Controlling Thinning - Some Concepts and Methods

[Peter Smallidge]

The title of this blog is that of the recent webinar by Dr. Ralph Nyland, presented on June 21, 2017.  The webinar is archived at www.youtube.com/ForestConnect and there is a direct link below.

Ralph focused his presentation on three topics. 

1. How much residual basal area (relative density) should you leave during a thinning? The short answer is 60% relative density, allowing regrowth to 80% before thinning again. An option to calculate relative density is provided by a link to an Excel file below, and an associated pdf.  The residual of 60% RD is because above that level there is mortality, though mostly in the lower crown classes. Also, at 60% the stand net production has maximized, so there is no additional benefit. Above 80% RD and mortality begins to appear in the upper crown class. 
2. What trees should be left? Here Ralph emphasized the need to retain upper crown class and vigorous stems.  The first thinning entry should especially remove unacceptable growing stock (UGS), those trees with >25% major branch dead or dying in upper crown, holes in the stem, or fruiting bodies.  Subsequent entry for thinning will continue to remove UGS, but there will be fewer to remove. Ralph explained how lower crown class trees will show improved growth as a residual, but that the rate of growth will be significantly less than the growth for upper crown class trees. 
3. What methods are used to allocate the cut? The basic approach is crown thinning, removing some codominant crown class trees, but not exceeding 35% of the basal area. Leave dominant crown classes and codominants of good form, striving for uniform spacing. Thinning from below is another option if there is a market for small diameter stems. Ralph shared a study of simulated forest stand response to diameter limit cutting as compared to thinning from below, and reported the thinning from below averaged about 1.25 times better yield over three cutting cycles.

Included below are links to provide downloads of (1) the Excel file that calculates relative density with both a NY and PA version, (2) the pdf that explains the Excel file, and (3) a pdf of the webinar. These materials are all provided courtesy of Dr. Nyland.  The PA version is used when the basal area of black cherry and white ash are greater than 50% of the stand

The direct link to the thinning webinar is HERE. It is worth noting that Dr. Nyland has given several webinars, which can be found by searching at www.youtube.com/ForestConnect ;

A word or two (or three) about the files to download. 

1. The webinar presentation is provided as parts 1 and 2.  The file was too big to upload to this site.
2. The instructions are important to download and read.  Page 1-47 give the background on stocking charts and relative density. Pages 48 - 57 guide you through the use of the Excel files.  Pages > 58 guide you through using the output of the Excel file for stand thinning prescriptions.  
3. Use the NY version if the total basal area of black cherry and white ash is less than 40 to 50 sq. ft.  Use the PA version if the total basal area of cherry and ash is greater than 50 to 60 sq ft.
4. Download the files by clicking on the hyperlink.  I suggest you save them to a folder named something like "Nyland Original Thinning Excel Files."  As you use them, you can copy and work with the copy just in case something goes awry.  You can always come back to the blog to recover the original files.
5. The first tab of the Excel file includes INSTRUCTIONS.  The instructions discuss how to manipulate a less than current version of Excel.  In the current version of Excel, those details are not applicable. The tab for FIELD DATA includes the species codes that are necessary to assign species to their respective group.
6. Practice with the practice data file (below).  Enter your personal field data in an Excel file and then copy into the NY or PA file. Don't enter field data directly into the program file.
7. After data entry, go through the tabs as described on the INSTRUCTIONS page.  Click the "calculate" buttons and the calculated data will populate the appropriate fields.  Check the practice data against the pdf for instructions to ensure you are working the file correctly.  Short answer, from SUM tab is that total basal area is 136.01 and relative density is 96.13.
8. Save the file and your work as "SAVE AS" and select Microsoft Excel Macro Enabled (or something similar).  

Attached Files to Download:

Webinar presentation  Part_1_webinar.pdf   Part_2.webinar.pdf

Instructions - calculating relative density  Calculating_RD_Prescriptions_Excel

Practice data set - practice.data.hbg97.xlsx

Excel Worksheet for NY  Excel(old).NY.xls  (Read instructions. Save as "macro enabled" then enter data)

Excel Worksheet for PA   Excel.PA.xls