The impact of pneumatic excavation on the roots and shoot growth of coppiced poplars

Abstract

Pneumatic air excavation of soils is being promoted and used increasingly by arboriculturists and contractors to excavate around tree roots and the bases of trees. High-pressure air is delivered through a specially designed lance. The nozzle at the tip of the lance directs compressed air, pumped via a mobile compressor, into a high-speed jet that can be controlled and directed by an operator at the site of the required excavation. The high-speed air jet breaks up the soil structure and displaces soil particles, leaving most visible roots of plants intact. Pipes and solid structures are unaffected. In small excavations on light soils, the soil can be blown out of the excavation pit. On larger excavations or on heavy soils, the loosened material may need to be removed from the pit by shovel. In this study, the root systems of coppiced clonal poplars were exposed by pneumatic excavation to assess the physical impact of the operation on the roots and subsequent shoot growth of the plants. A “Soil Pick SP125” attached to a standard air compressor with no oil suppressor was used to carry out the excavations. Excavations were undertaken in early March and early June 2009 and were backfilled after a period of approximately 20 min of exposure. The shoot extension growth of the plants was assessed over a two-year period and was compared to a set of control treatments. No significant measurable impact on the growth of the poplar plants resulted from the pneumatic excavations. Roots in the diameter range of 5–20 mm showed visible damage that included bruising, pitting and bark stripping. Roots between 0.2 and 5 mm in diameter showed little damage, whilst very fine roots, less than 0.1 mm in diameter, were stripped of their bark/periderm.