Grasslands are the surfaces of grass (in the broad sense), whose cultivation and defoliation are intended to feed farm animals, and more precisely ruminants and herbivores.
If not exploited, the grassland will naturally change towards moorland or forest under European climate. That means that grasslands exist only through farming and use by the animals, and thus consequently, by the activity of breeders and farmers.
Summer and mountain pastures – the areas above the mountain tree strata (around 1500 meters in Europe) – are the only exception to this rule in Europe. Elsewhere in the world, we find this exception in two regions: Chinese Inner Mongolia and Patagonia (Argentina). In these two configurations, the evolution towards moorland or forest is not possible due to a significant drought in the summer or winter and relatively cold climate.
The role of grasslands is not limited to the agricultural domain, but also extends to other sectors such as the environment (water quality, biodiversity, landscape structure, fixation of organic carbon in the soil), economy (since the forage is also sold on the worldwide market), and social structures (insofar as they ensure the wages of million of farmers around the world, as animals production is a central issue for the viability of small farms worldwide).
Grasslands cover 36% of the world continental surfaces.
Grasslands cover 20% of the mainland French territory. As comparison, the annual crops account for 26%, and the forests for 28%.
They represent 45% of the UAA (Useful Agricultural Area) in France, and from 30 to 90% of the UAA of the dairy farms.
Grasslands provide various ecosystem services
Following the guidelines of the Millenium Ecosystem Assesment (2005), it is posible to identify that grasslands provide many ecosystem services, contributing to the production of food, to the preservation of the environment and providing cultural services.
Grasslands, Biomass and Food
The main role of grasslands is to produce [glossary] biomass [/glossary] and as such to provide livestock with pastures consumed directly on site (grazing), as well as with fodder stocks for the winter months (hay, silage, haylage). But, the breeding of these herbivores (cattle, sheep, goats, horses) also provides various products to us – the consumers; like milk, butter, or meat. And also recreation in the case of horses.
Biomass quantity and quality (digestibility, protein content) are thus of critical importance, as they determine both the feeding value and the ability to produce high quality stocks, and the number of animals that can be fed per unit area.
Grasslands and Product Quality
Animal product quality is of major concern for the consumers. They must ensure a real food security, with no health risk for the consumer and also contributing to cover the metabolic needs of the consumers. Some metabolic compounds, especially fatty acids, in meat and milk may prevent health hazards. The composition of the animal diet determines, in a certain extent, the quality of the animal product.
Grasslands and Biodiversity
Grasslands play a key role for preservation of biodiversity. Several features explain this role of critical importance for our societies.
- Because of the very large acreage, this main component of all agricultural landscapes dramatically influences biodiversity;
- Grasslands are diverse, in their botanical composition, in their management, in the presence of animals. As such they induce a large diversity of environment that is favorable to hosted biodiversity;
- Most grasslands are perennial. This means low levels of perturbation, that is again favorable for biodiversity;
- Eventually, most grassland swards are composed of several grasses and legumes. This intra-sward botanical and genetic diversity is favourable to biodiversity.
This will be further presented in a dedicated chapter.
Grasslands and Climate Change
- As a consequence of the increase in the greenhouse gas, and especially the CO2 content in the atmosphere, climate change will on average induce an increase in the mean temperature, change the rainfall regime. This will influence the dynamics of dry matter production along seasons by grasslands and forage crops as well as the chemical composition and the feeding value of the biomass.
- Climate change will induce more variation among years. This means large variation in biomass production and as such raises a key question for the farmers who have to ensure a sufficient feed resource for their animals. Thus, the climate change will require more robustness in the farming systems.
- As climate change is induced by the emission of greenhouse gas (GHG) emissions, to which farming systems contribute, grasslands ans associated animal systems must seek for options to reduce their contributions to the GHG budget. Grasslands and associated animals systems contribute three GHG: CO2, either through direct (fuel) or indirect (produciton of fertilizers and equipments) ways, CH4 produced by ruminants as a counterpart of their ability to metabolise cellulose in the rumen, N2O as a consequence of the application of organic or mineral nitrogen fertilisers. Changes in grasslands botanical composition and management and in animal husbandry may significant modify the emission of GHG.
- Mitigation of climate change is possible thanks to the storage of C in the soils. The world initiative 4/1000 aims at sligthly increasing the C storage in the soils through modification of land use and crop management. Grasslands, because of their persistency may play an essential role to meet this key stake.
Role of Grasslands in Biogeochemical Cycles
In addition to their role in forage production, grasslands indeed play a very important role in the environment and environment preservation. They allow the maintenance of a certain biodiversity, plants and animals, but also control many biogeochemical cycles. They limit transfers of nitrogen towards surrounding waterways (including groundwater), they collect and store carbon, and facilitate accumulation of organic matter (OM) in the soils.
Increasingly, it seems that all these cycles are closely connected with the cycle of OM. Ultimately, these processes comprise and govern large atmospheric and hydrospheric flows, implying very long time periods. In the event of modification of one of these cycles, effects will be observed only several years, decades, even centuries later.
Among those biogeochemical cycles, nitrogen is a key element because of its role in soil fertility and plant growth, of its potential role as a pollutant (water and air quality) and above all because it is the core atom of the amino acids and proteins, those molecules that are essential to human life and not substituable.
Nitrogen and Grasslands
Grasslands are highly dependent on nitrogen, as it allows, among other things, to increase production and also to improve forage quality. However, this nitrogen naturally fixed by leguminous plants is increasingly supplied in form of nitrogen fertilisers by farmers. Indeed, in 2010, at the world level, 100 Mt of N were ‘fixed’ as ammonitrate, through the Haber-Bosch industrial process.
Since the 80s, nitrogen losses appear to be much larger than what was previously thought. Either by leaching or volatilisation, nitrogen can escape in form of nitrate (NO3) and pollute soil and surface waters. An increasing concern must be paid to reduce these losses and as such the close the cycles, at the plot, farms and landscape levels.
More detailed information is available on the dedicated page ‘Role of Nitrogen in Grasslands’.
Grasslands and Water Preservation
Grasslands act as a buffer in respect to pollution, that is to say, the polluting load decreases between “input” and “output” of the grassland. The value of this buffering effect evolving along time, on polluting substances and various other compounds, led to the introduction of the concept of buffer capacity which takes into account these different factors.
Water is obviously essential to all organisms that inhabit the earth. It is equally useful and necessary in many sectors, such as industry, as well as for individuals and recreation. But eventually, used for all these activities water is a rare commodity, and it is important to protect it in terms of quality and quantity.
Grasslands, as well as other vegetated areas such as forests or annual crops (cereals, etc..), play a key role in this protection, since they fully participate in the water cycle.
More detailed information is available on the dedicated page ‘Grasslands and Water’.