Effects of forest harvest and fertiliser amendment on soil biodiversity and function can persist for decades

Abstract

Effective management is critical to the establishment and growth of productive and sustainable planted forest ecosystems. Harvesting and nutrient applications can significantly disturb these ecosystems, and long-term studies are critical to evaluating the impacts of these events on the factors that contribute to sustainability. This study used long-term field trial sites to explore the direct and interactive effects of site, management, and other factors on the biogeochemical processes and phylogenetic diversity (bacterial and fungal community composition) within forest soil ecosystems. High throughput sequencing of bacterial (16S rRNA) and fungal (ITS rRNA) phylogenetic marker genes was used to characterise microbial communities in soils from two long-term soil productivity study (LTSP) sites (both >25 years old). The single species (Pinus radiata) trials, at Woodhill and Tarawera forests, allowed for testing of effects of forest management practices, including organic matter removal at harvest and fertiliser addition, on microbial communities. Addition of fertiliser resulted in distinct changes to both bacterial and fungal communities, while organic matter removal at harvest had persistent effects on the composition of fungal species in the soil ecosystem at Woodhill with smaller magnitude effects still seen at Tarawera. In contrast, there was no evidence of long-term effects related to organic matter removal at harvest on the composition of soil bacterial communities, irrespective of site. The two sites had differing soil physicochemical properties and these were also associated with location-based differences in bacterial communities. Overall, bacterial communities were relatively impervious to forest management practices, whereas fungal communities were responsive and the effects on community assemblage were enduring over time. This outcome highlights both the importance of investigating fungal and bacterial communities together in forest ecosystems, and the value of long-term field-based studies. We conclude that while conventional forestry management practices may improve the long-term physicochemical conditions and tree growth, their impacts on soil microbial populations are also enduring.