For terrestrial ecosystems, the most important direct drivers of change in ecosystem services in the past 50 years, in the aggregate, have been land cover change (in particular, conversion to cropland) and the application of new technologies (which have contributed significantly to the increased supply of services such as food, timber, and fiber) (CWG, S7.2.5, SG8.ES). In 9 of the 14 terrestrial biomes examined in the MA, between one half and one fifth of the area has been transformed, largely to croplands (C4.ES). Only biomes relatively unsuited to crop plants, such as deserts, boreal forests, and tundra, have remained largely untransformed by human action. Both land cover changes and the management practices and technologies used on lands may cause major changes in ecosystem services. New technologies have resulted in significant increases in the supply of some ecosystem services, such as through increases in agricultural yield. In the case of cereals, for example, from the mid-1980s to the late 1990s the global area under cereals fell by around 0.3% a year, while yields increased by about 1.2% a year (C26.4.1).
For marine ecosystems and their services, the most important direct driver of change in the past 50 years, in the aggregate, has been fishing (C18). At the beginning of the twenty-first century, the biological capability of commercially exploited fish stocks was probably at a historical low. FAO estimates that about half of the commercially exploited wild marine fish stocks for which information is available are fully exploited and offer no scope for increased catches (C8.2.2). As noted in Chapter 1, fishing pressure is so strong in some marine systems that the biomass of some targeted species, especially larger fishes, and those caught incidentally has been reduced to one tenth of levels prior to the onset of industrial fishing (C18.ES). Fishing has had a particularly significant impact in coastal areas but is now also affecting the open oceans.
For freshwater ecosystems and their services, depending on the region, the most important direct drivers of change in the past 50 years include modification of water regimes, invasive species, and pollution, particularly high levels of nutrient loading. It is speculated that 50% of inland water ecosystems (excluding large lakes and closed seas) were converted during the twentieth Century (C20.ES). Massive changes have been made in water regimes: in Asia, 78% of the total reservoir volume was constructed in the last decade, and in South America almost 60% of all reservoirs have been built since the 1980s (C20.4.2). The introduction of nonnative invasive species is one of the major causes of species extinction in freshwater systems. While the presence of nutrients such as phosphorus and nitrogen is necessary for biological systems, high levels of nutrient loading cause significant eutrophication of water bodies and contribute to high levels of nitrate in drinking water in some locations. (The nutrient load refers to the total amount of nitrogen or phosphorus entering the water during a given time.) Non-point pollution sources such as storm water runoff in urban areas, poor or nonexistent sanitation facilities in rural areas, and the flushing of livestock manure by rainfall and snowmelt are also cause of contamination (C20.4.5). Pollution from point sources such as mining has had devastating local and regional impacts on the biota of inland waters.
Coastal ecosystems are affected by multiple direct drivers. Fishing pressures in coastal ecosystems are compounded by a wide array of other drivers, including land-, river-, and ocean-based pollution, habitat loss, invasive species, and nutrient loading. Upstream freshwater diversion has meant a 30% decrease worldwide of water and sediment delivery to estuaries, which are key nursery areas and fishing grounds (C19.ES). Approximately 17% of the world lives within the boundaries of the MA coastal system (up to an elevation of 50 meters above sea level and no further than 100 kilometers from a coast), and approximately 40% live in the full area within 50 kilometers of a coast. And the absolute number is increasing through a combination of in-migration, high reproduction rates, and tourism (C.SDM). Demand on coastal space for shipping, waste disposal, military and security uses, recreation, and aquaculture is increasing.
The greatest threat to coastal systems is the development-related conversion of coastal habitats such as forests, wetlands, and coral reefs through coastal urban sprawl, resort and port development, aquaculture, and industrialization. Dredging, reclamation and destructive fishing also account for widespread, effectively irreversible destruction. Shore protection structures and engineering works (beach armoring, causeways, bridges, and so on), by changing coastal dynamics, have impacts extending beyond their direct footprints. Nitrogen loading to the coastal zone has increased by about 80% worldwide and has driven coral reef community shifts (C.SDM).