When Should Timber Be Harvested? Here’s What to Consider!
By far, the most important decision any timberland owner can make is whether to harvest the timber on their property. There is no other decision that will have a greater affect on the present and future of their forest and the returns (financial, recreational, or otherwise) it will provide. Unfortunately, there is no easy answer to when timber should be harvested, and it can be a complex judgement to juggle various values at hand. Despite this complexity, the optimum timing of a harvest and the necessary considerations should be a prime familiarity of every landowner serious about forest management.
To better analyze this issue, let’s look at the four main factors to consider when deciding whether it is the right time for a timber harvest:
- Standing Volume
- Average Stem Diameter
- Growth Rate of Standing Timber
- The Benefits of a Harvest for the Forest
Now let’s look more closely at each factor and see what’s involved in each and why they play a role in determining when timber should be harvested.
Standing Volume
One of the most basic factors one should consider when determining whether a harvest is appropriate is the standing volume of the land–how many cords per acre are there? In short, the more wood a stand of timber has, the more likely it is that a harvest is appropriate. This is because volume can be a proxy for stocking levels and density and the potential economic viability of a harvest.
Trees act similarly to vegetables in a garden. If garden bed has too many beets, growth gets choked out. Likewise with trees, if there are too many cords per acre, it can be indicative that the stand is over-stocked. If this is the case, growth can stagnate, and it can be more beneficial in the long-run to remove volume via harvesting. Of course, how this harvest should be done and what the objectives are depends on other factors (which we will explore later).
On the lower margins of stocking, however, (and particularly with thinning treatments) volume metrics help determine whether a harvest is even feasible. Timber harvesting is an expensive proposition, and loggers have to make a living. Moving logging equipment to the jobsite can alone cost thousands. Add to that fuel and labor costs, and one can understand why there must be enough timber to make a harvest economically feasible. If there is too little timber to harvest, it may not be possible for loggers to cut it at a cost-effective level. Typically speaking, fifteen cords per acre is a minimum level for a feasible harvest, with exceptions of course.
Average Stem Diameter
More important for harvest economics, however, is the average stem diameter. On every level of the forest supply chain, larger wood is more valuable. On the harvesting side, larger wood is easier to process and requires less machine movement per unit of wood (It may take only three trees to equal a cord instead of five, for example). On the sawmill side, larger trees are more versatile and can be used for a wider range of products. A five inch tree can only be used to make smaller boards, but larger trees can be used to make larger boards as well as smaller boards, and a certain percent of larger logs can even be sold as valuable veneer if the quality of the wood is particularly high. Moreover, larger logs tend to have better yield, as a smaller percent of overall volume is lost to kerf and slab wood.
It then follows that timberland full of larger-diameter timber is generally going to yield a higher return for the landowner, and thus average stem diameter is a prime consideration for deciding when timber should be harvested. However, because of how mills buy logs, it isn’t a perfectly graduated system whereby every additional inch in diameter will yield you so much more money per unit of volume. Instead, it operates in succinct pass/fail intervals that vary depending on the local mills. For example, once a log passes 12″ in diameter, it could be considered large sawtimber, and every cubic foot of that log will be worth the same as every cubic foot in a 16″ log. However, the volume of the 12″ log may be substantially higher than that of an 11″ log. Graphed out, it may look something like the representation below.
Understanding this principle is crucial for understanding the best time to harvest timber. Using the above graph of value as an example, if the average stem diameter of a stand is 11″, does it make sense to harvest now or wait five more years for that wood to reach the large sawtimber threshold and yield a much higher return for the landowner? The difference in the average yearly financial yield on those two scenarios could differ dramatically. Think first. Cut later.
The Growth Rate of Standing Timber
Deciding when timber should be harvested is also complicated by the variation of a stand’s growth rate through time. It is a common objective in forest management to optimize forest growth rates. After all, what landowner wouldn’t want to grow wood faster? If that is the goal, then the timing of a harvest can be crucial. To understand why, one must understand that the growth rates of trees (in terms of volume) resembles a sigmoid curve, as seen below.
Early in a tree’s life, growth is slow. It simply is not possible for a small tree to accumulate much volume. Even if a .5″ doubled in size in one year, it is still a 1″ diameter tree with minimal volume. As a tree grows larger, however, it can put on substantial amount of wood in a single year, even if the growth rate of diameter slows. For example, a .25″ increase on a 12″ log is a sizable increase to overall volume, despite being only a slight diameter increase. As a tree ages on, however, those diameter increases continue to diminish until the overall volume growth tapers as well, as you can see happening on this century-old black spruce below:
In short: middle-aged trees grow the fastest. To optimize growth rate, timber should be harvested at older ages as growth begins to taper. Harvest too early, and the stand will be sent back to the beginning, stuck in lower growth rates for quite some time. Harvest too late, and you risk the stand stagnating, producing little timber and little value.
Unfortunately, it can be difficult to determine a stand’s exact growth rate, but tools like increment borers can help you analyze rings without felling a tree, and qualitative observations, such as bark furrowing and crown size can give clues to a stand’s life stage (with proper experience).
The Benefits of Harvest for a Forest
Finally, the most important consideration of all: Will the forest benefit from a harvest? Forestry is always a long-term investment, and so timberland owners must always be looking toward the future. Thus, the most important consideration is whether a stand could benefit from silvicultural treatment, whether in the form of thinning, clearcut, or shelterwood. First though, to understand more about silviculture and how harvesting can be used to help a forest, it may be helpful to read our article on the different types of logging.
Are the trees still young, but over crowding and choking each other out? The stand could benefit from a thinning to make a small return for the owner and greatly increase the growth rate of residual timber.
Is the stand healthy and valuable, but becoming too mature and stagnating? It may be time to create a shelterwood harvest to regenerate the stand and promote the future growth of the most valuable species.
Is the stand unhealthy or full of less-valuable species? Is it an old plantation that is reaching maturity and ready to be replanted? A clearcut may be the answer.
Along with being the most important question, it can also be the most complicated. It is not always clear if a stand can benefit from timber harvest, and if so what the harvest should be. It can even take foresters years in school and on the job to get the hang of it, so don’t beat yourself up if you still have questions after reading this short article.
Deciding to Harvest Timber Is a Big Step
If there is one take away from this article, let it be this: Deciding that it is time to harvest the timber on your property is a major decision with great implications for the present and future returns on your investment. Mistakes are common, and there are no do-overs. To ensure the best outcome for your land (and your pocket) consult with a trained professional forester. Not only will they be able to walk you through whether your timber is ready to be harvested, but they can help you negotiate timber sales contracts and ensure that you get the best price for your wood, along with other crucial services. Nonetheless, landowners should seek to understand a reasonable amount about the practices on their land, so I am glad you are here!
Forestry is more art than science, in truth, and there are never easy answers in the world of art. Experience is crucial, and given the stakes at hand, you don’t want to have any regrets. Contact a forester. You will be glad you did.
