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Plant diversity varies immensely over large-scale gradients in temperature, precipitation, and seasonality at global and regional scales. This relationship may be driven in part by climatic variation in the relative importance of abiotic and biotic interactions to the diversity and composition of plant communities. In particular, biotic interactions may become stronger and more host specific with increasing precipitation and temperature, resulting in greater plant species richness in wetter and warmer environments. This hypothesis predicts that the many defensive compounds found in plants’ metabolomes should increase in richness and decrease in interspecific similarity with precipitation, temperature, and plant diversity. To test this prediction, we compared patterns of chemical and morphological trait diversity of 140 woody plant species among seven temperate forests in North America representing 16.2°C variation in mean annual temperature (MAT), 2,115 mm variation in mean annual precipitation (MAP), and from 10 to 68 co-occurring species. We used untargeted metabolomics methods based on data generated with liquid chromatography-tandem mass spectrometry to identify, classify, and compare 13,480 unique foliar metabolites and to quantify the metabolomic similarity of species in each community with respect to the whole metabolome and each of five broad classes of metabolites. In addition, we compiled morphological trait data from existing databases and field surveys for three commonly measured traits (specific leaf area [SLA], wood density, and seed mass) for comparison with foliar metabolomes. We found that chemical defense strategies and growth and allocation strategies reflected by these traits largely represented orthogonal axes of variation. In addition, functional dispersion of SLA increased with MAP, whereas functional richness of wood density and seed mass increased with MAT. In contrast, chemical similarity of co-occurring species decreased with both MAT and MAP, and metabolite richness increased with MAT. Variation in metabolite richness among communities was positively correlated with species richness, but variation in mean chemical similarity was not. Our results are consistent with the hypothesis that plant metabolomes play a more important role in community assembly in wetter and warmer climates, even at temperate latitudes, and suggest that metabolomic traits can provide unique insight to studies of trait-based community assembly.

Arbuscular mycorrhizal (AM) and ectomycorrhizal (EcM) associations are critical for host-tree performance. However, how mycorrhizal associations correlate with the latitudinal tree beta-diversity remains untested. Using a global dataset of 45 forest plots representing 2,804,270 trees across 3840 species, we test how AM and EcM trees contribute to total beta-diversity and its components (turnover and nestedness) of all trees. We find AM rather than EcM trees predominantly contribute to decreasing total beta-diversity and turnover and increasing nestedness with increasing latitude, probably because wide distributions of EcM trees do not generate strong compositional differences among localities. Environmental variables, especially temperature and precipitation, are strongly correlated with beta-diversity patterns for both AM trees and all trees rather than EcM trees. Results support our hypotheses that latitudinal beta-diversity patterns and environmental effects on these patterns are highly dependent on mycorrhizal types. Our findings highlight the importance of AM-dominated forests for conserving global forest biodiversity.

As the northern high latitude permafrost zone experiences accelerated warming, permafrost has become vulnerable to widespread thaw. Simultaneously, wildfire activity across northern boreal forest and Arctic/subarctic tundra regions impact permafrost stability through the combustion of insulating organic matter, vegetation and post-fire changes in albedo. Efforts to synthesise the impacts of wildfire on permafrost are limited and are typically reliant on antecedent pre-fire conditions. To address this, we created the FireALT dataset by soliciting data contributions that included thaw depth measurements, site conditions, and fire event details with paired measurements at environmentally comparable burned and unburned sites. The solicitation resulted in 52,466 thaw depth measurements from 18 contributors across North America and Russia. Because thaw depths were taken at various times throughout the thawing season, we also estimated end of season active layer thickness (ALT) for each measurement using a modified version of the Stefan equation. Here, we describe our methods for collecting and quality checking the data, estimating ALT, the data structure, strengths and limitations, and future research opportunities. The final dataset includes 47,952 ALT estimates (27,747 burned, 20,205 unburned) with 32 attributes. There are 193 unique paired burned/unburned sites spread across 12 ecozones that span Canada, Russia, and the United States. The data span fire events from 1900 to 2022. Time since fire ranges from zero to 114 years. The FireALT dataset addresses a key challenge: the ability to assess impacts of wildfire on ALT when measurements are taken at various times throughout the thaw season depending on the time of field campaigns (typically June through August) by estimating ALT at the end of season maximum. This dataset can be used to address understudied research areas particularly algorithm development, calibration, and validation for evolving process-based models as well as extrapolating across space and time, which could elucidate permafrost-wildfire interactions under accelerated warming across the high northern latitude permafrost zone. The FireALT dataset is available through the Arctic Data Center. [ABSTRACT FROM AUTHOR]

Northwestern Canada's boreal forest has experienced rapid warming, drying, and changes to permafrost, yet the growth responses and mechanisms driving productivity have been under-studied at broad scales. Forest responses are largely driven by black spruce (Picea mariana (Mill.) B.S.P.)--the region's most widespread and dominant tree. We collected tree ring samples from four black spruce-dominated sites across 15[degrees] of latitude, spanning gradients in climate and permafrost. We investigated (i) differences in growth patterns, (ii) variations in climatic drivers of growth, and (iii) trends in water use efficiency (WUE) through [sub.13]C isotope analysis from 1945 to 2006. We found positive growth trends at all sites except those at mid-latitude, where rapid permafrost thaw drove declines. Annual growth was lowest at the tree limit site and highest at the tree line. Climatic drivers of these growth patterns varied; positive growth responses at the northerly sites were associated with warmer winters, whereas [[DELTA].sup.13]C trends and climate-growth responses at mid-latitude sites indicated that growth was limited by moisture availability. [[DELTA].sup.13]C signatures indicated increased WUE at the southernmost site, with no significant trends at northern sites. These results suggest that warming will increase the growth of trees at the northern extent of black spruce, but southerly areas may face drought stress if precipitation does not balance evapotranspiration. Key words: Picea mariana, black spruce, dendrochronology, stable carbon isotope, climate warming. La foret boreale du nord-ouest du Canada a connu un rechauffement, un assechement et des changements rapides dans le pergelisol mais les reactions de la croissance et des mecanismes responsables de la productivite ont ete peu etudies a grande echelle. Les reactions de la foret sont largement determinees par l'epinette noire (Picea mariana (Mill.) B.S.P.), l'espece d'arbre la plus dominante et la plus repandue dans cette region. Nous avons recueilli des echantillons de cernes annuels dans quatre stations dominees par l'epinette noire et reparties sur 15[degrees] de latitude avec des gradients en ce qui a trait au climat et au pergelisol. Nous avons etudie (i) les differences dans les patrons de croissance, (ii) les variations dans les facteurs climatiques qui influencent la croissance, et (iii) les tendances dans l'efficacite en matiere d'utilisation de l'eau (EUE) par le biais de l'analyse isotopique du carbone (13C) de 1945 a 2006. Nous avons observe des tendances de croissance positives dans toutes les stations a l'exception de la latitude moyenne ou le degel rapide du pergelisol causait du deperissement. La croissance annuelle etait la plus faible dans la station situee a la limite des arbres et la plus elevee a la limite forestiere. Les facteurs climatiques responsables de ces patrons de croissance variaient; des reactions positives de la croissance dans les stations septentrionales etaient associees a des hivers plus chauds, alors que les tendances de [[DELTA].sup.13]C et les reactions de la croissance au climat dans les stations situees a la latitude moyenne indiquaient que la disponibilite de l'humidite limitait la croissance. Selon la signature de [[DELTA].sup.13]C, l'EUE augmentait dans la station la plus meridionale alors qu'on ne decelait pas de tendances significatives dans les stations septentrionales. Ces resultats indiquent que le rechauffement augmentera la croissance des arbres a la limite septentrionale de l'epinette noire mais que les regions plus au sud pourraient faire face a un stress cause par la secheresse si la precipitation n'arrive pas a equilibrer l'evapotranspiration. [Traduit par la Redaction] Mots-cles: Picea mariana, epinette noire, dendrochronologie, isotope stable du carbone, rechauffement climatique., Introduction Climate is a major driver of the productivity of the boreal forest, an area characterized by a short growing season, harsh winters, and generally low nutrient availability owing to [...]

Aerial seeding with drones has great potential in forest restoration but faces enormous challenges to be efficient and scalable. Current protocols use blanket seeding throughout the area to be restored, meaning a high demand for seed since many seeds arrive in sites unsuitable for establishment. High precision seeding directed to safe microsites at submeter scale could reduce seed use per hectare, reducing economic and ecological costs, while increasing establishment success. Here, we propose an alternative, precision approach to make drone seeding more successful and efficient. This requires (1) submeter‐scale selection of target microsites for seeding founded in ecological knowledge; (2) high‐resolution remote sensing imagery to train artificial intelligence (AI) systems in target microsite recognition; and (3) process automation by transferring target microsite coordinates from the AI system to the drone. This will reduce seed inputs per unit area, seedling establishment failure risks, and drone operation costs. [ABSTRACT FROM AUTHOR]

Boreal forest fires emit large amounts of carbon into the atmosphere primarily through the combustion of soil organic matter.sup.1-3. During each fire, a portion of this soil beneath the burned layer can escape combustion, leading to a net accumulation of carbon in forests over multiple fire events.sup.4. Climate warming and drying has led to more severe and frequent forest fires.sup.5-7, which threaten to shift the carbon balance of the boreal ecosystem from net accumulation to net loss.sup.1, resulting in a positive climate feedback.sup.8. This feedback will occur if organic-soil carbon that escaped burning in previous fires, termed 'legacy carbon', combusts. Here we use soil radiocarbon dating to quantitatively assess legacy carbon loss in the 2014 wildfires in the Northwest Territories of Canada.sup.2. We found no evidence for the combustion of legacy carbon in forests that were older than the historic fire-return interval of northwestern boreal forests.sup.9. In forests that were in dry landscapes and less than 60 years old at the time of the fire, legacy carbon that had escaped burning in the previous fire cycle was combusted. We estimate that 0.34 million hectares of young forests ( Soil radiocarbon dating reveals that combusted 'legacy carbon'--soil carbon that escaped burning during previous fires--could shift the carbon balance of boreal ecosystems, resulting in a positive climate feedback., Author(s): Xanthe J. Walker [sup.1] , Jennifer L. Baltzer [sup.2] , Steven G. Cumming [sup.3] , Nicola J. Day [sup.2] , Christopher Ebert [sup.1] , Scott Goetz [sup.1] [sup.4] [sup.5] [...]

Over the past several decades, various trends in vegetation productivity, from increases to decreases, have been observed throughout Arctic–Boreal ecosystems. While some of this variation can be explained by recent climate warming and increased disturbance, very little is known about the impacts of permafrost thaw on productivity across diverse vegetation communities. Active layer thickness data from 135 permafrost monitoring sites along a 10° latitudinal transect of the Northwest Territories, Canada, paired with a Landsat time series of normalized difference vegetation index from 1984 to 2019, were used to quantify the impacts of changing permafrost conditions on vegetation productivity. We found that active layer thickness contributed to the observed variation in vegetation productivity in recent decades in the northwestern Arctic–Boreal, with the highest rates of greening occurring at sites where the near‐surface permafrost recently had thawed. However, the greening associated with permafrost thaw was not sustained after prolonged periods of thaw and appeared to diminish after the thaw front extended outside the plants' rooting zone. Highest rates of greening were found at the mid‐transect sites, between 62.4° N and 65.2° N, suggesting that more southernly sites may have already surpassed the period of beneficial permafrost thaw, while more northern sites may have yet to reach a level of thaw that supports enhanced vegetation productivity. These results indicate that the response of vegetation productivity to permafrost thaw is highly dependent on the extent of active layer thickening and that increases in productivity may not continue in the coming decades. [ABSTRACT FROM AUTHOR]

The maximum carboxylation rate (Vcmax) is an important parameter for the coupled simulation of gross primary production (GPP) and evapotranspiration (ET) in terrestrial biosphere models (TBMs) such as the Canadian Land Surface Scheme Including biogeochemical Cycles (CLASSIC). Observations of Vcmax show it to vary both spatially and temporally, but it is often prescribed as constant in time and space for plant functional types (PFTs) in TBMs, which introduces large errors over North America's boreal biome. To reduce this uncertainty, we used a Bayesian algorithm to optimize Vcmax25 (Vcmax at 25 °C) in CLASSIC against eddy covariance observations at eight mature boreal forest stands in North America for six representative PFTs (two trees, two shrubs, and two herbs). As expected, the simulated GPP and ET using the optimized parameters generally obtained reduced root mean square deviation values compared with eddy covariance observations and corresponding stand-level estimates obtained from gridded global data products. The optimized Vcmax25 values for each PFT compared reasonably well with reported estimates derived from leaf-level gas exchange measurements. However, a large spatial variability of Vcmax25 was identified, especially for the shrub and herb PFTs. We found that the site characteristics, particularly latitude for the shrub PFTs and air temperature for evergreen needleleaf tree, explained much of the spatial variability, providing a basis to improve Vcmax25 parameterizations in TBMs at regional scales. [ABSTRACT FROM AUTHOR]