Biology subjects

Ellison, A.

Publications and source records attributed to Ellison, A..

5 recordsLinked to original sources

bioRxiv2017

Three Decades as an NSF REU Site: Lessons and Recommendations

NSFs Research Experiences for Undergraduates (REU) program supports thousands of undergraduate researchers annually. REU sites operate independently with regards to their research mission and structure, leading to a complex educational milieu distinct from traditional classrooms and labs. Overall, REU sites are perceived as providing highly formative experiences for developing researchers. However, given improved assessment practices over REUs three decades, best practices for student learning and evaluation of long-term impacts remain limited. To address this limitation, we recommend the use of systems-based theoretical frameworks when studying REU programs. We outline how one such framework, cultural-historical activity theory (CHAT), could inform the collection of assessment data. Among other strengths, CHAT guides collection of quantitative and qualitative information that can help characterize REU programs in an educationally meaningful context. Adoption of CHAT and similar approaches by REU Sites could improve dialogue among programs, encourage collaborations, and improve evidence-based practices.

scientific communication and education↗

bioRxiv2017

Spring frost controls spring tree phenology along elevational gradients on the southeastern Tibetan Plateau

Temperature is considered to be a main driver of spring phenology, whereas the role of climate extremes (such as spring frosts) has long been neglected. A large elevational gradient of mature forests on the Tibetan Plateau provides a powerful space-for-time natural experiment to explore driving forces of spring phenology. Combining 5-yr of in situ phenological observations of Smith fir (Abies georgei var. smithii) with concurrent air temperature data along two altitudinal gradients on the southeastern Tibetan Plateau, we tested the hypothesis that spring frost was a major factor regulating the timing of spring phenology. Onset of bud swelling and leaf unfolding in the study years occurred {approx} 18 or 17 days earlier, respectively, at the lowest (3800 m a.s.l.) elevation relative to upper treelines (4360 or 4380 m a.s.l.). The frequency of freezing events and last freezing date were critical factors in determining the timing of bud swelling along two altitudinal gradients, whereas onset of leaf unfolding was primarily controlled by the onset of bud swelling. This finding provides evidence for detrimental impacts of spring frost on spring phenology, which have been underappreciated in research on phenological sensitivity to climate but should be included in phenology models. It contributes to explain the declining global warming effects on spring phenophases, because climatic extreme events (e.g. spring frosts) tend to increase with warming.

ecology↗

bioRxiv2017

Red wood-ant nests are traps for fault-related CH4 micro-seepage

Methane (CH4) is common on Earth, forms the major commercial natural gas reservoirs, and is a key component of the global carbon cycle, but its natural sources are not well-characterized. We present a geochemical dataset acquired from a red wood-ant (RWA; Formica polyctena) nest in the Neuwied Basin, a part of the East Eifel Volcanic Field (EEVF), focusing on methane (CH4), stable carbon isotope of methane ({delta}13C-CH4), RWA activity patterns, earthquakes, and earth tides. Nest gas and ambient air were continuously sampled in-situ and analyzed to detect microbial, thermogenic, and abiotic fault-related micro-seepage. Methane degassing was not synchronized with earth tides. Elevated CH4 concentrations in nest gas appear to result from a combination of microbial activity and fault-related emissions moving via through fault networks through the RWA nest. Two {delta}13C-CH4 signatures were identified in nest gas: -69{per thousand} and -37{per thousand}. The -69{per thousand} signature of {delta}13C-CH4 within the RWA nest is attributed to microbial decomposition of organic matter. This finding supports previous findings that RWA nests are hot-spots of microbial CH4. Additionally, the -37% {delta}13C-CH4 signature is the first evidence that RWA nests also serve as traps for fault-related emissions of CH4. The -37{per thousand} {delta}13C-CH4 signature can be attributed either to thermogenic/fault-related or to abiotic/fault-related CH4 formation originating from e.g. low-temperature gas-water-rock reactions in a continental setting at shallow depths (microseepage). Sources of these micro-seeps could be Devonian schists (\"Sphaerosiderith Schiefer\") with iron concretions (\"Eisengallen\"), sandstones, or the iron-bearing \"Klerf Schichten\". We cannot exclude overlapping micro-seepage of magmatic CH4 from the Eifel plume. Given the abundance of RWA nests on the landscape, their role as sources of microbial CH4 and traps for abiotically-derived CH4 should be included in estimation of methane emissions that are contributing to climatic change.

ecology↗

bioRxiv2017

Assessment of the World Largest Afforestation Program: Success, Failure, and Future Directions

The Three-North Afforestation Program (TNAP), initiated in 1978 and scheduled to be completed in 2050, is the worlds largest afforestation project and covers 4.07 x 106 km2 (42.4%) of China. We systematically assessed goals and outcomes of the first 30 years of the TNAP using high-resolution remote sensing and ground survey data. With almost 23 billion dollars invested between 1978 and 2008, the forested area within the TNAP region increased by 1.20 x 107 ha, but the proportion of high quality forests declined by 15.8%. The establishment of shelterbelts improved crop yield by 1.7%, much lower than the 5.9% expected once all crop fields are fully protected by shelterbelts. The area subjected to soil erosion by water decreased by 36.0% from 6.72 x 107 to 4.27 x 107 ha; the largest reductions occurred in areas where soil erosion had been most severe and forests contributed more than half of this improvement. Desertification area increased from 1978 to 2000 but decreased from 2000 to 2008; the 30-year net reduction was 13.0% (4.05x106 ha), with 8.0% being accounted for by afforestation in areas with only slight, prior desertification. In addition to its direct impacts, the TNAP has enhanced peoples awareness of environmental protection and attracted consistent attention and long-term commitment from the Chinese government to the restoration and protection of fragile ecosystems in the vast Three-North region. The significant decline in forest quality, limited success in reducing desertification, and low coverage of shelterbelts are aspects of the TNAP in need of re-assessment, and additional ca. 34 billion dollars will be needed to ensure the completion of the TNAP.

ecology↗

bioRxiv2016

Critical minimum temperature limits xylogenesis and maintains treelines on the Tibetan Plateau

Physiological and ecological mechanisms that define treelines are still debated. It is suggested that the absence of trees above the treeline is caused by the low temperature that limits growth. Thus, we raise the hypothesis that there is a critical minimum temperature (CTmin) preventing xylogenesis at treeline. We tested this hypothesis by examining weekly xylogenesis across three and four growing seasons in two natural Smith fir (Abies georgei var. smithii) treeline sites on the south-eastern Tibetan Plateau. Despite differences in the timing of cell differentiation among years, minimum air temperature was the dominant climatic variable associated with xylem growth; the critical minimum temperature (CTmin) for the onset and end of xylogenesis occurred at 0.7{+/-}0.4 {degrees}C. A process-based-modeled chronology of tree-ring formation using this CTmin was consistent with actual tree-ring data. This extremely low CTmin permits Smith fir growing at treeline to complete annual xylem production and maturation and provides both support and a mechanism for treeline formation.

ecology↗