| Summary: | Land degradation is a process that causes the reduction in resource potential of natural
rangelands and occurs widespread throughout southern Africa. This process is mainly
characterized by the loss in vegetation cover, which leads to the occurrence of bare
and denuded patches, increased soil erosion, changes in species composition as well
as bush encroachment by indigenous and alien invasive plant species in savannah
areas.
Degradation of rangelands has drastically extended at an alarming rate during the last
few decades with the main causes being overstocking, extended periods of drought,
global climate change, overgrazing and general mismanagement of the land. Many
researchers, however, feel that rangeland degradation is mainly caused by a
combination of changes in land use practices and climate variability.
Land users have, however, been applying a variety of technologies over the years in
order to restore affected rangelands and mitigate the effect of degradation. These
technologies include passive and active intervention methods, aimed at restoring bare
and denuded areas and controlling indigenous bush and alien plant species
encroachment. Bush control can be carried out by applying different technologies,
involving chemical, mechanical, manual or biological control.
The focal point of this study is on bush encroachment, the factors causing the
problem, the possible ways of controlling this phenomenon and lastly the
incorporation of such information into a user-friendly Decision Support System
(DSS). The Decision Support System comprises of two databases as well as a related
expert system. Bush encroachment is a matter of great concern in most southern
African countries. This study therefore mainly included data from Namibia and to a
lesser extent, South Africa, as the main study areas, seeing that this form of
degradation greatly influences the biodiversity of rangelands in both these countries.
The Namibia Agricultural Union (NLU) identified the need for the development of a
user-friendly Decision Support System, in which case studies concerning the different
bush control technologies could be stored in a database. Restoration technologies,
regarding the occurrence of bare and denuded areas, that have been applied by the
land users over a period of time and in a specific environment in the past, have been
captured in a computerized database and expert system, serving as a Decision Support
System (DSS) and user-friendly consulting tool in a similar study, carried out by Mr.
Van der Merwe (1997). This DSS was based on CBR (Case Based Reasoning)
methodologies by which a number of case studies, that have previously been stored in
the database, can be searched by means of an expert system approach to advise the
land user concerning the most appropriate solution (action) to similar degradation
problems. The DSS developed by Mr. Van der Merwe was never published or made
accessible to the land user in a format that could be consulted by either CD-ROM or
the internet. Seeing that the NLU identified the need for a similar DSS containing
bush control technologies, it was decided to incorporate both these databases into a
single DSS, concerning bush control as well as the restoration of bare and denuded
patches. The newly converted DSS is currently known as EcoRestore and consists on
two databases: Grass Expert, which focuses on technologies to reclaim degraded
rangelands, and Bush Expert, which is more focused on the control of bush
encroachment and combating of alien invasives.
As mentioned, this study focussed on the development of the Bush Expert database
and will therefore only include results, discussions and conclusions of these case
studies.
The case studies in the Bush Expert database consist of results obtained by means of a
questionnaire completed by the land user, in collaboration with the agricultural
extension officer, as well as a quantitative vegetation assessment, to determine the
success rate of the applied technology.
The Bush Expert questionnaire, comprises of questions concerning personal
information of the land user (e.g. location of the farm), the situation on the farm
before bush control was applied (e.g. information on the environmental factors, such
as density of problem trees), as well as the type of control technology applied and the
situation of the rangeland after control (e.g. establishment of the herbaceous species).
The quantitative vegetation assessments involved the sampling of the woody and
herbaceous components in the area where a specific control technology was applied.
The density and height classes of the woody component were determined by means of
the belt-transect method. By using the descending-point method, the herbaceous
component was surveyed to determine the abundance/frequency of the annual and
perennial grass species.
In order to increase the success of any restoration project, it is important to take the
existing indigenous knowledge of local land users, concerning the problem of
degradation and mitigation thereof, into consideration. By doing so, the local people
and communities have greater control and responsibility over their resources and are
able to command a greater range and level of resourcefulness. Taking indigenous
knowledge into consideration finally enables the local land users to actively
participate in and influence higher-level decision-making processes by which they are
affected.
A total of 175 case studies in Namibia and nine case studies in South Africa were
surveyed. The Namibian case studies were surveyed in the central and northern arid
and semi-arid regions, and South African case studies in a limited location within the
Limpopo Province. Only 100 of the Namibian case studies have thus far been
incorporated into the Bush Expert database.
Multivariate data analyses techniques, analysis of variance and correlation analyses
were used to analyse the data obtained from the questionnaires and quantitative
vegetation surveys. Results were represented in the form of histogrammes, tables and
multivariate analysis ordinations.
From the results obtained for the Bush Expert database, it was clear that chemical
control technologies were most often applied in Namibian and South African case
studies (61%). The herbicides most commonly applied as chemical control technology
in Namibia included Grazer (20%) and Savana (15%), whilst in South Africa these
included Access (33.3%) and Tordon Super (33.3%). Herbicides were mostly applied
by means of aerial application (46%) methods in Namibia and as cut-stump treatment
(55.5%) by means of knapsack spraying or with a brush in South Africa.
The dominant woody species causing bush encroachment problems in Namibia were
found to be Acacia mellifera, Acacia reficiens and Dichrostachys cinerea, whereas in
South Africa these species included Dichrostachys cinerea, Acacia erubescens and
Acacia karroo.
The wood of the controlled problem species (dead woody material) is mostly not
utilized after control, but rather left on the land to disintegrate and thus contribute to
the organic material content in the soil. Dead branches are also used for brush packing,
which forms and ideal micro-climate for the germination and establishment of grass
seeds, which serves as an erosion control medium and protects grass seedlings against
grazing impacts. Some land users do however produce charcoal from certain
controlled woody species, in order to recover some of the input costs of bush control.
The majority of the case study sites (68%) in Namibia occurred within the 300-450
mm short- and long-term rainfall zones and in South Africa the majority of case study
sites occurred within the short-term rainfall zone of 550-600 mm (66.6%) and 400-
500 mm long-term rainfall zone (55.5%).
Case studies where chemical and manual bush control technologies were applied
indicated the highest success rates after control (81.7% and 75.2% respectively).
Success rate as an entity was greatly influenced by the type of control technology
applied, the density of the problem woody species after bush control as well as
environmental variables such as rainfall and soil clay percentage.
No definite trend could be determined concerning the application of a specific bush
control technology and a certain problem species. Land users tend to apply a chosen
control technology, according to the resources available, such as labour, mechanical
implements and finances. The only positive correlation between control technologies
and the type of problem species could be found regarding Dichrostachys cinerea. This
species was mainly chemically controlled by means of the application of certain
herbicides.
The most important lesson to be learnt from the surveys completed in the two
countries is that it is an absolute necessity to apply a proper after-care programme as a
management practice following the initial control of problem woody species. The
implementation of after-care determines the final success rate of any applied bush
control technology as a restoration practice within a rangeland. Only 11% of the case
studies surveyed for Namibia and South Africa indicated the implementation of an
after-care programme, which usually involved biological control (e.g. browsing by
boer goats or the use of controlled or accidental natural veld fires).
The EcoRestore Decision Support System is currently available as an online webversion
(www.puk.ac.za/EcoRestore), as well as a CD-ROM version. The CD-ROM
version is available in a package containing the CD and user's manual. An example of
the package is included in this dissertation.
In consulting the databases through question-and-answer procedures, the best action
will be proposed to the land user for future rangeland restoration, either the
reclamation of denuded areas or the control of bush encroachment. Since the case
studies are based on past and existing experiences and research, the land user will
have an indication of the expected outcome, should the same advised technology be
applied.
The EcoRestore DSS does not only offer a consulting tool for extension workers and
technicians, but also creates networking and participation between land users and
researchers, both locally and between neighbouring countries. The DSS is linked to
other national and international websites and databases, to offer users a wider range of
information and technologies with regard to agricultural and conservation practices.
Better awareness is created amongst land users concerning the problem of rangeland
degradation, which might encourage closer monitoring of the degradation and
mitigation processes.
The EcoRestore DSS was developed in such a way for it to be as user-friendly as
possible, in order to reach as many parties involved in current or future restoration
programmes. This study involved the development of the first version of the DSS
(Version 1.0) and is thus only the prototype system. It is proposed that the Bush
Expert database of the EcoRestore DSS, will be expanded in future and additional
bush control case studies from other southern African countries will be included. The
addition of such case studies will ultimately increase the effectivity of this DSS. === Thesis (M.Sc. (Botany))--North-West University, Potchefstroom Campus, 2004.
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