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Joining forces to monitor the iconic quiver trees of Augrabies
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Collaboration is key to understanding matters as complex and widespread as the effects of global change, land-use changes and growing threats to biodiversity.
SAEON recently joined hands with SANParks (South African National Parks) and DENC (Northern Cape Department of Environment and Nature Conservation) in order to come to grips with the current status and predicted future trends of quiver tree (Aloe dichotoma) populations in the Northern Cape Province.
Iconic species of the arid lands
The quiver tree is an iconic species of the arid parts of South Africa and Namibia. Wild populations occur in a narrow band from the north of Namibia to as far south in South Africa as Calvinia in the west and Carnarvon in the east (Figure 1). Despite this, the species faces various threats and therefore finds itself listed under CITES Appendix II as a protected species.
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Conservation biologist Wendy Foden and her co-workers identified climate change as a key threat and argued that quiver trees are undergoing a southward shift in their range. They also demonstrated that damage to the canopies or stems of the trees (often caused by wild animals, but also domestic livestock) lead to higher mortality rates in a population.
Quiver trees are popular ornamental plants, and although it has not been documented or formally studied, poaching is thought to be a significant threat to the survival of the species. It is especially a concern for populations that occur near public roads.
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Also not mentioned in the literature is the increasing development of grape production on the slightly undulating granite plains along the Orange River, which forms part of the quiver tree’s habitat.
Strategic importance
In view of these threats, the quiver tree population in Augrabies Falls National Park is of strategic importance, especially considering that it is the most south-easterly population occurring in a conservation area (Figure 1). For the park itself, the quiver tree is a priority species as it serves to attract visitors.
The Augrabies population has been the focus of nine previous studies. However, due to the involvement of different researchers and the difference in research questions, methods differed and the datasets are not entirely comparable. In addition, the sites (and therefore sub-populations) studied differed. In response to this, SANParks set out to develop a protocol for long-term monitoring of the Augrabies population.
Monitoring for conservation
SANParks saw the opportunity to collaborate with SAEON and DENC to design their monitoring in such a way that it would contribute to our knowledge of the metapopulation (populations at different locations with limited interconnections) and therefore to the conservation of the species as a whole.
SAEON Arid Lands Node field technician, Marco Pauw, who was involved with the Node’s initial monitoring of four sub-populations near Carnarvon in the Northern Cape Province, was asked to assist. The methods used by DENC and SAEON and subsequently adapted by SANParks, have all been based on those of Foden (2002). So, although each organisation has adapted the methods slightly to address specific questions, the datasets are all compatible.
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In September 2015, Pauw assisted a SANParks team led by Dr Hugo Bezuidenhout to monitor three quiver tree sub-populations within the Augrabies Falls National Park (Zeekoeisteek, Daberas and Coppenhagen). The results of this monitoring activity as well as previous research results have been summarised in a report published in March 2016.
The aims of the report were to record the distribution pattern of quiver trees in the park, assess the structure of populations and measure physical damage to individual trees. The report highlights the need for more directed research to answer new questions that have emerged, such as why one population seems to be less successful than the other two in recruitment and establishment; and why the trees in one population are shorter?
Two more sub-populations (on south-facing slopes of granite hills in the park) were identified and the first surveys of those will soon be undertaken.
SAEON, SANParks and DENC are currently collating the different datasets to assess the quiver tree metapopulation across the Northern Cape Province. They are also creating a monitoring action plan for the metapopulation to ensure the survival of this iconic protected species.
