Hotter summers are transforming endangered bunchgrass prairies

In a new study from PLOS, researchers set out to investigate the effects of climate change on bunchgrass prairies. Focusing on the National Bison Range in Montana, the experts found that dramatic seasonal changes are the biggest threat to the long-term survival of bunchgrass prairies.

Intermountain bunchgrass prairies are some of the most endangered ecosystems in North America. These prairies now cover less than one percent of the area they once covered. 

Over the past century, bunchgrass prairies have become hotter and drier, and this trend will persist alongside human-driven climate change. 

Based on 40 years of monitoring, the experts determined that annual climate trends are not as damaging to prairies as intense seasonal changes, especially hotter summers.

The researchers analyzed multiple observations of plant growth and production, abundances of different plant species, and availability of nitrogen to produce a 40-year timeline of ecosystem changes across the National Bison Range.

The analysis showed that annual temperatures increased as precipitation declined in the prairie, which made the region more susceptible to fire. 

The researchers were surprised to find that the amount of plant material produced every year increased by 110 percent. This boost in annual above-ground plant production was associated with increased precipitation and cooler temperatures during the important growing period of late May through June.

However, there were also some major changes in plant composition across the prairie, including 108 percent more invasive species. The non-native species with higher drought tolerance were the most favored overall. 

There were also other ecosystem changes that followed seasonal climate trends – instead of annual trends. For example, summer temperatures were higher than what was expected based on annual trends.

Hotter summers are turning grasslands brown earlier in the year and making it more difficult for plants to resume production in the fall. 

According to the study authors, intermountain bunchgrass prairie could be morphing into a previously unknown type of grassland.

“Forecasting climate change effects on plant production based on expected average annual increased temperature and decreased precipitation may not be appropriate, because seasonal climate changes may be more important and may not follow average annual expectations,” said study co-author Dr. Gary Belovsky.

The study is published in the journal PLOS ONE.

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By Chrissy Sexton, Earth.com Staff Writer