Romain Jacquet-Lagrze trains his camera on high-altitude spaces in Mong Kok, To Kwa Wan, Quarry Bay and Sai Wan for his new photo book, Echoing Above. For the French photographer who has lived in Hong Kong since 2009, it is in these old and congested districts that the city's tall and colorful buildings truly come alive - a bit like protagonists in a drama that also includes the trees, birds and menial laborers at work around them.

"The facades are uneven, with architectural elements or air conditioners sticking out, offering birds a space to land and scatter seeds that might later sprout a plant, eventually spreading its roots across the concrete," the photographer says. Once such a parasite becomes large enough to put the building on which it grows at risk, bamboo scaffoldings are constructed to remove them. "Then another bird will come, bringing seeds of a different tree, and perch on another building facade close by. It's like an echo of life, sounding in different parts of the city over a period of time."

The Chinese banyan, raising its head through cracked concrete, appears in several photos. "Its roots absorb water from the humidity in the air," says Jacquet-Lagrze, explaining why banyan plants growing from cornices are so ubiquitous in the urban areas of Hong Kong. "Its fruits delight the birds, and they help scatter its seeds everywhere. It only needs to find a tiny crevice on a wall in order to thrive."

Among the photos included in the book, one of them, 29 Fort Street, which shows plants sprouting from the walls of high-rise apartment blocks in the foreground and the tiny figure of an air conditioner repairer perched outside a window far away in the distance, comes across as particularly poignant. There are a number of pictures showing bamboo scaffold builders at work. Holding On to the Rope illustrates the risks involved in the job. Jacquet-Lagrze says that he thought it was important to document workers in the process of erecting bamboo scaffolds, especially seeing that Hong Kong's Development Bureau is in favor of phasing out this centuries-old construction technique.

Jacquet-Lagrze is also interested in how birds live in Hong Kong's forest of skyscrapers. He has photographed sparrows, spotted doves, red-whiskered bulbuls, red-billed blue magpies, black kites and the critically endangered but relatively abundant in Hong Kong, yellow-crested cockatoo. Echoes of Flight captures a flock of birds soaring against the backdrop of a red high-rise building, conveying a spirit of freedom while creating a striking contrast of moods and colors.

Jacquet-Lagrze says most of the time he is exploring the relationship "between a complex built environment and the life it shelters". He counts Fan Ho, known for his compelling black-and-white photos of Hong Kong street scenes in the '50s and '60s, and Greg Girard - who captured the dark underside of the Kowloon Walled City from 1986 to 1993, when it was pulled down - among his inspirations.

"Echoing Above offers a beautiful exploration of the often-unseen life in the spaces high above the ground in Hong Kong, inviting us to look up and discover a new perspective," says Sarah Greene, founder of the Blue Lotus Gallery, where a selection of photos from the book was exhibited in May. "Having worked with Romain for the past 15 years, I continue to be impressed by his ability to capture the essence of this city in fresh and surprising ways."