ISLAMABAD (Reuters) — Spring has arrived in the Pakistani capital bringing clear skies and balmy weather but for many residents of Islamabad, spring heralds weeks of suffering and for some, it could mean death.Spring brings an explosion of pollen from paper mulberry trees, an east Asian species planted when the city was built in the 1960s that has thrived and infested its open spaces.

The trees produce levels of pollen that experts say are among the highest in the world.

“This is one of the severest forms of pollen allergy ever documented worldwide,” said Mohammad Osman Yusuf, a prominent Pakistani allergy and asthma specialist.

“Many deaths have occurred but unfortunately there is no system of reporting allergy deaths.”

Saeed Anwar, an economist working at an embassy, suffers severely every spring. He said he has known three people who have died as a result of pollen allergy in the past 10 years. “It’s very scary,” he said.

“It gets so bad I can’t breath through my nose at all, no matter how many decongestants and tablets I take. For 40 days I have to breath through my mouth.”

“I have to sleep, if at all, sitting. I can’t lie down. I use inhalers, I’m on medication three times a day.”

Manzoor Wahid has lived in Islamabad for 15 years but it is only in the last four or five that he has suffered from severe pollen allergy.

“Your eyes start burning, you get a lot of nasal discharge and your throat pains as if you’ve got a cactus sticking in there,” said Wahid, a finance manager at a foreign firm.

“The biggest problem is asthma. You wake up in the night and can’t breathe.”

Islamabad was purpose-built in the 1960s, a small city with wide boulevards and plenty of greenery, on the edge of the Punjab plain, up against the foothills of the Himalayas.

Designers planted paper mulberry on a massive scale. The trees were seen as ideal: they grow fast, provide good shade and bind the soil well. And they flourished.

“At that time, the people who were doing it did not know it would become a problem,” says Mazhar Hussain, director of the city’s environment department, who is overseeing efforts to tackle the problem.

The trees showed no mercy on native species. They have conquered most green areas, crowding out local flora and blanketing banks of the numerous streams that flow out of the hills and through the city.

“This is a very aggressive tree. It spreads so quickly. It grows fast and regenerates fast by all means,” Hussain said.

“The result was the number of trees increased in a small area, in one town, and with a lot of production of pollen at one time.”

By the early 1990s, people were wondering what was causing the epidemic of allergies that brought untold misery and filled hospitals every spring. Studies soon determined the main culprit was the male paper mulberry.

At the end of February the pollen from the male trees begins drifting through the air. In March it erupts, producing counts of up to 40,000 pollen grains per cubic metre of air. In the West, a pollen count of 1,500 is considered dangerous, said Shahina Maqbool, medical columnist for the News newspaper who has written extensively on the problem.

“There, it is almost unheard of for people to die of acute respiratory failure due to pollen allergy,” Maqbool said.

“When doctors search medical literature about the cutting of trees as a measure to prevent pollen allergy they find none as Islamabad is unique in its high pollen count,” she said.

City authorities began cutting the trees in the mid-1990s but outraged environmentalists soon halted the campaign.

Caught between the environmentalists and allergy sufferers, Hussain said the city was taking a middle path: “Cutting and replacing with environment-friendly trees in phases, gradually.”

He said 36,000 mature paper mulberry trees had been cut, 14,000 in the last two years.

This year, the city is concentrating on hacking back the mulberry saplings that sprout so prolifically and also produce pollen. Workers have been cutting and bull-dozing, and spraying herbicide on inaccessible stream banks, he said.

“Ultimately, we will have to replace each and every paper mulberry tree in urban areas,” he said.

But for those who suffer, such pledges ring hollow.

“If they gave me permission, and if I had a chain saw, I would start doing it myself,” said Anwar.

“It’s not nice to say, but I’m hoping one of these big decision-makers gets this so they know what we go through. Until that happens, I don’t think there’s much the government will do.”