Permanent grasslands or temporary grasslands may have positive effects on hosted biodiversity.
The positive effects are partly related to the complexity of the hosted flora and partly to the control methods of the grasslands.
These effects are either direct or indirect.
As direct effects, some of the animal species are dependent on one or more grassland plant species.
In the same way, certain grassland species constitute a major trophic resource for numerous animal species. They are generally plant species, which don’t belong to the grasses or to the legumes, and can be found in the low exploited environment.
The presence of these various plant species depends on the fertility and the control method of the grasslands, and in particular on the harvesting methods.
Thus, the control of the grasslands, in particular the level of fertilisation and the dates of harvests, will be major determinants to support or not the biodiversity accommodated by the grasslands.
A particularly remarkable example is that of the corncrake (Crex crex), dependent species to the easily flooded grasslands whose population in France presented a severe collapse. The reduction of these populations has been stopped by changing agricultural practices in these easily flooded grasslands (Broyer, 2001 (Broyer J., 2001. Plaidoyer pour une politique européenne en faveur des écosystèmes prairiaux. Le Courrier de l’Environnement 43, 41-50)).
In fact, this bird, identifiable by its song, breeds in wet meadows and nests at ground level. Consequently, when the exploitation and cut of these grasslands happens before the chicks are autonomous; any early mowing leads to the destruction of part or all of a population.
Under the action of ONCFS (French National Hunting and Wildlife Agency), agreements were made with the farmers working in these wetlands. This helped to increase their population in the Saone and Loire valleys.
However this evolution of practices and the harvest dates is not always a success. Thus, equivalent attempts to preserve partridge populations in the Massif Central did not have the same success.
The heterogeneity of the meadow is the first element contributing to the indirect positive effect of biodiversity. The diversity of vegetation structures, the variations of relative predominance between species, in particular between the grass family and legume family, can be favourable to the abundance of certain species and the construction of populations of the hosted species.
A positive role of the heterogeneity of landscapes, associated to some extent with the presence of grasslands, should be emphasised as much more important.
This heterogeneity, the abundance of various forage species, in particular that of Lucerne, and the method of control or the agronomic practices on these forage surfaces, explain the abundance of a patrimonial species of Avifauna: the Little Bustard (Tetrax tetrax).
The cause of the relation between the heterogeneity of the landscape, practices and crops, is indirect, and is explained by the abundance of grasshoppers, dependent on the grasslands, serving as food for the bustard’s chicks.
Among the indirect effects, it is also advisable to underline the benefit on biodiversity generated by the fixed elements of the landscape frequently associated with the grasslands.
Among those, two are very important: hedgerows and ponds.
Hedgerows, by their biological diversity and their specific diversity, which constitute sources of food and additional sources of shelter, by their physical structure, and the fact that they constitute particular biological corridors, the hedgerows constitute extremely beneficial elements for safeguarding and the enrichment of biodiversity.
This assumes, however, that their maintenance is adapted and in particular that it does not have recourse to flail cutter.
Ponds, the second element favourable to biodiversity, are the wetlands favourable to the watering of the animal populations (mammals and insects), which contribute to the heterogeneity of the landscapes.
In this case too, the properly adapted maintenance of these wetlands is paramount: water quality plays an important role in maximising the beneficial effect of ponds.
Grasslands and Pollinators
Grasslands and forage crops can play a particularly important role for a group of species, namely pollinators, domestic and wild.
In fact, grasslands can host species that are rich in pollen and highly nectarous, providing, through flower production, pollen and nectar throughout the year.
They thus supply an important food resource to pollinators at times when the resources resulting from the annual crops (colza and sunflower) are particularly limited.
The increase in the number of plant species leads to an increase in the number of hosted pollinator species (Banaszak, 19921)).
As for the other aspects of biodiversity, the link with fixed landscape elements (hedgerows) has a significant impact on the density of pollinators.
¹Banaszak J., 1992. Strategy for conservation of wild bees in an agricultural landscape. Symp. On agroecology and conservation issues in tropical and temperate regions. Sep 26-29, 1990, Padua, Italy. Agriculture ecosystems and Environment 40, 179-192