Response of surface horizons in an oak forest to prescribed burning

The reduction of forest floor ground cover and litter layers by prescribed fires may alter the morphology (field and micro) and physical properties of surface horizons. This study determined long-term (35 yr) changes in surface horizon bulk density, organic matter concentration and content, and morphology in response to periodic (5 yr) and annual (1 yr) prescribed fires. Soils were fine-silty, siliceous, thermic Glossic Fragiuldults, supporting mixed oak vegetation in middle Tennessee. Upper mineral soils (0- to 2-cm and 0- to 7.6-cm depths) were sampled and detailed field descriptions made. Periodic and control plots had a thin layer of Oi, Oe, and Oa horizons 5 yr after the 1993 burn, whereas on annual burn plots a 1- to 2-cm charred layer was present. Significant reductions in organic matter concentration and mean thickness of the A horizon were found from burning (A horizons thicknesses were 6.4, 4.6, and 2.9 cm in control, periodic, and annual plots, respectively). Periodic burns did not significantly alter the organic matter and bulk density of the upper 7.6 cm of mineral soil; however, annual burns did result in significantly higher bulk densities (1.01, 1.07, and 1.29 Mg m-3 in control, periodic, and annual plots, respectively) and lower organic matter concentrations and contents. Microscopic investigations confirmed that compaction was increased from annual burning. Thin sections also revealed that the granular structure of the A horizons in control and periodic plots resulted from bioterbation of macro and mesofauna, fungi, and roots. Long-term annual burning greatly affected surface soil properties, whereas periodic burning on a 5-yr cycle had only limited effects.

Fast, quantitative nucleoside protection under solvent-free conditions

Persilylation of nucleoside hydroxyls was effected in quantitative yields under solvent-free conditions using a ball mill. In addition, one-pot persilylation and acylation of cytidine was performed as an exemplar reaction demonstrating the utility of solvent-free approaches to nucleoside chemistry.

Forest fires and insects: palaeoentomological research from a sub-fossil burnt forest.

The role of fire within Pinus-mire ecosystems is explored by focusing on a palaeoentomological investigation of the extensive burnt fossil forest preserved within the basal deposits of the raised mires of Thorne and Hatfield Moors, Humberhead Levels, eastern England. Remains of charred tree macrofossils (roots, stumps and trunks) are widely distributed across both sites, mainly comprising Pinus and Betula. Evidence from this research and elsewhere suggest fires were a common event on Pinus mires, and may indicate that such episodes played an important role in the development of raised bogs. A fire-loving (pyrophilous) insect fauna appears to have been attracted to the burnt areas and the decline and extirpation in Britain of a number of pyrophilous species (e.g. Stagetus borealis Isrealsson) suggests the former importance of this type of habitat within British Pinus-mire systems. The lack of consideration given to the role of natural fires within the British landscape is questioned and the interpretation of charcoal within mire deposits as a possible anthropogenic indicator is highlighted as an area that would benefit some reconsideration.

Retrodirective Antenna Spatial Data Protection

In this letter, we show how a 2.4-GHz retrodirective array operating in a multipath rich environment can be utilized in order to spatially encrypt digital data. For the first time, we give experimental evidence that digital data that has no mathematical encryption applied to it can be successfully recovered only when it is detected with a receiver that is polarization-matched to that of a reference continuous-wave (CW) pilot tone signal. In addition, we show that successful detection with low bit error rate (BER) will only occur within a highly constrained spatial region colocated close to the position of the CW reference signal. These effects mean that the signal cannot be intercepted and its modulated data recovered at locations other than the constrained spatial region around the position from which the retrodirective communication was initiated.