February 2007 … revisited 2009
We now know that global warming is neither a Greenie scare tactic nor an unproven theory. Rather, it is a scientific fact that the globe is getting warmer and the world’s climate is changing as a result of greenhouse gas emissions. When the mercury shot up to 45ºC in December, evaporating what little moisture there was, withering the new growth of grass and turning it from green to blue grey, exacerbated by the total absence of rain in that critical month – well, I was convinced.
In my world this was a sure sign, the beginning of the end in this rain-driven environment. As the northern lowveld is already hot and semi-arid, the change in these two important limiting factors, namely more heat and less rain, would undoubtedly have a negative effect on the ecosystem. Although I was understandably depressed, before reaching for a double dose of Prozac and looking at retirement homes in Greenland, I was reminded of Christmas 1982, while working in Botswana’s Tuli Block.
The day was spent up to our chins in the lukewarm, but nonetheless relatively cool water of a concrete reservoir as the ambient temperature was hovering around 47ºC in the shade! The cicadas appeared to be the only creatures unaffected by the oppressive heat; it was almost as if, the hotter it got, the more intense their staccato song. It would be interesting to know at what ambient temperature they stop ‘zizzing’. Nothing else except them dared expend a single kilojoule of energy – even the emerald spotted wood doves were conspicuously quiet. A number of small birds of various species congregated on the concrete stoep floor of the main house, obviously the coolest spot they could find. I recall that the fork-tailed drongos and white helmet shrikes appeared to be particularly susceptible to the heat as many of them actually died. An African goshawk squatted on its long legs, undignified, open-beaked and wide-eyed, surrounded by dozens of panting and dying birds. Clearly focused on staying alive, it showed absolutely no interest in the other birds and they in turn were too stressed to care or move away.
Using chunks of ice taken from the deep freeze, we cooled the water in the nearby bird-bath and those birds that had the energy to drink did so. A garden sprayer was turned on; it proved to be a life saver for many of the birds when they moved into the fine spray, and competed for space as they fluffed and shook their feathers in an attempt to absorb the cooling moisture. So, yes, there have been some hot days in the past and summer temperatures in the mid-forties are not a recent phenomenon. Anthropological evidence of early hominids in East Africa’s Olduvai gorge suggests that they lived in a hot climate and perspired a lot, millions of years ago. How do they reach these intimate conclusions from a few fossil fragments? How do they determine that they once belonged to a sweaty creature, or is this perhaps a hypothesis based on evidence of what the climate was like at the time, particularly the ambient temperatures? What a fantastic avenue of science anthropology is … I find the piecing together of our origins fascinating, and have no doubt that I would have pursued this as a career, had I not gone into nature conservation.
Knowing that it was as hot, if not hotter, years ago, should allow us to believe that maybe we are not becoming less tolerant of the heat per se, but rather that we are becoming less tolerant of the effect of direct sunlight on our skin. It definitely feels harsher and is becoming progressively more so – and there is no doubt that ozone depletion is the culprit here, something early man did not have to put up with.
When I visited Italy in the height of their summer, even though the ambient temperatures were in the low thirties, you could walk around all day in the sun provided you were adequately hydrated. The sun’s intensity was never intolerable, nor for that matter did I ever feel sunburned, as I do in similar conditions in South Africa.
This contributes to my belief that the intensity of the sun varies quite dramatically, depending where you are on the planet. For example, the Chilean town of Punta Arenas on the southern tip of South America is apparently drenched in UV, so definitely not the place for ‘gingers’.
Opening our rainfall record book to write up the miserably few millimetres of rain that followed December’s heat, I came across the rainfall figures for the reserve from 1986 to 2008, which I studied with interest.
On the face of it, there’s nothing abnormal in the figures and nothing jumps out at you to suggest that, here on Olifants, our rainfall allocation from on high has been adversely affected over the years. We have accurately recorded 22 consecutive years of rainfall, and the variance is a mere 3 mm! There is, obviously, no evidence of a gradual descent into the abyss. Those sceptics among us who believe that this is enough to muffle the alarm bells and who wish to bury their heads in the sand will, in light of the following, hopefully change their minds. It is now 2009, 22 years later, and our rainfall for last season was 402 mm, which is slightly above average. The 2009 season’s figures sit at 585 mm as I write, so we’re getting more rain than before, not less.
Why then are we concerned? Whilst a cursory glance at the chart is cause for optimism, it does not tell the whole story. In our case, our specific veld conditions are deteriorating despite the quantity of rain received. It’s the quality, not the quantity, that’s the problem.
Our rainfall pattern within each period recorded is erratic. Let me concoct a couple of extreme examples to demonstrate the point. If we received 3 mm of rain every day for a year, we would have received three times our annual average, but nothing would grow. Conversely, if we received a metre of rain in a day, Olifants would be an eroded wasteland once the floodwater had subsided. Our actual quality of rainfall isn’t as bad as either of those scenarios, but there are some similarities in effect.
Spacing of rainfalls, how far apart the falls occur, the timing of the rainfalls both in terms of time of day and position within a season, and quantity of rain received in a measured period of time, all combine to become the key to our decline or otherwise – and, of course, the ‘wild card’ is global warming, which is impossible to quantify on such a microcosmic scale as Olifants.
It is not how much you eat but rather what you eat and when you eat that helps you maintain good health. So too is the health of our rain-driven ecosystem dependent on quality rather than quantity. We are now beginning to understand the characteristics of rainfall in relation to vegetative growth. It is becoming increasingly apparent that the cumulative amount of rainfall recorded for a particular period is not as significant as the effectiveness of the falls. The question is, then, what influence has global warming had on the quality of the rain as opposed to the quantity? What we’re finding is noticeable variations in summer rainfall patterns and the nature of the rainfalls. They have become more erratic and inconsistent, resulting in less benefit to the vegetation and subsequently lower productivity.
Examples of negative effects include lack of timeous follow-up rains. As a result, seeds germinate only to have the young shoots burned off. Another example is the erosion of topsoil and the destruction of seed beds as a result of heavy falls early in the season. We tend to focus primarily on summer rainfall patterns, while relatively little is known about the effects of winter rainfall. Statistically these dry season figures for the lowveld have shown the most dramatic drop. Some authorities suspect there is a significant link between winter rainfall and the decline of sable and roan antelope in the Kruger Park.
You must be wondering why I am expressing some reservations about what I am saying. You might even detect a hint of contradiction. Well, neither applies, really, I’d just prefer to try and put things in the perspective of reality rather than in some convenient hypothetical model. We recognise that ecology is not an exact science, so we cannot rely on statistics alone. We also know that in order for a system to tick over, a complete and complex set of conditions is necessary, and that’s mostly beyond our control.
I believe we need to accept that some things are just bigger than us at this point in time. Even though the numbers and statistics of those factors in play appear normal, there are abnormalities in function, but not yet abnormal enough or so out of control that we need to ring the doomsday bells. I do not unreservedly support the belief that we are teetering on a knife edge of environmental tolerances at this stage.
Having said that, I’d prefer we erred on the side of caution rather than complacency and adopt ‘a stitch in time saves nine’ attitude. There is already some light at the end of this tunnel, too, in that the biggest culprits contributing to global warming are the very countries with the expertise and ability to do something about it before it’s too late (as Al Gore is trying to do something about it, whether you agree or disagree with the smoke and mirrors he employs).
Pragmatically speaking, there is comfort in the fact that organisms have responded and adapted to various environmental stimuli since life began. Some make it, others don’t; it’s Darwin’s theory being put to the test again. After all, man had nothing to do with the onset of the Ice Age, the erupting of Krakatoa, or the extinction of the dinosaurs.
The optimist in me believes that in the event of this region getting progressively hotter and drier to some as yet undefined peak, the vast majority of Olifants’ fauna and flora will adapt and cope. As compensation, there are actually many species which will thrive in those conditions.
The bottom line is that we can draw on the recorded history of our rainfall to paint a positive picture of the quantity of rainfall we can expect. At the same time, we cannot draw on those figures to interpolate anything to do with the quality of the rainfall. As an example of this, come with me to 1995/1996, and my son’s third birthday and the best rainfall season in 22 years.
Olifants River Game Reserve rainfall 1986–2009
|
Year |
Total mm |
|
1986–1987 |
343 |
|
1987–1988 |
442 |
|
1988–1989 |
318 |
|
1989–1990 |
464 |
|
1990–1991 |
393 |
|
1991–1992 |
135 |
|
1992–1993 |
395 |
|
1993–1994 |
257 |
|
1994–1995 |
403 |
|
1995–1996 |
718 |
|
1996–1997 |
398 |
|
1997–1998 |
229 |
|
1998–1999 |
424 |
|
1999–2000 |
660 |
|
2001–2002 |
428 |
|
2002–2003 |
155 |
|
2003–2004 |
408 |
|
2004–2005 |
329 |
|
2005–2006 |
531 |
|
2006–2007 |
465 |
|
2007–2008 |
402 |
Over the years the lowest rainfall was 135 mm in 1991/1992 and the highest 718 mm in 1995/1996.
My son Dino was three years old when he felt the first raindrop on his face! I can still see him on the concrete pathway to our back door, looking up at the source of the drops, only to have another pelt him in the eye. Holding his hands out, palms upward, with an occasional sideways and upward sneak peek, he giggled with pleasure at the new experience. Although it does rain here sometimes, this was his first encounter with this phenomenon, and little did we know then, that he would see a lot more later on in the season. In fact, 1996 would be the highest rainfall recorded for 22 years. But, it was not just the quantity, it was the quality that made such a difference. The reserve had good rains to begin with; in a little over two months, nearly 400 mm of rain had fallen, 25 per cent more than was recorded for the previous 12 months, and the total for the year was well over 700 mm, nearly twice our annual average. In the Olifants River catchment area it rained enough to produce the heaviest flooding in 60 years.
This rain-driven ecosystem wasted no time responding. Within a week the bush began the transformation from apparently lifeless grey stubble to the new spring green, or first green, ‘prima vera’ as the Italians say. Regular, well-spaced follow-up rains kept the new flush of life moist and nurtured and it wasn’t long before the vegetation took on a more mature, verdant, green hue. Even to those of us living here and able to monitor the change from day to day, the vegetation appeared to erupt rather than grow. Species of mostly alien plants whose seeds had been lying dormant for the right rainfall conditions to germinate did so.
Amongst others these included thatching grass Hyperina sp., lantana, black jacks and khakibos, but fortunately for us growth was restricted to isolated pockets, mainly where we had brought in feed for the rhino, along the supply road, transport routes and the river floodplain. That was the only time I had ever seen blackjacks or khakibos in such profusion, until 2008/2009 when an unusually wet season resulted in a similar eruption of these weeds.
Driven by the desperate drought conditions of the previous winter, elephant had pushed down, ring-barked and uprooted trees in search of moisture and nutrition. What at the time appeared to be senseless destruction for little or no return is now providing seed reservoirs for the vegetation component of which our reserve is so critically short.
The perennial grasses, buffalo grass Pannicum maximum and finger grass Digitaria sp. are typical examples. These grasses can be identified by their heavily laden inflorescence competing for sunlight in dense thickets, or standing proud of the thorny, twisted branches that were once the crowns of tall trees. These tangled shrouds now form micro-environments that provide protection from grazing pressure and create the conditions conducive to propagating healthy seed beds for the future seasons’ growth.
In contrast, the rate of recovery on the cleared areas is understandably slower. The effect of heavy grazing pressure, combined with severe drought conditions, means that these exposed areas will need a succession of growth to aid the recovery process and therefore will take more time to recover. At present, the vegetation on these open areas consists primarily of pioneer plants, mainly recovery weeds, herbs, and forbs, interspersed with annual grasses of low to medium palatability. These under-utilised plants, most of which are unpalatable, are left to allow their root systems to perform the necessary function of binding the soil. This effectively helps control soil erosion, while mulch forms from uneaten vegetation and also serves to trap seeds, which prepares the way for the next stage of vegetative growth. Basic conditions for recovery on these areas are now greatly improved.
The most recent vegetation analysis, done by the Agricultural Research Council (ARC), indicates that Balule has the lowest yield of vegetation per hectare, when compared to the other reserves in the association. However, this conclusion is qualified by the fact that, relatively speaking, Balule is carrying the largest biomass of plains game. Furthermore, the ratio of plains game species is more representative and proportionately better balanced on this reserve than anywhere else in the APNR. So it is clear that you cannot have your cake and eat it. With an average of just over 400 mm of rain per year, the reserve is presently carrying too much game to allow for a noticeable recovery of the vegetation in the short term.
In the long term, if we are to see the vegetation improve, we have to make some serious, far-reaching decisions pertaining to water provision and animal biomass management. No decisions, no improvement!
We just can’t rely on natural progression, particularly in the light of the relatively unquantified effects of global warming on our environment. As humans, we can use brain power (and science) to cope, but many organisms out there cannot employ that mechanism for survival, no matter that Darwin said survival of the fittest and strongest would be the defining law of the jungle.