The secret senses of african plants
But if you read the fantastic book written by Daniel Chamowitz called What A Plant Knows: A Field Guide to the Senses, you will discover that plants do have senses like sight, smell, touch, and hearing.
Acacia karroo (Mimosoideae)
Giraffe (Giraffa tippelskirchi) maschio
Impala (Aepyceros melampus) femmina
Here we have to come back to the plants’ senses we’re talking about before. The plants uses smell, among the other senses! Yes, you have understood.
As we all know, smell is the ability to identify compounds in the air carrying different chemical signals interpreted then by our nose nerves. Plants don’t have a nervous system and a brain as such, but they can “smell” chemical compounds in the air and react to those accordingly.
Vachellia tortilis (Acacia a ombrello)
Some studies reveal that the tannin content of leaves on a Senegalia nigrescens went up within 2 minutes from being “attacked” by a giraffe.
Isn’t this awesome?
But that’s more.. a study that includes a group of South African scientists has found that spiny plants only appeared about 15 million years ago, which means 40 million years after mammals replaced dinosaurs. For most of this time, Africa was a continent dominated by forests and now-extinct ancestors of browsing elephants and hyrax. Probably spines just didn’t work as a plant defense against these small ancient mammals. So why plants evolved thorns around 15 millions years ago? Because at that time medium and large-sized browsers like impala and kudu invaded Africa from Europe and Asia.
“After presenting my herbivore biomass data at a conference, Dr. Tristan Charles-Dominique (the lead author on the paper, from the University of Cape Town) said he had to show me something. We placed our laptops next to each other and compared his spiny tree abundance maps with my animal density maps. The match with medium and large browsing species was remarkable!”
This study found that the arrival of browsing medium sized antelopes was probably what turned Africa’s ancient forests into the open savannas. What we know is that the Great Rift Valley formation played also an important role in marking the end of the dense cover of rainforests present in East Africa. Unsurprisingly, East african Rift Valley formation started just 15 millions years ago. It doesn’t seem a coincidence and probably the formation of savannah biome is a result of these two factors.
We will talk more about plant senses and their strategies in a new post.