Shareholder project: Grass Survey

One of the aspects which attracted us to invest in LL was the opportunity to get involved and understand more about what goes on in the bush.  Greg mentioned that one important subject is to understand the distribution of the flora, especially the grasses, as this defines the game carrying capacity.  Consequently in April/May this year my wife and I undertook a high-level vegetation survey.

This survey was aimed at understanding how the vegetation varied across the Reserve and how the data could be linked to satellite images so that someone could firstly define vegetation zones and then ultimately, once more data is collected, calculate and monitor the changes in game carrying capacity.  We are not specialists in this area and we recognise that in order to calculate the game carrying capacity, a more thorough analysis is needed.  However, Greg felt that the study was worthwhile as it would create a framework around which future studies by the various students could be based.

For the survey we stopped every 500m along two north-south roads and three east-west roads, walked 50m into the bush to avoid the effect of the road (all the while noting Greg’s guidelines on how to walk safely in the bush), and then recorded the vegetation within a 10m radius.  For the survey we recorded the dominant, sub-dominant and other bush and grass species present, the approximate height and spacing of the bush, the approximate density of grass cover (good, average, poor), the % ground covered by “forbs” (herbaceous flowering plants), the tree types, and the ground conditions (loose red sand, rock outcrops, wash zone, etc.).  We also took photographs in an East, South, West and Northerly direction at each site, so that a specialist could then assess whether our estimate of Good / Average / Poor ground cover was consistent with the judgement of other surveyors.

We used “Guide to Grassess of Southern Africa” by Frits van Oudtshoorn as our guidebook for the grasses and “Field Guide to trees of Southern Africa” by Piet van Wyk and Braam van Wyk for the bushes & trees.  For the grass identification it is sometimes necessary to look for hairs or at details of the seed shape.  Greg taught us that a binocular can act as a microscope when inverted and the subject is just a few centimetres from the lens – try it; we didn’t believe him either but it worked!

We identified 24 grass types, most of which are classified as having low grazing value.  These are the ones you see still intact in the dry season but these too are eventually grazed.

 

Species Grazing status Plant succession Grazing value
Aristida canescens  3  2  Low
Aristida congesta barbicollis  3  1  Low
Aristida congesta congesta  3  1  Low
Aristida diffusa  4  2/3  Low
Aristida rhiniochloa  3  1  Low
Aristida stipitata  1/2  Low
Aristida vestita
Cenchrus ciliaris  1  2/3  High
Chloris virgata  3  1  Average
Digitara eriantha  1  3  High
Digitaria velutina  3  1/2  Low
Enneapogon desvauxii  3  1/2  Average
Enneapogon scoparius  4  3  Low
Eragrostis nindensis  3  2  Average
Eragrostis patentipilosa  3  1  Low
Eragrostis rigidior  3  2  Average
Melinis repens  3  1/2  Low
Panicum maximum  1  2/3  High
Pogonarthria squarrosa  3  2  Low
Schmidtia pappophoroides  1/3  2/3  High
Stipagrostis uniplumis  3  2  Average
Tragus berteronianus  3  1  Low
Tricholaena monachne  3  2  Average
Urochloa trichopus

Most common species highlighted in bold.

Grazing status:

  1. Decreaser. Abundant in good veld but decrease when either under- or over-grazed. Palatable climax grass;
  2. Increaser I. Grasses that are abundant in under-utilised veld. Usually unpalatable, robust climax species.
  3. Increaser II. Grasses that are abundant in over-grazed veld. These grasses increase due to disturbing effects of overgrazing. Mainly pioneer or sub-climax grasses. Common in lower rainfall areas.
  4. Increaser III. Commonly found in over-grazed veld and in higher rainfall areas. Usually unpalatable, sub-climax grasses. Strong competitors and increase when palatable grasses are weakened through overgrazing.
  5. Invaders. Grasses which are not indigenous to the area.

Plant succession:

  1. Pioneer. Hardened annual that can grow in unfavourable conditions. Usually have advanced seed dispersal strategies. These grasses improve the conditions, for perennial grasses to take over.
  2. Sub-Climax. Denser than pioneer and provide more protection to the soil.. Mainly weak perennials with life spans of 2-5 years.
  3. Climax. Strong perennial plants which are well adapted to the conditions and provide strong protection to the soil against wind, sun and flooding.

We then linked the survey to satellite images we bought and have donated to the Reserve. These are SPOT 6 images with 1.5m resolution – one was taken 20 March this year and the other 27-29 July last year. Below is a colour enhanced image of the reserve from March this year. Red denotes healthy vegetation, yellow-green and white represent bare earth, black represents stoney areas.

grass-survey-1

 

Some features stand out.

  • The dark curved area in the upper left hand quadrant is where dolomitic rocks (metamorphosed limestone) outcrops. Here the ground tends to be stoney with little grass cover and the bushes mainly types of thorn bushes.
  • The bright red in the Longope watercourse represents trees whilst the white zones bordering the watercourse represents wash zones where the rains scour the surface clean of any vegetation.
  • The “freckles” in the top right quadrant are the magnificent kirkia syringe trees
  • The bright yellow-green areas north of Lipadi Hill and the Northern Plains show the effect of the clearing there.
  • Below is the detail of the area north of Black Rock (just visible in the bottom of the picture). The “contours” are zones of either bands of mopane and other bushes grow or clearings where layers of rock outcrop.

grass-survey-2

Computer enhancement can also be used to measure the vegetation index (NVDI – Normalized Difference Vegetation Index). Below is a comparison of strong vegetation in the dry season and the wet season. Green denotes vegetation. This shows that the area surrounding the Longope stream and the Eastern side of the Reserve carry more vegetation during the dry season than the west side does. Also of interest is that the rocky area in the top left quadrant of the reserve also acts to trap more water.

grass-survey-3

The next stage in our project will be to enter the data into a database, develop a Geographical Information System (GIS) which we will give to the new Reserve Manager, and write up a report which will include a print-out of the records for each data point so that more experienced scientists can review and correct our work as necessary. We hope this will be ready for the AGM.

From discussions with Greg, the next steps would then be to repeat some of the surveys in January-February to see whether we recorded all of the grass species or whether the more palatable grasses had already been cropped, leaving the less palatable ones for us to record. Also, Greg planned to then engage a student to actually measure the quantity of grass in selected sample sites and then using the GIS and the satellite image, denote zones of common characteristics to then develop a better understanding of the game carrying capacity.

If you have any questions on this you can contact either my wife or myself on silurian48@outlook.com.