Biodiversity is under serious threat as a result of human activities. The main dangers worldwide are population growth and resource consumption, climate change and global warming, habitat conversion and urbanisation, invasive alien species, over-exploitation of natural resources and environmental degradation.
The links between human impacts and biodiversity loss are illustrated by the figure below, extracted from the second "Global Biodiversity Outlook" (2006), published by the Convention on Biological Diversity.
In Belgium, the main reasons for the decline of biodiversity are more specifically the destruction and fragmentation of natural habitats, pollution and eutrophication caused by agricultural and industrial practices, excessive water catchments in some areas, climate change and perturbations linked to leisure and tourism. In marine areas, some specific threats can be added to those mentioned above, such as overfishing or sand and gravel extraction.
The table below summarise the main threats occurring in our country. It is extracted from the brochure "Biodiversity in Belgium, a vital question" (published in 2007, in French and Dutch).
|Some underlying causes
|Threats in terrestrial areas
|Degradation, destruction and fragmentation of natural habitats
|Spread of the urbanised areas, road network and industrial areas and associated problems (noise, pollution); abandon of former agricultural practices that were favourable to biodiversity
|Decrease in the capacity of the agricultural areas to host wildlife
|Intensification of agricultural practices (yielding pollution and disturbance) and disappearance of landscape elements that provide food and shelter that are exploitable by wildlife (such as hedges, trees, ponds, etc.)
|Pollution of soils, air and water
|Excess of heavy metals (industry, roads), manure and pesticides (agriculture) and other pollutants
|Invasions by alien species
|International trade and transport (roads, railways, rivers), gardening practices, exotic trees in forestry, exotic pests released in the wild, climate change, etc.
|Epidemics affecting wildlife
|Arrivals of pathogens that are favoured by the introduction of exotic species, pollution and the destruction of habitats
|Carbon emissions, deforestation and other land use changes due to human activities
|Dessication of soils and wetlands
|Excess pumping of underground water tables
|Recreation and leisure
|Overuse of green open spaces and wild areas, little respect for nature, mountain biking and motor sports in fragile areas, dogs not on leash
|Threats in marine areas
|Overfishing and decline of species
|Industrial fishing, overexploitation of target species, by-catch species
|Pollution and eutrophication
|Land-based activities (river run-off), atmospheric deposition, maritime traffic
|Degradation and destruction of the sea floor
|Beam trawling, dredging, sand and gravel extraction
|Alien species introductions
|Maritime trade (ballast waters, fouling), leisure navigation, mariculture, climate change
|Leisure and tourism
|Coastal development, water quality in summer (high population), mechanical beach cleaning, noise and other perturbations due to the high population
Species often become threatened or disappear when several of these factors are combined. The fragmentation of habitats decreases the size of populations and make these more vulnerable to other factors. Once the population is weakened, small external perturbations such as disease can wipe out the remaining individuals entirely.
For example, frogs and toads are particularly threatened in Belgium. The main cause is the disappearance of habitats (ponds, humid areas, etc.). Once the habitats get too small for confort, other factors add to the stress: pesticides and other chemicals found in water can cause malformations and weaken the animals. Some species need stable climatic conditions for reproduction, but with climate change their life cycle can be perturbated. Epidemics (viruses, fungi) have also been observed. Road traffic adds to the burden by killing many individuals when they look for adequate places for reproduction in spring time. All these factors combined leave few chances of survival for species which are not very common.
On the other hand, exotic species - species originating from natural habitats of other parts of the world - regularly appear in our country. The ring-necked parakeet, the multicolored Asian ladybird and the Pacific oyster are well-known animal examples, while the giant hogweed, the Japanese knotweed or the narrow-leaved ragwort are examples of plants.
Even though these newcomers seem to be welcome additions to our fauna and flora, they may actually be rather threatening for biodiversity when they enter into competition with the indigenous species. Some exotic species may become pests and cause important damage to agricultural crops, horticultural plants, trees, riverbanks, etc. Others can cause sanitary problems, as is the case with parasites.