My Graduation Research on Trees and Arthropods in South Africa

This week, I’m excited to share with you another significant step on my journey to Africa. To complete my bachelor’s degree, I needed to undertake graduation research. Commonly referred to as a thesis or dissertation, depending on the country’s terminology. I was determined to secure my own placement for this research, with a strong preference for conducting it in Africa. After countless emails and a considerable amount of time invested. I stumbled upon the Grootbos Foundation, affiliated with the Grootbos Private Nature Reserve in the Western Cape of South Africa. They graciously welcomed me to conduct my graduate research within their reserve.

The name “Grootbos” translates to ‘big forest,’ which may seem a bit ironic considering its location in the Fynbos ecosystem, an environment typically devoid of trees. However, it takes its name from the stunning Milkwood forests, a unique habitat found within the fynbos. These forests thrive in sheltered valleys, are safe from wildfires, and benefit from more abundant water sources. Interestingly, this was also the focus of my research. The Western Cape Milkwood Forest remains a relatively underexplored subject. It’s an endangered vegetation type characterized by a fragmented distribution range and faces potential threats from development. Today, I’m eager to share some of the most captivating aspects of my graduation research in this unique setting.

Graduation research

For my university degree, I had to undertake graduation research and thesis writing, a semester-long endeavour amounting to 30 credits. This comprehensive task spanned over five months, equivalent to 22 weeks, during which I needed to conduct fieldwork in a tropical country, analyze the collected data, and complete the report. My thesis journey commenced in September and was slated for submission in the first week of January. Given the tropical nature of my research, the timeline was quite tight. To optimize efficiency, I coordinated with my supervisor to have my research proposal finalized during the preceding summer.

This meant that I found myself drafting the entire research proposal while travelling through Australia! It was a challenging endeavour, but my determination to complete everything within a single semester drove me forward. Thanks to the pre-prepared research proposal. I was able to depart for South Africa in early September upon my arrival, I dived right into the preparations for the upcoming fieldwork. There was no time to waste!

Grootbos Private Nature Reserve

As the name suggests, Grootbos is a privately owned nature reserve. The owner of this reserve made a conscious decision to contribute to the well-being of the local community and the natural environment within and around the reserve. To achieve this, the Grootbos Foundation was established, comprising both conservation and community-oriented initiatives.

The conservation team primarily directs its efforts toward the incredible biodiversity of the fynbos ecosystem. Encompassing both its plant life and wildlife. An annual highlight involves the collective effort to manage controlled fires. An essential practice for stimulating the fynbos since this biome relies on fire as a natural process. Regrettably, I missed participating in these fiery endeavours.

While my temporary colleagues were deeply engrossed in studying the fynbos. My focus was set on the ancient Milkwood forest nestled within the valleys of the reserve. Given my particular affinity for trees, I was fortunate to be presented with an opportunity to conduct my graduation research. Contributing to a deeper understanding of the biodiversity within this remarkable forest ecosystem. My research aimed to analyze the tree species composition and the arthropod assemblages, shedding light on this unique habitat.

Milkwood Forest

Within the reserve, five distinct patches of Milkwood forest exist. However, considering my limited timeframe, we opted to focus on three specific patches: ‘Garden Lodge,’ ‘Forest Lodge,’ and ‘Witvoetskloof.’ These patches vary in size, with Garden Lodge spanning 18 hectares, Forest Lodge covering 17.4 hectares, and Witvoetskloof, the smallest of the three, measuring 3 hectares. Each of these patches was selected for its unique characteristics, providing a diverse representation of the Milkwood forest ecosystem.

Garden Lodge, characterized by its substantial size and pristine condition, offered an excellent example of an undisturbed forest. In contrast, Forest Lodge, while also extensive, had been impacted by a significant fire that swept through the reserve in 2006. Making it an intriguing study area to observe post-fire recovery dynamics. Witvoetskloof, though small and somewhat isolated, held its significance due to its proximity to an underground spring, potentially influencing its ecological dynamics. These three patches were chosen strategically to capture a broad spectrum of conditions and ecological nuances within the Milkwood forest.

Tree composition

The initial phase of my graduate research involved assessing the tree composition within each of the forest patches. To accomplish this, I employed a systematic approach, employing 15 plots within each forest patch, organized into 3 clusters. These cluster locations were strategically chosen to account for variations within the forest, spanning from the forest edge to its interior. Each plot measured 20 by 20 meters, and within these plots, I meticulously recorded data for trees with a diameter exceeding 5 cm, measured at a standard height of 1.30 meters, often referred to as ‘diameter breast height’ (DBH). For each tree, I documented the species name, DBH, and coordinates. Additionally, I determined the canopy cover percentage at the most representative spot within each plot.

With this comprehensive dataset, I was able to perform various analyses. I calculated tree species richness per plot and per forest patch, as well as beta-diversity, and evenness, and employed the Shannon-Wiener and Simpson diversity indices. These methods provided insights into the diversity of tree species within the different forest patches of my study area. Furthermore, I conducted forestry-related calculations, such as mean DBH, which serves as an indicator of forest patch age. Additionally, I determined the number of trees per hectare, offering insights into age and forest structure. Lastly, I calculated the Basal Area in square meters per hectare. Which provided valuable information regarding timber presence, thereby shedding light on the age and structural aspects of the forest.

Arthropod assemblage

The second phase of my graduate research focused on examining the arthropod assemblage, with the aim of using it as an indicator of forest health. I sought to establish a connection between arthropod data, tree composition, and known information about specific animal groups. To collect the arthropods, I employed a leaf litter collection method in conjunction with Berlese funnels.

Within each plot, I gathered leaf litter from a 30×30 cm area, directly beneath the location where I recorded canopy cover data. This decision was made considering the potential influence of canopy cover on the arthropod assemblage. I transported the collected leaf litter back to the office laboratory. Where I employed a heated device to extract arthropods from the leaf litter. Most arthropods, including moths and spiders, react differently to heat and tend to move away from it, descending into the funnel from which they fell into a jar. Once in the jar, they were unable to escape, allowing me to examine them at the order level.

Using the data about the arthropods I captured, I conducted various analyses. I calculated diverse biodiversity indices, similar to those mentioned in the ‘tree composition’ section. As well as the average tree composition. Additionally, I explored the potential use of arthropods as bioindicators. As some species exhibit distinct responses to disturbances, such as the significant fire that occurred in 2006.

Results from my graduation research

The results of my research yielded notable differences between the two components. First, regarding tree compositions, Witvoetskloof stood out with the highest biodiversity across all previously mentioned methods. This forest patch boasted a remarkable diversity of tree species, mainly attributed to its proximity to an underground spring. In the Western Cape, dry months can lead to water shortages, limiting the growth of many tree species typically found in ‘Afromontane’ forests, which are situated in wetter regions. However, thanks to the presence of this spring, certain Afromontane species were able to thrive in Witvoetskloof.

Conversely, when it came to arthropods, I observed contrasting outcomes. Witvoetskloof exhibited the lowest arthropod biodiversity, while Garden Lodge displayed the highest. This discrepancy can be attributed to Witvoetskloof’s small size and isolation. Arthropods, being small creatures, often struggle to cover long distances, and they simply do not have the opportunity to reach this area. On the other hand, Garden Lodge and Forest Lodge were adjacent to each other, providing arthropods with the chance to move between these locations. Nevertheless, Forest Lodge presented significantly lower biodiversity compared to Garden Lodge, primarily due to the fire damage it sustained.


As mentioned earlier, I also aimed to utilize the arthropods as potential bioindicators. Unfortunately, I didn’t capture a sufficient number of individuals to draw significant conclusions in this regard. The only notable difference I observed was a higher percentage of predator arthropods in Forest Lodge compared to the other patches. An increased presence of predators, particularly spiders, could indicate some level of disturbance, which aligns with the results we obtained regarding tree composition and our knowledge of the past fire event.

This serves as a brief overview of my graduation research, with limited information on the results. I have much more to share on this topic, but delving into further detail would make this blog post significantly longer. If there’s any aspect you find particularly interesting, please don’t hesitate to let me know! I’d be delighted to provide more insights into my incredible experience in the Milkwood forests.

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