Multi-species mixtures promote yield stability under rainfed AND drought conditions

Overview
Higher plant diversity in intensively managed agricultural grasslands resulted in higher yields AND less variation in yield. This represents gold-standard yield stability. We found this under undisturbed (rainfed) and disturbed conditions (experimental drought for 9 weeks).


Climate change is expected to cause an increase in the frequency and intensity of drought events. Intensively managed agricultural grasslands are economically important and contribute to food security. Little is known, however, about their response to extreme weather events.


Our research shows that a modest increase in the number of agronomic species in agricultural swards is a practical, farm-scale adaptation measure to extreme weather events.


From an ecological perspective, this research demonstrates a positive relationship between diversity and ecosystem function observed under regular conditions being maintained under disturbed conditions.

3m x 5m rain shelters were used to simulate drought.
The shelters excluded rainfall, but were open at the top,
sides and bottom to prevent large increase in temperature.

What we did...
Over two years we investigated the effects of experimentally imposed drought on intensively managed grassland communities (5 m x 6 m plots) of varying richness (1, 2 and 4 species), and comprising four species (Lolium perenne L., Cichorium intybus L., Trifolium repens L., Trifolium pratense L.). In each year a summer drought period of nine weeks with complete exclusion of precipitation was simulated, inducing severe drought stress at Reckenholz (Zürich, Switzerland), and extreme drought stress at Wexford (Ireland).


Main result: species richness = higher yield, and lower variation in yield
Mean yield and plot-to-plot variance of yield were measured across harvests during drought and after a subsequent post-drought recovery period. At both sites, there was a positive relationship between species richness and yield under both the rainfed control conditions and under drought. Under rainfed control conditions, mean yields of four-species communities were 32% (Wexford, Ireland) and 51% (Zürich, Switzerland) higher than the average of the four monocultures. This positive relationship was also evident under drought, despite significant average yield reductions due to drought (-27% at Wexford; -21% at Zürich).
At both sites, four-species communities had lower plot-to-plot variance of yield compared to monoculture or two-species communities under both rainfed (-49% smaller standard deviation) and drought conditions (-24%), which demonstrates higher yield stability in four-species communities.

Effects of species richness and drought on yield mean and standard deviation (SD) across harvests under rainfed control and drought conditions at Wexford (A) and Zürich (B). Different letters indicate a difference at P < 0.05 based on regression analysis, except SD under drought at Zürich, which is at P < 0.1 (means: inference in black upper-case letters; SD: inference in grey lower case letters). See Haughey et al. 2018 for details.

REFERENCES

Haughey, E., Suter, M., Hofer, D., Hoekstra, N.J., McElwain, J.C., Lüscher, A and Finn, J.A. 2018. Higher species richness enhances yield stability in intensively managed grasslands with experimental disturbance. Nature Scientific Reports.8:15047. Open Access paper with R code in supplement, and data available in Dryad.

Hofer, D., M. Suter, E. Haughey, J. A. Finn, N. J. Hoekstra, N. Buchmann, and A. Lüscher. 2016. Yield of temperate forage grassland species is either largely resistant or resilient to experimental summer drought. Journal of Applied Ecology 53:1023-1034.

Acknowledgements
A contribution to the research leading to these results was conducted as part of the AnimalChange project (FP7/2007-2013), grant agreement 266018. E.H was supported by the Teagasc Walsh Fellowship programme.