Midwest

The Midwest is home to over 60 million people, and its active economy represents 18% of the U.S. gross domestic product. The region is probably best known for agricultural production. Increases in growingseason temperature in the Midwest are projected to be the largest contributing factor to declines in the productivity of U.S. agriculture. Increases in humidity in spring through mid-century are expected to increase rainfall, which will increase the potential for soil erosion and further reduce planting-season workdays due to waterlogged soil

Decadal changes in fire frequencies shift tree communities and functional traits

Global change has resulted in chronic shifts in fire regimes. Variability in the sensitivity of tree communities to multi-decadal changes in fire regimes is critical to anticipating shifts in ecosystem structure and function, yet remains poorly understood. Here, we address the overall effects of fire on tree communities and the factors controlling their sensitivity in 29 sites that experienced multi-decadal alterations in fire frequencies in savanna and forest ecosystems across tropical and temperate regions. Fire had a strong overall effect on tree communities, with an average fire frequency (one fire every three years) reducing stem density by 48% and basal area by 53% after 50 years, relative to unburned plots. The largest changes occurred in savanna ecosystems and in sites with strong wet seasons or strong dry seasons, pointing to fire characteristics and species composition as important. Analyses of functional traits highlighted the impact of fire-driven changes in soil nutrients because frequent burning favoured trees with low biomass nitrogen and phosphorus content, and with more efficient nitrogen acquisition through ectomycorrhizal symbioses. Taken together, the response of trees to altered fire frequencies depends both on climatic and vegetation determinants of fire behaviour and tree growth, and the coupling between fire-driven nutrient losses and plant traits

THE INFLUENCE OF FIRE ON THE RADIOCARBON SIGNATURE AND CHARACTER OF SOIL ORGANIC MATTER IN THE SISKIYOU NATIONAL FOREST, OREGON, USA

ABSTRACT Forest fires contribute a significant amount of CO 2 to the atmosphere each year, and CO 2 emissions from fires are likely to increase under projected conditions of global climate change. In addition to volatilizing aboveground biomass and litter layers, forest fires have a profound effect on belowground carbon (C) pools and the cycling of soil organic matter as a whole. However, the influence of fire on belowground organic matter cycling is not well defined and varies widely with fire severity. We measured soil organic matter (SOM) characteristics across a range of fire severities two years after the 2002 Biscuit Fire in southwest Oregon, USA, to address the following questions: (1) Which C pools are preferentially volatilized or transformed to charcoal under low-se- RESUMEN Los incendios forestales contribuyen significativamente al incremento anual de CO 2 en la atmósfera, y es probable que las emisiones de CO 2 provenientes de estos incendios incrementen en las condiciones proyectadas de cambio climático global. Además de volatilizar la biomasa superficial y la hojarasca, los incendios forestales tienen un profundo efecto sobre los depósitos de carbono (C) subterrá-neo y en el ciclo de la materia orgánica. Sin embargo, la influencia de los incendios en el ciclo de la materia orgánica subterránea no ha sido totalmente comprendida y varía mucho en función de la severidad de cada incendio. En este estudio medimos las características de la materia orgánica del suelo (MOS) en un rango diverso de severidades de fuego dos años después del incendio Biscuit, ocurrido en 2002 en el sureste de Oregon, en los EUA y formulamos las siguientes preguntas: ¿Cuáles depósitos de C son volatilizados o transformados en carbono vegetal bajo incendios de alta y baja severidad? (2) ¿A raíz del incendio, cómo cambia la distribución de la SOM en sus distintas fracciones en cuanto a densidad y profundidad del suelo? (3) ¿Cómo afecta el incendio el carácter general de la SOM incluyendo aquellas variables como abundancia, relación C:N, y abundancia de 13 C y 14 C? Examinamos suelos provenientes de bosques perennifolios mixtos de crecimiento lento a lo largo del siguiente rango de severidades de fuego: sin quemar, baja, mixta y alta. Los resultados indicaron que el incremento en la severidad del incendio lleva a la pérdida progresiva de la masa del suelo forestal, pero no a pérdidas progresivas de carbono en el suelo mineral. Aunque el incendio incrementó significativamente el contenido de carbono en el suelo, no produjo cambios significativos en la MOS en sus distintas fracciones. Otros cambios significativos en las características de la MOS incluyeron un incremento progresivo en el nitrógeno (N) a medida que aumentó la severidad, debido posiblemente al incremento en arbustos fijadores de nitrógeno después de la pérdida de vegetación nativa. Aunque los cambios cualitativos en la abundancia total de raíces fueron notables después del incendio, éstos no fueron significativos entre los distintos niveles de severidad. Los incrementos observados en la concentración de fragmentos de rocas en áreas quemadas podrían sugerir procesos erosivos, lo que ha sido documentado anteriormente por estudios previos. Aunque la abundancia de 13 C fue similar en parcelas quemadas y no quemadas, el 14 C en las parcelas quemadas severamente disminuyó significativamente en relación a las parcelas no quemadas. Este agotamiento en el 14 C es probablemente el resultado de los efectos combinados de la erosión y la combustión de compuestos orgánicos enriquecidos con 14 C y relativos a la masa total del suelo, que probablemente reflejen el patrón histórico de incidencia y la intensidad de los incendios en el paisaje

Douglas-fir soil C and N properties a decade after termination of urea fertilization

Chemical and microbial soil properties were assessed in paired unfertilized and urea fertilized (>89 g N·m–2) plots in 13 second-growth Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stands distributed throughout western Washington and Oregon. A decade following the termination of fertilization, fertilized plots averaged 28% higher total N in the O layer than unfertilized plots, 24% higher total N in surface (0–5 cm) mineral soil, and up to four times the amount of extractable ammonium and nitrate. Decreased pH (0.2 pH units) caused by fertilization may have been due to nitrification or enhanced cation uptake. In some soil layers, fertilization decreased cellulase activity and soil respiration but increased wood decomposition. There was no effect of fertilization on concentrations of light and heavy fractions, labile carbohydrates, and phosphatase and xylanase activities. No increase in soil organic C was detected, although variability precluded observing an increase of less than -15%. Lack of a regionwide fertilization influence on soil organic C contrasts with several site-specific forest and agricultural studies that have shown C increases resulting from fertilization. Overall, the results indicate a substantial residual influence on soil N a decade after urea fertilization but much more limited influence on soil C processes and pools

Adaptation pathways: ecoregion and land ownership influences on climate adaptation decision-making in forest management

© 2017, Springer Science+Business Media Dordrecht (outside the USA). Climate adaptation planning and implementation are likely to increase rapidly within the forest sector not only as climate continues to change but also as we intentionally learn from real-world examples. We sought to better understand how adaptation is being incorporated in land management decision-making across diverse land ownership types in the Midwest by evaluating project-level adaptation plans from a suite of forest management projects developed through the Climate Change Response Framework. We used quantitative content analysis to evaluate 44 adaptation-planning documents developed through the Framework’s Adaptation Workbook within two ecoregional provinces of the Midwest. This approach was used to assess the components of adaptation planning, including the resources that adaptation actions targeted within planning documents, the climate changes and impacts of concern, and the adaptation strategies managers identified. Analyses of adaptation plans show that the most frequent climate changes and impacts of concern included alterations in the amount and timing of precipitation, increased vegetation moisture stress, and forest pest and pathogen impacts. Individual projects identified a diversity of adaptation options, rather than focusing singly on actions that aimed to resist climate impacts, enhance resilience, or transition systems. Multivariate analyses indicate that ecoregion and land ownership influenced adaptation planning, while the type of resources and the climate change impacts managers were concerned with were significantly correlated with the adaptation strategies selected during planning. This finding reinforces the idea that one-size-fits-all guidance on adaptation will be insufficient for land managers. Perceptions of relevant climate impacts differ based on regional and ownership contexts, which naturally leads to differences in preferred adaptation actions

Vulnerability of forests of the Midwest and Northeast United States to climate change

© 2017, Springer Science+Business Media Dordrecht (outside the USA). Forests of the Midwest and Northeast significantly define the character, culture, and economy of this large region but face an uncertain future as the climate continues to change. Forests vary widely across the region, and vulnerabilities are strongly influenced by regional differences in climate impacts and adaptive capacity. Not all forests are vulnerable; longer growing seasons and warmer temperatures will increase suitable habitat and biomass for many temperate species. Upland systems dominated by oak species generally have low vulnerability due to greater tolerance of hot and dry conditions, and some oak, hickory, and pine species are expected to become more competitive under hotter and physiologically drier conditions. However, changes in precipitation patterns, disturbance regimes, soil moisture, pest and disease outbreaks, and nonnative invasive species are expected to contribute forest vulnerability across the region. Northern, boreal, and montane forests have the greatest assessed vulnerability as many of their dominant tree species are projected to decline under warmer conditions. Coastal forests have high vulnerability, as sea level rise along the Atlantic coast increases damage from inundation, greater coastal erosion, flooding, and saltwater intrusion. Considering these potential forest vulnerabilities and opportunities is a critical step in making climate-informed decisions in long-term conservation planning

Midwest

The Midwest is home to over 60 million people, and its active economy represents 18% of the U.S. gross domestic product. The region is probably best known for agricultural production. Increases in growingseason temperature in the Midwest are projected to be the largest contributing factor to declines in the productivity of U.S. agriculture. Increases in humidity in spring through mid-century are expected to increase rainfall, which will increase the potential for soil erosion and further reduce planting-season workdays due to waterlogged soil.This chapter is published as Angel, J., C. Swanston, B.M. Boustead, K.C. Conlon, K.R. Hall, J.L. Jorns, K.E. Kunkel, M.C. Lemos, B. Lofgren, T.A. Ontl, J. Posey, K. Stone, G. Takle, and D. Todey, 2018: Midwest. In Impacts, Risks, and Adaptation in the United States: Fourth National Climate Assessment, Volume II [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 872–940. doi: 10.7930/NCA4.2018.CH21.</p

The Enriched Background Isotope Study (EBIS)

A unique, large release of radiocarbon occurred near the Oak Ridge Reservation (ORR), Oak Ridge, TN in July/August 1999. Measurements of 14C in tree ring cellulose throughout the ORR area demonstrate that the 1999 release was unprecedented in its uptake by vegetation. We are taking advantage of the whole-ecosystem isotopic label generated by this release to address five outstanding issues in the terrestrial carbon cycle: (1) partitioning of soil respiration between autotrophic and heterotrophic sources, and quantification of that partitioning seasonally and inter-annually, (2) partitioning of heterotrophic respiration sources between above-ground litter decomposition and below-ground root detritus decomposition, (3) identification of pathways leading from leaf and root detritus to long-term stabilization of soil organic matter, including the role of soil fauna, (4) the role of dissolved organic carbon (DOC) transport in distributing carbon within the soil profile, and (5) the longevity and turnover time of fine roots. The first four issues are being addressed through a reciprocal litter transplant experiment set up at four sites on the ORR encompassing two soil types and two levels of 14C exposure in 1999. The fifth issue, longevity and turnover of fine roots, is being addressed by tracing the radiocarbon label through the fine root pool over time. With a combination of incubation, soil surface chamber and soil CO2 profiles, and continuous measurements of soil temperature and moisture controls, we are tracking changes in soil respiration partitioning over several years. The nature and source of organic matter pools that reside in soils for years to decades are being tracked with differently labeled root and surface litter, and experiments to exclude soil fauna have been initiated to elucidate their role in vertical transport. Periodic sampling of soils and soil solutions and the use of inert tracers, allow us to investigate the chemical nature and form of DOC and its transport in surface soil horizons. Results from these field observations will be used to parameterize and refine existing carbon dynamics models. Such models will then be used to quantitatively address the long-term fate of ecosystem carbon inputs and the potential for ecosystem carbon sequestration