Showing papers by "Paul J. Hanson published in 2012"

Forest phenology and a warmer climate – growing season extension in relation to climatic provenance

Abstract: Predicting forest responses to warming climates relies on assumptions about niche and temperature sensitivity that remain largely untested. Observational studies have related current and historical temperatures to phenological shifts, but experimental evidence is sparse, particularly for autumn responses. A 4 year field experiment exposed four deciduous forest species from contrasting climates (Liquidambar styraciflua, Quercus rubra, Populus grandidentata, and Betula alleghaniensis) to air temperatures 2 and 4 °C above ambient controls, using temperature-controlled open top chambers. Impacts of year-round warming on bud burst (BB), senescence, and abscission were evaluated in relation to thermal provenance. Leaves emerged earlier in all species by an average of 4–9 days at +2 °C and 6–14 days at +4 °C. Magnitude of advance varied with species and year, but was larger for the first 2 °C increment than for the second. Effect of warming increased with early BB, favoring Liquidambar, but even BB of northern species advanced, despite temperatures exceeding those of the realized niche. Treatment differences in BB were inadequately explained by temperature sums alone. In autumn, chlorophyll was retained an average of 4 and 7 days longer in +2 and +4 °C treatments, respectively, and abscission delayed by 8 and 13 days. Growing seasons in the warmer atmospheres averaged 5–18 days (E2) and 6–28 days (E4) longer, according to species, with the least impact in Quercus. Results are compared with a 16 years record of canopy onset and offset in a nearby upland deciduous forest, where BB showed similar responsiveness to spring temperatures (2–4 days °C−1). Offset dates in the stand tracked August–September temperatures, except when late summer drought caused premature senescence. The common garden-like experiment provides evidence that warming alone extends the growing season, at both ends, even if stand-level impacts may be complicated by variation in other environmental factors.

Uncertainty in Peat Volume and Soil Carbon Estimated Using Ground-Penetrating Radar and Probing

Abstract: Estimating soil C stock in a peatland is highly dependent on accurate measurement of the peat volume. In this study, we evaluated the uncertainty in calculations of peat volume using high-resolution data to resolve the three-dimensional structure of a peat basin based on both direct (push probes) and indirect geophysical (ground-penetrating radar) measurements. We compared volumetric estimates from both approaches, accounting for potential sources of error, with values from the literature. Approximate uncertainty of 14 to 23% was observed in the basin volume, and the total uncertainty roughly doubled when incorporating peat properties to derive the estimated C pool. Uncertainties in final C stock values are based on the uncertainty of the basin volumes and the variability in the peat properties and range between 31 and 38%. The results indicate that the well-established ground-penetrating radar technique that is scalable to larger peatlands can be used to obtain estimates of peat basin volumes at uncertainty levels similar to those for invasive direct probe surveys. This investigation demonstrated that ground-penetrating radar can quantify peat basin volumes at uniquely high spatial resolution without the need for extensive and invasive direct probing.

Simulation of carbon cycling, including dissolved organic carbon transport, in forest soil locally enriched with 14C

Abstract: The DyDOC model was used to simulate the soil carbon cycle of a deciduous forest at the Oak Ridge Reservation (Tennessee, USA). The model application relied on extensive data from the Enriched Background Isotope Study (EBIS), which exploited a short-term local atmospheric enrichment of radiocarbon to establish a large-scale manipulation experiment with different inputs of 14C from both above-ground and below-ground litter. The model was first fitted to hydrological data, then observed pools and fluxes of carbon and 14C data were used to fit parameters describing metabolic transformations of soil organic matter (SOM) components and the transport and sorption of dissolved organic matter (DOM). This produced a detailed quantitative description of soil C cycling in the three horizons (O, A, B) of the soil profile. According to the parameterised model, SOM turnover within the thin O-horizon rapidly produces DOM (46 gC m−2 a−1), which is predominantly hydrophobic. This DOM is nearly all adsorbed in the A- and B-horizons, and while most is mineralised relatively quickly, 11 gC m−2 a−1 undergoes a “maturing” reaction, producing mineral-associated stable SOM pools with mean residence times of 100–200 years. Only a small flux (~1 gC m−2 a−1) of hydrophilic DOM leaves the B-horizon. The SOM not associated with mineral matter is assumed to be derived from root litter, and turns over quite quickly (mean residence time 20–30 years). Although DyDOC was successfully fitted to C pools, annual fluxes and 14C data, it accounted less well for short-term variations in DOC concentrations.

From systems biology to photosynthesis and whole-plant physiology: a conceptual model for integrating multi-scale networks.

Abstract: Network analysis is now a common statistical tool for molecular biologists. Network algorithms are readily used to model gene, protein and metabolic correlations providing insight into pathways driving biological phenomenon. One output from such an analysis is a candidate gene list that can be responsible, in part, for the biological process of interest. The question remains, however, as to whether molecular network analysis can be used to inform process models at higher levels of biological organization. In our previous work, transcriptional networks derived from three plant species were constructed, interrogated for orthology and then correlated with photosynthetic inhibition at elevated temperature. One unique aspect of that study was the link from co-expression networks to net photosynthesis. In this addendum, we propose a conceptual model where traditional network analysis can be linked to whole-plant models thereby informing predictions on key processes such as photosynthesis, nutrient uptake and as...

Effects of climatic variability and change

Abstract: Climate profoundly shapes forests. Forest species composition, productivity, availability of goods and services, disturbance regimes, and location on the landscape are all regulated by climate. Much research attention has focused on the problem of projecting the response of forests to changing climate, elevated atmospheric carbon dioxide (CO2) concentrations, and nitrogen deposition, deepening our understanding since the publication of the last forest sector assessment (Ryan et al. 2008). We have many new examples of how changes in climate over the period 1971–2000 have affected forest ecosystems, including long-term monitoring data on forest change, multifactor experiments that document the potential interactions between temperature and elevated CO2, and new modeling approaches that project the effect of projected changes in climate on forest ecosystems, their goods and services, and their disturbance regimes. Climate projections are being done on a finer spatial scale, and global climate models include more detail and feedbacks with terrestrial processes. Downscaled estimates from these models are more readily available and have been used for more regional and local assessments. Despite the large amount of new research, this new information has not substantially altered the primary projections made in the last assessment (Ryan et al. 2008). In this assessment, we have added more detail about the effects covered in the last assessment (especially altered disturbance regimes and potential effects on hydrologic processes), provided more information about regional effects, and covered additional topics.

Tree-ring growth and wood chemistry response to manipulated precipitation variation for two temperate quercus species

Abstract: We examined the relationship among ambient and manipulated precipitation, wood chemistry, and their relationship with radial growth for two oak species in eastern Tennessee. The study took place on the Walker Branch Throughfall Displacement Experiment (TDE) site, located at the Oak Ridge National Laboratory in Oak Ridge, TN. Two dominant species, white oak (Quercus alba) and chestnut oak (Quercus prinus), were selected for study from a 13-year experiment of whole-stand precipitation manipulation (wet, ambient and dry). The relationships between tree-ring width and climate were compared for both species to determine the impact of precipitation manipulations on ring width index. This study used experimental spectroscopy techniques to measure the sensitivity of tree-ring responses to directional changes in precipitation over 13 years, and the results suggest that oaks at this study site are resilient to imposed changes, but sensitive to inter-annual variations in climate. Laser-induced breakdown spe...

Air flow and heat transfer in a temperature-controlled open top enclosure

Abstract: A large 12-meter-diameter open top enclosure (OTE) equipped with two unique belowground and above ground heating systems was built and intensively tested in Oak Ridge, TN, USA. The OTE is a prototype for use within an environmental change experiment, in which replica units will be built in Minnesota to assess the response of northern peatland ecosystems to increases in temperature and elevated atmospheric CO2. For several months, temperatures, energy, wind speed and relative humidity were monitored throughout the enclosure space to assess the enclosure performance and efficiency. In parallel, Computational Fluid Dynamics (CFD) simulations were performed with ANSYS-CFX to investigate the impacts of external wind, buoyancy, and OTE design on the temperatures achieved within the enclosure. The addition of a frustum that partially reduced the top opening was also investigated experimentally and numerically. The OTE is capable of achieving a temperature differential of at least +6°C for air using a combination of 8 electrical heaters. Differential temperatures were sustained for several months. The experimental data and the numerical results showed that the addition of a frustum dramatically decreases the operating cost of the OTE and leads to better control over the differential air temperature in the enclosure. Buoyancy forces and winds heavily impacted enclosure performance. It was also found that the heating efficiency of the OTE depends mainly on the wind speed, and that there exists a critical wind speed at which the heating efficiency is the highest.Copyright © 2012 by ASME

© 2012 Landes Bioscience. Do not distribute. From systems biology to photosynthesis and whole-plant physiology A conceptual model for integrating multi-scale networks

Abstract: Network analysis is now a common statistical tool for molecular biologists. Network algorithms are readily used to model gene, protein and metabolic correlations providing insight into pathways driving biological phenomenon. One output from such an analysis is a candidate gene list that can be responsible, in part, for the biological process of interest. The question remains, however, as to whether molecular network analysis can be used to inform process models at higher levels of biological organization. In our previous work, transcriptional networks derived from three plant species were constructed, interrogated for orthology and then correlated with photosynthetic inhibition at elevated temperature. One unique aspect of that study was the link from co-expression networks to net photosynthesis. In this addendum, we propose a conceptual model where traditional network analysis can be linked to whole-plant models thereby informing predictions on key processes such as photosynthesis, nutrient uptake and assimilation, and C partitioning.