What is a Timber Inventory?Many timberland owners, as well asprofessional foresters, think timberinventory is a method used to deter-mine how much timber is in a givenarea. However, a timber inventory actu-ally includes not only the amount, butalso the type and spatial location oftimber currently standing on a timber-land parcel. Determining a timberinventory is complex because of thespatial extent over which a timberinventory is found, and because eachindividual tree is a unique organismwith unique size and product charac-teristics. Thus, special techniques havebeen developed to help professionalforesters obtain estimates of currentstanding inventory.

Unfortunately, not all timber inven-tory estimation techniques and appli-cations are created equally. In fact, it isfair to say that some timber inventoryestimates that result from ill-advised or

inappropriate timber estimation tech-niques may be of less value than notimber inventory information at all,since poor timber inventory informa-tion can lead to poor timber manage-ment decisions.

The requirements for timberlandowners who want to make appropriatetimber management decisions in anobjective fashion herein assume thatthe timberland owner wants to earnreturn on invested capital, eventhough he or she may also want to pur-sue other objectives as well, such asrecreational activities, improvedwildlife habitat, etc..

Important Timber InventoryPointsTo help make timber managementdecisions, timber inventory informa-tion is required at certain points in thelife of a timber stand as describedbelow.

Professional foresters usually makeuse of a sampling approach at each ofthese inventory points (Shiver andBorders 1996). Useful sample designswill make use of sample informationobtained from many different loca-tions in a stand. The sample locationsare usually distributed across the standon some type of a sampling grid. Thatis, a starting sample location will beestablished near a stand corner andthen additional locations will be identi-fied by following a pre-defined com-pass bearing to define a sample line.Within this sample line, additionalsample locations will be established ona given interval (e.g. every 150 feet).When the forester runs into the edgeof the stand, a new line will be estab-lished by traveling a pre-defined dis-tance 90 degrees from the originalsample line. Sample locations will thenbe established on the new sample line,and the entire stand will be sampled ina similar fashion resulting in a grid ofsample locations established across thestand.

Regeneration Inventory The objective of a regeneration inven-tory is to determine if the regenerationprocess has been successful. A timber-land owner can perform his or herown check on regeneration success inboth planted and natural stands. Inplanted pine stands, it is important todetermine if enough stems have sur-vived the first growing season so as toeventually produce a viable stand.Usually, a minimum number of stemsper acre is defined to produce a viablestand. For example, we may plantapproximately 550 trees per acre (8-foot spacing within rows by 10-footspacing between rows), and, if we have

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Timber Inventory: Managing Timberlands in theSouthern U.S.Bruce E. Borders and Barry D. Shiver

W hat is your current timber inventory? How many pine sawtimber stemsare currently growing on your property? Where are they located andhow much are they worth? How many pre-merchantable pine stands

do you have on your property? How old are they, how dense are they, how muchcompetition is growing in these stands? When do you expect your pre-mer-chantable pine stands to be ready for a fertilization treatment or a woody releasetreatment or for a first thinning? How many stands of timber do you have thatwere thinned in the past three years? Where are they, how much timber volumedo they currently contain, should they be thinned again and if so, when? If youare in the timber growing business, these questions go on and on, and if you can-not answer these questions, you are in the same boat as most timberland businessowners.

Clearly, inventory information is critical to any business that producesgoods/products to sell into the market place. This includes the timber manage-ment/growing business. Unfortunately, obtaining good estimates of timberinventory is a much more complex and daunting task than is estimating invento-ry for a retail establishment. There are certain points in the life of timber standsthat are important inventory points, and there are established methods forobtaining inventory information that timberland owners can discuss with theirforesters.

at least 300 trees per acre survivingafter the first growing season, we willassume the stand to be viable.However, if we have fewer than 300trees per acre surviving, we may notbelieve the stand will produce a viablestand, and hence we will need to re-plant during the next growing season.

A very simple way for a landowner toget information to make this decisionis to walk through the stand and countthe number of live and dead stemsfound in various areas throughout thestand. It will become evident veryquickly whether a landowner is findinga significant number of dead seedlingscompared to live seedlings. In theexample of wanting at least 300 liveseedlings per acre, we would have tofind at least 6 out of every 10 seedlingsalive. If we only finds 2 or 3 out of 10alive, we have a pretty good indicationthat your survival is not as high as wewould like, and hence we may have toreplant. A similar walk through can bedone following natural stand regenera-tion. However, in natural stand regen-eration we are looking not only for ahigh proportion of live seedlings, butalso an even distribution of liveseedlings throughout the stand.

If the landowner hires a professionalforester to carry out a regenerationinventory, the professional forester willmake use of some type of sample.Below are questions that landownerscan ask foresters concerning a regener-ation inventory, as well as some guid-ance as to the appropriate answers tothese questions:• What size and shape sample plot will

be used?Circular or rectangular fixed area sampleplots of at least 1/50th of an acre in size.Bigger plots are even better. Most foresterswill not usually use a fixed area plot larg-er than 1/30th of an acre for regenera-tion surveys.

• How many sample plots will be usedand what is the average number ofacres represented by each sampleplot?

One sample plot per 2 or 3 acres is usual-ly the highest intensity sample that will beused in a regeneration survey. Usinglower intensity samples than this mayresult in very poor quality informationand may not pick up relatively large areaswhere survival is poor.

• What is the estimated sampling errorfor the estimate of surviving stemsper acre?A sampling error of 20 percent and loweris good. If possible, a relatively high inten-sity of sampling is also desired.

Post-Crown Closure/Pre-First ThinInventoryIn planted southern pine stands, thisinventory will often occur between theages of 8 and 12 years. In naturalsouthern pine stands, this inventorywill occur closer to 15 to 20 years. Theobjective of this inventory is to helpdetermine if the stand is in need ofsome type of cultural treatment andwhen the stand should be scheduledfor a first thin operation. It is best torely on a forester for this inventoryinformation. The forester will be ableto judge the vitality of the stand andthe nature of competing hardwoods soas to help the landowner decidewhether the stand should be fertilizedor considered for a hardwood controltreatment using herbicide. In addition,the forester will apply a samplingdesign that will provide estimates oftrees per acre, basal area per acre, anda stand table (number of trees per acreby diameter class). A professionalforester would then plug this data intoa timber management planning toolsuch as the SiMS 2006 timber growthand yield stand simulator (ForesTechInternational, LLC, www.forestech.us).

Questions a landowner should askthe forester about this inventory infor-mation:• What size and shape sample plot will

be used?Usually, a fixed area sample plot of1/40th of an acre or larger should beused. If smaller sample plots are used, the

estimates may not be representative of theconditions in the stand.

Note that foresters should not use asample “point” for this inventory.There are many reasons for this, notthe least of which is that “point” sam-pling will not work well in these rela-tively young stands. You can also askthe second and third questions dis-cussed above for regeneration invento-ries. The same answers apply in gener-al. However, to help make appropriatethinning decisions, it may be prudentto try to achieve sampling error of 15percent or less in terms of basal areaper acre.

Post-Thin InventoryFollowing a thinning operation in astand, it is wise to obtain a new inven-tory. This inventory helps the landown-er know whether the logger carried outthe inventory in the appropriate fash-ion. More importantly, it will providethe information necessary to plan thenext thinning operation or final har-vest. Again, using the service of a pro-fessional forester when obtaining thisinventory information is advisable. Theobjective of the inventory is much thesame as the post-crown closure/pre-first thin inventory: estimates of treesper acre, basal area per acre, a standtable, as well as estimates of standingtons of various products (e.g. pulp-wood, chip-n-saw, sawtimber).

Questions a landowner should askthe forester about this inventory infor-mation:• What size and shape sample plot will

be used?Usually, a fixed area sample plot of1/20th of an acre or larger should beused. Sample points can also be used atthis inventory point. A Basal Area Factor(BAF) 10 or 20 sample point can be usedwithout too much problem in these post-thinned stands. Note that you can alsoask the second and third questions dis-cussed above for regeneration inventories.The same answers apply in general.

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However, to help make appropriate futurethinning or final harvest decisions, itmay be prudent to try to achieve samplingerror of 15 percent or less in terms of basalarea per acre.

Mature Stand Thin/Final HarvestInventoryThis inventory point is that which mostlandowners have the most experience.It is the time at which the value ofstanding inventory is being estimatedfor sale purposes. As such, it is veryimportant to use the services of a pro-fessional forester, since fair marketvalue of the timber will be determinedfrom this inventory.

Questions a landowner should askthe forester about this inventory infor-mation:• What size and shape sample plot will

be used?Usually, a fixed area sample plot of1/20th of an acre or larger should beused. Sample points can also be used atthis inventory point. In fact, point sam-

pling carried out by an experiencedforester is the preferred sampling methodin mature timber. If the expected basalarea in the stand is above 120 squarefeet, a BAF 20 sample point should beused, otherwise a BAF 10 sample pointcan be used. Note that you can also askthe second and third questions discussedabove for regeneration inventories. Thesame answers apply in general. However,if the timber is very valuable, it may bewise to use as many as one sample pointper acre. Additionally, when the timber isvery valuable, sampling error of 10 per-cent or lower can help insure that fairmarket value is well established.

SummaryManaging timber in a fiscally soundway requires timber inventory informa-tion. This information helps thelandowner make well-informed deci-sions about cultural treatments, as wellas thinning and harvest decisions. Thecomplexity of timber inventory usuallyrequires the assistance of a profession-

al forester.

About the AuthorsBarry D. Shiver is a partner withForesTech International, LLC, aforestry consulting and software devel-opment firm. He is Emeritus Professorof Forest Management with theWarnell School of Forestry and NaturalResources at the University of Georgia.He can be contacted atbshiver@forestech.us or through hiswebsite: www.forestech.us. Bruce E.Borders is Professor of Biometrics andForest Mangement with the WarnellSchool of Forestry and NaturalResources at the University of Georgia.He can be contacted at borders@warnell.uga.edu.

Literature CitedShiver, B.D. and B.E. Borders. 1996.

Sampling Techniques for ForestResource Inventory. John Wiley &Sons, Inc. New York, NY 356pp.

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