Research
Research topics:
Primeval forest research and ecological effects of forest management
Global climate warming and its impact on ecosystems
Climate warming and land use in Central Asia
Anthropogenic element inputs
Diversity and ecology of lichens, bryophytes, and fungi
Nature conservation
Primeval forest research and ecological effects of forest management
Forests represent the dominant vegetation type in the temperate belt as well as in the humid subtropics and tropics. This includes Central Europe, where many sites would be dominated by European beech in the absence of human disturbance. Accordingly, forest ecosystems play a pivotal role for conserving global biodiversity. Forests also have important ecosystem functions, including the regulation of the heat and water balance on the landscape level or the sequestration of organic carbon, which is highly significant for the protection of the global climate.
Humans have removed most of the global forest area more or less from its original state by land use activities and disturbance. The most direct impact is exerted by timber harvesting and the initiation of changes in the tree species composition in the course of forest management. In addition, vast forest areas were lost due to deforestation – in Central Europe starting in the Neolithic, in many other regions continuing until today.
We are interested in how humans influence the structure, dynamics, biodiversity, and ecosystem functions of forests and investigate this in forests differing in land use intensity.
Remnant of primeval spruce (Picea abies) forest on Mt. Brocken in the Harz Mountains, Germany
Global climate warming and its impact on ecosystems
Global warming has effects on the biodiversity and functioning of ecosystems across all biomes on earth. Since the mid twentieth century, manifold changes have occurred in the distribution and dominance of species as well as the productivity of ecosystems, which are attributable to climate warming. Increased tree mortality and reduced forest regeneration are typical consequences of climate change in forested regions, which can ultimately lead to deforestation.
Climate warming is particularly strong in the Arctic and the adjacent boreal forest region as well as in maritime Antarctica. However, there is also a strong impact in the temperate belt and even in the wet tropics. In Central Europe, climate warming affects, aside from the vegetation of high mountains, most notably the productivity and vitality of European beech (Fagus sylvatica) and Norway spruce (Picea abies) and thus the quantitatively most important tree species.
We work on the effects of climate warming on plant diversity and the productivity of ecosystems. A key aspect of our research is the study of climate warming effects in forest ecosystems, where we analyze stemwood increment, forest regeneration, and tree mortality in response to climate using dendrochronological methods. Applying ecophysiological tools, we investigate the mechanisms behind climate warming effects on plants.
Trends in the annual stemwood increment of European beech (Fagus sylvatica) at two sites in Baden-Württemberg, Germany. In the Odenwald (on the graph to the left), the increment decreases due to increased summer drought as the result of climate warming. At higher elevations of the Black forest with ample water supply, beech is benefitting from increasing temperatures resulting in increased stemwood increment. Sites with reduced increment are generally more widespread than sites with increasing productivity. After Dulamsuren et al. in Trees 31: 673-686, 2017.
Climate warming and land use in Central Asia
Central Asia is coined by its highly continental climate with hot summers, extremely cold winters and mostly low and variable precipitation. Large parts of the region are characterized by steppe vegetation, whereas the drier parts are desert and semidesert. In addition to forests in mountains, floodplains and oases, the southernmost extensions of the Siberian taiga extend into the north of Central Asia.
Central Asia and southern Siberia belong to the most rapidly warming regions on earth. Radical economic changes as the result of the breakdown of the Soviet Union as well as population growth are additional key factors determining the basic conditions of Central Asia’s ecosystems.
We study the biodiversity and functioning of forest and grassland ecosystems in Central Asia. So far, our geographical focus was on Mongolia, Kazakhstan, Kyrgyzstan, and the Tibetan Plateau. In addition to biodiversity studies, we work with dendrochronological and ecophysiological methods in Central Asia and on estimates of the organic carbon pools of forest and grassland ecosystems. Furthermore, we are interested in the socioeconomics and socioecology of traditional land use, including pastoral nomadism, in Central Asia.
Mobile livestock herding in the forest-steppe of the Mongolian Altai
Anthropogenic element inputs
In addition to climate warming and land use, element inputs from the atmosphere represent an important factor causing change in ecosystems and influencing the distribution of plant species. While sulfur dioxide was the dominant pollutant causing ecological damage in Central Europe until the late twentieth century, resulting in forest dieback, soil acidification, and the decline of epiphytes, today the deposition of atmospheric nitrogen is of outstanding significance. The increased deposition rates of reactive nitrogen primarily derive from anthropogenic emissions from fossil fuel combustion and agriculture.
Moderate increases in nitrogen deposition stimulate vegetation productivity, but discriminate against oligotrophic species and cause shifts in the dominance of individual species. High loads of reactive nitrogen lead to eutrophication and thus the extinction of species and interfere with ecosystem functions. Our research interests include the effects of nitrogen deposition on biodiversity, the vitality of plants, the productivity of ecosystems and on litter decomposition.
Diversity and ecology of lichens, bryophytes, and fungi
In addition to vascular plants, lichens, bryophytes, and fungi represent a major part of the biodiversity of ecosystems and play important functional roles. Bryophytes and especially lichens representing autotrophic organisms or symbiotic communities avoid the competition of the faster-growing vascular plants by colonizing sites that are extreme in terms of climate or nutrient relations. Fungi play an important role in the decomposition of litter and deadwood. Mycorrhizal fungi support the nutrient and water uptake in vascular plants.
We focus on effects of land use (and forest management in particular), eutrophication, climate warming, acidic air pollutants, and heavy metals on the diversity of lichens, bryophytes, and fungi and their functional roles in ecosystems. In the case of lichens, we are also interested in research on taxonomy, distribution, and ecophysiology. In the field of chemical ecology, we study the function of secondary metabolites (lichen substances), from which lichens form several hundred different substances and the natural occurrence of which is mostly restricted to the lichen symbiosis.
Evernia mesomorpha, a boreal epiphytic lichen species typical for continental climate
Nature conservation
Many of our research topics are related to nature conservation. This is true for studies on effects of forest management, forest pasture and land use in non-forested ecosystems. In addition to the analysis of anthropogenic disturbance, which affects the species diversity and species composition of the vegetation, we are also interested in the quantification of changes in the vegetation over multidecadal or centennial scales. As a link to the application of scientific results, we also contributed to the compilation of Red Lists of threatened species.