Forest Transect Diagrams

The forest transect diagrams used on our website were part of a Ph.D. study by Leen Kuiper, from the Wageningen Agricultural University in The Netherlands. Fieldwork was conducted in 1984 in close cooperation with the Faculty of Forestry of the University of Washington in Seattle (Dr. Chad Oliver) and the Forestry Sciences Lab in Corvallis (Dr. Jerry Franklin).

This method of making realistic drawings of forest structures was developed in the tropics in the 1980's by various researchers including Oldeman and Hallé. Because it was used to quantify and visualize the architecture of complex forest ecosystems, this method of recording forest structure became known as architectural analysis. It proved to be a useful analytical tool for other woodlands as well. Since then, forestry students have created hundreds of diagrams for various forest types in both the tropical and temperate zones. When these plots are measured 5 or 10 years later, changes in forest structure become readily apparent.

Below, Leen describes how he makes forest transect diagrams:

Start with setting out a baseline of 100m, preferably in east-west direction, intersecting an interesting looking part of the forest. Expand the baseline to a 100x10m or 100x20m plot. Use sticks and flagging tape to indicate the corner posts of each 10x10m section.

Measure the position of all the trees in the plot with a DBH over 10cm. Next, make a drawing of the crown cover of all these trees by walking away from the stem base until the point where the vertical crown projection ends. Measure this distance to the stem and do this for at least 4 directions. Make a sketch of the crown projection by walking around the periphery of the crown. Check the crown map to see where tree crowns overlap and where the holes in the canopy are and adjust the map accordingly. Also include down dead wood on the crown map. Also measure the diameter at breast height for all trees in the plot. Put a compass arrow on the map to indicate where the north is.

Next, the vertical tree characteristics (side views) are measured for all trees on the plot. Walk away from the tree to a distance about the height of the tree. Measure the tree heights with a Suunto measuring device which has a percentage scale. The tree height is a percentage of the distance you are standing from the tree. Measure the height of all remarkable aspects of each tree crown, such as lumps in the crown, forks in the stem, typical fan-shaped branch systems, etc. Draw a sketch of the side view based on the measured heights. The previously made crown projection map indicates how wide the tree crowns actually are. Adjust the sketch accordingly.

Back home at the drawing table, put all side view sketches in place by following the crown map from left to right and from front to back. The provisional draft diagram is checked once more in the field to see if the drawing corresponds to reality and that no trees are missed.

It takes about a full day of work by two persons to do all the measurements in the field to construct a diagram for a 100x10 m plot. It will take another day to finalize the drawings at the office.