They were in a bind, no doubt about it.

Wearing little but cotton shorts, the four men huddled on a streambank deep in the Bornean rain forest. Water dripped from their soggy clothes, making muddy pools around their feet as they assessed the situation.

They were surrounded by a forest so vast that it would take three days walking just to reach the nearest house. They had no food, no shoes, not even a knife.

Minutes earlier, they had been floating downstream in a rough bark canoe they had made that morning, assured that they would eventually find their way out of the forest, just as the stream did.

They heard the waterfall’s roar too late and despite their best efforts to save the clumsy craft, had been forced to bail out and swim for shore.

From the waterfall’s pool, they retrieved only a small bamboo container holding four matches. Feet bare and stomachs empty, they set out, slogging all day until that evening when, to their horror, they realized they’d marched full circle.

The rain forest was testing Peter Ashton again. Over the years he spent in its humid depths, Ashton, who would go on to become Bullard Professor of Forestry at Harvard, endured many physical hardships. He saw companions die — one in flames, one in water — and was nearly killed himself by a pit viper’s poison.

But he learned from the forest. Whether from the data that helped him explain tree diversity and distribution, or from the local people versed in the forests’ ways, or from hard experience, Ashton made a career out of listening to what the forest had to say.

On that ill-fated trip many years ago, the men did what the forest required. They rested through the night, climbed a tree to get their bearings, and set out, marching until they couldn’t march anymore. They filled their bellies with a milky clay that satisfied even if it didn’t nourish. And when one of them became too weak to continue, Ashton stayed with him while the others went on.

Ashton and his companion waited by the stream for three days until they heard the sound of an outboard. It was their comrades who had reached the longhouse of a friendly tribe and returned, led by the chief and his son. To this day, Ashton remembers the food — fish and condensed milk — carried in the canoe.

“We poured the condensed milk over the salt fish and it was one of the best meals I ever had. It was absolutely fantastic,” Ashton said, relish evident in his voice even decades later.

After years of listening to the forest, Ashton has shifted tactics. Today he is putting a bullhorn to the forest’s mouth so the whole world can hear its message about climate change. Though retired from teaching, Ashton is still active, using an expanding network of forest plots to find out how trees around the world are responding to changes in the environment. His work has brought him prestigious official honors — the Japan Prize and the Sultan Quaboos Prize from the United Nations Educational, Scientific, and Cultural Organization (UNESCO). It’s also brought him academia’s highest unofficial prize: the accolades of the scientists whose lives he’s touched, including many in the countries where he’s worked over the years.

“I can certainly say my career is all due to him,” said Paul Chai, who worked for Ashton when, early in his career, Ashton was a government forest botanist in the Malaysian state of Sarawak. Chai came into the job as a young kid just looking to make a living. When Chai left two years later, however, it was not for another job but for school. He eventually earned a doctorate and returned to assume Ashton’s role as government forest botanist.

“When I started work I didn’t know anything about [forest trees]. He introduced me to tropical botany and ecology,” Chai said. “I wouldn’t have gotten into this career without him.”

Infected by beauty on the wind

Though Ashton’s career in tropical forests is largely an intellectual pursuit, he was initially drawn to the natural world by its beauty. As a boy growing up in the south of England during World War II, Ashton often wandered forests near his home. The war’s fighting left French fields untended and sparked a mini population explosion of continental insects that drifted over the Channel.

“Butterflies came across the channel that had not been seen in any number of years, perhaps since the beginning of the Industrial Revolution in the 18th century,” Ashton said. “It was an incredibly exciting time for a young, beginning naturalist.”

Ashton, who has 10 plant species named after him and has written six books and more than 200 scholarly articles, got his first taste of a tropical forest as an undergraduate at Cambridge University in the 1950s, when he and a friend traveled to the Amazon one summer.

“I actually went as an entomologist. I got overcome with the excitement of the forest itself,” Ashton said.

When he graduated in 1956, Ashton wanted to do his graduate studies with John Corner, the professor who had encouraged him on the Amazon trip. But Corner didn’t think school was the right place for him.

“He actually declined and said, ‘If you stay here, your knowledge will be based on the knowledge of others. If you’re interested in tropical forests, what you really need to do is go out and get your own personal experience and decide what you think about these things,’” Ashton recalled. “That was really good advice.”

With Corner’s help, Ashton landed a job as a government forest botanist in Brunei, with orders to catalog the nation’s timber resources. Ashton spent the next 10 years on the island of Borneo, first in Brunei and later in the Malaysian state of Sarawak. He also continued his studies at Cambridge, earning a doctorate in 1962.

In 1966, Ashton and his wife Mary — to whom Ashton credits much of his success — decided it was time to return to the United Kingdom with their three children. Ashton took a job at Aberdeen University in Scotland, where he was a lecturer and then senior lecturer in botany.

Though Ashton began his career studying the extraordinary diversity of tropical forest trees — a single plot can hold as many tree species as exist in the entire United States and Canada — he wasn’t content with that.

Ashton expanded his studies to examine why different trees exist in different places, focusing on tree communities living in different soil types. Unlike temperate forests that may be dominated by two or three tree species, the tropical forest is characterized by a far more complex mosaic spread across the forest floor. In this jigsaw puzzle community, tree species can be represented by single individuals separated by large distances from other members of the same species.

Ashton examined how tree distribution is related to their reproductive habits. He looked at how the trees pollinate each other over such large distances and whether, given the relatively constant conditions day to day and year to year, there was much genetic variability among the trees, an important consideration in the operation of natural selection.

As he puzzled over these questions, he realized that the answers lay hundreds of feet above the ground in the rainforest canopy and that somehow, someone had to get out to where reproduction happens: the flowers growing on the flimsy tips of the trees’ branches.

Though he was studying tropical forests, Ashton said he was lucky at the time to be based in Aberdeen, where the oil industry was booming.

“We got engineers to design a kind of tree prosthetic, an aluminum alloy boom that was extensible with ropes, so you can actually manipulate the twigs and flowers in the canopy,” Ashton said. He added, with his typical humor, “On the other end you don’t suspend yourself, of course, you suspend one of your graduate students. All this is happening at night — to make it extra exciting — while I’m down below barking out commands.”

What they found in those hard-to-reach flowers was considerable genetic variability among the trees as well as specific insects that carried pollen from one tree to another, fertilizing the flowers despite the distances between the trees.

Colleagues describe Ashton as friendly and enthusiastic but tough, both physically and mentally, and as one who cares greatly for the local people in the nations where he works. Sitting in a room with Ashton, it’s difficult to go 30 minutes without him breaking into laughter at least once, one colleague said. Another described him as friendly, but also very firm. The local tree-climbers in Sarawak gave him the nickname “Taji Buloh,” or “bamboo spur” in the local tongue, a reference to the spurs attached to roosters during cockfights.

“What he did was physically immensely challenging,” said Cambridge University Professor Emeritus Peter Grubb, who attended Cambridge with Ashton and has kept in touch with him over the years. “He’s a very, very tough man.”

Ashton came to Harvard in 1978, attracted by the Arnold Arboretum’s herbarium and library, which he called one of the world’s best for research on Asian plants and forests. He served as the Arnold Arboretum’s director and the Arnold Professor of Botany. In 1991, he became the Charles Bullard Professor of Forestry, a post he held until his retirement in 2005. Today he is Charles Bullard Professor of Forestry Emeritus.

The arboretum’s current director and Arnold Professor Robert Cook called Ashton a naturalist and scientist in the tradition of Pellegrino University Professor Emeritus E.O. Wilson and famed evolutionary biologist Ernst Mayer, whose scientific work was informed by a personal understanding of their subjects born from years in the field.

Cook said Ashton’s nine years as Arboretum director, which ended in 1987, created a vision for the institution as a comparative research facility that endures today, in the construction of a $42 million research laboratory dedicated to fundamental studies of plant biology enabled by the genomics revolution.

“The truth is, the real vision belongs to Peter; I’ve merely been the midwife,” Cook said. “As a consequence, our new Weld Hill research facility, and its immense promise for our future scientific reputation, ensures that the Arnold Arboretum will continue to be a unique source of pleasure and intellectual inspiration for all the people for many generations to come.”

A forest chain to measure climate change

In the early 1980s, Ashton had an encounter with scientist Stephen Hubbell that sowed the seeds for the establishment of a unique, global network of forest plots that not only allow scientists to study trees within individual forests, but also allow comparative studies of exhaustively documented forests around the world.

Their work led to the founding of the Center for Tropical Forest Science, a collaboration between the Arnold Arboretum and the Smithsonian Tropical Research Institute. The center expands on Ashton’s and Hubbell’s ideas and creates a network of 18 forest plots in Southeast Asia, Africa, and South America. The plots hold 6,000 species and 3 million individual trees, measured every five years.

Exhaustively documented, the plots have proven invaluable resources to scientists around the world studying a variety of aspects of tropical forest dynamics, including the impact of climate change.

Grubb said that it was Ashton’s people skills, as well as his knowledge of the area and the local governments that were key to establishing the plots.

“He knew where to put the plots in Southeast Asia,” Grubb said. “He knew the plants and he knew the people.”

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