Increasing fire and the decline of fire adapted black spruce in the boreal forest.

Intensifying wildfire activity and climate change can drive rapid forest compositional shifts. In boreal North America, black spruce shapes forest flammability and depends on fire for regeneration. This relationship has helped black spruce maintain its dominance through much of the Holocene. However, with climate change and more frequent and severe fires, shifts away from black spruce dominance to broadleaf or pine species are emerging, with implications for ecosystem functions including carbon sequestration, water and energy fluxes, and wildlife habitat. Here, we predict that such reductions in black spruce after fire may already be widespread given current trends in climate and fire. To test this, we synthesize data from 1,538 field sites across boreal North America to evaluate compositional changes in tree species following 58 recent fires (1989 to 2014). While black spruce was resilient following most fires (62%), loss of resilience was common, and spruce regeneration failed completely in 18% of 1,140 black spruce sites. In contrast, postfire regeneration never failed in forests dominated by jack pine, which also possesses an aerial seed bank, or broad-leaved trees. More complete combustion of the soil organic layer, which often occurs in better-drained landscape positions and in dryer duff, promoted compositional changes throughout boreal North America. Forests in western North America, however, were more vulnerable to change due to greater long-term climate moisture deficits. While we find considerable remaining resilience in black spruce forests, predicted increases in climate moisture deficits and fire activity will erode this resilience, pushing the system toward a tipping point that has not been crossed in several thousand years.

Understanding the nasal airway: principles and practice.

LEARNING OBJECTIVES: After studying this article, the reader should be able to: 1. Describe the soft-tissue, cartilaginous, and bony anatomy of the nose. 2. Describe the anatomy and function of the nasal valves. 3. Discuss the governing physiologic principles responsible for airflow dynamics. 4. Discuss the various functions of the nose. 5. Demonstrate an appropriate evaluation of the nasal airway. 6. Discuss the differential diagnosis of nasal obstruction. 7. Discuss appropriate management options for nasal airway obstruction. The nose is a complex, multifunctional organ that requires respect and understanding from the rhinoplasty surgeon. The etiologic and pathologic characteristics of each patient's nasal airway problem determine the treatment of the nasal airway. Frequently, medical management is sufficient without operative intervention. Recent advances have shown that nasal valves in airway patency may play a more important role than the septum. The rhinoplasty surgeon's understanding of the anatomy and physiology of the nasal airway, along with the causes of obstruction, can pave the way for a proper evaluation and appropriate management of nasal airway problems. Lack of understanding can result in misdiagnosis and mismanagement. This article outlines current concepts of medical and surgical management of nasal airway problems and discusses in detail the key concepts and principles in the practical management of the nasal airway.