August 2016

The great Thakadu blow up!

FINALLY, WE DID IT! It only took 3 years to finally do our first experimental burn at Thakadu Game Farm. Photo by Emree Weaver.

Thomas and Thoralf took the lead in conducting this exercise. It had already started in January, when Thoralf and Laurie, the Thakadu Farm Manager, talked about potentially burning the coming summer. In fact the talks started 2 years earlier and we set up a bunch of control plots in the SW corner of the farm. Due to a combination of low rainfall and overgrazing of the area, the grass biomass was never high enough to light up the area. So, by the beginning of the year we changed the approach and identified a different area with adequate grass biomass. However, new plots needed to be set up and surveyed and firebreaks needed to be graded. While grading the firebreaks didn’t prove to be difficult, surveying 12 vegetation plots in 3 days proved to be quite a mission. We set up a total of 9 plots to be burned and 3 control plots, just on the other side of the cutline. All plots were assessed for vegetation structure, cover and total standing biomass. T & T also wanted to set up some temperature measurement stations. This proved to be even more complicated. We decided to set up two high accuracy measurement stations, where temperatures would be measured at 5 different heights (ground level to 2 m). With help from our mechanic in Maun, we designed the station in a fashion that they can be reused. The actual temperature sensor was a k-type thermocouple attached to a data logger. However, a lot of beverage was consumed over the thought of how to protect the actual data logger. The technical specs said “avoid temperatures in access of 40 degree Celsius”. Oops, these things need to go into a fire. However, we finally decided to get some small boxes made by the infamous ‘tin man’ of Maun. The box was filled with sand the logger place inside a Ziplog bag and then covered with sand. As a last layer of protection, we wetted the sand with water and closed the box. It works! Every single one of our ten loggers survived the fire and recorded the temperature accordingly. Earlier in the year, Thoralf came across some literature where flame temperatures were measured using some sort of a lacquer. This approach is not as accurate as the previous one but way cheaper. We had difficulties organizing this lacquer, even in South Africa, and it couldn’t be brought in on a plane, so we needed another idea.

The welding industry sometimes uses sticks similar to a piece of chalk to determine the correct temperature of a certain alloy. So we ordered a bunch of these sticks for various melting temperatures before leaving the US. However, they didn’t arrive on time, so they had to be mailed to Botswana where off course they got stuck at customs because nobody knew what that stuff is. After we finally got our hands on the sticks we quickly figured out that the chalk like pens DO NOT leave a mark. Big matata. It was challenging to ensure that the substance is exposed to flames, without getting blown away by the wind and to ensure we had an adequate number of measurements at multiple heights for multiple stations. Let’s just say we got a bit crafty at this point and designed an additional five stations. Check out the photos.

We recruited a bunch of volunteers from MODISA, in order to secure and monitor the firebreaks and on the 1st of August we lit the whole lot up!

Video by Emree Weaver.

The experimental burn plots were loaded with fuel. Photo by Emree Weaver.

Preparing the temperature measurement stations, to protect the data logger, 
we used a box filled with wet sand. Photo by Emree Weaver.

Due to the unequal distribution of (grass) biomass the area showed different degrees of damage 
after the fire. Here we are downloading the temperature data, approx. 30 min after the burn. 
Photo by Emree Weaver.

Temperature stations before (left) and after (right) the burn. Photos by Emree Weaver.

Temperature profile during the fire for one of our stations.

On of our analog temperature stations, these are the disks from the lowest level indicating 
temperatures of over 400 degrees celcius.

The temperatures reached during the fire decreases with height. Here is the ‘reading’ from 1 meters
 showing the first two disks have melted (temp > 100 deg. celsius), while the second set is uneffected
 (temp < 150deg. Celcius).

TnT assessing the fire damage. Photo by Emree Weaver/

Some flames reached heights in access of 2 meters causing severe damage to leafs, 
even on taller trees, in this case an Acacia erioloba.