The complex socio-ecological system of the lowveld marula bioeconomy catchment
Date
2021
Authors
Blair, Amy Marshall
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Abstract
The iconic species Sclerocarya birrea subsp. caffra, locally known as marula, is an ecologically
important savanna tree, valued as much culturally as it is economically. Marula is a keystone
species and vital natural resource with limited demographic data on the current population
status outside of conservation areas. Communities harvest marula within non-conservation area
communal lands in the lowveld region of far north-east South Africa. Across these non conservative savannas, marula is an important source of non-timber forest products (NTFP),
with populations affected by a range of socio-economic factors. Specifically, marula products
provide livelihood sustenance for local communities in these savanna woodlands of southern
Africa. However, the fruit products are increasingly being commercialized, which in addition to
heavy reliance on fuelwood, is increasing resource pressure and starting to degrade this
resource. As an ecologically important savanna species, it is imperative to understand if this
resource use is sustainable. Understanding environmental degradation requires examining
landscape changes over multiple spatial and temporal scales.
Landscape ecology emphasises patterns, processes and scales that result from combined
ecological and social drivers of change. Addressing environmental degradation within complex
socio-ecological systems (SES) necessitates the coupling of ecological and social sciences in
order to interrogate the mutual interactions between the social and environmental elements of
the system. Applying a socio-economic lens to environmental degradation further links social
meaning and symbolism to physical findings, allowing social ecologists to comprehend SES
contexts where ecological data alone tells an incomplete story. With increasing environmental
degradation, the imperative to combine quantitative data with qualitative research, in order to
address the underlying causes of SES change, has never been more pertinent. Considering the
context of the complex SES of the lowveld marula bioeconomy, marula trees are utilised for a
variety of socio-economic reasons across different land-use types in these non-conservation
areas. Understanding if resource use is sustainable requires therefore interrogating population
demography across different land-use types.
The aim of this study was to provide an updated inventory of marula population demographics
linked to resource utilisation practices. As a heavily utilised natural resource, marula
demographic data is used as a key indicator of population changes across not only land-use
types, but also geographical zones. The key ecological indicators of marula density, gender
ratios, mortality, tree damage, maturity ratios and size-class distributions were used to gauge
marula population demographics within the lowveld areas of Phalaborwa and Bushbuckridge.
Additionally, temporal comparisons are provided for the Bushbuckridge area, where a previous
data set exists, allowing for a 15-year comparison. Ecological data from 5832 surveyed marula
trees coupled with 240 individual household interviews and numerous informal focus groups
were combined to understand the marula bioeconomy catchment. Social data for different
behaviour patterns were used to provide context and explain anomalies in the population
demographic data.
Marula tree population data were gathered in rangeland transects and randomly selected fields
and yards from eight human settlements, divided equally between the Bushbuckridge and Ba Phalaborwa municipalities. Population structures can be gauged by comparing tree density and
size-class distribution (SCD) profiles across the three land-use types (homestead yards, fields
and rangelands) prevalent in these savanna socio-ecological systems. When combining density
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data with SCD profiling, it is apparent that land-use and harvesting practices are sustainable at
present and that marula population structures are stable. However, certain trends in the
ecological data suggest that there is cause for concern. In both Bushbuckridge (mean = 25.7±4.1
trees/ha) and Phalaborwa (mean = 13.9±1.9 trees/ha), overall density was highest in yards.
While this would appear to reject the hypothesis of decreasing density with increasing
anthropogenic interference, the ecological data alone only tells part of the story. Juvenile
populations comprising large numbers of seedlings were common in yards, which the social
data revealed was the direct result of discarded kernels from marula beer making. These
seedling populations caused elevated overall mean densities in yards. Respondents indicated
that these individuals are usually removed after a season, meaning that the majority do not
recruit through to adulthood. While comparisons with previous studies showed that overall
marula densities have increased in homestead yards, they have been rapidly decreasing in
rangelands over a 15-year period, suggesting intense resource use, particularly for fuelwood.
Female densities were higher than male densities in yards in both Bushbuckridge and
Phalabarwa but not in either fields or rangelands, with the social data once again revealing that
this selection is due to the prioritisation of female trees as the fruit producers. Male trees will
therefore be selectively cut when land is cleared for residential plots. The preference for the
female tree with it’s valuable fruit has resulted in a departure from the 1:1 ratio expected in
dioecious species, specifically in yards where the female tree is maintained for it’s combined
cultural and economic status. These findings are important as they indicate that value
attribution can lead to species conservation where the cultural capital of a specific natural
resource is high. Due to the numerous seedlings in homesteads, yards had negative size-class
distributions (SCD) in both locations, indicating strong recruitment, whereas rangelands
displayed positive slopes in both locations, indicating the opposite. This suggests possible
overharvesting in rangelands, with the collection of all available fruit under the parent tree as a
likely key-contributing factor to diminished recruitment. In both locations, adult and large adult
populations were highest in rangelands with the social surveys indicating that the larger trees
are chopped down in yards due to the concern that marula’s extensive branch and root systems
might destroy roofs and building foundations respectively. Furthermore, according to the social
accounts provided by respondents, the declining large trees across land-use types are attributed
to extended drought conditions. Mortality increased across the land-use types from yards to
rangelands in Phalaborwa, while the opposite trend occurred in Bushbuckridge with mortality
increasing from rangelands to yards. In both locations, primary damage increased along the
gradient from yards to rangelands. While instances of mortality and tree damage were minimal,
complete removal of chopped trees in yards and rangelands means that there is likely
insufficient evidence to create an accurate overall picture of negative resource practices.
Understanding the causes of resource conservation and degradation in the context of important
NTFPs is a key knowledge challenge. In light of demographic changes from increased resource
use in recent years, this study serves as an updated inventory benchmark for marula
populations in the area. Important lessons learned here can be applied to socio-ecological
contexts where key natural resources are responsible for sustaining livelihoods. By linking
marula population demographic data with the specific social behaviour patterns that shape
these data, it is possible to provide new insights regarding the use of a key non-timber forest
product (NTFP) within the complex socio-ecological system of the lowveld marula bioeconomy
catchment
Description
A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy to the Faculty of Science, School of Geography, Archaeology & Environmental Science, University of the Witwatersrand, Johannesburg, 2021