Studies into Fungal Decay of Wood In Ground Contact—Part 1: The Influence of Water-Holding Capacity, Moisture Content, and Temperature of Soil Substrates on Fungal Decay of Selected Timbers

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 (WHCₛₒᵢₗ [%]) and soil moisture content (MCₛₒᵢₗ [%WHCₛₒᵢₗ]) on the decay of five commercially important wood species; European beech (Fagus sylvatica), English oak heartwood (Quercus robur), Norway spruce (Picea abies), Douglas-fir heartwood (Pseudotsuga menziesii), and Scots pine sapwood (Pinus sylvestris), while keeping soil temperature (Tₛₒᵢₗ) constant. Combinations of soil mixtures with WHCₛₒᵢₗ of 30%, 60%, and 90%, and MCₛₒᵢₗ of 30%, 70%, and 95%WHCₛₒᵢₗ were utilized. A general trend showed higher wood decay, measured in oven-dry mass loss (MLwₒₒd [%]), for specimens of all species incubated in soils with WHCₛₒᵢₗ of 60% and 90% compared to 30%. Furthermore, drier soils (MCₛₒᵢₗ of 30 and 70%WHCₛₒᵢₗ) showed higher MLwₒₒd compared to wetter soils (95%WHCₛₒᵢₗ). The second study (B) built on the first’s findings, and sought to isolate the effect of Tₛₒᵢₗ and MCₛₒᵢₗ on the decay of European beech wood, while keeping WHCₛₒᵢₗ constant. The study used constant incubation temperature intervals (Tₛₒᵢₗ), 5–40 °C, and alternating intervals of 10/20, 10/30, and 20/30 °C. A general trend showed drier MCₛₒᵢₗ (60%WHCₛₒᵢₗ), and Tₛₒᵢₗ of 20–40 °C, delivered high wood decay (MLwₒₒd > 20%). Higher MCₛₒᵢₗ (90%WHCₛₒᵢₗ) and Tₛₒᵢₗ of 5–10 °C, delivered low wood decay (MLwₒₒd < 5%). Alternating Tₛₒᵢₗ generally delivered less MLwₒₒd compared to their mean constant Tₛₒᵢₗ counterparts (15, 20, 25 °C). The results suggest that differences in wood species and inoculum potential (WHCₛₒᵢₗ) between sites, as well as changes in MCₛₒᵢₗ and Tₛₒᵢₗ attributed to daily and seasonal weather patterns can influence in-ground wood decay rate.