African Wildlife & Environment Issue 81

FAUNA, FLORA & WILDLIFE

plants as they move quickly through the landscape) and deposit much of this eaten and semi-digested material as a layer of 'frass' (the politically correct name for insect poo). This frass is damp, inoculated with bacteria that digest cellulose, and is being deposited on damp soil where surface roots can access this natural 'fertilizer'. In their overnighting locust 'roosts' the layer of frass deposited can be 20-40 mm thick (just like sheep kraal sites! See also African Wildlife & Environment #67 Shepherding back biodiversity). What this means ecologically is that locusts are essential biogeochemical re-cycling agents of the arid and semi-arid rangelands.Thus, when we kill them off, we are interrupting this cycle and facilitating long- term nutrient deprivation of these rangelands.

Chris’s research taught me much more about locusts and the essential ecosystem services they provide. Did you know, for example, that there are two phases of adult locusts; those that are referred to as 'sitters' and those that are called 'flitters'? The former stay in their breeding grounds to lay again for the next generation, to ensure the longevity of the species, while the latter first hop off, and then ultimately, fly off to distant parts. These flitters are seeking new locations for colonisation and reproduction, that can be a considerable distance from where they hatched. What is fascinating to me is that I learned that the percentage of sitters and flitters in the hatching population, that will eventually go through several instar stages (sub-adult, flightless hoppers) to ultimately become winged adults, is determined by how good the past season was for forage production. Thus, in drier years the percentage of locusts that hatch are mostly sitters, and in wetter years many will grow to flitting adults. Makes good ecological sense really, because in good years when there is plenty of food, the chances of success in finding new and alternative far-off breeding grounds is better. Our own 'Trek Boers' knew this too; they certainly did not set out from the old Cape Dutch Colony to cross the Karoo after a series of poor seasons. Rather, they were opportunistic and set off after a season or two of good rains - to ensure that there would be ample grazing (and water) for their livestock while they slowly trekked north and east over the much more arid interior to better watered lands beyond. Thinking about locusts ecologically, and learning from Chris’ research, leads me to suggest that in fact locusts are essential to the long-term well-being of the rangelands, and our propensity to poison them is anti-ecological and driven by short-term thinking about money.What hearsay is this? I now also know that in arid areas, where locusts live, there is little or no decomposition of organic materials in dry years. Any litter that falls is so dried-out that it simply blows away. Thus, the only opportunity of any nutrient recycling, through the decomposition of organic material, can only occur in wetter years (AND by the way, it is only in these wetter years that the plants’ deeper roots can gather inorganic nutrients from greater depths and bring them to the surface). Now comes the really cool part of all of this. In years when locusts swarm, the mass of hoppers moving through the landscape strip off all the photosynthetic material available (but do not kill the

PRIMARY CONSUMERS GRAZERS & BROWSERS

PRIMARY PRODUCERS PLANTS

SECONDARY CONSUMERS CARNIVORS

DECOMPOSERS

MINERAL SOIL

ELEMENTARY NUTRIENT CYCLING MODEL

Just to step sideways for a moment, rangelands are regions where agricultural cultivation is impossible because the area is too dry. Thus, our rangelands in South Africa are those areas where free-ranging domestic livestock (mostly sheep, but with a more recent shift to goats) are the animals many farmers keep. In addition, some of our rangelands carry wildlife populations – sometimes together with domestic stock or simply as 'game' farms. How the land-owners make a living in these rangelands is by harvesting either the animals themselves, or from the wool clipped from sheep and goats. Now, for a moment, think about the long-term effects of this 'harvesting' – it is in fact the gradual removal of the existing plant-available nutrients from the rangelands. Thus, over time these plant nutrients from the pedoderm (the layer of top soil that is just a very few centimetres thick where maximum plant root activity occurs) are eventually depleted, resulting in less nutritious forage for animals.We have in fact already witnessed some big changes in the composition of important rangeland plants.

30 | African Wildlife & Environment | Issue 81 (2022)