Historical and Modern Fire Regimes in Piñon-Juniper Woodlands, Dinosaur National Monument, United States

Twentieth-century fire exclusion has produced unnatural and undesirable changes in vegetation structure and dynamics of many rangelands of western North America, but not all kinds of ecosystems have been so affected. A comparison of the historical and modern fire regimes, especially in peripheral populations that can be particularly vulnerable to climatic change, can help guide fire management planning with information on the degree to which a local area has been altered by past fire exclusion. Historical fire rotations in piñon-juniper (Pinus edlis Engelm.-Juniperus spp. L.) woodlands vary widely across woodland types, hence management applications should be specific to local historical and modern fire characteristics. We asked if the modern fire rotation is similar to or longer than the historical fire rotation before arrival of Euro-American settlers on the northern woodland boundary in northwestern Colorado and northeastern Utah. This study was initiated by managers from Dinosaur National Monument (DINO) concerned that lack of 20th-century fire may have allowed unnatural expansion of piñon-juniper woodlands into grasslands and shrublands. Fire history analysis using dendrochronology methods suggests a historical (pre-1900) fire rotation of ca. 550 yr, comparable with or longer than many other woodlands on the Colorado Plateau. In contrast, analysis of digital fire records reveals that the fire rotation between 1981 and 2010 was substantially shorter than historical; if only natural fires are considered, the piñon-juniper fire rotation was 364 yr, and if anthropogenic fires were included, the fire rotation was 233 yr. This shorter fire rotation supports a previously documented contraction in woodland extent in DINO during the past 90 yr. Our data support reducing the amount of fire in the landscape to preserve the integrity of the natural vegetation of this and other piñon-juniper woodlands, especially under projections of warmer and drier future climates. © 2017 The Society for Range Management. Published by Elsevier Inc. All rights reserved.The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information

Trajectories in the Evolution of Technology: A Multi-Level Study of Competition in Formula 1 Racing.

This paper explores the trajectories of three key technologies in Formula 1 racing at the component, firm and system levels of analysis. The purpose is to gain an understanding of the evolutionary forces that contribute to the emergence and survival of dominant designs. Based on archival data and contemporaneous accounts of the period 1967-1982, we develop a series of propositions specifying the evolutionary forces acting on technological trajectories within each level of analysis. The resulting framework leads to a set of predictions about relationships between technological transparency, co-evolution, and the emergence of dominant designs. Specifically, we argue that when the costs and difficulty associated with transferring component knowledge between firms is low (technological transparency is high), technologies tend to co-evolve across firms, leading to the development of complementary technologies and increasing the likelihood of industry dominance. Where transparency is low, however, technologies tend to co-evolve across functions within firms, leading to the development of competing technologies across firms, increasing the likelihood of a technology's dominance within the firm. The data and argument suggest that the forces acting on these two types of technological trajectories are self-reinforcing, so that as momentum builds behind a trajectory, it becomes more likely that its evolutionary path will end in either firm-or system-level dominance

Forest and woodland replacement patterns following drought-related mortality

Forest vulnerability to drought is expected to increase under anthropogenic climate change, and drought-induced mortality and community dynamics following drought have major ecological and societal impacts. Here, we show that tree mortality concomitant with drought has led to short-term (mean 5 y, range 1 to 23 y after mortality) vegetation-type conversion in multiple biomes across the world (131 sites). Self-replacement of the dominant tree species was only prevalent in 21% of the examined cases and forests and woodlands shifted to nonwoody vegetation in 10% of them. The ultimate temporal persistence of such changes remains unknown but, given the key role of biological legacies in long-term ecological succession, this emerging picture of postdrought ecological trajectories highlights the potential for major ecosystem reorganization in the coming decades. Community changes were less pronounced under wetter postmortality conditions. Replacement was also influenced by management intensity, and postdrought shrub dominance was higher when pathogens acted as codrivers of tree mortality. Early change in community composition indicates that forests dominated by mesic species generally shifted toward more xeric communities, with replacing tree and shrub species exhibiting drier bioclimatic optima and distribution ranges. However, shifts toward more mesic communities also occurred and multiple pathways of forest replacement were observed for some species. Drought characteristics, species-specific environmental preferences, plant traits, and ecosystem legacies govern postdrought species turnover and subsequent ecological trajectories, with potential far-reaching implications for forest biodiversity and ecosystem services