What is the most bio diverse place on the planet Earth?

The grass Cenchrus setaceus (Pennisetum setaceum) spikelets

If you ask people which place in the world has the most species in a given area, many of them would probably pick the tropical rainforests.

The concept of the tropical rainforests as being the most diverse ecological environment on Earth has been drummed into us continuously by popular culture, but it turns out that answer is only partially correct.

By Dukeabruzzi - Own work, CC BY-SA 4.0

When researchers counted the number of vascular plant species in different environments around the world, they discovered that the answer to that question depends on how large an area you consider when counting (Wilson et al, 2012).

The most diverse environment in the world when you look at an area greater than 100 m² is indeed the tropical rainforest. For example, a tropical rainforest in Ecuador had 942 species of vascular plants living in 1 hectare (10,000 m²) of land.

But when you look at smaller areas, the answer turns out to be different. When they counted the number of species of vascular plants in an area smaller than 100 m², they found out that the most diverse environments are actually temperate grasslands. For example, a mountain grassland in Argentina had an absolutely amazing 89 vascular plant species packed into a single square meter (click table below)! 

I'll admit that actually blew my mind because I can't imagine fitting almost 100 plant species (not individual plants, but different species!) into an area only half the size of a small twin bed.

(Wilson et al, 2012)

But the even more amazing thing is that a new study seems to indicate that researchers may be undercounting the total number of species in grasslands if they only look at aboveground structures, and that total species richness could be up to 65% higher (Rucinska et al, 2021).

In the end, the studies indicate grasslands were the most diverse environments at all the smaller scales that the researchers examined, and it and the tropical rainforests can thus be doubly crowned the most biodiverse places on planet Earth.

Given this fact, my hope is that people come to realize that our ancient and "old growth" grasslands can be just as diverse and species rich as rainforests, and must therefore be just as cherished and protected.

Spikelets of the native grass Little Bluestem (Schizachyrium scoparium)

References:

Anna Rucinska, Sebastian Swierszcz, Marcin Nobis, Szymon Zubek, Maja Boczkowska, Marcin Olszak, Jan G. Kosinski, Sylwia Nowak, Arkadiusz Nowak (2021).

Is it possible to understand a book missing a quarter of the letters? Unveiling the belowground species richness of grasslands. Agriculture, Ecosystems & Environment, 2021, 107683, ISSN 0167-8809

Wilson, J. Bastow; Peet, Robert K.; Dengler, Jürgen; Pärtel, Meelis (1 August 2012). "Plant species richness: the world records". Journal of Vegetation Science. 23 (4): 796–802.