Fire!

I've been thinking a lot about fire recently. Burning is, of course, Tanzania's national pass-time in this season, and is one of very few active management activities occuring in protected areas, and we found a nice fire to admite in Tarangire on our safari a couple of weeks ago.

Lots of smoke, and some big flames as a fire goes through bushes, Tarangire June 2011

But again, I've been pretty surprised by how little guides know about fire in savannas. I'm currently trying to put togher a big experiment that wll see us burning lots of areas around the Serengeti National Park (it burns every year anyway, all I want to do is tinker with the management in a controlled way to understand the impacts). As part of thinking about this I organised a meeting at the ATBC-SCB confere of lots of people interested in both the Serengeti ecosystem, and of those interested in fire throughout the savanna world. I also tracked down a number of people in South Africa when I was there in May to get their thoughts. As part of all this thinking, I've put together a document that pulls together lots of ideas, so I thought I'd share some of the introduction to that here:

Fire is generally considered a vital component of savannah ecology, with trees, grasses and animals all adapted to a fire prone ecosystem: in fact, globally, 85% of fires occur in savannah habitats. In most of Tanzania's protected areas, rangers deliberately set fires each year for a number of different purposes, including the encouragement of new grass growth for grazers and the control of bush spread. Recent evidence from a global study suggests that at least for those savannahs occurring in areas with over 1000mm of rainfall, the forest/savannah edge is often maintained primarily by fire, and that in it's absence many savannahs will revert to forest. There is some debate, however, about how much animals may take over this role when at particularly high densities and the benefits of fire in certain areas have been questioned. For example, in some areas of Tarangire National Park with high numbers of migrant animals during the dry season, fire has been totally suppressed for over 30 years with relatively little obvious difference between fire-suppressed and more frequently burnt areas: it is argued that in these areas fire simply burns potential animal forage. Similarly, in Kenya, the Kenya Wildlife Service has recently instigated an overall policy of fire suppression except where the fire is caused by natural events (essentially, lightening storms) in an attempt to encourage one view of naturalness. There are, of course, alternatives to these two extremes, where fire is sometimes suppressed and sometimes encouraged. Given that fire is one of very few activities under active management in these areas it seems sensible to understand more fully the consequences of these different management decisions.

Note the fire burns the grass, bigger bushes are untouched.

Traditionally, pastoralist communities in northern Tanzania have set fires towards the end of the dry season, in anticipation of the rains: they make a calculated gamble between burning possibly useful forage if the rains are delayed, and waiting too long and being unable to burn (and encourage the new growth that will come with the rains) if the rain comes before they have time to burn. Obviously, by this time of the year grazing animals will already have reduced fuel loads to relatively low levels in many areas, so late dry season fires will only occur in less grazed areas, with other areas remaining unburnt in any one year. Such management was also the norm in many protected areas (including Serengeti) until around 1970, when concern over the regeneration of trees prompted a switch in fire management towards controlled burns in the early dry season (mainly in June). Such fires are generally cooler and patchier, with possibly less impact on woody plants. They also prevent the late season burns that are likely to be hotter and less easy to control with consequent reduced concerns about tourism infrastructure. Recently, managers of the Grumeti Reserves in western Serengeti have attempted to suppress early season fires until later in the dry season, allowing the migrant wildebeest and zebra to graze unburnt areas and increasing the forage available to these animals to the extent that their residence times within the reserves have tripled. Fires are also set during the short dry season, in February, and grass growth rates are such that some areas of the national park burn twice per year. Observations suggest that areas burnt in February may be preferred by migrant ungulates during June, but beyond these patterns and the immediate, short-term responses of grazing animals, we understand relatively little about how fire impacts the ecology of Serengeti or other East African protected areas in the bimodal rainfall area. Whilst we know a little about the impacts on large mammals and early vegetation responses, we know almost nothing about the impacts on other taxa, or the soil fauna and nutrient flows of the savannah ecosystem.

In practice, over much of Serengeti, fires occur once or twice per year. If there are species within the ecosystem that are rather more sensitive to fire than others – for example, ground nesting birds, or various plant species – such frequent fires may have negative impacts on the population. On the other hand, burning in different seasons may affect different species in different ways. Whilst it is generally considered 'a good thing' to burn Serengeti whenever it can burn, maybe reducing this frequency doesn't actually have the negative impacts expected of it and could, instead, benefit other taxa not usually considered in protected area management plans? Quite how many unburnt seasons does it take before grass quality starts to decline? Would a general switch back to late-season burning be beneficial?

Lots of birds were making use of the fire to catch fleeing insects, including this lilac-breasted roller - both animals and plants in the savannah are adapted to fires.

There's lots more to fire in savanna too that's of interest to guides and their clients (like what do the animals actually do?!), so we'll revisit the topic. But maybe the ideas here will help some understand why I'm so interested in fire. It's not just that I want a bonfire big enough to see on Google Earth. Honest!