Clever orchard design for more nuts

The research team first investigated the role of insect pollinators in the nut production of macadamia trees. "Insect pollination of macadamia flowers is essential for production. A complete loss of insect pollinators would reduce the amount of nuts by 75 percent," says Professor Ingo Grass, Head of the Department of Ecology of Tropical Agricultural Systems at the University of Hohenheim. To find out which conditions encourage pollinators, the researchers observed and counted the bees and other insects on the macadamia flowers. "Surprisingly, it is less important how many honey bee colonies were established in the vicinity. The more important factor is how large the proportion of semi-natural habitats is in the vicinity of the plantation, since the majority of pollinators fly from the semi-natural habitats into the plantations," says first author Mina Anders, PhD student in Functional Agrobiodiversity, University of Göttingen.

The arrangement of the rows of trees in the plantations is therefore particularly important: 80 percent more nuts grew at the edge of the plantation, ie land that borders on semi-natural habitats, than in the middle of the plantation. Directly 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. "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. Agronomic practices such as artificial irrigation, on the other hand, did not increase the initial nut formation.

"Given the urgency to reduce the harmful environmental impacts of agricultural practices, we emphasise 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.