Beetle Disturbance Research Articles

Changing Community Variations in Perceptions and Activeness in Response to the Spruce Bark Beetle Outbreak in Alaska

Local sociocultural processes including community perceptions and actions represent the most visible social impacts of various economic and environmental changes. Comparative community analysis has been used to examine diverse community perspectives on a variety of socioeconomic and environmental issues. However, as the temporal dimension of community processes remains understudied, relatively little is known regarding how such community variations change over time. This study draws on longitudinal survey data from six communities on the Kenai Peninsula, Alaska to explore temporal shifts in community differences in perceptions and activeness in response to forest disturbance associated with an extensive spruce bark beetle outbreak. The surveys were implemented in two phases over a 4-year study period. Results show that while community perceptions on the bark beetle condition waned and coalesced in some ways, significant differences remained or emerged with respect to other facets of local reactions. These shifting variances in community dimensions of the beetle disturbance were related to community positions along the beetle outbreak timeline and general community socioeconomic and biophysical situations (community context). The analysis also revealed community differences and contexts held an even more important role in predicting local responses to beetles in the re-survey. Taken together, findings from this research contribute a better understanding of the persistence and change in community variability as well as the continuity of community contextual effects.

High-resolution mapping of time since disturbance and forest carbon flux from remote sensing and inventory data to assess harvest, fire, and beetle disturbance legacies in the Pacific Northwest

Abstract. Accurate assessment of forest carbon storage and uptake is central to policymaking aimed at mitigating climate change and understanding the role forests play in the global carbon cycle. Disturbances have highly diverse impacts on forest carbon dynamics, making them a challenge to quantify and report. Time since disturbance is a key intermediate determinant that aids the assessment of disturbance-driven carbon emissions and removals legacies. We propose a new methodology of quantifying time since disturbance and carbon flux across forested landscapes in the Pacific Northwest (PNW) at a fine scale (30 m) by combining remote sensing (RS)-based disturbance year, disturbance type, and above-ground biomass with forest inventory data. When a recent disturbance is detected, time since disturbance can be directly determined by combining three RS-derived disturbance products, or time since the last stand clearing can be inferred from a RS-derived 30 m biomass map and field inventory-derived species-specific biomass accumulation curves. Net ecosystem productivity (NEP) is further mapped based on carbon stock and flux trajectories derived from the Carnegie-Ames-Stanford Approach (CASA) model in our prior work that described how NEP changes with time following harvest, fire, or bark beetle disturbances of varying severity. Uncertainties from biomass map and forest inventory data were propagated by probabilistic sampling to provide a statistical distribution of stand age and NEP for each forest pixel. We mapped mean, standard deviation, and statistical distribution of stand age and NEP at 30 m in the PNW region. Our map indicated a net ecosystem productivity of 5.9 Tg C yr−1 for forestlands circa 2010 in the study area, with net uptake in relatively mature (> 24 years old) forests (13.6 Tg C yr−1) overwhelming net negative NEP from tracts that had recent harvests (−6.4 Tg C yr−1), fires (−0.5 Tg C yr−1), and bark beetle outbreaks (−0.8 Tg C yr−1). The approach will be applied to forestlands in other regions of the conterminous US to advance a more comprehensive monitoring, mapping, and reporting of the carbon consequences of forest change across the US.

Nutrient uptake and use efficiency in co‐occurring plants along a disturbance and nutrient availability gradient in the boreal forests of the southwest Yukon, Canada

AbstractAimIn boreal forest ecosystems plant productivity is typically constrained by mineral nutrient availability. In some boreal regions changes in nutrient availability have led to limited changes in productivity but large changes in plant composition. To determine the impact that a change in nutrient availability has on the plant communities it is important to understand how species use nutrients. Here we explore how plant species and functional types in a cold‐dry boreal forest community use available nutrients by quantifying their respective nutrient utilization and response efficiency.LocationBoreal forests in the southwest corner of the Yukon Territory, Canada.MethodsWe collected soil samples and total plant biomass from 29 plots from nine locations subjected to fire, harvesting or bark beetle disturbances. Nutrient analysis of all vegetation and soil samples were conducted to determine the concentration of macro‐ and micronutrients from both plant biomass and soils collected. Nutrient pools between stands with different disturbance histories are compared. Nutrient uptake, use and response efficiencies were then calculated and nutrient response profiles were developed for each species/functional type.ResultsWe found few differences between nutrient pools in plots with different disturbance histories. A clear separation of species and functional groups in elemental hyperspace suggesting divergent nutrient use in co‐occurring species was identified. The use efficiency analysis highlighted that the species with the highest uptake efficiency have lowest use efficiency and vice versa. Species showed either a monotonic or constant relationship between nutrient response efficiency and N, P, K, reflecting a lack of relationship between plant productivity and resource availability or a linear increase in productivity with increasing nutrient availability, respectively.ConclusionsOur findings indicate that species are maximizing nutrient use along different parts of the resource gradient, which has implications for understanding how species respond to changes in nutrient availability. Our findings also show that nutrient use by some species may be governed more by uptake efficiency than use efficiency, allowing them to respond to increases in resource availability by increasing uptake rather than use.

Assessing spatiotemporal relationships between wildfire and mountain pine beetle disturbances across multiple time lags

AbstractNative bark beetles and wildfire are among the most prominent natural disturbances in the conifer forests of western North America. Using multiple approaches and scales, researchers have sought to understand how each disturbance may, or may not, influence the subsequent likelihood or severity of the other disturbance. Our objectives were to complement existing research on the linkage of mountain pine beetle and wildfire disturbances by combining large‐scale spatial data at variable temporal resolutions to characterize the discrepancy between observed and expected overlap areas of fire and beetle disturbances. Multiple time lags, differing by 1‐yr intervals, spanning the 30‐yr period 1984–2014 in the U.S. states of Washington and Oregon were examined for wildfire following bark beetle epidemics and for beetle epidemics following wildfire. We used existing spatial data sets of wildfires and insect pest disturbances to perform overlay analyses to characterize the two relationships. We also compared years of peak vs. non‐peak fires, as well as the influence of several individual, large disturbances. We found a clear association of increased bark beetle epidemic shortly after wildfire. The evidence of an association between increased fire extent and severity following bark beetle epidemics was less straightforward, although it suggested that the nature of the observed patterns varied with fire severity. In some cases, individual disturbance seasons or events were highly influential on the overall trends. Variability in the results highlights the challenges of quantifying landscape‐level relationships among disturbance types and supports the existing calls for further analyses with additional ecological variables.

Landsat Imagery Spectral Trajectories—Important Variables for Spatially Predicting the Risks of Bark Beetle Disturbance

Tree mortality caused by bark beetle infestation has significant effects on the ecology and value of both natural and commercial forests. Therefore, prediction of bark beetle infestations is critical in forest management. Existing predictive models, however, rarely consider the influence of long-term stressors on forest susceptibility to bark beetle infestation. In this study we introduce pre-disturbance spectral trajectories from Landsat Thematic Mapper (TM) imagery as an indicator of long-term stress into models of bark beetle infestation together with commonly used environmental predictors. Observations for this study come from forests in the central part of the Šumava Mountains, in the border region between the Czech Republic and Germany, Central Europe. The areas of bark beetle-infested forest were delineated from aerial photographs taken in 1991 and in every year from 1994 to 2000. The environmental predictors represent forest stand attributes (e.g., tree density and distance to the infested forest from previous year) and common abiotic factors, such as topography, climate, geology, and soil. Pre-disturbance spectral trajectories were defined by the linear regression slope of Tasseled Cap components (Wetness, Brightness and Greenness) calculated from a time series of 16 Landsat TM images across years from 1984 until one year before the bark beetle infestation. Using logistic regression and multimodel inference, we calculated predictive models separately for each single year from 1994 to 2000 to account for a possible shift in importance of individual predictors during disturbance. Inclusion of two pre-disturbance spectral trajectories (Wetness slope and Brightness slope) significantly improved predictive ability of bark beetle infestation models. Wetness slope had the greatest predictive power, even relative to environmental predictors, and was relatively stable in its power over the years. Brightness slope improved the model only in the middle of the disturbance period (1996). Importantly, these pre-disturbance predictors were not correlated with other predictors, and therefore bring additional explanatory power to the model. Generally, the predictive power of most fitted model decreases as time progresses and models describing the initial phase of bark beetle outbreaks appear more reliable for conducting near-future predictions. The pre-disturbance spectral trajectories are valuable not only for assessing the risk of bark beetle infestation, but also for detection of long-term gradual changes even in non-forest ecosystems.

Climate change amplifies the interactions between wind and bark beetle disturbances in forest landscapes

ContextGrowing evidence suggests that climate change could substantially alter forest disturbances. Interactions between individual disturbance agents are a major component of disturbance regimes, yet how interactions contribute to their climate sensitivity remains largely unknown.ObjectivesHere, our aim was to assess the climate sensitivity of disturbance interactions, focusing on wind and bark beetle disturbances.MethodsWe developed a process-based model of bark beetle disturbance, integrated into the dynamic forest landscape model iLand (already including a detailed model of wind disturbance). We evaluated the integrated model against observations from three wind events and a subsequent bark beetle outbreak, affecting 530.2 ha (3.8 %) of a mountain forest landscape in Austria between 2007 and 2014. Subsequently, we conducted a factorial experiment determining the effect of changes in climate variables on the area disturbed by wind and bark beetles separately and in combination.ResultsiLand was well able to reproduce observations with regard to area, temporal sequence, and spatial pattern of disturbance. The observed disturbance dynamics was strongly driven by interactions, with 64.3 % of the area disturbed attributed to interaction effects. A +4 °C warming increased the disturbed area by +264.7 % and the area-weighted mean patch size by +1794.3 %. Interactions were found to have a ten times higher sensitivity to temperature changes than main effects, considerably amplifying the climate sensitivity of the disturbance regime.ConclusionsDisturbance interactions are a key component of the forest disturbance regime. Neglecting interaction effects can lead to a substantial underestimation of the climate change sensitivity of disturbance regimes.

Tree species and position matter: the role of pests for survival of other insects

Abstract We investigated insects overwintering in Norway spruce and Scots pine killed by cambium‐feeding beetles. The study was conducted in five large forests in north‐eastern Poland. Insects were reared from wood samples cut from the upper and lower parts of trees growing in both shaded and sun‐exposed conditions. We found that the species richness of overwintering insects on killed trees was mainly driven by the position in the lower trunk strata rather than in crowns or along a sun–shade gradient. Even though pine and spruce shared almost the same species composition, spruce hosted a significantly higher number of species, including beneficial ones. These results support the hypothesis that disturbance regimes change the spatial distribution of biodiversity, which is higher in low strata, as is known for abiotic disturbances that change the environment of the forest. One of the most important messages emerging from the present study is that pest beetle disturbance during non‐outbreak periods creates habitats that are necessary for the survival of myriads of other insects. Thus, maintaining parts of the trees that were killed by bark and wood‐boring beetles, especially high stumps, would help to support biodiversity in managed forests.

Biotic disturbance facilitates range shift at the trailing but not the leading edge of lodgepole pine's altitudinal distribution

AbstractAimClimate change will alter the geographic distribution of many species, but in forest communities, long‐lived trees often persist after the climate is no longer suitable for recruitment. Disturbance events may accelerate distribution shifts in forested ecosystems by removing persistent trees and creating new recruitment opportunities for species better adapted to the current climate. Here, we investigate how biological disturbances such as insect outbreaks may interact with climate change to initiate tree species range shifts.LocationSouthern Rocky Mountains, Colorado, USA.MethodsWe compared tree and seedling data from long‐term monitoring transects established in 1992–1995 and re‐sampled in 2012 following a widespread mountain pine beetle (Dendroctonus ponderosae Hopkins) outbreak. Transects are located along elevational gradients at the altitudinal range margins of lodgepole pine (Pinus contorta).ResultsWe found that recruitment had declined through time at the trailing edge of lodgepole pine's distribution (lower elevation range margin), where there are now many fewer seedlings compared to the leading edge (upper elevation range margin). At the trailing edge, mountain pine beetle increased mortality of mature lodgepole pines relative to background levels. This mortality was associated with an increase in recruitment of Douglas‐fir (Pseudotsuga menziesii), a lower elevation tree species. At the leading edge of lodgepole pine's distribution, overstorey mortality was associated with only a modest increase in the density of lodgepole pine seedlings (mean increase of 362 seedlings·ha−1), and instead favoured more shade‐tolerant competitors (mean increase of 2182 seedlings·ha−1).ConclusionWhile there is some evidence that climate change is beginning to alter the altitudinal range of lodgepole pine, mountain pine beetle disturbance will likely facilitate this process only at the trailing (lower elevation) range margin. At the leading (upper elevation) range margin, range expansion may be limited by competition with trees and seedlings of species not susceptible to mountain pine beetle. A physical disturbance such as fire that can eliminate competing species may be required for the upward expansion of lodgepole pine's leading range margin. For tree species such as lodgepole pine that are affected by periodic insect outbreaks, ranges may shrink in the near term if this disturbance–climate interaction continues to drive range retractions that outpace range expansions.

Fine-scale spruce mortality dynamics driven by bark beetle disturbance in Babia Góra National Park, Poland

Bark beetle outbreaks have had major impacts on Norway spruce forests in Europe. The large majority of these forests are located in areas under forest management; thus, few studies have investigated outbreak-driven spruce mortality patterns unaffected by humans. Our study examined spruce mortality resultant from a beetle outbreak in a high-elevation, unmanaged forest over a 17-year span. We analyzed three tree-level survivorship and DBH datasets collected during pre-, mid-, and post-outbreak conditions to evaluate long-term mortality dynamics. We measured changes in mortality severity, topographic and stand structure characteristics, and stand complexity using ANOVAs, and we assessed five topographic and stand structure mortality predictors by employing boosted regression trees. Our results showed that though spruce mortality increased significantly over time, such increases were disproportionate with spatial synchrony. Moreover, the outbreak did not significantly alter the living stand structure and had little effect on stand complexity, exhibiting the effects of an outbreak that spread throughout the forest without causing major stand-level damage. Larger trees at higher elevations on south-facing slopes were targeted most frequently, particularly during the later stages of the outbreak. Aspect, elevation, and slope were the best predictors of mortality, demonstrating moderate forecasting ability. We showed that bark beetle outbreaks can operate on patch-scale gradients, affecting microhabitat conditions, without resulting in sweeping, stand-altering mortality. Small-scale outbreaks may increase forest resilience against more severe outbreaks in the future by creating canopy gaps that facilitate regeneration, which leads to more complex age and size structures within the stand.

Frequent severe natural disturbances and non-equilibrium landscape dynamics shaped the mountain spruce forest in central Europe

Disturbances shape forest structure and composition, but the temporal dynamics of disturbance patterns, their influence on dynamics of forest structural complexity, and the potential impacts of ongoing climate changes are not fully understood. We addressed these issues by focusing on (1) long-term, landscape level retrospective analysis of disturbance dynamics of mountain Norway spruce (Picea abies) forest; (2) testing for the prevailing disturbance agent; and (3) the detection of disturbance drivers, particularly site conditions, using a dendrochronological approach.We had a unique opportunity to sample a large area of natural forest (in otherwise altered region) in Bohemian Forest, that was recently affected by extensive and severe wind and bark beetle disturbances raising management concerns. Tree-ring series of a minimum of 35 trees on each of the 26 study plots were analysed for signals of past disturbances that were indicated either by release from suppression (rapid growth increase) or rapid early growth rate (gap origin).A broad range of disturbance severities were detected across the landscape, but severe disturbances (>50% trees responded), with a short rotation period of 174years, best characterize the area. Reconstructed disturbances were associated with historically documented windstorms and bark beetle outbreaks. They were distributed across the landscape and affected its large portions with spatially variable severity. Over the last five centuries, disturbances peaked in the 1820s, but were rare after 1880. This non-equilibrium dynamics resulted into mature landscape structure at the end of 20th century and contributed to the large extent of disturbances in the last two decades. Disturbances were more frequent on wind-exposed locations such as mountain ridges and flatter terrain.Frequent disturbances did not allow the forest to develop into an old-growth phase; rather disturbance events of variable severities created structures important for biodiversity and could also preserve key early-seral phases in the landscape. We anticipate that potential future increase of disturbance intensities will not lead to comparable regime shifts in forests shaped by high-severity disturbances that kill largely mature trees (e.g., wind and bark beetle), because such disturbances are followed by resistant forest structure. Conservation areas should be large enough to allow for a wide range of disturbances. Emphasizing ecological functions needs understanding of biological legacies of natural disturbances and managers could partly rely on natural events to restore natural features into cultivated forests.

Can current management maintain forest landscape multifunctionality in the Eastern Alps in Austria under climate change?

In Central Europe, management of forests for multiple ecosystem services (ES) has a long tradition and is currently drawing much attention due to increasing interest in non-timber services. In face of a changing climate and diverse ES portfolios, a key issue for forest managers is to assess vulnerability of ES provisioning. In a case study catchment of 250 ha in the Eastern Alps, the currently practiced uneven-aged management regime (BAU; business as usual) which is based on irregularly shaped patch cuts along skyline corridors was analysed under historic climate (represented by the period 1961–1990) and five transient climate change scenarios (period 2010–2110) and compared to an unmanaged scenario (NOM). The study addressed (1) the future provisioning of timber, carbon sequestration, protection against gravitational hazards, and nature conservation values under BAU management, (2) the effect of spatial scale (1, 5, 10 ha grain size) in mapping ES indicators and (3) how the spatial scale of ES assessment affects the simultaneous provision of several ES (i.e. multifunctionality). The analysis employed the PICUS forest simulation model in combination with novel landscape assessment tools. In BAU management, timber harvests were smaller than periodic increments. The resulting increase in standing stock benefitted carbon sequestration. In four out of five climate change scenarios, volume increment was increasing. With the exception of the mildest climate change scenario (+2.6 °C, no change in precipitation), all other analysed climate change scenarios reduced standing tree volume, carbon pools and number of large old trees, and increased standing deadwood volume due to an intensifying bark beetle disturbance regime. However, increases in deadwood and patchy canopy openings benefitted bird habitat quality. Under historic climate, the NOM regime showed better performance in all non-timber ES. Under climate change conditions, the damages from bark beetle disturbances increased more in NOM compared with BAU. Despite favourable temperature conditions in climate change scenarios, the share of admixed broadleaved species was not increasing in BAU management, mainly due to the heavy browsing pressure by ungulates. In NOM, it even decreased and mean tree age increased. Thus, in the long run NOM may enter a phase of lower resilience compared with BAU. Most ES indicators were fairly insensitive to the spatial scale of indicator mapping. ES indicators that were based on sparse tree and stand attributes such as rare admixed tree species, large snags and live trees achieved better results when mapped at larger scales. The share of landscape area with simultaneous provisioning of ES at reasonable performance levels (i.e. multifunctionality) decreased with increasing number of considered ES, while it increased with increasing spatial scale of the assessment. In the case study, landscape between 53 and 100 % was classified as multifunctional, depending on number and combinations of ES.

Social-ecological dimensions of forest bark beetle disturbances: Past, present, and future

Social-ecological dimensions of forest bark beetle disturbances: Past, present, and future

Interactions among spruce beetle disturbance, climate change and forest dynamics captured by a forest landscape model

The risk of bark beetle outbreaks is widely predicted to increase because of a warming climate that accelerates temperature‐driven beetle population growth and drought stress that impairs host tree defenses. However, few if any studies have explicitly evaluated climatically enhanced beetle population dynamics in relation to climate‐driven changes in forest composition and structure that may alter forest suitability for beetle infestation. We synthesized current understanding of the interactions among climate, spruce beetles (Dendroctonus rufipennis) and forest dynamics to parameterize and further advance the bark beetle module of a dynamic forest landscape model (LandClim) that also integrates fire and wind disturbance and climate‐driven forest succession. We applied the model to a subalpine watershed in northwestern Colorado to examine the mechanisms and feedbacks that may lead to shifts in forest composition and spruce beetle disturbance under three climate change scenarios. Simulation results suggest increased drought‐ and beetle‐induced reduction of large Engelmann spruce (Picea engelmannii) trees while Douglas‐fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa) increased in dominance throughout the study area under all climate change scenarios. This shift in forest composition and structure counterbalances the enhancing effects of accelerated beetle population development and increased drought‐induced susceptibility of spruce to beetles. As a result, we projected a long‐term decrease in beetle‐induced spruce mortality to below historical values under all climate scenarios at low elevations (<2800 m asl). Beetle‐induced spruce mortality above 2800 m asl and under moderate climate change was slightly higher and more variable than under historical conditions but decreased to 36% and 6% of historical values under intermediate and extreme climate change, respectively. Because mechanisms driving beetle disturbance dynamics are similar across different bark beetle species, we argue that the depletion of host trees due to drought and beetle disturbance may also be important in other climate‐sensitive beetle‐host systems. We advocate for the consideration of climate‐driven shifts in forest and disturbance dynamics in devising adaptive management strategies.

Characterizing spectral–temporal patterns of defoliator and bark beetle disturbances using Landsat time series

Defoliators and bark beetles are natural disturbance agents in many forest ecosystems around the world. Mapping the spatial and temporal patterns of insect disturbance dynamics can help in understanding their impacts on forest ecosystem resilience and functioning, and in developing adaptive management strategies. In recent years, much progress has been made in landscape-level analyses of insect-induced disturbances using remotely sensed data. However, many studies have focused on single insect agents or aggregated different insect agents into a single group. In this study, we characterized the temporal-spectral patterns associated with bark beetle and defoliator disturbances using Landsat time series between 1990 and 2013, with the objective to test if the two insect disturbances can be separated with Landsat data. We analyzed a recent outbreak of mountain pine beetle (Dendroctonus ponderosae Hopkins) and western spruce budworm (Choristoneura freemani Razowski) in British Columbia, Canada. To characterize the disturbance and recovery trends associated with insect disturbances we used the LandTrendr segmentation algorithm. We fitted LandTrendr spectral trajectories to annual normalized burn ratio (NBR) and Tasseled Cap (TC) time series, from which we then extracted a set of disturbance metrics. With these disturbance metrics, two random forest models were trained to a) distinguish insect disturbances from harvest and fire disturbances; and to b) attribute the insect disturbances to the most likely agent, i.e. mountain pine beetle or western spruce budworm. Insect disturbances were successfully mapped with an overall accuracy of 76.8%, and agents were successfully attributed with overall accuracies ranging from 75.3% to 88.0%, depending on whether only pure host-stands or mixed stands with both insect hosts were considered. In the case of mixed host stands, nearly 45% of the western spruce budworm disturbances were falsely attributed to mountain pine beetle. Spectral metrics describing disturbance magnitude were more important for distinguishing the two insect agents than the disturbance duration. Spectral changes associated with western spruce budworm disturbances had generally lower magnitudes than mountain pine beetle disturbances. Moreover, disturbances by western spruce budworm were more strongly associated with changes in TC greenness, whereas disturbances by mountain pine beetle were more strongly associated with changes in TC brightness and wetness. The results reflect the ephemeral nature of defoliators versus the tree mortality impacts of bark beetles in our study area. This study demonstrates the potential of Landsat time series for mapping bark beetle and defoliator disturbances at the agent level and highlights the need for distinguishing between the two insect agents to adequately capture their impacts on ecosystem processes.

Light-lift helicopter logging operations in the Italian Alps: a preliminary study based on GNSS and a video camera system

Terrain access is a critical factor influencing the feasibility of forest operations in steep mountainous terrain. Long extraction distances coupled with terrain obstacles can favor the use of helicopters in timber extraction in such areas. However, helicopter logging in the Italian Alps is not commonplace when compared to other Alpine regions, for example, in Switzerland and Austria. The use of light-lift helicopters has recently caught the attention of practitioners as an alternative to more traditional medium- to heavy-lift aircraft in the Alps. This article reports the findings of two preliminary case studies using light-lift helicopters for the extraction of high value timber and fire-damaged timber subsequently exposed to bark beetle disturbance. In order to provide a comprehensive analysis of the factors affecting helicopter logging productivity, the two case studies were separately analyzed using time-element analysis supported by on-board global navigation satellite system (GNSS) devices. Additionally, an external video camera was used to continuously monitor the operations. The payload utilization was 86% for the extraction of high value timber and 70% for fire-damaged timber subsequently exposed to bark beetle disturbance. Variation in the turn time was mostly related to the hooking, choker return, and load times, as well as flying distance. Above all, the load hooking time explains c. 27% of the variance, revealing its critical influence on logging productivity.

The impacts of mountain pine beetle disturbance on the energy balance of snow during the melt period

AbstractMountain snowpacks provide most of the annual discharge of western US rivers, but the future of water resources in the western USA is tenuous, as climatic changes have resulted in earlier spring melts that have exacerbated summer droughts. Compounding changes to the physical environment are biotic disturbances including that of the mountain pine beetle (MPB), which has decimated millions of acres of western North American forests. At the watershed scale, MPB disturbance increases the peak hydrograph, and at the stand scale, the ‘grey’ phase of MPB canopy disturbance decreases canopy snow interception, increases snow albedo, increases net shortwave radiation, and decreases net longwave radiation versus the ‘red’ phase. Fewer studies have been conducted on the red phase of MPB disturbance and in the mixed coniferous stands that may follow MPB‐damaged forests. We measured the energy balance of four snowpacks representing different stages of MPB damage, management, and recovery: a lodgepole pine stand, an MPB‐infested stand in the red phase, a mixed coniferous stand (representing one successional trajectory), and a clear‐cut (representing reactive management) in the Tenderfoot Creek Experimental Forest in Montana, USA. Net longwave radiation was lower in the MPB‐infested stand despite higher basal area and plant area index of the other forests, suggesting that the desiccated needles serve as a less effective thermal buffer against longwave radiative losses. Eddy covariance observations of sensible and latent heat flux indicate that they are of similar but opposite magnitude, on the order of 20 MJ m−2 during the melt period. Further analyses reveal that net turbulent energy fluxes were near zero because of the temperature and atmospheric vapour pressure encountered during the melt period. Future research should place snow science in the context of forest succession and management and address important uncertainties regarding the timing and magnitude of needlefall events. Copyright © 2015 John Wiley & Sons, Ltd.

The disturbance regime of Norway spruce forests in Bulgaria

Natural disturbances are among the most important factors that shape forest dynamics and forest landscapes. However, the natural disturbance regime of Norway spruce (Picea abies (L.) Karst.) forests in Europe is not well understood. We studied the disturbance regimes in three forest reserves in Bulgaria (Parangalitsa, Bistrishko branishte, and Beglika), which are representative of the range of conditions typical for P. abies ecosystems in central and southern Europe. Our data indicated that large-scale disturbances were most numerous in forests that were between 120 and 160 years old, those with unimodal diameter at breast height (DBH) distributions, and especially those located in vulnerable topographic settings. Wind disturbances ranged up to 60 ha, followed in one case by a 200 ha Ips typographus (Linnaeus, 1758) outbreak. Older forests and those with more complex structures (i.e., reverse-J DBH) were characterized by numerous small gaps but were also affected by a few larger disturbances. In some old-growth forests at highly productive sites, gaps could be so numerous that the long-term existence of old trees may become an exception. Over the past centuries, the natural range of variability of these Norway spruce forests in Bulgaria appears to have been shaped mostly by wind and bark beetle disturbances of various sizes.

Functional response of lignicolous fungal guilds to bark beetle deforestation

Conifer-dominated forests in the northern hemisphere are prone to large-scale natural disturbances, yet our understanding of their effects beyond changes in species diversity is limited. Bark beetle disturbances provide dead wood for lignicolous fungal guilds and increase insolation but also desiccation. We investigated whether species richness of these guilds increases and functional diversity decreases after bark beetle disturbance, which would promote through habitat filtering the coexistence of species adapted to harsh conditions, i.e. light stress for lichens and substrate desiccation for wood-inhabiting fungi.We sampled epixylic and epiphytic lichens (primary producers) and wood-inhabiting fungi (mainly wood decomposers, some form ectomycorrhizas) in the Bohemian Forest (Long Term Ecological Research – LTER – Site Bavarian Forest National Park), an area in Central Europe most heavily affected by the bark beetle Ips typographus, on undisturbed plots and disturbed plots with spruce (Picea abies) dieback 8 years ago. We analysed species diversity, functional diversity (optimized by phylogeny), and functional compositions.Species richness of lichens but not that of wood-inhabiting fungi was higher on disturbed plots than on undisturbed plots. Community compositions of both guilds differed considerably on disturbed and undisturbed plots. On both types of plots, lichen communities were clustered according to functional diversity, which indicated habitat filtering, and fungal communities were overdispersed, which indicated competition. Disturbance increased the strength of these two patterns only slightly and was significant only for fungi. Single-trait analysis revealed changes in the functional composition; on disturbed plots, lichenous species with larger and more complex growth forms and fungi with large, perennial fruit bodies were favoured. Although the forest canopy changed tremendously because of the bark beetle disturbance, the most important driver of lichen and fungal diversity and mean trait assemblages seemed to be the enrichment of dead wood. The changes in insolation and moisture did not act as habitat filters for either guild. This indicated that the assembly patterns of lichen and fungal communities in coniferous forests are not affected by stand-replacing disturbances in contrast to the predictions for other disturbance regimes.

Effects of stand patchiness due to windthrow and bark beetle abatement measures on soil CO2 efflux and net ecosystem productivity of a managed temperate mountain forest

In central European mountain forests, bark beetle abatement measures implemented after wind and bark beetle disturbances represent a well-defined disturbance regime. We used a biometric approach extended by soil CO2 efflux measurements to study the effects of disturbance-induced stand patchiness on the net ecosystem productivity (NEP) of a mature Norway spruce (Picea abies L. Karst.) forest at the Integrated Monitoring (IM) Long Term Ecological Research (LTER) site “Zobelboden”, Austria. In the disturbed stand area, roughly 28 % of the spruce trees were salvaged after an initial disturbance and during small-scale bark beetle abatement actions in 2007 and 2008. Aboveground C stocks declined by approximately 33 %, resulting in a 31 and 29 % reduction of biomass NPP and litterfall during the study year 2011. Soil CO2 efflux in the disturbed area (7.5 ± 0.5 t C ha−1 y−1) was significantly lower than in the undisturbed area (9.3 ± 0.6 t C ha−1 y−1). The difference was mainly attributed to the fact that the autotrophic contributions in the disturbed area were lower (22 %) than in the undisturbed area (31 %). Heterotrophic soil respiration was similar in both stand areas (5.9 t C ha−1 y−1 in the disturbed and 6.5 t C ha−1 y−1 in the undisturbed area). Four years after the initial disturbance, the NEP estimated for the undisturbed area was 0.68 and 0.09 t C ha−1 y−1 for the disturbed stand area. Although disturbance and abatement measures substantially lowered the NEP, the C uptake of the remaining trees, along with their dampening effect on soil temperature, ensured that the disturbed forest still served as a weak C sink.

Radial growth response and vegetative sprouting of aspen following release from competition due to insect-induced conifer mortality

Eruptive bark beetle outbreaks such as the recent mountain pine beetle epidemic in western North America often result in substantial changes to species composition, abiotic factors, and a highly altered fuel complex. Little is known about the implications of these outbreaks to non-host species, such as aspen (Populus tremuloides Michx.), which may be beneficiaries due to release from competition. We investigated radial growth response in aspen following mountain pine beetle-induced conifer mortality in north-central Colorado through dendrochronological analysis using the percent growth change method based on 5-year and 10-year running medians, and we quantified regeneration responses in these areas compared to areas where beetle activity was largely absent. We hypothesized that growth in mature aspen would increase, expressed through wider annual growth rings, while vegetative regeneration (i.e. resprouting from the parent root system) would not increase in forests affected by bark beetles.Results showed a clear radial growth release in mixed aspen-conifer stands that were subject to extensive conifer mortality but not in forests that remained largely unaffected by beetles. Comparison of extent of suckering showed no significant differences, supporting our hypotheses and suggesting that additional resources due to release from competition were allocated towards radial growth rather than initiation of sucker growth, potentially indicating a trade-off between maintenance of existing stems and regeneration. Results from this study provide the first account of radial release detection in aspen following beetle-induced conifer mortality and help predict aspen persistence and future stand composition in these forests. Additional research, with a higher sample size and more time between sampling and bark beetle disturbance is highly recommended to confirm our findings and optimize release detection methods in aspen.