| Summary: | Stretches of forest along the Limpopo and Shashe Rivers have been classified as a unique forest type
in the vegetation of South Africa and are considered as being "critically endangered" by the South
African Biodiversity Institute. Roughly 400 hectares of this riverine forest area inside the western
section of the Mapungubwe National Park (MNP), a UNESCO World Heritage site, were deforested
and therefore degraded due to previous agricultural cultivation practices. Given the extent of forest
degradation that has occurred, the restoration of this area by means of the re–vegetation of indigenous
trees to its former composition is one of the objectives of the MNP's management plan. The successful
establishment of tree seedlings, especially in semi–arid systems, is however presented with a wide
range of constraints and limiting conditions, which often result in very high mortality rates during
restoration projects. An experimental exclosure, as identified by South African National Parks
(SANParks), was therefore fenced off inside the degraded old lands to act as a demonstration site for
the restoration of indigenous trees.
A pilot study conducted in 2006, involved the transplantation of selected indigenous tree species with
the aim of evaluating suitable re–vegetation technologies. The research contained in this dissertation
was also conducted inside the experimental exclosure, where recommendations derived from the pilot
study were evaluated, including the assessment of new re–vegetation technologies to enhance the
establishment of the indigenous trees. This study was therefore a follow–up project which involved
both field– and greenhouse trials. Seedlings of the following species were either transplanted into the
experimental exclosure (field trial) or cultivated inside a controlled environment in the greenhouse at
the North–West University: Acacia xanthophloea Benth. (fever tree), Berchemia discolor (Klotzsch)
Hemsl. (brown–ivory), Combretum imberbe Wawra (leadwood), Faidherbia albida (Delile) A. Chev.
(ana tree), Philenoptera violacea (Klotzsch) Schrire (apple–leaf), Salvadora australis Schweick.
(narrow–leaved mustard tree) and Xanthocercis zambesiaca (Baker) Dumaz–le–Grand (nyala tree).
During the follow–up study the effects of various enhancement treatments were tested regarding the
survival, growth and physiological performance of seedlings in both the field– and greenhouse trials.
The enhancement treatments consisted of the addition of compost and indigenous arbuscular
mycorrhizal fungi (AMF). In addition, seedlings transplanted during the pilot study, which did not
include enhancement treatments, were also monitored for establishment and growth. The potential use
of established Acacia tortilis Hayne trees to facilitate growth and establishment and to act as "nursing
plants", was also assessed. In addition, various pre–sowing treatments were also applied to seeds of
selected tree species in the greenhouse to assess the germination rate.
The survivorship and growth of seedlings in both the field– and greenhouse trial were determined by
using three growth parameters, namely "stem diameter at the base", "stem diameter 30 cm from the base", and "height of the tree in its natural growth form". Chlorophyll fluorescence induction (JIP test)
was measured on seedlings in both trials, using the multi–parametric expression, namely performance
index (PIABS), as a measure of the overall vitality of the plants of each species–treatment combination.
Physical and chemical analyses were carried out on the soil inside the experimental exclosure. Basic
descriptive statistics were used to analyse seedling survival and germination rates, and a two–way
analysis of variance (ANOVA) was used to determine the statistical significant effects of the various
enhancement treatments on diameter growth in each species (p < 0.05). Fluorescence data were
processed using the Biolyzer software and significant effects in each species were determined using
the Student's t–test (p < 0.05). Multivariate data ordinations using the CANOCO package were used to
determine the differences in soil types inside the experimental exclosure.
Moisture stress due to transplantation shock, competition with dense grass cover and herbivory,
resulted in an overall 55.8% seedling survival rate and negative stem diameter growth for transplanted
seedlings in the field. In comparison, seedlings cultivated in the greenhouse had much higher survival
rates and showed positive stem diameter growth. Most species in the greenhouse showed higher
growth rates and significantly higher vitality values when planted with enhancement treatments. The
responses of transplanted seedlings to the enhancement treatments were very species–specific in the
field trials. Based on these results, it was concluded that the enhancement treatments were beneficial
with regard to the establishment and growth of most of the species. The beneficial effect was however
cancelled out by the various abiotic and biotic factors encountered in the natural environment.
Seedlings transplanted in the understory of established pioneer A. tortilis trees had much lower
survival rates as the extensive root system of A. tortilis most likely out–competed the transplanted
seedlings for moisture and nutrients. Many seedlings were also predated by insects or small mammals
which reduced the growing potential. The germination trials recorded the highest germination rates for
most species when germinated in the compost–containing treatments. These trials also indicated that
all of the investigated species showed higher survival rates when pre–sowing treatments, such as
soaking, mechanical scarification and removing the seed from fruit, were applied. Various
recommendations emphasising long–term monitoring, proper maintenance and after–care of future
restoration efforts are made. These include experimental layout of exclosure plots and pretransplantation
treatments of seedlings while cultivated in the nursery. During this study, the
experimental exclosure was also used as a demonstration site for training and capacity building for
SANParks personnel and students from academic institutions. === Thesis (M.Sc. (Environmental Science))--North-West University, Potchefstroom Campus, 2011.
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