Ecosystems are classified based on ecological criteria as well as general climate and features recognizable from the field and from satellite imagery. Some are based on the seasonality of changes in the systems, such as changes in leaf characteristics, linked together with information on climate, elevation, humidity, and drainage. These criteria have been modified and adopted by 175 countries in the Convention on Biologic Diversity in Rio de Janeiro in June 1972. This convention had three main goals:
• conservation of biodiversity
• sustainable use of its components
• fair and equitable sharing of benefits arising from genetic resources.
Participants in this conference adopted a new, more encompassing definition of ecosystems as a "dynamic complex of plant, animal, and microorganism communities and their nonliving environment interacting as a functional unit."
Following the criteria and goals of the conference, several different ecological classification systems became widely used. The first is physiognomic-ecological classification of plant formations of the Earth, differentiating between the structures and appearance from above ground and underwater plant systems. The second is a land cover classification system (LCSS) developed by the Food and Agriculture Organization, based mainly on satellite-based observations.
An outcome of the increased attention on ecosystems is the definition of ecosystem services, which are fundamental life-support services on which civilization depends. Such services include pollination, flood control, food for cattle in natural grasslands, wood for the timber industry, erosion, nutrient cycling, natural products for the pharmaceutical industry, and bush meat for indigineous populations. More effort has been made in recent years to assign economic value to ecosystem services, which helps preserve these ecosystems by increasing society's awareness of their inherent value. Secondary services derived from natural ecosystems include natural reserves for populations to enjoy nature, water storage and controls, soil protection, and carbon sequestration. All of these can be assigned commercial values and treated as commodities that can be bartered against pressures to develop threatened ecosystems commercially.
Some of the less concrete values of preserving ecosystems come from the preservation of biodiversity, where preserving the natural environment may help individual organisms in the ecosystem be more resilient to change and avoid extinction, and may eventually contribute to the benefit of humans, for instance, by the discovery of new medicines or ecosystems critical to the stability of the planet's climate.
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