A meta-analysis of soil microbial and physicochemical properties following native forest conversion

The conversion of natural forest to artificial vegetation may deplete nutrients and thus affect the soil quality. However, little is known about synergetic changes of microbial and physicochemical dynamics in soils after natural forest conversion and their implications. In the current study, we synthesized the responses of soil microbial and physicochemical properties in the uppermost soil layer (<20 cm) following natural forest conversion, as reported in 51 published studies (127 sites). Our results showed that the response ratios of soil moisture, soil microbial carbon and nitrogen, bacteria, fungi, enzymatic activities, soil organic carbon, total carbon, total nitrogen, NO₃^–, total phosphorus, available phosphorus, cations (K⁺, Mg²⁺ and Ca²⁺), and cation exchange capacity (CEC) overall declined following natural forest replacement. In contrast, natural forest conversion caused significant increases in soil bulk density, soil pH and NH₄⁺. Reductions of microbial carbon, organic carbon and total nitrogen in soil were independent of revegetation type, but variations in soil pH, available phosphorus and fungi were correlated to land use. Soil CEC reduction increased soil pH, allowing soils to retain NH₄⁺, which promoted fungal growth. Moreover, natural forest replacement led to the loss of soil cations in regions of higher precipitation. Revegetation practices led to greater consumption of soil microbial and chemical nutrients and produced “harder” soils (increased soil compaction and decreased moisture content) in warmer regions. Stand age influenced ratios of soil carbon to nitrogen and ratios of bacteria to fungi following natural forest conversion. Altogether, our study suggests that natural forest conversion results in decreased soil microbial and chemical fertility, and desirable soil properties are more likely to be lost in warmer regions and over time as global climate warming exacerbates, which in turn may potentially damage ecosystem sustainability.