ORCID Profile
0000-0003-2358-9367
Current Organisations
Northern Arizona University
,
University of Oxford
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Publisher: Cold Spring Harbor Laboratory
Date: 11-12-2022
DOI: 10.1101/2022.12.07.518693
Abstract: Above Ground Biomass (AGB) is an important metric used to quantify the mass of carbon stored in terrestrial ecosystems. For forests, this is routinely estimated at the plot scale (typically ≥1 ha) using inventory measurements and allometry. In recent years, Terrestrial Laser Scanning (TLS) has appeared as a disruptive technology that can generate a more accurate assessment of tree and plot scale AGB however, operationalising TLS methods has had to overcome a number of challenges. One such challenge is the segmentation of in idual trees from plot level point clouds that are required to estimate woody volume, this is often done manually (e.g. with interactive point cloud editing software) and can be very time consuming. Here we present TLS2trees , an automated processing pipeline and set of Python command line tools that aims to redress this processing bottleneck. TLS2trees consists of existing and new methods and is specifically designed to be horizontally scalable. The processing pipeline is demonstrated across 10 plots of 7 forest types from open savanna to dense tropical rainforest, where a total of 10,557 trees are segmented. TLS2trees segmented trees are compared to 1,281 manually segmented trees. Results indicate that TLS2trees performs well, particularly for larger trees (i.e. the cohort of largest trees that comprise 50% of total plot volume), where plot-wise tree volume bias is ±0.4 m 3 and %RMSE is ~ 60%. To facilitate improvements to the presented methods as well as modification for other laser scanning modes (e.g. mobile and UAV laser scanning), TLS2trees is a free and open-source software (FOSS).
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/C9TA07508A
Abstract: Sodium ion batteries are a potential alternative to lithium ion batteries due to the low cost and natural abundance of sodium.
Publisher: Elsevier BV
Date: 11-2019
Publisher: Elsevier BV
Date: 08-2017
Publisher: Wiley
Date: 28-07-2014
DOI: 10.1111/AVSC.12125
Publisher: Wiley
Date: 26-05-2021
Abstract: A significant obstacle in the large‐scale applications of sodium borohydride (NaBH 4 ) for hydrogen storage is its high cost. Herein, we report a new method to synthesize NaBH 4 by ball milling hydrated sodium tetraborate (Na 2 B 4 O 7 ⋅ 10H 2 O) with low‐cost Al or Al 88 Si 12 , instead of Na, Mg or Ca. An effective strategy is developed to facilitate mass transfer during the reaction by introducing NaH to enable the formation of NaAlO 2 instead of dense Al 2 O 3 on Al surface, and by using Si as a milling additive to prevent agglomeration and also break up passivation layers. Another advantage of this process is that hydrogen in Na 2 B 4 O 7 ⋅ 10H 2 O serves as a hydrogen source for NaBH 4 generation. Considering the low cost of the starting materials and simplicity in operation, our studies demonstrate the potential of producing NaBH 4 in a more economical way than the commercial process.
Publisher: Wiley
Date: 24-09-2204
Abstract: Sodium borohydride (NaBH 4 ) is among the most studied hydrogen storage materials because it is able to deliver high‐purity H 2 at room temperature with controllable kinetics via hydrolysis however, its regeneration from the hydrolytic product has been challenging. Now, a facile method is reported to regenerate NaBH 4 with high yield and low costs. The hydrolytic product NaBO 2 in aqueous solution reacts with CO 2 , forming Na 2 B 4 O 7 ⋅10 H 2 O and Na 2 CO 3 , both of which are ball‐milled with Mg under ambient conditions to form NaBH 4 in high yield (close to 80 %). Compared with previous studies, this approach avoids expensive reducing agents such as MgH 2 , bypasses the energy‐intensive dehydration procedure to remove water from Na 2 B 4 O 7 ⋅10 H 2 O, and does not require high‐pressure H 2 gas, therefore leading to much reduced costs. This method is expected to effectively close the loop of NaBH 4 regeneration and hydrolysis, enabling a wide deployment of NaBH 4 for hydrogen storage.
Publisher: Wiley
Date: 28-06-2022
DOI: 10.1111/GCB.16302
Abstract: Data capturing multiple axes of tree size and shape, such as a tree's stem diameter, height and crown size, underpin a wide range of ecological research—from developing and testing theory on forest structure and dynamics, to estimating forest carbon stocks and their uncertainties, and integrating remote sensing imagery into forest monitoring programmes. However, these data can be surprisingly hard to come by, particularly for certain regions of the world and for specific taxonomic groups, posing a real barrier to progress in these fields. To overcome this challenge, we developed the Tallo database, a collection of 498,838 georeferenced and taxonomically standardized records of in idual trees for which stem diameter, height and/or crown radius have been measured. These data were collected at 61,856 globally distributed sites, spanning all major forested and non‐forested biomes. The majority of trees in the database are identified to species (88%), and collectively Tallo includes data for 5163 species distributed across 1453 genera and 187 plant families. The database is publicly archived under a CC‐BY 4.0 licence and can be access from: 0.5281/zenodo.6637599 . To demonstrate its value, here we present three case studies that highlight how the Tallo database can be used to address a range of theoretical and applied questions in ecology—from testing the predictions of metabolic scaling theory, to exploring the limits of tree allometric plasticity along environmental gradients and modelling global variation in maximum attainable tree height. In doing so, we provide a key resource for field ecologists, remote sensing researchers and the modelling community working together to better understand the role that trees play in regulating the terrestrial carbon cycle.
Publisher: Springer Science and Business Media LLC
Date: 16-05-2022
DOI: 10.1038/S41559-022-01747-6
Abstract: Tropical forests are some of the most bio erse ecosystems in the world, yet their functioning is threatened by anthropogenic disturbances and climate change. Global actions to conserve tropical forests could be enhanced by having local knowledge on the forests' functional ersity and functional redundancy as proxies for their capacity to respond to global environmental change. Here we create estimates of plant functional ersity and redundancy across the tropics by combining a dataset of 16 morphological, chemical and photosynthetic plant traits s led from 2,461 in idual trees from 74 sites distributed across four continents together with local climate data for the past half century. Our findings suggest a strong link between climate and functional ersity and redundancy with the three trait groups responding similarly across the tropics and climate gradient. We show that drier tropical forests are overall less functionally erse than wetter forests and that functional redundancy declines with increasing soil water and vapour pressure deficits. Areas with high functional ersity and high functional redundancy tend to better maintain ecosystem functioning, such as aboveground biomass, after extreme weather events. Our predictions suggest that the lower functional ersity and lower functional redundancy of drier tropical forests, in comparison with wetter forests, may leave them more at risk of shifting towards alternative states in face of further declines in water availability across tropical regions.
Publisher: Wiley
Date: 21-10-2023
Publisher: Elsevier BV
Date: 05-2017
Publisher: Elsevier BV
Date: 2021
Publisher: Elsevier BV
Date: 04-2023
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7TA02457F
Abstract: MoS 2 could significantly enhance the hydrolysis of Mg and the recycled MoS 2 catalyst exhibited high recycling stability.
Publisher: Wiley
Date: 02-05-2017
DOI: 10.1111/ELE.12771
Abstract: One of the major challenges in ecology is to understand how ecosystems respond to changes in environmental conditions, and how taxonomic and functional ersity mediate these changes. In this study, we use a trait-spectra and in idual-based model, to analyse variation in forest primary productivity along a 3.3 km elevation gradient in the Amazon-Andes. The model accurately predicted the magnitude and trends in forest productivity with elevation, with solar radiation and plant functional traits (leaf dry mass per area, leaf nitrogen and phosphorus concentration, and wood density) collectively accounting for productivity variation. Remarkably, explicit representation of temperature variation with elevation was not required to achieve accurate predictions of forest productivity, as trait variation driven by species turnover appears to capture the effect of temperature. Our semi-mechanistic model suggests that spatial variation in traits can potentially be used to estimate spatial variation in productivity at the landscape scale.
Publisher: Elsevier BV
Date: 05-2020
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2CC04504D
Abstract: Phenylphosphonic acid (PPOA) has been proposed as a new additive for carbonate electrolytes, in which the complexation reaction between PPOA and Li
Publisher: Wiley
Date: 22-12-2020
DOI: 10.1111/BTP.12901
Abstract: Do tropical trees close to death have a distinct change to their leaf spectral signature? Tree mortality rates have been increasing in tropical forests, reducing the global carbon sink. Upcoming hyperspectral satellites could be used to predict regions close to experiencing extensive tree mortality during periods of stress, such as drought. Here we show, for a tropical rainforest in Borneo, how imminent tropical tree mortality impacts leaf physiological traits and reflectance. We measured leaf reflectance (400–2500 nm), light‐saturated photosynthesis (A sat ), leaf dark respiration (R dark ), leaf mass area (LMA), and % leaf water across five c aigns in a six‐month period during which there were two causes of tree mortality: a major natural drought and a co‐incident tree stem girdling treatment. We find that prior to mortality, there were significant ( p 0.05) leaf spectral changes in the red (650–700 nm), the NIR (1,000–1,400 nm), and SWIR bands (2,000–2,400 nm) and significant reductions in the potential carbon balance of the leaves (increased R dark and reduced A sat ). We show that the partial least squares regression technique can predict mortality in tropical trees across different species and functional groups with medium precision but low accuracy ( r 2 of .65 and RMSE/mean of 0.58). However, most tree death in our study was due to girdling, which is not a natural form of death. More research is needed to determine if this spectroscopy technique can be applied to tropical forests in general.
Location: United States of America
Location: United States of America
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Alexander Shenkin.