Bark Beetle Activity Research Articles

Spruce bark beetle phenological modelling and drought risk within framework of TANABBO II model

Global warming plays a major role in the disruption of forest ecosystems by bark beetle outbreaks. Decreasing precipitation and more frequent droughts create the conditions for water stress in trees. The Eurasian spruce bark beetle (Ips typographus L.) is more dangerous for Norway spruce (Picea abies (L.) Karst.) forests in Central Europe under these conditions, because even healthy trees under water stress have a lower probability of survival during massive spruce bark beetle outbreaks. This critical issue highlights the importance of targeted research and intervention strategies in affected regions; hence, this study has a focus on the Horní Planá region in Central Europe, which is managed by the Military Forests and Farms of the Czech Republic (VLS).The study presents the results of the drought risk assessment of the operational part of TANABBO II and its validation. TANABBO is a high spatial resolution risk assessment tool for spruce bark beetle infestation in Central European forests, incorporating 30 m spatial resolution and extensive meteorological data, which outperforms existing models in its ability to accurately predict bark beetle activity based on the PHENIPS phenological model. The operational part integrates environmental factors such as global radiation, temperature, precipitation and, in particular, water stress, which is assessed by using a transpiration deficit. The drought risk assessment included the calculation of Drought Indices (DI) and Cumulative Transpiration Deficit Indices (CTDI) on a daily basis, and the estimation of spruce bark beetle swarming time using the PHENIPS model. The risk assessment was validated by comparing it with the number of bark beetles caught in traps and the value of the drought index. Generalised additive models (GAM) were used for validation, with the most effective models incorporating the CTDI. The model with the highest predictive accuracy achieved an adjusted R-squared value of 0.478. The study highlights the critical role of high-resolution environmental data in understanding and managing bark beetle outbreaks, particularly in the context of climate change.

Bark beetle-driven community and biogeochemical impacts in forest ecosystems: a review

Abstract Bark beetles are a principal source of tree mortality in conifer forests, with beetle distribution and beetle-associated tree mortality increasing in frequency and extent. While bark beetles are associated with large-scale outbreaks that affect landscape structure, function, and wood quality, they are also drivers of important ecological processes that modify forest ecosystems. Bark beetle activity may affect biogeochemistry and forest decomposition processes by mediating microbial and detrital communities and by facilitating the turnover of deadwood. The turnover of deadwood in bark beetle-attacked forests has important implications for forest biogeochemical cycling, as dead wood releases CO2 into the atmosphere and carbon, nitrogen, and other nutrients into surrounding soils. However, our understanding of how initial physical, chemical, and biotic changes to bark beetle-attacked trees affect the succession of detrital organisms and decomposition of beetle-generated deadwood remains poor. Furthermore, the relationship between woody decomposition and landscape-level changes in biogeochemical processes in forest ecosystems following bark beetle activity is not well unified. This review article bridges this divide and provides an interdisciplinary perspective on tree mortality, ecological succession, and woody decomposition mediated by bark beetles.

The State of Dark Coniferous Forests on the East European Plain Due to Climate Change.

As a result of global climate changes, negative processes have been recorded in the coniferous forests of the Northern Hemisphere. Similar processes are observed in the Urals, including in Udmurtia. In the course of this research, archival analysis methods were used, as well as field research methods. In the process of analyzing archival materials in the Urals, a reduction of spruce forests was observed. If in the 20th century the share of spruce forests in the region was 50%, then in the 21th century it decreased to 35%. As a result of this research, it was revealed that the most unfavorable sanitary condition was recorded in the boreal-subboreal zone of Udmurtia, with a sanitary condition index of 3.2 (from 2.62 to 3.73). The main reason for the unfavorable sanitary condition of spruce forests was the vital activity of Ips typographus L. According to our research, in 11 sample plots out of 18, a high score for sanitary condition was associated with the vital activity of bark beetles. The correlation coefficient of the index of the sanitary condition of plantings and the number of individuals of Picea obovata Ledeb. affected by Ips typographus L. was0.93. Bark beetle activity has increased in the 21th century, which is associated with changing climatic factors. Unstable precipitation over recent years (differences of more than 100 mm) and an average temperature increase of 1.2 °C were observed in the region. The most significant increase in temperature over the past 10 years was observed in winter, which in turn affected the high survival rate of insect pests.

Patterns and drivers of recent land cover change on two trailing-edge forest landscapes

Climate change is altering the distribution of woody plants by influencing demographic processes and modifying disturbance regimes. Trailing-edge forests may be particularly vulnerable to these effects because they exist at warm, dry margins of tree distributions. To better understand recent climate-driven changes in trailing-edge forests, we used Landsat time series and 1558 field reference plots to develop annual land cover maps from 1985 to 2020 in two large, biodiverse landscapes in central Arizona, USA. We then combined annual land cover maps with tree ring records and spatial data describing interannual climate, terrain, bark beetle (Curculionidae: Scolytinae) activity, wildfire, and harvest to quantify drivers of forest change. Throughout the two landscapes, forest extent declined by 0.3 % and 0.8 % from 1985 to 2020. However, considerable variation occurred within the study period, with abrupt (ca. 1–2 years) declines in forest extent followed by gradual (ca. 10 years) recovery on each landscape. Pinyon-juniper (Pinus edulis, Pinus monophylla, and/or Juniperus spp.) cover increased from 1985 to ca. 2000 but declined after 2000, a period of extreme drought and regional tree die-off. In contrast, pine-oak (Pinus ponderosa and Quercus spp.) cover increased from 2000 to 2020, primarily due to declines in ponderosa pine and mixed conifer cover over the same period. Wildfire was a key driver of transitions from forest to non-forest cover in our study area, with the occurrence of multiple compounded drought years playing an important role in unburned areas. By driving transitions to alternative forest types or non-forest cover, disturbance and drought will increasingly shape forest dynamics and ecosystem transformations throughout the southwestern US.

The Last Trees Standing: Climate modulates tree survival factors during a prolonged bark beetle outbreak in Europe

Plant traits are an expression of strategic tradeoffs in plant performance that determine variation in allocation of finite resources to alternate physiological functions. Climate factors interact with plant traits to mediate tree survival. This study investigated survival dynamics in Norway spruce (Picea abies) in relation to tree-level morphological traits during a prolonged multi-year outbreak of the bark beetle, Ips typographus, in Central Europe. We acquired datasets describing the trait attributes of individual spruce using remote sensing and field surveys. We used nonlinear regression in a hypothesis-driven framework to quantify survival probability as a function of tree size, crown morphology, intraspecific competition and a growing season water balance. Extant spruce trees that persisted through the outbreak were spatially clustered, suggesting that survival was a non-random process. Larger diameter trees were more susceptible to bark beetles, reflecting either life history tradeoffs or a dynamic interaction between defense capacity and insect aggregation behavior. Competition had a strong negative effect on survival, presumably through resource limitation. Trees with more extensive crowns were buffered against bark beetles, ostensibly by a more robust photosynthetic capability and greater carbon reserves. The outbreak spanned a warming trend and conditions of anomalous aridity. Sustained water limitation during this period amplified the consequences of other factors, rendering even smaller trees vulnerable to colonization by insects. Our results are in agreement with prior research indicating that climate change has the potential to intensify bark beetle activity. However, forest outcomes will depend on complex cross-scale interactions between global climate trends and tree-level trait factors, as well as feedback effects associated with landscape patterns of stand structural diversity.

Landscape predictions of western balsam bark beetle activity implicate warm temperatures, a longer growing season, and drought in widespread irruptions across British Columbia

Warming temperatures and drought are leading to unprecedented irruptions of forest insects worldwide. Altered climatic regimes have the potential to allow native forest insects to express novel behaviors and expand in latitude and elevation beyond their hypothesized thermal tolerances. Yet, disentangling the drivers of novel behaviors and range expansions is difficult due to cross-scalar interactions that dictate forest insect population dynamics. We investigated the irruptive dynamics of western balsam bark beetle (Dryocoetes confusus Swaine), which undergoes intermittent, long-lasting, but low-severity outbreaks in subalpine fir (Abies lasiocarpa Hook) forests. We compiled data from 1998 to 2019 across British Columbia, Canada, at 1 and 16 km2 resolutions to describe the spatiotemporal structure of beetle outbreaks, predict the landscape susceptibility to outbreaks, explain when outbreaks occur based on bioclimatic drivers, explore whether beetle populations exhibit self-driving growth, and determine whether the extent of outbreaks has increased. Overall, we found that outbreaks occur in discrete clusters and are synchronous at distances of 10–25 km. Further, we found that landscape susceptibility to beetle outbreaks was best explained by latitude*elevation (i.e., the product of latitude [m] and elevation [m] Z-standardized) and volume of fir (m3/ha; >17.5 cm size class; >100 yrs.) both within 8 km and each pixel. Meanwhile, a longer growing season, increased growing degree day accumulation, and drought best explained when outbreaks occurred. Further, we did not find evidence to suggest that beetle populations exhibit self-driving population growth. Finally, we found that the extent of beetle outbreaks has increased over the last 20 years and that increases in landscape susceptibility primarily occurred at higher latitude*elevations and were best explained by an increase in the mean growing season and degree day accumulation. In other words, abnormally warm temperatures have facilitated a northward and upward expansion of western balsam bark beetle. Collectively, these results serve as the first quantification of the spatiotemporal dynamics of this understudied insect and support previous modeling efforts to investigate the multi-scale drivers of western balsam bark beetle outbreaks. We propose that future work should identify specific supercooling points, the relationship between temperature and development rate, and how the relatively high within-stand variability in age and size class of subalpine fir affect the irruptive dynamics of this understudied bark beetle.

Comparison of field survey and remote sensing techniques for detection of bark beetle-infested trees

Detection in the early phase of bark beetle infestation is a vital task for proactive management strategies, as practiced in most Central European forests, to minimize economic losses due to bark beetle infestation and to mitigate their further spreading. For this work, remote sensing methods are coming to be in great demand as an objective approach to enable monitoring bark beetle infestation even at individual tree level.This case study monitored bark beetle (Ips typographus) activity at local level in Norway spruce forest in the Czech Republic. The main aim of this study was to compare the remote sensing methods against classical field survey conducted by forest workers in detecting newly infested trees.To compare these two methods, an extensive field and aerial campaign was conducted in the southern part of the Czech Republic during 2020. Bark beetle infestation was monitored by traditional methods (i.e. field survey) on a weekly basis from mid-March to mid-September. During the same period, aerial scans were performed once per month (seven in total) using a CASI-1500 hyperspectral sensor (visible and near-infrared, 400–1000 nm) with spatial resolution of 0.5 m. This work mapped transition from healthy up to red attack of 75 Norway spruce trees that were infested during the same week. The same number of healthy trees were added to the data set for hyperspectral data analysis. Both groups were analysed by vegetation indices, with emphasis on effect caused in the canopy by bark beetles.The success rate for bark beetle detection is always associated with acquisition time. In order to define the optimal time for data acquisition, we employed a phenology model for I. typographus (RITY 2.0) to take into consideration bark beetle development.The results of the experiment showed that classic field survey detected infested trees earlier than did analysis using remote sensing data from the visible and near-infrared region. The difference was 23 days for the most successful indices (i.e. REIP, PRI, and ANCB650–720) in our test. Nevertheless, both methods detected the infested trees within 6 weeks after infestation, which is the recommended period for taking measures to prevent bark beetles from spreading further, and thus hyperspectral imagery can be used as a valid information source for bark beetle detection.

Changes in Transpiration and Leaf Water Potential in Douglas-Fir Trees following Douglas-Fir Beetle Attack and Mechanical Girdling

Bark beetles and their associated fungi kill trees readily, but we often ignore which organism is the leading cause of tree mortality. While phloem feeding beetles inhibit photosynthate transport, their associated fungi block the tracheids disrupting transpiration. Within the family Pinaceae, knowledge of tree physiological decline following bark beetle and associated fungi colonization is limited to the genus Pinus. Here we investigate the physiological response of Pseudotsuga (P. menziesii) to bark beetles or its fungi. We hypothesized that fungi block water transport in Douglas-fir causing faster mortality than by bark beetle activity alone. We successfully lured Douglas-fir beetle to attack a subset of trees in our experimental area using pheromones and compared Beetle-Killed trees with mechanically Girdled, and Control trees. During spring snowmelt, nine months after treatments were applied, Control, Girdled, and five trees that Survived beetle attack had higher transpiration rates and less negative pre-dawn water potential than five Beetle-Killed trees. Declines in transpiration and leaf water potential in our Beetle-Killed trees occurred much earlier than those in studies of beetle-attacked lodgepole pines, suggesting stronger defensive traits in Douglas-fir. Our data suggest that, as in pines, bark beetle-associated fungi are the leading cause of mortality in Douglas-fir beetle-attacked trees.

Sub-fossil bark beetles as indicators of past disturbance events in temperate Picea abies mountain forests

Temperate mountain forests have experienced an increase in frequency and severity of natural disturbances (e.g., droughts, fires, windstorms and insect outbreaks) in recent decades due to climate and environmental change. Outbreaks of bark beetles have caused significant dieback of conifer forests in Central Europe and it is essential to model and predict the potential severity of future bark beetle outbreaks. However, to predict future bark beetle activity, historical baseline information is required to contextualize the magnitude of current and potential future outbreaks. A fossil beetle record from a forest hollow in the Tatra Mountains, Slovakia; one of the best-preserved national parks in Central Europe, was produced to identify insect outbreaks during the last millennia. Sub-fossil bark beetle remains were compared with parallel pollen and charcoal to assess whether peaks in conifer bark beetle remains correspond with indications of disturbance documented in historical or sedimentary fossil records. Three peaks in bark beetle remains were detected (1) post-2004, (2) AD 1140–1440, and (3) AD 930–1030. The abundance of species Pityogenes chalcographus and Pityophthorus pityographus in the two top samples can be linked directly to large bark beetle outbreaks in the High Tatra Mountains after 2004. P. chalcographus and P. pityographus are also the abundant species in the second peak (AD 1140–1440) while the third peak (AD 930–1030) consists of the species Polygraphus poligraphus. The most prominent conifer bark beetle in Central Europe, Ips typographus, was found to be present in most of the samples but always at very low numbers. It is plausible that P. chalcographus and P. pityographus fossils might be useful proxies for past conifer bark beetle outbreaks in Central Europe, as they occur together with fossils of I. typographus but appear to be well-preserved. A significant correlation was found between primary bark beetles and macroscopic charcoal densities in the sediment, highlighting the complex interactions between disturbance agents, bark beetles and fire, in this long-term regime of natural disturbances. Our 1400-year disturbance record shows how bark beetle outbreaks have been an important component of the regional natural disturbance regime for over a millennium and have intensified with increasing anthropogenic activity. Bark beetle outbreaks are likely one of the drivers promoting the future ecological stability of the temperate conifer ecosystem over decades to centuries.

Increasing rates of subalpine tree mortality linked to warmer and drier summers

Abstract Warming temperatures and rising moisture deficits are expected to increase the rates of background tree mortality–low amounts of tree mortality (~0.5%–2% year−1), characterizing the forest demographic processes in the absence of abrupt, coarse‐scale disturbance events (e.g. fire). When compounded over multiple decades and large areas, even minor increases in background tree mortality (e.g. <0.5% year−1) can cause changes to forest communities and carbon storage potential that are comparable to or greater than those caused by disturbances. We examine how temporal variability in rates of background tree mortality for four subalpine conifers reflects variability in climate and climate teleconnections using observations of tree mortality from 1982 to 2019 at Niwot Ridge, Colorado, USA. Individually marked trees (initial population 5,043) in 13 permanent plots—located across a range of site conditions, stand ages and species compositions—were censused for new mortality nine times over 37 years. Background tree mortality was primarily attributed to stress from unfavourable climate and competition (71.2%) and bark beetle activity (23.3%), whereas few trees died from wind (5.3%) and wildlife impacts (0.2%). Mean annualized tree mortality attributed to tree stress and bark beetles more than tripled across all stands between initial censuses (0.26% year−1, 1982–1993/1994) and recent censuses (0.82% year−1, 2008–2019). Higher rates of tree mortality were related to warmer maximum summer temperatures, greater summer moisture deficits, and negative anomalies in ENSO (La Niña), with greater effects of drought in some subpopulations (tree size, age and species). For example, in older stands (>250 years), larger and older trees were more likely to die than smaller and younger trees. Differences in tree mortality rates and sensitivity to climate among subpopulations that varied by stand type may lead to unexpected shifts in stand composition and structure. Synthesis. A strong relationship between higher rates of tree mortality and warmer, drier summer climate conditions implies that climate warming will continue to increase background mortality rates in subalpine forests. Combined with increases in disturbances and declining frequency of moist‐cool years suitable for seedling establishment, increasing rates of tree mortality have the potential to drive declines in subalpine tree populations.

Do bark beetle outbreaks amplify or dampen future bark beetle disturbances in Central Europe?

Bark beetle outbreaks have intensified in many forests around the globe in recent years. Yet, the legacy of these disturbances for future forest development remains unclear. Bark beetle disturbances are expected to increase further because of climate change. Consequently, feedbacks within the disturbance regime are of growing interest, for example, whether bark beetle outbreaks are amplifying future bark beetle activity (through the initiation of an even‐aged cohort of trees) or dampening it (through increased structural and compositional diversity).We studied bark beetle–vegetation–climate interactions in the Bavarian Forest National Park (Germany), an area characterised by unprecedented bark beetle activity in the recent past. We simulated the effect of future bark beetle outbreaks on forest structure and composition and analysed how disturbance‐mediated forest dynamics influence future bark beetle activity under different scenarios of climate change. We used process‐based simulation modelling in combination with machine learning to disentangle the long‐term interactions between vegetation, climate and bark beetles at the landscape scale.Disturbances by the European spruce bark beetle were strongly amplified by climate change, increasing between 59% and 221% compared to reference climate. Bark beetle outbreaks reduced the dominance of Norway spruce (Picea abies (L.) Karst.) on the landscape, increasing compositional diversity. Disturbances decreased structural diversity within stands (α diversity) and increased structural diversity between stands (β diversity). Overall, disturbance‐mediated changes in forest structure and composition dampened future disturbance activity (a reduction of up to −67%), but were not able to fully compensate for the amplifying effect of climate change. Synthesis. Our findings indicate that the recent disturbance episode at the Bavarian Forest National Park was caused by a convergence of highly susceptible forest structures with climatic conditions favourable for bark beetle outbreaks. While future climate is increasingly conducive to massive outbreaks, the emerging landscape structure is less and less likely to support them. This study improves our understanding of the long‐term legacies of ongoing bark beetle disturbances in Central Europe. It indicates that increased diversity provides an important dampening feedback, and suggests that preventing disturbances or homogenizing post‐disturbance forests could elevate the future susceptibility to large‐scale bark beetle outbreaks.

Patterns of woodboring beetle activity following fires and bark beetle outbreaks in montane forests of California, USA

BackgroundIncreasingly frequent and severe drought in the western United States has contributed to more frequent and severe wildfires, longer fire seasons, and more frequent bark beetle outbreaks that kill large numbers of trees. Climate change is expected to perpetuate these trends, especially in montane ecosystems, calling for improved strategies for managing Western forests and conserving the wildlife that they support. Woodboring beetles (e.g., Buprestidae and Cerambycidae) colonize dead and weakened trees and speed succession of habitats altered by fire or bark beetles, while serving as prey for some early-seral habitat specialists, including several woodpecker species. To understand how these ecologically important beetles respond to different sources of tree mortality, we sampled woodborers in 16 sites affected by wildfire or bark beetle outbreak in the previous one to eight years. Study sites were located in the Sierra Nevada, Modoc Plateau, Warner Mountains, and southern Cascades of California, USA. We used generalized linear mixed models to evaluate hypotheses concerning the response of woodboring beetles to disturbance type, severity, and timing; forest stand composition and structure; and tree characteristics.ResultsWoodborer activity was often similar in burned and bark beetle outbreak sites, tempered by localized responses to bark beetle activity, burn severity, tree characteristics, and apparent response to ignition date. Larval woodborer activity was inversely related to bark beetle sign within a sampling quadrat, was higher on pines, and—in burned sites—was higher on the south-facing sides of smaller trees. Adults—especially buprestids—were more abundant where burn severity was higher. Fires with intermediate ignition dates during the study period supported higher rates of larval woodborer activity and higher numbers of adult buprestids as well as cerambycids in the genus Monochamus Dejean 1821.ConclusionsWoodboring beetle abundance was related to bark beetle activity, burn severity, tree characteristics, and ignition date. Considering these patterns when managing disturbed forest stands could yield improved outcomes for wildlife, including species that prey on woodboring beetles. We also reported preliminary evidence that the current trend toward more frequent wildfires might not stimulate larger woodboring beetle populations if those fires increasingly occur outside the historical fire season.

Mammalian responses to changed forest conditions resulting from bark beetle outbreaks in the southern Rocky Mountains

AbstractSpruce beetle (Dendroctonus rufipennis) and mountain pine beetle (Dendroctonus ponderosae) outbreaks have impacted millions of acres of conifer forest from Alaska to northern Mexico. These species are native to North America, and periodic outbreaks have shaped the structure and composition of conifer forests for millennia. However, the extent and severity of current outbreaks, fueled by favorable climatic conditions and increased susceptibility of forests, are unmatched in recorded history. To characterize the response of a suite of mammalian species to beetle‐induced changes in vegetation in the southern Rocky Mountains, we deployed cameras at 300 randomly selected sites during summer 2013–2014. Selected sites spanned gradients of years elapsed since bark beetle outbreaks (YSO) and severity. We fit single‐season occupancy models to detection/non‐detection data collected for each species to examine a variety of plausible relationships between use of a given stand and YSO, severity, or both. Ungulates exhibited a positive association with bark beetle activity, although the nature of these associations varied by species. Elk (Cervus canadensis) were positively associated with severity, but not YSO; mule deer (Odocoileus hemionus) exhibited the opposite relationship. Moose (Alces alces) responded in a quadratic fashion; use of forest stands adjacent to preferred willow habitat peaked 3–7 yr after an outbreak commenced, but only at high severity. Similarly, yellow‐bellied marmot use of impacted stands adjacent to rock outcroppings followed a quadratic trend, but only at high severity. Red squirrel (Tamiasciurus hudsonicus) use declined in severely impacted stands, likely as a response to diminished cone crops. Golden‐mantled ground squirrels (Callospermophilus lateralis) and chipmunks (Neotamias spp.) exhibited a shallow negative relationship with YSO, as did coyotes (Canis latrans). Contrary to our hypotheses, black bears (Ursus americanus), American marten (Martes americana), snowshoe hares (Lepus americanus), and porcupines (Erethizon dorsatum) did not appear to be substantially influenced by beetle activity. Red fox (Vulpes vulpes) use was positively associated with YSO, but overall use declined as severity increased. Note that changes in probability of use described here could reflect changes in abundance, home range size, habitat use, or some combination, and in several cases, there was considerable uncertainty across competing models.

Delayed tree mortality, bark beetle activity, and regeneration dynamics five years following the Wallow Fire, Arizona, USA: Assessing trajectories towards resiliency

Warm/dry mixed conifer forests have undergone changes in disturbance regimes, forest structure, species composition, and surface fuel accumulation which have led to increased susceptibility to large, uncharacteristically severe wildfires and pathogenic outbreaks. Ecosystems resilient to fire events return to a similar set of structures (e.g., forest and understory composition and density) or processes (e.g., fire, decomposition rates); however, when exposed to disturbances outside the evolutionary envelope, may transition to a different state (e.g., type conversion). We sampled warm/dry mixed conifer forest stands treated prior to the 2011 Wallow Fire and paired untreated sites five years following the fire. Our objective was to evaluate mid-term ecosystem resiliency in terms of forest structure, bark beetle activity, and tree regeneration. We hypothesized that treated units would have higher mid-term post-fire resiliency compared to untreated units. In 2016, average total tree density remained significantly lower in treated compared to paired untreated units; conifer density and BA decreased in both treated and untreated units. Diameter distributions in 2016 treated units remained similar to those observed in 2012 with the exception of increased density in the smallest diameter class. In untreated units, the majority of tree density reductions occurred in the 10–30 cm dbh classes. Post-fire tree mortality was stable across treated and untreated units, with no significant differences; however, abundant ingrowth of small hardwoods occurred throughout the study area. Large-tree density decreased by about 20% in both treated and untreated units between 2012 and 2016. Evidence of post-fire bark beetles was generally low and patchy throughout the study site; however, beetle activity was more widespread in untreated units. Twice as many trees were attacked by bark beetles in untreated versus treated units suggesting treatments may have reduced post-fire beetle activity. Following wildfire, observed conifer regeneration was lower and hardwood regeneration was higher with increasing burn severity; conifer regeneration was nearly three times higher in treated units. This study suggests that pre-fire fuel reduction treatments contribute less to mid-term resiliency than to short-term resiliency of forested ecosystems. We observed trends of higher resilience to insect outbreaks and potential implications for type change from conifer to deciduous forest. Furthermore, our study underscores the importance of understanding mid-term post-fire recovery, and while it provides insights regarding recovery of these ecosystems, additional monitoring and research is needed to fully understand the implications toward long-term resiliency.

A framework for detecting conifer mortality across an ecoregion using high spatial resolution spaceborne imaging spectroscopy

Between 2013 and 2015, during a time of severe drought and elevated bark beetle (Dendroctonus spp.) activity in California, the amount of conifer mortality in the Southern Sierra Nevada increased greatly. Remote sensing is a critical means of providing up-to-date information on the location, magnitude, and extent of mortality across a broad geographic area. We used eleven Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) flight lines, resampled to 30 by 30 m pixel size and acquired on six separate dates as part of the HyspIRI Preparatory Campaign to simulate spaceborne imaging spectroscopy. We also spectrally degraded the AVIRIS images to simulate Landsat-8 data. We tested the ability of single-date and multi-temporal remote sensing to identify red stage conifer mortality, healthy conifer, and non-conifer dominated pixels using a random forest algorithm. Accuracy was assessed with an independent validation dataset acquired via WorldView imagery in areas spatially separate from where training data were collected, as well as through comparison with aerial detection survey and canopy water loss data, with generally good agreement. We found that classifications based on imaging spectroscopy significantly outperformed broadband multispectral feature sets (with a highest overall accuracy of 85.1% obtained by imaging spectroscopy and 80.2% obtained by the simulated multispectral images). We also found that classifications based on multi-temporal imaging spectroscopy were more accurate than single-date imaging spectroscopy (the highest overall accuracy obtained for single-date imaging spectroscopy was 83.4%). Imaging spectroscopy that included interseasonal data from the end of the drought outperformed all other datasets, including interannual data that included only images collected in the summer. Multi-date analysis also improved accuracy using broad band systems. Although current spaceborne assets are adequate for monitoring bark beetle mortality in a heterogeneous ecosystem, a spaceborne imaging spectrometer would further improve operational accuracy.

The impact of future forest dynamics on climate: interactive effects of changing vegetation and disturbance regimes.

Currently, the temperate forest biome cools the earth's climate and dampens anthropogenic climate change. However, climate change will substantially alter forest dynamics in the future, affecting the climate regulation function of forests. Increasing natural disturbances can reduce carbon uptake and evaporative cooling, but at the same time increase the albedo of a landscape. Simultaneous changes in vegetation composition can mitigate disturbance impacts, but also influence climate regulation directly (e.g., via albedo changes). As a result of a number of interactive drivers (changes in climate, vegetation, and disturbance) and their simultaneous effects on climate-relevant processes (carbon exchange, albedo, latent heat flux) the future climate regulation function of forests remains highly uncertain. Here we address these complex interactions to assess the effect of future forest dynamics on the climate system. Our specific objectives were (1) to investigate the long-term interactions between changing vegetation composition and disturbance regimes under climate change, (2) to quantify the response of climate regulation to changes in forest dynamics, and (3) to identify the main drivers of the future influence of forests on the climate system. We investigated these issues using the individual-based forest landscape and disturbance model (iLand). Simulations were run over 200 yr for Kalkalpen National Park (Austria), assuming different future climate projections, and incorporating dynamically responding wind and bark beetle disturbances. To consistently assess the net effect on climate the simulated responses of carbon exchange, albedo, and latent heat flux were expressed as contributions to radiative forcing. We found that climate change increased disturbances (+27.7% over 200 yr) and specifically bark beetle activity during the 21st century. However, negative feedbacks from a simultaneously changing tree species composition (+28.0% broadleaved species) decreased disturbance activity in the long run (-10.1%), mainly by reducing the host trees available for bark beetles. Climate change and the resulting future forest dynamics significantly reduced the climate regulation function of the landscape, increasing radiative forcing by up to +10.2% on average over 200 yr. Overall, radiative forcing was most strongly driven by carbon exchange. We conclude that future changes in forest dynamics can cause amplifying climate feedbacks from temperate forest ecosystems.

Inoculation of ophiostomatoid fungi in loblolly pine trees increases the presence of subterranean termites in fungal lesions

Many bluestain (ophiostomatoid) fungi are inoculated into trees via bark beetle activity, but their ecological roles are not fully understood, particularly for interactions with invertebrates outside bark beetle and phoretic mite associations. Recently, correlational field studies and small-scale laboratory feeding trials have demonstrated subterranean termites have increased presence on and preferential feeding of bluestain-infected wood, but experimental field evidence is lacking. To test the hypothesis that bluestain fungi increase termite presence in infected trees, we inoculated 72 loblolly pine trees in the southeastern USA with one of four bluestain fungi (Ophiostoma minus, O. ips, Leptographium terebrantis, L. procerum), a combination (O. minus + L. terebrantis), or H2O as a control. Over four years, all fungi-inoculated trees formed lesions around injection sites, while control trees formed no lesions except for two contaminated control trees that were excluded from analyses. Bluestain-inoculated trees had increased termite presence in and around fungal lesions, whereas control trees had no termites present. Specifically, termites were present on 35 % of fungi-inoculated trees, presence was consistent over time, and there was no difference among fungal species. This study experimentally demonstrates a link between bluestain fungi and subterranean termites in forests, which could impact tree dynamics post-bluestain infection.

Root disease can rival fire and harvest in reducing forest carbon storage

AbstractRoot diseases are known to suppress forest regeneration and reduce growth rates, and they may become more common as susceptible tree species become maladapted in parts of their historic ranges due to climate change. However, current ecosystem models do not track the effects of root disease on net productivity, and there has been little research on how the dynamics of root disease affect carbon (C) storage and productivity across infected landscapes. We compared the effects of root disease against the effects of other types of forest disturbance across six national forest landscapes, 1990–2011. This was enabled by a monitoring tool called the Forest Carbon Management Framework (ForCaMF), which makes use of ground inventory data, an empirical growth model, and time series of Landsat satellite imagery. Despite several large fires that burned across these landscapes during the study period, retrospective ForCaMFanalysis showed that fire and root disease had approximately equal impacts on C storage. Relative to C accumulation that would have occurred in their absence, fires from 1990 to 2011 were estimated to reduce regionwide C storage by 215.3 ± 19.1 g/m2 C, while disease in the same period was estimated to reduce storage by 211.4 ± 59.9 g/m2 C. Harvest (75.5 ± 13.5 g/m2 C) and bark beetle activity (14.8 ± 12.5 g/m2 C) were less important. While long‐term disturbance processes such as root disease have generally been ignored by tools informing management of forest C storage, the recent history of several national forests suggests that such disturbances can be just as important to the C cycle as more conspicuous events like wildfires.

Multi‐temporal ecological analysis of Jeffrey pine beetle outbreak dynamics within the Lake Tahoe Basin

AbstractFrom 1991 to 1996, Jeffrey pine beetles (Dendroctonus jeffreyi Hopkins) (JPB) caused tree mortality throughout the Lake Tahoe Basin during a severe drought. Census data were collected annually on 10,721 trees to assess patterns of JPB‐caused mortality. This represents the most extensive tree‐level, spatiotemporal dataset collected to‐date documenting bark beetle activity. Our study was an exploratory assessment of characteristics associated with the probability of successful JPB mass‐attack (PJPB) and group aggregation behavior that occurred throughout various outbreak phases. Numerous characteristics associated with PJPB varied by outbreak phase although population pressure and forest density had positive associations during all phases. During the incipient phase, JPBs caused mortality in individual trees and small groups within toeslope topographic positions and PJPB had a negative relationship with stem diameter. In the epidemic phase, JPB activity occurred in all topographic positions and caused mortality in spatially expanding clusters. PJPB had a curvilinear relationship with tree diameter and a negative relationship with proximity to nearest brood tree. Majority (92–96 %) of mass‐attacked trees were within 30 m of a brood tree during the peak epidemic years. During the post‐epidemic phase, mortality clusters progressively decreased while dispersal distances between mass‐attacked and brood trees increased. Post‐epidemic PJPB had a negative relationship with stem diameter and mortality was concentrated in the mid and upper‐slope topographic positions. Results indicate mortality predictions are reasonable for the epidemic phase but not for incipient and post‐epidemic phases. Ecological factors influencing JPB‐caused tree mortality, clustered mortality patterns, and transitions from environmental to dynamic determinism are discussed.

Forecasting bark beetle early flight activity with plant phenology

Bark beetle outbreaks are a major threat to forest productivity, and a robust forecast of early flight activity is necessary for inhibition or mitigation of large-scale infestations. We used spring phenology of common wild plants in a phenology-based forecasting approach for European spruce bark beetle Ips typographicus L. early flight activity in Bavaria, Southern Germany, and tested this novel approach against traditional thermal sum-based predictions. Our phenology- based forecast employing the 2 phenological phases of first flowering of common snowdrop Galanthus nivalis L. and leaf budburst of horse chestnut Aesculus hippocastanum L. proved to be more robust and accurate than the thermal sum-based forecast. This is explained by both bark beetle phenology and plant phenology being results of a complex control chain of environmental factors, which can be approximated by temperature sums only to a limited degree. However, our space-for-time approach demonstrates strong and unequivocal temperature sensitivity of bark beetle and plant phenology. This indicates a common pattern in bioclimatic mediation of ecophys- iological processes for both plants and insects as the mechanistic foundation for forecasting. In the case of costly bark beetle activity monitoring data often characterised by gaps and irregular sam- pling intervals, plant phenology can thus provide an easily observable alternative or complemen- tary predictor for early flight activity. Our results indicate that forest practitioners can benefit from simple phenological observations to improve the timing of adequate management measures to mitigate bark beetle mass infestations.