Eighty-year-old Rasmia Awase had left the best olive trees until last. She and her family had already harvested most of their crop when they went to a small plot near their home in Luban a-Sharqiya on Saturday morning.

Here were 40 trees that Awase had planted and tended herself, and they were now, two decades later, at their peak – the most productive of all the trees, which support 37 members of the extended family.

But Awase found that someone had got there before them and had chopped down the trees, leaving stumps in the ground and branches scattered about the plot. The family blame hardline Jewish settlers from the nearby Eli settlement.

"I was in shock, I lost my mind," she said. "I planted these trees with my bare hands, I gave them 20 years of hard work – and they are all gone." Each day of her long life was worse than the one before, she said with her eyes watering.

The Awase family are not alone in their experience. Among the tactics used by Jewish settlers this harvesting season are cutting down and torching trees, stealing fruit and attacking farmers trying to pick their crops, according to human rights organisations.

"It has reached a crescendo," said a spokeswoman for Yesh Din, one Israeli group monitoring incidents in the West Bank. "What might look like ad hoc violence is actually a tool the settlers are using to push back Palestinian farmers from their own land."

The upsurge in violence this year is attributed to a rise in settler militancy following the 10-month moratorium on settlement construction in the West Bank and uncertainty about the outcome of the current, although stalled, peace negotiations.

According to Oxfam, which is trying to help Palestinian olive farmers realise the economic potential of their crops, some families are too frightened to pick the fruit. "We have seen a lot of olive groves burning and trees which have been chopped down," said the charity's Catherine Weibel. "People are clearly very stressed and worried, always afraid the settlers are coming."

Olives have been cultivated in the rocky hills of what is now the West Bank for thousands of years. Around 95% of the harvest is used to make olive oil, worth up to 364m shekels (£64m) a year to the Palestinian economy. Most farmers are small scale, growing trees on land that has been in the families for generations.

In recent weeks, there have been numerous reports of trees being stripped of their fruit overnight. Rabbis for Human Rights claimed that the olives from about 600 trees near the settlement of Havat Gilad were stolen before their Palestinian owners could harvest them. Police confirmed they were investigating the alleged theft.

The police had received 27 official complaints about sabotage since the beginning of this year's harvest, said a spokesman, Micky Rosenfeld. Sixteen Israelis had been questioned. "There are a number of ongoing investigations into damage caused in the past few weeks," he said. "We are working to prevent incidents on the ground. This is an ongoing problem that we have to deal with."

Damage had also been caused to Israeli property, added Rosenfeld.

Akram Awase, Rasmia's son, was sceptical about the protection offered by the Israeli police and military. "In the old days the resistance used to stop them [settlers]," he said. "Now there is no resistance, all of them are in jail. You can't do anything. Who do you complain to? The soldiers protect the settlers. They have raped our land and they will never leave it."