Sample Trees Research Articles

Usporedba reakcijskoga i normalnog drva nekih komercijalnih vrsta drva

This study aims to analyze the reaction wood samples for some industrial tree species naturally grown in Kastamonu province in Turkey and compare them with the relevant standards. Some anatomical, chemical, fiber morphological, optical properties, and color changes before and after drying were analyzed for the reaction wood (RW) samples. While the holocellulose content of fir and pine compression wood (CW) was found to be lesser (~3-4 %), the lignin content was higher than those of the opposite wood (OW) (~34 % for pine and 12 % for fir). On the contrary, the amount of holocellulose was found to be higher (~1-4 %), and the lignin was lower (at about 6-15 %) in the tension wood (TW) samples. It was observed that average lengths are more extended in TW(~50-54 %) and shorter in CW (~13-17 %) than those of OW. Significant differences were observed between the anatomical structures of the coniferous and deciduous species studied. Although, the greatest color differences in wet and oven-dried samples of coniferous trees were measured in CW (~15-17 %), it has been found as about 0.7-3 % in TW for deciduous species. Some differences were observed in the anatomical, optical, fiber morphological, and chemical properties of the RW for the studied wood species. Due to its higher lignin content and better physical properties, CW can be used for producing small households and hand tools, ornaments, toys, etc. It will also be appropriate for use in milling and turning work. It is recommended that, because of the lower lignin content and higher polysaccharide ratio, TW should be primarily used for the cellulose, pulp, and paper industries, where high mechanical resistance values are required. Consequently, RW formation causes some physical, chemical, mechanical, anatomical, and optical differences compared to OW in deciduous and coniferous species.

First molecular record of Thielaviopsis punctulata, the causative agent of black scorch blight disease on date palms in Iraq

A laboratory study was conducted on samples of palm trees collected from Diyala Governorate, Iraq. The results of isolation and diagnosis of the samples that showed symptoms of black blight infection indicated that the fungus that causes the disease is Thielaviopsis punctulata. This is the first record of T. punctulata as a causative agent of black blight in Iraq. Moreover, the results of the microscopic examination showed that the fungus forms endoconidia from Phialidic conidiophores, and also produces aleoroconidia, thickened-walled chlamydial spores. In addition, the results of testing the pathogenic ability of the isolates on date palm seedlings showed that all the isolates of the pathogenic fungus showed the ability to cause the disease, but with different percentages compared to the percentage of the disease, where it was 0 in the comparison treatment that was free of pathogenic fungus, and isolate GP2 excelled, as it gave an infection severity of 100%, followed by the two isolates GP0 and GP1, which gave an infection severity of 93.33 and 80%, respectively.

Growth and yield patterns of black locust (Robinia pseudoacacia L.) sample trees affected by site conditions: case studies

The trees removed from the long-term experiment plots are available for the measurements as lying trees. Through the determination of the volume in sections along the stem, the stem form, the stem volume and other factors can be specified. The comparison of the stems of individual trees of first and third yield classes of black locust (Robinia pseudoacacia L.) stands shows that site conditions have a main effect on the yield (mean tree volume). The difference can be as high as 53% at the age of 30 depending on the sites. To determine the growth patterns based on tree volume is rather a new approach in the light of the relevant literature. The obtained results also highlight the importance of choosing the appropriate tree species for a given site.

Biomass estimation models for Acacia saligna trees in restored landscapes

Acacia saligna, originating from Australia, is a naturalized multipurpose tree species widely grown to restore degraded lands of Africa. The contribution of A. saligna in biomass restoration can be quantified using a precise estimation of tree biomass carbon. This study developed species-specific allometric models and evaluated the spatial variation of tree biomass across restored areas in exclosures and open grazing landscapes. These models could play a considerable role in the monitoring of carbon dynamics across A. saligna planation dominated areas. We harvested, excavated, and weighed twenty-one sample trees representing different size classes to develop allometric models for the estimation of aboveground (AGB), belowground (BGB) and total tree (TB) biomass. The average dry-to-fresh mass ratio and the root-to-shoot ratio was 0.47 (±0.13) and 0.28 (±0.14), respectively. Tree biomass significantly correlated with diameter at breast height (r = 0.93; P < 0.001), diameter at stump height (r = 0.88, P < 0.001) and tree height (r = 0.56, P < 0.05). Our best biomass estimation models explained 86%, 82% and 87% of variations in AGB, BGB, and TB, respectively. Models using DSH and DSH & H explained 70%–78% of the variation in AGB, BGB, and TB. Estimated C-stock showed a significant relationship with stem density (R 2 = 0.91, P < 0.01). Estimated TB varied between 1.5–18 Mg ha−1 on grazed land and exclosures. Estimated C-stocks in the exclosure exceeded the estimated C-stock in the open grazing land by ∼60%. This implies that with proper management practices and enrichment planting A. saligna significantly contributes to increasing carbon accumulation on degraded landscapes, playing a key role in climate change mitigation efforts while improving land productivity.

Non-destructive detection of tree deterioration due to termite attack in plant conservation areas

Cibodas Botanic Gardens (CBG) is an ex-situ conservation area in tropical highlands. Termites are one of the nuisance organisms in the collection that have conservation value. The number of attacks and the intensity of termite attacks require more strict attention. The main problem in tree health analysis is the difficulty in detecting internal weathering due to attacks by wood-destroying organisms which causes damage to the tree’s core (heart rot) and butt rot. Arborsonic is a tool used and developed to detect and assess tree damage, especially to the trunk. This study aimed to analyze the deterioration of the main trunk of a living tree with visual signs of termite attack using a non-destructive method. Termite observation plots were made in 4 replications to determine the type of termites that attack. Observations on termite baits in 4 plots showed no attack on the baits. Observations on 12 sample trees tested in 4 plots showed low-intensity damage. Visual signs of termite attack can be used as a sign of wood decay, but the effect is minor.

Seed exploration on Nusakambangan Island to enrich seeds collection in Bogor Botanic Garden

Seed exploration is one of the conservation strategies used to enhance the collection of seeds as natural resources in the seed bank. In 2020, we explored Nusakambangan Island from the West Nusakambangan nature reserve area, Batar Panjang coast, to Kali Jati Riverbanks. The exploratory approach and direct fruit tree sampling were employed. This study seeks to collect and preserve plant seeds and discover their biological seed characteristics. Thirty-two (32) collection numbers were obtained, consisting of 22 families and 27 genera. Moraceae and Euphorbiaceae (4 species) have the most fruiting trees in this exploration. Ficus variegata, Mucuna gigantea, and Ziziphus horsfieldii are new Bogor Botanic Gardens database collections. Most seeds (75%) we collect are orthodox and suitable for long-term storage. In addition, the specimens are not endemic or endangered trees; few still need identification. Also, this study provides information on biological seed characteristics that facilitate seed conservation storage at Bogor Botanical Garden Seed Bank.

In Vitro Evaluation of Potentially Edible Brazilian Trees and Shrubs in Ruminant Nutrition

The present study aims to evaluate the nutritional value of different tree and shrub leaves in Brazilian ruminant production systems. Eight potentially edible trees and shrubs were identified from interviews with 30 ruminant producers: Aroeira (ARO; Lithraea molleoides), Black Mulberry (BMU; Morus nigra), Candeia (CAN; Eremanthus erythropappus), Jatobá (JAT; Hymenaea courbaril), Gliricídia (GLI; Gliricidia sepium), Santa Bárbara tree (SBT; Mélia azedarach), Tithonia (TIT; Tithonia diversifolia), and White Mulberry (WMU; Morus alba). Four leaf samples of each edible tree were sampled, and chemical analyses and in vitro assays were performed. Edible trees (except CAN and JAT) had lower neutral detergent fiber content than Mombasa grass. In addition, SBT, BMU, WMU, and TIT had lower fiber content than the other evaluated edible trees. Consequently, SBT, TIT, BMU, and WMU had improved dry matter degradation. Among the edible trees and shrubs, SMW and WMU increased the potential for gas production (a parameter). On the other hand, CAN decreased the estimated gas production 48 h after incubation. Furthermore, TIT decreased methane production up to 24 h after in vitro fermentation. Thus, except ARO, CAN, and JAT, the edible trees evaluated in the present study are potential feeds in moderate- to high-producing animals. Additionally, TIT fermentation reduces in vitro methane production.

Peach tree response to low dosages of dicamba as repeated application or with various spray nozzles

Abstract Two low-dose dicamba exposure trials were conducted on container-grown peach trees in Fayetteville, AR. Peach trees were ‘July Prince’ scions grafted onto ‘Guardian’ rootstock, were transplanted into 19-L containers, and received experimental dicamba treatments in each year. Container trials were initiated in 2020 and repeated on new trees in 2021. In the repeated application trial, dicamba was applied at 5.6 g ae ha−1 (1/100X field rate) in five sequences: an untreated control receiving no herbicide, one treatment receiving only an initial application, and three treatments receiving an initial application plus sequential applications at the same rate occurring at 14 d, 28 d, and 14 d + 28 d after initial treatment (DAT). A separate trial assessed peach tree responses to dicamba applied at 11.2 g ae ha−1 (1/50X field rate) using a selection of nozzles with differing droplet spectrum characteristics: Turbo TeeJet® induction nozzle TTI11002, air induction turbo TwinJet® nozzle AITTJ60-11002, air induction extended-range (XR) TeeJet® nozzle AIXR11002, XR TeeJet® flat-fan nozzle XR11002, and XR TeeJet® flat-fan nozzle XR1100067. Peach tree height, tree cross-sectional area, and leaf chlorophyll content were not reduced in response to any sequence of dicamba application or nozzle selection. Repeated applications of dicamba at a 1/100X rate did not increase peach injury after 28 DAT. By 84 DAT, no effect of nozzle type on peach tree injury was discernable, and all treatments caused below 4% injury. No dicamba or dicamba metabolites were observed in leaf samples collected at 14, 69, or 85 DAT from trees treated with XR1100067 or in untreated controls. While peach tree injury was observed throughout the experiment, dicamba residues were detected consistently only in 2020 from leaf samples of trees treated with dicamba at a 1/50X rate using TTI1102, AITTJ60-11002, AIXR11002, and XR11002 nozzles.

Development Dynamics of Punica Diseases in Absheron District of Azerbaijan

The article describes the dynamics of the development of diseases of Punica in Absheron district. According to the methodology, visual inspection (5-25) of leaves, branches and fruits was carried out on 4 sides of the tree sample. Recorded samples of flower leaves, branches, stem bark and infected fruits were delivered to the laboratory; signs of the presence of pests and diseases: darkening, puncturing, spotting, drying, rotting, wilting, etc. Microscopic analyzes were carried out to determine species composition by recording characteristics. Using the method, the species composition of pomegranate mushroom seedlings was determined. Disease samples collected and delivered to the laboratory were analyzed according to the relevant methodological rules. A photograph of the pathogenic fungus spores was taken under a microscope. Under laboratory conditions in a thermostat, the development of ascospores of perithecia of the Sphaceloma punicae Bitanc. et Jenkins, which is a widespread disease of pomegranate, was partially controlled. When studying the spread of diseases affecting pomegranate plants in the region, route observations were carried out 3 times at 4-5 stations in the region at different stages of the growing season. At this time, visual observations were made of pomegranate bushes planted in different places (private courtyards and other enterprises, parks and roadsides).

Volumetric Modeling in the Amapá National Forest

Theoretical framework: Volumetric models are a crucial tool for forest management, as they use them to estimate the total volume of the forest. Objective: The study aimed to adjust a volumetric model to estimate commercial volume in a dense rainforest located in the municipality of Ferreira Gomes AP, Brazil. Method: Cubing data from 103 sample trees, from 5 species, were used to adjust 7 volumetric models, 5 of which were linear and 2 were non-linear. Results and discussion: After analysis, it was found that all models presented a good fit to the data, however the non-linear models presented the best statistics. Finally, the Schumacher and Hall model generated the best equation for estimating commercial volume in the Amapá national forest. Implications of the research: There is a general equation to estimate the volume of commercial species in the Amapá national forest. Originality/Value: Volume equations are essential for management plans in Amazonia, therefore, this is the first equation available for volume estimation in the Amapá national forest.

Environment-induced growth changes in forests of Finland revisited - a follow-up using an extended data set from the 1960s to the 2020s

After a rising trend for 1971 – 2013, during which the annual volume growth of the forests of Finland increased by more than 70 %, a recent reduction has been observed. We analyzed the development of annual growth in the forest of Finland, focusing on the component not explainable by changes in growing stock. The data originate from nine consecutive Finnish National Forest Inventories. In the data, diameter increments were measured from increment cores and tree height increments from standing sample trees in the field. We developed models predicting periodic (5 years) annual volume increment per hectare with properties of the trees and stands as predictor variables. Deviations from model-predicted values were interpreted to be induced by environmental variation. The development was analyzed for all tree species combined and separately for three species groups: Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.) and broadleaves. We observed a rising growth trend not solely explainable by increased growing stock. The species groups produced rather a similar pattern in different parts of Finland: from the 1960s to the mid-1990s, the observed volume increment was mainly below the model-predicted level, thereafter above it. During the current century, the difference between observed and predicted annual volume increment has shown a downward trend for Scots pine. For Norway spruce, the difference has continued to increase in southern Finland, but shows little change in the north. For broadleaved species, the difference between measured and predicted increment shows a recent increase as well, though not as large as for Norway spruce. The geographical pattern of the environment-induced increment component was described in more detail via maps using a 75 km × 75 km grid. The changing environment has enhanced forest productivity in Finland over a period of nearly six decades, but recent years have not been favorable for Scots pine, which represents 50 % of the growing stock volume of the forests of Finland.

Development of Spatiotemporal Whole-Stem Models for Estimating End-Product-Based Fibre Attribute Determinates for Jack Pine and Red Pine

The objective of this study was to develop spatiotemporal whole-stem wood quality prediction models for a suite of end-product-based fibre attribute determinates for jack pine (Pinus banksiana Lamb.) and red pine (Pinus resinosa Aiton): specifically, for wood density (Wd), microfibril angle (Ma), modulus of elasticity (Me), fibre coarseness (Co), tracheid wall thickness (Wt), tracheid radial diameter (Dr), tracheid tangential diameter (Dt), and specific surface area (Sa). Procedurally, these attributes were determined for each annual ring within pith-to-bark xylem sequences extracted from 610 jack pine and 223 red pine cross-sectional disks positioned throughout the main stem of 61 jack pine and 54 red pine sample trees growing within even-aged monospecific stands in central Canada. Deploying a block cross-validation-like approach in order to reduce serial data dependency and enable predictive performance assessments, species-specific calibration and validation data subsets consisting of cumulative moving average values were systematically generated from the 27,820 jack pine and 11,291 red pine attribute-specific annual ring values. Graphical, correlation, regression and validation analyses were used to specify, parameterize and assess the predictive performance of tertiary-level (ring-disk-tree) hierarchical mixed-effects whole-stem equations for each attribute by species. As a result, the jack pine equations explained 46, 66, 74, 63, 59, 72, 42 and 48% of the variation in Wd, Ma, Me, Co, Wt, Dr, Dt and Sa, respectively. The red pine equations explained slightly higher levels of variation except for Me: 50, 71, 31, 83, 72, 78, 56 and 71% of the variation in Wd, Ma, Me, Co, Wt, Dr, Dt and Sa, respectively. Graphical assessments and statistical metrics related to attribute and species-specific residual error patterns and goodness-of-fit, lack-of-fit and predictive error metrics, revealed an absence of systematic bias, misspecification or aberrant predictive performance. Consequently, the resultant parameterized models were acknowledged as acceptable functional descriptors of the intrinsic spatiotemporal cumulative developmental patterns of the studied end-product fibre attribute determinates, for these two pine species. Although predicted development patterns were similar between the species with the greatest degree of nonlinearity occurring before a cambial age of approximately 30 years, irrespective of attribute, jack pine exhibited a greater degree of nonlinearity in the Wd and Dt developmental trajectories, whereas red pine exhibited a greater degree of nonlinearity in the Ma, Me, Co, Wt, Dr and Sa developmental trajectories. Potential biomechanical linkages underlying the observed attribute distribution patterns, as well as the potential utility of the models in forest management, are also discussed.

Relationship between the Number Of Oecophylla smaragdina Fab. ant nests and the Intensity of Prays endocarpa Meyrick Attacks on Pamelo Citrus (Citrus maxima Merr)

This research on the relationship between the number of O. smaragdina nests and the intensity of P. endocarpa attacks has been conducted at the Pamelo citrus plantation of Gelengge in Pangkep Regency. The observation sample trees were those which had the O. smaragdina nests for three weeks in the Pamelo citrus trees. The sample trees were grouped into four categories namely: A) 1-2 nests per tree, B) 3-4 nests per tree, C) 5-6 nests per tree, and D) without nests (control). The observed parameters were the attack intensity of P. endocarpa on fruits on trees and on fallen fruits found under Pamelo citrus trees. The observation of the attack intensity was carried out after the Pamelo citrus fruits reached six weeks old, or after the fruits reached 50 mm-60 mm in size. The results showed the intensity of P. endocarpa attack on the fruits in the lowest tree was 36% in the trees with about 5-6 O. smaragdina nests, and the highest in the trees without nests was 66%. The attack intensity on the lowest falling fruit was 41.5% on the trees with 5-6 nests per tree, and the highest was 60.3% the in trees without the O. smaragdina nests. The regression analysis showed a relationship between the number of O. smaragdina nests with the attack intensity with the regression coefficients, respectively were r = 0.94 and r = 0.98.

Construction of universal equations for knot attributes of three coniferous species.

We constructed base model, dummy variable model, and mixture model with three variables including knot diameter, loose knot length, and sound knot length with three typical coniferous species, Pinus koraiensis, Larix olgensis, and Pinus sylvestris var. mongolica, from the Linkou Forestry Bureau and Mengjiagang forest farm in Heilongjiang Province in 2020. We analyzed the differences in knot properties among different tree species and simplified the modeling work. Firstly, we collected relevant knot property data through the sectioning method based on relevant literature, transformation of the model form and substitution of related variables to conduct a base model. We transformed the species into dummy variables as qualitative factors, and introduced the dummy variable model of the relevant attributes into the base model. We introduced the random effects of sample trees and sample plots when constructing the mixture model. By comparing evaluation indicators, such as Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC), the mixture model with the best fitting effect was selected. We selected the optimal universal equation by comparing the fitting accuracy of the base model, dummy variable model and mixture model. The fitting accuracy of the dummy variable model and mixture model was higher than that of the basic model. The evaluation indicators (AIC and BIC) showed that the mixture model had a better fitting effect on knot properties than the dummy variable model. In the model comparison results, R2 of mixture models for sound knot length, the loose knot length, and knot diameter increased by 13.2%, 84.8% and 40.3%, respectively. The predictive accuracy of the three base models for different tree species' knot attributes was above 90%, and both the prediction accuracy of the dummy variable model and mixture model were above 94%, indicating that the constructed models could well predict knot-related properties. From the perspective of tree species, the sound knot length, knot diameter, and loose knot length was in order of P. sylvestris var. mongolica > P. koraiensis > L. olgensis. Fitted results of the dummy variable model and the mixture model were superior to the basic model, with higher accuracy.

PENGUKURAN TINGGI DAN TUTUPAN KANOPI POHON DI TAMAN SAINS, KECAMATAN DUREN SAWIT, KOTA JAKARTA TIMUR

PENGUKURAN TINGGI DAN TUTUPAN KANOPI POHON DI TAMAN SAINS, KECAMATAN DUREN SAWIT, KOTA JAKARTA TIMUR

Diagnosis of Peach latent mosaic viroid (PLMVd) and Hop stunt viroid (HSVd) by RT-PCR using different extraction protocols

RT-PCR method was performed using four different nucleic acid extraction methods to identify viroids; peach latent mosaic viroid (PLMVd) and hop stunt viroid (HSVd) which causes serious damage to stone fruits. Leaf samples were collected from fruit orchards showing viroid-like symptoms in İzmir province. Silica capture, citric buffer, lithium chloride, and ames buffer methods were used to extract total nucleic acids. The four extraction methods were compared using samples collected during the vegetation period from naturally infected trees (plum, apricot, and peach). They were evaluated with RT-PCR tests. In 64 stone fruit tree samples, only the silica capture method gave reliable and accurate results in RT-PCR molecular tests for the detection of PLMVd and HSVd. The other wielded nucleic acid extraction methods were found to be ineffective for the isolation of the viroid RNAs.

Individual Tree Height Increment Model for Quercus mongolica Secondary Forest in the Northeastern China Using Generalized Nonlinear Two-Level Mixed-Effects Model

(1) Background: Mongolian oak secondary forest is widely distributed in the northeast of China, and most of these forests are formed after the overcutting of broad-leaved Pinus koraiensis mixed forest. Most of the forest productivity is low and the ecological function is degraded, due to insufficient understanding of Mongolian oak and lack of scientific management. Deepening the research on exploring reasonable management measures of Mongolian oak secondary forest to an improved stand status is the basis for improving its quality and promoting its forward succession process. (2) Methods: Twelve permanent plots with an area of 1 ha were established in the Mongolian oak secondary forest on Tazigou forest farm in Wangqing, Jilin Province of northeastern China. The response of tree height increment of Mongolian oak secondary forest is studied based on the survey data of 2013 and 2018. Two-level nonlinear mixed-effects models were constructed to predict the height of a single tree using sample plots and tree species as random effects, combined with a variety of tree size factors, site factors, and competitive factors as independent variables. (3) Results: The significant factors related to the height increment of Mongolian oak secondary forest are the initial diameter at breast height as the size of the tree itself (DBH), height (H), crown height ratio (CR), and site productivity index reflecting site quality (SPI). The distance-dependent and distance-independent competition indexes have no significant effect on tree height increment. The fitting accuracy of the two-level mixed-effects model that introduces plots and tree species as random effects has been greatly improved (coefficient of determination R2 increased by 51.8%). The prediction results show that the two trees with the largest DBH have the strongest prediction ability. (4) Conclusions: The generalized nonlinear two-level mixed-effects model constructed in this study can describe the height increment of an individual tree in the Mongolian oak secondary forest. Two sample trees, namely the two largest trees in each sub-plot, were applied for estimating the random effects when both measurement cost and potential errors of prediction were balanced.

Regional Characteristics of the Climatic Response of Tree-Ring Maximum Density in the Northern Hemisphere

The maximum latewood density (MXD) of tree rings can reflect the temperature of the growing season, but the timing of the response differs among regions. We selected 152 maximum latewood density chronologies from the Northern Hemisphere that showed a significant response to temperature. Based on a cluster analysis and the sensitivity of MXD to the monthly mean temperature, the chronologies were classified into six clusters. The clusters showed distinct regional characteristics, and the period and peak month of significant response of the chronologies in each cluster to temperature were different. Spatial synchronization of the MXDs revealed that the two clusters distributed in Europe showed the most consistency and the strongest response to the April–September monthly mean temperature compared with the other clusters. Temperature accounted for more than 40% of the total MXD variance in all clusters, whereas the effect of precipitation was much smaller. In addition to climatic factors, the random effect of the latitude and longitude of sampling sites, elevation, and tree species was a major factor contributing to the variance in MXD in each cluster. Latitude and longitude had the strongest influence among the three random effects, and tree species had the weakest influence, except at high latitudes. The MXD of each cluster showed sensitivity to temperature within a certain interval, with a positive linear response, and the sensitivity interval was greatest at high latitudes. Certain clusters showed a negative linear sensitivity to precipitation. The results provide a reference for studying the climatic threshold of large-scale tree-ring density formation.

Evaluation of some physical and mechanical properties of Acacia hybrid BV10 planted in Quy Chau, Nghe An

This study aimed to evaluate some major physical and mechanical properties of 7 year old Acacia hybrid BV10 planted in Quy Chau district, Nghe An province. Small specimens with dimensions of 20 (Radial) × 20 (Tangential) × 320 (Longitudinal) mm3 were cut near the pith and near the bark at breast height from each sample tree, then placed in a standard laboratory setting until their weights reached a constant value. The resulting mean air-dry density (AD), stress wave velocity (SWV), static modulus of elasticity (MOE) and modulus of rupture (MOR) were 0.53 g/cm3, 4,241 m/s, 10.00 GPa, and 82.17 MPa, respectively. Statistical analysis showed that SWV and these wood properties examined near the bark were always higher than those values measured near the pith. Stress wave technology can be used to predict MOE and MOR; however, AD is still a more reliable indicator for predicting mechanical properties since it showed a strong correlation with MOE (r = 0.86; P &lt; 0.001) and MOR (r = 0.80; P &lt; 0.001).

The Effect of Elevation on the Population Structure, Spatial Patterning and Intraspecific Interactions of Picea schrenkiana in the Eastern Tianshan Mountains: A Test of the Stress Gradient Hypothesis

Changes in age structure, spatial distribution and intraspecific interactions across environmental gradients often reflect adaptations of plant populations to their environment. Our study explored the growth status of the Picea schrenkiana population on the north slope of the eastern Tianshan Mountains and tested the stress gradient hypothesis (SGH) against changes in the age structure and spatial pattern of P. schrenkiana populations along the environmental gradient. We sampled the forests at eight elevational locations, comprising a total of 24 plots of 30 × 30 m area from 1800 to 2500 m a.s.l. in the Jiangbulake region. By scanning the 3D structure of the forests and sampling tree rings in each plot, we precisely determined the spatial location and diameter of the breast height (DBH) of each P. schrenkiana individual. By fitting the DBH-age power model and g(r) function of the point pattern, we examined the age structure, spatial patterning and intraspecific interactions of local P. schrenkiana populations within each plot and their correlation with habitat parameters. The results indicate that (1) juveniles dominate the overall population density, age structure and spatial patterning of the P. schrenkiana population. Trees of low–middle elevations represent younger forests with faster growth and better regeneration, while trees at high elevations form older forests with slower growth and poorer regeneration. (2) The aggregated population patterns and positive intraspecific interactions occur mostly at medium elevations (2000 and 2100 m a.s.l.). (3) Population density, aggregation intensity and intraspecific interaction strength are strongly and positively correlated (p &lt; 0.01). Our results did not fit the SGH but support a hump-shaped hypothesis that proposes that facilitation is stronger under medium stress along the elevational gradient. This study validates the spatial point pattern testing of the SGH of different types. We recommend the implementation of more intensive forest closure measures, together with a reduction in the harvesting intensity of trees to ensure the sustainable regeneration of P. schrenkiana forests in the eastern Tianshan Mountains.