If you are looking to buy timberland or are analyzing the potential return on a timber harvest, a prime question is how much wood there is on an acre of land. While there is a tremendous amount of variation, the average acre of forest land in the United States contains 15.7 cords (or 39.3 tons) of standing timber, growing at a rate of .59 cords per acre per year. These numbers, mind you, do not represent the maximum amount of timber that can grow on an acre, merely the average stocking level encompassing forest stands of all ages. Moreover, regional stocking levels can vary dramatically based on the forest biomes, species, and local harvest activities. Nonetheless, these numbers can be a useful starting point for finding how much wood is on a given acre of land.
To better understand how to answer the question, let’s first look into state-specific data.
Average Amount of Wood Per Acre by State
The above map is based on US FIA data for 2019. Looking at the state averages for timber stocking, clear trends can be distinguished. In the humid, deciduous regions of the US east, stocking levels run around 15-20 cords an acre with higher levels in states with less harvesting activity. In the central and western united states, however, there is far less wood per acre on average. This is partially do to smaller tree sizes, but also a drier climate conducive to fire regimes that create low-density timber stands. On the west coast, however, large, towering trees combined with more temperate climates create the conditions for stocking levels far in excess of what can be found elsewhere, particularly in Washington.
Likewise, there are some regional anomalies. Are the forests of Massachusetts sufficiently more productive than Maine that its forests hold twice the volume? No, of course not. Instead, Maine simply has younger forests. Massachusetts’ forests are more urban and locked in smaller tracts that do not see much (if any) timber harvesting. Maine, however, has a robust forest economy, and it is rare to find a forest that has not been logged at least once in the past 40 years. Thus, Maine has less cords per acre on average.
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Wood Volume Per Acre for a Given Stand
Of course, looking at state averages may not be incredibly useful if you are looking to find how much wood is on a specific acre of land, as extreme variability will make an average fairly useless and misleading. In the words of Nassim Taleb, “Never cross a river that is on average 4 feet deep.”
Luckily, we have volume tables that can help you determine the cords per acre for your forest.
To use these tables, you will need to know two pieces of information: the average total height, and the basal area per acre (which you can learn to measure here). Keep in mind also that while these provide only estimates of total volume and may not accurately represent the true amount of wood on a piece of land, and of course, every acre will vary substantially.
How Many MBF (Thousand Board Feet) Are on an Acre?
So far we have been talking in terms of cords, which is strictly a unit of volume, but what about yield? In most cases, the determination of value on an acre of timber comes from how many board feet of lumber there are on that acre. Because board feet are a measurement of yield, it is highly dependent on the quality of the timber. Nonetheless, we have the below chart to help us estimate based on the square feet of basal area and the average number of logs in each tree.
To learn more about merchandizing trees to determine the number of logs, we have an article on the subject here.
Average Forest Growth Rates
As important as knowing the volume per acre is the growth rate per acre. If an acre currently holds 20 cords, that’s great, but it doesn’t tell you how long it took to get there and how much wood will accumulate in the future. Thus, standing inventory is only a small part of the equation. Once the growth rate is determined, the picture becomes much more complete.
Like standing inventory measurements, averages can be misleading for growth rates. Species, site quality, and management practices can all create large variations. However, growth rates are more difficult to measure than standing volume, so using an average is probably a good idea, provided you understand the margin of error.
Looking at the map above, you can see clear patterns. In the southeast, where growing seasons are long and plantation forestry dominates the industry, growth rates are some of the highest in the country. In the northeastern deciduous forests, growth is slower but more consistent and less variable. Out west, growth rates are largely a function of moisture levels.
To learn more about forest growth rates and some of the factors that affect them, we have an article here.
How Many Cords Per Acre Are Needed to Harvest?
Determining the minimum threshold for a harvest is difficult. Cords per acre is an important metric for the economics for a harvest, but it is by no means the definitive metric. The problem with looking solely at volume is that it says nothing of the size of the wood or the rate at which it is growing. One could have 15 cords per acre locked in densely-packed 4-inch diameter trees that no mill would buy (and no logger would cut). Likewise, you could have 7 cords an acre of low-density, massive pine with a clean understory that would be the dream of any old-school chainsaw logger. And what if those pine are still growing quickly? Does it make sense to harvest?
To determine when to harvest, one should look primarily at a mix of four factors:
- Standing Volume
- The Growth Rate of the Stand of Timber
- Average Tree Diameter
- The Benefits of a Harvest for the Land
That said, we are talking about standing volume here, so as a general rule of thumb, the minimum amount of wood needed to harvest an acre of land would be the average standing volume for that area. A stand that is stocked at “below average” levels is likely too young or otherwise too low density. A stand that is average or above is likely better suited for a harvest. But remember: In forestry, the exception is the rule.
Timber Inventory Can Be Tricky
While these averages, rules of thumb, and volume tables are a usable and effective way to get a quick estimate of how much wood is on a given acre of land, it should be remembered that timber inventory can be tricky business. In fact, forest mensuration is an entire field of study with as much nuance as one can imagine, and it can take a long time to understand that nuance. In fact, in my time in the forest industry, I have seen firms hire teams and spend hundreds of thousands to answer the simple question of how much wood is on their land–only to come up with an extremely rough estimate that proved to be fairly inaccurate. In any case, as long as you understand the limitations of your data, the information here can give you usable (maybe even excellent) estimates of your own standing inventory. Use it wisely! If you want to learn more about forest mensuration and how to take proper volume estimates in your forest, Get our free guide with the link below:
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