Fragmentation écopaysagère

The expressions of fragmentation of the ecosystems , fragmentation of the habitats or “ fragmentation écopaysagère ” indicate any artificial phenomenon of parcelling out of the space, which can or could prevent one or more alive species from moving as they should and could it in the absence of factor of fragmentation. One uses also the expression of “ parcelling out (or fragmentation) ecological ”.

Avec the concept of heterogeneity , that of fragmentation is one of the theoretical bases of the Écologie of the landscape.

The individuals, the species and the populations are differently affected by the fragmentation of their habitat, according to their adaptive capacities, their degree of specialization or dependence with certain structures écopaysagères, and also according to their capacity to steal or cross the obstacles factors of fragmentation (walls, nettings, roads, zones treated by pesticides, etc), and according to the biology of their populations.

The scientific community (Évaluation of the ecosystems for the millenium) considers that ecological fragmentation became one of the first causes of attack to the biodiversity, before pollution. The Walloon observatory of the biodiversity estimates for example that in 2000,5 to 15% of the species already disappeared and that 30 to 50% are in regression and that the disappearance and the fragmentation of natural spaces is the first cause.

Origin of the concept

Gadroon & Forman in 1983 then in 1986; and Forman in 1995 formalized the bases of the quantitative analysis of the structure and the components of the landscape (included/understood here like a variable surface composed of a mosaic of ecosystems). They show that the fragmentation of a natural habitat is the shape of destruction of the habitat which (except for some species ubiquists and banal) affects initially the size of the populations by increasing the risks of extinction. Wiens in 1997 makes the point that fragmentation modifies the size, the forms and the insulation of the “spots” of the landscape, generating an impact on the functions écopaysagères elements thus insulated and - by effect second - on elements located at the higher or lower levels of the landscape. Fragmentation;

induces the replacement of elements écopaysagers by others,
modifies the space context, in particular by deteriorating the ecological Connectivité and thus the degree of éco-landscape Intégrité.
is a powerful factor of ecological insulation of natural environments (or semi-natural) within a “hostile” “matrix” more (because in the environmental conditions deteriorated by the secondary human activities or their consequences).
by the insularisation which it causes, by decreasing the rates of dispersion and immigration increases the risks of extinction.
modifies effect-borders them (écotone/edge effect), more or less according to the characteristics of the surrounding matrix.

In France the concept was in particular diffused by the network Man and Biosphère of UNESCO, and the work of Francoise Burel (Thesis at the University of Rennes) was the beginning of a succession of theses and work in Rennes, Montpellier and elsewhere.

Stakes

The principal stake is that of the ecological Intégrité of the medium, because the fragmentation of the habitats are opposed to the vital needs that have the fauna, the Fonge and the Flore of being able to move in the landscape.

The data of ground, as the comparative analyzes resulting from the Cartography of the biological corridors, satellite images, air photographs, or old Carte S show that the ecosystem S are more and more artificialisés and split up, by Infrastructure S of Transport of vehicles, goods or people or of energy (electric lines, phone lines). The hydroelectric stoppings are an equivalent visible and easy to include/understand for the river systems, but other ecological barriers not-physics exist (Pollution S by Pesticide S, Eutrophisant S or others Biocide S are also major factors of fragmentation, more discrete, but concerning vast spaces.

The individuals, but also the populations are confronted with a growing number of “ecological bolts” (barriers physical or immaterial) or “ necks of curiously ”, which - by splitting up the ecosystems abnormally - limits or prohibits the circulation of the individuals and populations and thus the mixture of genes within their normal surface of distribution, at the point to cause regressions or disappearances of species, or to threaten them in the short or the long term.

Even flying animals are affected: It was believed a long time that the birds and bat escaped the impacts from fragmentation by the forest roads , but in addition to certain species are very affected by the Roadkill, various experiments (of which in Guyana within the framework of the impact study and the compensatory measures of the RN2) or with the Brésil on an experimental site located at 80 km in the north of Manaus showed that even on little attended roads, the birds and the bat - in spite of their capacity to be flown - are affected by the presence of roads in the forests. On the attended and noisy ways, the only noise moves away the songbirds (until more than one km under the wind prevailing of highways in Great Britain) and the urban birds must adapt their songs to get along, in particular in the low frequencies ()

The Écologie of the landscape tries to answer crucial questions for the Nature conservation. Which minimal size of habitat and which quality of interconnectivity is it necessary to preserve to ensure the survival of the species which coévoluent there? Does one protect better a greater number of species and ecosystems in large a Natural reserve or several small?

Definition

Natural barriers exist in Nature. Most important are the long ones and high mountainous chains (ex: the Alps, the Pyrenees, the Andes, the Himalayas.). The large deserts, the arms of the sea constitute others of them (for the continental species). The oceans and the majority of the seas are physically inter-connected, but the zones deprived of nutrient, low in Plancton or with Température, particular Salinité or depth show characteristics which confer to them a function of barrier for certain species (coral for example).

These barriers cannot be crossed while circumventing them or, in the case of the mountains, by the collars and/or certain species (birds in particular). Let us note that the migratory birds being themselves carrying various parasites or involuntarily transported species, sometimes in the form of egg or of Spore, they twice a year contribute to transport various organizations, which constitute however only one negligible share of the Biodiversité.

For the continental species, in a normal area catchment (illustration), in fact the rivers if they are biological corridors for certain species, are the principal natural barriers. The rivers are less important obstacles and the still less brooks. The majority of the species, after a certain time can cross or circumvent the rivers. In nature the catchment area is entirely potentially accessible to many species. For the species which cross with difficulty a channel or a road, or have been unable to cross a field treated by Pesticide S, the landscape anthropized, such as it develops for a few decades becomes a succession of more or less insuperable obstacles.

The Homme takes little by little conscience that it is in the beginning the many ones and new ecological barriers which are either of the unsuitable zones to the life of many species, or of the simply unfavourable zones to the circulation and/or the reproduction of the species. They can be material and visible (a wall, a line of TGV or a Autoroute in France provided with a double-fence), but they are often invisible in our eyes (they then are said sometimes “immaterial”). It is possible that all the types of ecological barrier are not identified yet.

Examples of material barriers:

built infrastructures, such as Route S, Autoroute S, Railways, TGV, Canaux ( the Panama Canal or Suez cross and isolate from the continents ), rivers channeled, storage dam or hydroelectric, lines with high voltage, antenna S or cables on the corridors of migration, etc
residential areas and very devegetalized
artificialized zones
zones of Agriculture and intensive Sylviculture
zones of experimentation or culture GMO In addition to certain plants produce their own pesticide, these fields owe théoriquemnet managed not to facilitate the dispersion of Pollen S, seeds or others Propagule S.

Example of immaterial barriers:

Odor S (the odor left by a dog or human can during a few hours or days to disturb apprehensive animals which is very sensitive there)
Microclimat S (Température, Hygrométrie,…)
disturbance, Disturbance, sound Surfréquentation
Pollution
luminous Pollution
thermal Pollution of water, even of the air or the ground (badly isolated heating network)
atmospheric pollution (Biocide, Ozone, Heavy metals,…)

Effects of edge

Saunders and his/her colleagues in 1991, then Collinge in 1996 show that the edges artificially created by fragmentation undergo immediate deteriorations of big factors such as temperature, Hygrométrie, wind, luminosity Albédo, odors which disturb or block displacements of certain species. Other factors are often faded with means and more long run (quality of ground and water, level of the tablecloth, quality of the air, noise/disturbance, etc). These effect-edge disturb initially the animal, fungic and vegetable communities which are near the edge of the islands or small islands isolated by the phenomenon from fragmentation. Ranney and his/her colleagues in 1981, and Chen and its team in 1992 or Matlack in 1993 show this fact, noting for example, that " lisières" effects; are definitely measurable in the North-American forests fragmented on 15 to 240 meters according to the studied animal species and vegetable.

The drainage and the pumpings carried out in the " matrice" écopaysagère can - following the fall of the tablecloth - upset the ecology of a small island which seemed a priori saved, and this good beyond its edges, until in its heart and in-depth.

Outdistance between fragments

The distance between fragments is an important component of the model theory of the insularisation. It constituted one of the indices of fragmentation, practical for the cartography SIG. Nevertheless, as of 1986, Forman & Godron 1986 admit that in reality, the effect of the distance between fragments is relative. It varies according to the species (ubiquists, flying, swimming… or specialized and inapt for great displacements). And it is more or less reduced or to surpondérer according to other factors, such as:

the nature of the matrix (the medium which separates the small islands is more or less " hostile" with the insularized species),
the habitats which it shelters (habitats of substitutions sometimes),
the degree of similarity between the small islands and habitats of the matrix (close or on the contrary very " opposés"),
intensity, dates, and the types of activity human which proceed there, etc

Cut, volume and the shape of the fragments

They influence the relative gravity of the effects of edge, for geometrical ratios in particular, and according to their exposure to the wind, sun, rains, etc The small lengthened fragments or framents and too ends will be affected by the effects of edge, because they do not lay out any more in their center of important intact surfaces (sometimes known as " heart of habitat").

Example: Parcelling out by the grid systems

The most opaque infrastructures with animal and vegetable or high-risk displacements of " Roadkill " (mortality animal by collision with vehicles) remain the network of road transport, highway and railway (line TGV). The highway network and highway world continues to grow quickly. Its densified grid, is inter-connected and the roads are increasingly broad and “artificialisantes”. The number of passages to fauna is lower than the needs by far. The parcelling out impact of the roads was very underestimated, but one realized some only very recently. Fault of being able to quantify it, the impact studies continue to minimize it. For the small mammals, the insects, the micro-organisms and certain plants, the problem is generally purely and simply eluded.

the sound Pollution seems to be stabilized in the rich countries, but grows quickly in the developing countries. Contributing to the disturbance of the species, it relates to at least 70% of the urban green areas and particular gardens, and natural spaces bordering the main axes of displacements. For reasons of cost, she is considered only for the dwellings very close to the residential areas. Studies carried out in the United Kingdom along the highways highlighted a progressive disappearance of the songbirds on a tape of approximately 2 km (and up to 4 kilometers under the wind prevailing). This disappearance is correlated with the level of Décibel S, but also varies according to the proximity of the axis, the relief, the traffic, the wind prevailing, the nature of the coating, the quantity of trucks, the nature and the density of the vegetation, etc For this purpose is added those of the pollution deposited by the vehicles (Benzène, Plomb, metals of the group of the Platine resulting from the catalytic pots, etc).
It would be interesting to measure if the disturbance related to the noise is identical on the railways where the noise is often more important in decibels, but discontinuous in the temps.
Notons also that the air traffic increases in a continuous way (from 7 to 10% per annum) in the last years, and that its impact is very badly measured.
the luminous Pollution by the lighting of the buildings, monuments and infrastructures and by the headlights of the vehicles or is not analyzed very little. It is very important in the rich countries. It seems that it has impacts which under were also very estimated.
the parcelling out by the roads is not exerted that surfaces some, the effect-barrier also exists for the digger species of the ground or and for other species which use their galleries. The species whose spores, germs or seeds, organizations or propagules are transported by this one can also be affected. The soles of ploughing, the ploughing itself, the funds of road to which one often added lime and/or cement are homogenized, prepared and rammed at the point to have resistances equal to that of a concrete. They constitute an absolute physical barrier for the moles, microphone-mammals, worms of ground, insects and their processions of associated micro-organisms. These digger animals cannot exert their function of any more “tunnellers” décolmatant, draining and airing the ground, which takes part in the maintenance of the underground biological continuums which one discovers or redécouvre the importance for the trees in particular. One will find in the road sole some bacteria, but of which mobility is very reduced. So of the organic matter was hidden, only the mushrooms and some micro-organisms will circulate and possibly bore the macadam. Sometimes, the roots of the trees will bore the substrate where it is fragile or faulted, but without compensating for the absence of a surface continuum. The tunnels offer a means of circulating by preserving ecological continuities, but they are expensive and since the accident of the Tunnel of Mont Blanc, the developers limit them.
the barriers are sometimes chemical . The funds of road indeed sometimes consist of industrial dumps, toxic ashes of incinerators, blast-furnace slags rich in heavy metals and other microphone-pollutants, certain waste of foundry. Million tons of these products was accepted with contents of heavy metals and/or organic pollutants quite higher than the standards ground (standards AFNOR). In the same way, sometimes less officially, other waste known as inert or stabilized and which one realizes with use that they were not it, were used for example to restore banks of rivers or channels. In the acid and/or sandy argillaceous mediums (often naturally acid) the building sites are stabilized with lime and/or cement (until more than 10 kg per m). These products are “toxic” for a great number of species which live in the acid media. To also note that milts and products of streaming of the fresh special concretes, such as those which are used with the works as flagstones type, ditches, basins, low wall run on the spot, reach a pH of 11. Although the additives of manufacture, with saying their users are labellisés NF, these milts can present a spectacular neurotoxic character (paralysis and immediate death by simple contact) for the majority of the animals to cold blood… and this during several months.
On the low sides, dependence or fields close treaties with Pesticide S constitute an additional and absolute barrier for many species, often during the period of culture which is also the period of development of the species which would need to circulate on the territory. The Regrouping S and the agricultural intensification which often follow the construction of roads produced in almost all the countries of the field increasingly vast and hostile to the Biodiversity. The roads also contributed to the retreat of the scrap-metal and the networks of ditches and ways which formerly constituted an immense network making it possible the species to circulate. Thickening of transport, and their relative lower costs allowed the breeding except ground, which resulted in a retreat of the pasture to the profit of corn, which also has night with the species of the mediums open and enherbés, and with their possibilities of mobility.
Dryness and quality of the ground . The drainage and the proofing of the roads and their accesses are increasingly effective. The surface water (polluted) is collected in ditches sometimes completely impermeable, worms of the basins them also often impermeable and/or isolated (nettings of safety, abrupt and/or plasticized walls). Of course, the real risks of pollution of the Ground water, particularly in field-collecting justify the separation of water. But the absence of water or moisture in the ditches and under the roads is an additional factor of disappearance of species. A too dry basement is in addition inhospitable and impenetrable by the majority of the digger species. He is opposed to the underground circulation of fauna. The draining effect of the embedded roads is added to that of agriculture, and the sole of ploughing which extends in the campaigns blocks the digger species in a volume which entire is exposed to the plow shear and the thermo-hygrometrical shocks.
Rupture of the thermo-hygrometrical Continuum. joint measurements of temperature and moisture carried out in edge of road or waterproofed zones show that the effect of distinct (a road in a forest by ex) and the effects of edges can result in important and permanent falls of the hygroscopy with impacts which had been very underestimated:

total and durable Disappearance of the dew on a tape which can reach 40 m on the edge of certain exposed infrastructures (zones of plates with perched tablecloths, cliffs,…)
Abaissement of the ceiling of the tablecloth
Diverses hydrological and pedological disturbances can accompany and reinforce the phenomenon.
drying Effect. Broad and linear roads with the black macadam, like the forest trenches, where the devegetalisation of a ground sometimes exacerbate very strongly the dehydrating effect of the wind and the sun. They involve a fall of the very important hygroscopy (2 to 3 times less moisture) with figures which can sometimes be lower than the Saharan averages, including in wet tropical zone at the beginning of rain season (French Guiana). This phenomenon was even paradoxically observed above a stretch of water (stopping EDF Petit Jump in Guyana, where on a large surface, the trees were drowned and did not évapotranspirent more). Many insects and certain microphone-mammals express very Nets behaviors of avoidance of the zones discovered and devegetalized where the hygroscopy falls, where the temperature varies brutally. For certain species which are however fast and sharp with the race or the flight, this has been checked day like night and even on a road closed with circulation for several months. For these species, a road seems to be the equivalent of an invisible and insuperable vertical wall, of which the “thickness” can be quite higher than the road… For these same species, a vegetalized dirt track, a paved road or a semi-végétalisé carpark where the grass growth is not an obstacle. It was shown that even for a 10 m broad forest road where only 25 cars/days pass, the phenomenon exists. The impact on the birds is more complex and different according to the species. They are the domestic mammals (dogs, cats), and the wild mammals (Mustélidé S, Renard, Genette, Wild rabbit, Chevreuil, Sanglier, Hérisson, Rat S, Souris, Musaraigne) which seem the least constrained (and also the Amphibien S at the time of the migrations) but they are potential victims of the vehicles…

For all these reasons the highway network prohibits the transverse and longitudinal circulation of many species. By doing this, it strongly disturbs the diffusions and natural flows of genes essential to the normal functioning of the ecosystems. The fragmentation of the ecosystems is also responsible for the genetic loss of diversity: the species, confined in habitats increasingly restricted are condemned to the Endogamie, which causes problems of consanguinity and genetic drift.

The networks of infrastructures and the urbanization which they encourage continue moreover to consume of agricultural natural space (the equivalent surfaces of two departments already would be waterproofed and thus transformed into biological quasi-desert or space ecologically very impoverished of France; the proofing which has some practical advantages in the short run, is paid in Sécheresse, Inondation and erosion, pollution and harmful effects of all kinds).

Some rare species of microphone-mammals or birds (Black and white S, crow S, starling X, Pigeon S, falcons kestrels) found along the roads of the mediums of substitution. The highway network is nevertheless increasingly hostile and “impermeable” with the circulation of fauna and the flora (the concrete ditches, fences with small meshs, walls anti-noises, edges, parapets, quay levels or low walls central tight with the small fauna, drainage of the road and the banks, trenches increasingly broad, frequent mowing, use of pesticides and inhibiters of growth, cumulate their respective effects.)

Certain species are recognized like particularly useful or important for the operation of the ecosystems and for this reason protected by the law. Among them, the hedgehog and the Amphibians, of which respectively more than one million and several million of individuals are still each year victims of circulation, although their number does not cease being reduced. Same manner, some plant species were supported by the infrastructures, but they are often banal plants, ubiquists even invasive (Renouée of Japan, Balsamine, etc). The very homogeneous plantations (including genetically) of the edges of infrastructures also supported the diffusion of microbes or parasites (ex: bacterial Feu for rosacées which was formerly planted on the edges of highways).

Note: In Africa, and in many developing countries of the bands parallel with the roads were used the day by the walkers, the asses and horses and other animals of pack who went along the roads, allowing of night a use as biological corridor by certain wild species. Often, in particular because of many accidents, the authorities tend to widen the roads and to remove these vetgetalized verges.

Provisional solutions

To count the Amphibians and the reptiles which cross the road and/or to guide them towards a batrachoduc (tunnel allowing them to cross under the road, more in safety), of the collecting provisional devices (of panels type, covers or nets with very fine meshs) can be had on the edges of the roads near the known points of crossing at the moment of the migrations Amphibians (generally of the adults going to their zone of big shot at spring, or while returning). These devices are posed only at the time of the migrations and the animals collected in buckets are transported other side, or they are permanent if there exists a batrachoduc. The tritons knowing to climb a vertical wall smoothes, an edge is often envisaged on the high part. Écoducs can then be positioned at the judicious points, which one can have also located by counting the corpses of animals. These devices, if they are not also correctly buried are sometimes less effective for the young people of the year who turn over in the wooded or meadow mediums, measuring only a few millimetres, they sometimes pass under the judicious rigid plates to guide them and die then many, dehydrated or crushed on the road.

See too

Internal bonds

External bonds

Document IFEN (Oct. 20006) on certain impacts of the roads and vehicles
Page of Site PDBFF of the project devoted to the study of the fragmentation of the Brazilian Amazon forest
teaching Note of the Ministry for Walloon Envionnement on ecological fragmentation
Thesis of doctorate entitled " Mode of use of the medium split up by species forest with the discrete practices, the marten of the pines Martes martes " , by Vincent Pereboom (75 pages)

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