The lucrative nature of the industry was highlighted in December, when customs officers in Macau caught a group trying to smuggle nearly US$3 million worth of incense timber (known commonly as agarwood) into the mainland. In Hong Kong, hikers and villagers have increasingly been reporting signs of illegal harvesting, among them makeshift camps and sightings of what they believe to be gangs of harvesters from across the border.

"They can do it so fast, so quickly," says Ho, who has been tracking the handiwork of tree poachers for the past few years. "They can travel to Hong Kong easily, legally, and they go hiking. And the AFCD [Agriculture, Fisheries and Conservation Department] always tells me, 'We don't have adequate people to inspect the places.' But Hong Kong has a vast countryside and this is not good enough."

"Most of the bigger trees have already been stolen," Jim Chi-yung, a tree expert and professor of geography at the University of Hong Kong, told the last year. "The poaching is very serious. With the larger trees gone, the poachers are beginning to move to the lesser trees."

Just a few kilometres from Hong Kong's border with the mainland, Ho leads us further into Pat Sin Leng Country Park, pointing out stumps and marked trunks (when a cut is made, a suitable tree will start secreting resin). She offers eco-tours regularly, with the help of a few other volunteers, hoping to raise awareness of forest crimes. Ho says reports now come in weekly.

"In Lantau, most of the incense-tree species have been chopped down and now the [poachers] have moved to the northeast [of the New Territories]," she says. "There are still quite a lot of the trees here, but they are being chopped down with fast machines, so probably not for long."

Formerly a language lecturer at the Institute of Vocational Education (IVE), Ho, 52, founded the Association for Tai O Environment and Development in the late 90s, when development proposals for the fishing village on Lantau Island threatened local wildlife. Finding it to be a full-time job, she quit the IVE and now spends her days helping local groups organise and lobby the government on environmental issues.

Sparely funded, Ho's group survives largely on the work of volunteers. Core members spend hours trekking through remote parts of the countryside, pursuing leads. Last year, the AFCD reported more than 70 cases of tree poaching (both Buddhist pine and incense trees), yet her team's findings suggest that this represents just a small fraction of the problem, which they blame on a lack of political will. The government has responded with replanting programmes, with as many as 10,000 incense-tree saplings having been planted in each of the past five years.

Ho remains dismissive.

"It is the old trees that have great ecological and cultural value," she says. "A sapling cannot replace a 100-year-old tree. We must focus on prevention."

at the root of Hong Kong's identity. Local manufacturers sourced agarwood from plantations across southern China - including what is now Hong Kong's New Territories - as far back as the Song dynasty (960-1279) and shipped the timber and joss sticks as far afield as the Arabian peninsula. The resin also supplied the Chinese traditional medicine trade.

New Territories timber was transported by land to what is now Tsim Sha Tsui, and by sampan to Aberdeen harbour for export. It was this trade that saw first Aberdeen, and then the entire island, named "Hong Kong" - meaning "incense harbour" or the more poetic "fragrant harbour". The trade subsided as Hong Kong developed and faster-growing crops and other products became more lucrative.

Even after the trade declined, villagers across the territory continued to plant incense trees as a key species in fung shui woods, which were established for the good fortune of their communities. It is here that some of the oldest wild specimens are now found. Other 100-year-old and 200-year-old trees were once often found next to temples and monasteries.

Part of Ho's work, she says, is reviving these old traditions.

"Many of the farming families are illiterate, so a lot of the stories have been lost," she says. "I'm trying to protect what's still there. I want them to remember the way their ancestors would value these trees, and the way they used to farm them, sustainably."

Another Hongkonger is trying to do something similar, but in a rather different way. Telecommunications pioneer Paul Kan Man-lok owns, in the estimation of experts in the trade, one of the largest collections of agarwood in the world. It is worth "hundreds of millions, if not billions" of Hong Kong dollars, he says. While Kan keeps some of it at home, he also has big hunks of the stuff secreted away on a high floor of an anonymous building, oozing gently inside industrial refrigerators.

Aware that few Hong Kong people have the chance to experience agarwood in its true form, Kan started the Institute of Agarwood, in Chai Wan, and opened the Imperial Museum, in Central.

"Agarwood is an incredible example of nature's bounty and has such an important place in Hong Kong history, and civilisation generally," he says. "You go to Kyoto, you go to Saudi Arabia - all the serious places of worship use it in different ways, as the most expensive offering to God. It was important for me to share that, especially with the younger generation."

By appointment only, the museum reveals a richly scented series of rooms, with thousands of intricately carved religious sculptures, rosary beads and antique perfumes.

"It's like with wine vintages," says Kan, hovering over a series of "sniffable" displays. "The real experts can tell which blossoms grew and decayed near the tree, even which animals defecated there."

The most common misconception, he says, is that all incense trees are valuable.

"It takes time for the antibodies to build up and get really powerful, and this only happens when a tree has been fighting to survive for years, unless you use a special process to infect it," he says, lamenting that too many young trees are poached years before they become valuable.

"It's just such a waste!" he sighs.

incense trees were recognised as being at risk by the International Union for Conservation of Nature. The protection level set by its Convention on International Trade in Endangered Species of Wild Fauna and Flora (Cites) - placing it alongside seahorses and American black bears - restricted its trade and transport and, in 1998, it made the Red List of threatened species. This was great news for the small number of licensed, sustainable plantations that feed the international fragrance market.

Asia Plantation Capital (APC), for example, one of the largest commercial growers of incense trees, estimates the industry is worth between US$6 billion and US$12 billion a year, thanks largely to perfume ranges such as those of Tom Ford, Christian Dior and Fragrance Du Bois.

Yet, the wild trees are also an increasingly lucrative haul and, across Southeast Asia, reports of tree poaching are on the rise. In southern China, in particular, the species has fallen victim to overharvesting and urban development, and with the cross-border trade becoming so profitable, Ho and her team are worried that Hong Kong villagers are getting drawn in.

"The trees are hard to distinguish and the forest areas difficult to navigate," she explains, noting that her team are starting to find red ribbons marking trails or tied around incense trees. "I think the mainland collective definitely has support from the Hong Kong side - people who know the countryside well."

Some have made it clear that her investigations near their villages aren't welcome, Ho says.

Her association is lobbying for involvement from the AFCD - starting with a full mapping of the tree population. Once there is proof that the incense tree is at risk, something Ho claims is often denied by government spokesmen, better monitoring and patrolling can be organised and tougher, specific penalties created for poachers in line with Cites.

the mainland border, Chan Koon-wing shows off a row of incense-tree saplings in what is now the only licensed operation in Hong Kong. Chan moved back from Northern Ireland about five years ago to revive the 10,000-square-metre plant-ation started by his family generations ago, near the village of Shing Ping, near Ping Che.

Known locally as the "agarwood king", he was last month asked by a newspaper to assess a chunk of wood a local fisherman had netted in international waters and - wrongly, according to Chan - judged to be agarwood.

Since reviving the plantation, Chan has made a meagre living, he says, from people who contact him online to buy his harvest of saplings, most a few years old, and worth between US$500 and US$1,000 each.

He remembers hearing about other incense-tree plantations, back in his grandfather's time, "but because the cultivation takes a long time, and the income wasn't so high before, they all decided to cultivate other crops instead", he explains.

Though incense trees have been disappearing from the land around him, he says, his plantation has not been touched.

"Nothing's happened yet," he says, with a shrug, "and sometimes I have workers sleeping nearby."

It was shortly after Chan's story began to surface in the English-language press that APC approached the small-time farmer about a joint venture. The deal would provide the support and expertise needed to develop long-term commercial opportunities, along with 45,000 new saplings, each tagged with a global-positioning-system chip to deter smugglers. The company would also open a tree nursery and a visitors' centre. APC, which owns the patents on a method of resin creation in which incense trees are deliberately infected, also plans to set up Hong Kong's first agarwood distillery in more than a century, to process oud oil (" is the Middle Eastern word for "agarwood").

APC will seek individual investors who can buy rights to the trees and get a share of the profit from oil sold to the perfume market, says business development manager Patrick Yiu. It'll also bring in a perfume expert from Grasse, France, to create a limited-edition scent for Fragrance Du Bois.

While Chan's plantation is too small to generate much profit, says APC sales director Gerard McGuirk, it is in the company's interest to help protect the diversity of incense trees in the wild, which covers a broad range of species across Asia's subtropics.

"The wild trees are extremely important for future generations of the tree as they produce the seeds for future growth," says McGuirk. "So if we can produce more commercial agarwood to try to meet demand, this in turn will ease the pressure on wild trees."

Claiming little interest or skill in business development, and with children who may not take over the plantation, Chan says he is happy to partner with APC as it will allow him to focus on his passion.

"My only concern is growing the trees," he says.

Back at his village house, Chan hands around chunks of mature, resin-heavy agarwood from two large piles. When asked, Chan says the wood is left over from his grandfather's time.

According to recent reports in the Chinese-language media, burglars got away with HK$400,000 in cash and a Rolex watch after breaking into Chan's home. So is the prized wood safe here?

"They didn't take any of the wood," he says, patting a newly installed surveillance system, amid a throng of guard dogs.

Ho, also party to the show, is intrigued but uncomfortable.

"I cannot say where the wood pieces are from," she says quietly, later. "But many seem over 100 years old and I have only seen such trees in the wild."

She says residents nearby have been telling her about fellow villagers illegally harvesting wild trees and asking around for someone who will sell them on the black market.

"The secret worlds of agarwood can be mysterious," says McGuirk, wryly. "Mr Chan is happy to show his world off, but he keeps his cards close to his chest. It's not always clear how it all fits in together."

Ho believes APC's arrival in Hong Kong holds promise for her conservation efforts and that the company has a sincere interest in helping to protect the species in the wild. Staff have consulted her on the local situation, taken the eco-tour and asked her group to contribute material to the visitors' centre. Ho and APC have also discussed working together to mobilise support from the AFCD and the police, she says.

"I think [APC] can help because they have experience protecting trees in Thailand," she says. "So we can work with the government, using their techniques."

Meanwhile, the conservationists' work appears to be paying off. Last month, Secretary for the Environment Wong Kam-sing acknowledged in the Legislative Council that there is no record of the incense-tree population, and that imposing a heavier penalty on their felling "could provide a stronger deterrence, and enhance the protection of incense trees". He also said patrols would be stepped up - something the AFCD says has already happened and Ho's association has long been advocating for.

Although, she says, she isn't counting her chickens just yet, with the guardianship expanding and increased awareness, the incense tree could still be saved from extinction.