What is a Savanna?
Have you ever driven around Kruger National Park wondering about the processes that drives and maintains its diverse ecosystems? Perhaps you stopped next to a herd of impala and pondered why exactly there are so many of them? Maybe you have queried the fact that sable and roan are so rare and only seen in specific limited locations? Perhaps, after many Kruger excursions, you are well versed in the ways of mammals and want to move on to other subjects such as birds, trees and even geology? You are way past ticking off the big five and long for a deeper understanding of how everything you see on your visits are connected to each other. Well, this Forum Topic is for you!
Let me start off by saying that I am neither a scientist nor an ecologist. I am just a normal Kruger-addict with a passion and an unquenchable thirst for knowledge when it comes to the ecology of African savannas.
I love sharing the wonders of nature with others. So I decided to start this topic on Kruger’s ecology. My intention is to condense what I have learned from scientific papers, articles, books and from personal experience, into a format and series of topics which can be understood by anyone (hopefully…
). My wish is that this will awaken people’s interest in other subjects away from the big five and that it will enhance their experience during future Kruger visits.
Please feel free to comment on my posts and add any extra info. This is a forum after all and I am sure there are many bush boffins out there. I will provide my references at the end of each post to ensure that the rightful people get the recognition they deserve and also to enhance the credibility of what I have written.
So let’s begin!What is a savanna?
To start off we first need to set the scene for our upcoming discussions. The Kruger National Park falls within the savanna biome. Savannas cover approximately 20% of the earth’s land surface and about 40% of Africa.
Before we go into more detail, we first need to establish what exactly can be classified as savannas.
In general, savannas can broadly be described as areas where grasses and woody plants (trees and shrubs) co-dominate the plant life. This definition may sound simple, but savannas tend to be extremely varied in appearance and sometimes difficult to classify. For instance, an overgrazed game farm might be totally covered by sickle bush with very little grass cover. Of course, no one would argue with the farm owner still referring to his property as a little piece of bushveld (a South African term for savannas), even though woody plants totally dominate the area. Therefore we also need to take into account time and space. In other words: the general state an area and its surrounds should achieve over a significant period of time.
In the book, “An African Savanna – Synthesis of the Nylsvley study”, the authors provide a set of characteristics one has to look for to establish if you are actually finding yourself in a savanna area. These characteristics are:
• The monthly mean temperature must exceed 10 degrees Celsius throughout the year
• The wet period of the year must be warmer than the dry period
• Water needed for plant growth should be available for at least 60 days per year on average
• There are also on average at least 60 continuous days per year where water availability is insufficient for plant growth
• Tree canopy cover is at least 5% but not more than 80%
• On average, the grass cover is at least 5%
• Grasses and trees should grow in the same areas and should not be spatially separated (such as in forest clumps found amongst grasslands)
• The top of the woody plant cover should be taller than 2 meters
You will be pleased to know that Kruger satisfies the whole list above and is therefore not in danger of being declared a desert or a forest! Of course, within the above set of criteria you could classify a whole host of different landscapes as savannas, especially if you look at the tree cover and height parameters. This wonderful diversity is exactly what makes savannas so interesting to study. Diverse landscapes host diverse life forms, each with its own set of habitat requirements and ecological contributions it brings to the community it lives in.
To end off this first chapter in our discussion of Kruger’s ecology, I should briefly mention some terms often used to describe different types of savanna and which will also be referred to in upcoming chapters. Basically, different types of savannas can be classified according to the overall tree canopy cover as well as average tree height in the area.
The following types of savannas can be distinguished:
• Tree savanna: Tree canopy cover of less than 35%
• Bushveld: Tree canopy cover of more than 35% and average height of less than 5 meters
• Thickets: Tree canopy cover near 80% and average height less than 5 meters
• Woodland: Tree canopy cover of more than 35% and average height exceeding 5 meters
More than 75% of Kruger falls within the Bushveld-category.
Now you should be able to identify a savanna wherever you find yourself in the country! Next time we will identify the main drivers that influence the structure and composition of landscapes in the Kruger National Park.Tree savanna at Witpens waterhole, north of Satara, KNPReferences:
Eckhardt, Holger & Scholes, Robert & Venter, Freek. The Kruger Experience: Ecology and Management of savanna heterogeneity, Chapter 5: The abiotic template and its associated vegetation pattern.
Washington DC-USA: Island Press, 2003. Print.
Scholes, Robert and Walker, B.H. An African Savanna: Synthesis of the Nylsvley study.
Cambridge-UK: Cambridge University Press, 2004. Print.