IAP-25-077

Role of Plant Functional Diversity in Modulating Grassland Responses to Grazing and Drought

Grasslands are globally important biomes that play a critical role in supporting biodiversity and delivering key ecosystem services, such as carbon sequestration; regulation of climate, nutrient and water cycles; pollination; and provision of food (Bengtsson et al., 2019). Changes in UK policy priorities mean that grasslands are under increasing pressure to deliver multiple ecosystem services beyond food production, including biodiversity enhancement and carbon removal (Magistrali et al., 2021). In the current policy context, UK grasslands have the potential to play a crucial role in the diversification and decarbonisation of UK agriculture (Bengtsson et al., 2019, Magistrali et al., 2021).

Regenerative farming has become increasingly popular among practitioners as a means of sustainably managing agricultural systems (Morris, 2021, Khangura et al., 2023, Magistrali et al., 2021). In grazing systems, regenerative practices are designed to enhance the functional diversity of the plant community, improve soil health, and regulate the frequency and intensity of grazing to minimise land and soil degradation (Morris, 2021, Khangura et al., 2023, Kreyling et al., 2017, Magistrali et al., 2021). These nature-positive measures are thought to maintain or increase yields, while simultaneously enhancing biodiversity, soil carbon storage, and increasing ecosystem resilience to climate shocks, such as drought (Morris, 2021, Khangura et al., 2023, Kreyling et al., 2017, Cole et al., 2019, Magistrali et al., 2021). Notable agri-food businesses, such as Unilever, Nestle, Waitrose, and Cargill, have signalled their support for regenerative farming by funding large-scale field trials, farmer support programmes, or privately-financed incentive schemes (Gazette, 2024, Unilever, 2024, Cargill, 2025).

However, while there is evidence that higher biodiversity promotes ecosystem prcoesses and resilience to disturbance at a global scale, less is known about the ecological mechanisms that underpin plant dynamics in regeneratively farmed grasslands (Kreyling et al., 2017, Cole et al., 2019, Morris, 2021, Khangura et al., 2023, Magistrali et al., 2021). At present, the scientific evidence for the costs, benefits and trade-offs of regenerative practices lags adoption and implementation by practitioners and industry. Development of this evidence base is urgently required to inform best practice guidelines, policy actions, and private investment given the rapid pace of change.

To address this knowledge gap, we will investigate if and how plant functional traits modulate grassland responses to grazing and drought, comparing conventional with regenerative grazing systems in the North of England. We hypothesise that:
H1. Ecosystem resilience will be contingent on the functional composition of the plant community—More rapid recovery occurs in ecosystems where the plant community contains functional traits that favour compensatory growth (Table 1) (Zhou et al., 2022, Reinelt et al., 2023, Chandregowda et al., 2023)
H2. Responses to grazing or drought will differ depending on the combination of plant functional traits—Recovery patterns will depend on the relative abundance of specific functional traits because some traits (e.g. specific leaf area) confers greater resilience to grazing and other traits to drought (Table 1) (Díaz et al., 2001, Wellstein et al., 2017)

We build on Newcastle University’s considerable expertise on this topic and will utilise existing field-scale regenerative farming trials set-up at Newcastle University’s Farms (NUFarms), including the Defra-funded Mob Grazing trial and the EU Horizon Sustainable Permanent Grassland (Super-G) programme.

Field experiments will be conducted at NUFarms, which hosts several externally-funded projects that explore the impacts of regenerative practices on yield, animal welfare, soil health, and greenhouse gas exchange. This project builds on the existing research infrastructure to deepen our understanding of how plant functional diversity influences ecosystem responses to grazing and drought.

Experiments will consist of field and greenhouse experiments. In the field, we will investigate how variations in functional trait composition modulate ecosystem responses to different grazing regimes and drought. We will quantify plant species diversity and key functional traits (Table 1) across different experimental sites prior to the imposition of disturbance. We will quantify key response variables (e.g. growth rates, photosynthesis, NPP, plant and soil nutrient content) before and after disturbance. Post-disturbance recovery of these response variables will be used as an index of ecosystem resilience. Conventional and regenerative grazing will be simulated by regulating livestock access to the treatment plots in accordance with established protocols developed for the Defra Mob Grazing trial. Drought will be simulated using rain shelters to limit rainwater input to soil, with electric fencing employed to regulate livestock access.

Complementary greenhouse studies will manipulate plant functional traits through direct planting, using realistic admixtures of plants. These plant assemblages will then be exposed to simulated grazing (e.g. clipping), drought, and grazing x drought treatments. Key response variables will parallel those for the field experiment.

Year 1

• Literature review.
• Planning and design of field experiments.
• Establishment of field plots, including rain exclusion studies, and collection of baseline data on plant diversity, functional traits, and soil properties.
• Implementation of grazing and drought experiments and quantification of ecosystem responses to the experimental treatments.

Year 2

• Continuing laboratory analysis of plant and soil samples collected during Year 1.
• Statistical analysis of the field data; preparation of the data for public presentation (e.g. conference or seminar presentation)
• Implementation of grazing and drought experiments and quantification of ecosystem responses to the experimental treatments for a second growing season.
• Planning, design and implementation of greenhouse experiments.
• Laboratory analysis of plant and soil samples collected for the greenhouse experiments.
• Statistical analysis of the greenhouse data.

Year 3

• Continuing laboratory analysis of plant and soil samples collected during Year 2.
• Continuing statistical analysis of the field and greenhouse data.
• Preparation of the datasets for publication.

Year 3.5

• Data synthesis and preparation of the final PhD thesis.
• Continuing preparation of the datasets for publication.

Key knowledge and skills developed over the course of the project include:
• Logistics and project management.
• Experimental design and statistical analysis.
• Applied knowledge of ecosystem science, including plant physiological ecology, plant-soil interactions, and soil biogeochemistry.
• Ecological sampling techniques, including plant species identification, quantification of plant functional traits, ecosystem processes (e.g. NPP), and soil biological and chemical properties.
• Science communication and academic writing, including presentation of data to public fora (e.g. conferences, workshops) and preparation of datasets for publication.