Restoration of mountain big sagebrush steppe following prescribed burning to control western juniper.

Western juniper (Juniperus occidentalis ssp. occidentalis Hook) encroachment into mountain big sagebrush (Artemisia tridentata spp. vaseyana (Rydb.) Beetle) steppe has reduced livestock forage production, increased erosion risk, and degraded sagebrush-associated wildlife habitat. Western juniper has been successfully controlled with partial cutting followed by prescribed burning the next fall, but the herbaceous understory and sagebrush may be slow to recover. We evaluated the effectiveness of seeding perennial herbaceous vegetation and sagebrush at five sites where juniper was controlled by partially cutting and prescribed burning. Treatments tested at each site included an unseeded control, herbaceous seed mix (aerially seeded), and the herbaceous seed mix plus sagebrush seed. In the third year post-treatment, perennial grass cover and density were twice as high in plots receiving the herbaceous seed mix compared to the control plots. Sagebrush cover and density in the sagebrush seeded plots were between 74- and 290-fold and 62- and 155-fold greater than the other treatments. By the third year after treatment, sagebrush cover was as high as 12 % in the sagebrush seeded plots and between 0 % and 0.4 % where it was not seeded. These results indicate that aerial seeding perennial herbaceous vegetation can accelerate the recovery of perennial grasses which likely stabilize the site. Our results also suggest that seeding mountain big sagebrush after prescribed burning encroaching juniper can rapidly recover sagebrush cover and density. In areas where sagebrush habitat is limited, seeding sagebrush after juniper control may increase sagebrush habitat and decrease the risks to sagebrush-associated species.

Comparing burned and mowed treatments in mountain big sagebrush steppe.

Fires in mountain big sagebrush [Artemisia tridentata spp. vaseyana (Rydb.) Beetle] plant communities historically shifted dominance from woody to herbaceous vegetation. However, fire return intervals have lengthened with European settlement, and sagebrush dominance has increased at the expense of herbaceous vegetation in some plant communities. Management actions may be needed to decrease sagebrush in dense sagebrush stands to increase herbaceous vegetation. Prescribed fire is often used to remove sagebrush; however, mechanical treatments, such as mowing, are increasingly used because they are more controllable and do not pose an inherent risk of escape compared with fire. However, information on the effects of burned and mowed treatments on herbaceous vegetation and whether fire and mowed applications elicit similar vegetation responses are limited. We evaluated the effects of prescribed burning and mowing for 3 years after treatment in mountain big sagebrush plant communities. The burned and mowed treatments generally increased herbaceous cover, density, and production compared with untreated controls (P < 0.05). However, neither treatment induced a response in native perennial forb cover, density, or biomass (P > 0.05). In contrast, annual forb (predominately natives) cover, density, and biomass increased with mowing and burning (P < 0.05). Vegetation generally responded similarly in burned and mowed treatments; however, the burned treatment had less sagebrush, greater herbaceous vegetation production, and more bare ground than the mowed treatment (P < 0.05). These differences should be considered when selecting treatments to decrease sagebrush.

Interaction of historical and nonhistorical disturbances maintains native plant communities.

Historical disturbance regimes are often considered a critical element in maintaining native plant communities. However, the response of plant communities to disturbance may be fundamentally altered as a consequence of invasive plants, climate change, or prior disturbances. The appropriateness of historical disturbance patterns under modern conditions and the interactions among disturbances are issues that ecologists must address to protect and restore native plant communities. We evaluated the response of Artemisia tridentata ssp. wyomingensis (Beetle & A. Young) S.L. Welsh plant communities to their historical disturbance regime compared to other disturbance regimes. The historical disturbance regime of these plant communities was periodic fires with minimal grazing by large herbivores. We also investigated the influence of prior disturbance (grazing) on the response of these communities to subsequent disturbance (burning). Treatments were: (1) ungrazed (livestock grazing excluded since 1936) and unburned, (2) grazed and unburned, (3) ungrazed and burned (burned in 1993), and (4) grazed and burned. The ungrazed-burned treatment emulated the historical disturbance regime. Vegetation cover, density, and biomass production were measured the 12th, 13th, and 14th year post-burning. Prior to burning the presence of Bromus tectorum L., an exotic annual grass, was minimal (<0.5% cover), and vegetation characteristics were similar between grazed and ungrazed treatments. However, litter accumulation was almost twofold greater in ungrazed than in grazed treatments. Long-term grazing exclusion followed by burning resulted in a substantial B. tectorum invasion, but burning the grazed areas did not produce an invasion. The ungrazed-burned treatment also had less perennial vegetation than other treatments. The accumulation of litter (fuel) in ungrazed treatments may have resulted in greater fire-induced mortality of perennial vegetation in ungrazed compared to grazed treatments. Our results demonstrate that prior disturbances exert a strong influence on the response of plant communities to subsequent disturbances and suggest that low-severity disturbances may be needed in some plant communities to increase their resilience to more severe disturbances. Modern deviations from historical conditions can alter ecosystem response to disturbances, thus restoring the historical disturbance regime may not be an appropriate strategy for all ecosystems.

Predicting upper lip response to 4-piece maxillary LeFort I osteotomy.

The purpose of this retrospective study was to understand and predict the multidimensional changes in upper lip morphologic features after segmental (4-piece) maxillary Le Fort I advancement/impaction with VY closure and alar base cinch sutures. The study evaluated longitudinal lateral cephalograms of 57 patients (42 women, 15 men) 27.5 +/- 11.2 years of age before surgery. Lateral cephalograms with teeth in occlusion and lips in repose were taken 2 weeks before surgery and at least 6 months after the operation. Mean postsurgical duration was 15.5 months. The upper lip predictably moved anteriorly in a graduated fashion, from 50% (subnasale) to 90% (labrale superius) the amount of the underlying osseous anterior movement, and showed a slight lengthening (0.73 +/- 1.9 mm) from subnasale to upper lip stomion. The upper lip surface contour was also straightened as a result of the surgical movement. Multiple regression models showed that the anterior changes in the landmarks prosthion and facial surface of the upper incisor were the most important variables in predicting upper lip response. The prediction equations for horizontal movements explained 86% to 94% of the variation, with errors of the estimates that range between 1.27 mm and 1.65 mm. The models, when applied to an independent validation sample of 14 subjects, explained between 86% and 94% of the total variation. The conclusion is that upper lip response after 4-piece Le Fort I advancement/impaction (VY closure and alar base cinch suture) can be accurately predicted.

Surgical modification for the correction of chin deformities.

This article describes a design of osseous chin surgery based on the principle of the tenon and mortise. This modification allows for precision of movement, ease of repositioning, and adaptation of rigid skeletal stabilization of mobilized osseous segments in the chin. With this technique, the inferior border of the mandible can be moved superiorly, inferiorly, anteriorly, posteriorly, or transversely or in any combination of these directions.