What is a Forest Inventory?

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What is a forest inventory?  Why should you inventory your property?  What kinds of information do you need from an inventory?  Whom do you ask for assistance in cruising your forest property?  This article will help you to answer these important questions. 

A forest inventory or cruise determines the location of timber and estimates its quantity by species, product potential, size, quality, or other characteristics.  
A cruise may be conducted for land acquisition or sale, a timber sale, or other objectives. 

A cruise can also assist in assessing other forest values such as wildlife habitat (mast, crops, snags, wetlands, dens, nests, thickets, etc.), watershed, recreational opportunities, or other management opportunities that exist on the property.  

Why Should You Cruise Your Property? 
The reasons for conducting a cruise vary among landowners, and these reasons are dictated by the goals and objectives landowners have for their properties, financial or otherwise.  Some common reasons why landowners cruise their forest lands are: 

  • To provide a basis for evaluating present conditions
  • To provide a basis for future resource planning

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Forestry Services 

Prior conducting the inventory/cruise you should at least have experience with the following: 

1Land Measurements 

  • chaining horizontal distances
  • pacing horizontal distances
  • using a compass
  • using topographic maps
  • a simple closed traverse
2Measuring Standing Trees 
  • tree diameters
  • tree heights (merchantable vs. total)
  • tree age
  • tree form expressions
3Volume Calculations 
  • using yield and volume tables
4Sampling and Estimation 
  • statistical concepts
  • common sampling designs

5Estimating Site Stocking and Density   

Before the Cruise 

There are some things that you should do before the cruise to make sure all the background information is in order. 


Get a Map  
If you don’t already own a map of your property, get one.  Your county courthouse, library, or a surveyor’s office are good places to find the information needed to obtain the appropriate map which shows your property.  If your property is small, the section of the map showing your property can be blown up to a more convenient scale. 

Do Some Recce  
Dig out your records and make sure that the location and size of your area are clearly specified.  Walk the boundaries as they are described on the map and be certain that they are clearly marked.
 

Take a few days to go trekking around with the map, a compass, and some field guides on the plants and animals of your region.  Note any specific details such as water bodies, large trees, wildlife habitat, hazards, or any other sites of significance on the map.  After a thorough informal survey, write a brief description of your findings. 

Compartmentalize the Land  
If your forest property is large (over 300 acres) and contains several different forest types based on site characteristics, species, and stage of tree growth, it may be necessary to organize your property into specific compartments or management units.  Why would this be necessary? 

  • Some stands require specific management activities.
  • Some stands have greater timber-producing potential than others.
  • This makes it easier to keep financial and work-progress records.
  • It may be necessary to keep records for tax purposes.

Aerial Photographs 

An aerial photograph of your land will help you determine the types of forest communities you have and to organize your property into compartments if necessary.  

Sample Size  

The purpose of the cruise is to find out what you own.  This could be done by measuring every tree on your property, but it is often more economical to measure an adequate sample of the trees.  Make sure that the sampling percentage is large enough to give you a reasonable estimate.
 

The size of the sample will depend on the total area, the purpose of the inventory, and the species, size, distribution, and value of the timber.  In general, a comprehensive inventory requires a 20% sample for areas under 300 acres, and a 10% sample for areas larger than 300 acres. 
Information 

Once the sampling system is determined, it is necessary to decide how much information to gather.  In other words, what do you want to know about your land? 

If you wanted to know how many stems of pine regeneration or a particular wildlife food plant there are per acre, the cruise must show how many stems of the plant there are at each plot sampled.  For this type of measurement, it is often helpful to divide each plot into quadrants and sample smaller vegetation in terms of percent cover.  This information can be used to describe the overall structure of the understory vegetation, which can be translated into wildlife habitat conditions. 

Other Information


Growth Projections 
Another important part of some cruises is an evaluation of growth rates for projection of future tree sizes and volume.  Growth rates can be determined by using an increment borer.  A few trees in each diameter class should be sampled by counting the number of growth rings in the outside inch of the borer sample for each sampled tree. 

For example, if there are two rings in the outside inch of a borer sample, it took two years for that tree to acquire an inch of radial growth

Soil 
An important part of the cruise is an evaluation of the soil.  The productive capacity among different soil types is variable.  Some acres may produce twice as much wood volume as others, and recognizing this could offer you excellent opportunities.  

The measure of soil capacity is called site index.  Site index is the total height (in feet) to which the dominant trees in a timber stand will grow in 25 or 50 years. 
 

For example, an acre with a site index of 90, base age 50, will grow a stand of trees in which the dominant ones will be 90 feet tall at age 50.  Terms and ages vary with species and geography but the principle is always the same. 

Written Report  

The cruise should include a written report on stand conditions, particularly for areas that need cultural treatments or are ready for harvest.  These areas should be shown on the map. 

The information gathered in your cruise may shape the goals and objectives you formulate for your forest land.  The broader the range of information you get in your cruise, the richer an understanding you will have of the conditions on your property.  This understanding will help you make sound decisions about the long-term management of your land. 
After the Cruise 
When the cruise is complete you need to make sure that the information is complete according to your objectives. 


The following records should be at hand

  • a description of the sampling system (technique, sample size, parameters)
  • a copy of all field measurements
  • a summary of tables, by compartment, of tree sizes and stocking
  • a resource analysis report including a map
  • estimates of resource value
  • cost estimates for all phases of the inventory

The storage of this information is as important as the information itself.  Make sure you have all computer files backed up and all hard copies duplicated and filed in a safe place. 

Concluding Remarks 

Keep in mind that a cruise will be most helpful if: 
  • it yields enough information for you to make sound decisions about the long-term management of your forest land;
  • it is accurate;
  • the information from the cruise is accompanied by descriptive, qualitative information;
  • the information is available for future reference.

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For correction and improvements please use the comments section below.

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