Part III

The previous chapters focused on plants (Part I: Molecular Ecology) and their reactions to (mainly) the environment (Part II: Physiological and Biophysical Plant Ecology), but plants do not grow in isolation. They interact with each other as well as with microorganisms and animals, they rely on carbon dioxide, water and nutrients, and they are affected by climatic conditions, disturbances and by land management. Plants can even shape their environment. Supporting Lovelock’s original Gaia hypothesis (1979), which in parts has been adopted in Ecology and Earth System Science, the biosphere affects certain properties of the abiotic environment, for example the Earth’s temperature and oxygen concentrations. All these interactions take place at the site (or habitat) where plants grow, where they reproduce and where they die: in an ecosystem. A terrestrial ecosystem includes the soil, microorganisms (both in the soil and aboveground), vegetation and animals as well as the lower level of the atmosphere, all interacting with each other. Terrestrial ecosystems are functional units in a given heterogeneous landscape and are present in all climatic zones, ranging from tropical forests to arctic tundra. Their size ranges from a couple of square metres, for example a dwarf heather ecosystem at alpine elevations, to a couple of square kilometres, for example a uniform agricultural field or a boreal coniferous forest. In any case, terrestrial ecosystems are the functional unit where biogeochemical processes happen, such as nitrogen mineralisation, where these processes provide the necessary inputs, such as plant available nitrogen forms, to ensure plant performance, such as growth, and where organisms compete with each other and interact with their environment. In addition, terrestrial ecosystems must also be considered thermodynamically “open” ecosystems, where water and nutrients get lost, for example as emissions to the atmosphere or via leaching and run-off, thereby also affecting the environment. Terrestrial ecosystems are also the management unit that agriculture and forestry use (Part V: Global Ecology). Thus, terrestrial ecosystems are the organisational unit where processes such as primary productivity and water use need to be understood to predict the impacts of natural and anthropogenic disturbances on the provisioning of services, such as food and timber production.

The science of (terrestrial) ecosystem ecology has grown considerably over the last several decades. Various scientific approaches are being used, ranging from classical observations to manipulation experiments, from plot to continental scales, from empirical or statistical modelling to dynamic vegetation models combined with biogeochemistry models. Over the last several decades, measurement techniques used in ecosystem ecology have been developed and improved tremendously, adding techniques from formerly neighbouring disciplines as well, nowadays for example including high-tech systems to measure biospheric-atmospheric greenhouse gas fluxes and their isotopic signatures as well as remote sensing techniques used on airborne platforms or at tall towers. Terrestrial ecosystem ecology draws on many disciplines, from soil science and hydrology, microbiology, animal and plant sciences to meteorology and atmospheric sciences. However, the link between community ecology (Part IV; mainly focusing on environmental effects on communities and community dynamics) and ecosystem ecology (mainly focusing on pools and fluxes) has only developed over the last decade, triggered by the wish to understand how species and communities, affected by environmental change, in turn affect ecosystem processes and services. Thus, ecosystem ecology is truly interdisciplinary, that is scientists from different disciplines work together to jointly address their research objectives. Sometimes ecosystem scientists even reach out to stakeholders, such as farmers, foresters, nature conservationists or politicians, and therefore ecosystem ecology has become transdisciplinary.

Here we will focus on terrestrial ecosystems, neglecting aquatic ecosystems on land, such as rivers or lakes (i.e. freshwater systems). We will consider managed and unmanaged ecosystems, the latter sometimes erroneously called “natural” ecosystems, although most ecosystems on Earth are managed in one way or another, from agricultural production to protection for nature conservation. Furthermore, all ecosystems are affected by environmental and human drivers, independent of management. Thus, we must realise that all global ecosystems are affected by human activities, even very remote ones (Part V). We will first explain the concept of an ecosystem and describe the characteristics of a terrestrial ecosystem as functional, not as hierarchical unit (Chap. 13: Ecosystem Characteristics). Then different approaches will be illustrated that are used to study terrestrial ecosystems, and insights into representative ecosystem studies will be given (Chap. 14: Approaches to Study Terrestrial Ecosystems). We will then give an overview about ecosystem modelling (Chap. 15: Approaches to Model Processes at the Ecosystem Level). Finally, a process-oriented view will be adopted, and selected biogeochemical fluxes into, within and out of terrestrial ecosystems will be discussed, such as those of water, carbon and nitrogen, as well as nutrients (Chap. 16: Biogeochemical Fluxes in Terrestrial Ecosystems).

Reference

Lovelock JE (1979) Gaia: a new look at life on earth. Oxford University Press, Oxford