John Grace

Tropical forests and atmospheric carbon dioxide

Tropical forests play a major role in determining the current atmospheric concentration of CO2, as both sources of CO2 following deforestation and sinks of CO2 probably resulting from CO2 stimulation of forest photosynthesis. Recently, researchers have tried to quantify this role. The results suggest that both the carbon sources and sinks in tropical forests are significantly greater than previously thought.

Carbon dioxide transfer over a Central Amazonian rain forest

Tropical rain forests are among the most important and least monitored of terrestrial ecosystems. In recent years, their influence on atmospheric concentrations of carbon dioxide and water vapor has become the subject of much speculation. Here we present results from a yearlong study of CO2 fluxes at a tropical forest in central Amazonia, using the micrometeorological technique of eddy covariance. The diurnal cycle of CO2 flux was consistent with previous short-term studies in tropical rain forests, implying that the Amazonian rain forest shows a fair degree of spatial uniformity in bulk ecophysiological characteristics. Typical peak daytime photosynthesis rates were 24–28 μmol CO2 m−2 s−1, and respiration rates were 6–8 μmol CO2 m−2 s−1. There was significant seasonality in peak photosynthesis over the year, which appeared strongly correlated with soil moisture content. On the other hand, there was no evidence of strong seasonality in soil respiration. Central Amazonia has only a short, 3-month dry season, not atypical of tropical rain forest, and it is therefore likely that large areas of Amazonia exhibit significant seasonality in photosynthetic capacity. The gross primary production was calculated to be 30 t C ha−1 yr−1. An analysis of data quality is included in the appendix.

Biogeochemical cycling of carbon, water, energy, trace gases, and aerosols in Amazonia: The LBA-EUSTACH experiments

The biogeochemical cycling of carbon, water, energy, aerosols, and trace gases in the Amazon Basin was investigated in the project European Studies on Trace Gases and Atmospheric Chemistry as a Contribution to the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA-EUSTACH). We present an overview of the design of the project, the measurement sites and methods, and the meteorological conditions during the experiment. The main results from LBA-EUSTACH are: Eddy correlation studies in three regions of the Amazon Basin consistently show a large net carbon sink in the undisturbed rain forest. Nitrogen emitted by forest soils is subject to chemical cycling within the canopy space, which results in re-uptake of a large fraction of soil-derived NOx by the vegetation. The forest vegetation is both a sink and a source of volatile organic compounds, with net deposition being particularly important for partially oxidized organics. Concentrations of aerosol and cloud condensation nuclei (CCN) are highly seasonal, with a pronounced maximum in the dry (burning) season. High CCN concentrations from biomass burning have a pronounced impact on cloud microphysics, rainfall production mechanisms, and probably on large-scale climate dynamics.

Plant-atmosphere relationships.

1 Conditions for life.- 1.1 Radiant energy.- 1.2 The atmosphere.- 2 Radiation coupling.- 2.1 Introduction.- 2.2 Plant responses to light.- 3 Coupling through boundary layers.- 3.1 Electrical analogues.- 3.2 Coupling through resistance chains.- 3.3 Physiologically-influenced resistances.- 3.4 Micrometeorological stomatal resistance.- 4 Heat and water exchange at plant surfaces.- 4.1 Introduction.- 4.2 Energy balance.- 4.3 Calculations.- 5 Field observations.- 5.1 Structure of vegetation.- 5.2 Vegetation height.- 5.3 Leaf survival and design.- Appendix 1 Specific heats.- Appendix 2 Physical constants.- Appendix 3 Thermocouple data.- Appendix 5 Saturated vapour pressure and black body radiation.- Appendix 6 Useful formulae.- Appendix 7 Symbols and abbreviations.- Appendix 8 Units.- Appendix 9 Metric multiples and submultiples.- References.

Greenhouse gas sinks

Bringing together leading researchers from around the world, this book reviews how vegetation and soils act as naturally occurring buffers which use up the gases responsible for global warming and the greenhouse effect. It provides in-depth information on the importance of these sinks, how they may respond to increased greenhouse gas emissions, how we can protect them and how they can help us mitigate climate change.

Productivity of Tropical Rain Forests

Tropical rain forests exist in a broad band across the Earths warm, moist equatorial regions. They are characterized by their great stature, a wide range of life forms (including many trees with buttresses, thick stemmed climbers, and herbaceous epiphytes), and a large number of tree species. Despite the importance of tropical rain forests as a store of carbon, their role in the carbon cycle is not well understood because they are extensive, variable, and generally more difficult to study than other vegetation types. This chapter discusses the progress in understanding the controls on net primary productivity and the related quantity, and the net ecosystem productivity, which requires close collaboration between disciplines. Studies at the leaf and stand scale, using eco physiological and eddy covariance techniques, are advancing ones understanding of the temporal changes. Thereafter, scaling up to whole regions and biomes still requires remotely sensed data on the distribution of land-surface cover, as well as the use of interpolated climatological data from the ground or from global circulation models to drive the models. There is a need to develop new approaches to this difficult problem, perhaps using large-scale experimentation and observation. One aspect of environmental change that has received attention is the influence of forest edges that are created during logging and burning.

Conditions for life

Solar radiation is the primary source of energy on Earth, and life depends on it. We are well aware of the flux of radiant energy from the sun as about half of it is in the part of the spectrum sensed by our eyes. We are generally much less aware of the emission of longwave radiant energy by all surfaces around us. The first part of this chapter briefly introduces these two components of radiation which play such an important role in the heat balance of vegetation, to be considered in later chapters.