Assessing the Relationship between Forest Structure and Fire Severity on the North Rim of the Grand Canyon

While operational fire severity products inform fire management decisions in Grand Canyon National Park (GRCA), managers have expressed the need for better quantification of the consequences of severity, specifically forest structure. In this study we computed metrics related to the forest structure from airborne laser scanning (ALS) data and investigated the influence that fires that burned in the decade previous had on forest structure on the North Rim of the Grand Canyon in Arizona. We found that fire severity best explains the occurrence of structure classes that include canopy cover, vertical fuel distribution, and surface roughness. In general we found that high fire severity resulted in structure types that exhibit lower canopy cover and higher surface roughness. Areas that burned more frequently with lower fire severity in general had a more closed canopy and a lower surface roughness, with less brush and less conifer regeneration. In a random forests modeling exercise to examine the relationship between severity and structure we found mean canopy height to be a powerful explanatory variable, but still proved less informative than the three-component structure classification. We show that fire severity not only impacts forest structure but also brings heterogeneity to vegetation types along the elevation gradient on the Kaibab plateau. This work provides managers with a unique dataset, usable in conjunction with vegetation, fuels and fire history data, to support management decisions at GRCA.

The Ideology of Rim-Sin II of Larsa

The great rebellion against Samsuiluna of Babylon represents a watershed moment in the history of ancient Mesopotamia. In the span of a single year, most of the major cities of the south rose up against Babylon, catching Samsuiluna off guard and plunging the entire region into crisis. The Kassites made their first appearance in history, fighting against both Babylon and the rebels, and when Samsuiluna finally restored his kingdom four years later, the damage caused by the fighting was so severe that much of the south was abandoned, forcing the Babylonian king to accommodate large numbers of refugees and reconsolidate his rule in the north. Rim-Sin II, the leader of the rebellion, remains, nonetheless, an enigmatic figure. Hailing from Larsa and taking his name from the famous Larsite king of a generation before, he was eventually defeated and killed by Samsuiluna, but not before he had taken steps to secure his place as king of the entire south. Based on his year names and a letter, Rim-Sin II clearly saw himself as the legitimate king of southern Mesopotamia, using culturally weighted ideology to secure the support of important figures in the cities he sought to control. This study considers how he appealed to past kings for ideological justification as he attempted to cleave his own state away from that of Babylon, and how he aligned himself to the standard Old Babylonian royal narrative of divine selection to justify his claim to power.

Complexes of Poliovirus Serotypes with Their Common Cellular Receptor, CD155

ABSTRACT Structures of all three poliovirus (PV) serotypes (PV1, PV2, and PV3) complexed with their cellular receptor, PV receptor (PVR or CD155), were determined by cryoelectron microscopy. Both glycosylated and fully deglycosylated CD155 exhibited similar binding sites and orientations in the viral canyon for all three PV serotypes, showing that all three serotypes use a common mechanism for cell entry. Difference maps between the glycosylated and deglycosylated CD155 complexes determined the sites of the carbohydrate moieties that, in turn, helped to verify the position of the receptor relative to the viral surface. The proximity of the CD155 carbohydrate site at Asn105 to the viral surface in the receptor-virus complex suggests that it might interfere with receptor docking, an observation consistent with the properties of mutant CD155. The footprints of CD155 on PV surfaces indicate that the south rim of the canyon dominates the virus-receptor interactions and may correspond to the initial CD155 binding state of the receptor-mediated viral uncoating. In contrast, the interaction of CD155 with the north rim of the canyon, especially the region immediately outside the viral hydrophobic pocket that normally binds a cellular “pocket factor,” may be critical for the release of the pocket factor, decreasing the virus stability and hence initiating uncoating. The large area of the CD155 footprint on the PV surface, in comparison with other picornavirus-receptor interactions, could be a potential limitation on the viability of PV escape mutants from antibody neutralization. Many of these are likely to have lost their ability to bind CD155, resulting in there being only three PV serotypes.

Assessing fire regimes on Grand Canyon landscapes with fire-scar and fire-record data

Fire regimes were reconstructed from fire-scarred trees on five large forested study sites (135–810 ha) on the North and South Rims at Grand Canyon National Park. Adequacy of sampling was tested with cumulative sample curves, effectiveness of fire recording on individual trees, tree age data, and the occurrence of 20th Century fires which permitted comparison of fire-scar data with fire-record data, a form of modern calibration for the interpretation of fire-scar results. Fire scars identified all 13 recorded fires >8 ha on the study sites since 1924, when record keeping started. Records of fire season and size corresponded well with fire-scar data. We concluded that the sampling and analysis methods were appropriate and accurate for this area, in contrast to the suggestion that these methods are highly uncertain in ponderosa pine forests. Prior to 1880, fires were most frequent on low-elevation ‘islands’ of ponderosa pine forest formed by plateaus or points (Weibull Median Probability Intervals [WMPI] 3.0–3.9 years for all fires, 6.3–8.6 years for ‘large’ fires scarring 25% or more of the sampled trees). Fires were less frequent on a higher-elevation ‘mainland’ site located further to the interior of the North Rim (WMPI 5.1 years all fires, 8.7 years large fires), but fires tended to occur in relatively drier years and individual fires were more likely to burn larger portions of the study site. In contrast to the North Rim pattern of declining fire frequency with elevation, a low-elevation ‘mainland’ site on the South Rim had the longest fire-free intervals prior to European settlement (WMPI 6.5 years all fires, 8.9 years large fires). As in much of western North America, surface fire regimes were interrupted around European settlement, 1879 on the North Rim and 1887 on the South Rim. However, either two or three large surface fires have burned across each of the geographically remote point and plateau study sites of the western North Rim since settlement. To some extent, these sites may be rare representatives of nearly-natural conditions due to the relatively undisrupted fire regimes in a never-harvested forest setting.