Landscape-Scale Drivers of Resistance and Resilience to Bark Beetles: A Conceptual Susceptibility Model

Bark beetle (Dendroctonus spp.) outbreaks in the middle latitudes of western North America cause large amounts of tree mortality, outstripping wildfire by an order of magnitude. While temperatures play an important, and direct role in the population dynamics of ectothermic bark beetles, an equally important influence is the nature of the host substrate—the structure and composition of forested communities. For many of the dominant tree species in the western United States, “hazard” indices have been developed for specific bark beetles, which generally include three key variables—host tree size, absolute or relative density of the stand, and percentage of host composition. We provide a conceptual model to apply these three variables across forest ecosystems and bark beetles that shifts the thinking from a species–specific model to a model which focuses on the underlying ecological factors related to bark beetle outbreak susceptibility. We explored the use of our model across multiple scales using the Forest Inventory and Analysis database: Interior West, USA; the states of Colorado and Arizona; and specific national forests within Arizona that are implementing a large-scale restoration effort. We demonstrated that across the Interior West and Colorado, the vast majority of forests have moderate to high susceptibility to bark beetles. Our conceptual model maintains the simplicity of previous “hazard” models but acknowledges the need to consider scale when managing bark beetles. It also shifts the management approach from resistance thinking to the development of “associational resilience”, where the focus is not on any one individual stand or area but the longer-term perspective of forest persistence across the landscape.

A climatic dipole drives short- and long-term patterns of postfire forest recovery in the western United States

Researchers are increasingly examining patterns and drivers of postfire forest recovery amid growing concern that climate change and intensifying fires will trigger ecosystem transformations. Diminished seed availability and postfire drought have emerged as key constraints on conifer recruitment. However, the spatial and temporal extent to which recurring modes of climatic variability shape patterns of postfire recovery remain largely unexplored. Here, we identify a north–south dipole in annual climatic moisture deficit anomalies across the Interior West of the US and characterize its influence on forest recovery from fire. We use annually resolved establishment models from dendrochronological records to correlate this climatic dipole with short-term postfire juvenile recruitment. We also examine longer-term recovery trajectories using Forest Inventory and Analysis data from 989 burned plots. We show that annual postfire ponderosa pine recruitment probabilities in the northern Rocky Mountains (NR) and the southwestern US (SW) track the strength of the dipole, while declining overall due to increasing aridity. This indicates that divergent recovery trajectories may be triggered concurrently across large spatial scales: favorable conditions in the SW can correspond to drought in the NR that inhibits ponderosa pine establishment, and vice versa. The imprint of this climatic dipole is manifest for years postfire, as evidenced by dampened long-term likelihoods of juvenile ponderosa pine presence in areas that experienced postfire drought. These findings underscore the importance of climatic variability at multiple spatiotemporal scales in driving cross-regional patterns of forest recovery and have implications for understanding ecosystem transformations and species range dynamics under global change.

Shopocracy

This chapter explores the development of West End shopping between 1850 and 1914. The big change was the coming of the department store which in turn transformed Oxford Street in particular. The chapter shows the difference that Selfridge’s made although it argues that smaller shops were at least as important. Both allowed for the feminization of the West End as middle-class women increasingly found a trip into the district essential to keeping up with fashions and constructing the domestic interior. West End shops supplied a form of education in taste, fashion, and status. They dramatized capitalist abundance within a frame shaped by orientalism and cosmopolitanism. The chapter looks in particular at Liberty’s and Selfridge’s but also emphasizes the labour that made shops possible in the form of shopgirls.

Topographic control of forest species distributions in the Interior West USA

Background The geographic distribution of forest and woodland ecosystems in the Interior West United States is strongly influenced by topographic gradients that, in part, control moisture availability through their effect on insolation, and precipitation capture and retention. Through an empirical approach, we use unique, plot-level data from the Forest Inventory and Analysis Program ( n = 13,437) over eight ecoregions within eight Interior West states to characterize the distribution of the 12 most abundant tree species with respect to the effects of elevation, slope aspect, and slope steepness. Results Across species, elevation, and aspect, most plots occurred on gentle slopes and the number decreased with increasing slope. Species-specific differences to microenvironmental conditions were evident in the variation between observed (plots containing a subject tree) and expected (all forest plots from the systematic sample) numbers of plots across the gradient combinations. Species groups, broadly defined as woodland, montane, and subalpine, generally exhibited similar responses and revealed more generality than hypothesized. Only Douglas-fir, white fir, subalpine fir, and Engelmann spruce exhibited significant patterns of affinity for particular aspects—most often on north and least often on south—with the relative importance of south aspects decreasing with increasing elevation. Limber pine showed unique, unimodal patterns of affinity for moderately steep slopes, with no consistent patterns by aspect or elevation. Although not significant, at high elevations woodland species exhibited a tendency to occur more often on south aspects on gentle to intermediate slopes, and less often on north aspects. Conclusions Unique microenvironments created by interactions between aspect, slope, and elevation create some predictability in patterns of geographic distribution. However, the general lack of species-specific response suggests that patterns of occurrence in relation to physiographic gradients is much broader than in common generalizations.