Long-term monitoring expands our knowledge of the Succulent Karoo

By Helga van der Merwe, SAEON Arid Lands Node Tweet

The recent publication of a Special Issue on the Karoo in the African Journal of Range and Forage Science highlighted findings from scientific studies across the Karoo.

Papers were diverse and not limited to only the Nama Karoo Biome but included papers on the Succulent Karoo Biome, an arid hotspot of diversity.

The Karoo Special Issue featured three long-term vegetation monitoring projects in the Succulent Karoo with survey data generated over 15 to 26 years. In all three cases, the researchers that initiated the studies at these sites are still involved with the projects.

These researchers re-survey the sites at yearly (for two projects) and five-yearly (for one project) intervals. This is rare and adds crucial continuity in field survey methodology and species identification. The researchers’ expertise and experience over a decade or two at the same sites also aids interpretation of the findings, thereby adding value to these lengthy studies.

Diverse study locations

The three Succulent Karoo study locations were diverse: (1) Leliefontein communal area and adjacent privately-owned farmland, (2) Goegap Nature Reserve, and (3) Soebatsfontein communal farmland. Each project used different research methodologies to investigate vegetation change over time.

A line transect on the plains of Goegap Nature Reserve (Photo: Helga van der Merwe) The Leliefontein communal area (Photo: Joh Henschel)                                                          The Soebatsfontein Observatory in Namaqualand (Photo: Helga van der Merwe)

One study comparing a fence-line contrast between the continually grazed Leliefontein communal area with adjacent rotationally grazed private farmland found a decline in total vegetation cover on both communal and privately-owned farmland in the later monitoring period. This decline was attributed to the low rainfall and the large reduction in the annual plant component.

In another study in which SAEON is involved, the effect of high grazing pressure by wildlife on the plains of Goegap Nature Reserve was found to decrease total plant cover and reduce grazing-sensitive species. Additionally, perennial species composition had changed over the >20-year period, while annual species changes that occurred were dependent on timing and amount of rainfall.

Overall, on the Soebatsfontein communal farmland, with stocking rates currently much lower than when privately farmed, vegetation cover of shrubs and annuals decreased and a strong dependence of vegetation on rainfall and temperature, or just rainfall, was found.

Research findings

Findings were similar across these locations exhibiting diverse land uses, historical and current management practices as well as different research methodologies. All three studies confirmed that rainfall had an important effect on total annual plant cover.

Historical and current grazing regimes were found to slowly affect perennial plant cover and composition under livestock and wildlife utilisation. All three projects confirmed that long-term studies are essential to gain an understanding of vegetation change in the Succulent Karoo as vegetation change occurs slowly under the arid conditions that prevail in this biome.