Flowering plants are disappearing from Dutch nature due to a shortage of insects

• Rolf Schuttenhelm

  editor Climate

A shortage of bees and other pollinators is killing wild plants in Dutch nature. This is the conclusion of researchers from Leiden University, Naturalis and the Netherlands Institute for Ecology (NIOO-KNAW) in a new study. They examined 87 years of measurements at more than 365,000 locations.

Species that were once common grassland flowers, such as the cuckoo flower, daisy, meadow milkweed, knapweed and many dozens of others, are in steep decline. Those flowers were the first to disappear from the farmland. Causes: over-fertilization and the disappearance of moist hay fields.

But the flowers are also declining sharply in the remaining natural grasslands. This decline has several causes, including nitrogen pollution and desiccation of the landscape.

On top of this is a decline due to a decrease in pollination, lead researcher Kaixuan Pan from Leiden University tells NOS. “Between 1930 and 2017, the number of plants pollinated by insects fell by more than a sixth on average. This decline threatens ecosystem stability and food security.”

Plants that depend on insects often produce colorful flowers, with nectar and pollen. If that pollen is not exchanged by insects, (fertile) seeds often do not form and the plant cannot sow itself. The spot is then occupied by plants that are pollinated by the wind, such as grasses. That is a much smaller part of plant wealth: globally, about 90 percent of all plants are (partly) dependent on insects for pollination, including many food crops.

Research leader Geert de Snoo of NIOO-KNAW finds the declining flower pollination extra worrying, because it can lead to a vicious circle. Insects, in turn, are declining partly due to a decrease in the supply of nectar and (suitable) pollen in the landscape. In short: fewer bees means fewer flowers, which means even fewer bees. “This looks very much like a downward spiral,” says De Snoo.

Hans de Kroon, professor of plant ecology at Radboud University, also has this concern. “Plants and insects are interdependent.” De Kroon is not involved in the new research, but previously led an insect study that had a huge impact in 2017: the number of flying insects in nature reserves appeared to have decreased by as much as 76 percent in 27 years.

“We are in danger of forgetting what is normal,” says De Kroon. “This also applies to flowery places: there should be more flies there than you can currently observe. This is because large numbers of insects are disappearing elsewhere in the landscape.”

A research team led by NIOO-KNAW previously published a ‘master plan’ for insect recovery. This advocates a series of simultaneous measures, including restoration of small-scale diversity in the landscape and a decrease in the use of agricultural poisons, another major cause of insect mortality.

“The great trick is ultimately to get back into a positive spiral,” De Kroon concludes.