Tuesday, 7 August 2012

Do fires stop the Serengeti migration?

Dr Kate Parr lighting a controlled fire in the Serengeti Ecosystem
There's been a bit in the East African press recently claiming that Tanzania has been deliberately setting fires in the Serengeti NP to block the migration. The Tanzanian National Park Authority (TANAPA) have, of course, denied this. Reading the articles and press releases there's obviously both some serious ignorance and some seriously bad journalism going on here, and I thought it might be useful to share a few of my observations.

Each fire burns differently, so to study
their impacts you must observe closely
Firstly, let's look at the fires themselves. It is actually easy to see where fires are burning and how large they are - almost real time data are plotted on the NASA website and with a little fiddling I managed to set the parameters for the week in question for everyone to see here. Each cell is 500m square, and a fire may have occurred anywhere within that box, but has to be of a certain size before it is detected. Where there are lots of overlapping cells you can be pretty sure there's a big fire happening across a large area. From this map you'll see (a) that it's hard to see any fires in northern Serengeti during the week in question that could come even slightly close to being big enough to block the migration and (b) that there has been some really big fires elsewhere in Serengeti during the period, particularly around Seronera. So the TANAPA statement that the fires in question were under half a km were not exactly accurate, but nor is there anything big enough to ever create an obstacle for animals even if fires could do that.
Has this tagged tree seedling been killed by the fire,
or will it resprout in the rains?

What about that shoddy journalism then? Well, you only have to compare the press release from TANAPA with the headlines like "Tanzania refutes allegation of fire deliberately set in Serengeti" to see there's no doubt who set these fires at all, nor that they were deliberate. And,in my experience, if you talk to rangers in northern Serengeti about why they set fires you might well find (sad to say) that they state that they set fires to keep the animals in Tanzania. It's not what's in the fire management plan, but I've failed to find many rangers on the ground who can give any of the real reasons why and when they burn. Why do they think it will keep animals in Serengeti? Because fires should promote nutritious grass growth. Does it work? Certainly, for a while. Immediately after a fire, whilst it's still smoking, animals come on and lick the ash. A week or so later, there's a flush of new growth that keeps animals very happy for as long as it lasts - which depends on how many animals there are and how much moisture there is in the soil. Now, the question is, given that the wildebeest population in Serengeti is food-limited, is the reduction in poor quality grazing (by burning it off) compensated by the smaller volume of higher quality forage? And the truth is that we simply don't know because researchers have mostly been asking the wrong questions. Instead of studying a range of alternative management options, they have simply compared early burns with no burns. Does that mean early burns are better than late burns? Does that mean burns every year are better than burns every two years? Sadly, we simply don't know. But I do know that change in the fire regime within Grumeti reserves is responsible for the relatively later arrival of wildebeest in northern Serengeti for the past few years - Grumeti tries to prevent fires there until the migration has passed through, and the increased food availability has kept the animals in the protected area much longer than before.

Highly technical beer cans can help tell you how hot the fire was!
[BTW Where the other random statements about the reasons for the migration that the TANAPA spokesperson has come up with - e.g. avoiding inbreeding - I really have no idea! Any suggestions, do let me know - what scientists tend to think about the drivers of the migration at the moment is summarised in this blog post... I do agree with them that few animals in Kenya by late July is hardly unusual - presumably wishful thinking on the behalf of tourism folk in the Maasai Mara!]

Overall, this just makes me more confident than ever that what we really need is a good, controlled experiment on the impacts of different fire regimes across the Serengeti ecosystem, and I'm really glad we've got it started (that's one of the things I've been busy doing whilst I've no been active here for a few weeks! Sorry...)

Main Reference:
ResearchBlogging.orgShombe N. Hassan, Graciela M. Rusch, HÃ¥kan Hytteborn, Christina Skarpe, & Idris Kikula (2008). Effects of fire on sward structure and grazing in western Serengeti, Tanzania African Journal of Ecology, 46 (2), 174-185 DOI: 10.1111/j.1365-2028.2007.00831.x

No comments:

Post a Comment