In a previous post (The flattening of the waterscape and unrecorded loss of thirst-refugia: how does this affect plant biodiversity? ), I discussed how the area that is readily accessible to animals has increased dramatically because a fundamental resource — water — has been homogenised across the landscape (by humans).
A major driver of this homogenisation process is the advent of fencing the landscape to control both domestic and wild animals. This has a long, and relatively recent, history with many fences being put up from the 1950s onwards using government farming subsidies. However, if animals are going to be kept on a parcel of land, there has to be water. And thus, fencing went hand-in-hand with building dams, waterholes and watertroughs (initially windmill-driven). Every parcel of land had to have at least one water point.
Fast forward a few decades to the present where many farms have been consolidated or repurposed into larger farms — usually resulting in the removal of inner boundary fences — we have larger parcels of land, but watering points are very rarely removed. Thus, herbivores have greater freedom to roam the landscape, but their densities can remain high because of the short-distances to available water.
Here we need to jump briefly to a different topic — high failure rates of restoration initiatives in the subtropical thicket using Portulacaria afra (commonly known as "Spekboom"). We have demonstrated that part of this is due to planting in the wrong parts of the landscape (e.g. in frost zones; Duker et al. 2015a,b). But there is a strong herbivory component to this failure — although this has not been directly measured, but field observations suggest that this is a very important part of the puzzle.
Herbivory can come in the form of domestic or wild herbivores. Farmers may keep some stock animals on degraded land — but their effect on growth and survival of planted spekboom can be devastating. What is the primary reason why limited stock can be kept on degraded land? — the presence of a water point.
Dr Robbert Duker and Dr Marius van der Vyver (both excellent thicket ecologists) report high densities of Greater Kudu retarding the growth rate of spekboom planted in the great Thicket-Wide Plot experiments and neighbouring intact thicket. I suspect the increased densities of Greater Kudu across the subtropical thicket is cause for alarm — this is not in line with how this ecosystem worked previously. For example, Jack Skead records that the first sighting of Greater Kudu in 300 years in the Steytlerville area was in 1956 — Kudu were unknown in this region before and yet their densities are so high now that driving at night is considered dangerous as the chance of hitting a Kudu is quite high.
And these Kudu are also found in very degraded areas (note that most fences are not barriers to Kudu who readily leap >2 m). Why? The availability of water.
Thus, if we are to give restoration efforts the best chance at succeeding, we need to try and increase the thirstscape — to do this, we need to close watering points! There will be areas that are have natural water points (i.e. near rivers), so don't target these for restoration. Thus, any analysis of spekboom restoration potential for the Eastern Cape landscapes should include the waterscape. Target areas that are away from natural or anthropogenic water sources, or include the shutdown of anthropogenic water sources as part of the restoration toolset.
References
Duker, R., Cowling, R.M., du Preez, D.R., Potts, A.J., 2015a. Frost, Portulacaria afra Jacq., and the boundary between the Albany Subtropical Thicket and Nama-Karoo biomes. South African Journal of Botany 101, 112-119.
Duker, R., Cowling, R.M., du Preez, D.R., van der Vyver, M.L., Weatherall-Thomas, C.R., Potts, A.J., 2015b. Community-level assessment of freezing tolerance: frost dictates the biome boundary between Albany Subtropical Thicket and Nama-Karoo in South Africa. Journal of Biogeography 42, 167–178.
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