Another important research objective is the monitoring of vegetation and trees, especially the most common small tree, Acacia drepanolobium, also known as the Whistling Thorn Tree of Africa, named for the sound the wind makes while blowing through the galls and thorns. This important food source is essential for the survival of the black rhinos in the reserve, as well as being an major component of the diet of elephants and giraffes. Because of this competition, major stands of the Acacia forest needs constant observation, measurement and analysis.
On one of our Tree Plot mornings, Joanne and I were joined by Graham, an Earthwatch volunteer from England. He and Christopher, our guard for the day, examine a small Acacia drepanolobium for any damage or the presence of ants. Plainly visible are the galls that the ants use for shelter. Above is a close-up of one acacia, with galls and thorns and the ants, their abdomens raised as they swarm to attack. Click on the image for a closer view of some red-red-black ants.
Measuring Device, 2006 (left). One of the most important activities was measuring the growth of the Acacia drepanolobium trees. (Above left) Bernard and I check for ants and for damage. (Above right) I extend the measuring device to the topmost point on the tree (above photos by Joanne Ferri).
Elephant Damage, 2006 (below, left and right). 'Reverse' growth occurs when animals or natural causes damage the tree and reduces its size. Here are two trees broken off at the trunk by elephants.
Bernard Leads Us to Our Plot, 2006. The Reserve has dozens of Tree Plots, and the volunteers are usually visiting each plot at least once per year. After going to these plots year after year, the guards have a good idea of where they are and how far we need to walk to get there. Still, the volunteers are given a pre-set GPS device to locate the first tree more accurately. Here, Bernard shoulders his rifle as he leads us to our morning's work. With a good field of view and no animals in sight, we feel pretty safe as we approach the tree plot.
Acacia Seedling and Measuring Device, 2006.
(Left) This seedling was easy to find. Many other were almost totally hidden in the grass or growing almost horizontally. In such a case as that, we'd have to feel around in the grass (never a good thing) in order to measure the stem at its base. (Above) Measuring seedlings meant using only the bottom portion of our measuring device, since we only measured seedlings that were less than . 50 centimeters (1/2 meter) tall.
Acacia drepanolobium, 2006.
"The vegetation within the Reserve is a mosaic of open grassland (above left), acacia dominated wooded grassland (left), Euclea dominated scrub woodland (above right), and riverine woodland. The acacia woodland covers about 40% of the 9,200 hectare Reserve. These acacia trees form a large proportion of the diet of the rhinos and giraffes, as well as being eaten by elephants." -- Earthwatch Expedition Briefing.
Above right, growing much smaller and in thicker stands around this Acacia xanthophloea (a much larger cousin of A. drepanolobium) is the more dominant Euclea divinorum. It is here that many of the animals in the Reserve spend the hot days, resting in the shade. And it is here that our guides are most alert when leading us on our field work. Once you enter the Euclea, you never know what might be beyond the next bush.
Downloading the Data, 2006.
Back at the Research Center, a freshened and happy Joanne and Megumi watch as Linus Gatimu, the Principal Investigator of this Earthwatch Project, instructs Graham on how to download our collected data from the palm pilot to the laptop. The transfer of data from field notes to palm pilot to laptop is extremely important. This is the true purpose of our visit to Sweetwaters, and the data will be invaluable in helping to determine the viability and sustainability of enclosed game reserves.
Tagged Tree, 2006.
The acacia trees are all about 3 to 12 feet tall, and are usually spread out over the grassland. In each plot, about 50 trees are tagged with these numbered tin plates. We would have to find the first tagged tree, then follow directions for each subsequent one. Often, the tags or the trees themselves would be missing.
Joanne at the Seedling Plot, 2006. Long mornings in the field can be exhausting. Here, Joanne is able to sit down while Bernard and I measure the seedlings and call out our findings. But sitting isn't always a good idea: you are an easy target for wandering ants, and hidden thorns could be waiting for you in the grass.
Zebras, 2006. Of course, one of the perks of this kind of research is our access to wildlife. Here, a small herd of common zebra move lazily into our area, about 40 meters away, grazing on the grass and unconcerned with our presence. What a treat to have while working in the field.
Seedling Sample Plots:
Seedling Plot, 2006.
The most difficult activity was the Seedling Sample Plot. Measuring off an area of 400 square meters, our team of Joanne, Bernard and myself would locate each Acacia drepanolobium seedling under half a meter tall (left), measure each one in height, width and circumference of its trunk (above), and record the details in a palm pilot. (Left) Bernard and I measure out the plot, 20 x 20 meters square. Using light plastic tape, we had to contend with a constant wind that wanted to rearrange our lines, as well as thread it through thick shrubs and grass. If that wasn't enough, we only had two 20-meter tapes with cloth markers tied to each two-meter point, but just one measuring tape with which to measure it all.
Click on any image for a larger view.
Seedling Plot, 2006. Before we could even locate the seedlings, we had to mark off our study area. Here, Joanne pulls a line tight in order to get the most accurate starting point. Even with her sore wrist, she had to perform in the field, just like the rest of us. Later, while we were on the Vegetation Plot (another of our activities) she stepped into an aardvark hole and twisted her ankle. Being the trooper that she is, she gallantly worked on for another three hours, finishing all three of our plots that morning.
Seedling Plot, 2006. Here, Bernard kneels to clear away the tall grass from one seedling, while Joanne enters data on the palm pilot. My job was constant kneeling and bending to measure the height and diameter of each seedling, and inspect each one for ants or damage. In this plot, we found and measured 179 seedlings, which I think must have been some kind of record, at least for Team III. Did I say difficult? I picked numerous thorns out of my knees over the next few days, not to mention the many times that my hands were pricked by the thorns or ants crawled up my sleeve and bit me.
