Carbon isotope discrimination and water stress in trembling aspen following variable retention harvesting

Variable retention harvesting (VRH) has been proposed as a silvicultural practice to maintain biodiversity and ecosystem integrity. No previous study has examined tree carbon isotope discrimination to provide insights into water stress that could lead to dieback and mortality of trees following VRH. We measured and compared the carbon isotope ratios (δ13C) in stem wood of trembling aspen (Populus tremuloides Michx.) before and after VRH. Eight trees were sampled from isolated residual, edge and control (interior of unharvested stand) positions from each of seven plots in three regions (Calling Lake and Drayton Valley, Alberta and Lac Duparquet, Qu

A Global Index for Mapping the Exposure of Water Resources to Wildfire

Wildfires are keystone components of natural disturbance regimes that maintain ecosystem structure and functions, such as the hydrological cycle, in many parts of the world. Consequently, critical surface freshwater resources can be exposed to post-fire effects disrupting their quantity, quality and regularity. Although well studied at the local scale, the potential extent of these effects has not been examined at the global scale. We take the first step toward a global assessment of the wildfire water risk (WWR) by presenting a spatially explicit index of exposure. Several variables related to fire activity and water availability were identified and normalized for use as exposure indicators. Additive aggregation of those indicators was then carried out according to their individual weight. The resulting index shows the greatest exposure risk in the tropical wet and dry forests. Intermediate exposure is indicated in mountain ranges and dry shrublands, whereas the lowest index scores are mostly associated with high latitudes. We believe that such an approach can provide important insights for water security by guiding global freshwater resource preservation.Keywords: wildfire hazard, global index, water security, water resources exposure, wildfire water ris

Sediment source fingerprinting: benchmarking recent outputs, remaining challenges and emerging themes

Abstract: Purpose: This review of sediment source fingerprinting assesses the current state-of-the-art, remaining challenges and emerging themes. It combines inputs from international scientists either with track records in the approach or with expertise relevant to progressing the science. Methods: Web of Science and Google Scholar were used to review published papers spanning the period 2013–2019, inclusive, to confirm publication trends in quantities of papers by study area country and the types of tracers used. The most recent (2018–2019, inclusive) papers were also benchmarked using a methodological decision-tree published in 2017. Scope: Areas requiring further research and international consensus on methodological detail are reviewed, and these comprise spatial variability in tracers and corresponding sampling implications for end-members, temporal variability in tracers and sampling implications for end-members and target sediment, tracer conservation and knowledge-based pre-selection, the physico-chemical basis for source discrimination and dissemination of fingerprinting results to stakeholders. Emerging themes are also discussed: novel tracers, concentration-dependence for biomarkers, combining sediment fingerprinting and age-dating, applications to sediment-bound pollutants, incorporation of supportive spatial information to augment discrimination and modelling, aeolian sediment source fingerprinting, integration with process-based models and development of open-access software tools for data processing. Conclusions: The popularity of sediment source fingerprinting continues on an upward trend globally, but with this growth comes issues surrounding lack of standardisation and procedural diversity. Nonetheless, the last 2 years have also evidenced growing uptake of critical requirements for robust applications and this review is intended to signpost investigators, both old and new, towards these benchmarks and remaining research challenges for, and emerging options for different applications of, the fingerprinting approach

Stand Structure Governs the Crown Collisions of Lodgepole Pine

We investigated tree sway and crown collision behavior of even-aged lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) stands of different structure in Alberta, Canada, to examine how these factors might affect loss of leaf area as stands mature. The Two Creeks stand (TC) had high density and slender trees, while the Chickadee stand (CH) had stout trees. The TC stand was then thinned (TCT) to reduce the stand density. For each stand, simultaneous tree sways of a group of 10 trees were monitored with biaxial clinometers during wind speed of 5 m/s (canopy top). Crown collisions were reconstructed by combining sway displacement of individual trees with their respective crown dimensions. Comparing the sway statistics between stands with contrasting mean bole slenderness (TC and CH) indicated that more slender trees have greater sway displacements, faster sway speeds, and a greater depth of collision. Disturbance by thinning increased sway displacements, sway speeds, and depth of collisions at TCT. Tree sway patterns were circular in shape and not aligned with wind direction, but patterns were elongated after thinning. This demonstrates the high frequency of crown collision experienced by stands with slender trees and supports the notion that crown collisions result in empty space between crowns of trees

Utilizing pioneer species as a hydrological nurse crop to lower water table for reforestation of poorly drained boreal sites

- On cold and wet sites in the boreal forest, high water table and anaerobic soil conditions limit the establishment of planted white spruce. In a controlled-environment experiment we determined physiological and morphological responses of a grass Calamagrostis canadensis and two shrubs Salix planifolia and Alnus crispa to water table and soil temperature and evaluated their capacity to lower the water table on wet sites. All three species tended to grow better at the warmer soil temperatures and imperfectly drained treatments but C. canadensis actually developed the greatest leaf area in the near saturated conditions. Similarly, C. canadensis and A. crispa had greatest transpiration rates in the imperfectly drained and warm soil treatments. In contrast, S. planifolia had the greatest transpiration at 5 °C soils. We suggest that C. canadensis is suitable as a hydrological nurse species on these wet sites, but in light of its competitive nature, the shrubs particularly S. planifolia would be preferable.- Utilisation d’espèces pionnières susceptibles de jouer un rôle hydrologique en abaissant le niveau du plan d’eau pour faciliter le boisement de stations boréales mal drainées. Dans les stations froides et humides de la forêt boréale, le haut niveau du plan d’eau et les conditions d’anaérobie du sol sont défavorables au reboisement en épicéa blanc. Une expérimentation en milieu contrôlé a permis de déterminer les réponses physiologiques et morphologiques d’une espèce herbacée Calamagrostis canadensis et de deux arbustes, Salix planifolia et Alnus crispa, au niveau du plan d’eau et à la température du sol, et d’évaluer leur capacité à abaisser le niveau du plan d’eau sur stations humides. Les trois espèces tendent à mieux se développer avec les traitements où la température du sol est plus élevée avec drainage médiocre ; mais C. canadensis présente un développement de surface foliaire nettement plus grand dans des conditions de sol proches de la saturation. De même, pour C. canadensis et A. crispa on enregistre les taux de transpiration les plus élevés pour les traitements sol chaud et drainage médiocre. Par contre, S. planifolia manifeste un maximum de transpiration avec une température du sol de 5 °C. Nous suggérons que C. canadensis peut jouer le rôle d’espèce nurse hydrologique sur ces stations humides ; mais compte tenu des problèmes de concurrence, on devrait préférer les arbustes, et en particulier S. planifolia

Treatment of Severely-Deteriorated Post-Fire Runoff: A Comparison of Conventional and High-Rate Clarification to Demonstrate Key Drinking Water Treatment Capabilities and Challenges

The ability to treat worst-case scenario, “black water” resulting from wildfire ash transport directly from hillslopes to source waters was investigated—this has not been reported previously. The treatment response capabilities of conventional chemical pre-treatment and high rate clarification processes were evaluated at bench scale; these included: sand-ballasted flocculation (SBF), SBF with enhanced coagulation, and SBF with powdered activated carbon (PAC).Fresh ash was collected from the Thuya Lake Road (TLR) wildfire (+51.4098 latitude, -120.2435 longitude; burn area 556 ha), which was part of the Little Fort Fire Complex that burned in July 2017, near Little Fort, British Columbia, Canada. The ash was used to prepare a severely-deteriorated source water matrix. It was added to high quality river water (Elbow River, Calgary, Alberta) to reflect post-fire water quality conditions when ash is mobilized off the landscape to receiving waters during a major runoff event.Prior to mixing, ash was sieved through a 1 mm screen to remove any large debris and conifer needles that typically would not be found in water treatment plant influent streams. Three concentrations of ash in river water were prepared (2.0, 10.0, and 20.0 g×L-1 of ash; five replicates of each) by adding ash to 1000 mL of Elbow River water in 2-L plastic square beakers, and mixed using a jar test apparatus (Phipps & Bird, PB-900 Series Programmable 6-Paddle Jar Tester, Richmond, VA) at 120 RPM for 2 minutes. Turbidity and dissolved organic carbon (DOC) concentrations consistent with or slightly higher than the levels that have been reported following severe wildfire (i.e., >1000 NTU and >15mg×L-1, respectively) were targeted. These water matrices were black-colored, in a manner consistent with previous reports of severely-deteriorated water conditions after wildfire. Standard methods were used to evaluate turbidity (Method 2130B; Hach 2100 N turbidimeter, Loveland, CO), pH (4500-H+B Electrometric method; Orion 720A pH meter, Thermo Fisher Scientific, Waltham, MA), DOC concentration (filtration through pre-rinsed 0.45 µm Nylaflo membranes, Pall, Port Washington, NY; Method 5310C; Shimadzu TOC-V WP analyzer, Kyoto, Japan), and UVA254 (Method 5910B; 1 cm quartz cell; Hach DR 5000 Spectrophotometer, Loveland, CO). Specific ultraviolet absorbance at 254 nm (SUVA) was calculated by dividing UVA254 absorbance by the DOC concentration.</div

Sapwood hydraulic recovery following thinning in lodgepole pine

Sapflow in lodgepole pine (Pinus contorta) was measured over the summer of 2002 to assess the impact of reduced sapwood permeability ($k)$ after thinning on tree water use. Lodgepole pine in recently thinned (RT), thinned five years prior (5T), and un-thinned (C) stands were instrumented with thermal dissipation sap flow sensors. Daily water use varied considerably (10.8–0.04 L Day$^{-1})$, but trees in the thinned areas used more water. Despite lower $k$ and leaf specific hydraulic capacity ($Q_{\rm L})$ in both RT and 5T trees, leaf related sapflow rates ($Q_{\rm l})$ were generally higher than for C trees. RT trees appeared to experience water stress immediately following thinning in June, but by mid August maintained higher $Q_{\rm l}$ and canopy stomatal conductance than both 5T and C trees. Allocation to radial growth following thinning appears to maintain sufficient sapwood area, and may offset damage to conducting tissues enabling lodgepole pine trees to tolerate periodic water stress.Rétablissement hydraulique de l'aubier suivant une éclaircie chez Pinus contorta. Le flux de sève a été mesuré chez Pinus contorta pendant l'été 2002 afin d'estimer l'impact de la réduction de perméabilité des tissus de l'aubier ($k)$ sur l'utilisation de l'eau par l'arbre après éclaircie. Des détecteurs de dissipation thermique destinés à mesurer le flux de sève ont été installés sur plusieurs arbres dans différentes parcelles : récemment éclaircie (RT), éclaircie depuis 5 ans (T) et parcelle témoin non éclaircie (C). La consommation quotidienne d'eau varie considérablement (10,8 à 0,04 L par jour), mais les arbres des peuplements éclaircis consomment davantage d'eau que les arbres témoins. Malgré une baisse de $k$ et de la capacité hydraulique foliaire spécifique ($QL)$, le taux foliaire du flux de sève ($Ql)$ était généralement plus élevé pour RT et T que pour C. Les arbres du traitement RT ont semblé subir un stress hydrique immédiatement après l'éclaircie en juin, mais à la mi-août ils ont gardé un $Ql$ et une conductance stomatique plus élevés que les arbres des traitements 5T et C. La croissance radiale après éclaircie semble maintenir une surface d'aubier suffisante et compenser les dommages causés à l'aubier et permettre aux arbres de tolérer des stress hydriques périodiques