Cover crops enhance vineyard arthropod diversity

by | Aug 1, 2021 | Viticulture research, Winetech Technical

Intensive agriculture threatens arthropod biodiversity,1,2,3 impacts the functioning of ecosystems,4 and threatens the sustainable production of farming systems due to the loss of vital ecosystem services5,6,7 e.g., pollination and pest control.

Vineyard with established, grass-dominant cover crop. (Photo: Marinus Geldenhuys.)

Introduction

The growing concern over the future sustainability of intensive agriculture has already led to the adoption of a wide range of agroecological farming methods worldwide.8,9 These approaches generally aim to soften agriculture10,11 and enhance farmland habitat quality.8

There are a number of studies that highlight management practices that can effectively promote arthropod diversity e.g., preserving and diversifying non-crop vegetation,12,13 reducing agrochemical applications,5,14 reducing tillage intensity,15 and crop diversification.16,17 But these studies were mostly done in Western European and North American systems8,18 and the effectiveness of these methods are site-specific, meaning tailored strategies are needed for farms in different settings.19,20 Thus, identifying local practices that promote biodiversity will provide valuable guidance to farmland conservation efforts. These practices should be relevant to both small- and large-scale farmers and should be easy to apply in order to be an attractive option.21,22

On the other hand, a holistic approach, such as organic farming, has also been shown to benefit biodiversity.23,24,25 Organic farms use a combination of environmental-friendly practices, i.e. avoiding insecticides and synthetic fertilisers, and use a range of regenerative practices that aim to improve resilience in the agroecosystem. Using a combination of complementary practices generates the greatest positive effect for the environment, and may even have synergistic effects.24,26 However, it has not really been tested whether a carefully selected individual practice or a holistic approach holds the greatest benefit for biodiversity.24

Study area

The Cape Floristic Region (CFR) of South Africa is a Mediterranean-type ecosystem and a global biodiversity hotspot.27 The CFR supports an exceptional diversity of endemic plants,28,29 with a similar trend in the diversity of arthropods.30,31,32 However, a large area of the CFR has been transformed to agriculture,33 with vineyards alone covering around 88 366 ha.34 Globally, there is a trend for vineyard intensification and vineyards have the potential to support high levels of biodiversity.35,36 It is therefore important to understand which factors create favourable conditions for biodiversity in vineyards, as it will contribute to conservation in vineyard-dominated landscapes.

We assessed the effect of various management practices, i.e. application intensity of agrochemicals, tillage, cover crop characteristics, soil compaction, and the volume of plant litter on arthropod diversity in vineyards across the CFR, and whether there is added benefit of a holistic approach compared to an integrated approach. In particular, we tested these effects for spiders, beetles, and true bugs that live on the ground, on the cover crop, and on the vine foliage. Additionally, we tested these effects on predators, herbivores, and detritivores.

Findings

Effect of management practices

We expected different arthropods to respond differently due to their wide range of resource requirements, sensitivity to agricultural disturbances,37,38 and microhabitat preference.39 However, there was a consistent, strong positive effect of vegetation-related variables on arthropods. Increased herbaceous vegetation in the cover crops positively influenced the species richness of arthropods in each of the taxonomic, microhabitat, and feeding guild groups. Additionally, the volume of plant litter, number of plant species, and vegetation height in vineyard inter-rows positively influenced arthropod species richness, whereas grass cover promoted arthropod richness on the vines.

Our findings are in line with results from recent global reviews showing that extensive vegetation management can significantly enhance biodiversity in vineyards36,40 and in other crops.12,13 The effect is possibly due to a greater diversity of resources that a more diverse and dense cover crop provides, i.e. food and hosts, as well as greater structural complexity, refuge, and moderated microclimate in the crop fields41,42 being provided by both the live plants and plant litter. Increasing vineyard cover crop diversity can promote important services provided by arthropods in vineyards, such as natural pest control.39,43,44 It can also promote the conservation of wild bees45 and specialist butterflies.46 An important advantage that perennial crops have over annual crops is the permanence of the crop. This allows the establishment of more diverse and longer lasting cover crops that can provide alternative microhabitats47 and resources for longer periods of the year.48

Effect of overall farming approach

Globally, organic farming has been shown to mitigate the ongoing loss of biodiversity,23 but the effects vary for different taxa and systems.37,38 Studies on organic farming in the CFR have also shown mixed results for different taxa.49,50,51 Here, organic vineyards did not have a significantly positive effect compared to integrated vineyards. This may be due to most wine farms already complying with international wine industry sustainability through the Integrated Production of Wine Scheme of South Africa (IPW) (http://www.ipw.co.za). Although the use of conventional agrochemicals is permitted under IPW guidelines, farmers use it cautiously, i.e. for spot treatments only, and usually in combination with non-chemical plant protection measures e.g., biological releases of beneficial insects. Another reason for the lack of positive effects may be due to the proportion of organic farms in the landscape being too low. It has been shown that higher proportions of organic farms in a landscape can enhance field-scale arthropod diversity, and that an organic farming approach works best as an area-wide management strategy.52,53 Thus, increasing the number of organic farms in agricultural landscapes will have greater benefits to arthropod biodiversity.

Suction sampling of arthropods in the vine foliage layer. (Photo: Susan Geldenhuys.)

Conclusion

We demonstrated clear benefits of vineyard cover crops on arthropod diversity in the CFR, which corresponds with global recommendations for improving vineyard sustainability.36,40 Furthermore, diversifying cover crops in vineyards may have broader benefits, such as biological pest control, recycling of nutrients, regulating microclimate and hydrological processes, and reducing soil erosion.54 Managing a diverse cover crop can therefore be an effective multi-functional practice in vineyards. It is a low-cost practice, easy to implement, and is already implemented in many vineyards worldwide.

The findings of this study are vital for ensuring the sustainability of viticulture in a global biodiversity hotspot, and for gaining the continued support and approval from the general public. This is important as there is a growing demand for sustainably produced products in South Africa.55 Over time the increased demand for sustainably sourced products should motivate more and more farmers to adopt an environmental-friendly approach which will hold benefits to biodiversity and wine production within the CFR.

Abstract

Intensive agriculture threatens our global biodiversity and requires a shift to environmental-friendly farming. Identifying farm management practices that can also enhance biodiversity, will help guide future conservation efforts in farmlands. We therefore assessed how individual management practices affect arthropod diversity in vineyards. We also looked at whether these effects were different on arthropods that occur on integrated vs. organic vineyards. Increased herbaceous vegetation in vineyard cover crops consistently had a strong positive effect on arthropod diversity. Additionally, plant litter on the vineyard floor, the number of plant species and the height of plants in the cover crop positively influenced arthropod diversity. We did not find major differences in the effects of organic vs. integrated management practices on the studied arthropods. Our results show that managing a dense and diverse cover crop in vineyards is a strategic and cost-effective way to enhance arthropod diversity, through minimal adjustment to current management practices, regardless of the farming approach.

Acknowledgements

This study was conducted by Stellenbosch University and funded by the Mapula Trust and The Lewis Foundation. We would like to thank the Cape Winelands Biosphere Reserve and all landowners, farm managers and viticulturalists that made their vineyards and management information available to us. The sampling of arthropods was approved by Cape Nature, permit number AAA007-00144-0056.

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– For more information, contact Marinus Geldenhuys at marinusgeldenhuys1@gmail.com.

 

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