Influence of termites on the soil seed bank in an African savannah

In savannah ecosystems, termites drive key ecosystem processes, such as primary production through creation of patchiness in soil nutrients availability around their nests. In this study, we evaluated the role of termites in altering the soil seed bank size, an important ecosystem component that has often been overlooked in previous work. Data on above ground vegetation and soil seed bank samples were collected from four microhabitats, that is, the wooded mound, unwooded mound, tree sub‐ canopy and the open grassland matrix in a protected game reserve in south‐central Zimbabwe. The seedling emergence method was then used to identify species present in the soil samples. One‐way analysis of variance followed by Tukey's multiple comparison tests was executed to test for significant differences in plant species richness among the four microhabitats. The results indicate that plant species richness was high on wooded termite mound but did not differ between the unwooded and the sub‐canopy microhabitats

Assessing the variation of river channel reach inflows on transmission losses

Arid and semi-arid regions are characterized by limited water availability throughout the year and highly variable streamflows. River channel transmission losses add another uncertainty to the complex flow regimes. However, the contribution of different factors influencing to transmission losses is poorly understood. In this work we determined whether variations in river channel transmission losses along five reaches of varying lengths could be related to reach inflows in Runde River catchment in Zimbabwe. We directly estimated transmission losses as the difference between reach inflow and outflow discharges. Using simple bivariate regression equations, channel transmission losses were modelled as response variables while reach inflows were the predictor variables. Our results indicate statistically significant positive relationships (p = .000, R2 > 0.05) between inflows and transmission losses for all minor, moderate, and major flow events. This simple approach can be applied in similar settings to understand the variations in transmission losse

Modelling the distribution of the invasive Ziziphus mauritiana along road corridors in Zimbabwe

We investigate how human fruit consumption affects the spread of the alien invasive Ziziphus mauritiana along road corridors in northern Zimbabwe. A field survey was conducted to identify and map Z. Mauritiana stems at 25 randomly located 6‐ha plots placed along two main roads connecting the Zambezi Valley to the Highveld region. The L‐function was used to test for evidence of significant spatial clustering of the stems. The inhomogeneous point model fitted by maximum likelihood was also applied to check whether distance from the road explains variation in the number of stems per unit area. Finally, a t test was executed on log‐transformed abundance data to test for significant differences in the mean number of saplings and adults between the Zambezi Valley and the Highveld. Results of the L‐function indicated that Z. mauritiana had a clustered and linear distribution along roads both in the Zambezi Valley and Highveld regions. Results of the t test showed that the mean number of saplings per plot in the Zambezi Valley (μ1 = 275) was three times higher than in the Highveld (μ2 = 78), with p < 0.01. The mean number of adult trees was also significantly higher in the Zambezi Valley than in the Highveld

Frequent burning promotes invasions of alien plants into a mesic African savanna

Fire is both inevitable and necessary for maintaining the structure and functioning of mesic savannas. Without disturbances such as fire and herbivory, tree cover can increase at the expense of grass cover and over time dominate mesic savannas. Consequently, repeated burning is widely used to suppress tree recruitment and control bush encroachment. However, the effect of regular burning on invasion by alien plant species is little understood. Here, vegetation data from a long-term fire experiment, which began in 1953 in a mesic Zimbabwean savanna, were used to test whether the frequency of burning promoted alien plant invasion. The fire treatments consisted of late season fires, lit at 1-, 2-, 3-, and 4-year intervals, and these regularly burnt plots were compared with unburnt plots. Results show that over half a century of frequent burning promoted the invasion by alien plants relative to areas where fire was excluded. More alien plant species became established in plots that had a higher frequency of burning. The proportion of alien species in the species assemblage was highest in the annually burnt plots followed by plots burnt biennially. Alien plant invasion was lowest in plots protected from fire but did not differ significantly between plots burnt triennially and quadrennially. Further, the abundance of five alien forbs increased significantly as the interval (in years) between fires became shorter. On average, the density of these alien forbs in annually burnt plots was at least ten times as high as the density of unburnt plots. Plant diversity was also altered by long-term burning. Total plant species richness was significantly lower in the unburnt plots compared to regularly burnt plots. These findings suggest that frequent burning of mesic savannas enhances invasion by alien plants, with short intervals between fires favouring alien forbs. Therefore, reducing the frequency of burning may be a key to minimising the risk of alien plant spread into mesic savannas, which is important because invasive plants pose a threat to native biodiversity and may alter savanna functioning

Solid Waste Disposal in Victoria Falls Town: Spatial Dynamics, Environmental Impacts, Health Threats and Socio-economic Benefits.

The sanitary disposal of solid wastes constitutes one of the most pressing challenges facing urban authorities in Zimbabwe. In recent years, there has been considerable increase in illegal waste dumping, which indicates that throughout the country, urban waste disposal systems are inefficient and environmentally unsafe. While there are numerous studies, which have focused on solid waste management in Zimbabwe, existing research has concentrated mostly on: (i) large cities especially Harare and sidelined small towns; and (ii) all elements of the solid waste management system and accorded least attention to disposal. To date, no study has attempted to quantify the impacts of urban solid waste disposal in Zimbabwe. Against the above backdrop, this study analyses the spatial dynamics, environmental impacts, health threats and socio-economic benefits of solid waste disposal in Victoria Falls town. In order to satisfy the above objectives, 14 soil samples were collected from study plots systematically positioned along 2 transects at the municipal dump and analysed for cadmium, lead and zinc content using the atomic absorption method at the Institute of Mining Research at the University of Zimbabwe. Data regarding the number, location, and size of solid waste dumps in Victoria Falls town, were obtained through field surveys and use of a Global Positioning System (GPS) receiver. The area occupied by each waste dump was calculated using Integrated Land and Water Information System (ILWIS) 3.1 Geographical Information System (GIS) software package. Analogue maps such as soil, topographical and land use maps of Victoria Falls town were converted into digital format through scanning and onscreen digitising using ILWIS GIS. This was done to facilitate spatial data analysis through measurement and overlay operations. Data on the population and feeding habits of Papio ursinus (chacma baboons) were obtained from field surveys involving physical counts and tracking of troops. To gather information on solid waste management practices and various impacts of waste disposal in Victoria Falls town, a total of 262 questionnaires were administered over a two-week period in October of 2002 using the face-to-face interview method. Respondents who included household heads, municipal officials, Parks and Wildlife Management Authority officials, representatives of commercial establishments, workers employed in the solid waste management sector and informal waste harvesters were selected using stratified random, purposeful and convenient sampling methods. Secondary data were obtained from detailed review of available literature especially municipal budget statements, clinical records, waste generation records and relevant publications. The study established that solid waste disposal, which is achieved mostly through crude tipping and widespread illegal dumping in Victoria Falls town has resulted in the emergence of 14 open waste dumps that have become quasi-permanent features of the town’s landscape. These open waste dumps, 13 of which are illegal, spoil 3.318ha of municipal land. The study also established that solid waste disposal practices in the town particularly crude dumping cause soil contamination by heavy metals, visual pollution and seriously threaten public health with waste workers and residents of Chinotimba high density residential area and informal settlements being the most vulnerable. The beneficial impacts identified are that crude waste dumping tends to stabilise and boost the population of some wildlife species especially P. ursinus, which scavenges daily from the municipal dump. The study further established that solid waste harvesting and recycling are now some of the major sources of food and cash incomes for some of the economically disadvantaged communities in Victoria Falls town. Based on the above findings, the study recommends that Victoria Falls Municipality should speedily eliminate all open waste dumps starting by those in residential areas; increase fines for illegal dumping so that they act as strong deterrents to illegal dumpers; increase refuse charges to keep them in line with rising inflation; and provide protective clothing to all employees involved in street sweeping, refuse collection and dumpsite management so as to safeguard their health

Including shaded leaves in a sample affects the accuracy of remotely estimating foliar nitrogen

The remote estimation of foliar nitrogen (N) has largely assumed that the spectral reflectance value measured on a remote sensing platform comes from only the sunlit leaves of the canopy. Whilst this could have been valid for leaf-level spectroscopy studies, the landscape level estimation of foliar N presents new challenges that need investigation. In addition, a growing interest in the application of broadband satellites in foliar N estimation has triggered the need to understand the confounding factors affecting the relationship between N and spectral reflectance. Field sampling criteria is therefore critical in obtaining representative foliar samples. However, the effect of using leaf samples drawn from different levels in the canopy on the accuracy of remotely estimating N is still poorly understood. Our study was carried out in the expansive miombo woodlands. A bootstrapped random forest regression technique, in the R environment, was used to predict foliar N from sentinel-2 broadband satellite remote sensing image. A weighted mean of foliar N was calculated by considering values from two levels in the canopy, from 0% to 100% at intervals of 10%. Our results showed that the most accurate model was the one where the mean N had equal weighting from both levels. Furthermore, there were significant (p < 0.05) differences amongst the root-mean-square errors (RMSE) of prediction of the models considered. We conclude that sampling leaves from two levels in the canopy improves the accuracy of remotely estimating N. This finding is significant in the canopy sampling for remotely estimating foliar N

Remote sensing of nutrients in a subtropical African reservoir: testing utility of Landsat 8

Remote sensing is useful for water quality assessments but current remote sensing applications favour parameters that are easy to detect such as chlorophyll-a. An assessment of the utility of Landsat 8 for detecting nutrients was conducted in Mazvikadei reservoir in Zimbabwe. The main objective was to determine whether nutrients often overlooked by remote sensing and yet are the main determinants of water quality can be remotely sensed. Sampling targeted ammonia, nitrates and reactive phosphorus from May to October 2015. In situ nutrient concentrations were regressed against reflectance derived from Landsat 8 imagery. Strong negative relationships were found between ammonia and the near-infrared band in July (R2 = 0.80, p < 0.05) as well as between nitrates and the blue band (R2 = 0.67, p < 0.05) in June. Overall, the results suggest that the cool dry season is the optimum time to use Landsat 8 for monitoring nutrients in tropical lakes

Evaluating the Applications of the Near-Infrared Region in Mapping Foliar N in the Miombo Woodlands

Remote sensing has been widely used to estimate the distribution of foliar nitrogen (N) in a cost-effective manner. Although hyperspectral remote sensing targeting the red edge and shortwave infrared regions has proved successful at estimating foliar N, research has recently shifted to include exploring the benefits of using the near-infrared (NIR) region, especially when using broadband sensing. Bootstrapped random forest regression analysis was applied on Sentinel 2 data to test the significance of using the NIR in foliar N estimation in miombo woodlands. The results revealed a low ranking for individual NIR bands, but the ranking improved when spectral indices were used. In addition, the results indicated a marginal increase in the normalised root mean square error of prediction (nRMSE) from 11.35% N when all bands were used to 11.69% N when the NIR bands were excluded from the model. Bootstrapping results show higher accuracy and better consistency in the prediction of foliar N using combined spectral indices and individual bands. This study therefore underscores the significance of spectral indices to increase the NIR region’s importance in estimating the distribution of foliar N as a key indicator of ecosystem health at the landscape scale in miombo systems