Karen J. Esler

Spatial pattern analysis in Namaqualand desert plant communities: evidence for general positive interactions

This paper investigates of the spatial arrangement of individual plants in mapped plots in two desert communities in the winter rainfall region of South Africa. In both communities there was a very strong tendency towards clumped patterns when all plants were considered together. There was also a predominance of clumped patterns when the most abundant species in both communities were considered individually. When the arrangement of the most abundant species was considered relative to the arrangement of all other individuals at the within-clump scale, there was a high frequency of positive associations in both communities (62% and 65%). We speculate that these patterns represent a combination of seed dispersal strategies that favour clumped patterns and a predominance of positive interactions between plants in both of the communities. When specific pairwise associations between the most abundant species were considered at the within-clump scale, differences were apparent between the two communities. In the short strandveld community neutral associations predominated, while in the medium strandveld, neutral and positive association accounted for equal proportions of the associations. This between-plot difference was also apparent when the volumes of plants were related to an index of neighbourhood competitiveness. In the short strandveld there were no significant relationships while in the medium strandveld there were some weak (but significant) relationships. These differences were not altogether unexpected. If we assume that plants in the medium strandveld are generally longer-lived, then interactions between plants are likely to develop over a longer time and, therefore, are likely to be stronger.

How wide is the “knowing-doing” gap in invasion biology?

Invasion biology is a growing discipline with clear ecological, social and economic implications. A wide range of research effort is thus required to address the invasion problem, and literature on the topic is extensive. However, the extent to which the invasion biology research is addressing the challenges associated with management and mitigation of the impacts of invasions has been questioned. Using bibliometric analysis, we investigated the extent to which the literature on the subject contributes to implementation of knowledge generated, by addressing aspects of management, policy, and/or implementation; the impact of these papers as indicated by the number of citations they attract; and the geopolitical scale of focus of invasion ecology papers, particularly those that attempt to bridge the knowing-doing gap. We then compared these findings with the information needs of conservation practitioners. We first looked globally at popular search engines and then narrowed our focus to South Africa—one of three regions outside USA where researchers producing highly cited papers in invasion ecology are well represented. At this level, we conducted a content analysis of invasion ecology-related papers, of which at least one author was affiliated to a South African institution. The knowledge base in the field of invasion biology is comprised largely of research oriented towards “knowing”, while research aimed at strategically applying or implementing that knowledge is poorly represented in the scientific literature, and the scale of its emphasis is not local. Conservation practitioners clearly indicate a need for basic knowledge. However, invasion science must develop channels for effective engagement to ensure that the research is contextualised, and will deal with the complex ecological, social and economic challenges posed by invasions.

Are ecosystem services adequately quantified

Summary Quantification of ecosystem services (ES) is an important step in operationalizing the concept for management and decision-making. With the exponential increase in ES research, ES have become a ‘catch-all phrase’, which some suggest has led to a poorly defined, impractical and ambiguous concept. An overview of the methods used in ES quantification is needed to examine their scientific rigour and provide guidelines for selecting appropriate measures. We present a systematic review of 405 peer-reviewed ES research papers to address the question: ‘Is the biophysical and socio-economic reality of ES adequately quantified? First, we considered whether ES measures are scientifically rigorous enough by considering four predefined criteria (the type of data used, quantification of uncertainty, validation done and data reported). Secondly, using a novel approach, we determined which part of the ES cascade was measured: the ecosystem property, function, service, benefit or value. Our results showed that each of the 21 ES analysed had on average 24 different measures, which may indicate the complex reality of ES and/or suggest a potential lack of consensus on what constitutes an ES. We found that uncertainty is often not included and validation mostly missing. When analysing which part(s) of the ES cascade each measure corresponded to, we found that for regulating ES, ecosystem properties and functions (ecological aspects) are more commonly quantified (67% of measures). Conversely for provisioning ES, benefits and values (socio-economic aspects) are more commonly quantified (68%). Cultural ES are predominantly quantified using scores (35%). In conclusion, ES appear to be poorly quantified in many cases, as often only one side of the cascade is considered (either the ecological or socio-economic side) and oversimplified and variable indicators are often used. Policy implications. This review provides a detailed overview of ecosystem services (ES) quantification (ranging from simple scores to advanced methods) with the aim to support future ES quantification and ultimately the successful application of the ES concept.

Ecological and phylogenetic patterns of carbon isotope discrimination in the winter-rainfall flora of the Richtersveld, South Africa

Leaf tissues of vascular plant species from the arid Richtersveld of northern Namaqualand (Succulent Karoo), South Africa, show a great range of variation in carbon isotope discrimination. Analyses of Δ values for species with obligate C3 metabolism demonstrated that the water use efficiency indicated by these values varies between species and within a species population both between seedlings and mature shrubs and between sites along an aridity gradient. An expected pattern of increasing water use efficiency with greater longevity in these species was not present, however. Only among ephemerals were there taxa with high Δ values associated with low water use efficiency, but these high values were balanced by other ephemeral species with low Δ values comparable to those typical of moderate to long-lived shrubs. The extent to which putative CAM species in the succulent flora rely entirely on nocturnal carbon fixation is highly variable. Species of Crassulaceae and Aloe (Asphodelaceae) relied almost exclusively on CAM photosynthesis, although Crassulaceae from more mesic environments may be CAM-flexible. Succulent-leaved species of Senecio and leaves of stem-succulent Euphorbia were CAM-flexible in their Δ values, while shrubby species of Ceraria (Portulacaceae) appeared to rely primarily on C3 photosynthesis. Variable patterns of reliance on CAM photosynthesis were present in the ecologically dominant Mesembryanthema of the Aizoaceae. Shrubby species of the subfamily Mesembryanthemoideae, although capable of CAM-flexibility in less xeric habitats, relied largely on CAM fixation of carbon in our field sites. Within the subfamily Ruschioideae, there was a wide range of Δ values indicating species with CAM, CAM flexibility, and primary reliance on C3 photosynthesis. Low Δ values indicative of typical CAM fixation were associated with species with greater longevity, suggesting that a positive correlation may exist between the degree of reliance on CAM photosynthesis and plant life span.

Opportunities and challenges for mainstreaming ecosystem services in development planning: perspectives from a landscape level

Despite much progress in ecosystem services research, a gap still appears to exist between this research and the implementation of landscape management and development activities on the ground, especially within a developing country context. If ecosystem service science is to be operationalised and used by decision-makers directing local development, an in-depth understanding of the implementation context for landscape planning and management, and of the opportunities and challenges for ecosystem services in this context are needed. Very little is known about these opportunities and constraints, largely because of the absence of methods to explore the complexity of the landscape planning, management and implementation context and the possibilities of integrating scientific information into these processes within a real-world setting. This study aims to address this need for information and methods, by focusing on a region in South Africa with a long history of ecosystem service research and stakeholder engagement, and testing a social science approach to explore opportunities and challenges for integrating ecosystem services in landscape planning processes and policies. Our methodological approach recognises the importance of social processes and legitimacy in decision-making, emphasizing the need to engage with the potential end-users of ecosystem service research in order to ensure the relevance of the research. While we discovered challenges for mainstreaming ecosystem service at a local level, we also found strong opportunities in the multi-sectoral planning processes driving development and in how the concept of ecosystem services is framed and aligned with development priorities, especially those relating to disaster risk reduction.

Bioassessment of the ecological integrity of river ecosystems using aquatic macroinvertebrates: an overview with a focus on South Africa

An overview is given of the bioassessment of the ecological integrity of river ecosystems using aquatic macroinvertebrates, focussing on the South African situation within a global context. Biotic indices and their use in aquatic bioassessment are covered, and comparative descriptions of the more important and/or widely used macroinvertebrate-based biotic indices are given. For each biotic index described, information is provided on the biotopes sampled, the sampling equipment used, the sampling protocol followed, the level of taxonomic resolution, whether identifications are laboratory- or field-based, the range of the final index value, and its current usage. A discussion on using biotic indices and interpreting bioassessment data follows. The multimetric and multivariate approaches to bioassessment are compared, as are the regional and multivariate approaches to the derivation of reference conditions. The use of invertebrate habitat assessment in river bioassessment studies is briefly discussed and the South African spatial framework for analysing bioassessment data is described. In conclusion, a number of potential avenues for further research regarding the use of macroinvertebrates in the bioassessment of river ecosystems are identified.

Microbial diversity and community structure in Fynbos soil

The Fynbos biome in South Africa is renowned for its high plant diversity and the conservation of this area is particularly important for the region. This is especially true in the case of endangered vegetation types on the lowlands such as Sand Fynbos, of which only small fragments remain. The question is thus whether the diversity of the above‐ground flora is mirrored in the below‐ground microbial communities. In order to determine the relationship of the above‐ and below‐ground communities, the soil community composition of both fungal and bacterial groups in Sand Fynbos was characterized over space and time. A molecular approach was used based on the isolation of total soil genomic DNA and automated ribosomal intergenic spacer analysis of bacterial and fungal communities. Soil from four different sites was compared to resolve the microbial diversity of eubacterial and fungal groups on a local (alpha diversity) scale as well as a landscape scale (beta diversity). The community structures from different sites were compared and found to exhibit strong spatial patterns which remained stable over time. The plant community data were compared with the fungal and the bacterial communities. We concluded that the microbial communities in the Sand Fynbos are highly diverse and closely linked to the above‐ground floral communities.

Stakeholder Perceptions of an Ecosystem Services Approach to Clearing Invasive Alien Plants on Private Land

Incentivizing private landowners and other stakeholders is central to the effective conservation of ecosystem services in working landscapes. To better understand how to design effective incentives, the perceptions of landowners and other stakeholders are explored regarding a proposed approach to clearing invasive alien plants on private land in the Western Cape Province, South Africa. The public funded national program, Working for Water, conserves ecosystem services while employing and training people from marginalized sectors of society to clear these plants. Private landowner involvement is a key conservation challenge, because without adequate landowner involvement, invasive alien plants persist on the landscape and continuously reinvade cleared areas. We collected interview data from private landowners in three study sites, and websurvey data from conservation professionals and Working for Water managers, in order to compare stakeholder perceptions of (1) government and landowners’ responsibilities for clearing invasive alien plants; (2) existing and proposed policy tools; and (3) the extent to which stakeholders consider the proposed financial incentive to be sufficient. There was significant consensus among stakeholders concerning their preference for shared landowner and government responsibility and for a policy mix that combines incentives with disincentives. Landowners from the three study sites differed in the level of responsibility they were willing to assume. Stakeholders also diverged in terms of their perceptions of the proposed financial incentives. Furthermore, the perspectives of landowners were strongly associated with ecological and social features of the landscapes in which they are located. Understanding stakeholders’ points of view within their differing contexts is shown to be a valuable means of gaining insight into the opportunities and constraints that face ecosystem service conservation in working landscapes.

Biogeography of prostrate-leaved geophytes in semi-arid South Africa: hypotheses on functionality

Nowhere is the species diversity of geophytes greater than in the five mediterranean-climate ecosystems of the world. Of these, the Cape mediterranean zone of South Africa is the most speciose. While the relative diversity and importance of geophytes of all of the other four mediterranean regions of the world drops off sharply as one moves into adjacent winter-rainfall desert regions, geophytes in the semi-arid to arid Succulent Karoo (including Namaqualand) remain a very important component of the flora, both in terms of abundance and diversity (comprising 13 to 29% of the regional floras in this region). Apart from species richness, there are also a number of interesting geophyte growth forms in this region. One unusual growth form is geophytes with flattened leaves that lie prostrate on the soil surface. At least eight families (Amaryllidaceae, Colchicaceae, Eriospermaceae, Geraniaceae, Hyacinthaceae, Iridaceae, Orchidaceae and Oxalidaceae) exhibit this growth form. While this growth form is relatively common in many geophyte lineages in the Succulent Karoo biome and the Cape mediterranean zone (Fynbos biome), and occurs infrequently through the summer-rainfall temperate regions of Africa, it is virtually absent in other regions worldwide. A null hypothesis is that the prostrate leaved trait is a neutral characteristic, however biogeographical data do not support this. A neutral trait would be unlikely to show such a clear pattern of distribution. Several alternative hypotheses on the adaptive significance of this growth form are discussed. These include: avoidance of herbivory, reduction in competition from neighbors, creation of a CO2 enriched environment below the leaves, reduction of water loss around the roots, reduction of water loss through transpiration, precipitation of dew on the leaves and maintenance of optimal leaf temperatures for growth.

Live fast, die young: estimating size-age relations and mortality pattern of shrubs species in the semi-arid Karoo, South Africa

We present a technique for estimating size-age relations and size-dependent mortality patterns of long-lived plants. The technique requires two sets of size data of individual (non-marked) plants that should be collected with a time-lag of several years in the same area of a study site. The basic idea of our technique is to assume general (three parameter) families of size-dependent functions which describe growth and mortality that occurred between the two data gathering events. We apply these growth and mortality functions to the size data of the early data set and construct predicted size-class distributions to compare it, in a systematic way, to the size-class distribution of the later data set. In a next step we calculate the size-age relations from the resulting growth functions, which yield the smallest difference between observed and predicted size-class distribution. Applying this technique to size data of five dominant shrub species at the Tierberg study site in the semiarid Karoo, South Africa produced new insight into the biology of these species which otherwise cannot be obtained without frequent measurements of marked plants. We could relate characteristics of growth behavior and mortality, for certain subgroups of the five species, to the life-history attributes evergreen vs. deciduous, succulent vs. woody, and early reproductive vs. late reproductive. The results of our pilot-study suggest a broad applicability of our technique to other shrublands of the world. This requires at least one older record of (individual) shrub-size data and performance of resampling.