Scientist, Author, Educator, Tree Canopy Biologist

Helper becomes an invader

The best time to plant a tree is twenty years ago. The next best time is now. — African proverb

Nature's Secrets by CanopyMegI am swallowing mouthfuls of dust each day, driving long distances in Ethiopia during the dry season. The majority of roads are not only dusty, but the dirt surfaces give us a rodeo-ride experience in a four-wheel drive without shock absorbers.

As a conservation biologist working with locals in Ethiopia on forest sustainability, I have become one of Mother Nature’s sleuths — to find, identify, and determine the health of this country’s declining native trees.

Less than 5 percent of original forest remains in northern Ethiopia, a very serious conservation challenge. But the predominantly brown and dry landscape is increasingly interrupted with many shades of bluish- and gray-green. These patches and roadside swaths represent eucalypt trees, native to Australia.

At the end of the 1800s, these trees were introduced to Ethiopia (and elsewhere) as a source of firewood and construction timber. In the absence of their native enemies, eucalypts (or gum trees, as the Aussies call them) grew fast and were initially considered an amazing solution to deforestation of native species.

In the absence of the insect pests and fungal diseases that plague eucalypts in their homeland, they are very successful when transplanted to new places. Shades of blue-gray-green gum canopies are starting to outpace the dark richer greens of the native trees in Ethiopia, but at a huge cost.

Invasive species now cost over $150 billion annually in America: invasive pythons in the Everglades, zebra mussels in the Great Lakes, and a multitude of insect pests in tree canopies cost the taxpayer enormous amounts of money and frustration. In Ethiopia, eucalypts behave like typical invasive species — they grow unchecked!

Although gum trees were initially planted purposefully and considered a salvation for much of Africa, they are now becoming a curse. The local Orthodox priests call them the “evil tree,” because gum trees are invading their native tree canopies surrounding the Orthodox churches, called church forests.

The eucalypts require up to four times more water than the native tree species, are toxic to most native wildlife, and do not provide the same benefits (including medicines) as native trees. To make matters worse, eucalypts reproduce profusely and, once established, are difficult to remove. This very successful invader is now a big threat to Ethiopia’s rural water supply and to native biodiversity, as well as to their cultural heritage.

What an ethical dilemma! The gum trees are needed for firewood, and they make great straight poles useful for building homes. But they now threaten two important ecosystem services: water and biodiversity (including pollinators).

Ironically, I spent almost a decade in Australia in the 1980s, solving the devastating eucalypt dieback epidemics that threatened gum trees in their native homeland. A few insect pest outbreaks killed off millions of native eucalypts in New South Wales, and fungal pathogen killed off similar numbers in Western Australia. These diebacks of native forests cost the Australian government billions of dollars through losses in livestock, timber and tourism.

Like most invasive species, eucalypts grow more successfully than in their native habitat, until pest agents manage to catch up to them, which they invariably do. For now, Ethiopia has a challenge: how to provide adequate firewood for hungry families, but also conserve native biodiversity and the cultural heritage of the church forests for future generations.

Stay tuned, as the unique team of religious leaders and scientists struggle to make tough decisions about gum trees invading northern Ethiopia’s church forests. Not all green is the same, and invasive eucalypts in many countries represent an enormous sustainability dilemma.

Meg Lowman, a longtime Sarasota-based scientist and educator, is chief of science and sustainability at the California Academy of Sciences.

Originally posted in the Sarasota Herald-Tribune.