Monday, 15 August 2011

Burning Mwiba

Back from my trip now, I thought I'd make a few posts based on the things we've seen on safari. As I've been writing up my thoughts about one place already today, I thought I'd use that as the basis for this first post.
Buffalo are a major grazer in Mwiba, note the relatively short grass.

Mwiba Game Ranch is a new private game reserve within the Serengeti ecosystem. I've been before when I put together a bird list for the area. This time it was a trip to see the place in the dry season with a view to including it within my big Serengeti Fire experiment. For those who know Serengeti , Mwiba is squeezed into the corner between NCA and Maswa GR, right down in the south of the ecosystem. (NB, we usually define the Serengeti/Mara ecosystem as the area that encompasses the wildebeest movements - Mwiba includes some of the calving grounds, particularly important during drier years.) This puts it right in the driest region of the ecosystem, with around 400mm of rain per year and as you'd expect at that end of the gradient it's largely Acacia-Commiphora woodland, though there's a surprising number of nice Albizia in there too. It's also interesting because it's got a number of interesting mammals not found or not easy to see in the rest of Serengeti - we saw both Greater Kudu and Roan Antelope again this trip. Anyway, I was there to talk fire, but knowing that we're in a low rainfall part of the ecosystem is important, because water availablity is one of the big four drivers in the savannah (fire, grazing/browsing and nutrients being the other three, of which we'll visit two more shortly). Low rainfall means low productivity - the grass even on the highest nutrient soil never grows tall and thick like in other parts of the Serengeti, but what does grow tends to be nutrient rich annuals, so pretty good grazing, even if it isn't plentiful.
Zebra are the other big grazer - the grass here has already been grazed a bit

Rich grass means plenty of game, with the main dry-season grazers being large populations of buffalo and zebra thanks to the numerous perrenial springs around the ranch. Already, only half way through the dry season the grass in the areas around the waterholes and by the denser thickets is heavily grazed - by October it seems unlikely there'll be much left at all as the grazing impact spreads further from the water points. A lot of the area is pretty dense bush though, with some good thickets in places along the (seasonal) rivers.
Nearby areas with many cattle are already completely denuded, what will they do until the rains come?
 In recent years this area (as with most of Serengeti) has been subject to an early burning management regime - fires being set as soon as the vegetation starts to dry in June. Fires are important in the savannah for a number of reasons we've gone into elsewhere, but the two most important issues to bear in mind here are bush control - there were lots of seedlings in the grassy areas of Mwiba that have been prevented from forming to thick bush by regular burning - and grazing management, maintaining and encouraging new growth of nutritious grass. The early burning policy that has become the norm in Serengeti and most other Tanzanian protected areas ensures fires are controlled and generally are rather cooler than fires set at the end of the dry season when the fuel is drier.  But here in the drier areas with lower water availability it also means the fires burn regularly - you can be fairly sure there's enough fuel to burn early in the dry season, whilst later on all those animals will have eaten so much there might not be anything left to burn. That's good if you want regular firest to control bush encroachment, but isn't so good if you happen to be a buffalo wanting to eat during the dry season and all the nice grass gets burnt at the start. In fact, the ranch manager is of the impression that this year, when for the first time in a long time no fires have been set during the early season, there are lots more animals on the ranch than last year thanks to the availability of unburnt grass.
There's a sand river that forms a firebreak between the grass and the bush - frequent early burns have removed thicket vegetation from the upwind side of the river.

Mwiba's springs attract a lot of wildlife (and reflect sunset)
So, what to do? Maybe late burns will be possible at a lower frequency - give the land a few years to build up sufficient fuel reserves left over at the end of the dry season to allow a fire to take with regular enough frequency to control bush encroachment. Or maybe early burns are the only option to allow fires in these low rainfall areas to carry - though they probably don't need setting each year, balancing fire options against forage loss. The only real way of finding out will be through a big experiment, of course, which is exactly what I intend to do! Watch this space for the answers...

No comments:

Post a Comment