Browsing by Author "Cronin, Kate"

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    Aliens in the nursery : assessing the awareness and attitudes of Cape Town nursery managers in regard to invasive species regulations
    (2015) Cronin, Kate; Hoffman, Timm; Kaplan, Haylee
    The horticultural industry is recognised as one of the major pathways for the introduction and spread of invasive alien plants (IAPs). In recognition of this, the South African government has recently enacted a new set of Alien and Invasive Species regulations, under the National Environmental Management Biodiversity Act (NEMBA), that are intended, in part, to improve controls on the horticultural industry's role in the spread of IAPs. In order to assess, and possibly enhance, the likely effectiveness of NEMBA, it is critical to build an understanding of stakeholders' awareness and attitudes towards the control of IAPs and associated regulatory policies. A two-pronged approach – involving nursery manager interviews (n=30) and plant stock audit assessments (n=41) - was used to gauge the awareness, compliance and attitudes of Cape Town nursery managers towards the NEMBA regulations. Results showed that less than ten percent of the city's audited nurseries were compliant with the NEMBA regulations, and that over fifty percent were stocking IAPs that have been regulated for at least thirteen years under a previous set of regulations (the Conservation of Agricultural Resources Act, CARA). This is despite high levels of awareness about the CARA regulations reported in the interviews, reported enthusiasm for compliance, apparent concern for the environment, evidence that managers understand the problems that IAPs cause, extensive reported support for the control of IAPs, and a reportedly strong sense of duty to protect the environment. The vast majority (73.5%) of IAP species found in nurseries were NEMBA category 1b invaders such as Nerium oleander, Lantana montevidensis and Canna indica. These are species that are widespread and well-established invaders that require control. This study suggests that a range of factors are likely to negatively influence compliance including a perceived lack of enforcement, weak communication from government, issues related to the clarity of the regulations, the lack of inclusion of the industry in the regulatory process, and a lack of awareness, with at least half of the managers reporting that they had not heard about the enactment of NEMBA. Any attempt to improve the impact of the new regulations will need to adequately address each of these factors. The results of the study suggest that enhancing the impact of NEMBA will require improving aspects of the legislation itself, and supplementing the current top-down approach to regulation with an inclusive partner-centred approach.
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    A long-term record of the physiological plasticity of stomatal condactance in Proteaceae
    (2013) Cronin, Kate; West, Adam
    Bioclimatic models suggest that Protea species are likely to be severely affected by predicted increases in temperature and reductions in rainfall in the Western Cape. However, throughout their 400 million year history, land plants have been exposed to considerable climatic variations that have driven physiological adaptations promoting long-term resilience. A principal response of plants to increases in atmospheric CO2 concentration and changing rainfall regimes is to minimise water loss by reducing stomatal conductance (gs) and simultaneously increasing intrinsic water-use efficiency (iWUE). Plasticity in these two physiological traits may enhance the ability of plants to survive future climate change. There is considerable evidence in the literature for major changes in gs and iWUE in response to both short-term and long-term changes in environmental conditions. However, to date, the effects of decadal climate change on plant physiology are still largely uncertain. In this study, the responses of gs and iWUE to perturbations in rainfall and atmospheric CO2 are reconstructed from a chronological sequence of herbarium and modern Protea specimens. The results indicate that in the two high-altitude study species, P.cryophila (t= -2.44, df=7, p= 0.045) and P.venusta (t=3.08, df=5, p=0.027), stomatal conductance has significantly declined in response to increasing atmospheric CO2 concentrations over the past century. The low altitude species appears to maintain fixed stomatal conductance trajectories as a response to more xeric conditions. It is difficult to draw inferences about stomatal physiological plasticity from iWUE data as it is not possible to distinguish between the effects of physiological reductions in stomatal conductance and biochemical enhancement of photosynthesis. Microhabitat sensitivity in iWUE is a further factor confounding interpretation. This highlights the importance of using multiple parameters as analytical tools for assessing long-term physiological change. A key contribution of this study is that it has confirmed the value of using archival material and highlights methodologies that may aid future herbarium-based interpretations. In addition, despite some methodological limitations, the study has identified interesting trends at climate change-relevant timescales that point the way for further research to understand relative vulnerabilities and inform conservation strategies. Specifically, it suggests that future research and conservation efforts may need to be focused on species occurring at low altitudes because of their apparently more limited physiological plasticity.
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    Reconstructing the late pleistocene palaeoenvironment of the Richtersveld using fossil charcoal
    (2013) Cronin, Kate; Hoffman, Timm; February, Edmund C
    The Succulent Karoo is recognised as an important biodiversity hotspot and many of the key plant lineages that characterise the biome are thought to have originated during the Pleistocene epoch. However, due to the paucity of palaeobiological proxy data available for the Succulent Karoo, relatively little is known about its environmental history and how an important core of this region, Namaqualand and its subregion the Richtersveld, may have responded to Pleistocene changes. Recent excavations at Spitzkloof Rockshelter A in the Richtersveld have provided a rare source of palaeoenvironmental data in the form of fossil wood charcoal assemblages that span a sequence from the last glacial maximum (LGM) to ~14 500 yrs BP. The present study analysed the fossil charcoal deposits from the rockshelter in order to reconstruct woody species assemblage patterns as a proxy for late Pleistocene palaeoclimate. Identification of the fossil charcoal specimens was achieved by anatomical comparison with transverse section photomicrographs of identified reference specimens of woody taxa currently growing at the site. Patterns in the charcoal data set were sought by assessing the changes in woody species assemblages over time. An assessment of the environmental correlates of the contemporary distributions of taxa found in the archaeological sequence provided the basis for palaeoenvironmental reconstruction. Based on the current generalisation for glacial climates in the winter rainfall zone (WRZ), it was hypothesised that the study region experienced an increase in rainfall at the LGM, and a steady aridification towards the terminal Pleistocene. However, Spitzkloof's charcoal records provide little evidence to suggest that the LGM supported a more mesic vegetation community than more recent time-periods. Instead, results suggest that the region experienced fairly limited climatic change as there is compelling evidence for the persistence of Succulent Karoo elements – namely Stoeberia arborea, Hermannia disermifolia and Lycium spp. - throughout the late Pleistocene. The localised appearance at the terminal Pleistocene (~14 ka) of all of the most abundant taxa at the site today is interpreted as a consequence of terminal Pleistocene changes in sea-level and CO2 concentration within a persistent context of minimal climatic change. These results have important implications for the applicability of a generalised WRZ model of climate change to the Succulent Karoo and for hypothetical predictions of future climate change impacts in the biome.