https://hal.archives-ouvertes.fr/hal-00457602/document

A global overview of drought and heat-induced tree mortality reveals emerging climate change risks for forests

Climatic changes are predicted to significantly affect the frequency and severity of disturbances that shape forest ecosystems. We provide a synthesis of climate change effects on native bark beetles, important mortality agents of conifers in western North America. Because of differences in temperature-dependent life-history strategies, including cold-induced mortality and developmental timing, responses to warming will differ among and within bark beetle species. The success of bark beetle populations will also be influenced indirectly by the effects of climate on community associates and host-tree vigor, although little information is available to quantify these relationships. We used available population models and climate forecasts to explore the responses of two eruptive bark beetle species. Based on projected warming, increases in thermal regimes conducive to population success are predicted for Dendroctonus rufipennis (Kirby) and Dendroctonus ponderosae Hopkins, although there is considerable spatial and temporal variability. These predictions from population models suggest a movement of temperature suitability to higher latitudes and elevations and identify regions with a high potential for bark beetle outbreaks and associated tree mortality in the coming century.

https://www.fs.fed.us/rm/pubs_other/rmrs_2010_bentz_b001.pdf

Climate Change and Bark Beetles of the Western United States and Canada: Direct and Indirect Effects

Forest insects and pathogens are major disturbance agents that have affected millions of hectares in North America in recent decades, implying significant impacts to the carbon (C) cycle. Here, we review and synthesize published studies of the effects of biotic disturbances on forest C cycling in the United States and Canada. Primary productivity in stands was reduced, sometimes considerably, immediately following insect or pathogen attack. After repeated growth reductions caused by some insects or pathogens or a single infestation by some bark beetle species, tree mortality occurred, altering productivity and decomposition. In the years following disturbance, primary productivity in some cases increased rapidly as a result of enhanced growth by surviving vegetation, and in other cases increased slowly because of lower forest regrowth. In the decades following tree mortality, decomposition increased as a result of the large amount of dead organic matter. Net ecosystem productivity decreased immediately following attack, with some studies reporting a switch to a C source to the atmosphere, and increased afterward as the forest regrew and dead organic matter decomposed. Large variability in C cycle responses arose from several factors, including type of insect or pathogen, time since disturbance, number of trees affected, and capacity of remaining vegetation to increase growth rates following outbreak. We identified significant knowledge gaps, including limited understanding of carbon cycle impacts among different biotic disturbance types (particularly pathogens), their impacts at landscape and regional scales, and limited capacity to predict disturbance events and their consequences for carbon cycling. We conclude that biotic disturbances can have major impacts on forest C stocks and fluxes and can be large enough to affect regional C cycling. However, additional research is needed to reduce the uncertainties associated with quantifying biotic disturbance effects on the North American C budget.

/pdf/effects-of-biotic-disturbances-on-forest-carbon-cycling-in-tsbjeaejek.pdf

Effects of biotic disturbances on forest carbon cycling in the United States and Canada

aclimate-drivengrowthequationbyusingclimaterecordstopredict annual ring widths. Forests within the southwestern United States appear particularly sensitive to drought and warmth. We input 21st century climate projections to the equations to predict growth responses. Our results suggest that if temperature and aridity rise as they are projected to, southwestern trees will experience sub- stantially reduced growth during this century. As tree growth declines, mortality rates may increase at many sites. Increases in wildfires and bark-beetle outbreaks in the most recent decade are likely related to extreme drought and high temperatures during this period. Using satellite imagery and aerial survey data, we conserva- tively calculate that ≈2.7% of southwestern forest and woodland areaexperienced substantialmortalityduetowildfires from1984 to 2006,and ≈7.6%experiencedmortalityassociatedwithbarkbeetles from 1997 to 2008. We estimate that up to ≈18% of southwestern forest area (excluding woodlands) experienced mortality due to

/pdf/forest-responses-to-increasing-aridity-and-warmth-in-the-2pntbcqe1b.pdf

Forest responses to increasing aridity and warmth in the southwestern United States

About one-third of North America is forested. These forests are of incalculable value to human society in terms of harvested resources and ecosystem services and are sensitive to disturbance regimes. Epidemics of forest insects and diseases are the dominant sources of disturbance to North American forests. Here we review current understanding of climatic effects on the abundance of forest insects and diseases in North America, and of the ecological and socioeconomic impacts of biotic disturbances. We identified 27 insects (6 nonindigenous) and 22 diseases (9 nonindigenous) that are notable agents of disturbance in North American forests. The distribution and abundance of forest insects and pathogens respond rapidly to climatic variation due to their physiological sensitivity to temperature, high mobility, short generation times, and high reproductive potential. Additionally, climate affects tree defenses, tree tolerance, and community interactions involving enemies, competitors, and mutualists of insects ...

/pdf/consequences-of-climate-change-for-biotic-disturbances-in-1e27omooox.pdf

Consequences of climate change for biotic disturbances in North American forests

Since 1990, native bark beetles have killed billions of trees across millions of acres of forest from Alaska to northern Mexico. Although bark beetle infestations are a regular force of natural change in forested ecosystems, several of the current outbreaks, which are occurring simultaneously across western North America, are the largest and most severe in recorded history.

https://www.fs.fed.us/rm/pubs_other/rmrs_2009_bentz_b001.pdf

Bark beetle outbreaks in western North America: Causes and consequences

The banded elm bark beetle (BEBB) (Scolytus schevyrewi) is an invasive beetle from Asia that attacks elm (Ulmus spp.) trees and may vector the fungal pathogen causing Dutch elm disease, Ophiostoma ulmi. BEBB shares a similar biology to an established invasive, the European elm bark beetle (EEBB) (Scolytus multistriatus). However, BEBB seems to attack standing trees more aggressively and appears now more abundant than EEBB in the Rocky Mountain region, suggesting that BEBB may have displaced EEBB and/or is better able to colonize regions beyond EEBB's range. Our objectives were to determine the relative abundance of BEBB and EEBB in seven states and compare how each species locates host elms for attack. To monitor abundance, a trap Siberian elm log, baited funnel trap, and passive plexiglass trap were set up at four sites in each state and checked from April/May to September. BEBB was less common than EEBB in California (13%), BEBB increased in abundance in Nevada (68%) and Utah (65%), and it was highest in Colorado (89%) and Wyoming (83%). BEBB populations were minor moving east to Kansas (3.3%) and Missouri (2.7%). This survey suggests that BEBB may be displacing EEBB because EEBB is no longer commonly found in Colorado where it was often found in the past. Flight toward uninfested and variously infested elm logs was monitored for BEBB in Colorado and Wyoming and for EEBB in California. BEBB responded strongly to elm odors and showed no preference for elm infested with females or males. EEBB responded somewhat to elm odors but more so to pheromones from an elm that was infested by EEBB females for 48 to 96 hours. Colonizing female EEBB required a few days to produce an attractive pheromone. In Nevada, BEBB responded indiscriminately to all elm logs regardless of whether the log was infested with BEBB, EEBB, or both. Thus, when a new elm is available, BEBB may have a competitive advantage attacking first, whereas EEBB may attack in greater numbers later, following pheromone production from the initial attacks of EEBB females

https://www.nrs.fs.fed.us/pubs/gtr/gtr-nrs-p-36papers/34lee-p-36.pdf

Jeff Witcosky

Papers

Bark beetle outbreaks in western North America: Causes and consequences

Bark beetle outbreaks in western North America: Causes and consequences

Trend of two invasives: the banded and European elm bark beetles