The Christmas season may look a little different in the US state of Oregon this year, as extreme heat and wildfires continue to rage across parts of the state, including Jacob Hemphill's Christmas tree farm.

Hemphill, the owner of Hemphill Tree Farm, estimates that he has lost over $100,000 in Christmas trees this year as a result of the recent heat dome event, which saw temperatures of 46C in some parts of the Portland metro area.

The losses will take a toll on his family this year, Hemphill said.

"It'll affect us a lot. I mean, I'm a farmer 365 days a year, that's how I make my income, so if I can't sell Christmas trees, I really don't really put food on the table for my kids. So it's a tough deal."

But he has hope things will improve next year.

"Nothing you can really do. I mean, you just kind of got to roll with the punches.

"And replant next year and plant a few more and hopefully make up for the loss that we're gonna have in the future the eight, nine years from now when the trees were going to be mature.

"That's when they really see the problem."

Beyond Christmas trees, Reuters spoke to several farmers across the Willamette Valley who said the heat wave earlier this year damaged their crops to unprecedented levels.

The so-called Bootleg fire has blackened 157,260 hectares of desiccated brush and timber in and around the Fremont-Winema National Forest, about 300km south of Portland, since erupting 6 July.

Only three other Oregon wildfires over the past century have burned more territory.

At least 67 homes have been destroyed and another 3,400 were listed as threatened, with an estimated 2,100 people under orders to evacuate or be ready to flee at a moment's notice.

The western conflagrations, marking a heavier-than-normal start of the wildfire season, have coincided with record-shattering heat that has baked much of the region in recent weeks and caused hundreds of deaths.

Scientists have said the growing frequency and intensity of wildfires are largely attributable to prolonged drought and increasing bouts of excessive heat that are symptomatic of climate change.

The Bootleg fire is so large that it has at times generated its own weather - towering pyrocumulus clouds of condensed moisture sucked up through the fire's smoke column from burned vegetation and the surrounding air.

These clouds can spawn lightning storms and high winds capable igniting new fires and spreading the flames.