28 February 2024
Hollows – dug by hand or mechanically to collect water and seeds – help restore bare patches of land in dry areas.
This is evident from the experiments conducted during some of the worst droughts in the Karoo by Dr Sue Milton and students from Nelson Mandela University at Wolwekraal Nature Reserve near Prince Albert.
Milton and Ken Coetzee from Conservation Management Services wrote about this in Grassroots, the online bulletin of the Grassland Society of Southern Africa. According to them, concentrating available water by making hollows in the ground is the best way to establish plants on bare soil.
The hollows must be dug so that any runoff water is trapped. Where the hollows are on sloping ground, “gutters” must be made on the edges at the bottom to retain water. The depth of the hollows depends on the texture of the soil.
Sandy soils drain quickly and dry out quickly, so the hollows must be deeper. Hollows in clay soil, on the other hand, retain water for so long that seedlings can drown.
“In ideal conditions, the hollows and the surrounding soil should remain moist for at least a week after rainfall to allow for germination and the establishment of seedlings.”
A cover over the hollows helps retain moisture. It can also prevent soil with a fine texture from cracking or forming layers, lifting seedlings out of the ground. Thorn branches over the hollows can deter animals until seeds have germinated and plants have established.
Milton and Coetzee wrote that bushes can be packed on bare ground without hollows to stabilise the soil and promote seed germination in certain areas. However, this method did not work in Prince Albert.
“This is possible because the packed bushes could not retain water, and where they were packed very tightly, they excluded light.” The preferred way to restore bare patches is to make hollows, wait for rain, and expect seeds to blow in from neighbouring fields.
However, seeds must be sown if not many are available in the vicinity due to heavy grazing, drought or clearing of fields.
Their experiments showed that about a quarter of all plants that emerged in the four to five years of the trials were from the seed mixture sown when the experiments began. More seed and a greater variety improve the chances of success, as shown by research in dry areas worldwide.
