Ian R. Noble

Recent patterns and mechanisms of carbon exchange by terrestrial ecosystems

Knowledge of carbon exchange between the atmosphere, land and the oceans is important, given that the terrestrial and marine environments are currently absorbing about half of the carbon dioxide that is emitted by fossil-fuel combustion. This carbon uptake is therefore limiting the extent of atmospheric and climatic change, but its long-term nature remains uncertain. Here we provide an overview of the current state of knowledge of global and regional patterns of carbon exchange by terrestrial ecosystems. Atmospheric carbon dioxide and oxygen data confirm that the terrestrial biosphere was largely neutral with respect to net carbon exchange during the 1980s, but became a net carbon sink in the 1990s. This recent sink can be largely attributed to northern extratropical areas, and is roughly split between North America and Eurasia. Tropical land areas, however, were approximately in balance with respect to carbon exchange, implying a carbon sink that offset emissions due to tropical deforestation. The evolution of the terrestrial carbon sink is largely the result of changes in land use over time, such as regrowth on abandoned agricultural land and fire prevention, in addition to responses to environmental changes, such as longer growing seasons, and fertilization by carbon dioxide and nitrogen. Nevertheless, there remain considerable uncertainties as to the magnitude of the sink in different regions and the contribution of different processes.

On the direct effect of clouds and atmospheric particles on the productivity and structure of vegetation

The volume of shade within vegetation canopies is reduced by more than an order of magnitude on cloudy and/or very hazy days compared to clear sunny days because of an increase in the diffuse fraction of the solar radiance. Here we show that vegetation is directly sensitive to changes in the diffuse fraction and we conclude that the productivity and structure of vegetation is strongly influenced by clouds and other atmospheric particles. We also propose that the unexpected decline in atmospheric [CO2] which was observed following the Mt. Pinatubo eruption was in part caused by increased vegetation uptake following an anomalous enhancement of the diffuse fraction by volcanic aerosols that would have reduced the volume of shade within vegetation canopies. These results have important implications for both understanding and modelling the productivity and structure of terrestrial vegetation as well as the global carbon cycle and the climate system.

Sustainable development goals for people and planet

Planetary stability must be integrated with United Nations targets to fight poverty and secure human well-being, argue David Griggs and colleagues.

Predicting the multiple pathways of plant succession

Classical concepts view succession as a deterministic, mechanistic regeneration of the disturbed community, and thus have limited applicability to fire-prone ecosystems, A recently developed multiple pathway succession model appears to have more realism and applicability in frequently disturbed ecosystems. It includes a set of species-specific attributes that are vital to reproduction and survival, and permits variable succession pathways depending on the stands age (and thus species composition) when disturbed. Examples from Australia and the northern Rocky Mountains (USA) are presented, as are approaches to refining and improving the model.

A MODEL OF THE RESPONSES OF ECOTONES TO CLIMATE CHANGE

It has been suggested that global climatic change may be detected by monitoring the positions of ecotones. I built a model of the dynamics of ecotones similar to those found in altitudinal or latitudinal treelines, where a slow tendency for the ecotone to advance is counterbalanced by disturbances such as fire or landslides. The model showed that the response of such ecotones to a wide range of simulated climate changes was slow and that the ecotone front was dissected. It would appear that such ecotones would not make suitable sites for monitoring climate change.

An individualistic model of vegetation stand dynamics

FATE (Functional Attributes in Terrestrial Ecosystems) is a new, general model of vegetation dynamics which is based on a model of the functioning of individual plants in a stand. It has been designed to predict vegetation dynamics with a low resolution and from a simple parameter set. This makes it suitable for use by managers of extensive natural areas. FATE also provides age structure information about communities. We have divided plant function into three main areas (life history, responses of plants to their immediate environment and their responses to natural disturbance), and built the FATE model by constructing a simple representation of essential features of each of these processes. Examples from Australian forest and woodland communities are used to demonstrate the operation of the model and to compare it withother modelling approaches. The limitations of FATE and possible extensions are also discussed.

An integrated framework for sustainable development goals

The United Nations (UN) Rio+20 summit committed nations to develop a set of universal sustainable development goals (SDGs) to build on the millennium development goals (MDGs) set to expire in 2015. Research now indicates that humanitys impact on Earths life support system is so great that further global environmental change risks undermining long-term prosperity and poverty eradication goals. Socioeconomic development and global sustainability are often posed as being in conflict because of tradeoffs between a growing world population, as well as higher standards of living, and managing the effects of production and consumption on the global environment. We have established a framework for an evidence-based architecture for new goals and targets. Building on six SDGs, which integrate development and environmental considerations, we developed a comprehensive framework of goals and associated targets, which demonstrate that it is possible, and necessary, to develop integrated targets relating to food, energy, water, and ecosystem services goals; thus providing a neutral evidence-based approach to support SDG target discussions. Global analyses, using an integrated global target equation, are close to providing indicators for these targets. Alongside development-only targets and environment-only targets, these integrated targets would ensure that synergies are maximized and trade-offs are managed in the implementation of SDGs.

A critical overview of model estimates of net primary productivity for the Australian continent

Net primary production links the biosphere and the climate system through the global cycling of carbon, water and nutrients. Accurate quantification of net primary productivity (NPP) is therefore critical in understanding the response of the worlds ecosystems to global climate change, and how changes in ecosystems might themselves feed back to the climate system.

A FOREST SIMULATION MODEL FOR PREDICTING EUCALYPT DYNAMICS AND HABITAT QUALITY FOR ARBOREAL MARSUPIALS

A forest simulation model (called EDEN) of eucalypt dynamics in southeastern Australia is presented to predict habitat quality for arboreal marsupials. The model is presented as a tool for testing alternative hypotheses of forest management in the study area. EDEN uses a forest gap simulation (JABOWA/FORET type) model as a pattern generator of habitat in different landscape positions and under different harvesting regimes and predicts the habitat quality of this habitat for arboreal marsupials. Application of the model is illustrated by simulating four environmental scenarios (gullies and ridges, at low and at high soil nutrient levels) and three harvesting regimes for each environmental scenario (no harvesting, low-intensity harvesting, and high-intensity harvesting). The changes in tree species composition and diversity and the changes in habitat quality for the arboreal marsupials are presented for the 12 scenarios. The predicted vegetation composition is different in the different environmental scenar...

Interactions between tussock grass (Poa spp.) and Eucalyptus pauciflora seedlings near treeline in South-Eastern Australia

SummaryObservations of tussock grasses (mainly Poa species) and tree seedlings (Eucalyptus pauciflora) growing near treeline suggested that the tussocks may physically protect and compete with the tree seedlings. An analysis of nearest neighbour data from sites burnt in 1972–3 showed the there is a minimum separation between seedlings and tussocks, indicating that competition is taking place. Correlation and principal components analyses show that seedlings growing close to tussocks tend to be taller, with fewer stems and leaves than those growing further away. This same trend from tall, few-stemmed individuals to shorter multistemmed individuals also occurs with an increase in altitude. It is concluded that the trend in habit is related to exposure to environmental extremes. The concept of the regeneration niche and its application to E. pauciflora seedlings is discussed.