Wolwekraal Conservation and Research Organisation (WCRO) applied to the GCBR Flexible Micro Fund for funding to carry out a repeat survey of drought and porcupine damage to the Kraal Aloe (Aloe claviflora) population in Wolwekraal Nature Reserve. Funding of R18,250 was granted to WCRO in August 2021. Here we report on the work done, preliminary findings, and further action taken.
Aloe claviflora is widespread across the arid interior of the Northern, Western and Eastern Cape of South Africa and across southern Namibia on well-drained rocky ground. This slow-growing aloe starts life in clumps of shrubs, and after 50 years or so, starts to flower and produce suckers. After many decades, probably centuries, a single aloe forms a circle of heads or a “kraal”, hence the common name. The flowers are unusual in that they radiate out horizontally from the kraal. In 2016, Gina Arena – then a SAEON intern with Renu-Karoo in Prince Albert – recorded the position, size and health of 257 kraal aloes (1355 heads) on Wolwekraal Nature Reserve (Figure 1, Google image), and using trap cameras also recorded the pollinators which turned out to be birds, bees and elephant shrews (Arena 2018).
During the five years since Gina Arena surveyed the Aloes the drought worsened. Although Aloe claviflora is drought tolerant, the plants were unable to flower. Moreover, many of them were damaged or killed (Figure 2) by porcupines which consumed the stems and inner leaves of the aloe rosettes. We assume that porcupines started to browse aloes because they were drought stressed and in need of food and moisture.
The Prince Albert area received 164mm of rain between January and December 2020, and a further 75 mm between January and August 2021most of which fell in the autumn, resulting in some flowering by the remaining aloes. In August 2021 Gina Arena, with the assistance of WCRO/Renu-Karoo intern Stefan Short (Figure 3), resurveyed the entire marked A. claviflora population on Wolwekraal to answer the following questions:
- What proportion of the population has died?
- What is the apparent cause of mortality?
- In which microsites is survival best (open, under shrubs, among rocks)?
- What proportion of the population flowered in 2021?
- Are pollinators still available in the area to visit the flowers?
Survival, mortality and flowering
Between 2016 and 2021, 60% of the sampled aloe head population died (806 heads), most of them having been destroyed by foraging porcupines. Porcupines appeared initially to target larger aloe clumps, foraging on these repeatedly over time until the entire clump had been killed. A year after damage there was no sign that the browsed aloes were able to re-sprout. Aloes partly-protected by rocks or overhanging shrubs survive better than those in exposed positions that were more accessible to porcupines. Although many of these overhanging shrubs (e.g., Rhigozum obovatum and Lycium spp.) have also been negatively affected by the drought, they currently still afford greater protection of aloes from foraging porcupines. Porcupines continue to forage on aloe heads and are targeting the smaller clumps, or individual aloe heads, as the larger ones are progressively destroyed.
In 2016, 34% of the population of 1355 aloe heads produced flowers. Following 164mm of rain in 2020 and 75mm in 2021, of the 549 surviving aloe heads, 30% produced flowers in August 2021. Trap cameras confirmed that the elephant shrew, birds and insect pollinators were present, and the seed set in October 2021 appears to be good.
Aloe flower visitors
Trap camera records of flower visitors from 16 August until 22 September 2021 revealed that birds (Dusky, Lesser Double-collared, Malachite sunbirds and Pied starlings) visited during the flowering peak display (Figure 4a-c) whereas elephant shrews drank from the flowers at night throughout the flowering period (Figure 4d). Other nocturnal visitors to flowers included a Scrub Hare which browsed aloe petals and a Hairy-footed Gerbil (Figure 4e-f).
Honey bees and megachillid bee were seen on fully-open flowers during the day.
Insectivores including Blue-headed Agama and Familiar Chat in the day and Barking Gecko at night hunted on or under aloe inflorescences presumably to intercept their insect prey (Figure 5a-c).
In spite of the drought, an increase in the amount of rainfall in 2020 and 75mm in 2021 was sufficient to allow aloes to flower, which has shown to be a vital resource of food for attracting a variety of animals to the area.
PREDATORS OF INVERTEBRATES ON FLOWERS
Following the completion of the aloe survey, Gina Arena, Stefan Short, Sue and Richard Dean discussed possible ways to protect a sample of Kraal aloes of various sizes from porcupines. We decided to cage some of the aloes in such a way as to enable access to pollinators while excluding porcupines. Gina selected 12 aloes of various sizes from the monitored population. During September 2021, Stefan Short constructed and erected low wire cages around these individuals (Figure 6). We will monitor these cages monthly to see whether they are serving their intended purpose.
Co-funding from the Plant Conservation Unit, University of Cape Town
Gina Arena, who recently completed her PhD thesis supervised by Professor Timm Hoffman (Director of the Plant Conservation Unit), has been working for the university as a research assistant at the PCU until she graduates in December 2021. The PCU kindly offered to cover part of the Aloe project costs to allow Gina to travel to Prince Albert to conduct the fieldwork at Wolwekraal Nature Reserve in August 2021 during her appointment at the university. The PCU covered travel expenses from Cape Town to Prince Albert and back, as well as the cost of accommodation and meals for her stay in Prince Albert between 2 and 5 August 2021. Subsequent publications of the results from the Aloe project will, in kind, carry her affiliation to the Plant Conservation Unit, in addition to those of her co-authors.
Communication of information
Gina will present the preliminary findings at the Arid Zone Ecology Forum Virtual Conference between 11 and 15 October 2021. This is a pre-recorded presentation which can be made available after the conference. She also plans to publish the results of the two surveys in a peer-reviewed journal over the next year, and possibly write a second popular article for the Veld and Flora magazine and a blog article for GCBR. These contributions would acknowledge GCBR support for the research. Links to articles as well as the final report could be displayed on the GCBR website. We have posted photos of the Aloe pollinators on the WCRO Facebook site.
Contributions to GCBR vision and goals
This study advances the GCBR vision of People and Nature Living in Harmony by supporting the following GCBR themes and goals:
Theme 1. Land and Landscapes. Goal Sustainable use and landscape management which promotes maintenance of ecosystems. This study will help us understand how the interaction of drought and herbivores influence survival and distribution of Aloe claviflora. This knowledge will assist landowners to make informed decisions about protection of certain plants or habitats from porcupines during drought.
Theme 3. Biodiversity. Arrest the loss of indigenous biodiversity. The study found that local persistence of the slow-growing, but wide-spread Aloe claviflora could be threatened in future by the interactions of climate change and herbivory, and thereby negatively impact other wildlife that rely on Aloe claviflora as a food source. This knowledge could be used to prioritize one or more sites for special protection.
Theme 5. Education, Knowledge and Learning. More people in the GCBR domain embrace sustainable living practices in their daily lives. The WCRO/Renu-Karoo intern who assisted in the aloe monitoring work is a third year NMU Nature Conservation student and this work forms part of his training in resource conservation. The effects of drought and herbivory on the aloes is discussed on all the guided walks undertaken on Wolwekraal Nature Reserve and visitors are shown the aloe cage experiment. All information acquired will be published and made available to local landowners, conservation agencies and academics. As a result of access to information more people in the GCBR domain are likely to take an interest in the surrounding natural environment and become more aware of the vulnerability of ecosystems to climate change and land management.
Arena, G. 2018. Kraalaalwyn – an oasis in the drought. Veld & Flora March pages 26-29 (article attached to this application)
Arena, G. & Milton, S.J. 2021. The impact of drought-induced porcupine herbivory on a population of Aloe claviflora on the Wolwekraal Nature Reserve, Prince Albert. Talk presented at the virtual conference of the Arid Zone Ecology Forum on 12 October 2021 at 9.55
Compiled by Sue Milton and Richard Dean For Wolwekraal Conservation and Research Organisation
Photos courtesy of Sue Milton and Richard Dean