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Daily temperature fluctuations trigger physical and metabolic processes in the xylem, affecting the timing and yield of maple sap production. This study evaluates sap production dynamics, examining the effects of mean monthly temperatures and freeze-thaw cycles before and during the sugar season. We developed a predictive model estimating sap phenology, i.e. the timings of sap season and their climatic drivers, under future warming scenarios in Quebec, Canada. We collected air temperatures and daily sap production at four study sites in 2022 and 2023 using rain gauges for simulating a gravity collection of sap. We estimated sap phenology using a neural network model based on average monthly temperatures. The length of the sugar season was consistent across and within sites, with the highly productive days showing similar occurrence across sites. Sap yields ranged from 9.28 to 23.8 liters in 2022 and 3.8 to 13.6 liters in 2023. Freeze-thaw events occurred on 64% of the days when sap was exuded. Our neural network model predicted that a 2°C increase in mean monthly temperatures would advance the sugar season start by 17 days and end by 13 days. Any mismatch between tapping and favorable weather conditions can significantly reduce sap production. With climate change, producers will be forced to progressively readjust the schedule of their field activities and tapping to match the shifting sugar season. [ABSTRACT FROM AUTHOR] more...

The interactions between sugar maple (Acer saccharum , Marshall) and its microbial communities are important for tree fitness, growth, and establishment. Despite recent progress in our understanding of the rhizosphere and phyllosphere microbial communities of sugar maple, many outstanding knowledge gaps remain. This review delves into the relationships between sugar maple and its microbes, as climate change alters plant species distributions. It highlights the multifaceted roles of key microbes, such as arbuscular mycorrhizal (AM) fungi and pathogens, in affecting the distribution and establishment of sugar maple in novel habitats. Furthermore, this review examines how microbial communities in different compartments contribute to tree fitness. Finally, it explores how microbial dispersal and altered species interactions under changing environmental conditions can affect sugar maple's ability to migrate beyond its current range, emphasizing the different scenarios associated with such shifts. In the rhizosphere, AM fungi are known for their roles in nutrient acquisition and improving stress tolerance. Yet, key questions remain about how these fungi interact with other microbes, how soil chemistry and climate change alter these interactions, and how the presence of beneficial microbes influences sugar maple's establishment. Additionally, the role of dark septate endophytes (DSE) in sugar maple's fitness remains underexplored, emphasizing the need for more research on their diversity and functions. In the phyllosphere, microbial communities are subject to shifts due to rising global change, with potential impacts on sugar maple's fitness. These changes may influence the tree's resistance to pathogens, tolerance to environmental stress, and overall health. Yet, our understanding of these interactions relies mostly on short-read sequencing methods targeting marker genes (e.g., 16S, ITS, 18S), which often fail to identify microbes at the species level. Limitations in molecular techniques and poor microbial reference databases hinder our ability to fully characterize tree-associated microbial diversity and functions. Future research should thus prioritize advanced molecular tools such as shotgun, hybrid, or long-read sequencing. Controlled experiments are also needed to establish causal links between sugar maple fitness and microbial communities, and to study whether microbial communities change throughout the tree's lifespan. [ABSTRACT FROM AUTHOR] more...

In northern hardwood forests, litter decomposition might be affected by nutrient availability, species composition, stand age, or access by decomposers. We investigated these factors at the Bartlett Experimental Forest in New Hampshire. Leaf litter of early and late successional species was collected from four stands that had full factorial nitrogen and phosphorus additions to the soil and were deployed in bags of two mesh sizes (63 µm and 2 mm) in two young and two mature stands. Litter bags were collected three times over the next 2 years, and mass loss was described as an exponential function of time represented by a thermal sum. Litter from young stands had higher initial N and P concentrations and decomposed more quickly than litter from mature stands (p = 0.005), regardless of where it was deployed. Litter decomposed more quickly in fine mesh bags that excluded mesofauna (p < 0.001), which might be explained by the greater rigidity of the large mesh material making poor contact with the soil. Neither nutrient addition (p = 0.94 for N, p = 0.26 for P) nor the age of the stand in which bags were deployed (p = 0.36) had a detectable effect on rates of litter decomposition. [ABSTRACT FROM AUTHOR] more...

Bacterial canker caused by Clavibacter michiganensis subsp. michiganensis (Cmm) is a worldwide bacterial disease affecting tomato plants. Very few control methods exist and their efficacy is limited. In recent years, plant extracts were studied for their potential as a safe and eco‐friendly alternative to the use of chemical pesticides to control plant diseases. Recent work performed by our group revealed the antibacterial activity of an ethanolic sugar maple autumn‐shed leaf (SMASL) extract against bacterial plant pathogens. To further investigate the antibacterial and prophylactic potential of SMASL against bacterial canker, assays were performed (a) to determine the polyphenol content and the in vitro antibacterial activity of sugar maple leaf extracts against Cmm, (b) to evaluate the potential of SMASL extracts as a seed treatment against Cmm and (c) as a foliar application to control bacterial canker development in greenhouse‐ and field‐grown tomato plants. Variations in polyphenol content and antibacterial activity of sugar maple leaf extracts were studied monthly for a period of 2 years. Although polyphenol contents varied significantly, minimum inhibitory concentrations were constant between 1.56 and 3.13 mg/mL and minimum bactericidal concentrations between 12.5 and 25 mg/mL. SMASL extract at 25 mg/mL completely eliminated the pathogen from tomato seeds without negatively impacting on germination. SMASL extract foliar spray applications using concentrations of 6.25 and 12.5 mg/mL significantly repressed disease development under greenhouse and field conditions, showing better efficacy than copper octanoate. The antibacterial activity of SMASL extracts against Cmm shows great potential to control Cmm and bacterial canker in tomato. [ABSTRACT FROM AUTHOR] more...

Abstract Forest ecosystems with altered nutrient limitations are a common legacy of acidic deposition in North America. Continued acidic deposition has lowered soil pH and revealed phosphorus (P) limitations in many temperate forest ecosystems. Previous studies exploring P limitations or co‐limitations are often short term, and thus may potentially show a response to limitation that is not sustained over time. To better understand how a forest's response to P limitation and acidic deposition can change over time, we added P, limestone to raise pH, and a cross‐treatment where both P and limestone were added to 3 different northeastern Ohio forest stands over a 12‐year period. We tracked diameter at breast height of the trees annually, conducted foliar nutrient analyses, and collected tree roots to assess treatment impacts on mycorrhizal colonization. We analyzed our dataset in three sections: the first 6 years after manipulation, the latter 6 years, and the entire 12‐year period. These sections allowed us to compare differences between early responses to manipulation and later responses. Here, we found that P additions increased basal area growth across multiple species and throughout the entire study, confirming that our forest trees are P‐limited. Cross‐treatments similarly increased basal area growth, but not as much as P additions alone. Some species saw waning effects of treatment in the second half of the study. This could be due to changes in weather patterns, an adjustment of the study system's equilibrium, or the emergence of beech leaf disease in 2014, which has led to the decline of Fagus grandifolia. Early successional species such as Acer rubrum began to benefit from treatments after beech leaf disease killed canopy F. grandifolia trees, perhaps first being light‐limited, but later able to take advantage of the nutrient additions and pH alteration of their soils. Our results suggest that in forests subject to acidic deposition, soil P may co‐limit tree growth, but responses are species dependent. more...

Daily temperature fluctuations trigger physical and metabolic processes in the xylem, affecting the timing and yield of maple sap production. This study evaluates sap production dynamics, examining the effects of mean monthly temperatures and freeze-thaw cycles before and during the sugar season. We developed a predictive model estimating sap phenology, i.e. the timings of sap season and their climatic drivers, under future warming scenarios in Quebec, Canada. We collected air temperatures and daily sap production at four study sites in 2022 and 2023 using rain gauges for simulating a gravity collection of sap. We estimated sap phenology using a neural network model based on average monthly temperatures. The length of the sugar season was consistent across and within sites, with the highly productive days showing similar occurrence across sites. Sap yields ranged from 9.28 to 23.8 liters in 2022 and 3.8 to 13.6 liters in 2023. Freeze-thaw events occurred on 64% of the days when sap was exuded. Our neural network model predicted that a 2°C increase in mean monthly temperatures would advance the sugar season start by 17 days and end by 13 days. Any mismatch between tapping and favorable weather conditions can significantly reduce sap production. With climate change, producers will be forced to progressively readjust the schedule of their field activities and tapping to match the shifting sugar season. more...

The interactions between sugar maple (Acer saccharum, Marshall) and its microbial communities are important for tree fitness, growth, and establishment. Despite recent progress in our understanding of the rhizosphere and phyllosphere microbial communities of sugar maple, many outstanding knowledge gaps remain. This review delves into the relationships between sugar maple and its microbes, as climate change alters plant species distributions. It highlights the multifaceted roles of key microbes, such as arbuscular mycorrhizal (AM) fungi and pathogens, in affecting the distribution and establishment of sugar maple in novel habitats. Furthermore, this review examines how microbial communities in different compartments contribute to tree fitness. Finally, it explores how microbial dispersal and altered species interactions under changing environmental conditions can affect sugar maple's ability to migrate beyond its current range, emphasizing the different scenarios associated with such shifts. In the rhizosphere, AM fungi are known for their roles in nutrient acquisition and improving stress tolerance. Yet, key questions remain about how these fungi interact with other microbes, how soil chemistry and climate change alter these interactions, and how the presence of beneficial microbes influences sugar maple's establishment. Additionally, the role of dark septate endophytes (DSE) in sugar maple's fitness remains underexplored, emphasizing the need for more research on their diversity and functions. In the phyllosphere, microbial communities are subject to shifts due to rising global change, with potential impacts on sugar maple's fitness. These changes may influence the tree's resistance to pathogens, tolerance to environmental stress, and overall health. Yet, our understanding of these interactions relies mostly on short-read sequencing methods targeting marker genes (e.g., 16S, ITS, 18S), which often fail to identify microbes at the species level. Limitations in molecular techniques and poor microbial reference databases hinder our ability to fully characterize tree-associated microbial diversity and functions. Future research should thus prioritize advanced molecular tools such as shotgun, hybrid, or long-read sequencing. Controlled experiments are also needed to establish causal links between sugar maple fitness and microbial communities, and to study whether microbial communities change throughout the tree's lifespan. more...

Arbuscular mycorrhizal fungi (AMF) are widespread obligate symbionts of plants. This dynamic symbiosis plays a large role in successful plant performance, given that AMF help to ameliorate plant responses to abiotic and biotic stressors. Although the importance of this symbiosis is clear, less is known about what may be driving this symbiosis, the plant's need for nutrients or the excess of plant photosynthate being transferred to the AMF, information critical to assess the functionality of this relationship. Characterizing the AMF community along a natural plant productivity gradient is a first step in understanding how this symbiosis may vary across the landscape. We surveyed the AMF community diversity at 12 sites along a plant productivity gradient driven by soil nitrogen availability. We found that AMF diversity in soil environmental DNA significantly increased along with the growth of the host plants Acerrubrum and A. saccharum., a widespread tree genus. These increases also coincided with a natural soil inorganic N availability gradient. We hypothesize photosynthate from the increased tree growth is being allocated to the belowground AMF community, leading to an increase in diversity. These findings contribute to understanding this complex symbiosis through the lens of AMF turnover and suggest that a more diverse AMF community is associated with increased host–plant performance. [ABSTRACT FROM AUTHOR] more...

The formation of a single species, recalcitrant understory vegetation layer can limit tree regeneration and, in the long term, modify the composition of forests. Few studies have investigated how recalcitrant vegetation influences competition for water resources although the formation of a dense understory is likely to modify the forest water balance. In eastern North American hardwood forests, the development of a dense understory layer of American beech (Fagus grandifolia) has been observed in stands dominated by sugar maple (Acer saccharum), a phenomenon that shares many characteristics associated with recalcitrant vegetation. Given that water availability is generally negatively correlated with stand density, we hypothesized that the formation of a dense understory beech layer increased competition for water resources, thus leading to reduced water use by sugar maple trees in beech‐dominated stands. Using thermal dissipation sensors, we measured sap flux density (Fd) of two sugar maple trees at three beech‐dominated sites and three control sites. During the growing season, Fd of sugar maple trees was significantly larger at beech‐dominated sites compared to control sites, indicating a greater rate of water use by sugar maples in stands with a dense understory beech layer. We provide two hypotheses to explain our results at the tree scale: (i) reduced cover by forest floor vegetation could limit transpiration by this layer, thus allowing increased water availability to supply transpiration by overstory trees, or (ii) increased tree transpiration rate could be a mechanism to satisfy nutrient requirements in beech‐dominated stands often associated with lower soil fertility. [ABSTRACT FROM AUTHOR] more...

Forests play a crucial role providing ecosystem services to humans, yet many aspects of forest dynamics remain unknown. One key area is how climate change might impact reproduction of tree species. While most studies have focused on predicting tree growth, understanding how reproduction may change will be vital to forecasting future forest communities. Of particular interest is the relationship between annual growth and reproductive output, which has often been hypothesized as a trade‐off between allocating resources to growth or to reproduction. Two proposed pathways of this trade‐off, resource accumulation, that is, storage of resources over time, and resource allocation, that is, same year allocation of resources to reproduction, have been widely explored in relation to masting events. It has also been proposed that there is no internal trade‐off between the two functions, but rather there exists one or more climate variables that are intrinsically linked to both, that is, the weather hypothesis. In this study, we use 15 years of dendrochronological data and seed rain collections from forest stands at two latitudes to determine whether one or more of these strategies are taking place in two commonly occurring tree species: red maple, Acer rubrum; and sugar maple, Acer saccharum. We found evidence of a trade‐off in both species. We also found a combination of strategies was the norm, and there appeared to be evidence to also support the weather hypothesis. However, in both species, the strategy which dictated the trade‐off switched between the northern and southern regions, indicating a degree of plasticity that could be beneficial under changing environmental conditions. By identifying the ways in which growth and reproduction are connected and how these connections vary between different populations, we can gain insights into how trees allocate resources in response to changing conditions. [ABSTRACT FROM AUTHOR] more...

DNA methylation is critical to the regulation of transposable elements and gene expression and can play an important role in the adaptation of stress response mechanisms in plants. Traditional methods of methylation quantification rely on bisulfite conversion that can compromise accuracy. Recent advances in long‐read sequencing technologies allow for methylation detection in real time. The associated algorithms that interpret these modifications have evolved from strictly statistical approaches to Hidden Markov Models and, recently, deep learning approaches. Much of the existing software focuses on methylation in the CG context, but methylation in other contexts is important to quantify, as it is extensively leveraged in plants. Here, we present methylation profiles for two maple species across the full range of 5mC sequence contexts using Oxford Nanopore Technologies (ONT) long‐reads. Hybrid and reference‐guided assemblies were generated for two new Acer accessions: Acer negundo (box elder; 65x ONT and 111X Illumina) and Acer saccharum (sugar maple; 93x ONT and 148X Illumina). The ONT reads generated for these assemblies were re‐basecalled, and methylation detection was conducted in a custom pipeline with the published Acer references (PacBio assemblies) and hybrid assemblies reported herein to generate four epigenomes. Examination of the transposable element landscape revealed the dominance of LTR Copia elements and patterns of methylation associated with different classes of TEs. Methylation distributions were examined at high resolution across gene and repeat density and described within the broader angiosperm context, and more narrowly in the context of gene family dynamics and candidate nutrient stress genes. [ABSTRACT FROM AUTHOR] more...

Abstract Arbuscular mycorrhizal fungi (AMF) are widespread obligate symbionts of plants. This dynamic symbiosis plays a large role in successful plant performance, given that AMF help to ameliorate plant responses to abiotic and biotic stressors. Although the importance of this symbiosis is clear, less is known about what may be driving this symbiosis, the plant's need for nutrients or the excess of plant photosynthate being transferred to the AMF, information critical to assess the functionality of this relationship. Characterizing the AMF community along a natural plant productivity gradient is a first step in understanding how this symbiosis may vary across the landscape. We surveyed the AMF community diversity at 12 sites along a plant productivity gradient driven by soil nitrogen availability. We found that AMF diversity in soil environmental DNA significantly increased along with the growth of the host plants Acer rubrum and A. saccharum., a widespread tree genus. These increases also coincided with a natural soil inorganic N availability gradient. We hypothesize photosynthate from the increased tree growth is being allocated to the belowground AMF community, leading to an increase in diversity. These findings contribute to understanding this complex symbiosis through the lens of AMF turnover and suggest that a more diverse AMF community is associated with increased host–plant performance. more...

Climate change is expected to increase the frequency and intensity of winter thaws, which could affect leaf phenology. Phenology could either be advanced through the acceleration of forcing accumulation or chilling completion, or be postponed through a reduction in chilling associated with warming air temperature. We tested the influence of winter thaws on budburst phenology by exposing 300 tree cuttings of sugar maple and yellow birch trees to five different frequencies and durations of winter thaws in the lab. In spring, half of the cuttings were exposed to air temperature in two cities representing an air temperature gradient of + 2.0 °C to mimic the ongoing climate warming and bud phenology was monitored three times a week. Irrespective of thaw treatment, yellow birch bud phenology occurred earlier in the warmer city, showing the importance of spring temperature in triggering budburst. The treatment with the highest frequency and duration of thawing increased bud mortality and delayed the onset of spring budburst whereas low frequency treatments did not, thereby identifying a tipping point (3 days twice a month) in the impact of winter thaws on bud phenology. Past this point, winter thaws could slow down bud phenology induced by warmer spring temperature and limit carbon uptake by delaying the closure of the canopy. Climate change simulations projected by the CMIP6 Canadian downscaled climate scenario show that winter thaws will increase in frequency Hence the expected advance in spring leaf emergence associated with warmer spring is not necessarily as straightforward as previously thought. more...

Abstract Forests play a crucial role providing ecosystem services to humans, yet many aspects of forest dynamics remain unknown. One key area is how climate change might impact reproduction of tree species. While most studies have focused on predicting tree growth, understanding how reproduction may change will be vital to forecasting future forest communities. Of particular interest is the relationship between annual growth and reproductive output, which has often been hypothesized as a trade‐off between allocating resources to growth or to reproduction. Two proposed pathways of this trade‐off, resource accumulation, that is, storage of resources over time, and resource allocation, that is, same year allocation of resources to reproduction, have been widely explored in relation to masting events. It has also been proposed that there is no internal trade‐off between the two functions, but rather there exists one or more climate variables that are intrinsically linked to both, that is, the weather hypothesis. In this study, we use 15 years of dendrochronological data and seed rain collections from forest stands at two latitudes to determine whether one or more of these strategies are taking place in two commonly occurring tree species: red maple, Acer rubrum; and sugar maple, Acer saccharum. We found evidence of a trade‐off in both species. We also found a combination of strategies was the norm, and there appeared to be evidence to also support the weather hypothesis. However, in both species, the strategy which dictated the trade‐off switched between the northern and southern regions, indicating a degree of plasticity that could be beneficial under changing environmental conditions. By identifying the ways in which growth and reproduction are connected and how these connections vary between different populations, we can gain insights into how trees allocate resources in response to changing conditions. more...

Silvicultural regeneration methods focus on manipulating the forest canopy, but success can depend on the use of site preparation to control competing vegetation, including the density of advance regeneration, and create suitable microsite conditions for germination and seedling establishment. Tip-up mounds are known to provide favorable conditions for some tree species, but the creation of tip-up mounds as a method of site preparation has scarcely been investigated. We assessed effects of artificial tip-up mounds on tree seedling composition across a gradient of regeneration methods and residual overstory densities 2–4 years post-implementation. We found that tree seedling communities on mounds in some treatments were compositionally distinct from untreated reference plots. However, no tree species exhibited a strong affinity for mounds when analyzed independently from the regeneration method, and much of the difference in composition was associated with lower dominance of maples (Acer spp. L.) on mounds. As maples are strong competitors in forests regenerated with selection systems, reduced maple competition on artificial mounds could advantage desired under-represented species and aid in natural regeneration over time. Therefore, in stands where promoting tree species diversity is desirable, implementing artificial tip-up mounds as part of a long-term strategy may be beneficial. [ABSTRACT FROM AUTHOR] more...

Plasticity is vital for plants to rapidly acclimate to environmental changes, especially under the climate change. Global warming could advance bud break and extend the growing season, but it also increases the risk of frost damage to developing leaves. In this study, we explored the phenological plasticity of bud burst of half-sib family sugar maple (Acer saccharum Marsh.) seedlings from 11 seed origins in two common gardens at the center and the northern edge of the species distribution in Quebec, Canada. Results showed that the phenological plasticity of sugar maple originating from inland was significantly higher than those from coastal areas at the beginning of leaf development. This discrepancy may result from the long-term frost change frequency of seed origins. Our study suggests that in the context of climate warming, the higher plasticity observed in sugar maple originating from inland areas may benefit from the phenological adaptation of sugar maple and the survival of local populations. It also suggests that inland populations may have a higher potential regarding to assisted migration, but this needs to be confirmed for other functional traits than phenology. more...

With climate change, climatic optima are shifting poleward more rapidly than tree migration processes, resulting in a mismatch between species distributions and bioclimatic envelopes. Temperate hardwood tree species may take advantage of the release of climate constraints and forest management to migrate into the boreal forest. Here, we use the SORTIE‐ND forest simulation model to determine the potential for the persistence of three temperate species (sugar maple, red maple and yellow birch) when introduced at seedling stage in typical balsam fir–paper birch (BF–PB) bioclimatic domain stands of eastern Canada, quantifying the consequences on the native species composition. SORTIE‐ND is a spatially explicit, individual‐based forest stand model that simulates tree growth, regeneration and mortality. We performed a novel parameterization of the SORTIE‐ND tree growth equation allowing for the inclusion of climate modifiers on tree growth. After validating our model with data from permanent forest inventory plots, we modeled the dynamics of unharvested stands at different successional stages, as well as post‐harvest stands, after the addition of sugar maple, red maple and yellow birch seedlings at different densities. Our results show that current BF–PB domain climate conditions do not limit growth and survival of temperate species in boreal stands. Of the temperate species introduced, sugar maple had the lowest ability to grow and survive by the end of the simulation. Species assemblages of host stands were impacted by the presence of temperate species when the addition of seedlings was above 5000 temperate seedlings per hectare at the beginning of the simulation. For stands that were recently clear cut, temperate seedlings were unable to grow due to intense competition from aspen regeneration. Our results suggest that both current climate and competitive interactions between temperate species and boreal species should not impede the ability of temperate species to grow and survive in the BF–PB domain. [ABSTRACT FROM AUTHOR] more...

Sugar maple (Acer saccharum Marshall) is a temperate tree species in the northeastern parts of the United States and is economically important for its hardwood and syrup production. Sugar maple trees are highly vulnerable to changing climatic conditions, especially drought, so understanding the physiological, biochemical, and molecular responses is critical. The sugar maple saplings were subjected to drought stress for 7, 14, and 21 days and physiological data collected at 7, 14, and 21 days after stress (DAS) showed significantly reduced chlorophyll and Normalized Difference Vegetation Index with increasing drought stress time. The drought stress-induced biochemical changes revealed a higher accumulation of malondialdehyde, proline, and peroxidase activity in response to drought stress. Transcriptome analysis identified a total of 14,099 differentially expressed genes (DEGs); 328 were common among all stress periods. Among the DEGs, transcription factors (including NAC, HSF, ZFPs, GRFs, and ERF), chloroplast-related and stress-responsive genes such as peroxidases, membrane transporters, kinases, and protein detoxifiers were predominant. GO enrichment and KEGG pathway analysis revealed significantly enriched processes related to protein phosphorylation, transmembrane transport, nucleic acids, and metabolic, secondary metabolite biosynthesis pathways, circadian rhythm-plant, and carotenoid biosynthesis in response to drought stress. Time-series transcriptomic analysis revealed changes in gene regulation patterns in eight different clusters, and pathway analysis by individual clusters revealed a hub of stress-responsive pathways. In addition, qRT-PCR validation of selected DEGs revealed that the expression patterns were consistent with transcriptome analysis. The results from this study provide insights into the dynamics of physiological, biochemical, and gene responses to progressive drought stress and reveal the important stress-adaptive mechanisms of sugar maple saplings in response to drought stress. [ABSTRACT FROM AUTHOR] more...

Global changes affect the growing conditions of terrestrial ecosystems, causing a mismatch between plant phenology and local climates in Northern regions. Due to their long lifespan and irregular regeneration periods, trees cannot respond quickly enough to climate variability through long-term genetic adaptation. In this study, we explored the phenological plasticity and genetic variation among populations of bud burst in sugar maple (Acer saccharum Marsh.) seedlings from 30 Canadian provenances with contrasting climates planted in two common gardens near and at the northern limit of the species’ range. We tested the hypothesis that phenotypic plasticity and genetic variation among populations affect bud phenology. We expect that phenotypic plasticity is more important in regulating bud phenology due to the high variability in short-term weather events characterizing this part of North America. Bud development and leafing occurred in April–May, with complete bud burst lasting between 21 and 29 days. On average, bud swelling differed by 12 days between common gardens. Both factors site (common gardens) and provenance significantly affected bud burst, demonstrating phenological plasticity and genetic variation of sugar maple, respectively. A significant interaction between site and provenance was also found. Overall, the site (11.8–90.3%) contributed more than provenance (0–3.1%) to the variance in timings of bud burst, indicating a dominant role of plasticity in regulating spring phenology. Our study demonstrated the concurring effects of genetic variation and phenological plasticity of sugar maple and revealed the dominant role of the latter factor. The high plasticity observed in sugar maple has a crucial role in the phenological adaptation of maple and the survival of its local populations in a context of changing climate. more...

Sugar maple (Acer saccharum Marshall) is a temperate tree species in the northeastern parts of the United States and is economically important for its hardwood and syrup production. Sugar maple trees are highly vulnerable to changing climatic conditions, especially drought, so understanding the physiological, biochemical, and molecular responses is critical. The sugar maple saplings were subjected to drought stress for 7, 14, and 21 days and physiological data collected at 7, 14, and 21 days after stress (DAS) showed significantly reduced chlorophyll and Normalized Difference Vegetation Index with increasing drought stress time. The drought stress-induced biochemical changes revealed a higher accumulation of malondialdehyde, proline, and peroxidase activity in response to drought stress. Transcriptome analysis identified a total of 14,099 differentially expressed genes (DEGs); 328 were common among all stress periods. Among the DEGs, transcription factors (including NAC, HSF, ZFPs, GRFs, and ERF), chloroplast-related and stress-responsive genes such as peroxidases, membrane transporters, kinases, and protein detoxifiers were predominant. GO enrichment and KEGG pathway analysis revealed significantly enriched processes related to protein phosphorylation, transmembrane transport, nucleic acids, and metabolic, secondary metabolite biosynthesis pathways, circadian rhythm-plant, and carotenoid biosynthesis in response to drought stress. Time-series transcriptomic analysis revealed changes in gene regulation patterns in eight different clusters, and pathway analysis by individual clusters revealed a hub of stress-responsive pathways. In addition, qRT-PCR validation of selected DEGs revealed that the expression patterns were consistent with transcriptome analysis. The results from this study provide insights into the dynamics of physiological, biochemical, and gene responses to progressive drought stress and reveal the important stress-adaptive mechanisms of sugar maple saplings in response to drought stress. more...

• Temperate species can colonize boreal mixedwood stands especially in young stands. • When considering climate change on adult growth, climate change did not influence temperate species to colonize boreal mixedwood stands. • The specific dispersal, mortality, and juvenile growth abilities of temperate trees will determine their colonization of mixedwood boreal stands. • The ability of temperate trees to colonize mixedwood boreal stands will be higher in younger stands, with low influence of climate change. Temperate hardwood tree species may take advantage of climate change to migrate northward tracking their optimal growth and survival niches. Other factors than climate could constrain or facilitate their establishment north of their actual range, such as competitive interactions, their ability to disperse, and forest management. The objectives of this study were to model the ability of temperate tree species to colonize boreal mixedwood stands of Eastern Canada from a few temperate tree seeders, considering the effects of climate change, competitive interactions, and specific successional stages of the receiving stands. We used the individual based forest model SORTIE-ND with adult growth forced by four different projected climate change scenarios. To mimic the natural colonization of temperate trees from marginal populations eventually established by long-distance migration, we replaced a patch in the center of the simulated stands with temperate tree species, i.e., red maple, sugar maple or yellow birch. We then performed a sensitivity analysis on the parameters determining the growth, dispersal, and mortality of temperate tree species to determine which of these processes was critical to their expansion. All three temperate tree species were able to colonize the boreal stands with higher performance in younger stands, and greater colonization skills for yellow birch. At the 2100 horizon, the impact of the climate scenarios on the final basal area of temperate tree species was minor. Processes mostly driven by competition and species auto-ecology, including dispersion, mortality, and juvenile growth parameters, were the most important for the colonization capacity. Our results suggest that the expansion of temperate tree species from already established northern marginal populations would be minimally affected by climate change, and that forest management could have a more significant impact by rejuvenating boreal mixedwood landscapes. [ABSTRACT FROM AUTHOR] more...

It has been proposed that ectomycorrhizal (EcM) fungi slow down decomposition by competing with free-living saprotrophs for organic nutrients and other soil resources (known as the "Gadgil effect"), thereby increasing soil carbon sequestration. As such, this Gadgil effect should depend on soil organic matter age and quality, but this remains unstudied. In addition, the Gadgil effect is not expected to occur in arbuscular mycorrhizal (AM) forests since AM fungi cannot access directly nutrients from soil organic matter, yet few direct comparisons between EcM and AM forests have been made. We performed a two-year reciprocal decomposition experiment of soil organic horizons (litter—L, fragmented—F, humic—H) in adjacent temperate deciduous forests dominated by EcM or AM trees. Mesh bags were made of different mesh sizes allowing or excluding ingrowth of external fungal hyphae, which are primarily mycorrhizal in these forests other than for the most recent superficial litter horizon. As expected, EcM stands stored more soil carbon (up to 20 cm depth) than AM stands. Also, organic matter originating from deeper horizons and from EcM stands was of lower quality (for example, higher lignin to nitrogen ratios) and decomposed more slowly. However, contrary to the Gadgil effect, organic matter exposed to external fungal hyphae (that is, primarily mycorrhizal) actually decomposed faster in both forest types, and this effect was strongest in EcM forests, particularly in the F horizon. Unexpectedly, organic matter decomposition was faster in EcM than in AM forests, regardless of organic matter origin. Overall, our study reinforces the view that temperate EcM forests store greater amounts of soil organic carbon than AM forests, but suggests that this is due to factors other than the Gadgil effect. [ABSTRACT FROM AUTHOR] more...

Sapling recruitment in hardwood forests is often suppressed by overstory shade, interspecific competition, and browsing pressure from white-tailed deer (Odocoileus virginianus Zimmerman). In some northern hardwood stands, these three interacting factors may cause persistent recruitment failure of the dominant canopy species, sugar maple (Acer saccharum Marsh.), into the sapling size class. In this study, we compared initial (two-year) sugar maple and hophornbeam (Ostrya virginiana ((Mill.) K. Koch) seedling and sapling recruitment in strip clearcuts to strip selection cuts, with combinations of herbicide and deer exclosures, in a northern hardwood forest with limited sugar maple sapling recruitment. We found that sugar maple sapling recruitment was higher in exclosures, particularly in strip clearcuts. Moreover, mixed models predicted that exclosures in strip clearcuts with herbicide tended to benefit sugar maple sapling recruitment, especially when the pre-treatment density was less than ~1500 stems ha−1. Sapling density of hophornbeam was also promoted in exclosure plots but was negatively affected by herbicide. Graminoid and Rubus spp. cover was also limited by herbicide following harvest, potentially alleviating constraints on future sugar maple sapling recruitment. Our findings indicate that sugar maple sapling recruitment in strip clearcuts is similar to strip selection cuts unless browsing pressure and interspecific competition are also alleviated. [ABSTRACT FROM AUTHOR] more...

Significance Statement: The first chromosome‐scale assemblies for North American members of the Acer genus, sugar maple (Acer saccharum) and boxelder (Acer negundo), as well as transcriptomic evaluation of the abiotic stress response in A. saccharum are reported. This integrated study describes in‐depth aspects contributing to each species' approach to tolerance and applies current knowledge in many areas of plant genome biology with Acer physiology to help convey the genomic complexities underlying tolerance in broadleaf tree species. [ABSTRACT FROM AUTHOR] more...

Phenological escape, a strategy that deciduous understory plants use to access direct light in spring by leafing out before the canopy closes, plays an important role in shaping the recruitment of temperate tree seedlings. Previous studies have investigated how climate change will alter these dynamics for herbaceous species, but there is a knowledge gap related to how woody species such as tree seedlings will be affected. Here, we modeled temperate tree seedling leaf‐out phenology and canopy close phenology in response to environmental drivers and used climate change projections to forecast changes to the duration of spring phenological escape. We then used these predictions to estimate changes in annual carbon assimilation while accounting for reduced carbon assimilation rates associated with hotter and drier summers. Lastly, we applied these estimates to previously published models of seedling growth and survival to investigate the net effect on seedling demographic performance. Our models predict that temperate tree seedlings will experience improved phenological escape and, therefore, increased spring carbon assimilation under climate change conditions. However, increased summer respiration costs will offset the gains in spring under extreme climate change leading to a net loss in annual carbon assimilation and demographic performance. Furthermore, we found that annual carbon assimilation predictions depend strongly on the species of nearby canopy tree that seedlings were planted near, with all seedlings projected to assimilate less carbon (and therefore experience worse demographic performance) when planted near Quercus rubra canopy trees as opposed to Acer saccharum canopy trees. We conclude that changes to spring phenological escape will have important effects on how tree seedling recruitment is affected by climate change, with the magnitude of these effects dependent upon climate change severity and biological interactions with neighboring adults. Thus, future studies of temperate forest recruitment should account for phenological escape dynamics in their models. [ABSTRACT FROM AUTHOR] more...

Understorey plants in deciduous forests often rely on access to ephemeral light availability before the canopy closes in spring and after the canopy reopens in fall, a strategy commonly referred to as phenological escape. Although there is evidence for a relationship between understorey plant phenology and demographic performance, a mechanistic link is still missing.In this study, we bridged this gap by estimating annual carbon assimilation as a function of foliar phenology and photosynthetic capacity for seedlings of two temperate tree species that commonly co‐occur across eastern North America. We then modelled the relationship between estimated carbon assimilation and observed seedling survival and growth.Our results indicate that seedlings of both species strongly depend on spring phenological escape to assimilate the majority of their annual carbon budget and that this mechanism significantly affects their likelihood of survival (but not growth). Foliar desiccation also played a strong role in driving patterns of seedling survival, suggesting that water availability will also help shape seedling recruitment dynamics. We found only weak associations between seedling senescence in fall and annual carbon assimilation, suggesting that phenological escape in fall plays a relatively minor role in seedling demographic performance.Our results indicate that spring phenological escape is critical for survival of these temperate tree species, and thus, any changes to this dynamic associated with climate change could strongly impact these species' recruitment. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR] more...

In temperate and boreal forests, competition for soil resources between free-living saprotrophs and ectomycorrhizal (EcM) fungi has been suggested to restrict saprotrophic fungal dominance to the most superficial organic soil horizons in forests dominated by EcM trees. By contrast, lower niche overlap with arbuscular mycorrhizal (AM) fungi could allow fungal saprotrophs to maintain this dominance into deeper soil horizons in AM-dominated forests. Here we used a natural gradient of adjacent forest patches that were dominated by either AM or EcM trees, or a mixture of both to determine how fungal communities characterized with high-throughput amplicon sequencing change across organic and mineral soil horizons. We found a general shift from saprotrophic to mycorrhizal fungal dominance with increasing soil depth in all forest mycorrhizal types, especially in organic horizons. Vertical changes in soil chemistry, including pH, organic matter, exchangeable cations, and extractable phosphorus, coincided with shifts in fungal community composition. Although fungal communities and soil chemistry differed among adjacent forest mycorrhizal types, variations were stronger within a given soil profile, pointing to the importance of considering horizons when characterizing soil fungal communities. Our results also suggest that in temperate forests, vertical shifts from saprotrophic to mycorrhizal fungi within organic and mineral horizons occur similarly in both ectomycorrhizal and arbuscular mycorrhizal forests. [ABSTRACT FROM AUTHOR] more...

Acer saccharum and Acer rubrum , two main maple species in North America, will be affected by ongoing global warming. Several studies predict a southern limit contraction but limited northward expansion of maple distribution for the future. We aimed to understand the main drivers of current maple distribution to quantify potential changes to maple habitat in this context. We identified the local conditions of maple stands and assessed the potential changes under warming scenarios. We selected two regions in Quebec, Canada, at the northern distribution of the species and applied probability distribution function and principal component analysis to identify the factors explaining the occurrence of maple compared with other forest species, croplands, and grasslands. Maple habitat was estimated under warming scenarios up to 2°C. We observed a lower density of maple stands in the north (7.76%), compared to the south (33.01%). Warming increased maple stands by 3.54 and 1.45% in the northernmost and southernmost regions, respectively, with the highest increases being estimated at the initial warming (+1.0°C). We conclude that maple of northern regions can benefit from local warming if precipitation does not become limiting. These changes could increase the potential for the regional maple industry and forest management. [ABSTRACT FROM AUTHOR] more...

The complex effects of global environmental changes on ecosystems result from the interaction of multiple stressors, their direct impacts on species and their indirect impacts on species interactions. Air pollution (and resulting depletion of soil base cations) and biotic invasion (e.g. beech bark disease [BBD] complex) are two stressors that are affecting the foundational tree species of northern hardwood forests, sugar maple and American beech, in northeastern North America.At the Hubbard Brook Experimental Forest in New Hampshire, a watershed‐scale calcium (Ca) addition in 1999 restored soil Ca that had been lost as a result of acid deposition in a maple‐beech forest that was severely affected by BBD beginning in the 1970s. We present historic data from the reference watershed for BBD progression, 20 years of comparative forest data from the treated and reference watersheds, and tree demographic rates for the most recent decade. We hypothesized that mitigation of soil acidification on the treated watershed in the presence of BBD would favour improved performance of sugar maple, a species that is particularly sensitive to base cation depletion.We observed significant responses of seed production, seedling bank composition, sapling survival and recruitment, and tree mortality and growth to the restoration of soil Ca, indicating that acid rain depletion of soil base cations has influenced demographic rates of maple and beech. Overall, the reduced performance of sugar maple on acidified soils may indirectly favour the persistence of diseased beech trees and a greater abundance of beech vegetative sprouts, effectively promoting the chronic presence of severe BBD in the population.Synthesis. The shifting conditions created by global change have altered long‐term demographic rates and may thereby impact competitive interactions in the current centre of these species ranges and have more profound implications for species persistence and migration potential than previously anticipated. [ABSTRACT FROM AUTHOR] more...

Effect of geraniin extracted from sugar maple (Acer saccharum) leaves on the viability of the phytopathogen Xanthomonas campestris pv. vitians was evaluated with the SYTOX Green nucleic acid stain, penetrating only compromised membranes, and plate counts. In parallel, structural changes of treated bacteria were examined in transmission electron microscopy (TEM). Based on SYTOX Green and plate counts, geraniin at the minimum bactericidal concentration (3.125 mg/ml) increased mortality after 45 min by 37% and 62%, respectively, when compared with controls. According to observations in TEM, geraniin caused morphological alterations of these rod-shaped bacteria, including degradation of their envelopes, as also suggested by the incorporation of SYTOX. These alterations were often accompanied by cytoplasm leakage and the formation of more pronounced whitish areas in the cytoplasm similar to vacuolization. Moreover, multi-membranous and/or –wall systems were at times formed in the treated bacteria. The presence of some extracellular electron-dense material was frequently noted around the treated bacteria. The matrix surrounding control bacteria tended to disappear after geraniin treatment. This study highlights for the first time the effect of geraniin on bacterial ultrastructure, thus contributing to a better understanding of the mechanism by which this molecule exerts antibacterial activity. [ABSTRACT FROM AUTHOR] more...

Aims: In temperate forests, small increases in winter temperature can lead to substantial decreases in snow accumulation, which may alter plant–consumer interactions such as seed predation. However, seed predation by small mammals may also be affected by local habitat structure (e.g., downed woody debris). We tested whether the effect of snow depth on seed predation by small mammals depends on habitat structure (woody debris) that may influence small-mammal foraging behavior. Location: Northern temperate forests in Wisconsin, USA. Methods: We performed a factorial manipulation of snow depth and woody debris presence at 10 sites that differed in site-level ambient woody debris. At these sites, we monitored seed removal of four temperate tree species (Abies balsamea, Acer rubrum, Acer saccharum, Pinus resinosa). Results: Mean rates of winter seed removal varied among species, as did the effects of snow depth and woody debris. The presence of woody debris decreased Abies balsamea seed removal in plots with snow removed. Regardless of woody debris, snow removal increased Acer saccharum seed removal. Acer rubrum seed removal was lowest at sites with high site-level woody debris volume, especially in plots with snow removed. Conclusions: Warming winter temperatures may amplify seed removal for some tree species, but local-scale heterogeneity in woody debris may modify these effects. Because the effects of woody debris and snow removal were much stronger for some tree species than others, changes in seed removal associated with reduced future snow cover or changes in forest management may accelerate regional changes in forest composition. [ABSTRACT FROM AUTHOR] more...

Some studies suggest that tapping sugar maple (Acer saccharum Marshall) trees can cause their growth to decline, particularly on poor and acidic soils. We tested this hypothesis in seven sugar bushes located in the Quebec Appalachians by comparing the growth of tapped trees with nearby untapped trees. The sites represented a range of soil fertility, from very good for sugar maple to strongly deficient in calcium. Trees were cored, and individual dendrochronology series were used to analyze trends in basal area growth, from a period of 10 years before, to 8–10 years after tapping began. Basal area growth of sugar maples did not appear to be influenced by tapping (p ≥ 0.134), except at one site (p < 0.001), where the growth of tapped trees decreased by 33% over 10 years. This decline could not be explained only by the poor soil fertility observed at the site. Although a tree biomass distribution budget indicated that maple syrup production represented only 4–6% of the carbon allocated annually to net primary production, the long-term relationship between maple syrup production and tree growth requires further study. [ABSTRACT FROM AUTHOR] more...

Crowley's Ridge is a low, narrow, eroded ridge that rises above the uniformly flat alluvial floodplain in the northeastern quadrat of Arkansas. The ridge is geologically unique because it consists largely of wind-blown soil (loess) deposited during the late Pleistocene. During June 2008, quantitative data on the composition and structure of all strata of forest vegetation were collected from ten 0.1 ha plots at two general localities on the southern portion of Crowley's Ridge. Acer saccharum (sugar maple) was the leading dominant in the large/ medium-sized tree stratum, followed by Quercus rubra (northern red oak), Q. velutina (black oak) and Q. stellata (post oak), all with importance value indices > 10. Other species present included Carya alba (mockernut hickory), Fraxinus americana (white ash), Fagus grandifolia (American beech), and Liriodendron tulipifera (tulip-tree). Except for post oak, these trees tend to be characteristic of the classic Mixed Mesophytic Forest Region of the southeastern United States. In six of the 10 plots, the combined importance values of species typically associated with mixed mesophytic forests represented 84% to 100% of the large/ medium-sized tree stratum. Twenty-three different species were recorded in this stratum, a level of diversity that is comparable to a mixed mesophytic forest. As such, the data presented herein indicate that at least some forests on Crowley's Ridge apparently represent the westernmost examples of this forest type. [ABSTRACT FROM AUTHOR] more...

Ethanolic crude extract prepared from autumn‐shed leaves of sugar maple (Acer saccharum Marsh.) was recently shown to have antibacterial activity against Pseudomonas cichorii and Xanthomonas campestris pv. vitians, two bacteria causing diseases in lettuce production. In this study, antibacterial activity of sugar maple autumn‐shed leaves (SMASL) extract was further investigated. SMASL ethanolic crude extract was fractionated using HPLC system and geraniin was identified as the antibacterial compound by UPLC/Q‐Tof‐MS system. Geraniin, an ellagitannin, was then purified from SMASL crude extract using a glass chromatographic C18‐reversed phase silica gel column (purification Step 1) and a semi‐preparative HPLC system equipped with 5 μm XTerra Prep MS C18 column (purification Step 2). Minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) of purified geraniin (purity of 96%) against P. cichorii and X. campestris pv. vitians were determined. X. campestris pv. vitians (MIC of 0.024 mg ml−1 and MBC of 3.125 mg ml−1) was more sensitive to geraniin than P. cichorii (MIC of 0.781 mg ml−1 and MBC of 6.25 mg ml−1). In the present study, geraniin is reported for the first time as the main antibacterial compound present in SMASL. [ABSTRACT FROM AUTHOR] more...

Aims: Respiration of sugar maple (Acer saccharum) surface fine roots has been shown to partially acclimate to experimentally increased soil temperature. In this study, we assessed how larger roots and roots at deeper depths responded to experimental warming. Methods: We quantified specific root respiration and root biomass for three different diameter classes (<1, 1–2, and 2–10 mm) from three soil depths (0–10, 10–30, and 30–50 cm) in a sugar maple forest that had received a factorial combination of increased soil temperature (4 to 5 °C above ambient) and supplemental precipitation for three growing seasons. Results: Partial temperature acclimation occurred for respiration of fine-roots (<1 mm) at 0–10 cm, limiting the increase to 30% above that for roots in the control treatment. In contrast, there was no evidence for acclimation of fine-roots at deeper depths, where soil warming caused respiration to more than double. There was evidence of acclimation for 1–2 mm roots at the 0–10 cm depth (20% reduction in respiration at an 18 °C reference temperature) but not for the larger diameter roots at any of the three soil depths. Root biomass was not altered by soil warming or moisture addition. Conclusions: Despite partial thermal acclimation in surface fine-root respiration, soil warming caused an overall 41% increase in the C flux to the atmosphere from respiration of roots in the upper 30 cm of soil, from 21.3 to 30.1 μmol m−2 s−1, potentially reducing C availability for biomass production. [ABSTRACT FROM AUTHOR] more...

Abstract Background Sugar maple (Acer saccharum Marsh.) is a hardwood tree species native to northeastern North America and economically valued for its wood and sap. Yet, few molecular genetic resources have been developed for this species to date. Microsatellite markers have been a useful tool in population genetics, e.g., to monitor genetic variation and to analyze gene flow patterns. The objective of this study is to develop a reference transcriptome and microsatellite markers in sugar maple. Findings A set of 117,861 putative unique transcripts were assembled using 29.2 Gb of RNA sequencing data derived from different tissues and stress treatments. From this set of sequences a total of 1068 microsatellite motifs were identified. Out of 58 genic microsatellite markers tested on a population of 47 sugar maple trees in upper Michigan, 22 amplified well, of which 16 were polymorphic and 6 were monomorphic. Values for expected heterozygosity varied from 0.224 to 0.726 for individual loci. Of the 16 polymorphic markers, 15 exhibited transferability to other Acer L. species. Conclusions Genic microsatellite markers can be applied to analyze genetic variation in potentially adaptive genes relative to genomic reference markers as a basis for the management of sugar maple genetic resources in the face of climate change. more...

Background Biological invasions are major drivers of environmental change that can significantly alter ecosystem function and diversity. In plants, soil microbes play an important role in plant establishment and growth; however, relatively little is known about the role they might play in biological invasions. A first step to assess whether root microbes may be playing a role in the invasion process is to find out if invasive plants host different microbes than neighbouring native plant species. Methods In this study we investigated differences in root associated microbes of native sugar maple (Acer saccharum Marsh.) and exotic Norway maple (A. platanoides L.) collected from a forested reserve in eastern Canada. We used microscopy to examine root fungi and high-throughput sequencing to characterize the bacterial, fungal and arbuscular mycorrhizal communities of both maple species over one growing season. Results We found differences in root associated bacterial and fungal communities between host species. Norway maple had a higher bacterial and fungal OTU (operational taxonomic units) richness compared to sugar maple, and the indicator species analysis revealed that nine fungal OTUs and three bacterial OTUs had a significant preference for sugar maple. The dominant bacterial phyla found on the roots of both maple species were Actinobacteria and Proteobacteria. The most common fungal orders associated with the Norway maple roots (in descending order) were Helotiales, Agaricales, Pleosporales, Hypocreales, Trechisporales while the Agaricales, Pleosporales, Helotiales, Capnodiales and Hypocreales were the dominant orders present in the sugar maple roots. Dark septate fungi colonization levels were higher in the sugar maple, but no differences in arbuscular mycorrhizal fungal communities and colonization rates were detected between maple species. Discussion Our findings show that two congeneric plant species grown in close proximity can harbor distinct root microbial communities. These findings provide further support for the importance of plant species in structuring root associated microbe communities. The high colonization levels observed in Norway maple demonstrates its compatibility with arbuscular mycorrhizal fungi in the introduced range. Plant-associated microbial communities can affect host fitness and function in many ways; therefore, the observed differences suggest a possibility that biotic interactions can influence the dynamics between native and invasive species. more...

We used data on a forest-based ecosystem service, sugar maple (Acer saccharum) sap, spanning sugar maple's latitudinal range to predict the role of climate variation on two aspects of sap productivity: sugar content and sap flow. The sugar in maple sap is derived from carbohydrate stores influenced by growing season conditions in the prior year, while sap flow is tied to freeze/thaw cycles during early spring. Our findings suggest optimal regions for sap production will move northward, with lower average production across nearly the entire range except for the far north, and provide spatially-explicit projections for forest managers and syrup producers making decisions on the location and viability of management for maple syrup production. Climate change is affecting the benefits society derives from forests. One such forest ecosystem service is maple syrup, which is primarily derived from Acer saccharum (sugar maple), currently an abundant and widespread tree species in eastern North America. Two climate sensitive components of sap affect syrup production: sugar content and sap flow. The sugar in maple sap derives from carbohydrate stores influenced by prior year growing season conditions. Sap flow is tied to freeze/thaw cycles during early spring. Predicting climate effects on syrup production thus requires integrating observations across scales and biological processes. We observed sap at 6 sugar maple stands spanning sugar maple's latitudinal range over 2–6 years to predict the role of climate variation on sugar content and sap flow. We found that the timing of sap collection advanced by 4.3 days for every 1 °C increase in March mean temperature, sap volume peaked at a January-May mean temperature of 1 °C, and sap sugar content declined by 0.1 °Brix for every 1 °C increase in previous May-October mean temperature. Using these empirical relationships, we projected that the sap collection season midpoint will be 1 month earlier and sap sugar content will decline by 0.7 °Brix across sugar maple's range by the year 2100 in an RCP 8.5 climate change scenario. The region of maximum sap flow is expected to shift northward by 400 km, from near the 43rd parallel to the 48th parallel by 2100. Our findings suggest climate change will have profound effects on syrup yield across most of sugar maple's range; drastic shifts in the timing of the tapping season accompanied by flat to moderate increases in syrup yield per tap in Canada contrast with declines in syrup yield and higher frequencies of poor syrup production years across most of the U.S. range. [ABSTRACT FROM AUTHOR] more...

Background. Biological invasions are major drivers of environmental change that can significantly alter ecosystem function and diversity. In plants, soil microbes play an important role in plant establishment and growth; however, relatively little is known about the role they might play in biological invasions. A first step to assess whether root microbes may be playing a role in the invasion process is to find out if invasive plants host different microbes than neighbouring native plant species. Methods. In this study we investigated differences in root associated microbes of native sugar maple (Acer saccharum Marsh.) and exotic Norway maple (A. platanoides L.) collected from a forested reserve in eastern Canada. We used microscopy to examine root fungi and high-throughput sequencing to characterize the bacterial, fungal and arbuscular mycorrhizal communities of both maple species over one growing season. Results. We found differences in root associated bacterial and fungal communities between host species. Norway maple had a higher bacterial and fungal OTU (operational taxonomic units) richness compared to sugar maple, and the indicator species analysis revealed that nine fungal OTUs and three bacterial OTUs had a significant preference for sugar maple. The dominant bacterial phyla found on the roots of both maple species were Actinobacteria and Proteobacteria. The most common fungal orders associated with the Norway maple roots (in descending order) were Helotiales, Agaricales, Pleosporales, Hypocreales, Trechisporales while the Agaricales, Pleosporales, Helotiales, Capnodiales and Hypocreales were the dominant orders present in the sugar maple roots. Dark septate fungi colonization levels were higher in the sugar maple, but no differences in arbuscular mycorrhizal fungal communities and colonization rates were detected between maple species. Discussion. Our findings show that two congeneric plant species grown in close proximity can harbor distinct root microbial communities. These findings provide further support for the importance of plant species in structuring root associated microbe communities. The high colonization levels observed in Norway maple demonstrates its compatibility with arbuscular mycorrhizal fungi in the introduced range. Plant-associated microbial communities can affect host fitness and function in many ways; therefore, the observed differences suggest a possibility that biotic interactions can influence the dynamics between native and invasive species. Cite this as [ABSTRACT FROM AUTHOR] more...

Temperate forests face a "regeneration debt" reflecting limited tree seedling survival and/or growth. Monitoring demographic processes allows us to identify when and how these debts are incurred and can help identify the factors responsible. If rates of survival and growth are steady, we can easily estimate cohort half-lives and the times it takes cohorts to transit through a range of heights. Dividing the estimated half-life by the transit time yields the Regeneration Ratio (RR). This new metric efficiently integrates survival and growth data into one dimensionless index, facilitating comparisons among regions, treatments, and species. Demographic data from 17 cohorts of white pine (Pinus strobus), sugar maple (Acer saccharum), and eastern hemlock (Tsuga canadensis) seedlings tracked for 7–20 years in the upper Midwest, USA, yielded different half-lives, transit times, and RRs among sites, experimental treatments, and species. Overall, RRs ranged from 0 to 4.8, showing higher sensitivity to local conditions than half-lives or transit times. Half-lives varied significantly among species, dominated variation in RR, and were uncorrelated with growth. Thus, increasing survival may enhance regeneration more than forming gaps to spur growth. Species differ in how RR covaries with transit time and half-life reflecting their distinct physiologies and life-history traits. Within hemlocks, regional differences in white-tailed deer density and forest and wildlife management increasingly affected survival and growth between 1991 and 2011. Tracking at least 50 seedlings for at least 3 years may yield useful estimates. These metrics give managers tools to evaluate and track regeneration success over time and across landscapes, helping them to identify and respond to factors threatening tree regeneration. • Demographic data on tree seedling surival and growth predict recruitment success. • We analyze seedling survival as a cohort's half-life and growth as its transit time through vulnerable sizes. • Dividing a cohort's half-life by its transit time yields a useful comparative metric we term the Regeneration Ratio (RR). • We compare half-lives, transit times, and RR's using field data from white pine, eastern hemlock, and sugar maple. • The Regeneration Ratio provides a convenient, versatile, and sensitive measure of regeneration success. [ABSTRACT FROM AUTHOR] more...