Tree Growth Rates Research Articles

Effect of changes in forest water balance and inferred root reinforcement on landslide occurrence and sediment generation following Pinus radiata harvest on Tertiary terrain, eastern North Island, New Zealand

Background: The frequent occurrence of storm-initiated landslides following harvesting of Pinus radiata D.Don in steep, Tertiary terrain, East Coast region, North Island, New Zealand, is of increasing concern. This paper documents the influence of tree removal and of replacement plantings on the canopy water balance and soil moisture regime when slopes are at their most vulnerable to landslide occurrence. Methods: At a previously established study site, rainfall, throughfall, and soil moisture data were collected before a mature stand of P. radiata was harvested. After harvesting, part of the study site was replanted with P. radiata at 1000 stems ha-1 and part with 500 stems ha-1. Relationships between hydrological changes and landslide occurrence are discussed in relation to planting density, site factors, root system development, silvicultural regimes, and alternative land use options for mitigating erosion in highly erodible hill country. Results: Following harvesting, soil moisture levels remained higher for longer than under a mature forest until rainfall interception and evapotranspiration returned to pre-harvest levels. This coincided with canopy closure, irrespective of planting density. After thinning, interception and evapotranspiration decreased, then regained the equivalent of a closed canopy 2 years later. Landslide occurrence was highest on slopes >25° and with a NE aspect. Sediment generation rates were highest in 2─4-year-old plantings, then decreased markedly with increasing tree age. Conclusions: Irrespective of planting density, P. radiata had little influence on the soil-water regime until canopy interception, evapotranspiration rates, soil-drying and recharge cycles returned to pre-harvest levels, coinciding with canopy closure. During this period, pore-water pressures at times of heavy or prolonged rainfall likely result in soil saturation and an increase in landslides. The progressive loss of root strength of the harvested trees had a secondary influence. The duration of the post-harvest period of heightened slope vulnerability to landslide initiation is a function of the combined influences of site factors on rates of tree growth and survival, and of the planting density regime on the canopy water balance and soil water content until the development of an effective live soil-root reinforcement system. For areas identified as high risk, the targeting of high-value timber species with longer rotation length, including consideration of coppicing species, would minimise the risk of slope failure at harvest. Very high-risk areas unsuited to rotational harvesting will ultimately require transitioning to a permanent indigenous forest cover.

Estimating the net effect of functional traits on fitness across species and environments

Abstract Functional traits affect the demographic performance of individuals in their environment, leading to fitness differences that scale up to drive population dynamics and community assembly. Understanding the links between traits and fitness is, therefore, critical for predicting how populations and communities respond to environmental change. However, the net effects of traits on species fitness are largely unknown because we have lacked a framework for estimating fitness across multiple species and environments. We present a modelling framework that integrates trait effects on demographic performance over the life cycles of individuals to estimate the net effect of traits on species fitness. This approach involves (1) modelling trait effects on individual demographic rates (growth, survival and recruitment) as multidimensional performance surfaces that vary with individual size and environment and (2) integrating these effects into a population model to project population growth rates (i.e., fitness) as a function of traits and environment. We illustrate our approach by estimating performance surfaces and fitness landscapes for trees across a temperature gradient in the eastern United States. Functional traits (wood density, specific leaf area and maximum height) interacted with individual size and temperature to influence tree growth, survival and recruitment rates, generating demographic trade‐offs and shaping the contours of fitness landscapes. Tall tree species had high survival, growth and fitness across the temperature gradient. Wood density and specific leaf area had interactive effects on demographic performance, resulting in fitness landscapes with multiple peaks. With this approach it is now possible to empirically estimate the net effect of traits on fitness, leading to an improved understanding of the selective forces that drive community assembly and permitting generalizable predictions of population and community dynamics in changing environments.

Xylem anatomical and hydraulic traits vary within crown but not respond to water and nitrogen addition in Populus tomentosa

Nitrogen (N) and water availability are the two crucial factors confining tree growth and forest productivity. Irrigation, fertilization, and combined fertigation are commonly applied to plantation forests for improving productivity. However, how xylem vasculature responds to these management practices remains poorly understood. Here we investigated the responses of tree growth, xylem anatomical structure, and hydraulics of the upper, middle, and lower canopy branches in a 6-year-old Populus tomentosa plantation subjected to four years of irrigation and fertigation treatments. The results showed that an improvement in tree growth only occurred in the irrigation treatment while the addition of N in fertigation treatments did not have a cumulative effect on tree growth. Most of the xylem anatomical traits, including vessel hydraulic diameter (Dh), vessel density (VD), vessel fraction (VF), double vessel wall thickness (t), potential specific sapwood hydraulic conductivity (Kp), fiber wall to lumen ratio (Tf/Df), vessel wall reinforcement (t/b)2, and wood density (WD) all showed conserved plasticity to long-term irrigation and fertigation, despite different tree growth rate, implying that aboveground biomass accumulation may have decoupled from the branch-level xylem traits. Besides, the alterations of other factors, including stomatal regulation strategy and crown structure with soil water and N availabilities, might better explain the variation in tree growth. In contrast, greater variations in branch xylem traits were detected across canopy layers. The upper canopy showed greater hydraulic safety characterized by narrower and denser vessels, higher cell wall to lumen ratio, and higher wood density compared to the lower canopy, while hydraulic efficiency (Kp) remained constant across the crown, thus highlighting the priority of hydraulic safety over efficiency in the construction of branch xylem. Overall, our study revealed the response pattern of P. tomentosa xylem structure to long-term water and N management, which facilitates a comprehensive understanding on the mechanisms underpinning the influence of water and nutrients regulation on the performance of fast-growing tree species’ plantations.

Net Climate Effects of Moose Browsing in Early Successional Boreal Forests by Integrating Carbon and Albedo Dynamics

AbstractMoose (Alces alces) is a large herbivore that can mediate boreal forest regeneration after timber harvest through selective browsing of tree species. Despite increasing evidence of moose browsing influence on tree growth in early successional forests, climate effects due to changes in carbon sequestration rates and biophysical factors such as albedo remain largely unexplored. We used 11 years of data from 44 pair‐sites of herbivore exclosures within clear‐cut forests in Norway to investigate how moose browsing alters aboveground tree biomass and albedo. We find a higher total aboveground tree biomass (mainly deciduous species) in unbrowsed than browsed forest plots, as moose browsing limited the growth of tree biomass. The effect of moose exclosure on relative tree abundances differed between sites, suggesting that moose browsing has stronger effects on forest structure than composition. At the same time, moose increased forest albedo relative to un‐browsed forests, driving biophysical cooling. When averaged at regional levels, climate effects due to changes in biomass and albedo are of similar magnitude, but contributions can diverge in specific locations. In a region with intensive forestry operations and high moose density, CO2 emissions from moose browsing in post‐harvested sites can be equal to about 40% of the annual emissions of fossil fuels from that region. Cooling effects from increased albedo can offset about two thirds of this impact. Given its influence on tree growth rates and climate impacts, management of moose browsing density should be integrated into forest management plans to optimize climate change mitigation and forest productivity.

The influence of forest harvesting activities on seismic line tree and shrub regeneration in upland mixedwood boreal forests

Alberta's forests are becoming increasingly disturbed and fragmented by the cumulative effects of anthropogenic disturbances exacerbated by the enduring footprint of seismic lines on the landscape. Forest harvesting and subsequent reforestation activities (e.g., site preparation and tree planting) may facilitate tree growth on seismic lines when forestry companies incorporate them into management areas. In this study, forest regeneration was assessed along transects on and off seismic lines within four cutblocks in northwestern Alberta. Tree, sapling, and shrub characteristics were measured, and tree cookies from a subset of trees on and off seismic lines were used to model height growth. No difference in total tree, sapling, or shrub counts on and off seismic lines was found although trees on seismic lines were growing at slightly slower rates compared to the adjacent cutblock, and Alnus viridis was more abundant on seismic lines. Our results suggest that, despite some species-level differences and modest differences in tree growth rates, trees on seismic lines within cutblocks are regenerating similarly to other trees growing in the post-harvest stand. These findings indicate that forest harvesting, and subsequent reforestation, could represent an important tool in conducting landscape-level restoration in mixedwood forests where seismic lines have not naturally recovered.

Urban tree inventories as a tool to assess tree growth and failure: The case for Australian cities

The delivery of services and benefits provided by urban forests is threatened by tree limited growth, decline and mortality. Determining drivers of tree decline and mortality is challenging but essential in urban forestry planning to reduce environmental and socio-economic losses associated with tree failures. Urban tree inventories (UTI) are essential for managing and monitoring urban forests, which can help to identify successes (i.e., good tree growth/health) and failures (i.e., removals/dead trees). However, UTI are rarely implemented to assess urban tree growth and failure rates. Here, we used UTI from two Australian cities to demonstrate how these inventories can aid in (1) assessing species' relative growth rates and (2) identifying species failures and their determinant. We found UTI are useful to assess tree growth and failures. However, they require recording trees at the time of planting, long-term monitoring (e.g., recording tree size, health), and incorporating management actions (e.g., irrigation, pruning, removals) to inform species performance and improve urban planning and management.

Soil fertility and drought interact to determine large variations in wood production for a hyperdominant Amazonian tree species

IntroductionThe productivity of the Amazon Rainforest is related to climate and soil fertility. However, the degrees to which these interactions influence multiannual to decadal variations in tree diameter growth are still poorly explored.MethodsTo fill this gap, we used radiocarbon measurements to evaluate the variation in tree growth rates over the past decades in an important hyperdominant species, Eschweilera coriacea (Lecythidaceae), from six sites in the Brazilian Amazon that span a range of soil properties and climate.ResultsUsing linear mixed-effects models, we show that temporal variations in mean annual diameter increment evaluated over a specific time period reflect interactions between soil fertility and the drought index (SPEI-Standardized Precipitation and Evapotranspiration Index).DiscussionOur results indicate that the growth response of trees to drought is strongly dependent on soil conditions, a facet of forest productivity that is still underexplored, and which has great potential for improving predictions of future tropical tree growth in the face of projected climate change.

Introduction of non-native Douglas fir reduces leaf damage on beech saplings and mature trees in European beech forests.

Recent ecological research suggests that, in general, mixtures are more resistant to insect herbivores and pathogens than monocultures. However, we know little about mixtures with non-native trees, where enemy release could lead to patterns that differ from commonly observed relationships among native species. This becomes particularly relevant when considering that adaptation strategies to climate change increasingly promote a larger share of non-native tree species, such as North American Douglas fir in Central Europe. We studied leaf damage on European beech (Fagus sylvatica) saplings and mature trees across a wide range of site conditions in monocultures and mixtures with phylogenetically distant conifers native Norway spruce (Picea abies) and non-native Douglas fir (Pseudotsuga menziesii). We analyzed leaf herbivory and pathogen damage in relation to tree diversity and composition effects, as well as effects of environmental factors and plant characteristics. We observed lower sapling herbivory and tree sucking damage on beech in non-native Douglas fir mixtures than in beech monocultures, probably due to a lower herbivore diversity on Douglas fir trees, and higher pathogen damage on beech saplings in Norway spruce than Douglas fir mixtures, possibly because of higher canopy openness. Our findings suggest that for low diversity gradients, tree diversity effects on leaf damage can strongly depend on tree species composition, in addition to modifications caused by feeding guild and tree ontogeny. Moreover, we found that nutrient capacity modulated the effects of tree diversity, composition, and environmental factors, with different responses in sites with low or high nutrient capacity. The existence of contrasting diversity effects based on tree species composition provides important information on our understanding of the relationships between tree diversity and plant-herbivore interactions in light of non-native tree species introductions. Especially with recent Norway spruce die-off, the planting of Douglas fir as replacement is likely to strongly increase in Central Europe. Our findings suggest that mixtures with Douglas fir could benefit the survival or growth rates of beech saplings and mature trees due to lower leaf damage, emphasizing the need to clearly identify and compare the potential benefits and ecological trade-offs of non-native tree species in forest management under ongoing environmental change.

Forest Stand Composition of the Tapanuli Orangutan (Pongo tapanuliensis) Habitat in the Nature Reserves

The Forest areas of Dolok Sipirok Nature Reserve (DSNR) and Dolok Sibual-Buali Nature Reserve (DBNR) are part of Batang Toru forest landscape which is also the habitat of some protected and endangered wildlife such as Tapanuli orangutans (Pongo tapanuliensis). However, the forest has continued to experience widespread pressure and degradation or reduction, mainly due to forest conversion. Therefore, it is very notable to assess the composition of forest vegetation of DSNR and DBNR considering their very important role for the survival of the Tapanuli orangutan populations. The composition of forest vegetation in this research is known by vegetation analysis. The method vegetation analysis used is line transect. The length of the line transect is 1000 m which consists of 10 plots of each transect with a distance between plots of 100 m. Measurements are carried out on the growth rate of seedlings, saplings, poles and trees. Furthermore, the processing of vegetation analysis data is carried out to find out the Important Value Index (IVI), diversity index (H’), evenness (E) and richness (d) of vegetation species in the research area. The results showed that the composition of orangutan habitat vegetation in DSNR consisted of 107 species from 39 families, while DBNR forest consisted of 117 species from 45 families. Tree Syzygium sp1. species consistently have the highest IVI scores at all forest vegetation growth rates of both reserves. The diversity, evenness and richness of DBNR forest vegetation species tends to be higher than DSNR forest.

Automatic Detection of Oil Palm Growth Rate Status with YOLOv5

Oil palm plantations are essential for Indonesia as a source of foreign exchange and a provider of employment opportunities. However, large-scale land clearing is considered a cause of deforestation, which harms the environment and society. So, it is necessary to manage plantations that are sustainable and still maintain the preservation of forests and biodiversity. One solution is to apply remote sensing technology. The research was conducted to develop a multi-class detection method for the growth rate of oil palm trees, with five categories: healthy palm, dead palm, yellowish palm, mismanaged palm, and smallish palm. The deep learning-based object detection method, YOLO Version 5 (YOLOv5), is used. This study compares the YOLOv5 network models, namely YOLOv5s, YOLOv5m, YOLOv5l, and YOLOv5x. Parameter setting is also carried out in the BCE (Binary Cross Entropy) with Logits Loss Function to handle the problem of unbalanced data distribution in each class. The YOLOv5 model with the highest mAP value is the YOLOv5l and YOLOv5x, the YOLOv5x requires longer training time. In this study, hyperparameter optimization was also carried out using hyperparameter evolution techniques. However, it has yet to provide increased results because the experiments conducted in this study are still limited.

RESEARCH ON ANCIENT AND MODERN ENVIRONMENTS IN THE PROGRAMME FOR BELIZE ARCHAEOLOGICAL PROJECT: FOCUS ON VEGETATION

We review research on ancient and modern environments in the Programme for Belize Archaeology Project (PfBAP), focusing on studies of the vegetation. A goal is to show how these studies complement each other. To describe the ancient environment, paleobotany uses fossil pollen, phytoliths, starch grains, and geochemical signatures. In recent research, phytoliths and starch grains are collected from surface samples and paired with geochemical signatures, floral inventories, and contemporary pollen signatures to construct environmental analogues of ancient environments. To study the modern environment, forest ecology uses repeated inventories of tree species in forest stands. These studies have shown how variable the old-growth forests of the area are in in space and in time. Forests range greatly in composition of tree species, tree stem density, number of tree species, and in rates of tree mortality, recruitment, and growth. This variation can be related to underlying variation in soil and slope, and patterns resulting from natural disturbance by flooding and wind. We give examples of synergy between the study of ancient and modern environments in the Maya region that demonstrate fruitful interactions between these disciplines for paleobotanists, ecologists, and archaeologists.

Ramificação lateral em diferentes mudas de macieira pela aplicação de reguladores de crescimento vegetal

Abstract Feathering in apple nursery trees is a critical operation used to increase the quality of planting material. Plant growth regulators (PGR) could be used to form feathers in apple nursery trees. The main goal was to study the impact of different PGR and concentrations on feathering promotion in different nursery apple trees. The study had three different trials where the specific aims were to study the impact of: i) different rates of 6-benzyladenine (6-BA); ii) different PGR (6-BA and 6-BA + GA4+7) on feathering promotion, and; iii) 6-BA on feathering promotion and prohexadione calcium (P-Ca) on trunk thickening under greenhouse conditions. Both 6-BA and 6-BA + GA4+7 were effective inducing feathering in the different cultivars tested. 6-BA reduced final young plants grafted height only in one out of three seasons, reducing an average of 15 and 10 cm on ‘Early Red One’ and ‘Fuji’ apple nursery trees, respectively. P-Ca reduced tree growth rate 4-5 weeks after sprayed, but the difference did not persist until the end of the season. Trunk diameter was not affected by the different plant growth regulators and concentrations tested. 6-BA alone or in combination with GA4+7 is an efficient tool to feathering formation in different nursery apple cultivars and conditions.

Keanekaragaman Jenis Mangrove di Kawasan Hutan Lindung Pakonjawai Kabupaten Sumba Timur

The purpose of this study was to determine the diversity of mangrove species in the Pakonjawai Protected Forest area, East Sumba Regency. The type of research in this study was an ecological descriptive study with a quantitative approach. The sampling technique used was a purposive sampling technique with sampling locations covering 3 observation stations using the line transect method (transect line plot). The results showed that the composition of the mangrove species found consisted of 5 families, 5 genera and 9 species with a total of 337 individuals consisting of 237 individual tree categories, 68 individual saplings and 32 individual seedlings. The mangrove species found were Rhizophora mucronata, Rhizophora apiculata, Rhizopora stylosa, Sonneratia alba, Sonneratia ovata, Avicennia alba, Bruguiera gymnorrhiza, and Sscyphiphora hydrophyllaceae. The diversity index at the tree growth rate was 1.9518, the sampling level was 2.0496 and the seedling level was 1.9588 which means that the diversity of mangrove species is "moderately abundant". The highest Important Value Index (IVI) at tree level was Sonneratia ovata with a value of 71.98 while the sapling level was for Rhizophora mucronata with a value of 38.15 and the seedling level for Rhizophora mucronata with a value of 45.41.

Analysis of Vegetation Analysis in The existing Areas Around in The Landslides in The City of Palopo

The composition and structure of vegetation is one of the parameters that must be considered in forest planning activities. It can also be defined that the structure of vegetation as a result of spatial planning by the components of the stand and the life form of the vegetation which is described through the conditions of diameter, height, distribution in space, canopy diversity, and species continuity. In order to be able to withstand the occurrence of landslides, especially those in sloping areas, it is very important to analyze the vegetation to determine the composition and structure of vegetation types so that the forest is maintained (Fahrul, 2007). The purpose of this study was to determine vegetation in the existing area around the landslides in Palopo city. Research methods. The method of determining plots is purposive sampling, to find out vegetation and tree classification based on the growth rate of the method, namely by making observation plots and placing them by census at the top of 12 landslide points with a size of 20 m x 20 m for trees, 10 m x 10 m for poles, 5 m x 5 m for saplings and 2 m x 2 m for seedlings. The results obtained for the growth rate of trees found 35 species with the highest IVI Litsea sp 95.94%, the growth rate of poles found 28 species with the highest IVI Litsea sp 71.15%, the growth rate of saplings found 62 species with the highest IVI Cinnamomum camphora 45.62 %, and the level of seedlings found 51 species with the highest IVI Nephrolepis cordifolia 40.78%. The biodiversity index found a sapling growth rate with the highest H' value of 3.41 in the high species diversity category. Likewise the highest evenness index on saplings with an E' value of 0.59 is in medium level of evenness.

Accelerated growth rates of Norway spruce and European beech saplings from Europe's temperate primary forests are related to warmer conditions

Global change outcomes for forests will be strongly influenced by the demography of juvenile trees. We used data from an extensive network of forest inventory plots in Europe to quantify relationships between climate factors and growth rates in sapling trees for two ecologically dominant species, Norway spruce and European beech. We fitted nonlinear regression models with annual radial growth measurements from ∼17,500 trees in primary forests to investigate the sensitivity of individuals to temperature and measures of water supply. We controlled for multiple, potentially confounding factors, including ontogeny, resource competition and the deposition of anthropogenic nitrogen and sulphur. The growth potential of spruce was markedly elevated relative to beech, reflecting species-specific relationships with environmental drivers. Declining water availability more strongly limited productivity in spruce, while beech was notably tolerant of observed levels of moisture limitation. Warming promoted growth in both species, but growing season temperatures that exceeded thermally optimum conditions constrained wood production. We identified long-term positive trends in reconstructed annual rates of juvenile tree growth since the early 19th century, likely driven by industrial-era warming. However, our findings suggest that sustained warming and more prevalent future drought may ultimately inhibit growth due to thermal thresholds and a differential tolerance of water stress. Consequently, global change factors may be expected to affect future species abundance patterns, biomass production, and the carbon sink capacity of forests in Europe.

Constitutive and inducible defense in Eucalyptus determines the feeding host of Gonipterus platensis, denoting specific plant-insect coevolution and a strategy for resistance improvement

Defoliation caused by Gonipterus platensis on Eucalyptus seriously impacts tree growth rate and forest production. The weevil’s feeding preference has sometimes limited which species of Eucalyptus to plant, although the plant’s metabolic features that govern such choice still need to be uncovered. We used metabolomics to reveal the chemical traits mediating this interaction, focusing on a model formed by two Eucalyptus species with markedly different susceptibility, E. globulus (susceptible), and E. nitens (resistant). Our results suggest that the insect’s feeding preference strongly depends on the Eucalyptus species’ constitutive metabolome, especially on the stilbenes and hydrolysable tannins accumulation. The susceptible E. globulus could not produce such classes of metabolite either constitutively or after herbivory, which indicated an apparent lack of critical enzymes for biosynthesis of these substances, such as stilbene synthase (STS) and gallate 1-β-glucosyltransferase. On the other hand, it seems that no matter how toxic the systemic defense induced in E. globulus after herbivory could be to an insect, counteradaptations, apparently evolved by the weevil, may efficiently detoxify them. This may result from plant-insect coevolution, given their common geographical origin. Inter-specific hybridizations between E. nitens and E. globulus have adapted hybrid species better to low temperatures and frost conditions, consequently being propagated for plantations in temperate regions. Thus, this research lays the groundwork for selecting the best parent genotypes and obtained hybrids, aiming to warrant the transfer of key resistance traits to progenies as an attractive strategy for future breeding programs.

Soil carbon pools are affected by species identity and productivity in a tree common garden experiment

The formation and turnover of soil organic carbon (C), the largest terrestrial C pool, is strongly impacted by the ultimate source of that C: leaves, wood, roots, and root exudates. The quantity and quality of these inputs is determined by the identity of the plants involved. Yet substantial uncertainty surrounds the complex relationships among plant traits and soil C, precluding efforts to maximize whole-ecosystem C uptake in nature-based climate mitigation scenarios. In this study, we leveraged a biodiversity-ecosystem function experiment with trees (IDENT) to explore the effects of interspecific variation in plant traits on soil C dynamics in the very early stages of stand development (9 years since planting). Mineral soil C stocks to 5 cm depth were quantified in monospecific plots of 19 tree species planted on a former agricultural field, and analyzed in relation to tree growth and functional traits. We found that tree species identity affected soil bulk density and, to a lesser extent, the carbon content of the topsoil, and thereby total C pools. Among species and across plots, mineral soil C stocks were positively correlated with rates of tree growth and were significantly larger beneath broadleaf trees with “fast” functional traits vs. conifers with more conservative leaf traits, when comparisons were made over equivalent soil depth increments. Thus, plant functional traits mediate interspecific differences in productivity, which in turn influence the magnitude of belowground C stocks. These results highlight important linkages between above- and belowground carbon cycles in the earliest stages of afforestation.

Potassium fertilization enhances xylem plasticity and growth recovery of Eucalyptus grandis trees in response to drastic changes in water availability

Most Eucalyptus plantations in Brazil are located in regions currently experiencing periods of water shortage, where fertilizers such as potassium (K) are intensively used to achieve high productivity. In a changing environment, improving our understanding of the effects of K nutrition on tree growth rates and xylem plasticity across tree ages as a function of climate is crucial for forest management. The objective of this study was to gain insight into the interactive effects of K fertilization, water availability, and tree age on stem growth and changes in xylem traits of E. grandis trees over a full rotation. Changes in growth and xylem traits in response to a severe drought that occurred in 2014 were also studied. An experimental plantation of E. grandis trees was established in São Paulo, Brazil and monitored over a full 6-year rotation period. The experiment consisted of a split-plot design with two water supply regimes (37 % throughfall reduction vs undisturbed throughfall) and two fertilization regimes (K supply vs control). Basal area increment (BAI) was monitored using band dendrometers at 14-day intervals from 1 to 6 years after planting. Xylem traits including wood density (WD), cell wall fraction (CWF), cell density (CDen), theoretical xylem specific hydraulic conductivity (Kst), vessel diameter (VD), vessel density (VDen), vessel area (VA), and the vulnerability index (VI) were measured in 6-month periods (rainy and dry seasons) throughout the rotation. K fertilization increased BAI by a factor of 3 in plots where throughfall was not disturbed but led to an interruption of tree growth during the severe drought in 2014. The growth patterns showed a positive effect of K for growth recovery following drought. Throughfall reduction affected growth only in K-fertilized trees and up to 30 months of age. K fertilization also increased changes in xylem traits in response to drought in E. grandis trees. The main changes occurred in vessel traits, with a 53 % decrease in Kst during the drought but recovery was rapid after the first rainfall events. High plasticity was also observed for WD, CWF, CDen, and VI.

Plant hydraulics provide guidance for irrigation management in mature polar plantation

Irrigation is essential for sustaining the productivity of plantation forests in arid, semi-arid, and seasonal drought regions. Current irrigation management is commonly scheduled based on time or soil water status, which often fails to capture plant physiological demand. Here we report on the variation of traits related to plant water use for 7-year-old Populus tomentosa plantations under different irrigation treatments in North China during two growth seasons with contrasting environmental dryness. Plant hydraulics were assessed by stomatal regulation strategy as well as hydraulic traits conferring water transport efficiency and safety, including branch hydraulic conductivity (Ks), thresholds for xylem embolism (Px) and percentage loss of leaf rehydration capacity (PLRC), leaf water potential at turgor loss point (Ψtlp) as well as hydraulic capacitance before and after turgor loss (Cbulk-pre and Cbulk-post respectively). Our results showed that both seasonal increases in rainfall and irrigation could modify stomatal regulation strategy, resulting in a more anisohydric stomatal behavior, but through different underlying mechanisms. Specifically, seasonal variation in stomatal regulation was primarily manipulated by the daily fluctuation of leaf water potential, Ψtlp, and possibly the water supply-demand relationship. At the same time, we speculated that irrigation-dependent alternation was presumably associated with shifted belowground traits. Seasonal variation in hydraulic traits was found for Ks and Ψtlp, with trees in the dry season displaying higher Ks and less negative Ψtlp regardless of irrigation, while other traits governing hydraulic functioning were essentially invariable across seasons or irrigation treatments. Tree growth rate was lower in the wet season and was independent of irrigation, which was likely explained by the occurrence of hydraulic impairment due to less stringent stomatal control. Overall, our results suggest that limited precipitation and high atmospheric vapor pressure deficit in the dry season would not compromise tree growth because of the tighter stomatal control, while hydraulic dysfunction could occur in the wet season due to excessive water use strategy, subsequently perhaps contributing to the reduction in growth rate. The findings of this study underscore the usefulness of physiological traits in guiding irrigation management and advocate reconsidering plantation water management strategy based on reliable indicators.

Aging phenomena in non-crosslinked polyolefin blend cable insulation material: Electrical treeing and thermal aging.

Non-crosslinked polyolefin blends have become a favorable alternative material to crosslinked polyethylene (XLPE) cable insulation owing to their low power consumption in the production process and good recyclability at the end of service life. Although studies on non-crosslinked materials have achieved significant results, the electrical and thermal aging properties of these materials undeniably need extensive research attention and systematic exploration. Aging performance is directly related to the lifetime and reliability of cables. In this study, the electrical treeing and thermal aging phenomena of 70wt.% linear low-density polyethylene (LLDPE) and 30wt.% high-density polyethylene (HDPE) blends (abbreviated as 70L-30H) were studied and compared with those of XLPE by investigating the microstructural feature, electrical treeing behavior, and mechanical performance during thermal aging. Electrical treeing tests show that 70L-30H blends exhibited smaller treeing dimensions and lower electrical tree growth rates than those of XLPE. Thermal aging tests exhibit that the mechanical property degradation of 70L-30H blends is less than that of XLPE under the same aging time. Through differential scanning calorimetry analysis and microstructure observation, the 70L-30H blend shows higher melting temperature, thicker lamellae, and higher crystallinity with a uniform and fine spherulite structure, which are responsible for good anti-aging performance. This study indicates that the blends exhibit better electrical and thermal aging resistance than XLPE, which provides a performance guarantee for its further application in the non-crosslinked cable system.