Conference insights 2

During the ATBC / SCB conference, we held a special session on the savannah / forest boundary. Organised by Prof. William Bond from University of Cape Town and Dr William Hoffmann of North Carolina State this session brough together people working on savannahs in Africa, South America, and Australia to share expertise and experience in these habitats. Many visitors to African savannahs are in this biome for the first time, and are un-aware of quite how widespread an important these biomes are to many people, worldwide. So it was fitting that the first talk of the session game some of the gloabl context. I was pretty staggered to hear that of all the primary productivity (IE all the plant growth) that happens anywhere in the world each year, 30% of it is in a savanah. In fact, savannahs cover 20% of all the land surface and are home to 20% of the world's human population too, so pretty important areas really. For visitors from the north, this is fairly extraordinary - there's little like a savannah where they come from.

Yep, it really can rain in savannahs! Wet January day at Dunia, Serengeti, 2011

We also covered the factors that drive the formation and distribution of savannah globally - primarily climate and fire (but maybe nutrients also play a part). It might not surprise those living in East Africa to hear that 85% of all fires in the world occur in savannahs, but it would be a big surprise to most visitors that this is actually a good thing! Moreover, we heard that globally, at least for areas with rainfall over 1000mm where both forest and savannah can survive, it's fire that determines whether there'll be any savannah at all. As well as existing within remarkably consistent rainfall areas around the world, the most important factor seemed to be the length of the dry season - if the dry season isn't at least 5 months long, there's unlikely to be a savannah there. This very strong dependency may, it seems, also be related to fire - a long dry season allows grass and other vegetation to dry enough to let the fire in, and it's the fire that keeps the forest back. On the nutrient front it's long been argued that soil deficiencies in Calcium, Potassium and Magnesium might also limit forest growth, allowing savannahs in the poorer nutrient areas, but we heard from Prof. Bond that, in fact, there's little evidence that at least at the soil depths where tree roots are found there's any real shortage at all - soils don't seem to be anywhere near as important as rainfall and fire in maintianing the global limits of the savannah biome, though they do have obvious impacts within it. All very intersting, and quite remarkable how similar the combination of fire and rainfall area globally in savannah areas.

I think those are probably the most relevant talks to this blog, though I did go to plenty of others too. But after the conference I had the pleasure of taking several of the conference atendees (including William and Bill) to Tarangire for a night, then for a day trip to Arusha NP where the education continued. You can read Ethan's comments on the Tangire trip over here, if you want - I'll give my own later here.