3-1 Old Growth

Measuring Old Growth Forest

How much old growth forest did we actually lose in the past few hundred years? How much was lost in your state? In this investigation, you can use image analysis software to determine the percent loss of old growth forests over time by analyzing the four maps on the previous page.


  • AnalyzingDigitalImages software (java version) from the GSS download page. Originally, there was a separate software called ForestAnalysis, but that software was incorporated into AnalyzingDigitalImages, but only the java version, not the Xojo version.
  • The images (Hint: Click on each image below to open a full-size version in a new browser window.  To save the images to your computer, Right-click or CMD + click the full-size image, then choose "Save Image As...")

What to do...
1. Launch ForestAnalysis. See “If You Don’t Have the Software...” section below*, for strategies of how to do “Forest Analysis” without software.

2. You'll find that it is a single-purpose program that allows you to explore the amount of old growth forest lost across the country according to the maps on page 25. The software allows you to draw a box in any area of the map and simultaneous identical boxes are drawn in the other 3 maps, with percentage of old growth shown for each near the bottom of the computer display.



Get TIFF format


Get TIFF format


Get TIFF format

Get TIFF format

Remaining Old Growth Forests. The shaded areas in the illustrations on this page show the remaining old growth forests in the United States in 1620, 1850, 1926, and 1990. Each dot represents an area of 25,000 acres of old growth forest. (Data are from Paullin, Charles Oscar, Atlas of the Historical Geography of the United States, Edited by John K. Wright, Greenwood Press, Westport, Connecticut, 1932, 1975; Findley, Rowe, and Blair, James P. "Will We Save Our Own? National Geographic, vol. 178, no. 3, September, 1990, page 120; and the Wilderness Society.


3.1 How much old growth forest was lost in your state?

3.2 How does your state compare with other states in terms of amount of old growth forest lost?*

3.2 How does your state compare with the national average and to other states in terms of amount of old growth forest lost? Since you are restricted to rectangular boxes which can't match most state boundaries, your measurements are necessarily approximations.

3.3 Which state lost the least old growth forest?

3.4 How much old growth forest was lost in your region, in a particular size box around your city or town?

3.5 Compare the loss of old growth forest in a particular size box around your city or town with that of identically sized boxes around cities or towns where you have friends, relatives, or a city/town that interests you.

3.6 Are there any areas that had an increase in old growth forest during a particular time? If so, how could this happen?

3.7 Prepare a written statement summarizing your findings and be ready to present it to your classmates. 

3.8 What additional questions come to your mind that you cannot answer with the data given? Write these along with your summary statement.

* If You Don’t Have the Software...
You can still do analysis by superimposing a grid over the maps and counting number of grid squares that have old growth forest in a particular region of interest. Some grid squares will be only partially filled, so you can estimate by counting squares as “full” if they are mostly full (black), “empty” if they are mostly empty, and “1/2 square” if they are close to 1/2 full.