Ecosystem Change

4. What are the most critical factors causing ecosystem changes?

• 4.1 What is a "driver" and how does it affect ecosystems?
• 4.2 What are the indirect drivers and how are they changing?
• 4.3 What are the direct drivers of changes in ecosystem services?

4.1 What is a "driver" and how does it affect ecosystems?

Natural or human-induced factors that directly or indirectly cause a change in an ecosystem are referred to as drivers.

• A direct driver, such as habitat change, explicitly influences ecosystem processes.
• An indirect driver, such as human population change, operates more diffusely, by altering one or more direct drivers.

Drivers affecting ecosystem services and human well-being range from local to global and from immediate to long-term, which makes both their assessment and management complex. Climate change may operate on a global or large regional scale; political change may operate at the scale of a nation or a municipal district. Socio-cultural change typically occurs slowly, on a time scale of decades, while economic changes tend to occur more rapidly. As a result of this spatial and temporal dependence of drivers, the forces that appear to be most significant at a particular location and time may not be the most significant over larger, or smaller, regions or time scales. More...

4.2 What are the indirect drivers and how are they changing?

4.2.1 Driving forces are almost always multiple and interactive, so that a one-to-one linkage between particular driving forces and particular changes in ecosystems rarely exists. Five major indirect drivers that influence ecosystems and ecosystem services are:

• Population change: This includes population growth and migration. World population has doubled in the past forty years, reaching 6 billion in 2000, with most of the growth taking place in developing countries. However, at present some developing countries have very low rates of population growth, whereas some high income countries have high rates because of immigration.
• Change in Economic activity: Global economic activity has increased nearly seven-fold in the last 50 years. As per capita income grows, demand for many ecosystem services increases and the structure of consumption also changes. The share of income devoted to food, for example, decreases in favor of industrial goods and services.
• Socio-Political factors: These factors include decision-making processes and the extent of public participation in them. The trend toward democratic institutions over the past 50 years has helped empower local communities. There has also been an increase in multilateral environmental agreements.
• Cultural and Religious factors: In this context, culture can be defined as the values, beliefs, and norms that a group of people share. It conditions individuals’ perceptions of the world, and suggests courses of action which can have important impacts on other drivers such as consumption behavior.
• Science and Technology: The 20th century saw tremendous advances in the understanding of how the world works and in the technical applications of that knowledge. Much of the increase in agricultural output over the past 40 years has come from an increase in yields per hectare rather than an expansion of area. At the same time, technological advances can also lead to degradation of ecosystem services. Advances in fishing technologies, for example, have contributed significantly to the depletion of marine fish stocks.

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4.2.2 Economic growth and consumption of ecosystem services are no longer as closely linked as they were in the past. Generally, the use of ecosystem services has grown much less over the past five decades than GDP. This reflects a change in economic structures but also an increase in the efficient use of services and in the availability of substitutes. However, the consumption of energy and materials continues to grow in absolute terms, since the growth in demand is faster than the increase in efficiency.

Trade of ecosystem services magnifies the effect of governance, regulations, and management practices, both good and bad. Increased trade can accelerate degradation of ecosystem services in exporting countries if their policy, regulatory, and management systems are inadequate. International trade is an important source of economic gains, as it enables comparative advantages to be exploited and accelerates the diffusion of more efficient technologies and practices.

Population and economic growth in urban centers has been increasing pressures on ecosystems. However, dense urban settlement is considered to be a lesser burden on the environment than urban and suburban sprawl. Moreover, pressures on some ecosystems have been significantly lowered by the movement of people to urban areas, leading to the reforestation of some parts of industrial countries. More...

4.3 What are the direct drivers of changes in ecosystem services?

Figure 4.3 Main Direct Drivers

Important direct drivers include habitat change, climate change, invasive species, overexploitation, and pollution. Most of the direct drivers of degradation in ecosystems and biodiversity currently remain constant or are growing in intensity in most ecosystems (see Figure 4.3). More...

4.3.1 Over the past 50 years, the most important direct drivers of change have been:

• In terrestrial ecosystems: land cover change, mainly by conversion to cropland, and the application of new technologies contributing to the increased supply of food, timber, and fiber. Only areas unsuited to crop plants, such as deserts, boreal forests, and tundra, remain largely untransformed by human action.
• In marine ecosystems: fishing. About half of the commercially exploited wild marine fish stocks for which information is available are fully exploited and without scope for increased catches. The impact of fishing has been particularly significant in coastal areas but is now also affecting the open oceans.
• In freshwater ecosystems: water regime changes, such as those following the construction of large dams; invasive species, which can lead to species extinction; and pollution, such as high levels of nutrient loading.

Coastal ecosystems are affected by multiple direct drivers. Worldwide, nearly 40% of people live on the thin fringe of land within 50 km of the ocean. Fishing pressures in those systems are linked to a wide array of other drivers including land-, river-, and ocean-based pollution, habitat loss, invasive species, and nutrient loading. The greatest threat to coastal systems is the conversion of coastal habitats through coastal urban sprawl, resort and port development, aquaculture, and industrialization. More...

4.3.2 Over the past four decades, excessive levels of nutrients in soil and water have emerged as one of the most important direct drivers of ecosystem change in terrestrial, freshwater, and marine ecosystems (see table 4.1). The use of fertilizers can increase crop productivity, but there are important adverse effects to other ecosystems. Excessive additions of nutrients to freshwater or coastal marine systems can lead to excessive plant and algae growth (a process referred to as eutrophication) and to further undesirable changes in ecosystems. This can in turn reduce or eliminate fish populations, increase outbreaks of microbes, increase the cost of water purification, and degrade cultural services by keeping people from swimming, boating, and otherwise enjoying lakes. Other effects of nutrient loading include air pollution, emission of greenhouse gases, and depletion of the ozone layer.

The climate has changed in the past century: global temperature has increased by about 0.6°C, precipitation patterns have been altered, and the average sea level has risen by 10 to 20 centimeters. Those changes have already had a measurable impact on ecosystems and are projected to continue throughout the 21st century. The effects of climate change on ecosystems include modifications in species distributions, population sizes, and the timing of reproduction or migrations, as well as an increase in pest and disease outbreaks. More...