Increasing Tree Height Research Articles

Groundcover improves nutrition and growth of citrus trees and reduces water runoff, soil erosion and nutrient loss on sloping farmland

IntroductionGroundcover management plays a crucial role in improving water retention and soil nutrition in orchard systems, thereby preventing environmental constrains by non-point source pollution. However, effectiveness of groundcover management in citrus orchards developed on sloping farmland with eroded purple soil has not been studied in detail. In particular, information on the soil nutrient losses, e.g., nitrogen (N) and phosphorus (P), through interflow and its effects on growth and nutrition of citrus plants has not been reported.MethodsThe present study evaluated the effects of different cover crops, i.e., Lolium perenne L. (Lolium), Vicia villosa Roth (Vicia) and Orychophragmus violaceus (Ory), on nutrition and growth of citrus trees as well as water, soil and nutrient retention in an orchard developed in sloping farmland during two consecutive years.Results and discussionThe results show that the groundcover species Lolium and Vicia mediated nursing effects on nutrition and growth of citrus trees. These nursing effects included enhanced foliar levels of carbon(C), N and P as well as increased tree height, stem diameter, and crown width. Groundcover management generally reduced the annual surface runoff, interflow, soil loss, total N loss and total P loss. Among the cover crop species studied, Lolium and Vicia were overall more efficient than Ory in this context. Lolium reduced the average annual total loss of N and P by 42.53% and 49.23%, respectively, compared with clean tillage. The estimated annual reduction potentials of soil, N and P losses in Southwestern China were 16.3, 3.4 and 8.5 million tons yr-1, respectively. Obviously, Lolium and Vicia provide highly beneficial ground coverage on sloping farmland and, thus, can be used for future sustainable development of citrus orchards.

A comprehensive framework to evaluate the financial impacts of genetic improvement on wood products from planted forests

Increasing the productivity of planted forests may efficiently provide an important part of the world’s growing demand for wood while protecting natural forests. In this study, we developed an integrated modelling framework to evaluate the financial impacts of improving productivity of planted forests by tree breeding. Using this framework, we compared three genetic improvement scenarios of white spruce plantations, a key reforestation species in North America, and evaluated the differences in the derived wood product assortments in terms of quantity, quality, and revenues. Favouring the production of wood volume appears as the best way to enhance financial gains from white spruce plantations in the current market. The scenario that focused on increasing tree height produced a greater volume of wood products and larger lumber pieces, which resulted in the greatest revenues. In comparison, favouring wood stiffness over volume led to poorer results, as the increased product quality was not sufficient to surpass the financial gain associated with greater wood volumes. While we successfully provided an evaluation of the product assortments derived from genetically improved plantations, the proposed framework would benefit from more data input to help maximize financial gains from a range of tree breeding strategies.

Nutrient Stoichiometry and Tree Development: Insights from a 5-Year Study on Catalpa bungei Fertilization

Short-term fertilization may provide limited improvements in tree growth and demonstrate suboptimal fertilizer efficiency; however, its benefits often fall short of expectations. Unfortunately, research addressing the sustained impacts of prolonged fertilization (e.g., beyond five years) on trees’ developmental dynamics and productivity remains relatively scarce. This study focused on a 7-year-old Catalpa bungei plantation located in Jinan City, Shandong Province, China. The study employed two fertilization techniques: hole fertilization (HF) and integrated water and fertilizer application (WF), with a no-fertilization treatment serving as the control (CK). The findings revealed that the WF significantly enhanced stand productivity. When comparing the different treatments, the productivity of WF stands demonstrated a remarkable increase of 39.7% compared to HF stands and 55.1% compared to CK stands. After five years of fertilization, the stands treated with WF exhibited a significant increase in volume accumulation, reaching 112.36 m3·hm−2. Additionally, the productivity of these WF-fertilized stands achieved an impressive 41.75 m3·hm−2·a−1. Fertilization notably enhanced the nitrogen content in the leaves and fine roots of C. bungei, as well as the potassium content in the coarse roots. These nutrients were found to be more concentrated in the corresponding organs within the WF stands. Over the entire growth cycle, there was a substantial consumption of key nutrients, with leaf nitrogen, phosphorus, and potassium contents decreasing by 30.5%, 18.8%, and 47.3%, respectively. Similarly, the coarse root potassium and fine root phosphorus content decreased by 24.7% and 24.4%, respectively. The enhancement in leaf nitrogen content following fertilization significantly contributed to increases in tree height, breast height diameter (DBH), and individual tree volume. Similarly, the enrichment of potassium in the branches and coarse roots was associated with improvements in DBH and tree volume. To maximize forest stand productivity, the WF fertilization method demonstrated superior results compared to HF. Therefore, WF should be prioritized in future fertilization experiments for C. bungei.

Modeling branch attributes and biomass for Catalpa bungei plantations under various fertilization regimes

The development and morphology of branches, a crucial step in producing high-quality large-diameter lumber, may be influenced by fertilization. The response of branch attributes to different fertilization regimes, however, is still poorly understood. The Catalpa bungei plantations, which had been growing for 6 years in northern China, were chosen to study how various fertilization measures affected branch attributes. The two fertilization techniques used were hole fertilization (HF) and water and fertilizer integration (WF), with no fertilization (CK) as a control. The quantity, density, morphology (e.g., diameter, length, and angle), and position (e.g., height and orientation) of branches, and organ biomass of 18 standard trees (total of 516 branches) were investigated. The results demonstrated a considerable increase in tree height, diameter at breast height (DBH), canopy ratio, branch quantity, and organ biomass following the addition of fertilizer. Both the maximum branch diameter and the number of branches rose with fertilization. Following fertilization, the number of branches rose by 16% (HF) and 28% (WF) compared to non-fertilized trees, while the maximum branch diameter increased by 3.5% (HF) and 17.3% (WF), respectively. WF led to an increase in the number of branches and largest branch diameter in comparison to CK and HF. The length, angle, and diameter of branches, however, were not affected significantly by different fertilization treatments. There were roughly equal amounts of branches in four orientations. The mixed-model analysis revealed that the number of branches was positively correlated with branch density and tree height. The branch diameter increased with the increase of branch length and angle. The branch length was negatively correlated with branch height and angle. The branch angle showed a larger angle at the bottom of the canopy. Tree height plus diameter at breast height combined, or just the diameter at breast height indicator alone, can both reliably predict the total biomass of trees. The branch models created in this research may offer some theoretical backing for understanding the crown dynamics of valuable tree species in northern China.

Agroforestry system construction in eastern coastal China: Insights from soil–plant interactions

AbstractAgroforestry, as a phytoremediation measure, shows great potential for mitigating land degradation by constructing multidimensional and efficient agroforestry composite systems through regulating the microenvironment of agroforestry sites and improving soil properties. However, the effects of different agroforestry composite management modes on saline soils and the interactions between soil–plant systems under salt stress conditions in coastal areas remain largely unexplored. In this study, two salt‐tolerant tree species (Sapium sebiferum (Linn.) Roxb and Zelkova serrata (Thunb.) Makino) and four crop species (Medicago sativa, Sesbania cannabina, Sorghum bicolour, and Avena sativa) were selected for intercropping in eight composite patterns via field experiments, with dynamics of soil physicochemical properties and crop photosynthesis observed. The results showed that treatments intercropped with M. sativa had the highest soil bulk density range (1.41–1.48 g cm−3). The dynamics of topsoil (0–10 cm) chemical properties showed similar change patterns among treatments, whereas those of the 10–40 cm soil chemical properties (especially soil pH, soil organic matter [SOM], and total nitrogen [TN]) showed heterogeneity. Moreover, planting S. sebiferum (L.) Roxb under the same crop conditions increased tree height growth rate and survival rate by 75%–114% and 14%–33%, respectively, relative to planting Z. serrata (T.) Makino. Furthermore, a significant negative correlation was observed between soil moisture with crop intercellular CO2 concentration (λ = −0.77), while significant positive correlations were found between crop net photosynthetic rate (Pn) with soil TN (λ = 0.71), as well as SOM with atmospheric CO2 content (λ = 0.72). Structural equation modeling showed significant direct effects between tree height growth rate with soil TN and SOM. Soil moisture (λ = 0.47) and tree height growth rate (λ = 0.53) were dominant drivers of crop Pn. Our findings provide useful information for the prevention of coastal saline soil degradation and sustainable development of agroforestry.

Comparison of Xylem Anatomy and Hydraulic Properties in Black Locust Trees at Two Growth Stages in Semiarid China

Tree species transitioning between different developmental phases requires homeostatic adjustments in order to maintain the integrity of the tree hydraulic system. Hence, adjustments related to hydraulic traits (e.g., xylem conduit diameter) are of key functional significance. However, critical information on the differences between different developmental stages is rare. Using sapwood samples from 36 black locust trees with different growth stages (actively growing and declining stages) and a soil water gradient along a hillslope, xylem conduits at stem apexes and breast height (1.3 m above ground) stems were measured. The results showed marked differences in vascular traits between actively growing and declining trees. In contrast to actively growing trees, declining trees exhibited a reduction in conduit diameters accompanied by increased frequency with a positively skewed distribution and a subsequent decline in cumulative theoretical hydraulic conductivity. Across all sampled trees, the hydraulically weighted mean conduit diameter tapered acropetally from breast height to the stem apex. The extent of conduit tapering in actively growing trees (0.244, 95% CI 0.201–0.287) aligned with predictions from the hydraulic optimality model. Conversely, trees in a declining status displayed significantly reduced conduit tapering (0.175, 95% CI 0.146–0.198), indicating an elevation in hydraulic resistance with increasing tree height. Variations in hydraulic properties predominantly resulted from differences in tree height rather than variations in stem diameter or soil water content. The correlation between conduit diameter and soil water content in both actively growing and declining trees stemmed indirectly from variations in tree height rather than presenting a direct response to drought stress.

Crown die-back of peri-urban forests after combined heatwave and drought was species-specific, size-dependent, and also related to tree neighbourhood characteristics

The Rhine River valley of Germany has been facing recurrent and intense spells of drought and heatwaves threatening the health of trees in peri-urban forests. Crown damage intensified by climate change accelerates tree mortality, threatening its ecological, economic, and social benefits; however, the pattern of crown die-back in peri-urban forests remained unclear. We performed a field inventory to estimate the crown die-back of 2578 trees of 51 species from 68 randomly selected peri-urban forest plots in Karlsruhe region on the right bank of the Rhine, after the catastrophic summer heatwave and drought of 2018. We related crown die-back to species-specific drought tolerance, wood anatomical traits, tree size, canopy surface temperature, tree density, Shannon's diversity and Gini coefficient for tree height. Regression results indicate that small-size trees were found to be more susceptible to canopy damage than large trees, with a 1-meter increase in tree height associated with a 0.8 % reduction in crown die-back. This size-dependent process is also species-specific. Among the 12 species with significant (p < 0.05) linear relationship between height and die-back, 9 species demonstrated negative correlations and 3 species showed positive relationships. Species tolerant to drought or cavitation (e.g., trees with diffuse porous xylem, 21 species) had significantly lower crown dieback. For example, with a 1-point-scale increase in drought tolerance crown die-back declined 14.35 %. Trees that experienced high canopy surface temperature and grew with high tree density and species diversity (Shannon's diversity) had more crown die-back. However, high structural diversity (Gini coefficient) was related to lower crown die-back. Our results suggested that future research should focus more on tree species-specific hydraulic and thermal traits and tree density and structure management to improve tree health and species selection in peri-urban forests under future climate change.

Contribution of urban trees in reducing land surface temperature: Evidence from china's major cities

Urban trees mitigate urban heat by altering evapotranspiration processes and providing shade to their surrounding environment. Nevertheless, the impact through which three-dimensional tree characteristics alleviate Land Surface Temperature (LST) remain uncertain, especially for climatic zone differences. In this study, we investigated the potential of trees to mitigate LST in 35 Chinese major cities and quantified the importance of diverse factors influencing the magnitude of cooling effects. Results showed that LST in tree-covered areas was about 2.23 °C lower than their surrounding built-up areas during summer, but an opposite temperature pattern was observed in winter and these cities are mostly distributed in Bs (arid-steppe) and Dw (cold-dry winter) climate zones. Moreover, we found that for every 1 m increase in tree height, LST decreased by ∼ 0.19 °C and ∼ 0.10 °C during summer and winter, respectively. Notably, we also found seasonal and climatic zone differences in the drivers of tree cooling intensity, with the digital elevation model (DEM = ∼13.21 %) as the key factor. These findings can help planners and architects better understand the effects of tree cooling, which can be a significant guide to reducing urban heat.

Optimal tree architecture for high‐yield yellowhorn (Xanthoceras sorbifolium) management

AbstractTree architectural attributes demonstrate a significant association with fruit yield. Yellowhorn is the future bioenergy tree in China; however, the species suffers from high reproductive energy and exceedingly low reproductive output. To optimize yellowhorn management and pinpoint priority trees featuring optimal architecture, we employed machine learning modeling to develop high fruit yielding predictive models using five yield indicators (dependent variables: FrW, SeW, ShW, FrW, and SeN) and five tree characteristics (independent variables: CA, TH, DGL, HLC, and MBN) of yellowhorn. Results showed that trees characterized by a substantial canopy area (&gt;1.70 m2) and a large diameter at ground level (&gt;3.71 cm) have been found to yield a higher fruit production. However, increased tree height does not invariably correlate with an elevated yield. Effective selection of high‐yielding individuals can be accomplished by restricting tree height within the range of 192–232.4 cm. This approach emphasizes the importance of integrating considerations of tree architecture into forestry management practices. Such integration can bolster productivity, thereby contributing to both the sustainability and economic viability of yellowhorn forests.

Modelling the impact of forest management and CO2-fertilisation on growth and demography in a Sitka spruce plantation

Afforestation and reforestation to meet ‘Net Zero’ emissions targets are considered a necessary policy by many countries. Their potential benefits are usually assessed through forest carbon and growth models. The implementation of vegetation demography gives scope to represent forest management and other size-dependent processes within land surface models (LSMs). In this paper, we evaluate the impact of including management within an LSM that represents demography, using both in-situ and reanalysis climate drivers at a mature, upland Sitka spruce plantation in Northumberland, UK. We compare historical simulations with fixed and variable CO2 concentrations, and with and without tree thinning implemented. Simulations are evaluated against the observed vegetation structure and carbon fluxes. Including thinning and the impact of increasing CO2 concentration (‘CO2 fertilisation’) gave more realistic estimates of stand-structure and physical characteristics. Historical CO2 fertilisation had a noticeable effect on the Gross Primary Productivity seasonal–diurnal cycle and contributed to approximately 7% higher stand biomass by 2018. The net effect of both processes resulted in a decrease of tree density and biomass, but an increase in tree height and leaf area index.

Extractives in Douglas firs (Pseudotsuga menziesii (Mirb.) Franco) from three sites in south-west Germany and potential opportunities for valorization

Owing to favorable wood properties and its resilience to the effects of climate change, Douglas fir (Pseudotsuga menziesii) is a promising tree species in Central Europe. Its wood and bark extractives could also serve as feedstock for the production of bio-based materials and platform chemicals. In this study, sapwood, heartwood, knotwood and bark extractives of Douglas firs originating from three differently aged stands in south-west Germany were investigated. Two different extraction methods with organic solvents were compared: a mixture of cyclohexane/ethanol and a successive method using petroleum ether, acetone and methanol. Extraction yields obtained with the successive method were higher, however one-step extraction was very efficient considering the number of samples that could be extracted and is therefore useful for a fast screening. At all sites, extract yields from sapwood, heartwood and bark were highest close to the tree top, while at the two older sites, an additional maximum was found at 1.3 m height. Knotwood extractives tended to decline with increasing tree height. The most abundant substance with economic importance was taxifolin, yielding up to 13% of dry weight in bark, whereas knotwood contained high amounts of resin acids and the lignan nortrachelogenin. Contrary to other studies, the present study found no evidence of a significant site effect on yield and composition of extracts. Overall, many different compounds for future bio-economic applications were found so that the preferential utilization of extractive-rich bark and crown material could foster an integral valorization of trees, supplementing with existing high grade timber production.

Study of introduced nut forms in the conditions of the Northern Caspian

A comprehensive assessment of the introduced forms of nuts according to economic and biological indicators is given and the most productive and adapted forms with good fruit quality are identified. The object of research was 32 forms of nuts. The early onset of the main phenological phases is characterized by varieties Xin-2, Ideal SI 1-2, Siebold nut (Tula), Siebold nut (Moscow). The earliest (6.05–8.05) flowering of female flowers was recorded in the forms Saratov ideal SI 1-2, Ideal SI 1-2 and Ideal SI 2-6. Male inflorescences were formed only in three varieties, the earliest flowering of male flowers was noted in the variety Ideal SI 1-2 (2.05). The maximum increase in tree height for the season in 2021 was noted in GF 1, Chili rounded, Ideal, Aral 2 (from 171 to 181 cm). The smallest increments were characterized by pecan DAOD-7, pecan DAOD-9 (4...80 cm). In other varieties and hybrids , the increase significantly varied from 103 to 170 cm . The maximum increase in the diameter of the stem was distinguished by the Elongated varieties (Volgograd), Large-fruited, GF 1 (5.0...5.3 cm). The smallest increments were characterized by pecan DAOD-7, pecan DAOD-9, which ranged from 0.2 to 0.5 cm. The pecan DOD had no increase at all, the other varieties and hybrids had an average increase (1.7...4.8 cm). The maximum productivity value was for the Chili variety elongated and reached 0.563 kg. The average weight of the fetus in the variants was 11.0...20.3 g, the largest mass of the fetus was in the form Ideal SI 2-6 (20.3 g). The largest in height and diameter of the fetus was B1D (Kyrgyzstan) – 5.1 and 3.4 cm, respectively.

Growth Rhythm Analysis of Young Stand and Selection of Superior Families in Choerospondias axillaris

As an important source of medicine, food, and high-quality wood, Choerospondias axillaris has been widely planted in South China. However, few studies of its growth traits and rhythm and concerning the selection of superior provenances/families were developed. In this study, 77 families from five provenances were studied and grouped. Tree height, diameter at breast height (DBH), and crown width within and between rows were measured. The relevance between growth traits and environmental factors was also analyzed. The results showed the height, DBH, and crown width within and between rows were divided into slow, mean, and fast growth periods, which was significantly related with sunshine hours in earlier months. Next, monthly rainfall showed an extremely positive correlation with the increase in tree height, DBH, and plant volume. Then, the monthly volume increment had a significantly positive correlation with five meteorological factors, excluding sunshine hours with increasing months, while the monthly growth of tree height and crown width within and between rows was significantly negatively correlated with sunshine hours. Based on these results, the superior families No. 15, 76, and 56, which originated from the Raoping provenance, were selected for their fast growth and available adaptation. These results provided the reliable growth rhythm of a young C. axillaris stand, which established a basis for fertilizing and forest tending. During these processes, meteorological factors, especially humidity and sunshine duration, had important effects on growth, implying that the external climate should be paid more attention to promote fast growth and prevent diseases and insect pests. Moreover, selecting superior families was helpful to further breeding and plantation.

In Arid Regions, Forage Mulching between Fruit Trees Rows Enhances Fruit Tree Light and Lowers Soil Salinity

Agroforestry is considered a means to provide sustainable and productive agriculture. This work aims to study the effect of fruit-grass agroforestry patterns on the soil moisture, salinity, growth, and yield of fruit trees, as well as to provide a reference for the development of agroforestry complex systems in Northwest China. The study has been designed with two cropping patterns: monocropped apple and apple-ryegrass intercropping. The results showed that compared to monocropped apples, intercropped apples have increased soil moisture content by 33.38–39.02%, net photosynthetic rate by 35.33–42.26%, transpiration rate by 29.62–29.76%, and stomatal conductance by 15.65–16.55% in the 0–60 cm soil layer. Intercrop reduced the total soil salt content by 36.41–38.58%, and the intercellular CO2 concentration decreased by 5.96–6.61%. In addition, intercropping improves fruit yield and quality by improving the orchard environment and increasing tree height, breast height, north-south crown spread, and east-west crown spread. Therefore, increased yield and quality can be achieved by changing the fruit tree and ryegrass planting method, which is beneficial to the sustainable development of agriculture in Northwest China.

Taller and slenderer trees in Swedish forests according to data from the National Forest Inventory

Changes over time in annual basal area growth and mean height for Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) over the period, 1983–2020 were studied using sample tree data from temporary plots recorded in the Swedish National Forest Inventory. The annual basal area growth was derived from the last measured full ring on increment cores. Using 20 to 60-year-old dominant trees, the mean height and annual basal area growth were examined as functions of tree, stand and site conditions, and trends were assessed mainly using residual analyses over time. A significant increase in mean height at a given age was found for both species, but the annual basal area growth level remained stable over the 38-year period. Currently, at a given age of 50 annual rings at breast height, the mean heights of pines and spruces increased on average by 10.1% (i.e. ∼2 m), compared to 50 year-old pines and spruces in the 1980s, and the increase was similar in the different regions. The results suggest that trees have become taller and slenderer in Swedish forests. Increasing tree height over time at a given age in Northern Europe has been documented in several reports and many causes have been suggested, such as changed forest management, increasing temperatures and nitrogen deposition. We suggest that elevated CO2 in the air and improved water-use efficiency for the trees might also be strong drivers.

Studies on the Performance of Custard Apple (Annona squamosal L.) Cultivars and Varieties Under Rainfed Vertisol Condition of Tamil Nadu

A study was conducted in block vertisol region of Southern part of Tamil Nadu with the view to find out suitable custard apple cultivars for the region. Twelve years old five cultivars viz., Mammoth, Raydurg, Arka Sahan, Balanagar, and APK (Ca)1 were undertaken for this study, which were planted at the spacing of 6 m x 6 m following randomized block design having three replications with ten trees in each replication. Results of three consecutive years of study clearly indicated that, the variety Arka Sahan showed increased tree height (6.28 m), number of primary branches (4.10), number of secondary branches (9.0), plant spread E-W (4.94 m) and plant spread N-S (4.77 m). The variety Mammoth recorded enhanced stem girth (85.67cm). Among the five custard apple varieties evaluated, Arka Sahan recorded the enhanced individual fruit weight(214.12g), less number of seeds / fruit (8.88), pulp weight (60.76g) and TSS (30.32 oBrix). The variety Raydurg showed less rind weight of 41.89 g / fruit. The variety Balanagar recorded the increased number of fruits/tree (250.36), yield / tree (22.79kg) and yield (6.15 tonnes/ha) followed by APK 1 showed number of fruits / tree (204.45), yield /tree (21.20 kg) and yield (5.72 tonnes/ha). TSS ranged from 21.67 to 30.32 oBrix. Considering overall performance, the cultivars Balanagar and APK (Ca) 1 are recommended for commercial cultivation in black vertisol region of Southern part of Tamil Nadu or in similar agro-climatic condition. The cultivar Arka Sahan showed enhanced growth and vegetative characters but special care (Artificial hand pollination) should be taken for fruit setting and retention.

Effect of inorganic and organic nitrogenous fertilizers on soil nutrient status, plant growth and yield of apricot (Prunus armeniaca L.)

The work is aimed to find out the most suitable substitute of CAN fertilizer to assess its effect on fertility, growth and yield of apricot. The experiment constituted 11 treatments replicated thrice in RBD design at the Research Farm of Department of Soil Science and Water Management, Nauni, Solan, India during 2015 and 2016. The highest organic carbon (1.34, 1.21%) was recorded with treatment T11 [100% urea enriched compost + 0% Ca (NO3)2] at 0–15 and 15–30 cm depths. There were significant variations and maximum available N and P contents were recorded under treatment T7 (urea 100% + lime 708 g/tree) while, maximum K was in T1 which indicated that available N, P and K increased by 16.95% and 16.58%; 34.83% and 32.36%; 19.98% and 12.76% over the initial values recorded, respectively at 0–15 and 15–30 cm depths. The highest available Ca (4.46 and 4.11[cmol (p+) kg−1]) was recorded under T1, Mg (2.11 and 1.95 [cmol (p+) kg−1]) under T6 and available S contents (56.46 kg ha−1and 51.67 kg ha−1) under T9 at surface and subsurface depths, respectively. Available Zn, Cu, Fe and Mn were highest under treatment T6 (urea100%+ 0%Ca (NO3)2). Maximum increase in tree height (0.40 m) and trunk girth (0.50 cm) was observed under T7 (urea 100% + lime 708 g/tree). Similarly, maximum fruit yield (30.03 kg/tree) was recorded with T7. From the present investigation, it is concluded that application of urea 100%+ lime 708 g/tree improved soil fertility, plant growth and yield during the study.

Divergence of hydraulic traits among tropical forest trees across topographic and vertical environment gradients in Borneo.

Summary Fine‐scale topographic–edaphic gradients are common in tropical forests and drive species spatial turnover and marked changes in forest structure and function. We evaluate how hydraulic traits of tropical tree species relate to vertical and horizontal spatial niche specialization along such a gradient.Along a topographic–edaphic gradient with uniform climate in Borneo, we measured six key hydraulic traits in 156 individuals of differing heights in 13 species of Dipterocarpaceae. We investigated how hydraulic traits relate to habitat, tree height and their interaction on this gradient.Embolism resistance increased in trees on sandy soils but did not vary with tree height. By contrast, water transport capacity increased on sandier soils and with increasing tree height. Habitat and height only interact for hydraulic efficiency, with slope for height changing from positive to negative from the clay‐rich to the sandier soil. Habitat type influenced trait–trait relationships for all traits except wood density.Our data reveal that variation in the hydraulic traits of dipterocarps is driven by a combination of topographic–edaphic conditions, tree height and taxonomic identity. Our work indicates that hydraulic traits play a significant role in shaping forest structure across topographic–edaphic and vertical gradients and may contribute to niche specialization among dipterocarp species.

DECAY RESISTANCE OF PRESERVATIVE INJECTED POPLAR AND ITS PROCESS OF PREVENTING WHITE ROT FUNGI INFECTION

This study initiallyinvestigated decay resistance of preservative injected poplar and its infection mechanismof preventing white rot fungi. The living poplar was injected with different concentrations (0.0, 0.5, 1.0 and 1.5 wt.%) of alkaline copper quaternary (ACQ). Using thescanning electron microscopy, the process of preservative injected poplar wood preventing white rot fungi infection at different tree heights were examined. The decay resistance test results showed that the decay resistance of preservative injected poplar at different tree heights was significantly different. With the increase in tree height, the decay resistance decreased, and the higher the ACQ concentration, the better the decay resistance. The white rot fungi infested the poplar wood with the vessels as the breakthrough point, being spread to other cells through pits. The white rot fungi degraded wood cell walls by secreting enzymes and preferentially degraded the parenchyma cells.

The impact of whitegrub (Coleoptera: Scarabaeidae) damage on growth of Eucalyptus grandis and Acacia mearnsii plantation trees in South Africa

ABSTRACT Eucalyptus grandis and Acacia mearnsii are among the South African forest industry’s most planted commercial species. Whitegrubs are high-status pests affecting plantation forestry; they are root-feeding insects and cause poor seedling growth and elevated mortality. The aim of this study was to elucidate the impact of whitegrub damage on the growth of E. grandis and A. mearnsii trees during the first year of the establishment stage in sites previously planted with A. mearnsii in the KwaZulu-Natal Midlands of South Africa. The hypothesis was that the prophylactic application of insecticides against whitegrubs would increase tree height at six or 12 months after planting. Seven insecticides were assessed in 12 treatments over three trials in Bloemendal, KwaZulu-Natal. Statistical analyses were performed using PRIMER and SAS. Whitegrubs were the predominant mortality factor (17.1%), followed by pathogens (3.3%) and 12 other factors that cumulatively caused the remaining (7.0%) mortality. Pegylis sommeri, Schizonycha affinis and two unknown Maladera species were the most important, typical and prevalent whitegrub species, but their ranking differed between A. mearnsii and E. grandis, suggesting a host preference. The prophylactic application of insecticides against whitegrubs significantly increased tree height for E. grandis. Acacia mearnsii tree height, however, did not consistently show a significant effect with insecticide control, presumably because of additional mortality by pathogens. The crop-rotation scenario may have potentially benefited E. grandis over A. mearnsii and warrants further investigation. Whitegrubs can kill seedlings and reduce tree height when left uncontrolled.