Merchantable volume vs. standing volume: what's the difference?
A cruise report and a carbon project baseline can both report "volume" for the same stand and land on different numbers, neither wrong. The gap is usually that one is standing volume and the other is merchantable volume, and the two answer different questions.
Standing volume: everything on the stem
Standing volume is the total wood volume of the trees on a tract, measured stump to tip or stump to a fixed top diameter, before anyone deducts for cull, rot, breakage, or sweep. It's a biological quantity, not a market one. A cruiser working up gross cubic volume by DBH class, or a growth-and-yield model running a stand table forward ten years, is working in standing volume. So is a carbon accounting method: aboveground biomass and the carbon stock derived from it are built on total standing volume, because a sequestered ton doesn't care whether the stem it's locked in would ever clear a sort yard.
This is also the number a height-based volume model produces. A canopy height surface gives you tree height and crown structure across a stand; regressed against local volume equations, that becomes a standing-volume estimate for the whole polygon, not a mill-ready figure. That's useful for a REIT reporting standing timber value across a portfolio or a developer documenting stock change for a project area, and it's a different deliverable than a cruise built to spec out a sale.
Merchantable volume: what a buyer will actually pay for
Merchantable volume is the share of standing volume that clears a utilization standard set for a particular sale or market: a minimum DBH at breast height, a merchantable top diameter (often 4 to 6 inches outside bark for pulpwood, higher for sawtimber), minimum log length, and a defect deduction for cull, fork, and crook. Cut a sawtimber sale to a 6-inch top and you leave standing volume in the tops and in the understory stems that never made the cut list. Shift the utilization standard to pulpwood and the merchantable figure climbs because more of the stem, and more of the stand, qualifies.
Stumpage is priced against merchantable volume, by product class, species group, and log grade, because that's the volume a mill or a buyer scales and pays for. Change the merchantable top diameter by two inches and the volume on a sale can move by double-digit percentages without a single tree being added to or dropped from the stand. That's the number that belongs in a timber sale appraisal or a harvest schedule.
Why the split matters for reporting
A REIT carrying standing timber value on the books and a carbon project developer reporting stock change are both working from standing volume, converted to biomass and then to carbon with a standard factor, independent of what any particular buyer would merchandise out of the stand. A harvest plan or stumpage appraisal needs merchantable volume instead, net of the defect and diameter limits the sale uses. Running a biomass layer through a merchantable conversion without saying so, or reporting a cruise's merchantable figure as total carbon stock, understates or overstates the number depending on which direction the error runs. Carbon registries and timberland appraisals both want to know which one they're looking at, and auditors ask.
A canopy surface model built from overlapping stereo passes reads standing volume across a holding or project area on an annual cycle, without a ground cruise crew walking every stand first. Get in touch to see how that fits a reporting cycle you're already running.