The new stands tall,elbows out the old

A grassland once destroyed by anthropogenic activity will not naturally return to its original state. A new grassland emerges, but its composition differs from the original, with fast-growing, opportunistic species taking over the land and edging out the established, slow-growing perennials. 

A recent paper by researchers from leading grassland institutes worldwide concludes that in secondary grasslands, plants are taller, have higher nitrogen content, greater leaf area, and lower dry weight (bit.ly/New-grass). In contrast, the indicator species of old grasslands were more resource conservative. They largely comprised slow-growing perennials with long roots that had adapted over millennia to survive natural cycles of disturbance, such as drought, fire, and grazing. The team analysed data on 742 plant species from 24 studies across six continents to understand how traits of plant species from established and secondary grasslands compare. 

"The restored grassland does not have the biodiversity of the original," says Ashish Nerlekar, a plant community ecologist at the Indian Institute of Science Education and Research (IISER) Pune. His work is largely on the tropical savannahs of western India. In a 2020 study, he noted changes in the composition of secondary grasslands. The current paper focuses on why the original flora does not return. "We noted in one case that the recovery did not happen even after 300 years," he says. 

The researchers also saw that while the composition of grasslands varies across geographies, they follow the same pattern of recovery. 

Often dismissed as tracts of low ecological importance, grasslands, however, play an important role in sustaining biodiversity, controlling erosion, and storing carbon. They also sustain local fauna. "The faster nitrogen cycle of secondary grasslands is not conducive to sustaining biodiversity," says Nerlekar. So while new grass springs up in abandoned mines, discarded fields, and deserted habitations, it cannot replace the original landscape. 

The study underscores the need to conserve ancient grasslands and actively monitor grassland recovery by sourcing and transplanting plants from the original grassland.