Soil ecological risks of increased use of lignocellulose

Forest use and management disrupt element cycles by removing lignocellulose together with woody biomass. Deadwood is known to provide habitat and nutrients, but is also the most important source for lignocellulose in forest soils. However, the role of wood-derived lignocellulose on soil properties and on the formation and stability of soil organic matter (SOM) has hardly been studied. 

In this project, the influence of lignocellulose and especially lignin on central soil properties and its decomposition products were studied. We hypothesized that a portion of lignin enters the soil, ameliorates soil properties, and contributes to enhanced C sequestration. We tested our hypothesis by analyzing soil samples taken next to European beech (Fagus sylvatica L.) deadwood and comparing these samples with reference samples more than 2 meters away from lying deadwood. Ten sample sites were selected throughout Southwest Germany.

Indeed, we observed that deadwood increased the content of particulate organic matter in soils of silicate sites. We observed that lignin-derived phenols increased in the forest floor or in the mineral soil depending on the type of forest floor. Furthermore, changes to the composition of lignin-derived phenols in the deadwood affected soil samples suggested that a substantial portion of those increases came from beech deadwood. Congruent increases in available plant nutrients and soil pore space in deadwood samples compared to reference samples were greater at silicate sites than at calcareous sites. Deadwood initiates soil-forming processes that are spatially and temporally limited, thus warranting the designation of “pedogenic hot-spots”.

In conclusion, our results confirm, that lignocellulose is an important component of soil organic matter. In addition to direct lignocellulose effects, the combination with other deadwood related effects (e.g. nutrient input) has to be considered. The suggestions for lignocellulose removal and for the closely related management of woody biomass in forest ecosystems are to develop site specific management strategies which consider the high potential of lignocellulose and of deadwood to improve ecological soil properties especially of acid and nutrient poor soils.