Research Articles (Conservation Ecology and Entomology)

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Browsing Research Articles (Conservation Ecology and Entomology) by Subject "Alien plants"

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    Conserving a geographically isolated Charaxes butterfly in response to habitat fragmentation and invasive alien plants
    (AOSIS Publishing, 2015-08) Crous, Casparus J.; Pryke, James S.; Samways, Michael J.
    In South Africa, much of the forest biome is vulnerable to human-induced disturbance. The forest-dwelling butterfly Charaxes xiphares occidentalis is naturally confined to a small forest region in the south-western Cape, South Africa. Most of the remaining habitat of this species is within a fragmented agricultural matrix. Furthermore, this geographical area is also heavily invaded by alien plants, especially Acacia mearnsii. We investigated how C. x. occidentalis behaviourally responds to different habitat conditions in the landscape. We were particularly interested in touring, patrolling and settling behaviour as a conservation proxy for preference of a certain habitat configuration in this agricultural matrix. Remnant forest patches in the agricultural matrix showed fewer behavioural incidents than in a reference protected area. Moreover, dense stands of A. mearnsii negatively influenced the incidence and settling pattern of this butterfly across the landscape, with fewer tree settlings associated with more heavily invaded forest patches. This settling pattern was predominantly seen in female butterflies. We also identified specific trees that were settled upon for longer periods by C. x. occidentalis. Distance to a neighbouring patch and patch size influenced behavioural incidences, suggesting that further patch degradation and isolation could be detrimental to this butterfly. Conservation implications: We highlight the importance of clearing invasive tree species from vulnerable forest ecosystems and identify key tree species to consider in habitat conservation and rehabilitation programmes for this butterfly. We also suggest retaining as much intact natural forest as possible. This information should be integrated in local biodiversity management plans.
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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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    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.