JERUSALEM — The trees on the Mount of Olives can withstand a lot — heat, drought, insects, even the occasional fire.

But the phenomenon known as the "grazing pilgrim" can raise an arborist's ire. When tourists trek to the area, linked in tradition to the crucifixion of Jesus, many can't avoid the temptation to pluck a souvenir.

"The branches, people will just rip them off," said Hans Mackrodt, the gardener in charge of the olive groves outside Dominus Flevit Church on the Mount of Olives. "I come over and say, 'Please don't do it — give me those and leave the grounds.' And they say, 'Why?' "

Tending trees that are such a deep part of Christian tradition might seem a delicate task. The sloping groves on an East Jerusalem hillside, just outside the walls of the Old City, are mentioned several times in the Old and New Testaments. They hold a particular importance for Christians as the place where Jesus often walked and where, in the nearby Garden of Gethsemane, he was betrayed on the eve of his crucifixion.

But, Mackrodt said, the horticulture is the easy part. Olive trees are well evolved for the local soil and climate. They are hardy by nature, and so far no outside pests have arrived to threaten them, he said.

A little extra water helps if the summer is particularly dry, and he likes to use a bit of fertilizer. Other than that, the only issue is whether to prune the trees so that the branches grow horizontal to the ground or up a bit into a ball shape.

He favors the horizontal method, on the grounds that it provides more shade and allows an easier harvest.

Mackrodt, who works with orchids in Germany and recently helped at a fruit orchard in Ecuador, arrived here five months ago to re-landscape the area around the church. He said he had to rehabilitate soil that had become "like concrete" and prune some of the trees for the first time in many years.

But the real challenge is how to keep the tourists in line.

Good Friday was particularly daunting. Jerusalem and the Old City teem with religious visitors during this time of year, in town to walk the Via Dolorosa and see other religious sites.

With streams of people coming in the gate of the small Dominus Flevit sanctuary, the chance to take home a piece of the Holy Land was too much for some to resist. Olive branches peeked from back pockets and purses as they walked out.

One tour group of about 20 bypassed a fence, walked into the olive grove and sat down for worship.

"What's that?" Mackrodt asked an assistant.

"They're reading the Bible," the assistant said.

"They can't do that. The soil is going to get compacted," Mackrodt said, rushing over to shoo the group to a nearby set of benches. Compacted soil, he explained, means rainfall doesn't soak to the roots of the trees.

Down the hill a bit, at the Garden of Gethsemane, the gnarled olive trees are surrounded by a gate that largely shields them from grasping hands. But attendant Suheil Bitar pointed to one or two that still get plucked — though they are among the younger trees in a grove whose roots date to the time of Jesus.

"It's happening all the time," he said, "We tell them, 'There is not going to be anything left.' "