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Mechanized logging equipment causes considerable soil disturbance, but little information is available regarding thresholds for impacts on soil nematodes—critical members of soil foodwebs which perform important ecological functions. We examined responses of nematode communities and soil physical characteristics to the increasing number of passes (one, three, or nine) by a tracked feller buncher during thinning of a xeric mixed conifer forest in New Mexico, USA. Within and between the harvester tracks, we measured soil surface penetration resistance and shear strength, quantified bulk density at four depth increments up to a maximum depth of 27 cm, and characterized nematode assemblages in the upper 10 cm. Eight months after treatment, nematode communities were less impacted than soil physical properties by harvester passes. Total nematode abundance was unaffected by any level of feller buncher disturbance, and sensitive K-selected nematode groups were reduced only at nine passes. Conversely, soil compaction occurred with a single pass and extended deep into the soil profile to at least 23–27 cm. The first pass also decreased surface penetration resistance and shear strength, indicating disruption of soil surface structural integrity. Additional passes did not further increase bulk density or decrease surface structural integrity. Our results indicate that low levels of logging machinery traffic may have negligible effects on nematode communities, but nevertheless emphasize the importance of minimizing areas subjected to disturbance because of impacts on soil physical properties.

Climate change is altering temperature and precipitation, resulting in widespread plant mortality and shifts in plant distributions. Plants growing in soil types with low water holding capacity may experience intensified effects of reduced water availability as a result of climate change. Furthermore, complex biotic interactions between plants and soil organisms may mitigate or exacerbate the effects of climate change. This 3-year field experiment observed the performance of Bouteloua gracilis ecotypes that were transplanted across an environmental gradient with either sympatric soil from the seed source location or allopatric soil from the location that plants were transplanted into. We also inoculated plants with either sympatric or allopatric soil biotic communities to test: (1) how changes in climate alone influence plant growth, (2) how soil types interact with climate to influence plant growth, and (3) the role of soil biota in mitigating plant migration to novel environments. As expected, plants moved to cooler-wetter sites exhibited enhanced growth; however, plants moved to warmer-drier sites responded variably depending on the provenance of their soil and inoculum. Soil and inoculum provenance had little influence on the performance of plants moved to cooler-wetter sites, but at warmer-drier sites they were important predictors of plant biomass, seed set, and specific leaf area. Specifically, transplants inoculated with their sympatric soil biota and grown in their sympatric soil were as large as or larger than reference plants grown at the seed source locations; however, individuals inoculated with allopatric soil biota were smaller than reference site individuals at warmer, drier sites. These findings demonstrate complicated plant responses to various aspects of environmental novelty where communities of soil organisms may help ameliorate stress. The belowground microbiome of plants should be considered to predict the responses of vegetation more accurately to climate change.

• We enumerated arbuscular mycorrhizal (AM) fungal spore communities for 3 yr as part of a long-term CO

The objectives of the Navy's CL-20 Manufacturing Technology project are to develop and implement advanced process technology that will improve the reproducibility and quality of CL-20, improve CL-20 sensitivity, and reduce the cost of CL-20. One subtask in this project was the identification of key factors and properties that influence the sensitivity of CL-20. A series of round robin tests was conducted where impact and friction sensitivity testing were run on 14 samples of CL-20. These samples were prepared using various synthesis and/or recrystallization techniques and having various impurity levels. Samples were supplied by the U.S. commercial supplier, ATK Thiokol Propulsion Company, the Navy (Naval Surface Warfare Center, Indian Head Division, and Naval Air Warfare Center Weapons Division, China Lake), and the Army (TACOM-ARDEC) as well as Aerojet and suppliers from outside the United States (Nexplo-Bofors and SNPE). Round robin results indicate that CL-20 sensitivity is largely unaffected by CL-20 preparation method, purity, and particle characteristics.