Restored Grasslands Need 75+ Years for Biodiversity to Recover, Study Finds

According to a new study, restored grasslands will require long-term management in order to bring back specialized pollinators and ultimately restore biodiversity.

The study, published in Journal of Applied Ecology, analyzed the pollination success of native plants for varying durations of grassland management at the ski slopes in Nagano Prefecture. The restored areas studied spanned between 2 and 75 years since grassland restoration, and researchers examined native plant pollination across 28 different pollination networks. Researchers also examined old grasslands in the area for comparison.

“There is no place better suited to survey restored grasslands with very different management durations within a relatively small area than ski slopes,” Gaku S. Hirayama, doctoral student at Kobe University and corresponding author of the study, said in a statement.

As explained by the study, land use changes like agriculture and development are causing rapid decline of grasslands. In 2021, a report by the World Wildlife Fund (WWF) determined that 1.6 million acres of grasslands in the Great Plains of North America alone were lost in just one year. In 2022, this number increased to 1.9 million acres in this region. As BirdLife International reported, half of all grasslands on Earth have been degraded in some capacity.

But while restoration helps improve biodiversity lost to land use changes, previous research has shown that undisturbed grasslands with long-standing management practices (over centuries to millennia) have much higher levels of biodiversity and climate resilience compared to restored grasslands, emphasizing an importance in not just restoring but preserving existing ecosystems. 

“The finding shows that once valuable old grasslands are lost, their restoration cannot be achieved quickly,” Hirayama said.

Over the course of the study, the researchers examined over 10,800 pollinator visits from 294 different pollinator species to 79 flowering plants in 2021. In 2022, they observed over 19,690 pollinator visits from 297 pollinator species to 88 flowering plants. Overall, they determined that older grasslands had a greater range of native plant biodiversity than younger, restored grasslands. 

Further, the results showed that plants’ reproductive success, pollination function and pollinator network-level specialization were all worse in grasslands restored after deforestation compared to older grasslands. Overall, the study revealed that newly restored grasslands need at least 75 years for pollinator specialization and function and for plant diversity to even begin to compare to the biodiversity of older grasslands.

Pollinator specialization is important to improving plant reproduction. As Kobe University reported, younger restored grasslands still had pollinators, like flies and hoverflies, but they are more general in their pollination behaviors. By comparison, specialized pollinators are more likely to transfer pollen between plants of the same species for proper pollination.

The findings revealed that both preservation of existing grasslands and close management of restored grasslands will be important in reclaiming biodiversity.

Atushi Ushimaru, ecologist at Kobe University and a co-author of the study, explained, “It may also indicate that grassland restoration should not just be left to nature, but could require active human involvement such as by sowing seeds or by planting seedlings of native bee- and butterfly-pollinated grassland plants.”