Throwback Thursday: The FPL Rotting Pit

Thanks to Grant Kirker for writing this fascinating look back into Forest Products Laboratory (FPL) history and science. Kirker is a Research Forest Products Technologist at FPL in the Durability and Wood Protection Research unit.

Throughout its 110-year history, FPL has participated in groundbreaking wood research both nationally and internationally. The FPL research libraries contain a virtual treasure trove of information pertaining to the wise use of wood and wood-based materials. Historical overviews like this would not be possible without them.

One of the earliest endeavors at the newly established Forest Products Laboratory, then located at 1509 University Avenue in Madison, Wisconsin, was the testing of preservative treated wood for the expanding railroad sector in the US. The swift growth of railways across the country had created a huge demand for suitable hardwoods. But high decline rates due to wood rot fungi was a constant concern leading to an unreasonable amount of wood being used to replace rapidly rotting railroad ties. The dawn of wood preservation research at FPL was aimed at increasing the service life of rail ties to reduce the demand on America’s forests.  

Original Forest Products Laboratory Building at 1509 University Avenue

Wood preservation researchers at FPL under the leadership of Howard Weiss built a specialized pit at the original FPL site to test wood durability in a quasi-controlled environment. The FPL rotting pit (referred to in FPL records as Project 170) was one of three international rotting pits located in the world at this time: one was located in Stendahl, Germany at the Rutgerswerke Aktiengelleschaft and the other was located at the newly established Canadian Forest Products Laboratory in Montreal.

The concept of the rotting pit was influenced by Hermann Von Schrenk, who had constructed a similar pit a few years earlier at the short-lived Mississippi Valley Research Station located at the Missouri Botanical Garden in St. Louis.

Blueprints of the original FPL building highlighting where the rotting pit was located.

The general layout of the rotting pit was a large hole in the floor (11 feet by 21 feet and 8 feet deep) that was divided into multiple sectors, which were intended to provide optimum ranges for the fungi of interest. The basic premise behind all three of these pits were to provide an environment conducive to fungal growth—one in which accelerated fungal growth was possible—and shorten the amount of time needed to obtain valuable service life data.

This data was considered more valuable at the time due to the constant temperature and moisture contained within the pit. Modern wood preservative testing is conducted at field sites where samples are exposed to natural cyclic wetting and drying, which are critical for development of decay and more indicative of the use of the product.

Unfortunately, the pit did not turn out to be as useful as originally thought. The main difficulty was maintaining conditions conducive to growth of the specific test fungi. Eventually other methods were pursued. In its heyday (1910-1916) the FPL rotting pit was a popular destination for tours and visitors to the lab.  

Five generations later, the heart and soil (Hah!) of the FPL rotting pit lives on in current research at FPL where researchers in Research Work Unit 4723 (Wood Durability and Preservation) are designing new and improved methods to accelerate decay of wood and wood-based materials. The goal of this research is to provide a state of the art, climate-controlled mesocosm for the managed biodegradation of wood and wood-based materials.

As has been the case for more than 100 years, increased understanding of the wood decay process provides vital information that can be used to theorize new protection strategies that reduce reliance on broad spectrum fungicides and provide reliable long-lasting forest products.

As technology improves, hopefully so will our ability to realize the dreams of our FPL forebearers.

To find out more about the amazing history and advancements our scientists are making, visit the Forest Products Laboratory at