After hearing three weeks of evidence the jury in a ground breaking manslaughter case into the death of a young forestry worker took little over two hours to reach its not guilty verdict.

Paul Robert Burr, 47, was charged with the manslaughter of 20-year-old Lincoln Kidd.

Mr Kidd was crushed by a tree felled by Mr Burr, his boss, on a Horowhenua forestry block in December 2013.

His death is the first such workplace incident subject to a manslaughter charge.

Mr Burr, who was operating a felling machine and did not realise Mr Kidd was standing close to him, also faced a health and safety charge over the death.

In the High Court at Palmerston North today, the jury also delivered a unanimous not guilty verdict for this.

This was greeted with sobs from many in the public gallery.

Earlier, Justice Brendan Brown spent two hours summing the case up for the 11-member jury.

He said Mr Kidd was standing 7m away from Mr Burr as the tree was felled, which crashed to the ground at an unexpected angle.

The Crown argued Mr Burr broke the a "cardinal rule" of forestry in not observing the two-tree lengths rule, which states nobody can be within that distance of a tree being chopped down.

But the Crown accepts Mr Burr didn't know Mr Kidd was so close to him, thinking he had left the felling area.

"[Prosecutor Ben Vanderkolk] suggested there has been a series of failures, oversights and assumptions at the site… and the focus has been on the wrong issue, that is production over safety," Justice Brown said.

He said Mr Vanderkolk identified failures of the company to take all necessary steps to ensure its employees' safety.

They included insufficient high-visibility clothing, lack of radio communication, not following the two-tree rule and Mr Burr's failure to check for workers in the area after a move from mechanical felling to manual and finally back to mechanical.

On the manslaughter charge, Mr Vanderkolk had said Mr Burr's actions were not a "simple" or "trifling" departure from the standard of care expected, but a "major" one.

"He argued that what elevated the conduct in question to a 'major departure' was ill-discipline."

Defence lawyer Jonathan Temm criticised both the state of evidence offered by the Crown and the WorkSafe NZ investigation.

"He submitted that what happened here was an accident and it was time to close the page," Justice Brown said.

Mr Temm also argued that because Mr Burr didn't know where Mr Kidd was at the time of the fatal felling, his company didn't either, so he could not be guilty of the health and safety charge.

"If Lincoln Kidd was there behind the Volvo [felling machine] of his own volition, that's doing something completely unexpected then how could Mr Burr -- that is the company -- know that," the judge said of Mr Temm's argument.

Mr Burr didn't give evidence at the trial, but Justice Brown told the jury not to read anything negative into that.

The judge took the jury through the legal aspects of the case, saying he disagreed with some of the defence's comments on the health and safety charge.

Justice Brown also mentioned some of the unknowns, such as how long Mr Kidd was behind the felling machine and what he was doing there.