Bees for trees: testing a potential tool for reducing human-elephant conflict

  • A study in South Africa’s Kruger National Park found that hanging pairs of beehives—one active, the other inactive—from tree branches was more effective than wrapping trunks with wire netting at protecting the trees from damage by hungry elephants.
  • Elephants damaged 2% of 50 bee-protected trees, 28% of wire-netted trees, and 54% of unprotected “control” trees, but even bees did not keep elephants from impacting neighboring trees.
  • Installing and maintaining beehives in tree branches is far more expensive than installing wire netting and requires more maintenance, but it offers reserves with sufficient resources an effective way to protect large, valuable trees from elephant impact.

When times are tough for elephants, knocking over a tree may be the best way to get at the food resources it offers. Trees with bees, however, may avoid damage by hungry elephants, even during a drought.

A recent study in South Africa’s Kruger National Park has found that hanging beehives containing African honeybees from tree branches may protect specific trees and their branches from damage by hungry elephants.

Elephants are known as ecosystem engineers for effectively dispersing large seeds of a variety of trees and for altering their environment by pushing and pulling down trees and branches. This latter behavior may benefit other grazing wildlife and maintain natural grasslands but can be destructive where space for elephants is restricted.

As poaching and human-wildlife conflict increasingly threaten populations of elephants and other large mammals, animals crowd into ever-smaller patches of native vegetation, and wildlife managers have turned to protecting them within enclosed reserves.

Reserve managers are, however, concerned that the resulting increase in elephant densities and compressing of their natural movement patterns may eliminate large, valuable trees. Earlier studies in southern Africa found that placing wire netting around tree trunks helps to deter elephants from stripping the bark from the tree. However, it does not prevent uprooting or damage to branches.

Protecting trees with bees – an experiment

In response to requests by Kruger Park managers for additional ways to mitigate damage to large trees, the researchers chose a big elephant favorite—the marula tree. People and wildlife love marula fruits, from which the popular liqueur Amarula is produced.

Elephants, in particular, are known to have a soft spot for marula fruit (though a traditional myth that such large animals get drunk on fermenting marula berries has been debunked). In fact, previous research has showed that elephants favor marula trees all year, compared to other large savanna trees. Elephants are important dispersers of marula and other seeds, but they also feed on the leaves, smaller branches, and bark, which they strip from the trunk, as well as the fruits.

Moreover, the study’s lead author, Robin Cook of the South African NGO Elephants Alive, told Mongabay-Wildtech, “some trees also receive impact from bulls for display or confidence-building purposes, thereby breaking branches or snapping the main stem of the tree and moving on without feeding.”

Keeping elephants from damaging particularly valuable trees is good for the health of the elephants, as well as the trees. According to Elephants Alive, “Marula trees represent important fruit-bearing trees, as they are considered of cultural significance and economic importance. Some would rather see elephant numbers reduced through legal and lethal killings than have iconic tree structures altered.”

Elephants are known to avoid contact with honeybees. This new study builds on research by Kenyan NGO Save the Elephants on the use of African honeybees to keep elephants out of crop fields. Cook and his South African and Kenyan colleagues examined the impact of elephants on 150 marula trees in Jejane Private Nature Reserve, adjacent to Kruger Park.

Dividing the trees into three groups, the researchers hung two beehives—one active and another dummy (inactive) hive—from the branches of 50 trees. They brought the active beehives into the reserve and hung them up at night to minimize disturbance to (and reaction from) the bees. Over the next year, they compared the negative impact from elephants on these trees to the impact on 50 trees with wire netting placed around each trunk and on 50 control (no treatment) trees.

Costs and benefits of keeping bees in trees

Over half of the 50 bee colonies brought to the study area abandoned their hive after several months, due, said the researchers, to an ongoing drought in the region and invasions by ants. The researchers successfully stopped ants from reaching and taking over the beehives by smearing Plantex glue on the nylon ropes from which the hives hung.

By supplementing the bees’ natural diet, first with sugar water and then with pollen and nectar, to compensate for the drought, the researchers slowed colony losses during the study period. Nevertheless, said Cook, the environment may not be able to support the artificially high density of bee colonies, particularly in a drought.

More generally, he added, “The movement of bees can be highly stressful to the colony, and there is always a chance that they will not be happy in their new environment and abandon the hive soon afterwards if the scouts have found a better location.”

Despite the loss of 26 colonies, the study found that beehives were more effective than wire netting at protecting trees from impact: elephants damaged only one of the 50 bee-protected trees, compared to 14 of the wire-netted trees and 27 of the control trees.

“The only beehive tree to receive any impact had the dummy hive ripped out of the branches by an elephant bull in musth,” said Cook. “This tree actually had an active hive on the opposite end. So it was not the case that trees with inactive hives fared worse than those with active hives.”

The results demonstrate the potential for combining active hives, which discourage elephants, with dummy hives, which reduce human effort and cost. Nevertheless, the authors state in their paper, more time is needed to see whether elephants will learn that they can forage safely at a tree with two inactive beehives or on the side of a tree with a dummy beehive, provided they don’t disturb the active beehive.

“This project illustrates the linkages between ecosystem components,” Michelle Henley, CEO of Elephants Alive, told Mongabay-Wildtech. “We have bees linked to trees in terms of pollinators, elephants linked to marulas as important seed dispersers, and bees’ hard work linked to people and ecosystem services in terms of the honey they produce. A neat ecosystem trio that has taught us so much.”

Bee benefits for small-scale and specialized tree protection

Installing and maintaining beehives is time- and labor-intensive, and its estimated cost per tree over 10 years (US $705) was 30 times greater than for wire netting ($21). The study found that while the beehives afforded greater protection than the wire wrapping, both treatments protected only the trees with the treatment, not other trees in the surrounding area. Moreover, despite the income beekeepers can collect from producing and selling the honey from active bee colonies (up to $5 per kilogram in Kenya), maintaining the protective beehives is labor-intensive work.

“Bee maintenance costs and effort are required across beehive sites, such as in Kenya and Sri Lanka, and comes as part of the beehive mitigation method,” said Cook. “Therefore, particularly for large tree protection, we recommend that private game reserves [or other landowners] with available financial and logistical resources use this method for specific iconic trees within their properties.”

Reference

Cook, R. M., Parrini, F., King, L. E., Witkowski, E. T. F., & Henley, M. D. (2018). African honeybees as a mitigation method for elephant impact on trees. Biological Conservation217, 329-336.


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