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Collapse of wild and cultivated biodiversity

  • 2020-02-01 09:34:30.0
  • 11463

Wild biodiversity is collapsing at a dizzying pace, compromising the maintenance of essential functions in cultivated ecosystems such as pollination, the regulation of pests and the maintenance of soil fertility. Cultivated diversity has also greatly diminished, making crops more vulnerable to disturbance and limiting their potential to adapt to new environmental conditions.

The scale and speed at which the diversity of life on Earth is declining today is comparable to what happened during the five great extinction crises of geological time. The current crisis is the result of the exploitation and destruction of ecosystems by industrialized societies. Populations of wild vertebrates have declined by 60% in about 40 years ( Figure 4 ) and around one million species are now threatened with extinction.

Figure 4 : Evolution of the Living Planet Index between 1970 and 2014. The Living Planet Index is an indicator of the state of global animal biodiversity. It measures the abundance of thousands of species of vertebrates around the world. It has collapsed 60% in 44 years. Source : WWF (2018).

In France, the now immaculate windshields of cars, which had to be cleaned regularly from the corpses of insects that littered them not even twenty years ago, testify to the annihilation of insect populations, and consequently of all the species which depend on it . A finding widely supported by numerous studies: 33% of birds in agricultural environments have disappeared in thirty years in France, 38% of bats in ten years, 75% of insects within 30 years in Germany in areas natural protected areas and 67% in grasslands in just ten years.

The industrial agricultural system degrades ecosystems and is found to be a major cause of the collapse of biodiversity in France,:
- The homogenization of the countryside (monocultures, expansion of plots, disappearance of hedges, wetlands, permanent meadows ...) reduces the ecological niches and the resources available for wild life ( Figure 5 ).
- The massive use of pesticides has catastrophic impacts on all of biodiversity, affecting all levels of food webs (food chains).
- Excessive use of fertilizer seriously disrupts the nitrogen and phosphorus cycles. The nutrients are washed away by the rains and join the aquatic ecosystems downstream, where certain algae or bacteria proliferate (eutrophication phenomenon). Their death and decomposition progressively deprive the environment of oxygen and lead to the death of other organisms (eg Breton green tides, coastal dead zones, etc.).
- Frequent and deep tillage , its compaction by the passage of agricultural machinery, and pesticide residues, degrade the biodiversity of this environment and its essential functions in maintaining fertility, protecting cultures or water retention.

Figure 5 : Map of France of agricultural areas with high natural value (in dark gray). Left: 1970; right: 2000. Agricultural areas with high natural value are particularly favorable environments for biodiversity. They combine (1) the presence of infrastructures of ecological interest such as hedges, (2) extensive agricultural practices, and (3) the diversity of rotations (crop rotations). Their surface area has decreased by 68% in 30 years. Source : Pointereau et al. (2010).

Globally, the expansion of agricultural land is responsible for 80% of deforestation, with tropical forests primarily affected. With them are destroyed ecosystems with the highest levels of biodiversity on the planet . The main agro-industrial sectors involved are extensive livestock farming and soybean cultivation in Latin America, and oil palm cultivation in Southeast Asia. In this region, intensive aquaculture is the main cause of destruction of coastal forests (mangroves). The French food system contributes to the strong worldwide demand for these products , used in animal or human food and in processing plants.

In addition, cultivated biodiversity has also been considerably impoverished . Of some 6,000 plant species that have been cultivated by mankind, only nine now account for two thirds of world production . The genetic diversity of cultivated species has also diminished, as multiple local varieties have been abandoned in favor of high-yielding varieties (see pathway to resilience n ° 4). These modern varieties are genetically very homogeneous and adapted to the practices of industrialized agriculture (irrigation, mineral fertilizers, pesticides). This lack of diversity becomes a vulnerability in an uncertain environment, conducive to climatic or biological disturbances .

The nine plants providing two thirds of world agricultural production. From left to right and top to bottom by importance of world production in 2017: sugar cane; corn ; rice; potato ; soy ; palm nuts; sugar beet and cassava. Crédits : Pngimg, CC BY.

Background degradation : less pollination of plants, erosion and loss of soil fertility, development of pests According to the FAO Director-General: “Less biodiversity means that plants and animals are more vulnerable to pests and diseases. In addition to our dependence on a decreasing number of species to feed us, the increasing loss of biodiversity for food and agriculture is jeopardizing our already fragile food security".

The disappearance of wild pollinating insects is one of the most emblematic threats . It is estimated that about three-quarters of crop species - accounting for more than one-third of global agricultural production - depend on insects for their pollination.

Underground biodiversity is a determining factor in soil fertility . Earthworms, insects, fungi and bacteria perform many essential functions, such as the release of nutrients by decomposing organic matter, the infiltration and retention of rainwater, and the nutrition and protection of plants. However, the practices of industrialized agriculture are not very favorable to a rich soil life: low inputs of organic matter, heavy tillage, heavy use of pesticides, disruption of nutrient cycles ... The degradation of the activity biological soil reduces them to the state of simple substrates whose fertility is based on increasing inputs of external inputs .

In addition, the proliferation and spread of pathogens, pests and invasive alien species are facilitated in more homogeneous agrosystems with low biodiversity. Many wild species are indeed predators or natural parasites of pests ; their regulatory effect on the latter is well documented.

Hoverfly (Scaeva selenitica) adult foraging on a silene flower (Silene latifolia). Syrphids are generalist pollinating insects in the adult stage. Larvae consume large quantities of aphids. Crédits : Hélène Rival, CC BY-SA, Wikimedia Commons.

Crisis situations : agricultural calamity of parasitic origin or wave of pests A historical example of a food crisis linked to low cultivated biodiversity is the great famine of Ireland in the mid-19th century . Much of the country's food security relied on a single, widely cultivated potato variety. The arrival of a pathogenic late blight fungus on the island and its rapid spread in homogeneous crops has caused production to drop by around 30%. This event, combined with a difficult economic and political situation, created a historic famine that led a quarter of the Irish population to death or exile.

A particularly worrying current case concerns wheat rusts, a disease caused by fungi of the genus Puccinia which can cause severe damage to straw cereal crops. Since these pathogens have been known for a long time, the obtaining of resistant varieties has been the subject of significant selection efforts for modern wheats and has been a real success. However, the emergence of particularly virulent strains and several recent epidemics in Africa, the Middle East and Europe raise fears of a return of these diseases. However, the close genetic proximity of modern varieties of wheat can make up to 90% of cultivated areas sensitive to certain new virulent forms of rust, and dangerously compromise food security .

Harvest from a field of triticale (a cereal similar to wheat) infested with yellow wheat rust in the Huesca region of Spain. The spores of the parasitic fungus Puccinia striiformis f.sp. tritici are the source of this yellow powder. Crédits : © Lluís Xanxo.

Ways of resilience : increase the agricultural population, preserve agricultural land, diversify cultivated varieties and develop autonomy in seeds, generalize agroecology, eat more plants

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