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Recent, widespread spruce beetle (Dendroctonus rufipennis) outbreaks have driven extensive tree mortality across western North America. Post-disturbance forest management often includes salvage logging to capture economic value of dead timber, reduce fire hazard, and meet other social or ecological objectives. Little is known about effects of salvage logging on surface fuel loads or plant understory communities in Engelmann spruce (Picea engelmannii)-dominated forests. We sampled fine and coarse woody debris, ground cover, and plant species composition along transects in spruce-beetle impacted stands in southwestern Colorado, USA. Twenty stands had been subject to clearcut 1–2 years prior to sampling; 32 stands were unlogged controls. Salvage logged stands exhibited altered surface fuels, ground cover, plant species cover, and community composition. Salvage increased 1-, 10-, and 100-hr fuels, and cover by bare ground and woody debris; cover by litter and cryptogams was reduced. Understory plant cover was reduced in salvaged stands, primarily due to losses of shrub cover. We found no difference in species diversity or richness between treated stands and controls. Salvage logging also drove shifts in plant community composition. Mean cover by non-native species was low, and not different, between control and salvage stands. Our study characterizes short-term effects that will undoubtedly change substantially over longer periods, in particular due to anticipated tree seedling growth and movement of standing dead wood from the canopy to the surface. In the near term, abundant fine woody surface fuels at salvage sites could influence the likelihood and rate of spread of surface fires, though over time we expect surface fuels in untreated stands to increase to comparable or greater levels than in salvaged stands. Differences in vascular plant cover and composition imparted by salvage harvests is also expected to change over time, though whether treated and untreated communities diverge or converge is not known. As such, we recommend that salvage harvest effects be monitored over extended time frames in order to detect longer-term trends.

The increasing incidence of wildfires across the southwestern United States (US) is altering the contemporary forest management template within historically frequent-fire conifer forests. An increasing fraction of southwestern conifer forests have recently burned, and many of these burned landscapes contain complex mosaics of surviving forest and severely burned patches without surviving conifer trees. These heterogeneous burned landscapes present unique social and ecological challenges. Severely burned patches can present numerous barriers to successful conifer regeneration, and often contain heavy downed fuels which have cascading effects on future fire behavior and conifer regeneration. Conversely, surviving forest patches are increasingly recognized for their value in postfire reforestation but often are overlooked from a management perspective. Here we present a decision-making framework for landscape-scale management of complex postfire landscapes that allows for adaptation to a warming climate and future fire. We focus specifically on historically frequent-fire forests of the southwestern US but make connections to other forest types and other regions. Our framework depends on a spatially-explicit assessment of the mosaic of conifer forest and severely burned patches in the postfire landscape, evaluates likely vegetation trajectories, and identifies critical decision points to direct vegetation change via manipulations of fuels and live vegetation. This framework includes detailed considerations for postfire fuels management (e.g., edge hardening within live forest patches and repeat burning) and for reforestation (e.g., balancing tradeoffs between intensive and extensive planting strategies, establishing patches of seed trees, spatial planning to optimize reforestation success, and improving nursery capacity). In a future of increasing fire activity in forests where repeated low- to moderate-severity fire is essential to ecosystem resilience, the decision-making framework developed here can easily be integrated with existing postfire management strategies to optimize allocation of limited resources and more actively manage burned landscapes.

Forest mastication treatments are increasingly utilized by land managers as a means of reducing tree cover for fire hazard mitigation and other habitat objectives in pinon-juniper (P-J) woodlands. Mastication converts trees into small pieces (e.g., wood chips), in the process creating canopy openings, redistributing fuel from the canopy to the surface, converting large diameter to small diameter fuels, and covering the ground with piles of woody debris. We measured vegetation and fuels at 192 sites in 24 pairs of 1–11-year-old mastication treatments and untreated adjacent controls in P-J woodlands of the Arkansas River valley, Colorado, and used paired t -tests, mixed-effects models, and gradient analysis (non-metric multidimensional scaling) to assess mastication effects. Treatments were associated with major, persistent ecological shifts relative to controls. Tree cover and canopy fuels were reduced in treatments; concomitantly, dead and down woody surface fuels, forb, and graminoid cover were elevated. Treatments exhibited much higher frequency, richness, and cover by a suite of non-native plant species including cheatgrass ( Bromus tectorum ). Non-native plant expansion appears linked to the disturbance associated with treatment activities, reductions in tree canopy, and alterations to ground cover, and effective mitigation of increases by these species may necessitate both pre- and post-treatment control measures. Shifts from native-dominated woodlands to open, weedy, herb- and shrub-dominated communities are likely to change patterns of abundance and habitat use by woodland- and forest-dependent wildlife. Decreased canopy fuels and increased herbaceous surface fuels including exotic annuals are expected to alter potential fire behavior. We encourage managers carrying out P-J mastication projects to explicitly address potential trade-offs between desired treatment outcomes and potentially unwelcome impacts, and how these might be mitigated. It may also be worth considering whether or not tree removal treatments will be warranted given anticipated climate change impacts to these woodlands.

Aspen stands in the Rocky Mountains form especially productive and diverse plant understory communities. However, little is known about canopy–understory relationships or understory dynamics, especially in light of widespread aspen decline. The purpose of our research was to assess recent aspen plant community dynamics by resampling 19 sites sampled in 1964 and 1994 near Crested Butte, Colorado. In 2010, we replicated previous sampling methods to measure canopy structure and understory composition at each site. In contrast with the conclusions of previous work in the study area, sampled aspen stands did not exhibit long-term stability, nor were they succeeding to conifers. Over the 46-year sample period, live aspen density and basal area both decreased significantly (3151–1605 stems ha−1; 39.2–33.7 m2 ha−1), with more pronounced decreases over the most recent sampling interval, 1994–2010. These changes appear linked to natural patterns of stand maturation, but may also have been enhanced by recent, drought-triggered mortality, as well as constraints on aspen regeneration imposed by elk and livestock. A striking decrease in the cover and frequency of fireweed (Chamerion angustifolium) was consistent with expectations of aging stands initiated by historic fire, and the expansion of Kentucky bluegrass (Poa pratensis) indicated strong effects of ungulate herbivory. Recent overstory losses had little effect on understory communities, which were dominated by a suite of large perennial herbs that showed little change over the sampling interval, including Fendler’s meadowrue (Thalictrum fendleri), osha (Ligusticum porteri), elk and dryspike sedge (Carex geyeri and C. siccata), and blue wildrye (Elymus glaucus). Understory community composition was not closely related to current stand conditions or light levels, but was linked with regional elevational and geographic gradients and historic (1994) stand structure.

Rocky Mountain bristlecone pine ( Pinus aristata ) and limber pine ( Pinus flexilis ) are important high-elevation pines of the southern Rockies that are forecast to decline due to the recent spread of white pine blister rust ( Cronartium ribicola ) into this region. Proactive management strategies to promote the evolution of rust resistance and maintain ecosystem function require an improved understanding of the role of disturbance on the population dynamics of both species and environmental conditions that favor seedling establishment. We examined patterns of bristlecone and limber pine regeneration across the perimeters of three, 29-year-old, high-severity burns in northern, central, and southern Colorado: Ouzel, Badger Mountain, and Maes Creek, respectively. Both species exhibited a very protracted regeneration response to these fires. Bristlecone pine regeneration was concentrated near burn edges and beneath surviving seed sources. This spatial pattern is consistent with limitations incurred by wind-dispersal, also borne out by the low occurrence of seedling clusters. Relative to unburned stands, the absolute abundance of bristlecone pine generally increased only on plots retaining some surviving trees. Limber pine regeneration pattern varied between sites: high in the burn interior at Ouzel, concentrated at burn edges at Badger, and mostly in unburned stands at Maes. Clark’s Nutcracker dispersal of limber pine in each study area was indicated by high seedling distance from possible seed sources and high frequencies of clustered stems. Except at Ouzel, the absolute abundance of limber pine decreased in burns. Across sites, establishment by both species was boosted by nearby nurse objects (rocks, fallen logs, and standing tree trunks), a relationship that extended out at least as far as the closest three such objects, usually found within 50 cm. Fire decreased the frequency of Pedicularis but increased Castilleja and Ribes species (alternate hosts of white pine blister rust), though only one species, R. cereum , was positively associated with either pine species. We conclude that regeneration of bristlecone and limber pine may benefit from natural disturbance or proactive management creating appropriately sized openings and microtopographic structure (e.g., abundant fallen logs); however, beneficial responses may require many decades to be achieved.