Every day up to 130 biological species go extinct on our planet. This extinction rate is by a
factor of 1000 higher than rates derived from the fossil record. At the same time, human
activity promotes the spread of alien species across the globe. How are ecosystem functions
influenced by the loss or addition of species? How does the presence or absence of particular
species or functional groups affect biogeochemical cycles? To what extent are these effects
mediated or even aggravated by climate-driven shifts in disturbance regimes? The group
‘Organismic Biogeochemistry’ addresses these questions by compiling and analyzing global
databases of functional plant traits and ecosystem properties. We closely collaborate with the
earth system modeling community and we also carry out field experiments and surveys in
Siberia, China, and Germany.
The work of the three focus groups presented below explores the impact of species diversity
and identity effects on biogeochemical cycles, vegetation changes and ecosystem behavior at
scales relevant in the context of global climate change.
Focus group 1: The role of plant functional diversity in the earth system (Jens Kattge,
Gerhard Boenisch, Stefanie Nöllert, Ulrike Stahl, Katherina Pietsch): Plant functional traits,
like leaf photosynthetic capacity, maximum plant height, or maximum rooting depth are key
features to understand the distribution and migration of plants, their interaction with
competitors and their impact on ecosystem functions. Many ecosystem and earth system
models employ functional traits as parameters, but modelers are still far from fully exploiting
the wealth of available botanical information. We connect the respective scientific
communities with the goal to efficiently (and correctly) channel plant ecological information
into earth system models. To this end we devise database tools and new statistical methods for
trait analysis.
We have developed a novel, generic database structure, which facilitates the consistent
compilation of plant functional traits together with the biotic and environmental variables that
influence them. Based on this new database structure the OBG group is realizing two
international projects: The FET (Functional Ecology of Trees) project is focused on tree
physiology, community and ecosystem ecology. The TRY initiative (www.try-db.org, with
more than 2.5 Million trait entries for over 60,000 plant species) is a communal effort to
merge existing plant trait databases in one consistent database hosted at the MPI in Jena. The
aim is to make these data available for the development of a new generation of terrestrial
ecosystem models. Deriving model parameters from plant traits and dealing with the
numerous interdependencies requires new statistical tools. We apply and develop inversion
techniques and Hierarchical Bayesian models. Typical results, that have also been applied in a
global models, are that differences in fire adaptation strategies in boreal trees lead to different
fire regimes in North America and Siberia; maximum photosynthetic rates in tropical trees are
much lower than previously thought with important consequences for climate predictions;
different functional groups of trees differ substantially in their wood decay rates with
important consequences for carbon storage and fire regimes.
Focus group 2: Synthesis of biodiversity experiments (Raphael Proulx, Karin Nadrowski,
Tanja Reinhold) Apart from the fascination of biological diversity, the functional significance
of biodiversity may be vital for sustaining ecosystems under climate change. Biodiversity
experiments offer the opportunity to test specific hypotheses regarding biodiversity and
ecosystem functioning that cannot be addressed in natural systems. Given the unprecedented
changes in environmental conditions, the understanding gained from biodiversity experiments
may enable us to not only react to changes, but to manage ecosystems in a previsional way.
We are currently involved in two large-scale diversity experiments, the Grassland
Biodiversity Experiment in Jena, Germany (the largest of its kind) and the BiodiversityEcosystem Functioning (BEF) Experiment in China (the first in the subtropics and on
complex terrain). Our research concentrates on synthesis and the model-based merging of the
data and understanding gained in thesesexperiments. For example, we are involved in the
development of a grassland model of the carbon and nitrogen cycle that accounts for plant
physiology and architecture in order to explore the mechanisms underlying the relationship
between species diversity and ecosystem functioning. Based on more than 400 variables
related to 12 ecosystem functions we found evidences that plant species diversity stabilizes
multiple ecosystem functions by making them less susceptible to environmental fluctuations
in time.
Focus group 3: The imprint of succession and disturbances (Susanne Tautenhahn, Veronika
Jäger, Angela Nüske, Anja Fankhänel, Henrik Hartmann). Succession describes how plant
communities and ecosystems develop and mature over time and it unfolds as a consequence
of plant-plant, plant-animal and plant-environment interactions. Depending on their severity,
disturbances may reset succession to earlier stages or modify the successional pathways.
Understanding the mechanisms of succession is therefore pivotal to predict vegetation
dynamics in a changing world. Global vegetation models try to incorporate these mechanisms,
but are still in their infancy. We carry out fieldwork to study the impact of disturbances on
successional processes and biogeochemical cycles in different forest ecosystems of the world.
In Siberia we are exploring the question whether increasing sizes of wildland fires may induce
a switch from conifer to broadleaved vegetation with important, albedo-driven, consequences
for vegetation-climate feedback. In subtropical China we study whether tree species diversity
reduces the susceptibility towards snow-break and thus reduces carbon losses from tree
mortality. In Germany we are measuring and modeling the impact of selective herbivory by
roe deer on forest regeneration and the long-term consequences for forest diversity and carbon
stocks. In a recent book project we could show that old-growth forests that occur late in
succession are still capable of sequestering appreciable amounts of carbon.
Portrait of the Group Leader: Christian Wirth is a plant ecologist by training and received
his PhD at the University of Bayreuth. He worked as a postdoc in Jena, Princeton, Fairbanks,
and Krasnoyarsk. His main interests: linking species diversity and biogeochemical cycles,
vegetation dynamics, disturbance ecology and the functioning of global forest vegetation.
With his independent junior research group “Organismic Biogeochemistry” he thrives to
reach a good balance between fieldwork, meta-analysis and modeling.
Global coverage of plant functional traits in the TRY database.