Browsing by Author "Milton, S. J."

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    Grasses as invasive alien plants in South Africa
    (Academy of Science for South Africa, 2004) Milton, S. J.
    Grasses are important, but often overlooked, elements of the South African alien flora. Current information shows that 15% of the grass genera and 12% of grass species in southern Africa are naturalized aliens. Many of these species are invasive in other parts of the world, where they are reducing the biodiversity of indigenous communities, changing ecosystem processes, retarding ecosystem restoration and reducing profits from ranching and arable agriculture. Their spread has been facilitated by domestic livestock, disturbance, long-distance transport and nitrogen addition to soils. Control is complicated by abundant seed production, persistent seed banks, positive response to disturbance, a dearth of biocontrol research and, in some cases, by herbicide resistance. This review of the impacts of alien grasses in other parts of the world suggests that alien grasses will become increasingly prevalent in South Africa, and that more research, aimed at identifying appropriate management responses, would be justified.
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    Scaling up from site-based research to a national research and monitoring network : lessons from Tierberg Karoo Research Centre and other design considerations
    (Academy of Science for South Africa, 2007) Milton, S. J.; Dean, W. R. J.; O'Connor, T. G.; Mills, A. J.
    South Africa is in the process of setting up a national environmental observatory system (SAEON) to monitor and gain a predictive understanding of the effects of climate change and land use on biodiversity, carbon and nutrient fluxes, soils and sediments, primary and secondary productivity, hydrology and disturbance regimes. It is intended that the data should be archived, analysed and translated into information accessible to decision-makers. We present a case that illustrates the infrastructural needs and challenges for long-term research and then discuss optimal designs and collaborations required to detect change in many variables, land-use types and geographical areas of South Africa.
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    Superiority in competition for light : a crucial attribute defining the impact of the invasive alien tree Schinus molle (Anacardiaceae) in South African savanna
    (Elsevier, 2008-05) Iponga, D. M.; Milton, S. J.; Richardson, David M.
    Invasion of ecosystems by woody alien plant species is a widespread phenomenon. Interspecific competition has often been suggested as a mechanism for replacement of one species by another, but this is rarely tested. We investigated the potential of an invasive alien tree to transform vegetation by quantifying the relative abilities of the alien tree Schinus molle and dominant native trees Acacia tortilis and Rhus lancea to compete for light when growing in association within a South African semi-arid savanna. Due to dispersal of its fruits by birds, seedlings of S. molle establish under tree canopies. Using canopy symmetry as an index of ability to compete for light, we found that the alien S. molle consistently out-competes the dominant native tree species. The results also show that pod production of A. tortilis was higher when it grew alone compared to when it grew with S. molle or R. lancea. The percentage of dead branches was higher on A. tortilis trees growing in association with the S. molle. The outcome is that the alien tree will gradually increase in abundance, changing woodland structure and ecosystem processes. Our findings provide evidence for the role of competition in the process of alien plant invasions. We suggest that S. molle, previously considered a benign naturalized species in South Africa, should be declared a noxious weed in some parts of that country. © 2007 Elsevier Ltd. All rights reserved.
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    The threat of alien invasive grasses to lowland Cape floral diversity : an empirical appraisal of the effectiveness of practical control strategies
    (Academy of Science for South Africa, 2005) Musil, C. F.; Milton, S. J.; Davis G. W.
    EUROPEAN ANNUAL GRASSES IN HIGHLY fragmented natural ecosystems along the South African west coast are displacing wildflowers, which form the basis of a growing lucrative, nature-based tourist industry. We examined the cost-effectiveness of different labour-intensive strategies linked to a national poverty relief programme for controlling invasive annual grasses in renosterveld. The treatments tested involved combinations of grass mowing, hand-clearing, light and intense burning and pre-emergent herbicide application randomized over forty-eight 100-m2 plots in the Tienie Versfeld Wildflower Reserve. Springtime vegetation responses were monitored over two successive years; labour, capital equipment and consumable costs were audited. Total clearing costs associated with intense burning of uncut grass (R415/ha), grass mowing (R924/ha) and light intensity burning of mowed grass (R1338/ha) were all less than those (up to R1 927/ha) reported for clearing dense stands of woody aliens. However, costs of hand-clearing of grass (R6743/ha) and pre-emergent herbicide application (R13 380/ha) were much greater. Intense burning, the cheapest strategy overall, was ineffective as this promoted recruitment of both alien invasive annual and perennial grasses and inhibited recruitment of native geophytes. We conclude that mowing of grass-infested renosterveld prior to grass seed maturation, and the removal of the cut grass biomass for use as fodder in restricted feed lots to offset clearing costs, provides the most credible strategy for controlling the annual grass populations to conserve native floral diversity over the short term.