•High surface area, magnetized Douglas fir biochar removed aqueous Pb2+ and Cd2+.•Capacities for lead with raw biochar were ∼40 and for magnetized were ∼16mg/g.•Lead and cadmium are widely ...distributed over the biochar surfaces.•Douglas fir biochars had far faster uptake kinetics (2min) than other biochars.
Magnetic biochar (MBC) was produced by magnetite (Fe3O4) precipitation onto Douglas fir biochar (NBC) that had been generated by wet fast pyrolysis. Treating an aqueous Fe3+/Fe2+ solution with NaOH induced Fe3O4 to nucleate and deposit on NBC. The NBC and the resulting MBC were used to remove Pb2+ and Cd2+ from water. Both biochars were characterized by SEM, EDX, TEM, PZC, XRD, elemental analysis, and surface area measurements. Batch sorption studies were carried out from pH 2–7 with adsorbate concentrations from 10 to 250mg/L at 25, 35 and 45°C. MBC and NBC suspensions in the contaminated solutions were vortexed for two min. Then MBC was magnetically removed, while NBC required filtration. Remediated solutions were then analyzed using AAS. The amounts of lead and cadmium adsorbed onto both NBC and MBC were lower at low pH values and increased with increasing pH. The Langmuir and Freundlich adsorption isotherm models were applied to describe equilibrium data. The maximum Langmuir adsorption capacities at pH 5 and 45°C for Pb2+ and Cd2+ uptake were ∼40 and ∼16mg/g for NBC and ∼27 and ∼11mg/g for MBC, respectively. NBC and MBC recycling was carried out after metal ion extraction with 0.1M HCl and water. Adsorption kinetics of NBC and MBC were compared with four other biochars (mixed feed, magnetized mixed feed, pinewood and magnetized switchgrass). Adsorption equilibria of Pb2+ and Cd2+ onto both NBC and MBC were reached within 2min while the other biochars required from 2 to 20h. NBC and MBC have potential as low cost, green adsorbents for rapid lead and cadmium remediation as replacements for more expensive commercial activated carbon.
In the context of ongoing climatic warming, certain landscapes could be near a tipping point where relatively small changes to their fire regimes or their postfire forest recovery dynamics could ...bring about extensive forest loss, with associated effects on biodiversity and carbon‐cycle feedbacks to climate change. Such concerns are particularly valid in the Klamath Region of northern California and southwestern Oregon, where severe fire initially converts montane conifer forests to systems dominated by broadleaf trees and shrubs. Conifers eventually overtop the competing vegetation, but until they do, these systems could be perpetuated by a cycle of reburning. To assess the vulnerability of conifer forests to increased fire activity and altered forest recovery dynamics in a warmer, drier climate, we characterized vegetation dynamics following severe fire in nine fire years over the last three decades across the climatic aridity gradient of montane conifer forests. Postfire conifer recruitment was limited to a narrow window, with 89% of recruitment in the first 4 years, and height growth tended to decrease as the lag between the fire year and the recruitment year increased. Growth reductions at longer lags were more pronounced at drier sites, where conifers comprised a smaller portion of live woody biomass. An interaction between seed‐source availability and climatic aridity drove substantial variation in the density of regenerating conifers. With increasing climatic water deficit, higher propagule pressure (i.e., smaller patch sizes for high‐severity fire) was needed to support a given conifer seedling density, which implies that projected future increases in aridity could limit postfire regeneration across a growing portion of the landscape. Under a more severe prospective warming scenario, by the end of the century more than half of the area currently capable of supporting montane conifer forest could become subject to minimal conifer regeneration in even moderate‐sized (10s of ha) high‐severity patches.
If climate change drives increases in wildfire activity while delaying postfire forest recovery, forested landscapes such as the Klamath Mountains (NW California/SW Oregon) could be at risk of extensive forest loss. To understand the vulnerability to such changes, we evaluated three decades of vegetation dynamics following high‐severity fire across the regional aridity gradient. Conifers faced a highly competitive environment following severe fire. They comprised only a small portion of live woody biomass, and recruitment was limited primarily to the first four years. Seedlings that established later faced pronounced growth suppression, particularly on drier sites. With increasing climatic aridity, more abundant seed sources were needed to support conifer recruitment at densities sufficient to develop a new forest canopy. Under a more severe warming scenario, by the end of the century just over half of the landscape could be at risk of minimal conifer recruitment following severe fire, even in relatively small high‐severity patches.
Aim: Bark beetle outbreaks have recently affected extensive areas of western North American forests, and factors explaining landscape patterns of tree mortality are poorly understood. The objective ...of this study was to determine the relative importance of stand structure, topography, soil characteristics, landscape context (the characteristics of the landscape surrounding the focal stand) and beetle pressure (the abundance of local beetle population eruptions around the focal stand a few years before the outbreak) to explain landscape patterns of tree mortality during outbreaks of three species: the mountain pine beetle, which attacks lodgepole pine and whitebark pine; the spruce beetle, which feeds on Engelmann spruce; and the Douglas-fir beetle, which attacks Douglas-fir. A second objective was to identify common variables that explain tree mortality among beetle—tree host pairings during outbreaks. Location: Greater Yellowstone ecosystem, Wyoming, USA. Methods: We used field surveys to quantify stand structure, soil characteristics and topography at the plot level in susceptible stands of each forest type showing different severities of infestation (0—98% mortality; n = 129 plots). We then used forest cover and beetle infestation maps derived from remote sensing to develop landscape context and beetle pressure metrics at different spatial scales. Plot-level and landscape-level variables were used to explain outbreak severity. Results: Engelmann spruce and Douglas-fir mortality were best predicted using landscape-level variables alone. Lodgepole pine mortality was best predicted by both landscape-level and plot-level variables. Whitebark pine mortality was best — although poorly — predicted by plot-level variables. Models including landscape context and beetle pressure were much better at predicting outbreak severity than models that only included plot-level measures, except for whitebark pine. Main conclusions: Landscape-level variables, particularly beetle pressure, were the most consistent predictors of subsequent outbreak severity within susceptible stands of all four host species. These results may help forest managers identify vulnerable locations during ongoing outbreaks.
A central challenge in global change research is the projection of the future behavior of a system based upon past observations. Tree‐ring data have been used increasingly over the last decade to ...project tree growth and forest ecosystem vulnerability under future climate conditions. But how can the response of tree growth to past climate variation predict the future, when the future does not look like the past? Space‐for‐time substitution (SFTS) is one way to overcome the problem of extrapolation: the response at a given location in a warmer future is assumed to follow the response at a warmer location today. Here we evaluated an SFTS approach to projecting future growth of Douglas‐fir (Pseudotsuga menziesii), a species that occupies an exceptionally large environmental space in North America. We fit a hierarchical mixed‐effects model to capture ring‐width variability in response to spatial and temporal variation in climate. We found opposing gradients for productivity and climate sensitivity with highest growth rates and weakest response to interannual climate variation in the mesic coastal part of Douglas‐fir's range; narrower rings and stronger climate sensitivity occurred across the semi‐arid interior. Ring‐width response to spatial versus temporal temperature variation was opposite in sign, suggesting that spatial variation in productivity, caused by local adaptation and other slow processes, cannot be used to anticipate changes in productivity caused by rapid climate change. We thus substituted only climate sensitivities when projecting future tree growth. Growth declines were projected across much of Douglas‐fir's distribution, with largest relative decreases in the semiarid U.S. Interior West and smallest in the mesic Pacific Northwest. We further highlight the strengths of mixed‐effects modeling for reviving a conceptual cornerstone of dendroecology, Cook's 1987 aggregate growth model, and the great potential to use tree‐ring networks and results as a calibration target for next‐generation vegetation models.
We evaluated a space‐for‐time substitution approach to projecting future growth of Douglas‐fir. Fitting a hierarchical mixed‐effects model, we found opposing gradients of productivity and climate sensitivity, with highest growth rates and weakest responses to interannual climate variability in the mesic coastal part of Douglas‐fir's range; narrower rings and stronger climate sensitivity occurred across the semi‐arid interior. Ring‐width response to spatial versus temporal temperature variation was opposite in sign, suggesting that spatial variation in productivity, caused by local adaptation and other slow processes, cannot be used to anticipate changes in productivity caused by rapid climate change.
Climate warming is contributing to increases in wildfire activity throughout the western United States, leading to potentially long-lasting shifts in vegetation. The response of forest ecosystems to ...wildfire is thus a crucial indicator of future vegetation trajectories, and these responses are contingent upon factors such as seed availability, interannual climate variability, average climate, and other components of the physical environment. To better understand variation in resilience to wildfire across vulnerable dry forests, we surveyed conifer seedling densities in 15 recent (1988–2010) wildfires and characterized temporal variation in seed cone production and seedling establishment. We then predicted postfire seedling densities at a 30-m resolution within each fire perimeter using downscaled climate data, monthly water balance models, and maps of surviving forest cover. Widespread ponderosa pine (Pinus ponderosa) seed cone production occurred at least twice following each fire surveyed, and pulses of conifer seedling establishment coincided with years of above-average moisture availability. Ponderosa pine and Douglas-fir (Pseudotsuga menziesii) seedling densities were higher on more mesic sites and adjacent to surviving trees, though there were also important interspecific differences, likely attributable to drought and shade tolerance. We estimated that postfire seedling densities in 42% (for ponderosa pine) and 69% (for Douglas-fir) of the total burned area were below the lowest reported historical tree densities in these forests. Spatial models demonstrated that an absence of mature conifers (particularly in the interior of large, high-severity patches) limited seedling densities in many areas, but 30-yr average actual evapotranspiration and climatic water deficit limited densities on marginal sites. A better understanding of the limitations to postfire forest recovery will refine models of vegetation dynamics and will help to improve strategies of adaptation to a warming climate and shifting fire activity.
Biochar adsorbents can remove environmental pollutants and the remediation of Cr(VI) and nitrate are considered. Cr(VI) is a proven carcinogen causing serious health issues in humans and nitrate ...induced eutrophication causes negative effect on aquatic systems around the world. Douglas fir biochar (DFBC), synthesized by fast pyrolysis during syn gas production, was treated with aniline. Then, a polyaniline biochar (PANIBC) composite containing 47 wt% PANI was prepared by precipitating PANI on DFBC surfaces by oxidative chemical polymerization of aniline in 2M HCl. PANIBC exhibited a point of zero charge (PZC) of 3.0 and 8.2 m2/g BET (N2) surface area. This modified biochar was characterized by thermogravimetric analysis (TGA), scanning electron microscopy (SEM) morphology and surface elements, and oxidation states by X-ray photoelectron spectroscopy (XPS). PANIBC exhibited positive surface charge below pH 3, making it an outstanding adsorbent, for Cr(VI) removal. Cr(VI) and nitrate removal mechanisms are presented based on XPS analysis. DFBC and PANIBC Cr(VI) and nitrate adsorption data were fitted to Langmuir and Freundlich isotherm models with maximum Langmuir adsorption capacities of 150 mg/g and 72 mg/g, respectively. Cr(VI) and nitrate removal at pH 2 and 6 were evaluated by reducing the amount of PANI (9 wt%) dispersed on to DFBC. Adsorption capacities verses temperature studies revealed that both Cr(VI) and nitrate adsorption are endothermic and thermodynamically favored. Regeneration studies were conducted on both DFBC and PANIBC using 0.1M NaOH and PANIBC exhibited excellent sorption capacities for Cr(VI) and nitrate in lake water samples and in the presence of competitive ions.
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•Composite prepared by precipitation of PANI by oxidative polymerization of aniline.•Adsorption capacities for Cr(VI) and nitrate were 150 and 72 mg/g respectively.•Three adsorption-regeneration cycles were successfully conducted.•Excellent sorption capacities in lake water and with competitive ions.
Biochar has become a popular research topic in sustainable chemistry for use both in agriculture and pollution abatement. To enhance aqueous Cr(VI), Pb(II) and Cd(II) removal efficiency, high surface ...area (535 m2/g) byproduct Douglas fir biochar (DFBC) from commercial syn-gas production obtained by fast pyrolysis (900–1000 °C, 1–10 s), was subjected to a KOH activation. KOH-activated biochar (KOHBC) underwent a remarkable surface area increase to 1049 m2/g and a three-fold increase in pore volume (BET analysis). Batch sorption studies on KOHBC verses pH revealed that the highest chromium, lead and cadmium removal capacities occurred at pH 2.0, 5.0 and 6.0, respectively. KOHBC exhibited much higher adsorption capacities than unactivated DFBC. Heavy metal loadings onto KOHBC were characterized by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. Sorption of Cr(VI), Pb(II) and Cd(II) all followed pseudo-second order kinetics and the Langmuir adsorption model. The highest Langmuir adsorption capacities at the respective pH’s of maximum adsorption were 140.0 mg g−1 Pb(II), 127.2 mg g-1 Cr(VI) and 29.0 mg g−1 Cd(II). Metal ions spiked into natural and laboratory waste water systems exhibited high sorption capacities. Desorption studies carried out using 0.1 M HCl revealed that Pb(II) adsorption onto the KOHBC surface is reversible. Portions of Cd(II) and Cr(VI) adsorbed strongly onto KOHBC were unable to be desorbed by 0.1 M HCl and 0.1 M NaOH.
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•KOH activation remarkably increased the biochar surface area from 535 to 1050 m2/g.•KOH activation of DFBC improved Cr(VI), Pb(II) and Cd(II) removal from natural and wastewater systems.•Adsorption followed pseudo-second order kinetics reaching equilibrium within 2 h.•High adsorption capacity was contributed to chelation, electrostatic-attraction, and ion exchange mechanisms.•KOHBC was recycled thrice while maintaining 75, 50 and 54% of its adsorption capacity for Cr(VI), Pb(II) and Cd(II).
Background: In forests subject to stand-replacing disturbances, conventional models of succession typically overlook early-seral stages as a simple re-organization/establishment period. These models ...treat structural development in essentially 'relay floristic' terms, with structural complexity (three-dimensional heterogeneity) developing primarily in old-growth stages, only after a closedcanopy 'self-thinning' phase and subsequent canopy gap formation. However, is it possible that early-successional forests can sometimes exhibit spatial complexity similar to that in old-growth forests — i.e. akin to an 'initial floristic' model of structural development? Hypothesis: Based on empirical observations, we present a hypothesis regarding an important alternative pathway in which protracted or sparse forest establishment and interspecific competition thin out tree densities early on — thereby precluding overstorey canopy closure or a traditionally defined self-thinning phase. Although historically viewed as an impediment to stand development, we suggest this process may actually advance certain forms of structural complexity. These young stands can exhibit qualities typically attributed only to old forests, including: (1) canopy gaps associated with clumped and widely spaced tree stems; (2) vertically heterogeneous canopies including under- and midstories, albeit lower stature; (3) co-existence of shade-tolerant and intolerant species; and (4) abundant dead wood. Moreover, some of these qualities may persist through succession, meaning that a significant portion of eventual old-growth spatial pattern may already be determined in this early stage. Implications: The relative frequency of this open-canopy pathway, and the degree to which precocious complexity supports functional complexity analogous to that of old forests, are largely unknown due to the paucity of naturally regenerating forests in many regions. Nevertheless, recognition of this potential is important for the understanding and management of early-successional forests.
Climate change is increasing fire activity in the western United States, which has the potential to accelerate climate-induced shifts in vegetation communities. Wildfire can catalyze vegetation ...change by killing adult trees that could otherwise persist in climate conditions no longer suitable for seedling establishment and survival. Recently documented declines in postfire conifer recruitment in thewestern United States may be an example of this phenomenon. However, the role of annual climate variation and its interaction with long-term climate trends in driving these changes is poorly resolved. Here we examine the relationship between annual climate and postfire tree regeneration of two dominant, low-elevation conifers (ponderosa pine and Douglas-fir) using annually resolved establishment dates from 2,935 destructively sampled trees from 33 wildfires across four regions in the western United States. We show that regeneration had a nonlinear response to annual climate conditions, with distinct thresholds for recruitment based on vapor pressure deficit, soil moisture, and maximum surface temperature. At dry sites across our study region, seasonal to annual climate conditions over the past 20 years have crossed these thresholds, such that conditions have become increasingly unsuitable for regeneration. High fire severity and low seed availability further reduced the probability of postfire regeneration. Together, our results demonstrate that climate change combined with high severity fire is leading to increasingly fewer opportunities for seedlings to establish after wildfires and may lead to ecosystem transitions in low-elevation ponderosa pine and Douglas-fir forests across the western United States.
Summary
Tree seedlings from populations native to drier regions are often assumed to be more drought tolerant than those from wetter provenances. However, intraspecific variation in drought tolerance ...has not been well‐characterized despite being critical for developing climate change mitigation and adaptation strategies, and for predicting the effects of drought on forests.
We used a large‐scale common garden drought‐to‐death experiment to assess range‐wide variation in drought tolerance, measured by decline of photosynthetic efficiency, growth, and plastic responses to extreme summer drought in seedlings of 73 natural populations of the two main varieties of Douglas‐fir (Pseudotsuga menziesii var. menziesii and var. glauca).
Local adaptation to drought was weak in var. glauca and nearly absent in menziesii. Var. glauca showed higher tolerance to drought but slower growth than var. menziesii. Clinal variation in drought tolerance and growth species‐wide was mainly associated with temperature rather than precipitation. A higher degree of plasticity for growth was observed in var. menziesii in response to extreme drought.
Genetic variation for drought tolerance in seedlings within varieties is maintained primarily within populations. Selective breeding within populations may facilitate adaptation to drought more than assisted gene flow.
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