Thursday, 4 August 2011

Waterholes and dams

A nice waterhole never did any harm, did it? Sasakwa Dam, Grumeti GR July 2009
I often hear questions about the impacts of artificial waterholes and I've spent some of today writing about this issue in a paper we're working on about management practices in the savannah enviornment, so I thought that whilst it was fresh in my mind I'd share those thoughts here. The topic usually comes up when we talk about South Africa, and the far more intensively managed parks that exist down there, but it's also often an issue that crops up when talking to managers of lodges and camps who are, understandibly, keen to have a nice waterhole infront of their property.

Grazers love artificial waterholes - the migration reaches Seronera, Nov 2010
Certainly, waterholes and perrenial rivers are a fantastic place to find wildlife, especially during the dry season. You only have to sit by a water hole for a few minutes and the animals (and sometimes clouds of birds!) start trickling in for a drink. And, of course, the predators know this too, so theyll just sit and wait until lunch laks up to them! So what's the problem? Everything loves a waterhole, it's great for tourists to see animals, let's dig them everywhere! And that's what has happened in some places in southern Africa - both in National Parks like Kruger, and even more in private grame reserves people have dug waterholes and pumped water. In some of the private reserves waterholes were dug every 2km, so even the most sedentary of animals could always have access to water. And, as expected, this made a huge difference to the distribution and populations of animals - particularly Zebra and other grazers, animals that are very strongly dependent on water and don't like to walk far to find it. So, everyone's happy, right?
Lions wait for thirst animals by a waterhole, Selous GR, June 2010

Roan Antelope, Mwiba Ranch, Jan 2011. Declines have been related to water provision
Wrong. Zebra are also pretty much the favourite food of lions, so if you increase the zebra population and let them go to areas they couldn't use before, you also increase the lion population and let them spread further afield in their hunt for zebra. That might sound good too - but it's not if you happen to be an animal that deals with predation risk by hiding away in areas predators don't go - like Roan and other large, slow antelope. In fact, mainly in recognition of the damage that has been caused by making water available throughout the landscape there has been a recent policy within Kruger and some other areas of closing (some of) the artificial waterholes to allow such sensitive species spaces where they can survive.
Elephant near dam, Kruger NP, June 2011 - and look at the invasives on the dam!

But that's not all artificial waterholes do, they also attract elephants. Now, there's a long running discussion between East and South Africans about elephant impacts (dare we say damage?) in protected areas that I'm not going to go into here. But impacts they certainly do have, especially in areas near waterholes as they're another species that doesn't like to travel far from water if they don't have to. So spreading waterholes across the landscape means elephants can easily get everywhere, especially during the crucial dry season when they are feeding on bushes (grasses during the wet season, remember) and have bigger impacts on the habitat. So providing waterholes for elephants everywhere means the vegetation never gets a chance to recover from browsing impact, and can easily start to cause problems throughout the landscape. So, another thing to be aware of.
Zebra drinking, Manyara Ranch, Sep 2010. Note how heavily grazed the land is around the dam.

Now, the last thing you might want to argue with me about, of course, is what happens in a dought? If you don't provide water for the animals, surely they die? And that's true, of course - but it turns out that if you do maintain artificial waterholes everywhere, the animals still die - not of thirst, but of starvation. During a drought there far less food around, especially in areas where everywhere is usually accessible to most animals because there are waterholes everwhere. If there are fewer waterholes and things get tough, animals (even those lazy zebra!) will make the decision to walk further to feed in areas they don't normally go and there'll be enough food to go around. So in a serious droung in the 1980s in southern Africa, one private game reserve with lots of waterholes where studies were made lost nearly 90% of grazing animals, whilst the next door Kruger, with fewer waterholes, only lost 35% of animals. So, no, I don't think waterholes are essentially a good idea, even during drought.

The unifying process at work here, with the lions, the elephants and the drought stress, is a loss of heterogeneity - variability in the landscape. With waterholes everywhere, lion predation risk was the same everywhere, elephant impact is the same everywhere, grazers are the same everywhere. Without artificial waterholes, there are refugia from lions, elephants and heavy grazing that can be used by other species and at other times when needs are greatest. Heterogeneity, as we'll see time and time again, is a key issue in maintaining functioning ecosystems.
Birds like waterholes too! This is a Black-winged Stilt near Ndutu, NCA. Jan 2011
 So, do I always think artificial waterholes are bad? In an ideal world, I'd say yes. But we don't live in an ideal world, so to be realistic I have to say usually. Some protected areas - such as Hwange in Zimbabwe - would once have only been wet-season dispersal areas, with no permanent waterholes. But here the seasonal movements have been blocked by people, so waterholes are needed to enable any of the ecosystem to survive. That said, I don't think they should be spread all over the park - rather, groups of pools in one or two areas would maintain the heterogeneity that is needed. And if climate change and human water abstraction continues to increase aroudn parks, we'll start loosing perrenial rivers, in which I'd I'd advocate maintaining some limited pools of permenant water along these routes artificially if necessary. Finally, of course, if there's already a nearby source of perrenial water, another waterhole nearby will probably have little additional effect (good news for lodge owners who are near rivers, but didn't negotiate the view!). But interferring with savannahs is not easy, and should never be attempted without considering all the impacts you might have. Let's keep waterholes natural!

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