Evaluation of three machines to remove Armillaria- and annosum-infected stumps.
Many root disease fungi survive as saprophytes in large roots and stumps, which is the primary means by which they persist on a site from one rotation to the next. A Vibro-Driver/Extractor (VDE) or backhoe excavator was used to remove root systems of 89 ponderosa pine (Pinus ponderosa) trees infested with Armillaria ostoyae in the Sante Fe National Park, New Mexico, USA, and a bulldozer was used to remove root systems of 40 white fir (Abies concolor) infested with A. ostoyae, Heterobasidion annosum, or both, on the Southern Ute Indian Reservation, also in New Mexico. Based on direct measurements of extracted biomass and models to predict biomass remaining in the soil, all machines removed at least 83% of the belowground coarse root biomass. The VDE was the most powerful machine and was able to extract the largest stumps. The backhoe excavator was used on the smallest stumps, yet left the highest proportion of large root biomass in the ground. Residual biomass following excavations should not be a significant source of root disease fungi as 90% of broken roots were less than 5 cm diameter and are likely to decay rapidly.