Timber stand improvement (tsi) is something I get asked about quite a bit. Allot of landowners hear about it and wonder if they need it.

What is tsi?


Timber stand improvement is really just a heading under which a few different forest management practices fall.

Crop tree release is one such prescription and is a major practice under the general heading of “tsi”.

Crop tree release means, basically, just what it says.

The process is done by selecting certain trees that the forest manager decides to keep, called “crop trees”. These desired trees are then marked with a band of tree paint (Or a big dot on 4-sides.  The dots are usually reserved just on the really big trees, to save paint!).

A look at an iowa woodland showing timber stand improvement and crop tree marks.

Although the red “crop tree paint line” is fading after five years or so, one can still see the chosen crop tree, white oak, in the foreground.


These crop trees are your “keepers” – the one’s you’ll be managing for. Most of the time these are young trees, those that appear in good health, are vigorously growing, and have, at least, good potential for lumber and/or wildlife value.

What crop tree release calls for, then, is to “release” the canopies of the selected crop trees. This means that any and all trees that have a canopy that is within a few feet of the crop tree should be killed.  You heard me right — killed!  This scares the daylights out of some people.  And I know exactly how they feel.  It’s not easy winding your way around a white or red oak with your old Jonsered chainsaw roaring!  It’s especially not easy the first time you do a tsi job.  I mean it’s hard to think about killing good tree species!

But the truth is, one has to kill lots of trees to make room for the fewer good ones that the site can adequately support.  And support in terms of allowing the crop trees to grow to their full capability.  This 4-sided kill “releases” the crop tree to receive full sunlight to all the leaves on all four sides of the tree.  Thus, crop tree release is done to enhance sunlight to the canopies of the chosen trees.

Picture of an Iowa woodland showing Timber stand improvement with a 3 to 4 -sided canopy release.

This photo shows the canopy of the large crop tree in the back right and a now-dead tree in the foreground. The ultimate goal for the woodland manager with crop tree release tsi is a 3 to 4-sided “release” of the canopy around the desired crop tree.


It has been shown that this process can increase oak mast – acorn — production by 7-10-times the normal amount and, also, can increase the speed of growth by up to 2-times that of comparable trees that have not been released.   Crop Tree Management (PDF from ISU) (tons of great Info Here!)

The value of crop tree release TSI is HUGE to most Iowa forestland acres and there is very little, if any, debate in regard to the benefits of crop tree release tsi.

It is a win-win procedure!

A win for the landowner, in terms of forestland value. (And let’s not forget that cost-share dollars are readily available for various tsi procedures across the state — these can pay you up to 75% of the cost to do a procedure!)

And a win for the wildlife, in terms of fruit and mast production.

Not only is forestland mast production increased, but also the ground cover on the forest floor is enhanced via crop tree release.

However, make no mistake, the GOAL of crop tree release tsi, from a pure forestry perspective, is that of enhanced tree value, growth, and mast production, it is really not to thicken ground cover. That is a wildlife goal and is one that just sort of happens by default in many situations when crop tree release is implemented properly.

So the wildlife and forestry managers all get good results through crop tree release, in most cases (If the wildlife goal is not to thicken the understory, though,  crop tree release may not be a wise choice).

Another prescription that falls under the general “TSI” heading is understory release or site preparation for natural regeneration (SPNR)

This practice is specifically done just prior to, or right after, a major tree harvest. The goal here is to get rid of all undesirable small trees and shrubs that exist (example ironwood, young elms, plums, prickly ash, multi-flora rose, Japanese honeysuckle, etc., down to about 1- inch in diameter). These are not desired because they will shade out and kill the growth of any natural, desired, regeneration that exists on the forest floor (seedling oaks, hickory, walnut, etc.,).

To be sure, and as you may imagine, site preparation for natural regeneration is hard work that is very labor intensive. Again, this procedure is usually done only just before or after major canopy, tree-top, areas are opened up from a harvest or other factor (such as wind damage).

Most Iowa woodlands can greatly benefit from some sort of TSI – most commonly the crop tree release procedure.

In regards to the wildlife end of things – and whitetail deer in particular – both TSI prescriptions really provide a boon to deer.

The increase in sun-light coming down to the forest floor after a tsi procedure encourages a thicker habitat – this means more food for deer. It also means more security cover as well! The end result is that the forested acres become more attractive to whitetails at all times of the year – not just when the acorns are dropping. The result is an increase in deer carrying capacity of your property.

And, think about this, if your timber produces 7-10 times more acorns than does your neighbor’s woods, guess where most of the deer will be during hunting season?

Guess where most of the giant bucks will prefer to be?

And, not just because they get more food and cover there but because that is where most of the does are as well. You guessed it – on your land!

Picture of an Iowa whitetail buck.

There is no doubt about it, deer live in the security cover that crop tree release can produce on the floor of the forest. Food and cover resources for deer are both enhanced by the crop tree release tsi procedure.



A picture of an Iowa woodland showing crop tree release and the thicker understory environment that often happens as a result of this sort of timber stand improvement procedure.

Crop tree release tsi often creates a thicker understory habitat which is highly favorable to deer and other wildlife!


Picture of an Iowa timber showing tsi.

Here you can see that it is OFTEN necessary to kill desired species to get higher quality crop trees. A couple of white oaks were killed here that were too closely spaced to the higher quality, and larger, white oak crop tree marked in the center.


Picture of and Iowa woodland showing crop tree release tsi.

It’s easy to see that crop tree release tsi normally results in a thicker understory habitat. The thicker understory habitat provides more food for deer and also better security and thermal cover as well. It also provides a favored nesting habitat for wild turkeys.


No doubt about it – TSI is not only a HUGE boon for your trees but it’s also a HUGE boon to your deer population!  Just to let you know, in case you may be wondering, timber stand improvement in general, and crop tree release tsi in particular, are the first things I do when I acquire a property.  It just makes your property better and more valuable!

Instead of asking why do tsi, the better question is why in the world not do timber stand improvement?

It’s certainly a win-win deal!