Proceedings of the 14th North American Forest Soils Conference

The 14th North American Forest Soils Conference (NAFSC) was held July 16–21, 2023, in Eugene, OR. This conference, which has occurred every 5 years, celebrated its 65th anniversary. The 2023 NAFSC included 28 oral presentations and 38 poster presentations that covered five theme areas: elemental cycles and forest productivity, carbon flow through forest soils, fire and forest soils, long-term observations of forest soil systems, and feedbacks between forest soil science and management. This special issue in Soil Science Society of America Journal includes 11 papers that were contributions to the meeting. Jim Boyle (2024), a long-time participant and conference organizing committee member, provides a retrospective look at the evolution of forest soil topics covered at the NAFSC since its inaugural meeting in 1958. He highlights that the 400+ papers from the previous 13 conferences have focused on a wide variety of subject areas from soil classification and mapping to understanding the critical role played by soil biotic communities in nutrient cycling and maintaining site productivity. The longevity of the NAFSC demonstrates its relevance both to scientists and forest land managers. It also reveals its specificity. Through the years, this conference has brought together people with interests in forest ecology, forest management, and soil science. DeLuca (2024), in his paper titled, “On being a forest soil scientist,” reflects not only on the role and importance of forest soil science, but specifically on the characteristics of the people who conduct research on forest soil and what may distinguish them from other researchers in related fields. He concludes by emphasizing the challenges and importance that forest soil scientists have in providing the key information needed to address issues of sustainability in a time of changing climate. Forests have long turnover times, with multi-annual or decadal processes at play. Three studies report on the results of long-term replicated experimental trials. The first one, Bowden et al. (2024) report on a DIRT (Detrital Input and Removal Treatment) trial where inputs of above- and belowground litter to the soil are controlled. This experiment has been running and maintained for 30 years. It revealed that changes in soil organic matter pools induced by changes in litter influx are still difficult to predict and often non-linear over time. The second study by Adams et al. (2024) reports on the long-term (25 years) effects of chronic acid deposition coupled with various intensities of biomass removal. Again, predictions were not always verified. For example, harvesting had a greater impact on soil carbon and nutrients than acidification. The third study by Foroughi et al. (2024), highlights the long timescale (over 60 years) for soil phosphorus pools to re-equilibrate after land conversion and nearly 150 years of intensive agriculture, before being reforested in the mid-1950s. Through multiple re-samplings (1962–2017), the study highlights that the phosphorus distribution in mineral soil profiles remains dynamic, and that the agricultural fertilization legacy is still influencing phosphorus cycling. Because almost half of the total organic carbon in terrestrial ecosystems is stored in forest soils (Mayer et al., 2020), studies on the understanding of soil carbon storage and sequestration and how forest management could alter soil carbon stocks make up a large portion of the contributions to the NAFSC. Prescott (2024) explains that, while research on the processes and modelling of soil carbon has been focusing on litter quality, new evidence shows that the fluxes of surplus carbon that tree produced under mild-to-moderate deficiencies of nutrients and water could drive the buildup of persistent soil organic matter. The process by which trees are providing a flux of labile carbon to the soil and its implications for forest management have yet to be explored. Holub et al. (2024) assessed changes in soil carbon storage over a 10-year period in Douglas-fir plantations using a very intensive sampling design. This study provides information on how to sample soils to estimate changes in carbon stocks. This study provides timely information, given the role of forest soil in climate change mitigation, the importance of correctly quantifying the effect of forest management on greenhouse gas emissions, and the emergence of carbon credit markets. Forest fires have received a lot of attention in the past decades and in North America, 2023 saw a record fire season. Two papers dealt with the effect of fire on soil properties and processes. Weatherholt and Johnson (2024) examined the distribution of soil water repellency (SWR) following the 2020 Green Ridge Fire in Oregon. The results revealed that predicting the occurrence of SWR is challenging. The spatial pattern of SWR is fine scale with spatial autocorrelation occurring at best at a few meters. The paper discusses how to better predict and assess SWR. Kolka et al. (2024) studied the effects of prescribed burning to restore and maintain imperiled barren communities in the Great Lakes Region. Prescribed burning lead to considerable emissions in carbon, nitrogen, and mercury, but these were just a small component of the regional emissions. This study provides estimates that will allow quantification of the greenhouse gas emissions when using prescribed burning as a conservation tool. Technological advances in digital soil mapping have the potential to improve the understanding of soil–plant relationships as well as to provide more precise and accurate geographic information on soil properties to land managers. Paré et al. (2024) conducted a literature review that illustrates how digital maps of soil properties could be useful in assessing four ecosystem services (timber production, soil carbon storage, regulation of water flow and provision of clean water, and the soil as a habitat for organisms). The study concludes that digital soil mapping products have the potential to improve the assessment of ecosystem services by promoting the use of quantitative relationships between soil and ecosystem services. As a nice application of digital soil mapping (DSM), Wilson and Prentice (2024) incorporated DSM to refine the USDA soil burn severity (SBS) map in the Creek Fire (154,000 ha in the Sierra Nevada range). This approach has the potential to shift SBS mapping towards a more quantitative soil landscape model. Littke et al. (2024) examined the utility of using in situ (12-week nutrient supply estimates) ion-exchange membranes (plant root simulator probes, PRS) compared against traditional lab analysis from quantitative pits in a series (38 paired treatment plots) of Douglas-fir plantations that had fertilized and unfertilized treatment areas. The authors found good correlations between the PRS nutrient supply estimates with nitrogen, calcium, and phosphorus contents sampled to 1 m, and were clearly able to differentiate the fertilizer tree volume response. As highlighted by Boyle (2024), the early NAFSCs had a heavier focus on describing soil patterns and processes in natural, mature forests or first rotation managed stands. However, many regions across North America are well into second and third rotation forestry, so there has been a growing emphasis on evaluating the effects of forest management practices on soil physical, chemical, and biological properties, that, in turn, all contribute to soil health. There are growing expectations for forests and forest soils to provide a broad range of ecosystem services, yet they are also faced with multiple natural and anthropogenic stressors that can result in cumulative effects on forest soils (see Figure 20.1 in Morris et al. [2019]), requiring forward-thinking and innovative forest management actions to ensure the continued conservation of the forest soil resource. Conferences like the NAFSC that focus on communication and linkages between soil scientists and land managers will be increasingly important in the future. The completion of this special issue closes the book on the 14th NAFSC, with planning underway for the next meeting in 2028. Stay tuned! David Pare: Conceptualization; writing—original draft; writing—review and editing. Dave Morris: Conceptualization; writing—original draft; writing—review and editing.

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