Tamm Review: Reforestation for resilience in dry western U.S. forests

The increasing frequency and severity of fire and drought events have negatively impacted the capacity and success of reforestation efforts in many dry, western U.S. forests. Challenges to reforestation include the cost and safety concerns of replanting large areas of standing dead trees, and high seedling and sapling mortality rates due to water stress, competing vegetation, and repeat fires that burn young plantations. Standard reforestation practices have emphasized establishing dense conifer cover with gridded planting, sometimes called \u27pines in lines\u27, followed by shrub control and pre-commercial thinning. Resources for such intensive management are increasingly limited, reducing the capacity for young plantations to develop early resilience to fire and drought. This paper summarizes recent research on the conditions under which current standard reforestation practices in the western U.S. may need adjustment, and suggests how these practices might be modified to improve their success. In particular we examine where and when plantations with regular tree spacing elevate the risk of future mortality, and how planting density, spatial arrangement, and species composition might be modified to increase seedling and sapling survival through recurring drought and fire events. Within large areas of contiguous mortality, we suggest a “three zone” approach to reforestation following a major disturbance that includes; (a) working with natural recruitment within a peripheral zone near live tree seed sources; (b) in a second zone, beyond effective seed dispersal range but in accessible areas, planting a combination of clustered and regularly spaced seedlings that varies with microsite water availability and potential fire behavior; and (c) a final zone defined by remote, steep terrain that in practice limits reforestation efforts to the establishment of founder stands. We also emphasize the early use of prescribed fire to build resilience in developing stands subject to increasingly common wildfires and drought events. Finally, we highlight limits to our current understanding of how young stands may respond and develop under these proposed planting and silvicultural practices, and identify areas where new research could help refine them

A multi-benefit framework for funding forest management in fire-driven ecosystems across the Western U.S.

Forests across the Western U.S. face unprecedented risk due to historic fire exclusion, environmental degradation, and climate change. Forest management activities like ecological thinning, prescribed burning, and meadow restoration can improve landscape resilience. Resilient forests are at a lower risk of high-intensity wildfires, drought, insects, and other disturbances and provide a wide range of benefits to ecosystems and communities. However, insufficient funding limits implementation of critically needed management. To address this challenge, we propose a multi-benefit framework that leverages the diverse benefits of forest management to engage a suite of stakeholders in sharing project costs. We take a three-pronged approach to develop our conceptual model: examining existing frameworks for environmental project implementation, conducting a literature review of forest management benefits, and evaluating case studies. Through our framework, we describe the steps to engage partners, starting by identifying benefits that could accrue to potential public and private beneficiaries, and moving through an iterative and collaborative process of valuing benefits, which can accrue over different spatial and temporal scales, in close consultation with potential beneficiaries themselves. The aim of this approach is to stack funding streams associated with each valued benefit to fully fund a given forest management project. The multi-benefit framework has the potential to unlock new sources of funding to meet the exceptional challenges of climate and wildfire disturbances. We apply the framework to dry forests of the Western U.S., but opportunities exist for expanding and modifying this approach to any geography or ecosystem where management provides multiple benefits

Variables to predict engraftment of umbilical cord blood into immunodeficient mice: usefulness of the non-obese diabetic--severe combined immunodeficient assay.

Umbilical cord blood is an alternative stem cell source for patients without matched family donors. In this study, we examined several parameters that have not been studied in detail -- radiation dose, cell dose, age of mice, and maternal and neonatal characteristics of the cord blood donor -- that affect engraftment of cord blood in non-obese diabetic-severe combined immunodeficient (NOD--scid) mice. Engraftment, measured using flow cytometry analyses of human CD45(+) cells, was highest in 400 cGy-treated mice. Successful engraftment was demonstrated up to 6 months, with a mean engraftment of 31% (range 0--67%) of human cells in recipient bone marrow. Engraftment was skewed to B lymphocytes. The radiation dose of 350 cGy resulted in superior survival of the murine recipients compared with 400 cGy (P = 0.03). The sex of the NOD--scid recipients had a significant effect on survival (female superior to male, P = 0.01), but not on engraftment. There were high levels of variability among different cord units and among animals injected with the same cord unit. This variability may limit the clinical usefulness of the NOD--scid mice as hosts for the quantification of human stem cells