| Summary: | This article presents the results from two separate studies investigating the decay of wood in ground contact using adapted versions of laboratory-based terrestrial microcosm (TMC) tests according to CEN/TS 15083-2:2005. The first study (A) sought to isolate the effect of soil water-holding capacity (WHC<sub>soil</sub> [%]) and soil moisture content (MC<sub>soil</sub> [%WHC<sub>soil</sub>]) on the decay of five commercially important wood species; European beech (<i>Fagus sylvatica</i>), English oak heartwood (<i>Quercus robur</i>), Norway spruce (<i>Picea abies</i>), Douglas-fir heartwood (<i>Pseudotsuga menziesii</i>), and Scots pine sapwood (<i>Pinus sylvestris</i>), while keeping soil temperature (T<sub>soil</sub>) constant. Combinations of soil mixtures with WHC<sub>soil</sub> of 30%, 60%, and 90%, and MC<sub>soil</sub> of 30%, 70%, and 95%WHC<sub>soil</sub> were utilized. A general trend showed higher wood decay, measured in oven-dry mass loss (ML<sub>wood</sub> [%]), for specimens of all species incubated in soils with WHC<sub>soil</sub> of 60% and 90% compared to 30%. Furthermore, drier soils (MC<sub>soil</sub> of 30 and 70%WHC<sub>soil</sub>) showed higher ML<sub>wood</sub> compared to wetter soils (95%WHC<sub>soil</sub>). The second study (B) built on the first’s findings, and sought to isolate the effect of T<sub>soil</sub> and MC<sub>soil</sub> on the decay of European beech wood, while keeping WHC<sub>soil</sub> constant. The study used constant incubation temperature intervals (T<sub>soil</sub>), 5–40 °C, and alternating intervals of 10/20, 10/30, and 20/30 °C. A general trend showed drier MC<sub>soil</sub> (60%WHC<sub>soil</sub>), and T<sub>soil</sub> of 20–40 °C, delivered high wood decay (ML<sub>wood</sub> > 20%). Higher MC<sub>soil</sub> (90%WHC<sub>soil</sub>) and T<sub>soil</sub> of 5–10 °C, delivered low wood decay (ML<sub>wood</sub> < 5%). Alternating T<sub>soil</sub> generally delivered less ML<sub>wood</sub> compared to their mean constant T<sub>soil</sub> counterparts (15, 20, 25 °C). The results suggest that differences in wood species and inoculum potential (WHC<sub>soil</sub>) between sites, as well as changes in MC<sub>soil</sub> and T<sub>soil</sub> attributed to daily and seasonal weather patterns can influence in-ground wood decay rate.
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