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Old trees (defined here as ≥ 150 years old) can be rare in many forests because of past timber harvest, uncharacteristically severe wildfires, and - increasingly - climate change. Old trees provide unique structural, ecological, scientific, and aesthetic values missing in forests containing only younger trees. Here we compile crossdated ages from over 10,000 living and dead trees sampled in montane forests of the central Rocky Mountains in Colorado and southern Wyoming, USA, to examine changes in age structure of the oldest trees since Euro-American settlement and to provide guidelines to aid in identification of old trees for retention during ecological restoration treatments. Eroded stumps (containing only heartwood) were found in over 93% of 179 randomly sampled plots. Number of stumps found in each plot was proportional to reconstructed historical (1860 C.E.) stand basal area. The regional median date of maximum plot tree recruitment was over 150 years older when including stumps versus only living trees, suggesting that if all those harvested trees had survived to the present, the ages of oldest trees would be substantially greater than it is today. However, the regional median age of oldest trees in 1860 before harvesting was not different from the median age of oldest living trees in the current forest (246 vs. 248 years), which alternatively suggests that the regional population of oldest trees has recovered to near historical levels in the time since early Euro-American harvests. Each living tree at the time of sampling was assigned to one of three potential age classes based on a subjective assessment of tree morphology: old (likely ≤ 150 years old), young (likely <150 years old), or transitional (containing a mixture of young and old tree characteristics). Trees assigned to the old and young morphology categories were classified correctly 88% to 96% of the time depending on species as confirmed by their crossdated ages. Regression tree analysis revealed that tree diameter at breast height was not as reliable a predictor of tree age as were morphological characteristics. A measure of site productivity was a significant variable to use to separate transitional morphology trees into old and young age classes, but classification accuracy was not high because of large variability in ages of these trees. Our results suggest that residual live old trees in the current forest, although perhaps not rare compared to historical age distributions, should be retained during restoration treatments, and that using simple morphological and environmental criteria to identify old trees is more reliable than tree size alone. [ABSTRACT FROM AUTHOR]

The 2010 Church's Park Fire burned beetle-killed lodgepole pine stands in Colorado, including recently salvage-logged areas, creating a fortuitous opportunity to compare the effects of salvage logging, wildfire and the combination of logging followed by wildfire. Here, we examine tree regeneration, surface fuels, understory plants, inorganic soil nitrogen and water infiltration in uncut and logged stands, outside and inside the fire perimeter. Subalpine fir recruitment was abundant in uncut, unburned, beetle-killed stands, whereas lodgepole pine recruitment was abundant in cut stands. Logging roughly doubled woody fuel cover and halved forb and shrub cover. Wildfire consumed all conifer seedlings in uncut and cut stands and did not stimulate new conifer regeneration within four years of the fire. Aspen regeneration, in contrast, was relatively unaffected by logging or burning, alone or combined. Wildfire also drastically reduced cover of soil organic horizons, fine woody fuels, graminoids and shrubs relative to unburned, uncut areas; moreover, the compound effect of logging and wildfire was generally similar to wildfire alone. This case study documents scarce conifer regeneration but ample aspen regeneration after a wildfire that occurred in the later stage of a severe beetle outbreak. Salvage logging had mixed effects on tree regeneration, understory plant and surface cover and soil nitrogen, but neither exacerbated nor ameliorated wildfire effects on those resources. [ABSTRACT FROM AUTHOR]

Mulching fuels treatments have been increasingly implemented by forest managers in the western USA to reduce crown fire hazard. These treatments use heavy machinery to masticate or chip unwanted shrubs and small-diameter trees and broadcast the mulched material on the ground. Because mulching treatments are relatively novel and have no natural analog, their ecological impacts are poorly understood. We initiated a study in 2007 to examine the effects of mulching on vascular understory plant communities and other ecological properties and processes. We established 15 study areas in Colorado, USA, distributed across three broadly-defined coniferous forest types: pinyon pine – juniper ( Pinus edulis – Juniperus spp.); ponderosa pine ( P. ponderosa ) and ponderosa pine – Douglas-fir ( Pseudotsuga menziesii ); and lodgepole pine ( P. contorta ) and mixed conifer (lodgepole pine, limber pine ( P. flexilis ), and other conifers). Measurements were conducted along 50-m transects 2–4 years post-treatment (2007 or 2008), and again 6–9 years post-treatment (2012), in three mulched and three untreated stands per study area. Mulching dramatically reduced overstory basal area (i.e., basal area of trees >1.4 m tall) and increased forest floor biomass (i.e., the biomass of litter, duff, and woody material <2.5 cm in diameter) for all three forest types, as evidenced by previous measurements conducted in our mulched and untreated stands 2–4 years post-treatment. The total richness and cover of understory plant species in mulched stands 2–4 years post-treatment were either similar to, or greater than, the richness and cover in untreated stands for the three forest types; however, by 6–9 years post-treatment, total understory plant richness and cover in mulched stands were always greater. The stimulatory effect of mulching on understory plants was largely driven by the response of graminoids and forbs; mulching had little effect on shrub richness or cover. The increases in total understory plant richness and cover in mulched stands 6–9 years post-treatment occurred despite the fact that understory plants tended to be heavily suppressed in localized areas where the forest floor layer was deep, because such areas were rare. Exotic plant richness and cover were commonly higher in mulched than untreated stands in both sampling periods, but nonetheless understory plant communities remained highly native-dominated. Taken as a whole, our findings suggest that mulching treatments promoted denser and more diverse native understory plant communities in these three Colorado coniferous forest types, particularly over the longer-term. [ABSTRACT FROM AUTHOR]

Altered fuels and climate change are transforming fire regimes in many of Earth's biomes. Postfire reassembly of vegetation - paramount to C storage and biodiversity conservation - frequently remains unpredictable and complicated by rapid global change. Using a unique data set of pre and long-term postfire data, combined with long-term data from nearby unburned areas, we examined 10 years of understory vegetation assembly after the 2002 Hayman Fire. This fire was the largest wildfire in recorded history in Colorado, USA. Resistance (initial postfire deviance from prefire condition) and resilience (return to prefire condition) declined with increasing fire severity. However, via both resistance and resilience, 'legacy' species of the prefire community constituted >75% of total plant cover within 3 years even in severely burned areas. Perseverance of legacy species, coupled with new colonizers, created a persistent increase in community species richness and cover over prefire levels. This was driven by a first-year increase (maintained over time) in forbs with short life spans; a 2-3-year delayed surge in long-lived forbs; and a consistent increase in graminoids through the 10th postfire year. Burning increased exotic plant invasion relative to prefire and unburned areas, but burned communities always were >89% native. This study informs debate in the literature regarding whether these increasingly large fires are 'ecological catastrophes.' Landscape-scale severe burning was catastrophic from a tree overstory perspective, but from an understory perspective, burning promoted rich and productive native understories, despite the entire 10-year postfire period receiving below-average precipitation. [ABSTRACT FROM AUTHOR]

Pile burning is a common means of disposing the woody residues of logging and for post-harvest site preparation operations, in spite of the practice’s potential negative effects. To examine the long-term implications of this practice we established a 50-year sequence of pile burns within recovering clear cuts in lodgepole pine forests. We compared tree, shrub and herbaceous plant abundance and documented indicators of soil degradation in openings where logging residue was piled and burned as part of post-harvest site preparation and the adjacent forests regenerating after clear cutting. We found that pile burning creates persistent 10–15 m diameter openings with lower tree densities (<500 trees ha −1 ; stems >2.54 cm diameter at 1.4 m height) compared to surrounding regenerating pine stands (2000–5000 trees ha −1 ). Low tree seedling and sapling densities (stems <2.54 cm diameter at 1.4 m height) in the openings (10–20% of regenerating forest), suggest they will remain poorly-stocked into the future. We observed evidence of high severity burning, including layers of soil charcoal and hardened red soil across the time series, but no sign that water infiltration, compaction or other indicators of soil degradation were consistent barriers to plant recolonization. Forb and graminoid cover, for example, was higher in the burn scar openings compared to regenerating forests. Pile burn openings are formed by the loss of pine seed during burning and short-term soil changes, but it is uncertain what factors maintain the openings during subsequent decades. As conducted for site preparation, the herbaceous plant-dominated openings are not extensive (<5% cover within clear cut units), and we found few invasive, non-native plants and no indication that soil conditions were sufficiently altered to explain 50 years of poor tree regeneration. Nevertheless, persistence of the openings and recent increases in the number and size of piles from fuels and bark beetle salvage treatments has prompted resource managers to consider options for utilization and on-site retention of harvest residue. [ABSTRACT FROM AUTHOR]

• Recently-burned area in southwestern US forests is increasing. • Landscape context, values, and future trajectories of change can inform management. • Postfire forest patches can be managed for resilience to future fires. • Novel reforestation practices may help adapt to future climate and fire in some areas. 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. [ABSTRACT FROM AUTHOR]

• Lodgepole pine regeneration density was highest in whole-tree harvest areas. • Soil moisture or nitrogen supply were similar in uncut and whole-tree harvest areas. • Planted pine grew best in bole-only areas where soil resources were highest. • The density of regeneration in uncut areas will ensure adequate post-beetle stocking. • Advance regeneration was the fastest-growing component of the forest growing stock. Recent mountain pine beetle (Dendroctonus ponderosae ; MPB) outbreaks have caused one of the most widespread and dramatic changes in forest condition in North American forests in more than a century and highlighted challenges facing resource managers. To address uncertainty regarding the consequences of post-harvest woody residue management on soil productivity and tree regeneration following MPB outbreaks in lodgepole pine-dominated forests we compared three treatment prescriptions (bole-only harvest, whole-tree harvest, and whole-tree harvest with scarification) and uncut stands. The study was replicated at twelve sites across a range of operational project areas and stand conditions in northern Colorado. Salvage logging generated a new cohort of lodgepole pine at densities far above the threshold considered adequate to develop into well-stocked stands (1700–2300 t ha−1 in logged compared to 537 t ha−1 in uncut areas). Regeneration density was generally highest in whole-tree harvested areas. Growth of planted and naturally regenerating lodgepole pine recruits was best in the bole-only, residue-retention treatment, where soil moisture and inorganic nitrogen supply was also highest. However, we found no indication that whole-tree harvesting lowered soil moisture, soil nitrogen supply or pools relative to uncut stands. The density of trees regenerating beneath uncut stands indicates that post-outbreak forest structure should recover without management in these forests. The cohort of trees that regenerated following MPB-related overstory mortality, but prior to harvesting, comprise the fastest-growing component of the growing stock and 30% of its density. The broader watershed-scale outcomes of these treatments and their implications for wildfire behavior and other effects remain uncertain. However, the soil and tree patterns we report during the initial post-treatment period inform on-going decisions regarding harvest and residue retention and create a platform to guide future forest management research. [ABSTRACT FROM AUTHOR]