Environmental policymakers value ancient forests, but ancient, or old-growth, grasslands have not received the same recognition. That’s a mistake, according to a new Texas A&M AgriLife study.

old-growth grassland bordered by a forest with deer at pond
Old-growth grasslands, like this savanna with Axis deer in central India, need frequent fires and herbivores to maintain their high plant diversity . (Texas A&M AgriLife photo by Ashish Nerlekar)

Joseph Veldman, Ph.D., assistant professor in the Department of Ecology and Conservation Biology in the College of Agriculture and Life Sciences at Texas A&M University, has been working to counter the misperception that Earth’s grasslands and savannas are ecologically depauperate places that are degraded by fire and large grazing animals.  

Back in 2015, Veldman led an international group of ecologists to publish a foundational paper, which argued that the concept of “old growth,” a term long applied to ancient forests, should be extended to ancient grasslands and savannas. Whereas antiquity in forests can often be seen in large trees, signs of age in old-growth grasslands are often hidden underground, in roots and buried stems, or in distinctive communities of rare or endemic plants.  

New old-growth grassland study

Now Ashish Nerlekar, a Texas A&M doctoral student, and Veldman are bringing a new scientific study to the discussion, with their recently published article “High plant diversity and slow assembly of old-growth grasslands” in the Proceedings of the National Academy of Sciences.

“The vegetation that forms after people clear forests can superficially resemble biodiverse grasslands like the north American prairies or African savannas,” Veldman said. “Consequently, ecologists have tended to lump all grassy places together, without always recognizing the distinct values of old-growth grasslands.”

“In biology textbooks, the sections on forest succession often depict grasslands as a temporary step on the way to forest formation,” Nerlekar said. “In my home country of India, savannas are often classified by the government as ‘degraded forests’ or ‘wastelands’ leading to suppression of frequent fires to ‘conserve’ and ‘restore’ the landscape.”

They said this successional narrative has contributed to a crisis in grassland conservation.

“Around the world, disturbance-dependent grasslands are widely misclassified as degraded forests, overlooked for their conservation value, targeted for agricultural conversion, and viewed as opportunities for carbon sequestration through tree planting and fire exclusion,” Nerlekar and Veldman contend in their article.

The team analyzed data on plant diversity from grasslands and savannas around the globe. Their results show that after old-growth grasslands are destroyed, the recovery of plant diversity requires hundreds to thousands of years.

Based on these findings, they concluded that “slow rates of recovery underscore the need to replace outdated models of forest succession with models that emphasize the importance of fire, herbivory and long periods of time to grassland biodiversity.”

Prioritizing for conservation

Veldman and Nerlekar said their study offers evidence that old-growth grasslands, like old-growth forests, should be prioritized for conservation, but that unfortunately, recent actions indicate some scientists and conservation planners still believe little is lost when these grasslands are converted to farmland or tree plantations.

“We are particularly concerned that recent research and emerging land-use policies, both meant to promote tree planting for carbon sequestration, are a threat to undervalued grassland biodiversity and ecosystem services,” they wrote.

Nerlekar and Veldman hope their research can be used by environmental policymakers to protect old-growth grasslands from tree planting and tillage agriculture, and to encourage land managers to maintain biodiverse grasslands with frequent fires and well-managed populations of native or domestic herbivores, like bison or cattle.

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