Abstract
The compaction of forest soils can deteriorate soil aeration, leading to decreased CH4 uptake and increased N2O efflux. Black alder (Alnus glutinosa) may accelerate soil structure regeneration as it can grow roots under anaerobic soil conditions. However, symbiotic nitrogen fixation by alder can have undesirable side-effects on greenhouse gas (GHG) fluxes. In this study, we evaluated the possible trade-off between alder-mediated structure recovery and GHG emissions. We compared two directly adjacent 15-year old beech (Fagus sylvatica) and alder stands (loamy texture, pH 5–6), including old planted skid trails. The last soil trafficking on the skid trails took place in 1999. GHG fluxes were measured over one year. Undisturbed plots with beech had a moderately higher total porosity and were lower in soil moisture and soil organic carbon than undisturbed alder plots. No differences in mineral nitrogen were found. N2O emissions in the undisturbed beech stand were 0.4 kg ha−1 y−1 and 3.1 kg ha−1 y−1 in the undisturbed alder stand. CH4 uptake was 4.0 kg ha−1 y−1 and 1.5 kg ha−1 y−1 under beech and alder, respectively. On the beech planted skid trail, topsoil compaction was still evident by reduced macro porosity and soil aeration; on the alder planted skid trail, soil structure of the uppermost soil layer was completely recovered. Skid trail N2O fluxes under beech were five times higher and CH4 oxidation was 0.6 times lower compared to the adjacent undisturbed beech stand. Under alder, no skid-trail-effects on GHG fluxes were evident. Multiple regression modelling revealed that N2O and CH4 emissions were mainly governed by soil aeration and soil temperature. Compared to beech, alder considerably increased net fluxes of GHG on undisturbed plots. However, for skid trails we suggest that black alder improves soil structure without deterioration of the stand’s greenhouse gas balance, when planted only on the compacted areas.
Highlights
Compaction and deformation of forest soils is a widespread issue caused by fully mechanized logging
It is well documented that reduced soil aeration can increase greenhouse gas (GHG) emissions from forest soils, the persistence of such changes is mostly unclear and little is known regarding tree species effects on soil structure recovery
Taking into account all variables, it became obvious that N2 O and CH4 fluxes were mainly governed by soil aeration and soil temperature
Summary
Compaction and deformation of forest soils is a widespread issue caused by fully mechanized logging. When soil trafficking during forest operations is restricted to permanent skid trails [1], the remaining forest stand is fully protected from soil compaction. When distances are 20 m, around 12–16% of the total operational stand area is affected by soil physical changes [2]. Coarse soil porosity decreases and pore continuity is interrupted, leading to reduced soil aeration [3,4]. It is well documented that reduced soil aeration can increase greenhouse gas (GHG) emissions from forest soils, the persistence of such changes is mostly unclear and little is known regarding tree species effects on soil structure recovery
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