Chemical properties of the soil water in a clearfelled Norway spruce forest in SW Sweden were monitored using lysimeters during a five‐year period. Measurements were made in plots treated as follows: (i) conventional harvest (CH), with slash and stumps remaining at the site, (ii) whole‐tree harvest (WHT), where only the slash was removed, and (iii) complete‐tree harvest (CTH), where both slash and stumps were harvested. Removal of slash from the clearcutting reduced concentrations of NO3 ‐, NH4 + and K+ in soil water below the rooting zone. In plots mechanically disturbed by stump harvesting, NH4 + concentrations increased strongly during the first year after felling. High levels were noted for two years, whereafter there was an additional two‐year period with elevated NO3 ‐ concentrations and reduced pH, indicating enhanced nitrification and NO3 ‐ leaching. The nitrate concentration drop coincided with a rapid expansion of the ground vegetation, mainly composed of Deschampsia flexuosa L. Trin., Carex pil...

Effects of slash removal and stump harvesting on soil water chemistry in a clearcutting in SW Sweden

A recent study conducted in Sweden investigated the chemical properties of soil water in a clearfelled Norway spruce forest over a period of five years. The researchers used lysimeters to collect water samples and monitored three different plots: those subjected to conventional harvest (CH), whole-tree harvest (WHT), and complete-tree harvest (CTH).

In the CH plots, where slash and stumps were left at the site, the researchers observed higher concentrations of NO3^-, NH4+, and K+ in the soil water below the rooting zone. This suggests that the slash and stumps acted as reservoirs, releasing these nutrients into the soil water.

On the other hand, in the WHT plots where only the slash was removed, the concentrations of NO3^-, NH4+, and K+ in the soil water were reduced below the rooting zone. This indicates that the removal of slash led to a decrease in nutrient concentrations in the soil water. But why does this happen?

The authors propose that the presence of slash promotes microbial activity in the soil, leading to increased nutrient mineralization and availability in the water. Therefore, by removing the slash, there is less organic matter for microbial decomposition, resulting in lower nutrient concentrations in the soil water.

The researchers also noticed a striking change in NH4+ concentrations in the soil water in the CTH plots, where both the slash and stumps were harvested. During the first year after felling, NH4+ concentrations significantly increased. This initial rise in NH4+ could be attributed to the mechanical disturbance caused by stump harvesting, which may have accelerated the decomposition of organic matter and released more NH4+ into the soil water.

Interestingly, this increase in NH4+ concentrations persisted for two years, followed by a two-year period of elevated NO3^- concentrations and reduced pH. These changes suggest enhanced nitrification and leaching of NO3^- from the soil. But why does this happen and how does it coincide with the growth of ground vegetation?

It is possible that the removal of the stumps disrupted the natural distribution and cycling of nutrients in the ecosystem. The rapid expansion of ground vegetation, particularly Deschampsia flexuosa L. Trin. and Carex pil..., which are known to be nutrient-demanding plants, may have taken advantage of the increased availability of NH4+ and other nutrients following stump harvesting.

As these plants uptake nutrients, the soil water concentrations of NH4+ gradually decrease, but a surplus of nutrients may have led to increased nitrification, resulting in higher NO3^- concentrations. The subsequent decrease in nitrate concentration could be attributed to the plants' efficient use of nitrogen, dilution effects from increased rainfall, or further leaching beyond the reach of the lysimeters.

In conclusion, this study sheds light on how different harvesting methods affect the chemical composition of soil water in a Norway spruce forest. The results demonstrate the importance of considering the role of organic matter, microbial activity, and plant uptake in nutrient dynamics, as well as the potential consequences of disturbance caused by harvest practices on soil water chemistry. Further research is needed to fully understand the long-term implications of these changes on ecosystem health and function.