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Global Biodiversity Outlook 3

Biodiversity in 2010
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Current pressures on biodiversity and responses
The persistence and in some cases intensification of the five principal pressures on biodiversity provide more evidence that the rate of biodiversity loss is not being significantly reduced. The overwhelming majority of governments reporting to the CBD cite these pressures or direct drivers as affecting biodiversity in their countries.
They are:
· Habitat loss and degradation

· Climate change

· Excessive nutrient load and other forms of pollution

· Over-exploitation and unsustainable use

· Invasive alien species

Habitat loss and degradation

Habitat loss and degradation create the biggest single source of pressure on biodiversity worldwide. For terrestrial ecosystems, habitat loss is largely accounted for by conversion of wild lands to agriculture, which now accounts for some 30% of land globally. In some areas, it has recently been partly driven by the demand for biofuels.

The IUCN Red List assessments show habitat loss driven by agriculture and unsustainable forest management to be the greatest cause of species moving closer towards extinction. The sharp decline of tropical species populations shown in the Living Planet Index mirrors widespread loss of habitat in those regions. For example, in one recent study the conversion of forest to oil palm plantations was shown to lead to the loss of 73- 83% of the bird and butterfly species of the ecosystem. As noted above, birds face an especially high risk of extinction in South-east Asia, the region that has seen the most extensive development of oil palm plantations, driven in part by the growing demand for biofuel.

Infrastructure developments, such as housing, industrial developments, mines and transport networks, are also an important contributor to conversion of terrestrial habitats, as is afforestation of non-forested lands. With more than half of the world's population now living in urban areas, urban sprawl has also led to the disappearance of many habitats, although the higher population density of cities can also reduce the negative impacts on biodiversity by requiring the direct conversion of less land for human habitation than more dispersed settlements.

Even though there are no signs at the global level that habitat loss is declining significantly as a driver of biodiversity loss, some countries have shown that, with determined action, historically persistent negative trends can be reversed. An example of global significance is the recent reduction in the rate of deforestation in the Brazilian Amazon, mentioned above.

For inland water ecosystems, habitat loss and degradation is largely accounted for by unsustainable water use and drainage for conversion to other land uses, such as agriculture and settlements.

The major pressure on water availability is abstraction of water for irrigated agriculture, which uses approximately 70 per cent of the world's withdrawals of fresh water, but water demands for cities, energy and industry are rapidly growing. The construction of dams and flood levees on rivers also causes habitat loss and fragmentation, by converting free-flowing rivers to reservoirs, reducing connectivity between different parts of river basins, and cutting off rivers from their floodplains.

In coastal ecosystems, habitat loss is driven by a range of factors including some forms of mariculture, especially shrimp farms in the tropics where they have often replaced mangroves.

Coastal developments, for housing, recreation, industry and transportation have had important impacts on marine ecosystems, through dredging, landfilling and disruption of currents, sediment flow and discharge through construction of jetties and other physical barriers. As noted above, use of bottom-trawling fishing gear can cause significant loss of seabed habitat.

Climate Change

Climate change is already having an impact on biodiversity, and is projected to become a progressively more significant threat in the coming decades. Loss of Arctic sea ice threatens biodiversity across an entire biome and beyond. The related pressure of ocean acidification, resulting from higher concentrations of carbon dioxide in the atmosphere, is also already being observed.

Ecosystems are already showing negative impacts under current levels of climate change (an increase of 0.74ºC in global mean surface temperature relative to pre-industrial levels), which is modest compared to future projected changes (2.4-6.4 ºC by 2100 without aggressive mitigation actions). In addition to warming temperatures, more frequent extreme weather events and changing patterns of rainfall and drought can be expected to have significant impacts on biodiversity.

Impacts of climate change on biodiversity vary widely in different regions of the world. For example, the highest rates of warming have been observed in high latitudes, around the Antarctic peninsula and in the Arctic, and this trend is projected to continue. The rapid reduction in the extent, age and thickness of Arctic sea ice, exceeding even recent scientific forecasts, has major biodiversity implications [See Box 15 and Figure 14].

Already, changes to the timing of flowering and migration patterns as well as to the distribution of species have been observed worldwide. In Europe, over the last forty years, the beginning of the growing season has advanced by 10 days on average. These types of changes can alter food chains and create mismatches within ecosystems where different species have evolved synchronized inter-dependence, for example between nesting and food availability, pollinators and fertilization. Climate change is also projected to shift the ranges of disease-carrying organisms, bringing them into contact with potential hosts that have not developed immunity. Freshwater habitats and wetlands, mangroves, coral reefs, Arctic and alpine ecosystems, dry and subhumid lands and cloud forests are particularly vulnerable to the impacts of climate change.

Some species will benefit from climate change. However, an assessment looking at European birds found that of 122 widespread species assessed, about three times as many were losing population as a result of climate change as those that were gaining numbers.

The specific impacts of climate change on biodiversity will largely depend on the ability of species to migrate and cope with more extreme climatic conditions. Ecosystems have adjusted to relatively stable climate conditions, and when those conditions are disrupted, the only options for species are to adapt, move or die.

It is expected that many species will be unable to keep up with the pace and scale of projected climate change, and as a result will be at an increased risk of extinction, both locally and globally. In general climate change will test the resilience of ecosystems, and their capacity for adaptation will be greatly affected by the intensity of other pressures that continue to be imposed. Those ecosystems that are already at, or close to, the extremes of temperature and precipitation tolerances are at particularly high risk.

Over the past 200 years, the oceans have absorbed approximately a quarter of the carbon dioxide produced from human activities, which would otherwise have accumulated in the atmosphere. This has caused the oceans (which on average are slightly alkaline) to become more acidic, lowering the average pH value of surface seawater by 0.1 units. Because pH values are on a logarithmic scale, this means that water is 30 per cent more acidic.

The impact on biodiversity is that the greater acidity depletes the carbonate ions, positivelycharged molecules in seawater, which are the building blocks needed by many marine organisms, such as corals, shellfish and many planktonic organisms, to build their outer skeletons. Concentrations of carbonate ions are now lower than at any time during the last 800,000 years. The impacts on ocean biological diversity and ecosystem functioning will likely be severe, though the precise timing and distribution of these impacts are uncertain.

 

Pollution and nutrient load

Pollution from nutrients (nitrogen and phosphorous) and other sources is a continuing and growing threat to biodiversity in terrestrial, inland water and coastal ecosystems.

Modern industrial processes such as the burning of fossil fuels and agricultural practices, in particular the use of fertilizers, have more than doubled the quantity of reactive nitrogen - nitrogen in the form that is available to stimulate plant growth - in the environment compared with pre-industrial times. Put another way, humans now add more reactive nitrogen to the environment than all natural processes, such as nitrogen-fixing plants, fires and lightning.

In terrestrial ecosystems, the largest impact is in nutrient-poor environments, where some plants that benefit from the added nutrients out-compete many other species and cause significant changes in plant composition. Typically, plants such as grasses and sedges will benefit at the expense of species such as dwarf shrubs, mosses and lichens.

Nitrogen deposition is already observed to be the major driver of species change in a range of temperate ecosystems, especially grasslands across Europe and North America, and high levels of nitrogen have also been recorded in southern China and parts of South and Southeast Asia. Biodiversity loss from this source may be more serious than first thought in other ecosystems including high-latitude boreal forests, Mediterranean systems, some tropical savannas and montane forests. Nitrogen has also been observed to be building up at significant levels in biodiversity hotspots, with potentially serious future impacts on a wide variety of plant species.

Large parts of Latin America and Africa, as well as Asia, are projected to experience elevated levels of nitrogen deposition in the next two decades. Although the impacts have mainly been studied in plants, nitrogen deposition may also affect animal biodiversity by changing the composition of available food.

In inland water and coastal ecosystems, the buildup of phosphorous and nitrogen, mainly through run-off from cropland and sewage pollution, stimulates the growth of algae and some forms of bacteria, threatening valuable ecosystem services in systems such as lakes and coral reefs, and affecting water quality. It also creates "dead zones" in oceans, generally where major rivers reach the sea. In these zones, decomposing algae use up oxygen in the water and leave large areas virtually devoid of marine life. The number of reported dead zones has been roughly doubling every ten years since the 1960s, and by 2007 had reached around 500 [See Figure 15].

While the increase in nutrient load is among the most significant changes humans are making to ecosystems, policies in some regions are showing that this pressure can be controlled and, in time, reversed. Among the most comprehensive measures to combat nutrient pollution is the European Union's Nitrates Directive [See Box 16 and Figure 16].

Overexploitation and unsustainable use

Overexploitation and destructive harvesting practices are at the heart of the threats being imposed on the world's biodiversity and ecosystems, and there has not been significant reduction in this pressure. Changes to fisheries management in some areas are leading to more sustainable practices, but most stocks still require reduced pressure in order to rebuild. Bushmeat hunting, which provides a significant proportion of protein for many rural households, appears to be taking place at unsustainable levels.

Overexploitation is the major pressure being exerted on marine ecosystems, with marine capture fisheries having quadrupled in size from the early 1950s to the mid 1990s. Total catches have fallen since then despite increased fishing effort, an indication that many stocks have been pushed beyond their capacity to replenish.

The FAO estimates that more than a quarter of marine fish stocks are overexploited (19%), depleted (8%) or recovering from depletion (1%) while more than half are fully exploited. Although there have been some recent signs that fishing authorities are imposing more realistic expectations on the size of catches that can safely be taken out of the oceans, some 63% of assessed fish stocks worldwide require rebuilding. Innovative approaches to the management of fisheries, such as those that give fishermen a stake in maintaining healthy stocks, are proving to be effective where they are applied[See Box 17].

Invasive alien species

Invasive alien species continue to be a major threat to all types of ecosystems and species. There are no signs of a significant reduction of this pressure on biodiversity, and some indications that it is increasing. Intervention to control alien invasive species has been successful in particular cases, but it is outweighed by the threat to biodiversity from new invasions.

In a sample of 57 countries, more than 542 alien species, including vascular plants, marine and freshwater fish, mammals, birds and amphibians, with a demonstrated impact on biodiversity have been found, with an average of over 50 such species per country (and a range from nine to over 220). This is most certainly an underestimate, as it excludes many alien species whose impact has not yet been examined, and includes countries known to lack data on alien species.

It is difficult to get an accurate picture of whether damage from this source is increasing, as in many areas attention has only recently been focused on the problem, so a rise in known invasive species impacts may partly reflect improved knowledge and awareness. However, in Europe where introduction of alien species has been recorded for many decades, the cumulative number continues to increase and has done so at least since the beginning of the 20th century. Although these are not necessarily invasive, more alien species present in a country means that in time, more may become invasive. It has been estimated that of some 11,000 alien species in Europe, around one in ten has ecological impacts and a slightly higher proportion causes economic damage [See Box 18]. Trade patterns worldwide suggest that the European picture is similar elsewhere and, as a consequence, that the size of the invasive alien species problem is increasing globally.

Eleven bird species (since 1988), five mammal species (since 1996) and one amphibian (since 1980) have substantially had their risk of extinction reduced due primarily to the successful control or eradication of alien invasive species. Without such actions, it is estimated that the average survival chances, as measured by the Red List Index, would have been more than 10% worse for bird species and almost 5% worse for mammals [See Box 19]. However, the Red List Index also shows that almost three times as many birds, almost twice as many mammals, and more than 200 times the number of amphibian species, have deteriorated in conservation status due largely to increased threats from invasive animals, plants or micro-organisms. Overall, birds, mammals and amphibian species have on average become more threatened due to invasive alien species. While other groups have not been fully assessed, it is known that invasive species are the second leading cause for extinction for freshwater mussels and more generally among endemic species.

Combined pressures and underlying causes of biodiversity loss

The direct drivers of biodiversity loss act together to create multiple pressures on biodiversity and ecosystems. Efforts to reduce direct pressures are challenged by the deep-rooted underlying causes or indirect drivers that determine the demand for natural resources and are much more difficult to control. The ecological footprint of humanity exceeds the biological capacity of the Earth by a wider margin than at the time the 2010 target was agreed.

The pressures or drivers outlined above do not act in isolation on biodiversity and ecosystems, but frequently, with one pressure exacerbating the impacts of another. For example:

✤ Fragmentation of habitats reduces the capacity of species to adapt to climate change, by limiting the possibilities of migration to areas with more suitable conditions.

✤ Pollution, overfishing, climate change and ocean acidification all combine to weaken the resilience of coral reefs and increase the tendency for them to shift to algae-dominated states with massive loss of biodiversity.

✤ Increased levels of nutrients combined with the presence of invasive alien species can promote the growth of hardy plants at the expense of native species. Climate change can further exacerbate the problem by making more habitats suitable for invasive species.

✤ Sea level rise caused by climate change combines with physical alteration of coastal habitats, accelerating change to coastal biodiversity and associated loss of ecosystem services.

An indication of the magnitude of the combined pressures we are placing on biodiversity and ecosystems is provided by humanity's ecological footprint, a calculation of the area of biologically-productive land and water needed to provide the resources we use and to absorb our waste. The ecological footprint for 2006, the latest year for which the figure is available, was estimated to exceed the Earth's biological capacity by 40 per cent. This "overshoot" has increased from some 20 per cent at the time the 2010 biodiversity target was agreed in 2002. As suggested above, specific measures can and do have an impact in tackling the direct drivers of biodiversity loss: alien species control, responsible management of farm waste and habitat protection and restoration are some examples. However, such measures must compete with a series of powerful underlying causes of biodiversity loss. These are even more challenging to control, as they tend to involve long-term social, economic and cultural trends. Examples of underlying causes include:

✤ Demographic change

✤ Economic activity

✤ Levels of international trade

✤ Per capita consumption patterns, linked to individual wealth

✤ Cultural and religious factors

✤ Scientific and technological change

Indirect drivers primarily act on biodiversity by influencing the quantity of resources used by human societies. So for example population increase, combined with higher per capita consumption, will tend to increase demand for energy, water and food - each of which will contribute to direct pressures such as habitat conversion, over-exploitation of resources, nutrient pollution and climate change. Increased world trade has been a key indirect driver of the introduction of invasive alien species.

Indirect drivers can have positive as well as negative impacts on biodiversity. For example, cultural and religious factors shape society's attitudes towards nature and influence the level of funds available for conservation. The loss of traditional knowledge can be particularly detrimental in this regard, as for many local and indigenous communities biodiversity is a central component of belief systems, worldviews and identity. Cultural changes such as the loss of indigenous languages can therefore act as indirect drivers of biodiversity loss by affecting local practices of conservation and sustainable use [See Box 20]. Equally, scientific and technological change can provide new opportunities for meeting society's demands while minimizing the use of natural resources - but can also lead to new pressures on biodiversity and ecosystems.

Strategies for decreasing the negative impacts of indirect drivers are suggested in the final section of this synthesis. They centre on "decoupling" indirect from direct drivers of biodiversity loss, primarily by using natural resources much more efficiently; and by managing ecosystems to provide a range of services for society, rather than only maximizing individual services such as crop production or hydro-electric power.

The trends from available indicators suggest that the state of biodiversity is declining, the pressures upon it are increasing, and the benefits derived by humans from biodiversity are diminishing, but that the responses to address its loss are increasing [See Figure 17]. The overall message from these indicators is that despite the many efforts taken around the world to conserve biodiversity and use it sustainably, responses so far have not been adequate to address the scale of biodiversity loss or reduce the pressure.

  • United Nations
  • United Nations Environment Programme