use scale are dry pastures used by sheep, one-cut and unfertilised meadows, and at the upper end, intensive grassland fields. In addition to the Swabian Alb Biosphere Reserve, the DFG also funds the Schorfheide-Chorin (Brandenburg) Biosphere Reserve and the Hainich-Dün National Park (Thuringia). The exploratories currently serve as joint research platform for 33 institutions involving around 250 students, doctoral students, postdocs, scientists and professors studying various aspects of the relationships between land use, biodiversity and ecosystem processes.
The novelty and uniqueness of the three biodiversity exploratories is due to their large scale and the fact that they are being studied over a period of many years and also cover the entire range of species diversity. Swen Renner, biologist and area manager of the Swabian Alb exploratory highlighted that individual aspects have been studied for quite some time already. However, such studies are usually terminated after around two years, which is far too short a period to obtain valid data. Therefore, it comes as little surprise that data that are collected over longer periods of time come into conflict with established doctrines. Long-term data obtained in the exploratories suggest that the presence of birds does not just depend on a few parameters as many ornithologists believe. Studies of the biodiversity exploratories suggest a “certain inexplicable noise” along with common parameters such as food supply, availability of nesting areas or forest structure. Renner believes that differences in bird species diversity might be either accidental or due to unknown factors. The occurrence of birds cannot be explained by two factors alone; it is far more complex, Renner says.
Although excellent data collected over a period of five to eight years are now available, they are not yet sufficient to identify trends. Ecologists need data series that cover several decades. The number of bird species can differ considerably from one year to another and between land-use types. In the Swabian Alb exploratory, the researchers observed that relatively few bird species were present between 2008 and 2009, that their number doubled over subsequent years, but decreased considerably again over the past two years. The ecologists are now trying to find an explanation for these fluctuations.
The researchers’ work starts with counting and determining; however, the exploratory approach goes further, it wants to explain things, Renner says. And explanations can only be given on the basis of manipulations and experiments: for example, biologists remove a blade of grass on a pasture in order to study the effect of this disturbance on the microfauna and microflora. Small greenhouses in the forest simulate a climatic stress situation (drought). In addition to simple observations, molecular genetic methods are also used for studying complex biological relationships. The technical infrastructure used for such studies is sometimes quite spectacular: drones and aircrafts are used to scan the area with lasers in order to obtain insights into the distribution of plant species in forests.
Renner called for understanding and patience vis-à-vis the scientists’ carefully formulated findings. “We are not just counting species, but also trying to understand the underlying processes.” Ecologists know only too well that their basic research work comes up with answers that are of importance for application-oriented conservationists. However, they refrain from giving recommendations: “We are scientists and as such want to have a reasonable amount of data before making any predictions.”
“Scientists agree that land use is the major reason for the silent disappearance of plants, animals, fungi and microorganisms,” said Steffen Boch, researcher in the Botanical Garden in Berne, Switzerland. In his overview presentation, Boch highlighted the difficulty the researchers are already facing today, i.e. the question as to whether the data from the three exploratories can be transferred to Germany as a whole. Boch is not so sure about this as some of the data from the three sites are quite contradictory. For the Swabian Alb area the researchers found that the more intensively grassland areas are used, the poorer the diversity of plants is. In contrast, other botanists were not able to show the same correlation for the Brandenburg exploratory.
Taking biodiversity as a measure of the success of nature conservation, which some people do, the current data pool on the Swabian Alb forest areas does not paint a very good picture: ecologists found that unused forest areas attracted fewer species than more intensely used forest areas. Studies showed that the greater the man-made disturbance, the greater the amount of light in the forest area and the greater the number of ‘light indicators’. Boch therefore concluded that findings that have been collected for forest areas cannot be transferred to other ecosystems. Beech forests, which are the most common type of forest in Germany, are home to fewer species than beech/spruce forests. Researchers already reached this conclusion when they looked at the species diversity of native tropical rainforests and slightly used ones. Moreover, in contrast to Poland and Scandinavia, Germany does not have any primeval forests; there are possibly some areas where forests have not been used for a period of 200 years, but this is still of course a relatively short period of time. Botanists have observed in all three exploratories that slight variations in the extensive use of land leads to an increase in the number of different organisms.
Prof. Dr. Nico Blüthgen from Darmstadt Technical University talked about biodiversity and factors that possibly lead to the reduction of biodiversity in the three locations. In 2007, biologists counted 105 types of flower, 586 insects and 18,746 animal-plant interactions on a grassland area 600 square metres in size. The numbers were even higher in 2008.
Flies account for the largest number of pollinating insects, followed by bees and other hymenopterous insects like butterflies. The Swabian Alb, where the researchers identified 24 bumblebee species, 104 beetle species and 50 butterfly species, has the highest biodiversity of all three German exploratories.
Previous studies of Swabian Alb grassland areas with different use intensity came up with the following findings: butterflies, beetles and bees are the great losers of intensive land use. Or put more generally: insects that pollinate only specific plants disappear as a result of intensive land use. However, a first, purely quantitative look at the situation is deceptive; in contrast to what most people would expect, biodiversity remains practically the same as the number of pollinating fly species (e.g. hoverflies) increases and therefore compensates for the loss of other insect species. Blüthgen concluded that it is mainly bees and butterflies that suffer from intensively used grasslands as insect magnets such as bellflowers and thistles disappear from heavily fertilised grassland areas.
Nadja Hersacher from the Department of Terrestric Ecology at Munich Technical University talked about spiders and other insects. She reported that although 486 insect and spider species of the Swabian Alb exploratory meadows and pastures being studied are on the Red List, the greater proportion of species identified is not endangered. Hersacher has been in charge of monitoring arthropods, in particular insects and spiders, in all the grassland and forest experimental plots of the tree exploratories since 2008. It is extremely hard work to catch and collect spiders, harvestmen, bugs, cicadas, beetles and grasshoppers and include information about them into species databases. Hersacher found that while the number of individuals differed only slightly between the three different regions, major differences were observed in the diversity of species between the three regions.
Kirsten Jung from the Institute of Experimental Ecology at the University of Ulm reported on the first standardised collection of information on bats in Europe (since 2008). All 1,200 bat species in Germany are perfectly adapted to their habitats, including Pipistrellus pipistrellus, a small bat species that is relatively common in the Swabian Alb biodiversity exploratory.
Jung was proud to be able to report that her team has collected a vast amount of data and is now able to predict the occurrence of bats in the Swabian Alb exploratory.
Few biodiversity differences were observed in forest and grassland areas. The Swabian Alb biodiversity exploratory has the lowest number of bat species of the three areas (identified with acoustic tracking). Land and soil use have a direct impact on the winged mammals. The researchers counted a larger number of bats in areas with a higher number of insects (e.g., meadows, mineral-containing or peaty soils).
Jung reported that landscape structures such as forest area, hedges, single trees and water areas are of major importance for bats. The researchers gained this knowledge using laser-assisted drones that collected three-dimensional information on the structure of the forest. They found that the typical Swabian Alb bat was hardly ever found in open areas; this particular bat species prefers to hunt close to forests.
Soil ecologist Stefan Scheu from the University of Göttingen shed light onto the darkness of soil food webs. Around 900 different species can be found on a cubic centimetre of soil, including fungal hyphae, bacteria, protozoa, nematodes, mites and springtails. Using carbon and nitrogen isotope measurements in the soil of beech forests, Scheu investigated the nutrient pathway of the different organisms.
Prior to Scheu’s investigations, the commonly held belief was that the underground network of decomposers fed largely on the leaf input into the soil. However, Scheu found out that it was fungi on tree roots that represent the major part of the underground food resources of the decomposers rather than the nutrient-poor leaves.
The fact that biodiversity also has an economic value has recently become fairly obvious through the decimation of the bee population, which can lead to major issues for the agricultural industry as there will not be enough bees to pollinate crops. It is not yet known whether the DFG will continue to fund the three biodiversity exploratories beyond 2017. However, Prof. Dr. Manfred Ayasse is sure that the studies have already led to a huge increase in knowledge and many papers have been published in renowned scientific journals. Manfred Ayasse is the director of the Institute of Experimental Ecology at the University of Ulm, which is one of several scientific core institutions involved in the biodiversity exploratories.