Grootfontein Camp 6 Trials - quantifying the increased grassiness of the Karoo

Technicians from SAEON and employees of Grootfontein re-survey the Camp 6 Trials, using the same wheel-point technique that was used during the 1950s to 1970s. Click to enlarge The initial aim of the Camp 6 Trials was to understand how the seasonality of grazing impacted vegetation communities and animal (sheep) productivity. SAEON’s Arid Lands Node and Grootfontein are also collaborating on the Bergkamp trials, which are nearly the same age as the Camp 6 Trials and reflect grass/dwarf-shrub/large-shrub interactions under a range of seasonal grazing treatments.

In 1934, long-term grazing trials were established at the Grootfontein Agricultural Development Institute (GADI) in the Eastern Cape by the late Dr Charles Tidmarsh.

The aim of the ‘Camp 6 Trials’ as they were known, was to understand how the seasonality of grazing impacted vegetation communities and animal (sheep) productivity. Intense botanical surveys were conducted on the experiment from the 1950s to the 1970s, whereafter it was discontinued as an official research project with the Department of Agriculture.

Oldest grazing trials in the world?

The value of the trials as a visual demonstration was recognised, however, and the treatments were maintained. The Camp 6 Trials are still in place, and may now be the oldest grazing trials in the world.

SAEON-GADI collaboration

In 2011, SAEON’s Arid Lands Node and GADI collaborated on a project to re-survey the Camp 6 Trials, using the same wheel-point technique that was used during the 1950s to 1970s. Technicians from SAEON and employees of Grootfontein conducted the surveys.

Results clearly reflect that there have been major shifts in species composition and growth forms from the 1960s to the present. These changes are evident as a shift from a shrub-dominated to a grass-dominated community (Figure 1), and a significant increase in basal cover (Figure 2).

Abundance and diversity of most shrubs have decreased, while those of perennial grasses have increased. The early-successional perennial grass Eragrostis lehmanniana now dominates, while the abundance of large, palatable, tufted grasses, notably Themeda triandra but also Digitaria eriantha, Sporobolus fimbriatus, and Heteropogon contortus has increased. Themeda triandra has interestingly formed large near-monocultures, especially in the winter-grazed treatments.

Why have grasses suddenly proliferated?

The increase is consistent with recent rainfall patterns, where the rainfall over the past fifteen years has been significantly higher during the hot summer months than it was in the past (Figure 3). c4 grasses can grow rapidly and reproduce in hot conditions provided sufficient water is available, which would explain their increasing abundance. Grasses are also highly competitive, being able to displace other growth forms under good growing conditions. This competitive effect would explain the corresponding reduction in the density of Karoo shrubs.

The Camp 6 Trials are a valuable ecological resource that can help quantify past changes as well as providing insight as to how semi-arid ecosystems will change in the future.

The SAEON Arid Lands Node and Grootfontein are also collaborating on other research projects involving long-term trials. The Bergkamp trials, nearly the same age as the Camp 6 Trials, reflect grass/dwarf-shrub/large-shrub interactions under a range of seasonal grazing treatments, while the discontinued Seligman Old Block Trials provide insight into ecosystem resilience and the longevity of the effects of livestock management systems.

Figure 1. Non-metric multidimensional scaling (NMMS) of Bray-Curtis distances among sites based on relative abundance (%) of species from 1962 (circles) and 2011 (squares). Abundant species have been overlaid on the ordination. Eraleh = Eragrostis lehmanniana, Hetcon = Heteropogon contortus, Aricon = Aristida congesta, Thetri = Themeda triandra, Digeri = Digitaria eriantha, Felmur = Felicia muricata, Ennsco = Enneapogon scoparius, Aridif = Aristida diffusa, Chlvir = Chloris virgate, Phypar = Phymaspermum parvifolium. Click to enlarge Figure 2. Contribution of perennial grass and perennial shrubs to total basal cover pooled across all treatments at Camp 6 for all survey years recorded to date. Figure 3. Early and recent rainfall distributions at Grootfontein. Note the considerably higher rainfall during December, January, and February.