When beef farmer Graham Freeman planted a small stand of California redwoods in 1983 he never thought he would be alive to harvest them himself.

Sequoia sempervirens are famous for reaching towering heights in the United States and they have not disappointed in northern Tasmania with some estimated to be more than 30 metres high already.

"It was a dream but I never thought I would actually see it," Mr Freeman said.

"Now that these are like this I wish I'd put in 5 or 10 hectares."

It was a sale at the local nursery that led him to experiment with half a hectare of redwoods on an unusable part of his property.

Redwood trees growing in northern Tasmania. ( ABC Rural: Hugh Hogan )

"This was just a steep rocky bank growing basically blackberries and ferns, full of rabbits and wallabies, really pretty useless," Mr Freeman said.

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"The cattle used to walk through, erode the banks and kick out the rocks onto the paddock below."

Now Mr Freeman is harvesting a third of the trees, something he thought only his children would be able to do.

"Just to open it up and give the rest a chance to improve their growth rates and put on a bit more," Mr Freeman said.

A redwood log being prepared for milling. ( ABC Rural: Hugh Hogan )

This will allow the rest of the trees to keep growing at a faster rate, and new sprouts will grow from the stumps to be harvested many years from now.

Mr Freeman said he could not bring himself to harvest them all, having grown fond of the trees.

"I think they're a friendly sort of a tree, you know, if you can put it that way — I know it's not very scientific."

Onsite milling

David Dean measures a redwood log for his portable mill. ( ABC Rural: Hugh Hogan )

David Dean has worked with many specialty timbers during his 55 years in the forestry industry, but never California redwoods.

"I was just blown away when I saw the age and the growth and the value of the trees," Mr Dean said.

Mr Dean is helping to mill the trees on site with his portable mill.

"I think about helping Graham cut this and looking at what he's achieved as being in Sequoia heaven — it's just a magnificent tree."

The timber is destined for a master builder in Hobart and is fetching $1,400 per cubic metre, but Mr Dean said if dried properly, it could get more than $5,000 a cubic metre.

The men have calculated the growth rate to be 30 cubic metres of timber per hectare per year for the past 36 years.

A redwood log being milled onsite with a portable mill. ( ABC Rural: Hugh Hogan )

Long-term investment

Mr Freeman had also experimented with other higher-value trees such as swamp gums and macrocarpa on his property.

"You can do something on a small area, [a] rough area of your farm that you or your children can utilise at their own leisure," he said.

"Thirty-six years might sound like a long time to get a return but it does go fairly quickly. Once you get older you find out how quickly it's gone past."