By Jeffrey Moyo
HARARE, Aug 19 (Thomson Reuters Foundation) - Eucalyptus trees, popularly known as gum trees, stand tall amid Zimbabwe's forests. But those dotting the Harare-Beitbridge roadside, just outside the capital, are in trouble, with their bark fraying off.
They - and other tree species - are suffering not only due to this year's severe El Niño-induced drought, experts say, but also from an onslaught of pests, first detected in 2015.
They include the eucalyptus leaf beetle which chews irregular notches along the edges of the trees' leaves.
"A war waged on forests by pests is gathering momentum, and besides wood poachers causing deforestation, the pests have become the new drivers of desertification," said Mevion Chagwiza, an environmental activist affiliated to the Zimbabwe Environmental Law Association.
The country's Forestry Commission lays some of the blame for the surge in forest pests on climate shifts, as global warming heats up the planet.
"These pest outbreaks are partly attributed to changes in climatic conditions which are now making previously unsuitable geographical areas amenable to 'occupation' by these alien species," said Forestry Commission spokeswoman Violet Makoto.
The insects attacking Zimbabwe's forests and plantations include the blue gum chalcid, a gall-inducing type of wasp, the bronze bug and the red gum lerp psyllid, all of Australian origin, Makoto said.
The bronze bug is a sapsucker that feeds on eucalyptus leaves, while the red gum lerp psyllid attacks the red gum and more than 25 other varieties of eucalyptus, with the female laying eggs on the leaves.
The pests damage tree foliage and young shoots, impairing growth. As a result of massive defoliation and disruption of physiological processes, the trees eventually die, Makoto said.
The commission says trade between countries and the increased movement of people around the globe have also contributed to the spread of the pests.
Even before the arrival of the pests towards the end of last year, the southern African nation's forests were dwindling.
The Ministry of Environment, Water and Climate says Zimbabwe has a deforestation rate of 330,000 trees per year.
From last September to the end of May, the ministry estimates that 43,000 eucalyptus trees succumbed to forest pests alone, in addition to some 24,000 trees of other species. But the pests are not forest enemy number one.
Some 57,000 trees perished due to drought linked to a strong El Niño event, which affected weather patterns worldwide, while another 80,000 were cut down for timber during the same period.
"In Zimbabwe, the major drivers of deforestation have been the conversion of forest land to agricultural land, which accounts for 80 percent of the deforestation rate," Oppah Muchinguri, Zimbabwe's environment minister, told the Thomson Reuters Foundation.
Still, experts say pests are a growing threat to forests.
"The pests destroying trees here have targeted eucalyptus trees the most, while on the other side tree-poaching is also affecting forests," said government ecologist Henry Kazingizi.
According to statistics from the Timber Producers Federation, the onset of gum tree diseases has reduced the amount of land used for commercial timber production to 80,000 hectares (197,684 acres) from over 108,000 hectares in the past decade. Eucalyptus plantations recorded the biggest decrease.
The Forestry Commission's research division says the devastating effects of alien invasive pest species are now widespread in many parts of the country where eucalyptus is grown.
"The pests affect almost all growth stages of the tree, beginning from the nursery to mature plants in the field," said the commission's Makoto.
Community wood lots throughout the country, which provide fuel wood for tobacco farmers and households, and eucalyptus plantations, which also provide timber and poles for industrial use, have all felt the pinch from the pests, she added.
Makoto warned that a drop in the availability of eucalyptus could expose indigenous tree species to exploitation for tobacco curing - "a scenario which is not ideal given the already alarming levels of deforestation".
The commission believes the explosion of forest pests should not deter eucalyptus growers.
"Very few species so far match eucalyptus in terms of (its) benefits," Makoto said. "It has just been unfortunate with these pests, but we believe it's a passing phase as we are working towards a solution."
The commission earlier this year partnered with the U.N. Food and Agriculture Organization to start implementing a biological control programme for the pests.
This involves importing a biological control agent, often referred to as a "natural enemy", which can keep down the pest population in the environment. The method relies on predation, parasitism and other natural mechanisms, but also involves management by humans.
Some experts, however, see the pests as a "necessary evil".
"Pests are considered to be a natural component of the forest ecosystem as they play a part in getting rid of feeble trees and recycling litter on the forest floor, which becomes food for birds and other animals," said Tracy Mutasa, a Harare-based agricultural extension officer.
(Reporting by Jeffrey Moyo; editing by Megan Rowling. Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women's rights, trafficking, property rights and climate change. Visit http://news.trust.org)
Our Standards: The Thomson Reuters Trust Principles.