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

[摘要] 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.

[发布机构] Stellenbosch University