Strategic pollinator habitats key to healthy macadamia nut harvests, researchers propose

23 Feb 2023 --- With the objective to reduce biodiversity loss in agricultural landscapes, research teams from the universities of Göttingen and Hohenheim in Germany and Venda in South Africa assessed the effects of pollination on macadamia cultivation at plantations on the Soutspansberg mountain range. The results were published in the Journal of Applied Ecology.

“We made an empirical study in conventional farms under realistic conditions, making our results applicable in “normal” macadamia farms, and potentially even for other crops that need pollination by insects, like almonds, apples or cherries,” Mina Anders, first author of the research and Ph.D. student in functional agrobiodiversity at the University of Göttingen tells NutritionInsight.

Tree nuts like macadamias are a great source of protein, healthy fats and fiber and when included in weight management programs can account for improved satiety and significant weight loss.

“I would recommend focusing on environmentally friendly ways to increase yield and nut quality and recognizing pollinators as valuable “co-workers” in the agroecosystem that need to be supported.”

The research team investigated the role of insect pollinators in the nut production of macadamia trees. The researchers observed and counted the bees and other insects on the macadamia flowers to identify the conditions that encourage pollinators.

The study “Smart orchard design improves crop pollination” demonstrated that crop pollination can be enhanced through smart orchard design, including spatial arrangement of trees, planting of multiple varieties per section and increasing semi-natural habitats adjacent to the production blocks.

Eco-forward cultivation designSouth Africa has developed into one of the world’s largest macadamia producers, but the production has led to the loss of large swathes of natural habitats (Credit: Mina Anders).
The study experiment was conducted in the Levuvhu Valley and at the southern foothills of the Soutpansberg mountain range, Limpopo Province, South Africa. The mountain range forms part of the Vhembe Biosphere Reserve. 

The region is characterized by a sub-tropical, dry to moist climate, with a rainy season in summer from November to April. Daily temperatures range between 15 and 40°C and 0 and 25°C in summer and winter, respectively.

The researchers conducted a pollination experiment to analyze the relevance of insect-mediated pollination, its potential limitations, and its effects on agronomic practices, orchard design, and landscape composition.

The utilization of managed pollinators varies in the different cultivation areas. In Australia and Hawaii, the intensive application of managed honeybees and stingless bees is very common. There is a vague recommendation of 1–3 colonies per hectare. 

“The use of managed honeybee colonies in South Africa depends on the local growing region,” Anders explains. 

“The density of managed honeybee colonies at the study sites was generally low (mean: 0.03 colonies per hectare). At half of the sites, there were even no managed colonies within a 1 km radius. This means, in our study the main pollinators were wild honeybees, emerging from semi-natural habitats and some managed honeybees.”

As semi-natural habitat is source for pollinators, its destruction should be avoided and its integration into the farm must be considered. For instance, at places where the planting of crop trees would not make sense (e.g., wetland patches, steep hillside, rocks etc.), semi-natural habitats should be preserved.

“The arrangement of different macadamia varieties closely together also increases the pollination success by cross-pollination and should be considered when planning a new orchard block or renewing a block,” says Anders.

When it is bordering semi-natural habitat, the rows should be oriented in perpendicular orientation to the border. This facilitates the access to the trees for the pollinators and enhances the pollination service. “Ideally, this goes in line with other important conditions for the row orientation, like the compass direction (solar radiation as important growth factor) or slope,” she explains.

Thirty-two racemes (flower clusters with separate flowers attached) were selected. Three pollination treatments were conducted, including pollinator exclusion with mesh bag, open pollination by wind and insects and supplemental hand pollination. The research team recorded flower visitation rates.

Beyond the design aesthetic Samples were taken during different stages of growth of the macadamias including the unripe nuts (Credit: Mina Anders)..
With the urgency to reduce the environmental impacts and carbon emission output of agricultural production, the researchers have provided recommendations on the potential of orchard design and landscape management of an economically important crop.

“We face many crises at the moment, making a resilient and responsible use of the earth indispensable. We need environmentally friendly agroecosystems to generate food and simultaneously conserve the ecosystems,” Anders continues.

“We further depend on healthy ecosystems and their services, like pollination, pest control or nutrition cycle. The insects globally suffer from the use of agrochemicals and are declining.”  

“Our study makes an important contribution by showing ways for ecological intensification,” she explains.

The region where the macadamia nut crops are cultivated is high in biodiversity and vulnerable to climate change and land degradation. 

The arrangement of the rows of trees in the plantations is particularly important. Eighty percent more nuts grew at the edge of the plantation on land that borders the semi-natural habitats as opposed to in the middle.

“Pollinators move more easily from their habitat to the plantations when the rows are perpendicular, as they prefer to fly along the rows rather than through them,” Anders explains. 

After flowering, the nut formation increased more than threefold in tree rows planted at right angles to semi-natural habitats, compared to rows planted parallel to the habitats. 

“If possible, the destruction of semi-natural habitat should be minimized, as it is an important source of pollinators,” Anders continues.

“The reduction of pesticides is also of interest to the companies who make macadamia-based products, as chemical residues could contaminate the products.”

Further studies are needed to investigate other ecosystem services, like biological pest control by bats and birds or by pest infesting insects.

Pollinators prefer spatial orchard structure
The researchers compared the effects of agronomic practices such as irrigation, spatial structure and landscape factors in 10 South African macadamia (Macadamia integrifolia) orchards. 

Unlike experimental pollinator exclusion, insect pollination increased the initial and final nut set by 304% and 23%, respectively. Flower visitation rates increased with the cover of semi-natural habitats in the surrounding landscape (1 km radius).Macadamias are a good source of protein and healthy fats. 

The initial nut set was 80% higher at the edge of semi-natural habitats than in the orchard center. In contrast, agronomic practices, such as irrigation, did not increase the initial nut set.

In entomophilous crops, insect pollination services can improve fruit set, yields and quality. Entomophilous crops have flowers, such as oilseeds, squash and orchard fruits and are essential to food security and the farming economy.

Meanwhile, in the EU, bees may be at risk of exposure to glyphosate – an active ingredient most commonly used in weed killers – via contaminated wildflower nectar. This could exacerbate the problem of food insecurity, according to research conducted by Trinity College Dublin and Dublin City University scientists and published in Heliyon.

Artificial agro methods ineffective 
Macadamia production in the Limpopo province is undergoing rapid agricultural expansion and intensification since it is a significant mainstay of South Africa’s tropical fruit industry. 

In recent years, the region has developed into one of the world’s largest macadamia producers, while the expansion of the orchards has led to the loss of natural forests and savannah habitats. 

Most crops (for example tomatoes, mangos, macadamia and avocados) are irrigated, and high volumes of chemical applications are used for fertilization and pest control to increase yields. However, this biodiversity hub remains under threat from climate change.

“Given the urgency to reduce the harmful environmental impacts of agricultural practices, we emphasize the enormous potential of supporting ecology through intelligent plantation design and the restoration and maintenance of semi-natural habitats in plantations and the surrounding landscape,” says Professor Catrin Westphal, head of functional agrobiodiversity at the University of Göttingen.

By Inga de Jong