Effect of limited compaction on soil solution chemistry in two acidic forest ecosystems: Changes, recovery and impact of liming

Abstract

Forest practices are rapidly becoming mechanised in France, resulting in unknown consequences for the current and long-term functioning and functions of ecosystems. Degradation of forest soil porosity cannot be remediated artificially, and restoration via natural processes is slow and not likely to include deep soil layers, where tree roots take up large amounts of water and nutrients. In 2007 and 2008, two experimental sites were set up in the Lorraine Plateau (France). The soils are Ruptic Luvisols and are classified as highly sensitive to compaction. We observed multiple parameters and studied weakly bound soil solutions, which are known to react to changes in ecosystem functioning. We hypothesised that (i) soil solution chemistry is a relevant indicator to assess soil changes after compaction and dynamics of soil recovery in the decade following compaction, (ii) restoration is greater at the more fertile site and (iii) soil pH is a relevant parameter to explain the behaviour of soil solutions. Our results showed that soil solution concentrations changed drastically after compaction and that restoration was more effective in the less fertile soil than in the more fertile one. Finally, a soil pH threshold of 4.5 was relevant for explaining the behaviour of nitrate, which is particularly useful for monitoring solution geochemistry in these acidic soils. Liming at the less fertile site increased the pH to more than 4.5, which changed the behaviour of nitrate and reinforced the utility of this threshold for explaining soil biogeochemical functioning. Soil solution is a relevant indicator of current soil functioning after compaction; however, this study demonstrated that additional information is required to understand its meaning accurately. This study highlights that long-term observation is needed to identify the consequences of soil compaction on long-living ecosystems.