Transitioning to organic agriculture : the changes in arthropod biodiversity and pests over time

Engelbrecht, Nina Margaret (2018-03)

Thesis (MScConsEcol)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: The Greater Cape Floristic Region (GCFR) is a unique area known for its incredible biodiversity. It is also the largest wine-grape producing area in South Africa. However, agriculture and more specifically viticulture, poses a threat to biodiversity in the GCFR. Alternative and environmentally sustainable agricultural practices, such as organic farming, could ensure the conservation of biodiversity and the continued provision of important ecosystem services. In this study, I investigated the benefits organic agriculture has for both conservation and production. I looked at how arthropod biodiversity and pest control change over time since transitioning to organic agriculture. I did so by comparing vineyards at different stages in the transition process i.e. a conventional vineyard, 1-year in transition to organic (1-year transition), 5-year and a 15-year organic vineyard. Arthropod biodiversity was sampled in December 2016 and January 2017 on the vines and in the non-crop inter-row vegetation using vacuum sampling. Species richness and abundance was determined for each vineyard treatment. The lowest species richness and abundance was found in the conventional vineyard and the highest in the 1-year transition vineyard. After the initial increase, the richness and abundance seems to decrease under organic management practices, where it then stayed constant over time, at higher levels than in the conventional vineyard. Arthropod assemblage structure was also analysed and a significant difference was found between the vineyard treatments. It does seem as if the assemblages stabilized over time, with the most similarity found between the 5- and 15-year organic vineyards. Spider and parasitoid (natural enemies) species richness and abundance showed a similar trend to overall arthropod biodiversity, with a general influx of natural enemies in the 1-year transition vineyard, from where it seems to decrease over time under organic management practices. Despite the influx of natural enemies in the 1-year transition vineyard, the proportion of natural enemies of the total arthropods sampled, was quite low compared to the other vineyards. Over time under organic management practices, the proportion of natural enemies seems to increase. Pest counts and damage were determined using a pest monitoring system, alongside the biodiversity sampling. Monitoring focused on the pests Phlyctinus callosus (Coleoptera, Curculionidae) and Plangia graminea (Orthoptera, Tettigoniidae). Visual inspection of 20 plots consisting of 5 vines per plot was done for every hectare. A trapping method supplemented the pest counts for Phlyctinus callosus in the vineyards. The pest counts did not show any discernible pattern and it did not relate to the pest damage. Pest damage was generally higher in the 1-year transition vineyard compared to the other vineyards. The overall damage decreased over time under organic managements practices, which indicates that the pest control ecosystem services does establish over time in organic vineyards. This study shows that the stabilisation time is an important consideration in organic agriculture. Although significant changes occur rapidly with the change in management practices, it does take time for the arthropod biodiversity and the pest control ecosystem services to return and for the agroecosystem to stabilize after conventional agriculture. Given time, these systems stabilise and become biologically resilient agricultural systems.

AFRIKAANSE OPSOMMING: The Kaapse Floristiese Ryk (KFR) is ‘n unieke area bekend vir die besonderse hoë biodiversiteit. Dit is ook een van die grootste wyndruif-produserende areas in Suid-Afrika. Landbou en meer spesifiek wingerdbou, bedryg egter die biodiversiteit in die KFR. Alternatiewe en volhoubare landbouproduksie, soos organiese landbou, kan die bewaring van biodiversiteit, asook die bewaring van belangrike ekosisteem-dienste beteken. In hiedie studie, ondersoek ek die voordele wat organiese landbou inhou vir beide bewaring en vir produksiedoeleindes. Ek ondersoek hoe die geleedpotige biodiversiteit en pesbeheer verskil oor tyd onder organiese bestuurspraktyke. Ek vergelyk wingerde, wat in verkillende stadiums in die transisie proses is, naamlik: ‘n konvenstionele-, 1-jaar in transisie na organies (1-jaar transisie), 5-jaar organies en ‘n 15-jaar organiese wingerd. Monsters van die geleedpotige biodiversiteit is in Desember 2016 en Januarie 2017 in die wingerde asook in die plantegroei tussen die wingerde geneem, deur gebruik te maak van die stofsuier metode. Die spesierykheid en getalrykheid is bereken vir elke wingerd. Die laagste spesierykheid en getalrykheid was in die konvenstionele wingerd en die hoogste in die 1-jaar transisie wingerd gevind. Na die aanvanklike toename, het die spesierykheid en getalrykheid afgeneem en afgeplat, by hoër vlakke as die konvenstionele wingerd. Die geleedpotige gemeenskapsamestelling was ook ondersoek en het ‘n beduidende verskil gewys tussen die behandelings. Dit lyk egter asof die gemeenskapsamestelling gestabiliseer het oor tyd, met die grootste ooreenstemming wat voorgekom het tussen die 5- en die 15-jaar organiese wingerde. Spinnekoppe en parasitoïede (natuurlike vyande) se spesierykheid en getalrykheid het dieselfde tendens as die algemene geleedpotige biodiversiteit getoon, met ‘n instroming van natuurlike vyande in die 1-jaar transisie wingerd, waarna dit afgeneem het en afgeplat het onder organiese bestuurspraktyke. Ten spyte van die instroming van natuurlike vyande in die 1-jaar transisie wingerd, was die proporsie natuurlike vyande van die totale geleedpotiges, relatief klein vergelyking metdie ander wingerde. Die proporsie natuurlike vyande het toegeneem oor tyd onder organiese bestuurspraktyke. Pestellings en -skade was bepaal deur gebruik te maak van ‘n pesmoniteringstelsel, wat tesame met die biodiversiteit monsters geneem is. Monitering was gefokusPhlyctinus callosus (Coleoptera, Curculionidae) en Plangia graminea (Orthoptera, Tettigoniidae). Visuele inspeksie van 20 persele, wat bestaan uit 5 wingerdstokke per perseel, is gedoen vir elke hektaar. ‘n Lokvalmetode was ook gedoen as aanvulling vir die pestellings vir die spesie Phlyctinus callosus. Die pestellings het nie enige tendense gewys nie en dit het ook nie ooreengestem met die pes skade nie. Die pesskade was oor die algemeen die hoogste in die 1-jaar transisie wingerd. Die pesskade het afgeneem oor tyd onder organiese bestuurspraktyke, wat aandui dat die pesbeheer ekosisteem-dienste vestig oor tyd onder organiese bestuurspraktyke. Hierdie studie wys dat die stabiliseringstyd belangrik is in organiese bestuurspraktyke. Alhoewel daar beduidende verskille waarneembaar is onmiddelik na die oorskakeling in bestuurspraktyke, neem dit tyd vir die geleedpotige biodiversiteit en die pesbeheer ekosisteem-dienste om te vestig. Dit lyk dus asof organiese sisteme stabiliseer oor tyd, wat aandui dat die biologiese veerkragtigheid versterk.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103303
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