This report is based on an article written by Ron Wenrich. Ron is a sawmill consultant and has extensive knowledge on how to inventory your forest using the point sampling method. It is written in three parts, this being the first part, and all links included were chosen by the editor.
For a timber cruise, other equipment besides the angle gauge will be needed. I like to do a systematic cruise where plots are taken at regular intervals throughout the stand. In addition to an angle gauge, a compass, and a property map, something to accurately determine diameter should be taken along. I will show you how to determine and find your points or "plot centers" later.
Each plot will represent a 1/10 acre sample. I generally do a 10% sample and take point samples at 200 ft intervals. This is a little better than a 10% cruise, but it is easy to plot on a map and is easy to locate on the ground. For a 10% sample, every acre will need 1 plot. A 5% cruise can be taken by taking point samples at 300 ft intervals.
There is no need to run cruise lines through fields or other treeless areas. It is also best to cruise when leaves are not a factor - spring and fall are best. Each plot will take about 5 to 10 minutes to locate and record, depending on conditions of both the area and the cruiser.
For point location, I use a compass and pace system. But before starting it is important to know how many paces you take to make 100 ft. To do this, measure 100 ft on a level surface. Simply walk the distance to find how many paces it takes to complete 100 ft. (some people use 66 ft. or a chain compute their grid using a chain length). When pacing it is important to remember that you are measuring level distances. On slopes, you will have to take a few more paces to find your level point.
The more severe the slope, the more paces that are necessary. Brushy conditions will also make it necessary to slip a few paces, since your gait will be altered. Walking downhill will cause your gait to be longer, so not as many paces will be needed to compensate as walking uphill. Accuracy is not factor in plot location, so if you're off, it won't impact your results.
Ok, let me get back to establishing points on which to take your plot information. Before the cruise, you will need to establish where your points are to be placed. Make a map of the property or you can use aerial photos. From a known starting point that can be found on the ground, start to run north-south and east-west lines in a grid at every 200 ft. for a 10% sample. Where the lines intersect is where the point samples are to be taken.
Successive plots do not have to be all in one line. Turning to get a plot is helpful and should be used where there are natural obstacles, such as wet areas, etc. For the actual cruise, it may be useful to take some sort of staff along to keep track of your plot center. Ribbon can also be used. I always take it down when done with the plot.
Starting at your known point, run your line to your first point. Along the way, you can mark on your map, anything that is of notice, such as a stream, road, fence, or timber type change. This will help if you are making a type map or are writing a management report. At the first point, take your angle gauge and count the number of trees that fall into your plot. For each plot, take note of each counted tree by species, diameter, and merchantable height.
Diameters should be tallied by 2" diameter classes. Tree form may also be noted. Any pertinent information should be noted before moving on to your next plot. I also note any trees that I would remove at each point. This can be used as a preliminary cruise for harvesting. Keep each plot information separate. After all the lines are run, you will have a complete map of your property. Just connect where roads, fences and other occurrences intersect.
Ronald D. Wenrich is a sawmill management consultant from Jonestown, Pennsylvania, USA. This Penn State graduate has logged timber, inspected treated forest products, been a mill foreman, procured wood, and is now a sawmilling specialist and consultant.