Tree Growth Rates Research Articles

Modeling of the Spatial Distribution of Forest Carbon Storage in a Tropical/Subtropical Island with Multiple Ecozones.

Visual data on the geographic distribution of carbon storage help policy makers to formulate countermeasures for global warming. However, Taiwan, as an island showing diversity in climate and topography, had lacked valid visual data on the distribution of forest carbon storage between the last two forest surveys (1993-2015). This study established a model to estimate and illustrate the distribution of forest carbon storage. This model uses land use, stand morphology, and carbon conversion coefficient databases accordingly for 51 types of major forests in Taiwan. An estimation in 2006 was conducted and shows an overall carbon storage of 165.65 Mt C, with forest carbon storage per unit area of 71.56 t C ha-1, where natural forests and plantations respectively contributed 114.15 Mt C (68.9%) and 51.50 Mt C (31.1%). By assuming no change in land use type, the carbon sequestration from 2006 to 2007 by the 51 forest types was estimated to be 5.21 Mt C yr-1 using historical tree growth and mortality rates. The result reflects the reality of the land use status and the events of coverage shifting with time by combining the two forest surveys in Taiwan.

Effect of Tree Size Heterogeneity on the Overall Growth Trend of Trees in Coniferous Forests of the Tibetan Plateau

Tree growth is under the combined influence of abiotic and biotic factors. Trees with different sizes may respond differently to these factors, implying that tree size heterogeneity may also modulate the overall growth trend. To test this hypothesis, we focused on the radial growth trends of natural subalpine forests on the Tibetan Plateau. We first extended the iterative growth model (IGM) to the tree ring scale (IGMR) to test the applicability of the generalized metabolic growth theory to tree growth. As predicted by the IGMR, the radial growth of trees at the aggregate scale is constrained by a unimodal pattern. Using the IGMR, we reconstructed the historical best growth trajectory (HBGT) of trees within the same community based on the tree with the largest radius and/or longest age in the community. From the average difference between the HBGT and the current radial growth rate of trees with different sizes, we constructed an indicator that can measure the overall variation in tree radial growth. Based on this indicator, we found a negative effect of tree size heterogeneity on the overall variability of tree growth across elevations. Further analysis also revealed that the radial growth rate of trees on the Tibetan Plateau has increased significantly compared to the past, where the growing season average temperature and annual minimum temperature were negatively and positively correlated with tree growth below and above the treeline, respectively. Our study not only confirmed that the overall variability of tree growth depends on tree size heterogeneity but also proposed an indicator that reveals net changes in the tree radial growth rate relative to the past. These theoretical advances are highly beneficial for understanding changes in the extent of subalpine forests.

Multiplex CRISPR editing of wood for sustainable fiber production.

The domestication of forest trees for a more sustainable fiber bioeconomy has long been hindered by the complexity and plasticity of lignin, a biopolymer in wood that is recalcitrant to chemical and enzymatic degradation. Here, we show that multiplex CRISPR editing enables precise woody feedstock design for combinatorial improvement of lignin composition and wood properties. By assessing every possible combination of 69,123 multigenic editing strategies for 21 lignin biosynthesis genes, we deduced seven different genome editing strategies targeting the concurrent alteration of up to six genes and produced 174 edited poplar variants. CRISPR editing increased the wood carbohydrate-to-lignin ratio up to 228% that of wild type, leading to more-efficient fiber pulping. The edited wood alleviates a major fiber-production bottleneck regardless of changes in tree growth rate and could bring unprecedented operational efficiencies, bioeconomic opportunities, and environmental benefits.

TREE HEALTH ASSESSMENT FOR ROADSIDE TREE IN KOTA KINABALU CITY CENTRE, SABAH

This study aimed to assess the health of main tree in the Kota Kinabalu City Centre, Sabah. In this study, principal evaluation standards were made by using visual observation of trees or Visual Tree Assessment (VTA). This study was conducted to identify any effect of damage or defect on trees via the observation of trees at their roots, stems, branches and leaves. There were five zones in the study area, namely from KK Lama and Jesselton Point (Zone 1) to Pasar Besar. The tree health parameters were evaluated from the presence of pests and diseases, trees health, foliage colour, the growth rate of trees, infections of the trees and potential failure of tree roots. In this study, nine of pathogens, pests and diseases of trees were observed, which were termites, fungi, aphid, mushrooms, epiphytes, parasites, ants, weeds and Whiteflies. This study showed that there were 23 species from the 688 stand of trees in the study area. The study found that the state average foliage colour was normal, a moderate growth rate and infection of the tree was still under controlled. The potential failure of tree root was found in low level as well. In a nutshell, the overall health of trees was found to be in good and moderate levels. This study was conducted as a reference in health detection of tree for The City Hall management (DBKK) and also as a reference for University students in conducting tree health assessment.

Pojava ženki velikog smrekinog likotoča Dendroctonus micans (Kugelann, 1794) na vitalnim stablima kavkaske smreke u Artvinu, Turska

Dendroctonus micans (Kugelann, 1794), which was first discovered in 1966 in Turkey, has established almost in all oriental spruce forests in the Eastern Black Sea region until the late 2000s. In its expanding front it is responsible for killing spruce trees representing millions of cubic meters of wood. In recent years, oriental spruce forests have endemic population of this pest. But extreme climatic conditions that cause extreme weather circumstances may trigger suitable environment that favors D. micans outbreaks. In this study, we aimed to examine tree vitality of naturally infested and uninfested trees in the forest. Field studies were performed at a pure spruce stand in Taşlıca Forest Sub-District, Artvin Directorate of Forestry in 2016. Both infested and uninfested trees were selected in the stand closure. One core per tree was extracted from 30 naturally infested and 30 uninfested oriental spruce trees at the same stand. Core samples were taken at the second week of September. Phloem thickness, recent tree growth rates, diameter of breast height and the average number of xylem cells in a radial file formed until the sampling date were studied. Phloem thickness, recent tree growth rates and number of xylem cells were higher in infested trees. Host selection of D. micans was discussed in relation to characteristics of infested and uninfested trees.

Field Performance of ‘Valencia’ Sweet Orange Trees Grafted onto Pummelo Interstocks and Swingle Citrumelo Rootstocks under Huanglongbing (HLB) Endemic Conditions

Interstocks have been used in fruit tree cultivation to regulate tree size and improve fruit production and quality. In this study, several Huanglongbing (HLB)-tolerant open-pollinated pummelo interstock candidates were evaluated as interstocks between the Swingle rootstock and the ‘Valencia’ scion, with Swingle serving as the control interstock. After 5 years in the field, most trees did not exhibit visual HLB symptoms, although the trees were infected with HLB, and the CaLas Ct values in the ‘Valencia’ leaves of the different interstock treatments ranged between 25.88 and 27.82. Although the foliar chlorophyll content among the interstock treatments was not highly significant (p-value = 0.0313), the foliar starch content was significantly different (p-value = 0.0018). ‘Valencia’ grafted onto 5-1-99-3 and HBJL-4 interstocks (both open pollinated seedlings of the Hirado Buntan pummelo) exhibited the highest total phenolic compound (TPC) levels (46.44 and 46.36 mg gallic acid g−1 FW). Transcripts of CsPR1 and CsPR2, two pathogenesis-related (PR) genes, were upregulated in ‘Valencia’ grafted onto open pollinated seedling selections of the red shaddock pummelo, Liang Ping Yau pummelo, and Hirado Buntan pummelo compared with ‘Valencia’ grafted onto Swingle. All interstocks influenced the tree growth rate and improved canopy volume in the field compared to the control trees without any interstocks (p-value = 0.0085). The 5-4-99-7 (red shaddock pummelo) and 8-1-99-1B (Liang Ping Yau pummelo) interstock trees had the highest canopy volume among all the treatments. We propose, based on our current results, that HLB-tolerant citrus accessions, when judiciously used as interstocks, may enhance plant defense and provide increased HLB tolerance to susceptible scions.

Root and branch hydraulic functioning and trait coordination across organs in drought-deciduous and evergreen tree species of a subtropical highland forest.

Vessel traits are key in understanding trees' hydraulic efficiency, and related characteristics like growth performance and drought tolerance. While most plant hydraulic studies have focused on aboveground organs, our understanding of root hydraulic functioning and trait coordination across organs remains limited. Furthermore, studies from seasonally dry (sub-)tropical ecosystems and mountain forests are virtually lacking and uncertainties remain regarding potentially different hydraulic strategies of plants differing in leaf habit. Here, we compared wood anatomical traits and specific hydraulic conductivities between coarse roots and small branches of five drought-deciduous and eight evergreen angiosperm tree species in a seasonally dry subtropical Afromontane forest in Ethiopia. We hypothesized that largest vessels and highest hydraulic conductivities are found in roots, with greater vessel tapering between roots and equally-sized branches in evergreen angiosperms due to their drought-tolerating strategy. We further hypothesized that the hydraulic efficiencies of root and branches cannot be predicted from wood density, but that wood densities across organs are generally related. Root-to-branch ratios of conduit diameters varied between 0.8 and 2.8, indicating considerable differences in tapering from coarse roots to small branches. While deciduous trees showed larger branch xylem vessels compared to evergreen angiosperms, root-to-branch ratios were highly variable within both leaf habit types, and evergreen species did not show a more pronounced degree of tapering. Empirically determined hydraulic conductivity and corresponding root-to-branch ratios were similar between both leaf habit types. Wood density of angiosperm roots was negatively related to hydraulic efficiency and vessel dimensions; weaker relationships were found in branches. Wood density of small branches was neither related to stem nor coarse root wood densities. We conclude that in seasonally dry subtropical forests, similar-sized coarse roots hold larger xylem vessels than small branches, but the degree of tapering from roots to branches is highly variable. Our results indicate that leaf habit does not necessarily influence the relationship between coarse root and branch hydraulic traits. However, larger conduits in branches and a low carbon investment in less dense wood may be a prerequisite for high growth rates of drought-deciduous trees during their shortened growing season. The correlation of stem and root wood densities with root hydraulic traits but not branch wood points toward large trade-offs in branch xylem towards mechanical properties.

Dynamically simulating spruce budworm in eastern Canada and its interactions with wildfire

Eastern Spruce Budworm (ESBW) is a major agent of disturbance in Eastern Canada's boreal forests. Outbreaks have historically led to widespread defoliation of its preferred host trees, fir and spruce species, leading to high rates of mortality. This in turn can result in significant economic losses and enhancement of fire potential in the region. Representation of such biotic disturbance has rarely been included in Dynamic Global Vegetation Models (DGVM), which have become essential tools in understanding and predicting forest dynamics in present and future contexts. We present novel representation of host-specific defoliation in a DGVM (LPJ-LMfire), to better represent disturbance regimes in the boreal forest of eastern Canada. Using host foliage density to trigger outbreak, we were able to calibrate and simulate general spatial patterns of defoliation relative to historical aerial sketch map data. Return intervals were thus sensitive to the growth rates of host trees. Modeled return intervals tended to be significantly longer than 30 years, the approximate observed return interval. A factorial experiment was performed on the interactions of ESBW with wildfire, which was found to be slightly enhanced in terms of burned areas after outbreaks due to increased fuel loads. Interactions between ESBW and fire were found to have higher interaction strength in the drier Western region of the boreal forest. Our study demonstrates that biotic disturbance and its interaction with wildfire can be effectively simulated in a DGVM. We show that bottom-up climatic controls are sufficient to drive simulated spatiotemporal patterns of ESBW that can be calibrated to generally match historical observations.

Effects of site productivity on individual tree maximum basal area growth rates of Eucalyptus pilularis in subtropical Australia

Inventory data were available from 96 plots of even-aged, monoculture, tall-open forests of Eucalyptus pilularis Smith, aged 2–63 years, growing in sub-tropical regions along the east coast of Australia. A model was developed relating the maximum possible stem basal area growth rate of individual trees to their stem basal area. For any tree size, this maximum increased as site productivity increased. However, the size at which this maximum occurred decreased as productivity increased. Much research has shown that, at any stand age, trees of a particular stem basal area are taller on more productive sites than on less productive ones. Taller trees incur greater respiratory costs to ensure maintenance of the photosynthetic capacity of their canopies; this reduces their growth rates. It was concluded that trees with larger basal areas will have the maximum possible growth rate on a less productive site, whilst trees with smaller basal areas will have the maximum possible on a more productive site. The model developed may constitute the first stage of a complete individual tree growth model system to predict wood yields from these forests.

Composition and similarity of vegetation types in the Mount Seulawah Agam geothermal area, Aceh Besar District

The Mount Seulawah Agam area is an active volcanic area that has an impact on the emergence of symptoms of volcanism. Such environmental conditions will cause the vegetation that grows in the area to be unique and not commonly found in other areas. Apart from that, the area is still relatively natural and has not experienced much disturbance by human activities. This study aims to determine the composition and similarity of vegetation types in the geothermal area of Mount Seulawah Agam, Aceh Besar District. Data collection in the field was carried out using the multiple square method which was placed in a stratified sampling based on the specified soil temperature zone. Each zone was laid out in 4 square plots in a systematic random manner. Each plant contained in the observation plot is recorded in the name of the plant species using a flora identification book, and the number of individuals of each type is recorded. Data analysis was carried out using the Important Value Index analysis, and the Sorenson Similarity Index. The results showed that there were 65 species from 611 individual plants identified starting from the growth rate of seedlings, sapling, poles, and trees. The similarity index of plant species at each growth stage in the Seulawah Agam geothermal area, Aceh Besar District generally has different species similarity in each observation zone, that is, the average is below 50%. This condition indicates that there are significant differences in plant structure at various growth rates in each zone

Influences of fern and vine coverage on the above-ground biomass recovery in a Bornean logged-over degraded secondary forest

ABSTRACT Tropical secondary forests are widespread in the anthropogenically modified landscapes. Because tropical secondary forests were known to show a steady rate of above-ground biomass (AGB) recovery, they were expected to play a crucial role in carbon sequestration. However, in a preliminary survey of logged-over forests in Borneo, some patches covered with ferns and vines do not seem to recover steadily despite the fact that several decades have passed since the last logging. The presence and abundance of fern/vine thickets may affect the AGB recovery, but few studies have investigated the effects of the thickets. We established a total of seventeen 20-m radius circular plots in logged-over forests, Sabah, Malaysia, with a varying degree of fern/vine coverage, and tested the hypothesis that the greater fern/vine coverage would retard the AGB recovery. The net AGB accumulation rate from 2014 to 2019 was lower in the forests with a higher fern/vine coverage. Our lower bound of the accumulation rate was much lower than the previously reported rates elsewhere. The number of newly recruited and small-diameter trees was lower, and the mortality of remnant trees was higher with increasing fern/vine coverage. The growth rate of the extant pioneer trees, which are expected to significantly contribute to the initial build-up phase of the secondary succession, was inhibited when ferns and vines covered the canopy. Our study suggests that the secondary succession is arrested and the recoverability of forest stands is lower than formerly predicted when they are covered by thick ferns and vines.

Savanna tree regrowth after defoliation explained by bud activation rather than reserve mobilization

Livestock rearing is increasing in savannas, so the ability of trees to regrow after consumption represents one of the critical aspects of savanna structure and functioning. Here, we identified specific traits—which may explain the mechanisms behind defoliation tolerance—in saplings of two encroacher tree species (Vachellia caven and Vachellia aroma). We carried out common garden and field experiments where manual defoliation treatments simulated the cattle grazing regime employed in the study region. At the end of the experiments, we recorded growth variables and, in the common garden experiment, root reserves concentration. In the common garden, defoliation decreased height and basal diameter growth but did not affect the aerial relative growth rate. Also, defoliation increased the number of branches per plant and decreased root relative growth rate. Starch concentration was higher or similar in defoliated plants than controls, depending on the species. In the field, defoliation decreased both species’ height and basal diameter growth. We found that tree saplings tolerated defoliation, and the mechanisms behind tolerance would be linked mainly to the axillary bud activation and not to storage reserve mobilization. Over time, these plant architectural changes might complicate cattle movement and management in these systems. From a long-term perspective, livestock rearing might retard juvenile recruitment into reproductive-size classes (e.g., adults) by reducing overall tree growth rates.

Developing Integrated Strategies to Address Emerging Weed Management Challenges in Christmas Tree Production

Weed control is an important aspect during the first few years of Christmas tree establishment, as weed competition directly relates to the rate of Christmas tree growth during this time. The objectives of this study were to evaluate the weed control efficacy of organic mulch and herbicide combinations and to determine their phytotoxic effects on four different species of Christmas trees during the establishment stage: Fraser fir (Abies fraseri (Pursh) Poir), blue spruce (Picea pungens Engelm.), white pine (Pinus strobus L.), and Scotch pine (Pinus sylvestris L.). Twelve weed control treatments were established in a complete randomized block design with four replications in each of five fields. Weed control treatments included cypress bark organic mulch and herbicides applied alone and in combinations as well as an untreated control. Herbicides included clopyralid, oxyfluorfen, and glyphosate. All herbicides were applied at their highest labeled rate. Data collection included visual estimations of weed control and phytotoxicity to trees at 30, 60, and 90 days after treatment (DAT). Tree growth and foliar nitrogen concentration were also measured. Mulch combined with herbicide provided 60%–100% weed control in all cases; at two farms, mulch provided a significant increase in weed control when compared to the same treatments without mulch. Combinations of mulch + clopyralid + glyphosate and clopyralid + oxyfluorfen + glyphosate resulted in the highest phytotoxicity ratings. Tree growth was decreased due to some treatments at Gobles farm, and foliar N did not differ among any of the treatments.

A comprehensive resilience assessment of Mexican tree species and their relationship with drought events over the last century.

The resilience of forests to drought events has become a major natural resource sustainability concern, especially in response to climate change. Yet, little is known about the legacy effects of repeated droughts, and tree species ability to respond across environmental gradients. In this study, we used a tree-ring database (121 sites) to evaluate the overall resilience of tree species to drought events in the last century. We investigated how climate and geography affected the response at the species level. We evaluated temporal trends of resilience using a predictive mixed linear modeling approach. We found that pointer years (e.g., tree growth reduction) occurred during 11.3% of the 20th century, with an average decrease in tree growth of 66% compared to the previous period. The occurrence of pointer years was associated with negative values of the Standardized Precipitation Index (SPI, 81.6%) and Palmer Drought Severity Index (PDSI, 77.3%). Tree species differed in their resilience capacity, however, species inhabiting xeric conditions were less resistant but with higher recovery rates (e.g., Abies concolor, Pinus lambertiana, and Pinus jeffreyi). On average, tree species needed 2.7 years to recover from drought events, with extreme cases requiring more than a decade to reach pre-drought tree growth rates. The main abiotic factor related to resilience was precipitation, confirming that some tree species are better adapted to resist the effects of droughts. We found a temporal variation for all tree resilience indices (scaled to 100), with a decreasing resistance (-0.56 by decade) and resilience (-0.22 by decade), but with a higher recovery (+1.72 by decade) and relative resilience rate (+0.33 by decade). Our results emphasize the importance of time series of forest resilience, particularly by distinguishing the species-level response in the context of legacy of droughts, which are likely to become more frequent and intense under a changing climate.

A Multifaceted Evaluation Approach for Greek Native Neglected and Underutilized Forest Fruit Trees and Shrubs as Natural Sources of Antioxidants: Consolidating the Framework for Their Sustainable Agronomic Exploitation.

Fruits from wild forest trees and shrubs represent a natural source of antioxidants against oxidative stress and a growing market for novel minor crops. This study presents a multifaceted approach which sets the basis for sustainable agronomic exploitation of selected Greek native germplasm of four traditional but neglected and underutilized forest fruit trees and shrubs, namely Amelanchier ovalis Medik., Cornus mas L., Rosa canina L., and Sambucus nigra L. The studied plant species are traditionally used in Greek ethnobotany but are currently neglected and underutilized in commercial terms, thus characterized as neglected and underutilized plant species (NUPs). The investigation includes new information on the evaluation of the ex situ cultivation of the Greek germplasm (three of the four focal NUPs), thus supplementing respective full datasets for their comparative evaluation based on four evaluation axes (documentation and molecular authentication of genotypes, phytochemical evaluation, asexual propagation via rooting of cuttings, and ex situ cultivation) after multi-year and multifaceted groundwork data previously acquired. Consecutively, the work includes feasibility and readiness timescale evaluation for the sustainable exploitation of each focal species based on existing literature and extant research experience. The feasibility for sustainable exploitation and readiness timescale evaluation results were very encouraging, showing high exploitation feasibility with an already achieved readiness timescale for R. canina and S. nigra, whereas C. mas and A. ovalis showed an achievable readiness in the short term. The comparative evaluation of the Greek native focal NUPs outlined the excellent potential of R. canina, S. nigra, and A. ovalis, and the high potential of C. mas. The results herein illustrate the very high fruit antioxidant potential (free radical scavenging activity) of all focal species, the diverse but effective asexual propagation capacity via cuttings at the species level, and summarize the results of a pilot cultivation trial set up in 2020 (still ongoing) outlining tree growth rates and the onset of fruit production among genotypes and species. Overall, the meta-analysis of previously published data in conjunction with new data generated herein may serve the sustainable exploitation of the studied NUPs.

Cover legumes promote the growth of young rubber trees by increasing organic carbon and organic nitrogen content in the soil

Cover crops are often intercropped in rubber plantations to improve utilization of understory space; however, how cover crops promote the growth rate (GR) of young rubber trees remains unclear, as these are largely dependent on the growth time and varieties of cover crops. We conducted a five-year experiment with five cover crop treatments of no cover crop (CK) and cover with four varieties of perennial leguminous crops, namely, Stylosanthes guianensis Reyan No. 2 (RY2), Reyan No. 5 (RY5), Reyan No. 7 (RY7), and Reyan No.10 (RY10). We analyzed changes in total organic carbon (TOC), total nitrogen (TN), and the fractions of labile organic carbon (LOC), mineral nitrogen (MN), and organic nitrogen (ON) in understory soil of young rubber plants (Hevea Brisiliensis cv. Reyan 7–33–97) in tropical China and their effects on the GR. The results showed that cover year and cover crop varieties significantly affected soil TOC, LOC fractions, TN, MN, and ON fractions, as well as GR. Compared to CK, the five-year average GRs of rubber trees covering the RY2, RY5, RY7, and RY10 increased by 12.8%, 41.5% 30.0%, and 43.1%, respectively. Compared with CK, the five-year average nutrients of RY5 and RY10 all increased after covering, whereas the soil NH4+-N of RY2 decreased by 0.3%. Meanwhile, the soil TOC, TN, acid-hydrolyzable ammonium nitrogen (AN), and amino acid nitrogen of RY7 decreased by 10.1%, 13.4%, 6.7%, and 21.3%, respectively. The soil nutrients all show a good linear relationship with GR. We identified TN and MN as the main nutrients for the growth of young rubber plants through linear regression and stepwise regression. In addition, structural equation modeling indicated that TOC was the carrier of nitrogen transformation and utilization in soil. The total effects of TOC, AN, and NH4+-N on GR of rubber trees were 0.55, 0.52, and 0.31, respectively. The results demonstrated that RY5 and RY10 are suitable for young rubber plantation in tropical China as these effectively improved soil nitrogen supply potential, improved soil fertility, and promoted the GR of young rubber trees.

Effects of Gradient Magnetic Field on Electrical Tree Growth Characteristics in Silicone Rubber

In this article, the positive and inverse gradient symmetric magnetic field and the asymmetric magnetic field with different angles are constructed. The influence of the magnetic field distribution on the electrical tree characteristics is investigated. The experimental results show that both the positive and the inverse gradient magnetic fields can promote the deterioration of the electrical trees. Under the symmetrical <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta 1.5$ </tex-math></inline-formula> T gradient magnetic field, the tree initiation probability increases from 55% to 100%, and the breakdown time decreases by 67.5%. Under the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta $ </tex-math></inline-formula> -1.5 T, the tree initiation probability increases from 55% to 75%, and the breakdown time declines by 57.5%. The morphology of the electrical trees is largely affected by the distribution of the magnetic field. The dispersion of the degradation channels increases with the enhancement of the magnetic field. Under the asymmetric magnetic field, the deterioration process is also accelerated, with the increase of the magnetic field. More importantly, the growth direction of the electric trees shifts to the side with the higher magnetic flux density. The magnetic field enhances the local electric field and promotes the occurrence of partial discharge by exerting a deflection force on the charges. Consequently, the growth rate and morphology of electrical trees are affected.

Mitigation of electrical treeing at high temperature in nano‐SiO2 doped epoxy resin

AbstractIn this work, electrical tree inception and ageing experiments were conducted to investigate the initiation, growth characteristics and structural characteristics of electrical trees of nano‐SiO2 doped epoxy resin at different temperatures. Electrical tree inception and ageing experiments were conducted using power frequency voltage of 15 kV at 20, 40, 60, 80 and 100°C. Electrical breakdown properties of epoxy resin were investigated by applying AC and DC voltages at 20, 40, 80 and 120°C. There are two major observations based on the experimental results. With the increase of temperature, the morphological structure of the electrical trees changes from dendritic to plexiform, the tree inception voltage decreases and the growth rate of the electrical trees increases obviously. Either under DC or AC voltage, the breakdown strength of the nano‐SiO2 doped epoxy resin decreases as the temperature increases. Finally, based on the space charge and the trap level measurement, the mechanism of the electrical tree propagation and breakdown in nano‐SiO2 doped epoxy resin was analysed.

Plant growth strategy determines the magnitude and direction of drought-induced changes in root exudates in subtropical forests.

Root exudates are an important pathway for plant-microbial interactions and are highly sensitive to climate change. However, how extreme drought affects root exudates and the main components, as well as species-specific differences in response magnitude and direction, are poorly understood. In this study, root exudation rates of total carbon (C) and its components (e.g., sugar, organic acid, and amino acid) were measured under the control and extreme drought treatments (i.e., 70% throughfall reduction) by in situ collection of four tree species with different growth rates in a subtropical forest. We also quantified soil properties, root morphological traits, and mycorrhizal infection rates to examine the driving factors underlying variations in root exudation. Our results showed that extreme drought significantly decreased root exudation rates of total C, sugar, and amino acid by 17.8%, 30.8%, and 35.0%, respectively, but increased root exudation rate of organic acid by 38.6%, which were largely associated with drought-induced changes in tree growth rates, root morphological traits, and mycorrhizal infection rates. Specifically, trees with relatively high growth rates were more responsive to drought for root exudation rates compared with those with relatively low growth rates, which were closely related to root morphological traits and mycorrhizal infection rates. These findings highlight the importance of plant growth strategy in mediating drought-induced changes in root exudation rates. The coordinations among root exudation rates, root morphological traits, and mycorrhizal symbioses in response to drought could be incorporated into land surface models to improve the prediction of climate change impacts on rhizosphere C dynamics in forest ecosystems.

Radial growth in mangrove Xylocarpus granatum J. Koenig is driven by salinity in the Sundarbans, Bangladesh

Albeit the Sundarbans provides protection and livelihood supports to ∼ 7.5 million climate vulnerable coastal people in Bangladesh and India, this sentinel mangrove ecosystem has been threatened by anthropogenic disturbances and rapid environmental changes including sea level rise (SLR). In this context, long-term tree growth data are increasingly essential to understand the effects of environmental changes on mangroves and also to formulate their management plans. In this study, we evaluate the nature and periodicity of growth rings in Xylocarpus granatum, an ecologically important mangrove tree species growing in the Bangladesh Sundarbans. In addition, we analyze the influences of climatic variables (i.e., precipitation and temperature) and river discharge on its radial growth. The results reveal that X. granatum forms distinct growth rings which are marked by a layer of parenchyma band consisting of 1–4 cells. The visual crossdating and the quality of chronology statistics indicate that the growth rings are crossdatable. A site-specific chronology was developed spanning from 1973 to 2020 based on the crossdated samples. The annual nature of X. granatum’s growth rings offer an opportunity to estimate tree age and growth rate. The ring width is influenced by salinity which is regulated mainly by freshwater influx through annual precipitation along with river discharge, particularly in July. This study suggests that growth rings could be used as a proxy in exploring X. granatum’s growth dynamics, especially in relation to environmental changes.