What percentage of the tree's mass is usually left in the forest after harvest?

[forestfan]

I saw a report claiming that 50% of the total biomass from a tree is left behind when standard logging practices are used.

Does that align with what you've seen?

What do you think are the main factors that would result in more or less of the tree's total biomass being either harvested or left behind?

Are the answers to these questions significantly different in some parts of the world versus others?

[beenthere]

Main factor would be money. Value of the material left in the woods will not pay its way out.

Are you working on a thesis in college?

 

[Kodiakmac]

That 50 percent figure sounds like something that would be tossed out by tree-huggers to paint us as wasteful knuckledraggers.  Maybe they're counting the stump and root system along with the trimmings.

[barbender]

 I would think that 50% is pretty accurate in some cases. There's a lot of variables though. In my experience, densely grow conifers leave a lot less slash than big hardwoods. But even with a mature red or white pine, there is a lit of biomass in the limbs and top. 

 It will depend on how the biomass is being measured, as well. Volume or weight?

 Another side to this is that much of the biomass that is left on site, is where all the nutrients are stored in the tree (limbs and bark). With all of our biomass plants shutting down its become a moot point, but the State if Minnesota's timber sale contracts specify a percentage of biomass that must be left and distributed evenly on the site, as they don't want all of the nutrients being stripped.

[barbender]

 Harvesting method will make a big difference in the percentage of merchantable timber vs slash/biomass left on site. I've had  several foresters male the "complaint" that cut to length logging always throws their cruise off. Say they cruise it at 600 cords, and it cuts 640 cords. It's easier to recover more of the small diameter wood with a ctl processor, so the yield of recoverable wood goes up. 

[barbender]

 Then there's whole tree chipping. Kinda hard to beat their recovery rate☺️

[forestfan]

Thanks all.

Main factor would be money. Value of the material left in the woods will not pay its way out.

Are you working on a thesis in college?

 

I'm not working on a thesis. Just curious about bioenergy, and whether any technology/policy changes make the business cases any more viable nowadays than in the past (I'm aware they haven't been the most successful).

How common do you think it is for logging companies to gather up slash and chip it up and trucking out?

I would think that 50% is pretty accurate in some cases. There's a lot of variables though. In my experience, densely grow conifers leave a lot less slash than big hardwoods. But even with a mature red or white pine, there is a lit of biomass in the limbs and top.

 It will depend on how the biomass is being measured, as well. Volume or weight?

 Another side to this is that much of the biomass that is left on site, is where all the nutrients are stored in the tree (limbs and bark). With all of our biomass plants shutting down its become a moot point, but the State if Minnesota's timber sale contracts specify a percentage of biomass that must be left and distributed evenly on the site, as they don't want all of the nutrients being stripped.

What are you referring to when you say biomass plants are shutting down? Are you talking about biomass energy plants, and if so, what regions?

[forestfan]

Then there's whole tree chipping. Kinda hard to beat their recovery rate☺️

In what parts of the world would this happen? What types of wood, and for what purposes do the chips get used for?

I'm surprised to hear this is a thing because I thought wood chips are usually one of the lowest value forms of wood, and that trunks and larger branches could usually be processed into higher value shapes (boards, etc).

[forestfan]

Harvesting method will make a big difference in the percentage of merchantable timber vs slash/biomass left on site. I've had  several foresters male the "complaint" that cut to length logging always throws their cruise off. Say they cruise it at 600 cords, and it cuts 640 cords. It's easier to recover more of the small diameter wood with a ctl processor, so the yield of recoverable wood goes up.

What does "cruise" refer to in this instance? And ctl processor?

And what do you think are the common harvesting methods these days?

[Kodiakmac]

The only things left behind on local clearcuts are stumps, sawdust, and the odd scraggly sapling. 

[barbender]

 I'm in northern Minnesota. We had 3 or 4 biomass fired energy plants that were started with government grants, and that were more or less government subsidized. Legislation was passed taking away the subsidies, and all of the plants shut down immediately. 

 On to whole tree chipping- on lower value species, some would be whole tree chipped for the biomass plants (fuel, or "dirty" chips). Other species are chipped for pulp production, those chippers are set up to produce clean chips. 

 Sometimes a job is set up to sort higher value "roundwood" like saw logs, and then chip the rest.

 A cruise by a forester is a survey and estimate of timber volume on a site.

 CTL= cut to length. This is a logging system that uses two machines, a harvester and a forwarder. The harvester fells the tree, delimbs and has computerized measuring for diameter and length. Different products are cut and sorted from the tree, right at the stump. The forwarder follows behind, and uses a hydraulic crane to load the wood and haul it out to roadside where transport trucks can access it. 

 Harvesting methods are varied depending on location and markets. 

[Magicman]

Remember that part of the mass that is left behind returns to the soil as nutrients, so what may seem like waste is not necessarily so.  Also the tops tend to shelter and protect new saplings as they take root and grow.  They also serve as water barriers and protect the soil from fast runoff.

I know that I would hate to see 100% of my forestland completely utilized and bare.