How to Use Plot Hound for the Most Accurate Estimates of Merchantable Height

When you cruise with our Plot Hound app, you have the option to record a “Merchantable Height” for each stem. The purpose of this post is to explain how we use that value in our volume reports, so you know how the merchantable heights you report affect the final data.

If you’d like to receive volume reports, contact us and we’ll get started setting you up right away.

In developing Plot Hound, one of the biggest challenges SilviaTerra faced was determining how best to handle ‘stopper’ heights in hardwood trees. Unlike conifers, which typically have a predictable growth form (mostly straight and up), hardwoods have a lot more branchiness. Botanically, this is the difference between excurrent and decurrent growth.

From a forester’s perspective, the highest possible merchantable height would be the height where the stem tapers to the minimum usable diameter for your product. (For example, the merchantable height for pine pulpwood would be the height at which the diameter tapers to 4”). However, in reality, true merchantable height is only as high as the stem goes before it becomes too branchy to produce a log of sufficient quality for your product. On decurrent hardwoods, this is often well below where you’d like it to be.

If you record a merchantable height for your tree, we treat that as a hard ‘stop’ in our virtual bucker (that system is described here).  We don’t calculate any volume for that particular stem above that height. So, if the stem is only going to be used as a sawlog, merchantable height should be recorded as the top of the sawlog. However, if the stem is going to be used for both sawlog and pulp log, the merchantable height should be recorded as the top of the pulp log (the higher of the two numbers).

If you don’t record a merchantable height, what happens?  For softwood species, we simply calculate the taper-based merchantable height and stop computing volume at the minimum diameter for the product.  

For hardwood species, because so many hardwoods have a true merchantable height well below the calculated merchantable height from the taper equations (due to branchiness, top breakage, and all of the other reasons you might record a lower merchantable height in the wood) we calculate a shorter merchantable height for each hardwood stem and ‘buck’ to that point instead.

The merchantable height we use for hardwood volumes is calculated from stem diameter and total height. We predict a variable ratio of merchantability calculated from a large dataset of hardwood stems on which both merchantable and total height were measured. This ratio is applied to the measured (or predicted) total height for that stem to get the merchantable height used in volume calculations.  We’ve found that the estimates of merchantable volume for hardwood stems and hardwood stands using this approach are much closer to published studies and foresters’ expectations than when we rely on taper equations alone to estimate the upper point of merchantability for a hardwood stem.

To sum up: Plot Hound reports the most accurate estimates of merchantable volume for hardwood stems in your cruise when you record a merchantable height for each stem. If you don’t, our process for estimating it has you covered! If there are other heights you need, such as stopper heights for a single product (such as sawlog height in a stem that will be used for saw and pulp), use the ‘Notes’ field to record that information.

Don’t forget to contact us before your next cruise to set up volume reports!

Volume Calculations and Rules, Part 3: SilviaTerra’s Volume Calculation Method

Volume Calculations and Rules, Part 3: SilviaTerra’s Volume Calculation Method

In the first post of this series, we discussed log rules in overview, and in the second we reviewed the shortcomings of form classes and why individual tree volume equations are preferable. Make sure to check those out, if you missed them.

This third part will highlight the methods and advantages of SilviaTerra’s volume calculation method - specifically, how our individual tree volume calculation methods are designed to save you time and energy.

At SilviaTerra, we use flexible, segmented equations for tree taper. Using the data you collect during your cruise, we fit a unique equation for each species you identify. Our team designs these equations to most closely represent the shape and taper of the specific trees from each cruise. This means that the equations will fit the trees in your stand, specifically. There’s no faster or easier way to get the highly reliable, customized volume estimates you need.

We’ve made it easy for you to record data while on your cruise. Our free app, Plot Hound, is available on the Appstore and Google Play. Its user friendly interface makes data entry quick and painless, and the app connects directly to our volume calculation system for automatic upload.

The more data you collect on your cruise, the better, but we use available historic data on similar trees in nearby areas to make estimates for measurements you don’t provide. For example, if you record the height, total or merchantable, for a particular stem, we will use the value you provide. But, if some of the stem measurements you record do not include a height measurement, we fill in the gaps using data from similar trees in your stand, and with historic data from similar nearby stands. This provides the most accurate estimate available.

When we receive your data, we analyze it to get a sense of your stand, especially the diversity of species and stem sizes. We compare what you’ve collected with data on the same species growing in similar conditions (such as stocking, location and species distribution) in nearby areas. Most of this data is publicly available from the U.S. Forest Service. Using their data provides us with more data points and allows for a more robust, and therefore more reliable, equation. The end result is a high-quality, custom-fit taper equation for every species in your stand.

Using these equations, we calculate volume on a stem-by-stem basis. We virtually ‘buck’ each measured tree into logs for the product or products that it may produce, based on the merchantability specifications you provide. Our system is designed to compute volumes in whatever units you need- cubic feet, tons, or board feet (International, Scribner, or Doyle).

The best part is that we’ve recently updated our system to get the results back to you more quickly than ever! Within a few hours, you’ll receive a free report on your data, organized into easy-to-understand tables.

If you need data analysis, we also offer more in-depth volume reports, which provide a summary of volumes by species and product, based on the ruleset you provide. Let us know ahead of time if you’d like to receive them so we can set you up in our system.

Plot Hound is the solution to your volume calculation needs. Give it a try! To learn even more about Plot Hound, click here. Please don’t hesitate to contact us if you have any questions or would like to receive our in-depth volume reports.

That wraps up our series on volume calculations and rules! We hope it has been a valuable resource for you.

Check back soon! We have more content and some exciting announcements coming just around the corner that you won’t want to miss. Subscribe to our blog or follow us on Facebook to stay up to date.

The Best Hardware for your Timber Cruise with Plot Hound

Plot Hound is a great app for collecting cruise data in the field. It’s free to collect data, so all you need is a standard consumer phone or tablet and you’ll be all set up. Today will focus on the tablet side. But which tablet should you buy for you and your team?

The first question to ask is whether you prefer Google Android or Apple iOS. Android devices are typically a little cheaper, but there’s also some really cheap Android hardware out there that will affect how Plot Hound runs and could affect the accuracy of the cruise. We really recommend sticking to our recommendations, if you go the Android route.

Because all iOS devices are made by Apple, we can guarantee that Plot Hound will look and work great on your iPads. And if all your team currently uses iPhones, then iOS would be a great way to go.

iOS Recommended Hardware

Since Apple owns this space completely, there’s not a big surprise we’re recommending iPads here. But which versions?

We recommend two Apple tablets in this space whose main difference is size and portability. If you prefer a larger screen, we recommend the Apple iPad Air 2. With its 9.7 inch screen, you’ll have a lot of real estate to enter your cruise data and check your maps. You can buy it straight from Amazon for around $450 with Wi-Fi connectivity.

But if portability and price are more important than screen size, we recommend the Apple iPad Mini 3. Its 7.9 inch screen is still big enough to easily collect data for a cruise. You can buy it straight from Amazon for around $370 with Wi-Fi connectivity.

Android Recommended Hardware

Our favorite tablets here are the Nexus line straight from Google. If you buy a Nexus tablet, you know that you’ll always be able to update the tablet to the latest supported version of Android, and that means that Plot Hound will always be the best it can be on your device.

The current Nexus tablet is the Nexus 9. Its 8.9 inch screen makes for easy data entry while still being very portable. You can buy the Nexus 9 straight from Amazon for about $375.

If you’re on the price conscious side, we also recommend the older Nexus 7. An investment in this hardware won’t last you as long as the Nexus 9, but if you need a cheap option now, the Nexus 7 is a great way to go. It’s not in production anymore, but it will still do a great job running Plot Hound. You buy the Nexus 7 straight from Amazon for between $150 and $250, depending on the exact technology specs.

And finally, if you’re willing to spend a bit more on your hardware, and you want a good rugged tablet, we recommend the Cedar CT7 rugged tablet. You can buy it straight from Amazon for $900. If you often find yourself dropping your cruising gear in a swamp, this could be a great tablet for you.

The question of whether “rugged” hardware is worth the additional cost and weight is really a matter of personal economics. Standard commercial products are often sturdy enough, and cheap to replace in the off chance that something goes wrong. However, if the cost to have increased assurance that you wont have a day ending event(e.g. tablet in water, or dropped on a rock) is $500 extra dollars - if you cruise more than 30% of your working days, and the loss of a day (or day’s data) is the loss of $500 worth of work - then “rugged” may be well worth it. We’ll explore this question more thoroughly in a forthcoming article!

Bonus Recommendations

There are a couple other products that make for better cruising with Plot Hound. Here are some other quick hit recommendations.

• These are products that can help  improve your devices GPS information and extend the battery life of your device in the field.
• Dual Electronics XGPS150A Universal Bluetooth GPS Receiver
• Garmin GLO Portable GPS

• These cases are cheap and will offer some protection out in the field.
• Rugged Case for your Nexus 9
• Rugged Case for your iPad Mini 3
• Rugged Case for your iPad Air 2
• Sometimes, glare can be tough when you’re using these devices in the field. Anti-glare screen protectors help keep the screen grime free in the field and cuts down on the sun’s reflection.
• Anti-glare Screen Protector for your Nexus 9
• Anti-glare Screen Protector for your iPad Mini 3
• Anti-glare Screen Protector for your iPad Air 2

Volume Calculations and Rules, Part 2: Individual Tree Volume Calculation Methods (and Why We Don’t use Form Classes)

Individual Tree Volume Calculation Methods (and Why We Don’t use Form Classes)

In our previous post, we reviewed the four primary logrules and explained the strengths, drawbacks, and best uses for each method.

Today, we’re going to explore the differences between estimating tree volume based on form classes and calculating the volume of trees with individual tree equations.

Some of the log rules we discussed in our last post can be easily converted into tables that will give an estimate of volume based on the diameter and length of the tree - no math required. For these tables, height is typically measured in bolts (8-foot length of tree stem) or logs (16- or 32-foot length of tree stem); however, more exact units (paired with more precise tables) may also be used. The log scaling tables themselves are often included on cruiser sticks for making fast and easy estimates while on a cruise.

Form classes:

As we discussed in the last post, some logrules take tree taper into account, while others do not.  For the logrules that do account for taper, ‘form classes’ have been developed to estimate volume based on typical tree taper for that region. The form class, also called a form quotient, is a ratio. Typically this is the ratio of dbh (diameter at breast height, 4.5 feet above ground) to inside-bark diameter at the top of the first 16-foot log, usually measured at 17.3 feet above the ground.

Photo credit: Travis Pond

Girard form class values (also called Girard-Mesavage, or Mesavage-Girard), the most commonly used in the US, were first developed in the 1940s by James Girard and Clement Mesavage of the US Forest Service. In order to use a Girard form class correctly, one must first estimate the total diameter of the tree at the end of the first log (the aforementioned 17.3 feet above ground), and then estimate how thick the bark is. Even the correct usage of Girard form classes are, at best, an estimate based on an estimate and are therefore inadequate.

This problem is amplified because the actual trees in any particular stand may deviate from the regional form classes, especially when comparing trees of different ages or species. Furthermore, volume measurements calculated by a combination of logrule and form class are based on the unfounded assumption that all stems will taper the same way above 17.3 feet. That is seldom the case. When these problems are taken together, it’s easy to see how significant errors can slip into volume estimates based on form class.

Individual tree equations:

In an effort to combat the errors that creep in using form classes, much research has been done over the past seventy years into equations that can describe the taper of individual trees, rather than assuming they are all alike. This trend has increased as technology has made the computations easier. Many of these individual tree equations use the same predictors as the lookup tables described previously- dbh and total height, but may also include height at the merchantable limit, diameter at 17.3 feet, and crown class. ‘Segmented’ equations are the best and most versatile of the individual tree equations because they break the tree into multiple sections that taper at different rates. This results in even more accurate calculations.

These individual tree taper equations are so useful because of their flexibility. In this paradigm, volume tables are based on a pre-determined set of merchantability requirements. As markets change, so do merchantability specs. It may become necessary, for example, to incorporate the grade of lumber, or mill output reductions due to log defects, in a calculation. This type of consideration could require several different tables to estimate, but a flexible taper equation is a lot more helpful in this endeavor than a form class equation. For example, it can  return an estimate of length at a set minimum diameter, or be used in conjunction with an individual tree volume equation to determine a more precise volume estimate for a stem by taking size, species, and local market requirements into consideration.

SilviaTerra’s volume system leverages large amounts of publicly available forestry data in conjunction with local cruise data to develop species and stand-specific volume coefficients which we can use to accurately estimate stem volume in any units required. These estimates may not match the values from a Form Class table, but, for all the reasons listed above, our numbers are more in tune with local variability and, therefore, more accurate.

That’s the basics of the differences between form classes and individual tree volume calculations. But there’s still so much to cover! Be sure to check back soon for our next blog post, in which we will go into more detail about the SilviaTerra volume calculation method.

Volume Calculations and Rules, Part 1: Log Rules in Overview

Over the next few posts, we’ll be diving into the wonderful world of log volume calculations. In this first post, we’ll provide a brief explanation of the four main log rules, or methods for determining log volume, as well as the primary strengths, drawbacks, and uses of each method. We know it can be hard to keep track of it all, so we’ve tried to simplify and summarize them in a way that makes sense.

Our hope is that this information will help you to be better informed when presenting the results of a cruise to a client, selecting a log rule for your next project, or even just getting to know your field better!

Tons and cubic feet

The first method is to estimate the volume based on weight, which is measured in tons. This method is usually employed when trying to determine the volume for pulpwood purposes, though used for sawtimber in some regions. It can also be useful for carbon accounting or other, non-lumber calculations. In this method, the tree or log is measured for length and diameter. These numbers are plugged into an equation (some treat the log as a cylinder, some as a cone, and some a combination of both), which yields an approximation of volume in the units of tons or cubic feet.

The next three log rules share a common volume unit, board feet. You probably remember that 1 board foot is equivalent to a 1”x12”x12” board. This makes it really easy to compare results from the different calculation methods, as the output units are the same.  These rules were originally developed to estimate mill output from standing timber or logs, and were used to guide sales.  Most were developed regionally, for specific mill and forest conditions, and continue to be used today despite advances in milling technology and more precise inventory methods.

Doyle

The Doyle log rule is widely used in many parts of the country because of its simplicity and versatility. It uses an equation to calculate board feet based on the length of the log and its diameter at the small end. The equation does not account for the taper of the log or saw kerf. Because of this, and the nature of the equation, volume estimates tend to be too low for small logs and too high for larger logs. However, the effect will basically cancel itself out in a stand of diverse age and size, so the total volume estimate will be fairly accurate.

Scribner Decimal C

The Scribner log rule works best for conifers and other tall, straight trees, so it is most commonly used in the Western United States. It’s very easy to use, because it doesn’t take things like the taper or species of the tree into consideration. It only needs the length and diameter of the tree, which corresponds to a point on the table that shows the approximate volume. Behind the scenes, the Scribner Decimal C log rule is a variation of the Scribner rule that rounds to the nearest 10 board feet. It also compensates for a ¼” saw kerf in the final product.

Photo credit: Charlie Houder.

International ¼”

The International ¼” log rule is the most accurate rule out there. Like the Doyle log rule, it uses geometric equations to determine the volume. The reason it’s so much more accurate is that it calculates the volume based on four-foot sections, while also accounting for the ¼” kerf. This significantly reduces the errors caused by tree taper, which can crop up in the other methods. 

Variations of this rule allow volume calculations for sections of differing lengths, but it can be very time-consuming to make all those calculations without an efficient, automated system.

It can be very challenging to determine which log rule is right for your project. Sometimes, regional variations or tree type will make it clear which rule is preferable, and sometimes the organization you are working for will demand a certain rule to be used, so it’s important to be familiar with all of them.

The good news is, here at SilviaTerra, we can do them all! We’ve specially designed our volume system to be 100% compatible with each of these main log rules, which makes your life, and your organization’s work, that much easier.

For more information, we recommend visiting the Dictionary of Forestry from the Society of American Foresters. They go into a lot of depth and get down into the nitty-gritty of the terms and definitions we’ve used here. The information in this post was drawn from Forest Measurements by Avery and Burkhart, and the aforementioned Dictionary of Forestry. We also recommend you check out this resource from Purdue University if you want to study log rules and log scaling in more detail.

Now that we’ve got the basics of log rules down, be sure to check back soon for our next post in the series, where we will dig into individual tree volume calculation methods and begin to discuss form classes.

Merging vector features in QGIS

QGIS is a free and open source geographic information system. At SilviaTerra, our clients often need to merge features in their vector files by metadata. We use QGIS to do this quickly and easily.

For example, this shapefile has 25 stands.

However, each has one of four values for its WTS_STAND metadata column.

We will merge them into four stands, one for each WTS_STAND value. Click Vector -> Geometry Tools -> Singleparts to multipart

For the Unique ID field, select WTS_STAND.

Click OK, and you're finished!

Volume reports are back and better than ever!

We are excited to tell you that we have just finished switching Plot Hound volume reports over to a more localized and more accurate volume calculation method. If you’ve submitted a volume report in the past few weeks, you may have noticed that it took a long time to get the report back.  We’d like to thank you for your patience. Reports are not only back on track now, but better than before! The long explanation for what we did, and why it matters for you and your work, will be discussed in blog posts for the rest of this year. If you have any questions about your new (or old) reports, send us an email or leave a comment below!