28 May 2020
Dispelling the myths of Malagasy grasslands
Grasslands are a widespread ancient part of Madagascar’s landscapes which support the livelihoods of millions of people. Their preservation is vital.
In Madagascar, from primary school, children learn how grasslands, which cover more than half of the country’s land surface, are a product of the degradation of forests caused by their ancestors.
This has discouraged researchers from examining the ecology of grasslands, resulting in an incredibly limited understanding of them.
This is not helped by the disconnect between paleontological and biodiversity studies.
While paleo records provide relatively little support for pre-human grasslands across Madagascar, taxonomic and biodiversity studies have documented a diverse ancient grass flora with numerous endemic species.
Natural ancient grasslands
Working with grass taxonomist Maria Vorontsova at Kew and Caroline Lehmann (Tropical Biologist at the Royal Botanic Garden of Edinburgh), I have been sampling different grassland sites across the Central Highlands of Madagascar in an effort to fill in the stark knowledge gaps around the ecology of these diverse ecosystems.
This has been part of my PhD project that I am currently undertaking at the University of Antananarivo but based at Kew’s Madagascar Conservation Centre.
Our research shows that the vast grasslands of the Central Highlands are not degraded forests.
Rather, they were shaped both by animals and fire over millions of years, supporting the narrative of grasslands as an ancient part of Malagasy landscapes.
We found that the grasslands are formed by at least two functionally distinct assemblages of grass species, each shaped by fire or grazing with 30-40% of these species unique (endemic) to Madagascar.
We observed a diversity of grass species that are dependent on grazing to proliferate and that would have rapidly become extinct without the presence of a grazer to keep their habitat open.
We know that because these assemblages of grasses are functionally equivalent to what we see across the channel in Africa, where grasslands have been closely studied for a hundred years and we well understand how animals shape these.
Millions of years before human arrival in Madagascar, a now-extinct megafauna including hippos and tortoises shaped the grazing-dependent grass assemblages.
The human introduction of cattle along with the addition of plants and other animals ca. 2300 BP introduced a megafaunal substitute that re-shaped the already existing grasslands.
Managing grasslands to support livelihoods
Regardless of the debate around ancient versus natural, Malagasy grassy ecosystems contribute to the livelihoods of people through the provision of essential food, cultural and financial resources.
However, land use policies and interventions in Madagascar focus on forest conservation, as grassy ecosystems are widely perceived to be of low conservation priority.
Fire and cattle grazing, which create two different types of grass communities, need to be productively managed to preserve these ecosystems.
Cattle rearing is an important activity across the Central Highlands, with cattle providing food and economic resources as well as cultural uses.
While a rich endemic grass flora that once supported abundant megafauna now supports millions of cattle, cattle health is often quite poor.
Research with the aims to improve the production and quality of native pastures and to maintain sustainable grazing systems is needed.
Given the human dependency on grasslands, it is imperative to develop ecological understanding to support land management in the face of changing climates where food security is precarious.
Solofondranohatra, C.L., Vorontsova, M.S., Hempson, G.P., Hackel, J., Cable, S., Vololoniaina, J. & Lehmann, C.E.R. (2020). Fire and grazing determined grasslands of central Madagascar represent ancient assemblages. Proc. R. Soc. B 287: 20200598