The notion that grassy biomes arise from degraded forests and therefore harbor low levels of biodiversity is not only inaccurate, it also helps drive the lack of concern over their fate.
Given the high rates of land-cover conversion, especially in Neotropical grassy biomes, however, they should be a high conservation priority and should be included in more protected areas, the authors argue.
The grassy biomes of tropical Africa and Australia are still relatively intact, making them the least vulnerable to biodiversity loss in the near future.
A new study finds that, contrary to popular belief, grassy biomes such as grasslands and savannas are species-rich ecosystems every bit as biodiverse as rainforests — yet little attention is being paid to the fact that they’re being destroyed at an even quicker pace.
When it comes to tropical biodiversity, the authors of the study, published in the Philosophical Transactions of the Royal Society B, note that “grassy biomes are considered poor cousins of the other dominant biome of the tropics—forests.” But this perception “cannot be supported” by the study’s findings.
The notion that grassy biomes arise from degraded forests and therefore harbor low levels of biodiversity is not only inaccurate, it also helps drive the lack of concern over their fate. Given the high rates of land-cover conversion, especially in Neotropical grassy biomes, however, they should be a high conservation priority and should be included in more protected areas, the authors write: “We argue that, like forests, [tropical grassy biomes] should be recognized as a critical — but increasingly threatened — store of global biodiversity.”
The grassy biomes of tropical Africa and Australia are still relatively intact, making them the least vulnerable to biodiversity loss in the near future, but fire needs to be actively maintained in savanna and grassland ecosystems and even reintroduced in the many areas that have seen decades of “inappropriate” fire exclusion, the researchers said.
A team led by researchers at Australia’s Charles Darwin University analyzed existing biodiversity data to examine the species richness of vascular plants and three important vertebrate taxa — amphibians, birds, and mammals (the study did not look at invertebrates because of the limited amount of available data) — across the tropics. They found that biodiversity in grassy biomes is comparable to that of rainforests within the same climatic region.
The researchers’ analysis suggested that while average species richness is consistently lower in tropical grassy biomes than in rainforest biomes, especially among vascular plants and amphibians, this can be largely attributed to lower rainfall, not to the biome type itself. Grassy biomes tend to occur in regions with lower rainfall, but the researchers found that when they occur along the same rainfall gradient as tropical forests, there is little difference in vertebrate species richness.
Tropical forests undoubtedly contain some of the most species-rich plant and animal communities on Earth, with unparalleled diversity among some groups, such as trees. But for species associated with open biomes, including grasses, megaherbivores (grazers and browsers), and the large carnivores that prey on megaherbivores, savannas and grasslands are critical biodiversity hotspots that represent some of the most iconic and spectacular examples of complex terrestrial foodwebs, like the Serengeti in East Africa.
“Clearly, the simplistic notion that [tropical grassy biomes] have low biodiversity is not valid,” the researchers concluded.
Caroline Lehmann, who edited the issue of the Philosophical Transactions of the Royal Society B in which the present study appears, pointed out the broader conservation significance of grassy biomes, which were the cradle of human evolution. To this day they support the livelihoods and well-being of over one billion people and sequester a significant amount of carbon, helping regulate the global climate.
“They provide a diverse set of services — they supply food, water, medicines, energy (wood and charcoal), fodder for cattle and building supplies (timber and thatching grass) through to the less tangible cultural and spiritual services to many millions of people across Africa, Asia, Australia and South America,” Lehmann said in a blog post on the journal’s website. “On a global scale, they house an important component of the world’s biodiversity, store 15% of the world’s carbon and play a critical role in regulating carbon and nutrient cycles.”
Large-scale land use change is the most serious threat to tropical grassy biome biodiversity globally, according to the study, especially in regions with higher rainfall, which makes intensive agriculture most viable. Savannas and grasslands have been converted at such high rates in recent decades, the researchers found, that they often exceed rates of tropical forest loss. The Brazilian Cerrado, for instance, has been cleared so extensively for agriculture that more than half has been lost over the past 50 years — a higher rate than deforestation in the Brazilian Amazon.
The tropical grassy biomes of mainland Southeast Asia and India have also been extensively cleared, while agricultural conversion in the savannas of Sub-Saharan and West Africa has been slowing down since the 1990s after a long period of conversion that began in the mid-1970s. Northern Australia’s sparsely populated, intact savannas are the largest on Earth, with just one percent loss — though the Australian government is currently pushing for large-scale agricultural development in the region.
There is no “one size fits all” conservation management approach that would work for all tropical grassy biomes, as policies and systems must be tailored to each unique ecosystem, the researchers said. But the key to their conservation is wider recognition among scientists, policy-makers, and the public that tropical grassy biomes are globally important stores of biodiversity worthy of concerted conservation effort.
“We hope that a greater appreciation of the high biodiversity of [tropical grassy biomes] will result in a justified increase in the conservation focus on these increasingly threatened biomes. Given the pressure for land-cover conversion, especially in high-rainfall [tropical grassy bioimes], networks of large and strategically located protected areas are critical.”
- Murphy, B. P., Andersen, A. N., & Parr, C. L. (2016). The underestimated biodiversity of tropical grassy biomes. Phil. Trans. R. Soc. B, 371(1703), 20150319. doi:10.1098/rstb.2015.0319