Nematode-based indices in soil ecology: Application, utility, and future directions

14 Pág.The health and functioning of soil ecosystems are the foundation of sustainable food production and land management. Of key importance in achieving sustainability, is the frequent measurement of soil health, and indices based on the community structure of nematodes are amongst the most widely used toolsets by soil ecologists. Thirty years after the development of the Maturity Index, we aimed to evaluate the application, utility, and future directions of nematode-based indices (NBIs). This review focused on NBIs that are calculated using the coloniser-persister classification of nematodes. Data from 672 empirical studies in terrestrial environments revealed that the NBIs presented a dissimilar usage trend. The Channel Index and Metabolic Footprints showed the strongest increase in application rates over time, thus indicating a greater interest in studying decomposition pathways and ecosystem functioning, respectively. Furthermore, nematode-based indices were mostly applied in agricultural systems associated with herbaceous crops and in studies investigating, for example, soil nutrient enrichment following manure and/or inorganic fertilizer application. We further provide a framework for selecting a focus-orientated subset of NBIs for testing hypotheses based on the underlying ecological mechanisms. Also, we highlight important considerations, including the unexpected behaviour of some nematode taxa, in the interpretation of NBIs. The improvement of NBIs relies on advancing our understanding of the autecology of nematodes. Finally, we deliver insight into the further development of NBIs considering recent methodological advancements. We highlight that NBIs have been and might become increasingly important in providing valuable information on soil ecosystem health and functioning, especially considering the urgent need for more sustainable land use.The contribution of JHS was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) — :— Project no. 420414676: “The self-regulatory potential of agro-ecosystems: Using nematodes as indicators for legume disease suppressive soils”.Peer reviewe

An urban ecological synthesis of socio-ecological systems dynamics in Potchefstroom, South Africa

PhD (Environmental Sciences), North-West University, Potchefstroom Campus, 2015As rural populations decrease and cities expand, the importance of urban ecological research becomes globally significant. Urban ecology seeks to understand the complex relationships between human settlements and their ecological contexts in an attempt to ensure sustainable futures. The discipline of urban ecology is at the forefront of the conflict between human perceptions, economy, and politics. Despite numerous studies conducted in urban areas in South Africa, no one city has yet synthesized all the amassed research conducted within its city limits. A shortage of detailed ecological data, therefore, led to an extensive study of urban open spaces in some cities of the North-West Province encompassing multiple disciplines. Consequently, this study attempts to consolidate and evaluate all the existing urban ecological research in South Africa and specifically, in the city of Potchefstroom. Firstly, a comprehensive overview of South African urban ecological literature discussing the early development, research themes and the future of urban ecology in South Africa was carried out. Three hundred and fourteen publications were reviewed and categorized into the following research themes: physical environment, biodiversity, management, conservation, planning, human needs, sustainability, public participation, ecosystem services, and resilience. Secondly, as researchers have long been interested in studying and explaining patterns of biodiversity in natural and anthropogenic landscapes, many theories have been proposed on the drivers of these patterns and numerous studies compare current land-use effects with biotic assemblages. However, a much-neglected perspective in urban ecological research is the impact of the history of the landscape. Consequently, the second paper investigated the possible time lags in the response of temperate natural grasslands to urbanization and the factors driving these changes. Thirdly, a study of the temporal vegetation dynamics of urban grasslands in Potchefstroom over a 17-year period was carried out. Open grasslands, woody vegetation sites, and vacant lots were resurveyed within the city limits. The potential change in species richness and abundance of species, and the differences in species composition between these three habitat types were compared. Lastly, the fourth paper synthesizes all the relevant existing interdisciplinary research carried out of urban open spaces in Potchefstroom. This is evaluated against municipal governance and management strategies, environmental law, public opinion and the steep spatially organized socio-economic gradient found in Potchefstroom, informing the progress towards a sustainable, liveable city. The results of the literature study indicated that there were various gaps within each theme that need to be addressed in future. In the study on the effects of urbanization history on observed vegetation patterns, the woody vegetation showed important time lags in the response of indigenous species richness to urbanization. The measures altitude and the road network density of natural areas were the most frequent predictors of species richness. Results of the temporal vegetation dynamics of urban grasslands indicated that in the relatively short 17 year period most vegetation diversity indices changed significantly, specifically a significant decrease in indigenous species richness of both grasslands and woody communities were noted. The synthesis of all the studies carried out in Potchefstroom revealed an impressive number of studies carried out, however most of the biodiversity groups were represented by a single investigation only. Evaluating the results with the IDP revealed than much of the known ecological information in Potchefstroom remains undiscovered by municipal policymakers. Moreover, proposed future development is planned for some of the highest biodiversity sites. This synthesis and the subsequent identification of the gaps in our understanding and research themes will allow a purposeful and informed advancement of the science of urban ecology in South Africa and the contribution thereof towards advancing urban ecology globally. In addition, the history of urbanization affects contemporary vegetation assemblages in urban areas indicating potential extinction debts. Moreover, the significant decreases in indigenous species richness of woody and grassland sites have important consequences for urban grassland conservation in South Africa. Subsequently, the knowledge and the identification of research gaps allow decision makers in Potchefstroom to plan for sustainable future solutions and for this city to emerge as a leading role player in the South African urban ecological context. The results of this thesis could be a substantial practical aid in policy and management strategies furthering decision makers in the pursuit of the elusive goal of developing sustainable cities.Doctora

Grassland ecology along an urban-rural gradient using GIS techniques in Klerksdorp, South Africa

Thesis (M. Environmental Science)--North-West University, Potchefstroom Campus, 2009.Urban areas represent complex assemblages of unique vegetation communities. The multitude of influences on cities adds to this complexity rendering them an intriguing study object from an ecological point of view. Understanding the underlying patterns and processes operating in urban areas becomes increasingly important with large scale urbanization, making urban areas potential conservation sites of the future. The urban-rural gradient approach often used to study these patterns and processes, aims to quantify the existing gradient allowing comparisons of vegetation at different locations, each with diverse human influences. However, accurately quantifying the urban areas became difficult with the realization that gradients are non-linear and complex. Most previous studies cannot be compared with each other due to differences in measures used to quantify the gradient and a lack of a well defined definition for urban areas. Our study in Klerksdorp focused on testing a model developed in Melbourne (Australia) in an attempt to contribute towards creating a standard set of broad measures to quantify the urban-rural gradient. The methods used in Melbourne aims to set a general standard with which to globally compare urbanized areas taking into account the entire extent of the study area allowing multidimensional insights into the unknown gradients. Thereby placing individual studies into an urbanization context. At the heart of it, the main objective is to observe if any global patterns emerge to shed light on urbanization influences and drivers of ecological processes. In our study, SPOT 5 HRV satellite imagery and GIS techniques were used to calculate measures representing demographic and physical variables, as well as landscape metrics. The accuracy of the demographic measures was constrained by the scale of the available census data and subsequently more information is needed. Results showed that density of people, landscape shape index, and the percent urban land cover best quantified the observed gradient. Potential changes in grassland ecology were identified with vegetation surveys studying both the extant and the soil seed bank. Clear differences were observed in the extant vegetation composition of comparable grassland patches at different locations along the gradient, showing that urbanization does influence grassland vegetation composition and survival in the greater Klerksdorp area. The plant species richness of the existing and the soil seed bank showed significant correlations to the specific soil properties of each sample plot. Both demographic and landscape metrics also correlated significantly to some of the species subsets, emphasizing that both are needed to accurately quantify the urban-rural gradient of the greater Klerksdorp area and identifying potential patterns of species distributions. The urban-rural gradient described in the greater Klerksdoip area is not associated with an increase of exotic species towards the urban centre, but with a decrease of indigenous species richness as one nears the urban centre. Patterns and processes emerging from the current study could meaningfully influence planning and implementation actions concerning human development and conservation of a critically endangered vegetation type.Master

The extended occurrence of Maputaland Woody Grassland further south in KwaZulu-Natal, South Africa

The distinctiveness of Maputaland Woody Grassland lies within its richness of geoxylic suffrutices and herbaceous flora. Since it is well documented in the literature and easy to distinguish from other grassland types, it was possible to confirm a locality of this unique vegetation unit west of Richards Bay, where it probably forms the southernmost outlier population of this vegetation unit in the Indian Ocean Coastal Belt Biome. Phytosociological data obtained from the study area were analysed to identify plant communities and subsequent mapping units. Floristic gradients obtained through ordination techniques revealed the relationship that exists between the Woody Grassland of the study area and the Maputaland Woody Grassland of Sileza Nature Reserve. This confirms the occurrence of Maputaland Woody Grassland at Richards Bay. Two of the plant communities identified from the Richards Bay site are distinctively different, despite previously being lumped together by different authorities as either Kwambonambi Grassland or Maputaland Woody Grassland

Phytosociological description of norite koppies in the Rustenburg area, North-West Province and refinement of the distribution of the Norite Koppies Bushveld on the national vegetation classification map of South Africa

The Norite Koppies Bushveld vegetation type boasts a distinctive and contrasting topography and species composition easily distinguished from that of surrounding areas. A phytosociological study was done on the leased mining area of the Impala Platinum Mining Company north of Rustenburg in the North-West Province. Similar norite koppies, situated west of the Norite Koppies Bushveld vegetation, and not yet mapped by Mucina & Rutherford (2006), were identified in the study area and phytosociologically described. Six plant communities and two subcommunities were identified. Multivariate statistical analyses (correspondence analyses) confirmed that the species composition of these areas corresponds with and does therefore form part of the Norite Koppies Bushveld vegetation type as described by Mucina & Rutherford (2006). Some of these communities contain Boscia albitrunca, a protected plant species, and should therefore be considered as areas with conservation value