Abstract
Swiss needle cast (SNC), caused by a fungal pathogen, Nothophaeocryptopus gaeumannii, is a major forest disease of Douglas-fir (Pseudotsuga menziesii) stands of the Pacific Northwest (PNW). ...There is mounting concern that the current SNC epidemic occurring in Oregon and Washington will continue to increase in severity, frequency and spatial extent with future warming. Nothophaeocryptopus gaeumannii occurs wherever its host is found, but very little is known about the history and spatial distribution of SNC and its effects on growth and physiological processes of mature and old-growth forests within the Douglas-fir region of the PNW. Our findings show that stem growth and physiological responses of infected Douglas-fir to climate and SNC were different between sites, growth periods and disease severity based on cellulosic stable carbon and oxygen isotope ratios and ring width data in tree rings. At a coastal Oregon site within the SNC impact zone, variations in stem growth and Δ13C were primarily influenced by disproportional reductions in stomatal conductance (gs) and assimilation (A) caused by a loss of functioning stomates through early needle abscission and stomatal occlusion by pseudothecia of N. gaeumannii. At the less severely infected inland sites on the west slopes of Oregon’s Cascade Range, stem growth correlated negatively with δ18O and positively with Δ13C, indicating that gs decreased in response to high evaporative demand with a concomitant reduction in A. Current- and previous-years summer vapor pressure deficit was the principal seasonal climatic variable affecting radial stem growth and the dual stable isotope ratios at all sites. Our results indicate that rising temperatures since the mid-1970s has strongly affected Douglas-fir growth in the PNW directly by a physiological response to higher evaporative demand during the annual summer drought and indirectly by a major SNC epidemic that is expanding regionally to higher latitudes and higher elevations.
It is well known that exposure to ambient O3 can decrease growth in many tree species in the United States (US). Our study reports experimental data from outdoor open-top chamber (OTC) studies that ...quantify total biomass response changes for seedlings of 16 species native to western and eastern North America, which were exposed to several levels of elevated O3 for one or more years. The primary objective of this study is to establish a reference set of parameters for these seedling exposure-response relationships using a 3-month (92 day) 12-hr W126 O3 metric used by US Environmental Protection Agency and other agencies to assess risk to trees from O3 exposure. We classified the 16 species according to their sensitivity, based on the biomass loss response functions to protect from a 5% biomass loss. The three-month 12-h W126 estimated to result in a 5% biomass loss was 2.5–9.2 ppm-h for sensitive species, 20.8–25.2 ppm-h for intermediate species, and >28.7 ppm-h for insensitive species. The most sensitive tree species include black cherry, ponderosa pine, quaking aspen, red alder, American sycamore, tulip poplar and winged sumac. These species are ecologically important and widespread across US. The effects of O3 on whole-plant biomass depended on exposure duration and dynamics and on the number of successive years of exposure. These species-specific exposure-response relationships will allow US agencies and other groups to better estimate biomass losses based on ozone exposures in North America and can be used in risk assessment and scenario analyses.
•Whole-plant biomass response to tropospheric ozone exposure varies by tree species.•Conifers are less ozone sensitive than broadleaves at ambient ozone concentrations.•Whole-plant biomass reductions typically occur after one year of ozone exposure but can be greater after two seasons of exposure.•Exposure-response relationships are reported for first time for chestnut oak and yellow buckeye.•Black cherry, tulip poplar and ponderosa pine are among the most ozone-sensitive North American tree species.
•Forest disturbances are beginning to show evidence of climate-mediated changes.•Biotic disturbances must be understood to predict responses of future forests.•We reviewed major biotic agents in the ...Douglas-fir region’s disturbance regime.•Interactions with climate change will likely vary among biotic disturbance agents.•These factors must be characterized by forest type to aid in adaptive management.
Forest disturbance regimes are beginning to show evidence of climate-mediated changes, such as increasing severity of droughts and insect outbreaks. We review the major insects and pathogens affecting the disturbance regime for coastal Douglas-fir forests in western Oregon and Washington State, USA, and ask how future climate changes may influence their role in disturbance ecology. Although the physiological constraints of light, temperature, and moisture largely control tree growth, episodic and chronic disturbances interacting with biological factors have substantial impacts on the structure and functioning of forest ecosystems in this region. Understanding insect and disease interactions is critical to predicting forest response to climate change and the consequences for ecosystem services, such as timber, clean water, fish and wildlife. We focused on future predictions for warmer wetter winters, hotter drier summers, and elevated atmospheric CO2 to hypothesize the response of Douglas-fir forests to the major insects and diseases influencing this forest type: Douglas-fir beetle, Swiss needle cast, black stain root disease, and laminated root rot. We hypothesize that (1) Douglas-fir beetle and black stain root disease could become more prevalent with increasing, fire, temperature stress, and moisture stress, (2) future impacts of Swiss needle cast are difficult to predict due to uncertainties in May-July leaf wetness, but warmer winters could contribute to intensification at higher elevations, and (3) laminated root rot will be influenced primarily by forest management, rather than climatic change. Furthermore, these biotic disturbance agents interact in complex ways that are poorly understood. Consequently, to inform management decisions, insect and disease influences on disturbance regimes must be characterized specifically by forest type and region in order to accurately capture these interactions in light of future climate-mediated changes.
Forest biological disturbance agents (BDAs) are insects, pathogens, and parasitic plants that affect tree decline, mortality, and forest ecosystems processes. BDAs are commonly thought to increase ...the likelihood and severity of fire by converting live standing trees to more flammable, dead and downed fuel. However, recent research indicates that BDAs do not necessarily increase, and can reduce, the likelihood or severity of fire. This has led to confusion regarding the role of BDAs in influencing fuels and fire in fire-prone western United States forests. Here, we review the existing literature on BDAs and their effects on fuels and fire in the western US and develop a conceptual framework to better understand the complex relationships between BDAs, fuels and fire. We ask: 1) What are the major BDA groups in western US forests that affect fuels? and 2) How do BDA-affected fuels influence fire risk and outcomes? The conceptual framework is rooted in the spatiotemporal aspects of BDA life histories, which drive forest impacts, fuel characteristics and if ignited, fire outcomes. Life histories vary among BDAs from episodic, landscape-scale outbreaks (bark beetles, defoliators), to chronic, localized disturbance effects (dwarf mistletoes, root rots). Generally, BDAs convert aboveground live biomass to dead biomass, decreasing canopy fuels and increasing surface fuels. However, the rate of conversion varies with time-since-event and among BDAs and forest types, resulting in a wide range of effects on the amount of dead fuels at any given time and place, which interacts with the structure and composition of the stand before and subsequent to BDA events. A major influence on fuels may be that BDAs have emerged as dominant agents of forest heterogeneity creation. Because BDAs play complex roles in fuels and fire heterogeneity across the western US which are further complicated by interactions with climate change, drought, and forest management (fire suppression), their impacts on fuels, fire and ecological consequences cannot be categorized simply as positive or negative but need to be evaluated within the context of BDA life histories and ecosystem dynamics.
•Pacific Northwest growth-climate-disease relations vary by site and climate regimes.•Douglas-fir growth is limited by dewpoint deficit and temperature regionally.•Growth response to temperature is ...modified by soil moisture and Swiss needle cast.•Swiss needle cast impacts on Douglas-fir growth are spatially extensive in the PNW.•PNW tree growth rates have changed in recent decades due to increasing temperature.
Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) growth in the Pacific Northwest is affected by climatic, edaphic factors and Swiss needle cast (SNC) disease. We examine Douglas-fir growth responses to temperature, dewpoint deficit (DPD), soil moisture, and SNC using time series intervention analysis of intra-annual tree-ring width data collected at nine forest stands in western Oregon, USA. Air temperature, previous-year DPD and SNC and their interactions were the primary factors influencing tree growth at all sites, whereas other key seasonal climatic factors limiting growth varied by site. Winter temperature was more important at high elevation cool sites, whereas summer temperature was more important at warm and dry sites. Growth rate increased with summer temperature to an optimum (Topt) then decreased at higher temperatures. At drier sites, temperature and water affected growth interactively such that Topt decreased with decreasing summer soil moisture. With increasing temperature due to climate change, growth rates increased at high elevation sites and declined at mid-elevation inland sites since ∼1990. Growth response to climate and SNC are confounded at all sites. We conclude that as temperature rises and precipitation patterns shift toward wetter winters and drier summers, Douglas-fir will experience greater temperature and water stress and an increase in severity of SNC.
•Seasonal patterns of bole water content were studied in old-growth Douglas-fir.•Maximum RWC occurred in mid-summer and the lowest during winter.•Bole water storage enables trees to extend carbon ...assimilation into drought periods.
Large conifer trees in the North American Pacific Northwest (PNW) use stored water to extend photosynthesis, both diurnally and seasonally. This is particularly important during the summer drought, which is characteristic of the region. In the PNW, climate change is predicted to result in hotter, drier summers and warmer, wetter winters with decreased snowpack by mid-century. Understanding seasonal bole water dynamics in relation to climate factors will enhance our ability to determine the vulnerability of forests to climate change. Seasonal patterns of bole water content in old-growth Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees were studied in the Cascade Mountains of western Oregon, USA. Relative water content (RWC) was monitored hourly in three 400+ and three ∼150 years-old trees using permanently mounted dielectric devices for 10 years. RWC increased during the late spring and early summer to maximum levels in August then decreased into fall and remained low over winter. The difference between minimum RWC in the winter and maximum in mid-summer averaged 4.5 and 2.3% for the older and younger trees, respectively, across all years. RWC closely followed growth and was positively correlated with air and soil temperature, vapor pressure deficit and photosynthetically active radiation, but lagged plant available soil water. The progressive decrease in RWC seen each year from mid-summer through fall was attributed to net daily loss of water during the summer drought. The marked increase in RWC observed from spring to mid-summer each year was hypothesized to be the period of embolism repair and water recharge in elastic tissues. We conclude that bole water content is an integral part of tree water dynamics enabling trees to extend carbon assimilation into drought periods and during periods when cold soil inhibits water uptake by roots, an adaptation that could benefit the survival of large PNW trees under climate change.
•The first study comparing the differences of SNC patterns between tree ages.•Disease severity was greater in young forests than mature forests.•Incidence of disease and foliage retention differed in ...young trees and mature trees.•Foliage nitrogen did not differ between young and mature trees.•Leaf wetness differences did not inform disease severity differences.
Swiss needle cast (SNC), caused by Nothophaeocryptopus gaeumannii, is an important foliage disease of Douglas-fir (Pseudotsuga menziesii) forests of the Pacific Northwest. The fungus lives endophytically within the foliage, until forming reproductive structures (pseudothecia) that plug stomates and cause carbon starvation. When pseudothecia appear on one- and two-year-old foliage, significant needle abscission can occur, which reduces productivity of the tree. While there is considerable evidence of SNC disease in coastal Douglas-fir plantations, the severity of SNC in mature and old-growth forests is poorly understood. We compared tree crowns of mature and old-growth conifer forests and nearby young forests at three locations in the Oregon Coast Range and four locations in the western Cascade Range of Oregon. We assessed disease severity for N. gaeumannii on two-year-old foliage, incidence by presence of N. gaeumannii on all foliage, foliage retention for the first four years, and foliar nitrogen of one-year-old foliage. We also compared leaf wetness at three heights in one mature and one young tree at five of the seven sites. Disease severity was greater in young forests than mature forests at all sites except for high elevation Cascade Range areas. Incidence of disease was highest for two-year-old needles in young trees and 3–5 year-old needles in mature trees, except for one coastal site. Retention of 1–4 year-old needle cohorts differed between young and mature trees, and mature trees had much larger complements of > four-year-old needles. Total foliar nitrogen (TN) concentration did not differ in needles of young and mature trees, but at some locations total N differed between canopy positions. Leaf wetness differences were not consistent between young and mature tree crowns. However, at one study site in the core epidemic area, the younger stand had longer periods of wetness in the upper crowns than a nearby old stand. Leaf wetness and foliar N were hypothesized to play a role in SNC disease severity, but they do not explain differences in adjacent young and mature trees. Although the fungus is present in old and young trees, the likelihood of disease expression and lower foliage retention appears to be greater in younger plantation trees than mature and older trees in western Oregon Douglas-fir forests.
is a common native, endophytic fungus of Douglas-fir foliage, which causes Swiss needle cast, an important foliage disease that is considered a threat to Douglas-fir plantations in Oregon. Disease ...expression is influenced by fungal fruiting bodies (pseudothecia), which plug the stomata and inhibit gas exchange. Trees are impacted when pseudothecia plug stomates on 1-year-old and older needles resulting in early needle abscission. Mature (100 years+) trees appear to be less impacted from disease, and we hypothesize this is due to the greater emergence of pseudothecia on older than younger needles, which allows for more needle retention. We measured the density of pseudothecia occluding stomates across 2- to 5-year-old needles from upper, middle, and lower canopy positions of mature trees at three sites in the Oregon Coast Range and two sites in the western Oregon Cascade Mountains. Binomial generalized linear mixed model (GLMM) was used to test for the effects of canopy position (upper, middle, and lower), sites, needle age (2-5 years old), and years (2016 and 2017), and their interactions on the pseudothecia density. Pseudothecia density varied annually depending on sites, needle age and canopy positions. Pseudothecia density peaked on 3-, and 4-year-old needles, however, needles emerging from the same year, like 2-year-old needles in 2016 and 3-year-old needles in 2017 both emerged in 2014, had consistently similar patterns of pseudothecia density for both years, across site and canopy positions. Canopy position was important for 3-, and 4-year-old needles, showing less pseudothecia in the lower canopy. This research confirms that
pseudothecia density is greatest in 3- and 4-year old needles in mature trees in contrast to plantations where pseudothecia density usually peaks on 2-year-old needles, and that pseudothecia density (disease severity) is generally lower in mature trees. Something about mature forest canopies and foliage appears to increase the time it takes for pseudothecia to emerge from the needles, in contrast to younger plantations, thus allowing the mature trees to have greater needle retention.
► Both temperature and moisture consistently limit forest growth during the summer. ► Temperature optima for growth decreased with decreasing soil moisture at dry sites. ► Douglas-fir will experience ...progressive temperature limitation with climate change.
Douglas-fir growth in the Pacific Northwest is thought to be water limited. However, discerning the relative influence of air temperature and plant available soil water (W) on growth is difficult because they interact with each other, with other climate factors and with the inherent seasonal timing of cambial activity. Douglas-fir growth response to air temperature and W patterns during the growing season was examined using time series regression analysis of dendrometer data collected at approximately four-week intervals from 1998 through 2009. Five study sites were located in mature forest stands along an elevation gradient from the Pacific coast to the west slope of the Cascade Mountains (∼1200m) in Oregon, USA. Maximum daily air temperature (T) and W were similar in relative importance to tree growth at four of the five sites. W was substantially more important at one site. Growth rate increased with T to an optimum (Topt) and decreased with higher T. At the two drier sites T and W affected growth interactively in that Topt decreased with decreasing W. We conclude that both T and W affect growth and that T consistently limits growth at three of the five sites and at all sites in years with above average summer temperature. Should climate change result in hotter summers in the region as predicted by climate models, we suggest that Douglas-fir will experience progressive temperature limitation.
Wildland fires (WLF) have become more frequent, larger, and severe with greater impacts to society and ecosystems and dramatic increases in firefighting costs. Forests throughout the range of ...ponderosa pine in Oregon and Washington are jeopardized by the interaction of anomalously dense forest structure, a warming and drying climate, and an expanding human population. These forests evolved with frequent interacting disturbances including low-severity surface fires, droughts, and biological disturbance agents (BDAs). Chronic low-severity disturbances were, and still are, critical to maintaining disturbance resistance, the property of an ecosystem to withstand disturbance while maintaining its structure and ecological function. Restoration of that historical resistance offers multiple social and ecological benefits.
Moving forward, we need a shared understanding of the ecology of ponderosa pine forests to appreciate how restoring resistance can reduce the impacts of disturbances. Given contemporary forest conditions, a warming climate, and growing human populations, we predict continued elevation of tree mortality from drought, BDAs, and the large high-severity WLFs that threaten lives and property as well as ecosystem functions and services. We recommend more comprehensive planning to promote greater use of prescribed fire and management of reported fires for ecological benefits, plus increased responsibility and preparedness of local agencies, communities and individual homeowners for WLF and smoke events. Ultimately, by more effectively preparing for fire in the wildland urban interface, and by increasing the resistance of ponderosa pine forests, we can greatly enhance our ability to live with fire and other disturbances.
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