20th Anniversary of the Wilde Lecture: Revisiting the Underground Forest.

This 20th anniversary of the Sergei Wilde lecture celebrates those pioneers that dug deeply into developing an understanding of whole forests. The term “underground forest”, coined by Earl Stone, an early Wilde grad student (M.S. 1940), was intended to describe the normally hidden half of forests below the soil surface just then beginning to be studied. Early efforts to measure maximum rooting depth of trees showed that defining, much less understanding, the underground forest would be a difficult task. Earl Stone’s publication “On the maximum extent of tree roots”, looked at 211 tree species worldwide and concluded “These data demonstrate the inherent capability of many species to develop deep or far-reaching roots…”. Modest words. In fact, in no case were tree roots found to be limited to depths < 1.0 m, and in many cases they were many meters deep. Many of the results of past and current studies show tree roots typically extend to the maximum depth that researchers are willing to put the effort into sampling. Early efforts were typically aimed primarily at understanding the nutrient and water resources which soils could provide for growing trees, and potential limits soil depth and rooting might place on productivity. A good example was the use of “effective soil depth” by Eugene Steinbrenner (M.S. with Wilde 1951) to help value cutover forestland for its potential future productivity. The impact of deep soil, including potential rooting depth, has been demonstrated clearly in many areas of the world with fast-growing plantation species, and continues to be a major incentive to study deep soil. Recently, understanding and monitoring soil carbon has received considerable attention due to soil’s potential, as the largest terrestrial carbon pool, to sequester or add to atmospheric carbon dioxide. Unfortuantely, many efforts, including major US and European soil carbon monitoring efforts, focus on surface soil horizons, and may miss quantifying and monitoring changes in dynamic subsurface soil carbon pools. In conclusion, most of the previous work studying the underground forest have shown that it is often extremely important, often neglected in study, and worthy of the efforts of current and future forest soil scientists.