A Global review of cumulative effects assessments of disturbances on forest ecosystems.

This paper reviews trends in the academic literature on cumulative effects assessment (CEA) of disturbance on forest ecosystems to advance research in the broader context of impact assessments. Disturbance is any distinct spatiotemporal event that disrupts the structure and composition of an ecosystem affecting resource availability. We developed a Python package to automate search term selection, write search strategies, reduce bias and improve the efficient and effective selection of articles from academic databases and grey literature. We identified 148 peer-reviewed literature published between 1986 and 2022 and conducted an inductive and deductive thematic analysis of the results. Our findings revealed that CEA studies are concentrated in the global north, with most publications from authors affiliated with government agencies in the USA and Canada. Methodological and analytical approaches are less interdisciplinary but mainly quantitative and expert-driven, involving modeling the impacts of disturbances on biophysical valued components. Furthermore, the assessment of socioeconomic valued components, including the effects of disturbance on Indigenous wellbeing connected to forests, has received less attention. Even though there is a high preference for regional assessment, challenges with data access, quality, and analysis, especially baseline data over long periods, are hampering effective CEA. Few articles examined CEA - policy/management nexus. Of the few studies, challenges such as the inadequate implementation of CEA mitigation strategies due to policy drawbacks and resource constraints, the high cost of monitoring multiple indicators, and poor connections between scenarios/modeling and management actions were paramount. Future CEA research is needed to broaden our understanding of how multiple disturbance affects forests in the global south and coupled social and ecological systems and their implications for sustainable forest management.

Temperature, moisture and freeze-thaw controls on CO2 production in soil incubations from northern peatlands.

Peat accumulation in high latitude wetlands represents a natural long-term carbon sink, resulting from the cumulative excess of growing season net ecosystem production over non-growing season (NGS) net mineralization in soils. With high latitudes experiencing warming at a faster pace than the global average, especially during the NGS, a major concern is that enhanced mineralization of soil organic carbon will steadily increase CO2 emissions from northern peatlands. In this study, we conducted laboratory incubations with soils from boreal and temperate peatlands across Canada. Peat soils were pretreated for different soil moisture levels, and CO2 production rates were measured at 12 sequential temperatures, covering a range from - 10 to + 35 °C including one freeze-thaw event. On average, the CO2 production rates in the boreal peat samples increased more sharply with temperature than in the temperate peat samples. For same temperature, optimum soil moisture levels for CO2 production were higher in the peat samples from more flooded sites. However, standard reaction kinetics (e.g., Q10 temperature coefficient and Arrhenius equation) failed to account for the apparent lack of temperature dependence of CO2 production rates measured below 0 °C, and a sudden increase after a freezing event. Thus, we caution against using the simple kinetic expressions to represent the CO2 emissions from northern peatlands, especially regarding the long NGS period with multiple soil freeze and thaw events.

Biogeography and organic matter removal shape long-term effects of timber harvesting on forest soil microbial communities.

The growing demand for renewable, carbon-neutral materials and energy is leading to intensified forest land-use. The long-term ecological challenges associated with maintaining soil fertility in managed forests are not yet known, in part due to the complexity of soil microbial communities and the heterogeneity of forest soils. This study determined the long-term effects of timber harvesting, accompanied by varied organic matter (OM) removal, on bacterial and fungal soil populations in 11- to 17-year-old reforested coniferous plantations at 18 sites across North America. Analysis of highly replicated 16 S rRNA gene and ITS region pyrotag libraries and shotgun metagenomes demonstrated consistent changes in microbial communities in harvested plots that included the expansion of desiccation- and heat-tolerant organisms and decline in diversity of ectomycorrhizal fungi. However, the majority of taxa, including the most abundant and cosmopolitan groups, were unaffected by harvesting. Shifts in microbial populations that corresponded to increased temperature and soil dryness were moderated by OM retention, which also selected for sub-populations of fungal decomposers. Biogeographical differences in the distribution of taxa as well as local edaphic and environmental conditions produced substantial variation in the effects of harvesting. This extensive molecular-based investigation of forest soil advances our understanding of forest disturbance and lays the foundation for monitoring long-term impacts of timber harvesting.