Optimising fertilisation to preserve grassland biodiversity and multifunctionality in the context of rising temperatures -PRABIES

Understanding the link between biodiversity and the level of ecosystem service supply is complex. The relationship is not linear or unidirectional and it can be influenced by climate variables. We studied this relationship through adapted statistical models, in a grassland context.

The project investigated how biodiversity, assessed using various metrics (species richness, functional diversity, evenness and rarity), is ‘transformed’ into effective ecosystem service packages through relevant agro-pastoral practices. For example, grasslands provide numerous ecosystem services such as fodder production, the maintenance of habitats for pollinators, or open and varied landscapes. PRABIES placed particular emphasis on the climate change adaptation service, i.e. the ability of ecosystems to adapt to climate change and variability, by analysing the buffering of hazards enabled by grassland plant diversity and the ability of plant communities to reassemble to provide a relevant bundle of ecosystem services under a new climate.

Approaches

PRABIES aimed to describe the impact of climate change adaptation practices on the supply of ecosystem services (ES) in grassland environments, to assess whether adaptation practices have a positive or negative effect on biodiversity, and the related ecosystem services.
 

PRABIES made it possible to describe the complex interactions between these factors through the use of structural equation modelling (SEM), a statistical tool for assessing the strength and significance of variables in direct and indirect interactions. This tool was applied to a dataset of 100 permanent grassland plots in the Massif Central according to an altitude and latitude gradient, including management data and proxies for three types of ecosystem services (provisioning, regulating, and cultural).

PRABIES also collected information through interviews with 15 dairy farmers in the Massif Central about their strategies. These interviews described the role of permanent grasslands in the livestock feeding system and their management, and in particular fertilization. They also made it possible to characterize farms where more than 75% of the crop rotation included forage crops. On some of these farms, farmers felt ready to face a new climate.

Results

Direct effects of climate change on permanent grasslands

The SEM showed that at an average temperature of 6.7°, multifunctionality was proportional to fertilization, whereas at an average temperature of 12.2°, the relationship between multifunctionality and fertilization took the form of a bell curve. This curve indicates that at 12.2° multifunctionality peaks at 70 kg of N per hectare. These patterns can be explained by the fact that multifunctionality is positively correlated with biodiversity and that biodiversity is more or less promoted by fertilization, depending on the temperature (due to processes of more or less strong competition between plant species).

Livestock farmers' climate change adaptation strategies

Adaptation strategies modulate:

• •    The maintenance of permanent grasslands by livestock farmers who view them positively, in a climate that is not very dry or cold;
• •    The conversion of permanent grasslands to forage crops or temporary grasslands by farmers who view them negatively, in hot and dry climates
• Adaptation strategies do not involve the level of fertilization.

Changes in multifunctionality resulting from a rise in temperature

Simulation of changes in multifunctionality resulting from a 1.5°C rise in temperature within a sample of permanent grasslands representative of forage systems shows that:

• The degradation and conversion of permanent grasslands do not affect the same systems.
• Some systems limit both phenomena, by purchasing more forage and concentrates per livestock unit (LU) and selling less milk per unit of area (ha) than others.

Participants

INRAE units involved

• UREP - Unité de recherche Écosystème Prairial
• UMR Herbivore - VetAgro Sup

Partners

• CBN - National Botanic Conservatory of the Massif Central