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June 21, 2024

Extreme Droughts Having Significant Impacts on Grasslands and Shrublands Globally

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Jan 9, 2024

New Research Shows Worsening Droughts Causing Lasting Damage to Vital Ecosystems

A series of new studies published this week reveal that extreme drought events are having alarming impacts on grasslands and shrublands worldwide. These important ecosystems are showing slow recovery rates even after drought conditions ease, leading to lasting degradation.

Researchers from over a dozen institutions contributed to a special issue of the Proceedings of the National Academy of Sciences examining the effects of extreme drought on grasslands and shrublands globally. The findings paint a concerning picture of extensive damage and transformation of these habitats, which cover about 40% of the world’s land areas excluding Greenland and Antarctica.

“What we see is that grasslands and shrublands are very vulnerable to extreme drought,” said Dr. Nona Chiariello, an ecologist at the University of California, Santa Cruz and co-author on several papers. “Regional droughts are having global impacts with potentially irreversible consequences like permanent loss of grass and shrubland habitat.”

Multiple Studies Show Drought Effects Persisting for Years Afterwards

The series of papers looked at extreme drought impacts across sites from California to South Africa to Australia. A consistent theme emerged – even years after severe drought ended, grass and shrubland sites showed limited recovery.

“The impacts don’t just stop when it starts raining again. These systems don’t bounce back quickly,” said Dr. Scott Collins, lead author of the overview paper summarizing the special issue’s findings. “We’re seeing sites where drought caused complete loss of the dominant grasses and shrubs. Years later, those areas remain bare with little sign of returning vegetation.”

Table 1: Key findings on extreme drought impacts from papers in PNAS special issue

Location Drought Years Key Findings
California 2012-2016
  • 31-100% mortality of dominant shrub species
  • Little shrub regrowth 3 years post-drought
  • Invasive grasses expanding in bare areas
South Africa 2015-2017
  • Up to 95% loss of dominant grasses
  • Invasive shrubs colonizing formerly grass-dominated areas
Southwest Australia 2010-2012
  • Widespread mortality of dominant shrubs
  • No return of shrubs 8 years later
  • Areas transitioned to non-native herbaceous plants

Cascading Impacts on Biodiversity, Carbon Storage and More

The habitat transformations triggered by extreme droughts have cascading ecological impacts beyond just the direct plant mortality. Researchers emphasize that grasslands and shrublands play vital roles in terms of biodiversity, carbon storage, water cycling, and more.

“These systems provide critical habitat for plant and animal species. When the habitat degrades or disappears, those species are put at risk,” said Dr. Melinda Smith, an ecologist at Yale involved with the studies. “And given the huge areas grasslands and shrublands cover globally, losing them as carbon sinks could compound climate change.”

There are also indications that the increasing encroachment of invasive plant species into degraded sites adds further barriers to ecosystem recovery. Several papers described aggressive exotic grasses and other invasive plants colonizing areas left bare by drought-driven loss of native vegetation.

“In a way these invasive species make use of disturbances like extreme drought to gain a foothold. And once established they can prevent the native system from returning,” noted Dr. SchemaMigration.

Ongoing Drought and Climate Change Raise Concerns

With extreme drought events projected to increase in frequency and severity due to climate change, researchers worry the transformations observed could presage future widespread degradation of grasslands and shrublands globally. This could have disruptive flow-on effects given the integral roles these ecosystems play.

“The changes we’re seeing in some areas are outside the bounds of natural variability. They reflect dangerous departures from historical norms caused by human-induced climate change,” said Dr. Collins. “And with ongoing drought in many regions, the window for recovery between extreme events seems to be shrinking.”

There are still uncertainties about ecosystem tipping points and whether advanced degradation reaches non-reversible thresholds. But authors agreed the observed impacts already pose troubling risks to biodiversity, food security, and climate resilience.

“The shifts we’re seeing should ring alarm bells on the vulnerabilities of these ecosystems to extreme climate events,” concluded Dr. Chiariello. “Their degraded state leaves grasslands and shrublands prone to undergoing abrupt, irrecoverable transitions. And that’s a frightening prospect.”

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By AiBot

AiBot scans breaking news and distills multiple news articles into a concise, easy-to-understand summary which reads just like a news story, saving users time while keeping them well-informed.

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