Browsing by Author "Magadzire, Nyasha"

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    Fire and life history affect the distribution of plant species in a biodiversity hotspot
    (Wiley, 2019) Magadzire, Nyasha; De Klerk, Helen M.; Esler, Karen J.; Slingsby, Jasper A.
    Aim: Species distribution models (SDMs) provide valuable insights into species–environment relationships and potential climate change impacts on diversity. Most SDMs do not account for the role of natural disturbance regimes such as fire in determining current and future species distributions, or how species traits mediate their response to these stressors. Here, we investigate the importance of fire in determining the distributions of species in fire‐prone fynbos vegetation, and how this varies in relation to different life history traits (growth form and fire‐response strategy). Location: Cape Floristic Region, South Africa. Methods: We modelled the distribution of 104 plant species with different life history traits, using Maxent. The model included five climatic variables, one edaphic and one fire variable. Post hoc analyses of model output and permutation procedures were conducted to assess variable importance across different life history traits. We accounted for phylogenetic autocorrelation using sister species comparisons. Results: Permutation importance scores identified fire return interval as a major determinant of fynbos species’ distributions. Linear mixed effect analyses revealed that seeder species were significantly more sensitive to fire than resprouters. Coefficients from the (linear) response curves of the different predictors indicated that the occurrence of species across all life histories was negatively associated with longer fire return intervals. Main conclusions: Fire and life history traits governing species’ response to fire are key factors determining species distributions in our study system. SDMs that ignore the role of fire in driving species distributions, and how this varies across different life history types, compromise our ability to understand species–environment relationships in fire‐prone ecosystems. There is great need for better spatial data describing historical, current and future fire regimes and for models that can incorporate different responses based on species life histories, to improve vulnerability assessments for fire‐prone ecosystems.
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    Reconstruction of a fire regime using MODIS burned area data : Charara Safari Area, Zimbabwe
    (Stellenbosch : Stellenbosch University, 2013-03) Magadzire, Nyasha; De Klerk, Helen Margaret; Stellenbosch University. Faculty of Arts and Social Sciences. Dept. of Geography and Environmental Studies.
    ENGLISH ABSTRACT: Current efforts to address Zimbabwe‘s decade long veld fire crisis has partly been hindered by a lack of financial resources and fire data. This study illustrates the potential of using the MODIS burned area product as an alternative cost- and time-effective method for reconstructing historical fire records in Zimbabwe. Two MODIS burned area products were evaluated, namely the MCD45A1 and WAMIS (Meraka Institute‘s MODIS burned area product). Both products yielded similar levels of accuracy despite the difference in algorithms. However, it is assumed that at certain thresholds, either in tree cover or fire intensity, WAMIS ceases to map fires as accurately as the MCD45A1. Ten years of fire data for Charara Safari Area (CSA) was extracted from the MCD45A1, and used as a basis to establish six parameters: fire incidence, extent, seasonality, fire size, frequency and fire return interval (FRI). It was observed that approximately 50% of CSA burned annually, with an average of 132 fires occurring every year. Although there was no overall increase or decrease in the extent of area burned over the 10 year study period, an increasing trend in fire incidence was noted. Through an assessment of effective fire size, it was established that more fires in CSA were gradually becoming smaller in size, while the extent of area burned remained fairly constant. Hence, the increase in fire incidences and lack of a corresponding increase in area burned. This study was also used to identify areas in the fire regime that may be a potential ecological risk to the miombo woodland in CSA. Three points of concern were revealed: firstly, a high prevalence of late season fires was observed in the northern bounds of CSA. Secondly, 64.2% of the total area burned in CSA burned between 6 and 10 times over the 10 year period, and lastly, 85% of the total area burned over the period 2001 and 2010 had a FRI of less than 2 years. The combination of late season fires, high fire frequency and short FRI in CSA is indicative of possible alterations in the state of the miombo woodlands, which may have negative socio-economic implications on CSA and its surrounding communities. This study has demonstrated that the MCD45A1 is a useful source of much needed fire information for Zimbabwe. Therefore, the possibility of integrating methods employed in this study into the current collection of fire data should be given due consideration.
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    Understanding distributional responses of vegetation to changes in climate and fire regime in the Cape Floristic Region
    (Stellenbosch : Stellenbosch University, 2018-12) Magadzire, Nyasha; De Klerk, Helen Margaret; Esler, Karen J.; Slingsby, Jasper; Stellenbosch University. Faculty of Arts and Social Sciences. Dept. of Geography and Environmental Studies.
    ENGLISH ABSTRACT: As evidence of climate change and its impact on biodiversity continues to grow, anticipating and understanding ecological responses to climate change is ever more critical. In fire-prone ecosystems, such as those found in the Cape Floristic Region (CFR), a major concern is that changes in climate will likely lead to dramatic shifts in fire activity (e.g. increased fire frequency) that will significantly affect the distribution, composition, and functioning of vegetation. Effectively mitigating and/or adapting to the potential loss of biodiversity and altered ecosystem function in this region hinges on an in-depth understanding of how vegetation in the CFR interacts with the environment and, more importantly, how vegetation will respond to changes in both climate and fire regime. Our understanding of how climate change may impact vegetation is largely derived from distribution models. Vegetation distribution models have been used for decades to investigate species-environment relationships, predict future distribution patterns, and test ecological theories. These models are founded on the premise that vegetation distributions are determined by the spatial distribution of environmental variables that are significantly correlated with, or limit, plant distributions. However, while much emphasis is placed on the role of climate and topography as key determinants of vegetation distributions, other critical ecosystem components (e.g. fire regime) that have significant effects on the composition and distribution of vegetation are rarely incorporated in vegetation distribution models. Given the importance of fire as a driver of vegetation formations and assemblages in the CFR, the exclusion of fire variables from vegetation distribution models potentially constrains the generation of accurate and appropriate information, critical for the management and conservation of biodiversity in the region. The exclusion of fire covariates from distribution studies is partly a result of a lack of fire data, coupled with the widely accepted, but limited, view that climate is the chief determinant of species distributions and also a key determinant of fire regime. To this end, a proxy for fire return interval data, derived from vegetation recovery rates estimated from satellite data, combined with climate and edaphic data, was used to model and analyse the distribution of fynbos vegetation in CFR. Firstly, the importance of fire as a determinant of fynbos species distributions, relative to climate, was evaluated. This was complimented by an assessment of the effect of life history traits on plant species sensitivity to changes in ecological regime. To achieve this first objective, the distributions of 52 closely related fynbos plant species pairs (104 species), classified across two growth forms Stellenbosch University https://scholar.sun.ac.za iii (graminoids and shrubs) and their respective fire response strategies (seeders and resprouters) were modelled using Maxent, and subsequently analyzed. Secondly, the potential impacts of changes in climate and fire regime on future fynbos distributions were assessed by modelling the future distributions of 22 fynbos vegetation types under 44 Phase 5 Coupled Model Intercomparison Project (CMIP5) general circulation models (GCMs) using multinomial linear regression. Lastly, an overlay analysis of projected distributions of fynbos species and vegetation types was used to assess whether fynbos species respond in unison or as individuals to changes in climate and fire regime. The selected species in this final analysis consisted of 74 endemic species and 358 important species (species that are either high in abundance or frequency of occurrence, or predominant in a given vegetation unit), which facilitated a comparison of the potential impacts of changes in climate and fire regime between the two sets of species. Findings from this research identified fire return interval as a major determinant of fynbos species distributions. Although, the predictive power of the fire variable was greatly reduced when considered in conjunction with the other climate and edaphic variables, it was still among the most important predictors, and including fire data has the potential to add to our understanding of plant species distributions in fire-prone ecosystems. This was particularly apparent in the case of seeder graminoids and shrubs, where both graminoids and shrubs were found to be negatively associated with longer fire return intervals, while seeder species were significantly more sensitive to fire than resprouters. Projected changes in fire return interval and temperature will potentially have a significant impact on future vegetation distributions, with vegetation types with longer fire return intervals and warmer summer and winter temperatures being at most risk. It was also noted that projected changes in fire regime will likely have a greater impact on vegetation distributions than changes in rainfall regime. Comparing the distribution models of endemic and important species with models for the major vegetation types highlighted that species responses to changes in climate and fire regime largely conformed to the Clementsian concept of communities as organisms, with less than 30% of the species showing individualistic responses. As a result, the species composition of all vegetation types was altered when projected under future scenarios, with species from the present-day vegetation types either being lost or retained, while others were gained, in the projected vegetation types. The change in species composition largely stemmed from the replacement of some species in the present-day vegetation type by the same number of different species in the corresponding future vegetation type. The implications of this is that the underlying species composition of fynbos vegetation types will likely be altered under future climate and fire regime, thus disrupting the functioning of those vegetation types. The role of natural disturbance regimes, such as fire, in determining species distributions is generally overshadowed by the long-standing view of climate being the chief driver of species distributions. This research provides evidence for the contribution of fire in shaping species' distributions in fire-prone ecosystems, and highlights the need for the development and inclusion of estimates of fire regime components in vegetation distribution studies and vulnerability assessments. This is especially important since fire regimes are sensitive to a range of global change drivers beyond just changing climate (e.g. land use and invasive species).