Strong biodiversity is an important factor in maintaining healthy landscapes, wild and agricultural alike. There is a plethora of research that suggests high flowering plant abundance promotes a high pollinator abundance. Some of these studies included biodiversity studies along ecological margins, which are essentially the boundaries between two plant communities. A classic example would be the margin between wild land and agricultural land. There have been numerous studies that suggest inserting pollinator friendly flowering plants into these margins can create higher abundance and biodiversity of pollinators, which in turn can lead to more favorable crop yields and a healthier agricultural space. However, many of these studies only take place over a span of a couple years; often the time it takes for a margin filled with transplanted or sowed plants to establish depending on the type of plant composition. Researchers from Europe wanted to take these studies a step further; by collecting data over a course of 8 years to see the interactions between plant abundance and pollinator abundance. These researchers created experimental margins around Hungarian crop fields using a pollinator friendly seed mix and sampled periodically the abundance of plants and pollinators during the growing season for 8 consecutive years in hopes to find some answers on how these communities change over time.
The “Operation Pollinator” seed mix was based on species of flowering plants known to be attractive to bees in the west Danube River region of Hungary containing a large amount of agricultural land. The seed mixture contained 72% perennials and 28% annuals. The perennials were 4 species of clover, Sativa sp, alfalfa, wild rye, trefoil, and Timothy grass. The annuals were buckwheat, purple tansy, and white mustard. In addition to these plant’s attractiveness to pollinators, it was interesting to note many of these plants can commonly be found in or around agricultural settings, whether for fodder for grazing animals, green manure (the process of using nitrogen fixing plants as fertilizer, tilling them into the soil), or in pastural margins surrounding crop stands.
The seed mix was planted on the margins of 96 Hungarian farms who primarily grew grains, sunflowers, and oilseed rape. There were control margins as well, which contained plants that were already established. The flower abundance, along with the pollinator abundance were recorded on warm, sunny days during the region’s growing season (May through September) between 2010 and 2018. Researchers would walk the perimeter of the margins, and every 30 meters they would stop and take counts of the plant and pollinator groups in 4-minute intervals. The ecological groups used for this study included honeybees, bumble bees, mining bees, trap-nesting bees (bees that nest in plant stems), hoverflies, and lepidoptera (moths & butterflies). The experimental margins were trimmed down several times a year to reduce grassy weeds. The surface area of the margins varied between 1 and 2 hectares (2.5 – 5.0 acres).
Statistical analyses reported that there was indeed an increase in pollinator abundance as plant abundance increased compared to the control margins for all pollinator groups. The largest pollinator increases were honeybees at 768%, followed by mining bees at 566%, then a 414% increase in bumblebees. However, the average abundance of the bumble bees, along with trap-nesting bees and Lepidopterans, did not significantly change over time. Possible explanations for the results found in bumblebees, trap-nesting bees, and lepidopterans proposed by the researchers were that as a margin matured it created favorable conditions for trap-nesting bees and bumblebees in terms of space to nest; and that these nesting conditions were more attractive than the actual forage. Additionally, the lepidopteran results could potentially be explained by the fact that the species of plants implemented in the study might not have been favorable as feeding grounds the lepidopteran caterpillars, which produced little attraction for the adult stage pollinators.
Honeybees, mining bees, and hoverflies also dropped in abundance as plant abundance lowered over time. Interestingly, honeybees’ abundance dropped sharply after only the first year and at a much faster rate than the corresponding plant abundance. Other studies like this one have not shown this sharp decrease. The researchers think several factors were at play. Firstly, honeybees are highly mobile with a highly advanced communication system, where colony scouts could communicate quickly where more favorable foraging grounds are located. Secondly, as honeybees are essentially livestock whose populations are highly managed by humans, which add a whole other variable not found in the wild pollinators. Lastly, in this study the experimental margins were not resown; which was not the case in other studies containing conflicting results. Because of this the researchers do recommend resowing of flower margins when used in real life agricultural practices.
To read the paper they published on this long term research study, follow this link.