Does forest tree species composition impact modelled soil recovery from acidic deposition?

Acidic deposition depleted soil base cation pools throughout central Ontario, particularly during the second half of the twentieth century. While sulphur (S) and nitrogen (N) deposition have declined in recent decades, forest harvesting may continue to remove base cations from soils, highlighting the need for reliable soil chemistry forecasts. This study investigated whether differences in soil chemistry among forest stands dominated by different tree species affected predictions using a dynamic biogeochemical model (VSD). Soil base saturation was modelled from 1850–2100 in stands dominated by balsam fir (<i>Abies balsamea</i> (L.) Mill.), eastern hemlock (<i>Tsuga canadensis</i> (L.) Carr.), white pine (<i>Pinus strobus</i> L.), sugar maple (<i>Acer saccharum</i> Marsh.), or yellow birch (<i>Betula alleghaniensis</i> Britt.). Three scenarios that manipulated future atmospheric S and N deposition and forest harvesting (2020–2100) were applied. When future atmospheric S and N deposition remained at 2020 levels and harvesting continued, base saturation increased marginally (2.0–4.5%) in all plots. Further increases in base saturation were minor (~1%) by 2100 when deposition reductions were implemented. When future forest harvesting was excluded, soil base saturation increased 3.4–8.5% from 2020–2100. These results suggest that tree species composition has minimal influence on modelled soil chemistry forecasts in response to changes in acidic deposition, and such models can be broadly applied for regional predictions.