Sustainability of terrestrial ecosystems
TERRESTRIAL ECOSYSTEMS are the foundation for social and economic well-being because they provide:
- The primary and largely unsubstitutable source of food, fuel, and materials for clothing and shelter;
- The main source of employment, income and material welfare for about half the world's population. For many developing countries, they are the dominant economic sector through commodity exports or tourism;
- Sources of freshwater for drinking, irrigation and industry;
- The major source of nutrients (and also pollutants) for coastal zones and the oceans. They influence fisheries productivity - the other main source of food and provide employment to millions of fishermen, fish processors and retailers;
- The home for much of the genetic diversity that sustains current agricultural systems and that provides the basis for predictable future natural resource needs and insurance against unknown new threats which may arise to human health and agricultural systems;
- Visual beauty and recreation.
Terrestrial ecosystems are also the major drivers for the atmospheric, biogeochemical and hydrological processes that shape and govern life on earth. In particular they:
- Play a primary role in soil formation and maintenance;
- Are a co-determinant of the surface energy balance through reflection, absorption, transmission, and transformation of radiative energy from the sun, and of the global hydrological cycle;
- Affect the storage and flow of surface and groundwater resources, and influence their quality;
- Are a source and sink for greenhouse gases, and provide major pathways for and influences on biogeochemical cycles;
- Receive, filter, buffer and transform nutritious and hazardous anthropogenic materials.
There are uncertainties about the ability of terrestrial ecosystems to sustain current production of food and other goods and maintain environmental services. There are even greater uncertainties about their ability, to meet and sustain indefinitely, the growing material and welfare needs and expectations of a human population which could double by 2050, in association with a possible quadrupling of per capita incomes over the same period.
Uncertainties surround the very basic question as to what is the sustainable population-supporting capacity of the world. Some argue that it is 8,000 million, which is clearly not compatible with the levelling off of global population currently projected at between 10,000 million and 12,000 million by the year 2050. Others calculate that land-based food production could support a population considerably greater than 12,000 million, even with an environment-oriented agriculture that minimizes the use of mineral fertilizers and pesticides.
These concerns and uncertainties about the ability of terrestrial ecosystems to meet future global needs are repeated at the local and regional level, where it has been suggested that population pressures are bringing terrestrial ecosystems to the point of collapse. In Southern Africa, for example, some analysts conclude that overgrazing is causing widespread erosion and rangeland degradation beyond the point of recovery. Other analysts - using more dynamic models with fuller representation of soil types and ecological processes - conclude that current livestock populations and productivity can be sustained for some 200 years. Such differences arise in part from lack of basic data, and will continue until there is regularly collected and compatible data on land cover and land-use change, rates and extents of land degradation, and shifts in ecosystem structure and plant productivity through soil erosion.
Such uncertainties are a major constraint to development strategies and policy planning at all levels from the local to the global. The removal of these uncertainties is highly dependent on the type of data and understanding that GTOS is designed to supply, and for which there is no other adequate mechanism.
Climate change is one of the major areas of uncertainty. Although there is a scientific consensus within the Intergovernmental Panel on Climate Change (IPCC) that global average temperatures could rise 1.5-4.0 degrees centigrade by the middle of the next century, there is great uncertainty about the timing, spatial distribution and impact on terrestrial ecosystems of such a rise. Predictions from the various General Circulation Models (GCMs) are not in agreement, for example, regarding the nature of regional shifts and impacts of climate change. It is generally recognized that some of the refinements required in these models to improve their predictive powers are dependent on better data on land surface properties, terrestrial ecosystem processes and possible responses to climate change.
Consequently, it has been recommended that GTOS, as part of its support role to GCOS, should be the primary mechanism for the collection of such data. Moreover, the uncertainties related to climate change go beyond questions of temperature and moisture distribution. They include changes in carbon sinks to sources that may affect plant growth, and alterations to low-level UV-B and ozone concentrations which could have adverse effects on human health and crop growth.
In addition, the GCMs as with biogeochemical, hydrological, and other global change models, need to be calibrated more accurately, and coupled more closely with regional or zonal models, and with ocean circulation models. One of the key requirements for such improvements is better terrestrial data, especially on land cover and land use change, on trace gas and dust (including volcanic dust) fluxes from terrestrial ecosystems, and carbon sequestration. GTOS is the only way of getting comprehensive, continuous, and comparable data of these types.
Further information: Why GTOS | Terrestrial ecosystems | What GTOS will do | Global change issues | User needs
Go to: Document index | Overview