Pain or gain: the dual role of afforestation effects on soil pH at the global scale

PurposeThe aim of the study is to assess how afforestation may affect soil pH at the global scale.MethodsUsing 2642 paired observations from 451 peer-reviewed publications, we assessed the effects and driving factors of afforestation on soil pH.ResultsWe found that (1) afforestation significantly decreased soil pH by an average of 0.07 unit, but its effects varied with different afforestation patterns, with soil pH significantly decreased by 0.16 and 0.08 unit following shrub and tree afforestation, respectively, but increased by 0.37 unit following afforestation with trees, shrubs, and grass; (2) afforestation effects were significantly affected by plantation type, mycorrhizal association, and land use type, with higher negative effects following conifer (than broadleaved) afforestation, ectomycorrhiza (ECM) species (than arbuscular mycorrhiza [AM] species or species associated with both AM and ECM fungi) afforestation, and afforestation in non-mining (than mining) lands, respectively; (3) species richness and phosphorous effects size positively impacted afforestation effects, but stand age, initial soil pH, and the effect sizes of soil organic carbon, available nitrogen, and available phosphorous showed negative impacts; and (4) among the moderator variables showed significant impacts on afforestation effects, effect size of soil available nitrogen and mycorrhizal association were the most important.ConclusionOur results showed that afforestation may lead to soil acidification, but its negative effects can be reversed into positive if the afforestation was carried out with the combinations of trees, shrubs, and grasses. These results will help us to better understand the interactions between plant and soil following afforestation.

Automated summary

The aim of this study was to assess the impact of afforestation on soil pH at a global scale. By analyzing data from 2642 paired observations, we found that afforestation led to a significant decrease in soil pH, with the effects varying depending on the type of afforestation. Additionally, the driving factors behind these effects were identified, including plantation type, mycorrhizal association, and land use type.