Do Multiple Extreme Weather Events Threaten Grassland Functioning?
Grasslands are an important ecosystem, covering around 7% of the world's land area. They provide many benefits like food production, biodiversity, and regulation of water, climate and pollution. However, climate change is bringing more extreme weather like heavy rainfall leading to floods or lack of rain causing droughts. Professor David Chadwick and colleagues conducted field experiments to see how grasslands respond to single extreme events of flooding or drought. They also looked at the impact of back-to-back "double whammy" events - flooding followed closely by drought. Would two extremes be worse than one?
In this study they flooded large areas of grassland in spring then later imposed a summer drought on the same plots. Grassland performance was measured using a wide range of ecosystem service indicators above and below ground before, during and after the extreme weather.
The results showed that the flood had a much bigger impact than the drought overall. More measurements were changed by the flood immediately and these lasted longer. For example, the numbers and types of soil microbes took over a year to recover after the flood but bounced back quickly after the drought. Overall, the grassland proved resilient to extreme events.
Contrary to expectation, having a flood followed by drought did not make things even worse than the flood on its own. In fact, some soil measurements recovered faster when the extra drought dried out the soil after the flood.
However, earthworm numbers increased after the flood as young ones hatched but then crashed when the drought hit, showing how one extreme after another can seriously affect soil life. Persistent changes to plants and microbes after the flood will probably affect the grassland's health and ability to provide benefits in the long-term.
This study shows clearly that extreme floods and droughts hit grasslands in different ways. But weather extremes one after another do not necessarily have an even worse impact. Drying out after a flood might even help soils recover better. However, big shifts in soil life could change how well grasslands can cope with future climate shocks.
This highlights the need for more studies on how ecosystems respond to extreme events. Grasslands resisted or recovered from single events, but climate change is bringing more frequent and intense weather extremes. Farmers may need to adapt to sustain food production and other grassland services as compound disasters become the new normal.