#01 2021

Characterising vegetation in flux tower footprint at Benfontein Nature Reserve

By Buster Mogonong, Intern, EFTEON and SAEON Arid Lands Node

Vegetation biomass influences the ways in which terrestrial ecosystems interact with biogeochemical cycles such as those of carbon and water. Tracking vegetation changes, estimating biomass and cover, characterising the vegetation types and being able to track long-term changes in vegetation are crucial for understanding ecosystem fluxes of carbon and water cycles, with obvious impacts on understanding the effects and consequences of global change on carbon sequestration, water availability and the provision of ecosystem services such as grazing and regulatory services.  

In 2019, the Expanded Freshwater and Terrestrial Environmental Observation Network (EFTEON) erected two flux towers at Benfontein Nature Reserve in Kimberley to test the functioning of the eddy covariance instruments in this arid region. The eddy covariance instruments measure fluxes between terrestrial and atmospheric systems in the Savanna and Nama-Karoo biomes in the reserve.

Savanna and Nama-Karoo biomes where the EFTEON flux towers are located at Benfontein Nature Reserve. Left: Savanna flux tower; right: Nama-Karoo flux tower (Photos: Buster Mogonong)


To aid understanding of the ecosystem fluxes from the eddy covariance instruments, EFTEON staff members kick-started a research project to characterise the vegetation around the flux tower footprints at Benfontein following a protocol developed by the Socio-Ecological Observatory for Southern African Woodlands (SEOSAW) . The protocol is widely used in various woody vegetation sampling sites in Africa, including the Skukuza Flux tower site and sites in Hluhluwe-Imfolozi Park in South Africa.

This article shares information on the fieldwork recently initiated at the savanna flux tower site at Benfontein Nature Reserve.


EFTEON team members are currently sampling woody vegetation in the Savanna Biome at the Savanna flux tower to assess and characterise the woody vegetation around the site. We set up four plots in the traditional cardinal directions (N, S, W, E) from the flux tower. One additional plot is located near SAEON’s automated weather station (~300 m from the flux tower).

The plot located east of the flux tower covers a previously burnt patch in the landscape. The plots are one hectare in size, and the N, S, W and E plots are centred 100 m from the flux tower.

The centre of the plot was marked with a metal dropper and GPS readings were recorded. Each corner of the plot is marked by a dropper to demarcate the plot boundaries.

Woody vegetation was surveyed in each plot and parameters related to tree demography were recorded, together with other environmental variables such as signs of animal activity and the soil characteristics. We also kept track of the woody vegetation recruitment in these plots, whereby we surveyed tree and shrub seedlings and saplings.

Photographs of the site are taken from the centre of each plot at a height of 1.2 m towards the four cardinal directions (N, S, E, W). Repeat photographs will be taken from the same position when we revisit the plot.

Below are examples of photos taken by EFTEON’s Amukelani Maluleke from the centre of plot E1 in the four cardinal directions. The photos were taken from the centre of the plot at a height of 1.2 metres. The same procedure will be followed in all the other plots.

North of plot E1 from the centre

South of plot E1 from the centre

East of plot E1 from the centre

West of plot E1 from the centre

The photos below are examples of tree measurements to characterise the vegetation in the plots:

Intern Buster Mogonong (left) and Arid Lands Node field technician Tshililo Ramaswiela (right) measuring stem diameter at 0.3 m

Tree height measurement

Buster hammering a metal tag onto the tree

The SEOSAW protocol also accounts for herbaceous vegetation within the vegetation plot. We have not yet started this survey, but we intend to set up circular plots with a diameter of one metre along the four cardinal directions of the flux tower to assess herbaceous vegetation. Grass and forb biomass will be estimated in these plots and species counts will be undertaken.

Expected outcomes

The project is still in its early stages with field work only having started on 3 November 2020. However, from field observations we have found that the footprint of the Savanna flux tower is dominated by Vachellia erioloba and Vachellia tortilis. The herbaceous vegetation is expected to be dominated by Schmidtia pappophoroides, with pockets of Stipagrostis uniplumis and a variety of forbs.

The data will be analysed once all plots have been surveyed and vegetation characteristics around the flux tower footprint will be described. The information obtained from the analysis will be useful to further the understanding of how savanna systems behave in semi-arid regions.

Following the SEOSAW protocol is advantageous because it is an international database and standardised across African Savanna systems. The protocol captures the vegetation structure and demographics, allowing one to track changes in the woody vegetation in the reserve over time, including tracking Vachellia erioloba, a keystone species in the landscape.