Mean Annual Increment (MAI): What It Is and How to Use It
Mean annual increment (MAI) is the average volume a stand has added per hectare per year, from planting to the present: MAI = total volume ÷ age. It is expressed in m³/ha/year.
It is the single number that summarises site quality, species, genetics and management. A poor unmanaged site might run under 5; an excellent site with matched fast-growing material can exceed 30.
What MAI Means
If a stand holds 105 m³ per hectare at age 7, its MAI is 105 ÷ 7 = 15 m³/ha/year. That does not mean it grew 15 m³ every year — growth is slow at first, accelerates, then slows again. MAI is the average across the whole life so far.
MAI vs CAI
| Mean annual increment (MAI) | Current annual increment (CAI) | |
|---|---|---|
| Measures | Average growth over the whole life | Growth in this year alone |
| Formula | Total volume ÷ age | Volume this year − volume last year |
| Behaviour | Rises, peaks, then slowly declines | Rises fast, peaks earlier, then falls |
| Used for | Comparing sites, planning yield | Deciding when growth is slowing |
How Rotation Age Is Set
The MAI–CAI crossover
- Early on, CAI is above MAI — the stand is growing faster this year than its lifetime average, so the average is being pulled up.
- Later, CAI falls below MAI — this year's growth is below the average, so the average starts falling.
- The point where CAI crosses MAI is where MAI peaks. That age is the rotation of maximum volume production.
- It is the theoretical optimum for producing the most wood per hectare per year over the long run — but it is not automatically the most profitable rotation.
Why the financial optimum usually differs. Maximum volume is not maximum value. If larger diameters command disproportionately higher prices — as they do for sawlogs and premium timber — it can pay to grow beyond the MAI peak. Conversely, if capital is expensive or you need cash flow, cutting earlier can be right even at lower total volume.
Typical Values
| Situation | Indicative MAI (m³/ha/yr) |
|---|---|
| Poor site, unmanaged, mismatched species | Under 5 |
| Average smallholder plantation, partial weeding | 8 – 15 |
| Well-managed eucalyptus on a good site | 20 – 30 |
| Exceptional site, matched clonal material, full management | 30 – 40+ |
| Pine on a reasonable site | 10 – 20 |
| Teak | Lower — long rotation, high value per m³ |
| Slow temperate hardwood | 2 – 8 |
These are broad bands, not predictions. MAI varies with rainfall, soil depth, species, genetics, spacing and above all first-year weeding. National yield tables for your species and site class always beat a generic figure.
Want a real MAI for your stand rather than a band? That needs measurement.
Using MAI Properly
- It is a stand-level figure. Do not apply it to individual trees.
- It assumes even growth across the block. Real stands are patchy — better on the mid-slope, worse on the ridge — so a single MAI hides variation that matters.
- It gives total volume, not volume by grade. Price is set by grade. Two stands with identical MAI can be worth very different sums.
- Comparing MAI across species is only meaningful alongside value. A fast species producing low-value wood can lose to a slower one producing premium timber.
- Use it for planning and comparison. Use a measured inventory for selling.
Frequently Asked Questions
What does mean annual increment mean?
The average volume a stand has added per hectare per year since planting: total volume divided by age, expressed in cubic metres per hectare per year.
It summarises site quality, species, genetics and management in one number, which is why foresters use it to compare sites and plan yield.
What is the difference between MAI and CAI?
MAI is the lifetime average — total volume divided by age. CAI is current annual increment, the volume added in this year alone.
CAI peaks earlier and falls faster. Where CAI crosses below MAI is the point at which MAI peaks, and that age is the rotation of maximum volume production.
What is a good MAI?
It depends entirely on species and site. A well-managed eucalyptus plantation on good ground commonly runs 20–30 m³/ha/yr; average smallholder plantations sit nearer 8–15; pine typically 10–20.
Slow temperate hardwoods may only reach 2–8, but produce far more valuable timber per cubic metre.
Should I harvest at the MAI peak?
That is the rotation of maximum volume production, but not necessarily of maximum profit. If larger diameters command disproportionately higher prices, growing beyond the peak can pay.
Conversely, if capital is expensive or you need cash flow, cutting earlier can be right even at lower total volume.
How do I find the MAI for my plantation?
Measure standing volume through systematic sample plots and divide by the stand's age. That gives a real figure rather than a band from a table.
Published national yield tables for your species and site class are the next best thing, and always beat a generic figure from a website — including ours.
Get a Real Growth Figure
Published bands are for planning. Selling, financing or valuing needs a measured inventory of your actual stand.
Over a decade establishing, measuring and managing eucalyptus, pine and indigenous plantations across Uganda. Based in Wakiso, Kampala. Reviewed and updated September 6, 2026.
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These apply the same way in any country.
