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.
In recent years, increased awareness of the potential interactions between rising atmospheric
CO2
concentrations (
CO2
) and temperature has illustrated the importance of multifactorial ecosystem ...manipulation experiments for validating Earth System models. To address the urgent need for increased understanding of responses in multifactorial experiments, this article synthesizes how ecosystem productivity and soil processes respond to combined warming and
CO2
manipulation, and compares it with those obtained in single factor
CO2
and temperature manipulation experiments. Across all combined elevated
CO2
and warming experiments, biomass production and soil respiration were typically enhanced. Responses to the combined treatment were more similar to those in the
CO2
‐only treatment than to those in the warming‐only treatment. In contrast to warming‐only experiments, both the combined and the
CO2
‐only treatments elicited larger stimulation of fine root biomass than of aboveground biomass, consistently stimulated soil respiration, and decreased foliar nitrogen (N) concentration. Nonetheless, mineral N availability declined less in the combined treatment than in the
CO2
‐only treatment, possibly due to the warming‐induced acceleration of decomposition, implying that progressive nitrogen limitation (PNL) may not occur as commonly as anticipated from single factor
CO2
treatment studies. Responses of total plant biomass, especially of aboveground biomass, revealed antagonistic interactions between elevated
CO2
and warming, i.e. the response to the combined treatment was usually less‐than‐additive. This implies that productivity projections might be overestimated when models are parameterized based on single factor responses. Our results highlight the need for more (and especially more long‐term) multifactor manipulation experiments. Because single factor
CO2
responses often dominated over warming responses in the combined treatments, our results also suggest that projected responses to future global warming in Earth System models should not be parameterized using single factor warming experiments.
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.
•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.
Quantifying the routing of snowmelt to surface water is critical for predicting the impacts of atmospheric deposition and changing land use on water quality in montane catchments. To investigate ...solute sources and streamflow in the montane Provo River watershed (Utah, USA), we used time‐series 87Sr/86Sr ratios sampled at three sites (Soapstone, Woodland and Hailstone) across a gradient of bedrock types. Soils are influenced by aeolian dust contributions, with distinct 87Sr/86Sr ratios relative to siliciclastic bedrock, providing an opportunity to investigate shallow versus deeper flow paths for controlling water chemistry. At the most upstream site (Soapstone), Sr concentrations averaged ~17 μg/L with minimal dilution during snowmelt suggesting subsurface flow paths dominated streamflow. However, a decrease in 87Sr/86Sr ratios from ~0.717 during baseflow to as low as ~0.713 during snowmelt indicated the activation of shallow flow paths through dust‐derived soils. In contrast, downstream sites receiving water inputs from Sr‐rich carbonate bedrock (Woodland and Hailstone) exhibited strong dilution of Sr from ~120 to 20 μg/L and an increase in 87Sr/86Sr ratios from ~0.7095 to ~0.712 during snowmelt. A three‐component mixing model using 87Sr/86Sr ratios and Sr concentrations at Soapstone showed water inputs were dominated by direct snowmelt and flushed soil water during runoff and groundwater during baseflow. At Woodland and Hailstone, a two‐component mixing model showed that the river was a mixture of groundwater and up to 75% upstream channel water during snowmelt. Our findings highlight the importance of flushed soil water for controlling stream water discharge and chemistry during snowmelt, with the signal from the upstream site propagating downstream in a nested catchment. Further, aeolian dust contributes to the solute chemistry of montane streams with potential impacts on water quality along shallow flow paths. Potential contaminants in these surface soils (e.g., Pb deposition in dust) may have significant impacts on water quality during snowmelt runoff.
A three‐component mixing model using 87Sr/86Sr ratios and Sr concentrations at our upper sampling site showed water inputs during spring runoff were dominated by direct snowmelt and flushed soil water. Further downstream, a two‐component mixing model showed that the river was a mixture of groundwater and up to 75% upstream channel water during snowmelt. Aeolian dust affects water quality of montane streams as snowmelt water travels along shallow flow paths.
► 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.
Ease of access, size, and basalt as the dominant bedrock make Oahu an ideal locality for investigating chemical weathering-driven denudation rates as a function of climate (rainfall varies by an ...order of magnitude), water–rock contact time, and soil thickness. New and compiled surface and groundwater solute data permit calculation of mass balances for solute fluxes from Oahu, revealing that groundwater dominates surface water solute fluxes by a factor of 3–12.
Weathering reactions were written consistent with the mineralogy of Oahu soils, permitting denudation rates to be partitioned between dissolved and suspended loads. Total denudation rates, indexed to the leaching of SiO2, vary from 0.016 to 0.063m/ka, with about 70% of Si transport due to dissolved loads. Drier regions of Oahu have distinctly lower denudation rates, and areas with thick weathering profiles have suppressed surface-water solute loads.
Indexing denudation in basaltic terranes to dissolved SiO2 rather than other solutes leads to improved estimates of weathering rates. Other approaches require correction for the atmospheric depositions of sea salts based on Cl− abundances in waters that are assumed to derive solely from the ocean via atmospheric deposition.
Recent work indicates that Oahu is tectonically emerging at 0.060m/ka. As long as this uplift continues, the net size of the island will slowly increase and the Koolau Range should persist as an orographic trap to precipitation, maintaining relative aridity in the Waianae Range. Comparing emergence and denudation rates suggests that growth of the island will be non-uniform, with arid regions experiencing the greatest emergence with wet regions in balance with denudation. More importantly, however, this work offers an increased appreciation of the controls on the rates and mechanisms of denudation in basaltic and intermediate composition terranes in the tropics.
The interface between oxic surface water and anoxic groundwater plays an important role in trace element cycling in mountains streams. In this investigation, stream water and shallow groundwater were ...sampled in a semiarid mountain catchment at Red Canyon, Wyoming, USA to evaluate variability in redox conditions and trace element concentrations. Samples were collected in July 2013 during summer baseflow conditions and in May 2014 during snowmelt runoff. Field measurements showed dissolved oxygen-saturated stream water and anoxic groundwater, with relatively higher pH in surface water. Groundwater and surface water chemistry were remarkably similar during both the summer and spring sampling events, indicating overall stability of the oxic/anoxic transition and trace element concentrations. Similar stable water isotope values indicate a close connection between the surface water and groundwater (δ
18
O and δD ranged from − 18.1 to − 18.9‰ and from − 140 to − 147‰, respectively). Concentrations of most trace and major elements were a factor of two higher in groundwater relative to surface water. Notably, Mn, Fe, and Ce concentrations were 7–90-fold higher in groundwater relative to surface water. In contrast, As, Se, and V concentrations were 3–30-fold lower in groundwater relative to surface water, likely due to pH- and redox-driven changes in speciation and sorption. This study is important for characterizing trace element cycling in mountainous areas, where measurements are rare, and has implications for furthering understanding of the key biogeochemical processes that occur during groundwater–surface water interactions.
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