Assessment of mistletoe - host interactions in a highland savanna in Windhoek, Namibia
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Date
2017
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University of Namibia
Abstract
Mistletoes have detrimental effects in ecosystems where they occur. Mistletoes negatively reduce the growth of the host plants and increase the chance of tree mortality. Apart from tree mortality, infected trees suffer from reduced growth and loss of vigor hence contributing to overall low productivity of hosts and resulting in changes in the structure and function of savanna communities. This study’s aim was to determine and to compare mistletoe - host interactions between the Botanic Garden and the Aloe Trail in Windhoek. For the assessment of prevalence and infectivity of mistletoes on woody trees, plot based sampling techniques were used to select and demarcate fifty 20mx20m plots from both the Botanic Garden and the Aloe Trail. All woody plants in the plots were measured for height and stem diameter. Each woody plant was then examined for presence of mistletoes and the total number of mistletoes on each individual plant was determined. The host species sampled were Senegalia mellifera (Vahl) Seigler & Ebinger and Boscia albitrunca (Burch.) Gilg & Gilg-Ben. The mistletoes species studied were Tapinanthus oleifolius (J.C.Wendl.) Danser and Viscum rotundifolium L.f. The Aloe Trail had a significantly higher prevalence than the Botanic Garden (Mann-Whitney test U, Z = -0.4562, p < 0.001) because of the better management efforts such as removing the mistletoes. Infectivity of Senegalia erubescens and Dichrostachys cinerea was significantly high in the Aloe Trail than the Botanic Garden (Mann Whitney U test, Z = -0.4.568, p = 0.00<0.001 and Z = -2.883, p=0.04<0.05). Mistletoes were mainly associated with S. mellifera and S. erubescens (χ² = 9.084, df = 3, p = 0.028<0.05). This is because, these host species have a high mistletoe-host compatibility. The Spearman’s rank correlation showed that the number of mistletoes were poorly correlated to host - tree height in the Botanic Garden and in the Aloe Trail (r = -0.44, p = 0.732>0.05 and r = 0.67, p = 0.410>0.05) indicating that variation in infestation intensity may be related to other factors such as canopy diameter availability of nutrients and water and not host size. Photosynthetic rates between mistletoe host pairs were measured using a portable LI-6400XT Portable Photosynthesis System. The Wilcoxon signed - rank test (Z = -2.061, p < 0.05) revealed that hosts have higher photosynthetic rates than mistletoes because they have higher electron transport rates. Water potential between mistletoe host pairs was measured using a Scholander pressure chamber. Hosts had a lower water potential than mistletoes (Wilcoxon signed - rank test: Z = -6.313, p<0.001) because hosts make use of water efficiency mechanisms to conserve water. Management focus should be concentrated on species such as S. mellifera and S. erubescens because they were highly associated with mistletoes in both sites.
Description
A thesis submitted in fulfilment of the requirements for the Degree of Master of Science
Keywords
Mistletoe