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Amplified by warming temperatures and drought, recent outbreaks of native bark beetles (Curculionidae: Scolytinae) have caused extensive tree mortality throughout Europe and North America. Despite their ubiquitous nature and important effects on ecosystems, forest recovery following such disturbances is poorly understood, particularly across regions with varying abiotic conditions and outbreak effects.To better understand post‐outbreak recovery across a topographically complex region, we synthesized data from 16 field studies spanning subalpine forests in the Southern Rocky Mountains, USA. From 1997 to 2019, these forests were heavily affected by outbreaks of three native bark beetle species (Dendroctonus ponderosae, Dendroctonus rufipennis and Dryocoetes confusus). We compared pre‐ and post‐outbreak forest conditions and developed region‐wide predictive maps of post‐outbreak (1) live basal areas, (2) juvenile densities and (3) height growth rates for the most abundant tree species – aspen (Populus tremuloides), Engelmann spruce (Picea engelmannii), lodgepole pine (Pinus contorta) and subalpine fir (Abies lasiocarpa).Beetle‐caused tree mortality reduced the average diameter of live trees by 28.4% (5.6 cm), and species dominance was altered on 27.8% of field plots with shifts away from pine and spruce. However, most plots (82.1%) were likely to recover towards pre‐outbreak tree densities without additional regeneration. Region‐wide maps indicated that fir and aspen, non‐host species for bark beetle species with the most severe effects (i.e. Dendroctonus spp.), will benefit from outbreaks through increased compositional dominance. After accounting for individual size, height growth for all conifer species was more rapid in sites with low winter precipitation, high winter temperatures and severe outbreaks.Synthesis. In subalpine forests of the US Rocky Mountains, recent bark beetle outbreaks have reduced tree size and altered species composition. While eventual recovery of the pre‐outbreak forest structure is likely in most places, changes in species composition may persist for decades. Still, forest communities following bark beetle outbreaks are widely variable due to differences in pre‐outbreak conditions, outbreak severity and abiotic gradients. This regional variability has critical implications for ecosystem services and susceptibility to future disturbances. [ABSTRACT FROM AUTHOR]

Increased wildfire activity and climate change have intensified disturbance regimes globally and have raised concern among scientists and land managers about the resilience of disturbed landscapes. Here we test the effects of climate, topographic variation and pre‐fire stand structure on regeneration in lodgepole pine (Pinus contorta var. latifolia) forests following high‐severity fire over the past seven decades.We surveyed lodgepole pine regeneration 8–67 years after eight high‐severity fires in western Colorado and southern Wyoming. We used dendroecological methods and machine learning to (a) identify temporal trends in post‐fire regeneration and (b) examine influences of climate on post‐fire regeneration, with focus on post‐fire establishment, initial post‐fire density and radial growth.All burned sites reached a median stocking density of ≥150 seedlings/ ha, but there was a large range of spatial heterogeneity, with regeneration being absent or scarce in many plots, implying a trend of increasing patchiness with likely cascading effects on subsequent patterns and processes. Our analysis indicated that (a) post‐fire regeneration is influenced by pre‐fire stand structure (stand age and density), elevation and post‐fire minimum temperature; (b) pre‐fire densities of >14,000 stems/ha promoted successful stocking (≥150 seedlings/ha) and reduced lag between the disturbance and initial regeneration; and (c) minimum post‐fire temperatures >−1.6°C reduced lag of initial regeneration and promoted initial radial growth.Synthesis. Our study demonstrates that lodgepole pine in high‐elevation forests are regenerating following fires under recent climatic trends, but that regeneration is affected by post‐fire climatic conditions. Importantly, forest patchiness may be increasing in a way that affects future ecological dynamics and may compromise the resilience of these systems. [ABSTRACT FROM AUTHOR]

Biological invasions are a leading cause of rapid ecological change and often present a significant financial burden. As a vibrant discipline, invasion biology has made important strides in identifying, mapping, and beginning to manage invasions, but questions remain surrounding the mechanisms by which invasive species spread and the impacts they bring about. Frequent, multiscalar ecological monitoring such as that provided through the National Ecological Observatory Network (NEON) can be an important tool for addressing some of these questions. We articulate a set of major outstanding questions in invasion biology, consider how NEON data science is positioned to contribute to addressing these questions, and provide suggestions to help equip a growing contingent of NEON data users in solving invasion biology problems. We demonstrate these ideas through four case studies examining the mechanisms of plant invasions in the U.S. Intermountain West. In Case Study I, we evaluate the relationships between native species richness, non‐native species richness, and probability of invasion across scales. In Case Studies II and III, we explore the relationship between environmental factors and non‐native species presence to understand invasion mechanisms. Case Study IV outlines a method for improving the ability to distinguish invasive plants from native vegetation in remotely sensed data by leveraging temporal patterns of phenology. There are many novel elements in the NEON sampling design that make it uniquely poised to shed light on the mechanisms that can help us understand invasibility, prediction, and progression, as well as on the variability, longevity, and interactions of multiple invasive species' impacts. Thus, knowledge gained through analysis of NEON data is expected to inform sound decision‐making in unique ways for managers of systems experiencing biological invasions. [ABSTRACT FROM AUTHOR]

Subalpine forests that historically burned every 100–300 yr are expected to burn more frequently as climate warms, perhaps before trees reach reproductive maturity or produce a serotinous seedbank. Tree regeneration after short‐interval (<30‐yr) high‐severity fire will increasingly rely on seed dispersal from unburned trees, but how dispersal varies with age and structure of surrounding forest is poorly understood. We studied wind dispersal of three conifers (Picea engelmannii, Abies lasiocarpa, and Pinus contorta var. latifolia, which can be serotinous and nonserotinous) after a stand‐replacing fire that burned young (≤30 yr) and older (>100 yr) P. contorta forest in Grand Teton National Park (Wyoming, USA). We asked how propagule pressure varied with time since last fire, how seed delivery into burned forest varied with age and structure of live forest edges, what variables explained seed delivery into burned forest, and how spatial patterns of delivery across the burned area could vary with alternate patterns of surrounding live forest age. Seeds were collected in traps along 100‐m transects (n = 18) extending from live forest edges of varying age (18, 30, and >100 yr) into areas of recent (2‐yr) high‐severity fire, and along transects in live forests to measure propagule pressure. Propagule pressure was low in 18‐yr‐old stands (~8 seeds/m2) and similarly greater in 30‐ and 100‐yr‐old stands (~32 seeds/m2). Mean dispersal distance was lowest from 18‐yr‐old edges and greatest from >100‐yr‐old edges. Seed delivery into burned forest declined with increasing distance and increased with height of trees at live forest edges, and was consistently higher for P. contorta than for other conifers. Empirical dispersal kernels revealed that seed delivery from 18‐yr‐old edges was very low (≤2.4 seeds/m2) and concentrated within 10 m of the live edge, whereas seed delivery from >100‐yr‐old edges was >4.9 seeds/m2 out to 80 m. When extrapolated throughout the burned landscape, estimated seed delivery was low (<49,400 seeds/ha) in >70% of areas that burned in short‐interval fire (<30 yr). As fire frequency increases, immaturity risk will be compounded in short‐interval fires because seed dispersal from surrounding young trees is limited. [ABSTRACT FROM AUTHOR]

The ability to estimate and model future vegetation dynamics is a central focus of contemporary ecology and is essential for understanding future ecological trajectories. It is therefore critical to understand when the influence of initial post-disturbance regeneration versus stochastic processes dominates long-term post-disturbance ecological processes. Often, conclusions about post-disturbance dynamics are based upon initial regeneration in the years immediately after disturbances. However, the degree to which initial post-disturbance regeneration indicates longer-term trends is likely to be contingent on the types, intensities, and combinations of disturbances, as well as pre-disturbance ecosystem structure and composition. Our relatively limited understanding of why initial post-disturbance regeneration is sometimes a poor predictor of future ecosystem trajectories represents a critical gap in post-disturbance ecological forecasting. We studied the composition and density of regeneration of tree species following wind blowdown in 1997, wildfire in 2002, and compounded disturbances by blowdown and wildfire in subalpine forests of Colorado. We examined regeneration of Picea engelmannii, Abies lasiocarpa, Pinus contorta, and Populus tremuloides in 180 permanent plots across 12 sites (classified by pre-disturbance age and composition) in 2003, 2010, and 2015. At sites that were blown down but not burned, regeneration was dense and dominated by Picea and Abies. At these sites, regeneration observed from 2003 to 2005 (hereafter initial regeneration) was also highly predictive of regeneration 5–10 yr later. In contrast, at sites that were burned and sites that were blown down and burned, regeneration was less dense and dominated by a mix of species. At these sites, initial regeneration was a poor predictor of longer-term trends as species dominance and overall density fluctuated over the 13-yr period. These findings call into question our ability to confidently predict ecosystem trajectories based upon observations made in the years immediately after large, severe disturbances such as wildfires and compounded disturbances. As compounded disturbances become more common under climatically driven changes in disturbance regimes, post-disturbance ecosystem trajectories may become increasingly stochastic and unpredictable. [ABSTRACT FROM AUTHOR]

We present a 576-year tree-ring-based reconstruction of streamflow for northern Utah's Weber River that exhibits considerable interannual and decadal-scale variability. While the 20th Century instrumental period includes several extreme individual dry years, it was the century with the fewest such years of the entire reconstruction. Extended droughts were more severe in duration, magnitude, and intensity prior to the instrumental record, including the most protracted drought of the record, which spanned 16 years from 1703 to 1718. Extreme wet years and periods are also a regular feature of the reconstruction. A strong early 17th Century pluvial exceeds the early 20th Century pluvial in magnitude, duration, and intensity, and dwarfs the 1980s wet period that caused significant flooding along the Wasatch Front. The long-term hydroclimatology of northern Utah is marked by considerable uncertainty; hence, our reconstruction provides water managers with a more complete record of water resource variability for assessment of the risk of droughts and floods for one of the largest and most rapidly growing population centers in the Intermountain West. [ABSTRACT FROM AUTHOR]