Some of the most important tree species for the restoration and conservation of tropical forests rely heavily on bees as transporters of pollen.
Bees facilitate pollination over great distances, increase the genetic diversity of plants, and stimulate the reproduction and resilience of native species in degraded ecosystems.
That’s why conserving these declining insects should be a priority in forest restoration projects, according to a study by Brazilian scientists published in Ecological Applications.
The study analysed how different bee species responded to changes in Brazilian forest landscapes. It investigated how increasing bee populations may boost pollen dispersal when planting trees in restoration projects, and also help re-establish diverse forests in disturbed areas in Brazil.
Researchers carried out fieldwork in an agricultural area of the Atlantic Forest in the country’s south-east, which had been turned into sugarcane fields. Only about seven per cent of the original vegetation remains there, in small fragments of primary forest comprised of discontinuous canopies covered by vines and bordered by invasive grasses.
The team also included two other less degraded areas as reference ecosystems. One of these contained contahighly diverse trees reintroduced by researchers about two decades ago to increase forest cover, while the other consisted of wetlands, dominated by herbaceous vegetation.
In each of these landscapes, researchers installed “pan traps” — a standard method for capturing bees — with the aim of collecting insect samples at the peak of the flowering season, between October 2015 and January 2017.
They compared the abundance and diversity of bee populations in each habitat and analysed the pollen grains stuck to their bodies to determine which plant species the insects had interacted with.
The team collected 727 bees of 85 species, with different sizes and flight skills, social behaviour, nesting sites and diets, and found that these had interacted with 220 different plant species.
The abundance of bees responded negatively to habitat change, decreasing in highly disturbed environments — such as anthropogenic wetlands and sugarcane fields. But their number increased in areas where forest had been restored, as well as in original forest fragments, where large and medium-sized species that nest above-ground were predominant.
Small and medium-sized bee species that nest underground, with varying levels of social behaviour and diet, were unaffected by habitat change, and even tended to increase in some disturbed areas, researchers said.
Meanwhile, ‘oligolectic’ bees — which typically prefer pollen from a single genus of flowering plants — responded negatively to habitat change.
Ricardo Ribeiro Rodrigues is a biologist at the Luiz de Queiroz College of Agriculture at the University of São Paulo, who specialises in forest recovery and co-authored the study. He said the results suggested that “restoration programmes have the power to bring back bee populations, just as bees may stimulate the reproduction and resilience of native species in degraded ecosystems”.
“It is a system that positively feeds back,” he added. “So bee conservation should be prioritised in restoration programmes through the reintroduction of nesting materials in cases of locally extinct species.”
He explained that bees will return in time as trees get bigger and older, providing new nesting sites and other plant substrates for their reproduction.
Vera Lúcia Imperatriz-Fonseca, a biologist at the University of São Paulo’s Biosciences Institute, said: “Brazil is rich in species of pollinators such as bees, but we urgently need a more solid public policy that guarantees their conservation, as countries like the United States, United Kingdom, France and Norway are doing. Taking care of pollinators is a sure return for biodiversity.”
With bees disappearing in many regions of the world, the causes and consequences of this loss are already being analysed to find solutions, said Imperatriz-Fonseca.
“The results presented in the study may help guide public policy actions for restoring forest areas that include bees in their strategy,” she added.