OXFORD, United Kingdom — The International Tree Foundation is in the midst of an ambitious plan—plant 20 million trees in and around Kenya’s highland forests by 2024, the organization’s centenary.

That goal is one of the many living expressions of the ideals espoused by Richard St. Barbe Baker (1889-1982), founder of the organization. Mr. Baker, who was best known as St. Barbe, was a pioneering environmentalist and early British Baha’i who had a far-reaching vision and initiated practices that have become common and widespread today.

A re-evaluation of this influential environmental pioneer is now under way, thanks to the work of the International Tree Foundation and the publication of a new biography. The recent attention comes at a time that the consequences of global climate change are increasingly apparent to humanity.

“Long before the science of climate change was understood, he had warned of the impact of forest loss on climate,” writes Britain’s Prince Charles, in the foreword of the new biography about St. Barbe. “He raised the alarm and prescribed a solution: one third of every nation should be tree covered. He practiced permaculture and agro-ecology in Nigeria before those terms existed and was among the founding figures of organic farming in England.”

Having embraced the Baha’i Faith as a young man in 1924, throughout his adventurous life, St. Barbe found in the teachings of Baha’u’llah the embodiment of his highest aspirations for the world. His deep faith was expressed in a love for all forms of life and in his dedication to the natural environment.

“He talks about the inspiration he received from the Faith and from the writings of Baha’u’llah and ‘Abdu’l-Baha,” explains Paul Hanley, the author of a new biography about St. Barbe—Man of the Trees: Richard St. Barbe Baker, the First Global Conservationist. “St. Barbe had a world embracing vision at a time when that wasn’t really common. His frame of reference was the whole world.”

St. Barbe noted this connection with Baha’u’llah’s vision of the oneness of humanity when he went on pilgrimage to the Shrine of Baha’u’llah.

“(H)ere at Bahji (Baha’u’llah) must have spent his happiest days. He was a planter of trees and loved all growing things. When his devotees tried to bring him presents from Persia the only tokens of their esteem that he would accept were seeds or plants for his gardens,” St. Barbe later wrote in his diary, quoted in Mr. Hanley’s book.

St. Barbe then recalled a passage from Baha’u’llah’s writings: “‘Let not a man glory in this, that he loves his country; let him rather glory in this, that he loves his kind.’ Yes, I thought, humankind, humanity as a whole. Was it not this for which I had been striving to reclaim the waste places of the earth? These were the words of a planter of trees, a lover of men and of trees.”

St. Barbe also maintained a sustained contact with Shoghi Effendi, who encouraged him in dozens of letters and sought his advice when selecting trees for Baha’i Holy Places in Akka and Haifa. St. Barbe described how the inscribed copy of The Dawn-Breakers that Shoghi Effendi sent him became his “most treasured possession.”

“I would read it again and again, and each time capture the thrill that must come with the discovery of a New Manifestation,” St. Barbe wrote.

The International Tree Foundation, which St. Barbe originally named Men of the Trees, is just one of many organizations he established in his lifetime. It is estimated that, as a result of his efforts, the organizations he founded, and those he assisted, some 26 billion trees have been planted globally. He was so dedicated to tree planting, in fact, that he took an international trip at age 92 to plant a tree in memory of a close personal friend, a former prime minister of Canada. St. Barbe died a few days after accomplishing the purpose of that trip.

“I think people should know about Richard St. Barbe Baker because his legacy still lives on,” says the Foundation’s chief executive, Andy Egan.

“Today we try to walk in St. Barbe’s footsteps,” adds Paul Laird, the Foundation’s programs manager. “We have a sustainable community forestry program, which reaches out and tries to work particularly with groups and local community-based organizations that are close to the real situation—the people themselves doing things for themselves, who understand the threats of land degradation and forest loss, and what that actually means for them.”

From early childhood in England, St. Barbe was attracted to gardening, botany, and forestry. He would run among his family’s trees, saluting them as if they were toy soldiers. Later, as a young man awaiting the start of his university classes in 1912, he took a job as a logger where he lived in Saskatchewan, Canada. He could no longer treat the trees as his friends.

“This area had been virgin forest and one evening, as I surveyed the mass of stricken trees littering the ground, I wondered what would happen when all these fine trees had gone,” St. Barbe wrote at the time. “The felling was wasteful, and I felt sick at heart.”

That experience would be a defining one for St. Barbe. He decided to study forestry at Cambridge University, beginning a lifetime dedicated to global reforestation. Afterward, he moved to British-ruled Kenya, where he set up a tree nursery. While there, he witnessed the effects of centuries of land mismanagement.

Working as a colonial forester, St. Barbe was expected to employ top-down forest management practices. This went against the practices of the indigenous Kikuyu people, who used a traditional method of farming where they burned down trees to create rich soil. St. Barbe wanted to encourage a form of agriculture that promotes the growth of a forest conducive to farming while also protecting the soil from erosion and respecting the culture and wisdom of the local population. The tribal leaders were not open to the planting of new trees, calling this “God’s business.”

To honor the traditions of the Kikuyu people and promote an awareness of their significant role in tree planting and conservation, St. Barbe looked to one of their long-held traditional practices—holding dances to commemorate significant moments. From this integration of cultural values and environmental stewardship was born the Dance of the Trees in 1922.

“So instead of trying to push them and force them into tree planting, he said let’s make this consistent with the culture. So he approached the elders there, discussed it with them and they had this Dance of the Trees which led to the formation of the Men of the Trees,” says Mr. Hanley.

Along with the Men of the Trees’ co-founder, Chief Josiah Njonjo, St. Barbe developed a deeper understanding of the important ecological, social, and economic roles of trees in the life of humanity.

“Behind St. Barbe Baker's prescience was his deep spiritual conviction about the unity of life,” Charles, the Prince of Wales, writes. “He had listened intently to the indigenous people with whom he worked.”

St. Barbe’s ventures into what is now called social forestry were looked upon with some skepticism. As a colonial forester, he was expected to protect forests that belonged to governments.

“He was extraordinary in that he broke through that,” says Mr. Laird. “He saw that fundamentally these forests belonged to the people of Kenya and you needed to work with the people to conserve the forests.”

This community-led approach remains core to the work of the International Tree Foundation.

“His caring nature for all life is something that really shines through,” says Mr. Egan. “He very much helped to give birth to this idea that it wasn’t just a professional thing about planting trees. It was something that ordinary people in communities could and should be doing. In a way they’re in the best place to actually protect the forests…so their role should be very much recognized and supported and celebrated.”

In researching St. Barbe’s biography, Mr. Hanley discovered that the forester “was definitely very advanced in his thinking. And his whole philosophy of the integration and unity of human society, but also of the natural world, were fairly radical concepts at the time.”

When St. Barbe first encountered the teachings of Baha’u’llah in 1924, he found his ideas of nature and humanity confirmed. A Christian with a deep respect for indigenous religious traditions, St. Barbe recognized the truth in Baha’u’llah’s teachings about oneness—the oneness of religion, the oneness of humankind, and the interconnectedness of all life. The Faith’s writings also employ imagery from nature to help convey spiritual truths.

“I began to read some translations from the Persian,” St. Barbe wrote, reflecting on his pilgrimage to the Shrine of Baha’u’llah. “‘In the garden of thy heart plant naught but the rose of love.’ I was enthralled by the sublimity of the language. Here was beauty personified.”

In 1929, while on a mission to establish a branch of the Men of the Trees in the Holy Land, St. Barbe traveled to Haifa to visit Baha’i sacred sites. Pulling up in his car outside of the home of Shoghi Effendi, St. Barbe was surprised to see the Guardian of the Baha’i Faith coming out to welcome him and handing him an envelope. It contained a subscription to join the Men of the Trees, making Shoghi Effendi the organization’s first life member.

“He talks about the meeting with the Guardian as the most significant moment in his life, and it really…galvanized him,” says Mr. Hanley.

Through a continued correspondence, Shoghi Effendi encouraged St. Barbe’s efforts. For 12 consecutive years, he sent a message to the World Forestry Charter gatherings, another of St. Barbe’s initiatives, which were attended by ambassadors and dignitaries from scores of countries.

St. Barbe’s work took him to many countries. He was appointed Assistant Conservator of Forests for the southern provinces of Nigeria from 1925 to 1929. He also planned forests on the Gold Coast. In the United States, he launched a “Save The Redwoods” campaign and worked with President Franklin D. Roosevelt to establish the American Civilian Conservation Corps which involved some 6 million young people. After World War II, St. Barbe launched the Green Front Against the Desert to promote reforestation worldwide. One expedition in 1952 and 1953 saw him trek 25,000 miles around the Sahara, leading to a project to reclaim the desert through strategic tree planting. In his late 80s, St. Barbe traveled to Iran to promote a tree planting program. He stopped in Shiraz, the birthplace of the Baha’i Faith, where he was asked to inspect an ailing citrus tree at the House of the Bab, a place of pilgrimage for Baha’is.

The Men of the Trees grew into the first international non-governmental organization working with the environment. By the late 1930s, it had 5,000 members in 108 countries, and its own journal for members, titled Trees.

“Originally it was created because it seemed that St. Barbe just got so many letters and invites and correspondence,” says Nicola Lee Doyle, who today compiles the annual journal. “He was telling people constantly where he was going to be and what he was going to be talking about. So they needed a way to just give everybody the information, and that’s how it started—but then it developed.”

Today, Trees is the world’s longest-running environmental journal.

Successive generations of environmentalists have credited St. Barbe as igniting their passion for their work.

“Sometimes it was the little things he did—like writing an article, or doing a radio interview—that would connect with some youth in some distant country,” says Mr. Hanley. “And several of these people went on to become very significant figures in the environment movement.”

“His legacy is probably related to the fact that he was indefatigable,” Mr. Hanley adds. “It was quite incredible—thousands of interviews, thousands of radio broadcasts, trying to alert people to this idea, and it really did have an impact on the lives of many people who have gone out and protected and planted trees.”

St. Barbe’s pioneering thinking can be particularly valuable now as humanity grapples with the challenges presented by climate change. Indeed, one of humanity’s most pressing challenges is how a growing, rapidly developing, and not yet united global population can live in harmony with the planet and its resources.

“It is now clear that had we heeded the warnings of St. Barbe Baker and other visionaries, we might have avoided a good deal of the environmental crises we face today,” Prince Charles writes. “Richard St. Barbe Baker’s message is as relevant today as it was ninety years ago and I very much hope that it will be heeded.”