Farming Techniques Impact Biodiversity in Olive Groves

Research by María Noelia Jiménez and colleagues at the Andalusian Institute for Agricultural, Fisheries, Food and Ecological Production Research and Training shows how olive groves are farmed and how the soil is managed can significantly affect the diversity of plant life. The study, published in Renewable Agriculture and Food Systems, was conducted in southern Spain. The researchers found significant differences in the number of plant species, species types, and species distribution based on differing farming practices.

Olive cultivation is a significant part of Spain’s agricultural heritage and economy, but traditional farming methods can have adverse environmental impacts. Olive groves cover a vast area in Andalusia, often on sloping land where soil erosion and biodiversity loss are pressing concerns. Researchers investigated how different farming systems (conventional, organic, abandoned) and soil management techniques (native cover crop versus tillage) affected vascular plant species in 20 different locations.

Conventional olive groves that use tillage, or ploughing, to manage weeds had the lowest level of biodiversity, with just eight plant species on average. Surprisingly, organic olive groves that used tillage had only slightly higher biodiversity, with ten species on average. In contrast, organic groves using cover crops like clover or barley, which are planted to suppress weeds, had 28 species on average, comparable to abandoned groves that had been left unmanaged for some time.

The researchers suggest these findings show that cover crops, rather than tillage, are central to boosting biodiversity in olive groves, whether they are actively farmed or abandoned. Cover crops provide a more suitable habitat for a broader range of plant species. The environmental conditions, the slope of the groves, the age of the olive trees, and the intensity of surrounding land use also affected the number and types of species found.

The researchers measured biodiversity by recording every plant species along line transects through the groves and analyzing species’ abundance, richness and diversity. They found the farming system and soil management significantly impacted not only the total number of species but also the specific types of species, how common or rare they were, and their distribution. The life forms of plants, such as whether they were shrubs, grasses or broadleaf plants, were also affected.

Given the challenges of farming on steep slopes where many olive groves are found, the researchers suggest that organic farming with cover crops or abandoning the groves to allow natural vegetation to take over may be good options to boost biodiversity. Cover crops and natural vegetation provide habitat and food for wildlife, prevent soil erosion, and support a healthy soil ecosystem. In their article, Jiménez and colleagues also suggest considering abandonment as a strategy.

However, the abandonment of sloping olive groves could have a number of disadvantages, such as the loss of direct economic income, which might encourage people to leave rural areas, the loss of the associated sociocultural heritage and the increased risk of fires (Allen et al., 2006). At the same time, it could also be seen as a great opportunity to regenerate patches of forest inside agricultural landscapes, so creating islands of biodiversity of enormous interest as green infrastructure that provides ecosystem services to nearby crops (i.e., biological control of pests), wildlife refuges for endemic or local species and ecological corridors (Paredes et al., 2013). In fact, Guzmán-Álvarez and Navarro (2008) estimated that 75% of marginal olive groves in Andalusia could be afforested solely by natural processes. Our results show that: (i) the abandonment of sloping olive groves would be beneficial from a biological and environmental point of view (unlike other studies which suggested otherwise) and (ii) that in certain landscape contexts it might be advisable to offer farmers financial incentives to encourage them to do so.

Jiménez et al. 2023

If groves are to remain managed, then have suggestions to improve organic farming. In particular, they note the damage that tilling does to the soil. They write that a solution is to move to suppress weeds with cover crops:

The introduction of plant cover is currently prioritized and subsidized by governments, as is the conversion to organic agriculture, and this could be a great opportunity to monetize sloping olive groves. In this case, plant cover should be mandatory for olive groves (and other woody crops) on slopes of over 20% or perhaps even less, regardless of the farming system. In organic woody crops, tillage should not be allowed, especially on slopes (at present it is permitted under European organic farming regulations, despite being considered harmful for the soil). To this end, we suggest that organic certification schemes should incorporate additional or more specific criteria on farm soil and vegetation management, as proposed by De Leijster et al. (2020). The higher prices of organic olive oil (and other organic products such as almonds), together with EU subsidies for organic agriculture, should also help make these sloping olive groves more economically viable.

Jiménez et al. 2023

The olive groves of modern Andalusia are the latest generation of a practice that has been going on for thousands of years. It means that olive farming isn’t just an economic activity. It has a profound cultural value too. Jiménez and colleagues conclude by acknowledging that any plans for managing the olive groves have to look beyond the economic value of the trees.

The alternatives may imply public subsidies to redesign the olive old-field landscapes, promoting plant restoration in some cases or, in other cases, agri-environmental measures, linking extensive agricultural use (low input and non-tillage agriculture, organic agriculture and livestock management) with environment objectives (increasing biodiversity, introducing landscape-promoting elements such as hedgerows or forest patches, etc.). Whichever one of these alternatives implies, however, a previous and definitive step: admitting that olive landscapes fulfil non-economic purposes.

Jiménez et al. 2023

READ THE ARTICLE

Jiménez, M.N., Castro-Rodríguez, J. and Navarro, F.B. (2023) “The effects of farming system and soil management on floristic diversity in sloping olive groves,” Renewable Agriculture and Food Systems, 38(e15), p. e15. Available at: https://doi.org/10.1017/s1742170523000091.