Middle-aged Trees Research Articles

Estimation of phloem conductance at tree level in young, middle-aged and old-aged Scots pine trees growing in different climatic conditions in boreal forests.

In forests, a significant proportion of the carbon fixed by trees during photosynthesis is transported belowground along the conducting phloem, so variations in phloem anatomy can lead to variations in transport capacity. Phloem conductance at tree level (Ktree) is also affected by tree height. Both the phloem anatomy and the tree size change during ontogeny, and also differ under different environmental conditions. The goal of our work was to identify the main drivers of variation in Ktree in Scots pine trees growing in natural boreal forests. We conducted a phloem anatomical study and calculated Ktree in trees of three age groups growing in different climatic conditions along a latitudinal gradient from south to north. We found that Ktree was maintained at the same level in actively growing pine trees (25-80-years-old) but increased in old-aged trees (180-190-years-old), possibly reflecting the shift in source-sink relationships of aboveground and belowground parts of trees. Trees of the same age group growing in different climatic conditions demonstrated similar values of Ktree due to coordinated changes in the phloem anatomy and the tree height. In general, the negative influence of tree height on Ktree is offset by the positive influence of phloem width (or trunk diameter) and sieve cell diameter. The exception was young trees growing in the transition zone of the northern taiga subzone to the tundra, where Ktree was the highest in its age group and even exceeded Ktree of middle-aged trees.

Nitrogen addition enhances tree radial growth but weakens its recovery from drought impact in a temperate forest in northern China

Forest growth in the majority of northern China is currently limited by drought and low nitrogen (N) availability. Drought events with increasing intensity have threatened multiple ecosystem services provided by forests. Whether N addition will have a detrimental or beneficial moderation effect on forest resistance and recovery to drought events was unclear. Here, our study focuses on Pinus tabulaeformis, which is the main plantation forest species in northern China. We investigated the role of climate change and N addition in driving multi-year tree growth with an 8-year soil nitrogen fertilization experiment and analyzing 184 tree ring series. A moderate drought event occurred during the experiment, providing an opportunity for us to explore the effects of drought and N addition on tree resistance and recovery. We found that N addition was beneficial for increasing the resistance of middle-aged trees, but had no effect on mature trees. The recovery of trees weakened significantly with increasing N addition, and the reduction in fine root biomass caused by multiyear N addition was a key influencing factor limiting recovery after moderate drought. Our study implies that the combined effect of increasing drought and N deposition might increase the risk of pine forest mortality in northern China.

Shift of root nitrogen-acquisition strategy with tree age is mediated by root functional traits along the collaboration gradient of the root economics space.

Root nitrogen (N)-uptake rate and uptake preference, and their association with root morphological and chemical traits are important to characterize root N-acquisition strategies of trees. However, how the root N-acquisition strategy varies with tree age, especially for those species that coexist at a common site, remains unknown. In this study, a field isotopic hydroponic method was used to determine the uptake rate and contribution of NH4+, NO3- and glycine, for three coexisting ectomycorrhizal coniferous species [Pinus koraiensis (Korean pine), Picea koraiensis (Korean spruce) and Abies nephrolepis (smelly fir)] at three age classes (young, middle-aged and mature) in a temperate forest. Concurrently, root morphological and chemical traits, as well as mycorrhizal colonization rate were determined. Our results show that the root uptake rate of total N and NH4+ gradually decreased across all three species with increasing tree age. The three species at all age classes preferred NH4+, except for middle-aged Korean spruce and mature smelly fir, which preferred glycine. In contrast, all three species showed the lowest acquisition of NO3-. According to the conceptual framework of 'root economics space', only a 'collaboration' gradient (i.e. dimension of root diameter vs specific root length or area) was identified for each species, in which root N-uptake rate loaded heavily on the side of 'do-it-yourself' (i.e. foraging N more by roots). Young trees of all species tended to exhibit the 'do-it-yourself' strategy for N uptake, and mature trees had an 'outsourcing' strategy (i.e. foraging N by a mycorrhizal partner), whereas middle-aged trees showed a balanced strategy. These findings suggest that shifts of root N-acquisition strategy with tree age in these species are mainly mediated by root traits along the 'collaboration' gradient, which advances our understanding of belowground competition, species coexistence and N cycling in temperate forests.

Effects of slope aspect and age class on diseases of Juglans regia in Wild Walnut Nature Conservation Area of Xinjiang, China.

To understand the disease situation of vulnerable plant Juglans regia, we investigated the proportions of four diseases of J. regia with different age classes in different slope aspects in the Wild Walnut Nature Conservation Area of Xinjiang. We analyzed the correlation of disease types and disease grades with the diameter at breast height (DBH) of J. regia and slope aspects. The results showed that the main diseases of J. regia in the reserve were walnut brown spot disease (95.8%), walnut deadwood disease (90.5%), walnut black spot disease (74.4%), and walnut rot disease (7.7%). J. regia was susceptible to walnut brown spot disease in all the four slope aspects, with walnut deadwood disease on shady and semi-shady slopes, walnut black spot disease on sunny and shady slopes, and walnut rot disease on semi-sunny and semi-shady slopes. The proportion of diseased plants with the four diseases decreased with the increases of disease grades (1-4 grades) in the four slope aspects. Across the four slope aspects, the middle-aged trees had the largest proportion of walnut deadwood disease, walnut black spot disease and walnut brown spot disease, followed by old trees and young trees. No diseased seedlings were found. Walnut rot disease only occurred in old trees. There was significant positive correlation between DBH of J. regia and the four diseases. Walnut black spot disease had significant negative correlation with slope aspect. There was correlation between different disease grades of walnut deadwood disease, walnut rot disease and walnut black spot disease with DBH and slope aspects.

Species Composition and Diversity of Middle-Aged Trees among Different Urban Green Space Types and Tree Age Classes in Changchun, Northeast China

Middle-aged trees refer to trees aged between 50 and 99 years, which are the reserve resources of old trees (trees ≥ 100 years of age). They are vital parts of the urban ecosystem, with important ecological, landscape, cultural, and historical value. Conservation of middle-aged trees in urban areas is important for the development of large old trees in the future. In this study, we investigated the middle-aged trees in Changchun city and analyzed the species composition and diversity characteristics of different urban green space types and tree age classes. The results showed that there were 72 species and 22,376 plants of middle-aged trees in Changchun city, and the coniferous species prevailed. The top five species with a high importance value (IV) were Pinus tabuliformis var. mukdensis, Lavix olgensis, Salix matsudana, Ulmus pumila, and Abies holophylla. Green space type and tree age were important factors influencing the richness and diversity of middle-aged trees. Tree growth spaces were relatively sufficient, and land use was stable for park green spaces (PGS) and attached green spaces (AGS), which resulted in the abundant, richer, and diverse species richness (SR) of middle-aged trees. Road green spaces (RGS) and square green spaces (SGS) had fewer trees and lower species richness, Margalef richness index (dMa), Shannon–Wiener index (He) and evenness index (Je) which could be attributed to the high intensity of human interference and poor environmental quality. The SR of middle-aged trees decreased with an increase in age class, and the values of SR in Age Class 80–89 years and Age Class 90–99 years were lower than in Age Class 50–59 years. Age Class 70–79 years had the lowest values of dMa, He, and Je, which need to be protected urgently. The results of this study can provide a basis for the conservation and management of middle-aged trees in urban areas and the choice of species for urban greening.

The epiphytic bryophyte succession of Buxus sempervirens forests in the Fırtına Valley, Rize (North Türkiye)

In this study, the epiphytic bryophyte succession of the Buxus sempervirens L. forests in Fırtına Valley (Çamlıhemşin-Rize, North Türkiye), one of the nine biodiversity hotspots in Türkiye, were investigated. For this purpose, a total of 60 sampling plots were taken from the live trunks of the B. sempervirens trees of different ages. Twenty-nine epiphytic bryophyte species were determined (24 mosses and 5 liverworts) within the sample plots. Also, six different life form types and four different habitat affinity categories were determined. The mat type life form is in the first place with 34.4% whereas the and cortico-saxicolous species are the most common with 51.7%. Two-Way Indicator Species Analysis (TWINSPAN) classified the epiphytic bryophyte communities on the trunks of the B. sempervirens at the second level into two main clusters (A and B) and three sub-clusters (A1, B1 and, B2). Detrended Correspondence Analysis (DCA) axis 1 was interpreted as gradient along the height of the epiphytic habitat (from the lower base to the upper zone) on trunks and the DCA axis 2 was interpreted as gradient of moisture (from mesic to xeric). Exsertotheca crispa (Hedw.) S.Olsson, Enroth & D.Quandt was the species with the highest Index of Ecological Significance (IES) value on the lower bases of the aged trees. Species diversity and epiphytic cover in the upper zones were lower than in the basal and middle zones in the study area. While Metzgeria furcata, (L.) Corda, Oxyrrhynchium hians (Hedw.) Loeske, Plagiothecium nemorale (Mitt.) A.Jaeger, and Radula lindenbergiana Gottsche ex C.Hartm were only found on old trees, Ctenidium molluscum (Hedw.) Mitt. and Pseudoleskeella nervosa (Brid.) Nyholm were only found on middle-aged trees.

The epiphytic bryophyte succession of Picea orientalis forests on the Kumbet High Plateau (Giresun-Turkey)

In this study, the epiphytic bryophyte succession of Picea orientalis forests on the K?mbet High Plateau (Giresun-Turkey) were studied. A total of 21 epiphytic bryophyte species were determined (16 mosses and 5 liverworts). The epiphytic bryophyte communities were sampled in 60 sample plots taken from the trunks of Picea orientalis, each of which was 20 ? 20 cm in size. The Index of Ecological Significance (IES), based on a combination of the relative frequency and mean cover of epiphytic bryophytes, was used to evaluate the abundance of bryophyte communities in epiphytic habitats on the tree trunks. In addition, multivariate classification techniques (TWINSPAN and DECORANA) were used to classify the community structures in successional stages. TWINSPAN divided the 60 sample plots into two main groups: a) the lower base communities (LB) and b) the middleupper zone communities (MU). Moreover, the middle-upper zone communities (MU) were divided into two sub-groups associated with the successional gradient (MU1 and MU2). DECORANA classified these communities along the ordination axes 1 and 3 related to the height gradient of Picea orientalis and the moisture (from mesic to xeric) gradient of the epiphytic habitat. While Exsertotheca crispa, Cynodontium fallax, Lewinskya striata, and Habrodon perpusillus were only found on old spruce trees, Drepanium fastigiatum was only found on young trees and Lophocolea heterophylla was only found on middle-aged trees.

Measurements of the Load-bearing Structural Aspects of Pannónia Poplar from Sites in Western Transdanubia, Hungary

This study summarises the test results of Pannónia poplar (Populus × euramericana cv. Pannónia) originating from three plantation sites in Győr-Moson-Sopron County in the Western Transdanubia region of Hungary: Újrónafő 11G, Győr 540B, and Kapuvár 35A. The research primarily aimed to clarify the characteristics of radial growth depending on the plantation site and to predict the selected physical and mechanical properties of the xylem. Measuring the time-of-flight (TOF) in trees was performed with a non-destructive test technique using a “Fakopp” TreeSonic device. The stress wave velocity (SWV) values calculated from TOF data are significant in estimating the dynamic modulus of elasticity (MOE) of the xylem and, therefore, in the prediction of timber suitability for structural applications. During the on-site measurements, 50 trees – as random samples from every site – were investigated to determine the diameter at breast height (DBH) and the stress wave velocity in sapwood parallel to the grain. In addition to the non-destructive measurements, the laboratory analysis of the xylem from harvested logs (three logs per site, random sample) was also performed to determine the radial growth rate and density. The one-way ANOVA results revealed significant differences in SWV values between certain plantation groups. The difference between the average values of young and old plantations is 136.8 m/s, which is a significant difference. Similar findings occurred for the middle-aged and old plantation trees. The average values of the young and the middle-aged trees can be considered the same at the 0.05 level of significance. We also established that the trees in the young (22 years old) plantation site, Újrónafő 11G, planted with the closest spacing (3 m × 4 m), had the lowest average diameter of breast height naturally and showed the highest average value of SWV. Nevertheless, the sap- and heartwood samples from this plantation site had the highest average density values in a normal climate; therefore, the highest dynamic modulus of elasticity of the xylem can be expected in logs originating from this plantation site.

ВЛИЯНИЕ РЕКРЕАЦИОННОГО ВОЗДЕЙСТВИЯ В ЛЕСНЫХ СООБЩЕСТВАХ НА АЛЛЕЛОПАТИЧЕСКИЙ РЕЖИМ ДРЕВЕСНЫХ ЭДИФИКАТОРОВ

The allelopathic regime of the phytogenic field of model middle-aged trees of seven forest formations in the zone of humid subtropics of the Sochi Black Sea region was evaluated with an admissible range of stages of recreational digression. The method of biotesting of water extracts from forest litter, soil and roots was used to determine the spatial gradient of allelopathic activity of the phytogenic field environ-ment. The share of participation of the allelopathic factor in the formation of the phytogenic field at certain stages of recreational digression was established. It was determined that the value of allelopathic intensity of the phytogenic field, depending on the stage of recreational digression, field zones and edifi-cator species, can characterize the degree of resistance to the introduction of new species, recreational resistance and community stability.

Navel orange fine root nutrient content and rhizosphere effects varied with tree ages and soil depths in a hilly red soil region of China

ABSTRACT Root nutrients are required for the growth and development of roots and shoots, which are closely related to soil quality and fruit productivity. In this study, trees of contrasting stand ages, including young, middle-aged, and old trees, were selected in field sites with common management practices in the navel orange (Citrus sinensis) orchards of Southern China. The fine root N decreased with soil depth and the fine root P was higher of old trees (1.82 g kg-1) than young (1.57 g.kg-1) and middle-aged trees (1.37 g. kg-1). Soil organic C, total N, and P generally increased with plant age in the rhizosphere and bulk soils, while reverse trend was found for sucrase and urease activities. Interestingly, acid phosphatase activity was much higher at a lower depth (202 and 82 g.kg-1 OC d-1 for rhizosphere and bulk soils, respectively) than at an upper depth (46 and 43 g.kg-1 OC d-1 for rhizosphere and bulk soils, respectively). In conclusion, root and soil nutrients generally increased with plant growth. Fine root N decreased while fine root P remained unchanged with soil depth due to the content and rhizosphere effect of index at different soil layers related to N and P, respectively.

PECULIARITIES OF BIOECOLOGY OF HARMFUL VIRUSES IN APPLE PLANTS

The prevalence of harmful viruses of Apple stem grooving virus (ASGV), Apple stem pitting virus (ASPV), Apple chlorotic leaf spot virus (ACLSV), Apple mosaic virus (ApMV), depending on the location, age, and varietal composition of plantings, was studied. Sandwich ELISA was used in serological tests. Diagnostic kits from «Loewe» (Germany) were used for the analyzes. Leaves were taken as samples. The results of the analysis were recorded using a «Stat Fax 2100» photometer. On apple varieties and clonal rootstocks, the frequency of viruses was 36-54 % and 24 %, respectively. In the Moscow region, the ASPV virus (23 %) prevailed, in the Ryazan region — ApMV (33 %), in the Yaroslavl region — ACLSV (54 %). At the end of the 20th century, the ACLSV virus was more often detected on the apple tree, and in the last decade, we have established an increase in the infection of this crop with the more harmful ASPV and ASGV viruses. The highest prevalence of latent viruses was noted on old domestic apple varieties and foreign varieties (50 % each). A tendency to an increase in the indices of infection with most of the studied viruses was revealed with an increase in the age of trees. In apple trees of old age (over 20 years), the indices of infection with the ASPV virus increased by 25 %, ASGV — by 20 %, ACLSV — by 43 % compared to middle-aged trees (8-10 years). Apple plants of 15 varieties and apple rootstocks of 2 forms 54-118 and 57-490 were found free from the main harmful viruses

Effects of ontogenetic stage and leaf age on leaf functional traits and the relationships between traits in Pinus koraiensis

Investigating the effects of ontogenetic stage and leaf age on leaf traits is important for understanding the utilization and distribution of resources in the process of plant growth. However, few studies have been conducted to show how traits and trait-trait relationships change across a range of ontogenetic stage and leaf age for evergreen coniferous species. We divided 67 Pinus koraiensis Sieb. et Zucc. of various sizes (0.3–100 cm diameter at breast height, DBH) into four ontogenetic stages, i.e., young trees, middle-aged trees, mature trees and over-mature trees, and measured the leaf mass per area (LMA), leaf dry matter content (LDMC), and mass-based leaf nitrogen content (N) and phosphorus content (P) of each leaf age group for each sampled tree. One-way analysis of variance (ANOVA) was used to describe the variation in leaf traits by ontogenetic stage and leaf age. The standardized major axis method was used to explore the effects of ontogenetic stage and leaf age on trait-trait relationships. We found that LMA and LDMC increased significantly and N and P decreased significantly with increases in the ontogenetic stage and leaf age. Most trait-trait relationships were consistent with the leaf economic spectrum (LES) at a global scale. Among them, leaf N content and LDMC showed a significant negative correlation, leaf N and P contents showed a significant positive correlation, and the absolute value of the slopes of the trait-trait relationships showed a gradually increasing trend with an increasing ontogenetic stage. LMA and LDMC showed a significant positive correlation, and the slopes of the trait-trait relationships showed a gradually decreasing trend with leaf age. Additionally, there were no significant relationships between leaf N content and LMA in most groups, which is contrary to the expectation of the LES. Overall, in the early ontogenetic stages and leaf ages, the leaf traits tend to be related to a "low investment-quick returns" resource strategy. In contrast, in the late ontogenetic stages and leaf ages, they tend to be related to a "high investment-slow returns" resource strategy. Our results reflect the optimal allocation of resources in Pinus koraiensis according to its functional needs during tree and leaf ontogeny.

Natural Restoration of Norway Maple Stands in the Conditions of the Republic of Tatarstan

The article provides an analysis of changes in the areas of Norway maple stands in the forests of the Republic of Tatarstan from 1944 to 2019. According to the accounting data of the forest fund as of 01.01.2020, the area occupied by maple in the Republic of Tatarstan is 29.3 thousand hectares (2.5 % of the forest fund area), including 5.0 thousand hectares of young growth of the 1st and 2nd age class, 21.4 thousand hectares of middle-aged trees, 1.9 thousand hectares of ripening trees and 1.0 thousand hectares of ripe trees. A reliable relationship was revealed between a decrease in the area of maple after extremely low frosts of 1939–1940, 1941–1942 and 1978–1979, and an increase in its area after the drought of 2010. After the drought of 2010, there is a natural replacement of highly productive birch stands with low-quality maple stands, which will lead to a deterioration of the commodity structure of the felling fund of the Republic of Tatarstan. Maple plantations have a mixed composition and farming in them should be aimed at increasing the proportion of species valuable for these conditions – oak and birch.

Long observation period improves growth prediction in old Sugi (Cryptomeria japonica) forest plantations

ABSTRACT It is important to predict the growth of Sugi forest plantations in old age. When predictions about the growth of Sugi forest plantations are made and there is a lack of growth data from older trees, it is possible that the accuracy of these predictions becomes worse. For example, it is known that the growth of Sugi does not get slower at older ages as expected from past growth predictions based on growth data from young to middle-aged trees. This study investigated the changes in extrapolated values of diameter at breast height (DBH) in old Sugi forest plantations with changes in the observation period of training data for model calibration. The study sites were long-term growth observation sites of Sugi forest plantations in the University of Tokyo Chiba Forest and Chichibu Forest. In this study, both DBH of individual trees and mean DBH of stands were analyzed by fitting Richards growth functions. The results showed that the accuracy of growth predictions in old ages was improved by including growth data from a sufficient number of older trees. From another point of view, growth prediction in old ages tended to underestimate actual growth if growth data did not include enough older trees.

Typological structure and productivity of pine forests of the Mountain Crimea

The study of the features of the territorial distribution, productivity and typological structure of natural pine stands in the Mountain Crimea was conducted. Crimean pine plantations dominate by the area here. The most productive and long-lived stands are C l-Скр under the conditions of dry sudubrava Ci. Taxational characteristics of Crimean pine plantations in different high-altitude zones reflect the peculiarities of high-altitude dynamics of their age composition. The lower belt is dominated by plants of small height and with a small trunk diameter. The stands of the upper belt have the most significant taxation characteristics. According to the level of living state, the stands of Crimean pine of the lower belt are mostly characterized by an unsatisfactory assessment. This is due not only to the negative anthropogenic impact, but also to the more severe action of limiting factors in the regional territory of natural growth of Crimean pine on the southern macroslope of the Main ridge of the Crimean mountains. Natural stands of common pine form forests in the edaphotopes of dry pinewood Bi, dry sudubrava Ci and fresh sudubrava C2. Under the conditions of dry sudubrava Ci there is an increase in the productive capacity of common pine stands. The level of use of the forest typological potential of a pine stand depends on its age. The ratio of age groups characterizes the pine stands as cyclo-multiplc-agcd. The fullness of stands of common pine varies within the range of 0.3-0.9, the average is 0.6. The most common planrings have the fullness of 0.4 and 0.5. The structure of the typological macrocomplex of stands of Stankevich pine is represented in a greater degree by communities of dry sudubrava Ci. Unfavorable abiotic factors have a direct impact on the composition of stands of Stankevich pine, the age structure of which is characterized by a predominance of young and middle-aged trees and a noticeable decrease in the number of ripening and ripe stands and a very small representation of high-aged plantations. The relative increase in the number of trees at the age of 200 240 years is evidence that in the past the conditions for the growth and renewal of stands of Stankevich pine in the Mountain Crimea were more favorable.

Using of morphometric and phenological parameters of <i>Tilia cordata</i> Mill. for bioindication

The paper contains the results of long-term bioindication studies of assessing the state ofTilia cordataMill. in the conditions of Yoshkar-Ola city, which differ in the degree of environmental pollution by industrial transport emissions. The work analyzes a variability ofTilia cordataindividuals of various ontogenetic states of the generative period according to a complex of morphological and phenological characters using statistical methods of principal components and an analysis of variance. The heterogeneity of ontogenetic groups of trees according to morphological and phenological characteristics is established. The individuals of the mesobiontic speciesT.cordataunder the conditions of an average degree of pollution of the urban environment are considered to be small-leaved. With an increase in anthropogenic load the area of the leaf blade decreases, but the area of its damage increases. The index of fluctuating asymmetry of the leaf blade does not differ concerning the trees growing in various environmental conditions. A method of principal components helped to identifyT. cordatasmost variable signs of shoots and rhythms of seasonal development, which can be used for bioindication: sizes and number of structural elements of buds and shoots, terms and duration of phenophases. The most sensitive to habitat pollution are middle-aged generative trees ofT.cordata.

Tree age did not affect the leaf anatomical structure or ultrastructure of Platycladus orientalis L. (Cupressaceae)

Tree aging is a new research area and has attracted research interest in recent years. Trees show extraordinary longevity; Platycladus orientalis L. (Cupressaceae) has a lifespan of thousands of years. Ancient trees are precious historical heritage and scientific research materials. However, tree aging and tree senescence have different definitions and are poorly understood. Since leaves are the most sensitive organ of a tree, we studied the structural response of leaves to tree age. Experiments investigating the leaf morphological structure, anatomical structure and ultrastructure were conducted in healthy P. orientalis at three different ages (ancient trees >2,000 years, 200 years < middle-aged trees <500 years, young trees <50 years) at the world’s largest planted pure forest in the Mausoleum of the Yellow Emperor, Shaanxi Province, China. Interestingly, tree age did not significantly impact leaf cellular structure. Ancient P. orientalis trees in forests older than 2,000 years still have very strong vitality, and their leaves still maintained a perfect anatomical structure and ultrastructure. Our observations provide new evidence for the unique pattern of tree aging, especially healthy aging. Understanding the relationships between leaf structure and tree age will enhance the understanding of tree aging.

Spatial distribution patterns and intra-specific competition of pine (Pinus yunnanensis) in abandoned farmland under the Sloping Land Conservation Program

The Sloping Land Conversion Program is also known as the ‘Returning Farmland to Forest Program’ intent to gradually recreate farmlands back to the original forested state. Providing cognition on the effects of the policy on the distribution of dominant species is important to better understand plant community structures, development dynamics, regeneration conditions, and possible underlying ecological mechanisms. The purport of this study is to inspect the population structure of Pinus yunnanensis in a 2500 m2 area of abandoned farmland where restituted to forest in 2004. The results showed that the population structure of P. yunnanensis settled on tree age formed an inverted J-distribution (20.1% seedlings, 34.2% young trees, 38.5% middle-aged trees, and 7.1% adult trees) since 2009, whereas seedlings, young trees, and middle-aged trees showed clustered distribution. Seedlings showed the highest aggregation degree (g(r) = 6.4), followed by young trees (g(r) = 2.3) and middle-aged trees (g(r) = 1.7), but a random distribution showed in adults throughout the research area. The spatial relationships among seedlings, young trees, middle-aged trees, and adults indicated that the aggregation consequences increased with the decreasing difference in the diameter at breast height. Furthermore, the correlation of canopy height and diameter at breast height decreased with the increasing competition among the individuals signified that seedlings and young trees growing in the same area might use fewer resources than needed. Generally, the study illustrated that intra-specific competition due to environmental resources is a rarely occurring event.

Leaf Age Compared to Tree Age Plays a Dominant Role in Leaf δ13C and δ15N of Qinghai Spruce (Picea crassifolia Kom.)

Leaf stable isotope compositions (δ13C and δ15N) are influenced by various abiotic and biotic factors. Qinghai spruce (Picea crassifolia Kom.) as one of the dominant tree species in Qilian Mountains plays a key role in the ecological stability of arid region in the northwest of China. However, our knowledge of the relative importance of multiple factors on leaf δ13C and δ15N remains incomplete. In this work, we investigated the relationships of δ13C and δ15N to leaf age, tree age and leaf nutrients to examine the patterns and controls of leaf δ13C and δ15N variation of Picea crassifolia. Results showed that 13C and 15N of current-year leaves were more enriched than older ones at each tree age level. There was no significant difference in leaf δ13C values among trees of different ages, while juvenile trees (&lt;50 years old) were 15N depleted compared to middle-aged trees (50–100 years old) at each leaf age level except for 1-year-old leaves. Meanwhile, relative importance analysis has demonstrated that leaf age was one of the most important indicators for leaf δ13C and δ15N. Moreover, leaf N concentrations played a dominant role in the variations of δ13C and δ15N. Above all, these results provide valuable information on the eco-physiological responses of P. crassifolia in arid and semi-arid regions.

Some Factors Involved in the Success of Side Veneer Grafting of Pinus engelmannii Carr.

The establishment of clonal seed orchards is a viable option for the continuous production of improved seed of desired genotypes. Grafting is the main technique used to establish clonal seed orchards. The objective of this study was to examine how the geographic location and the age class of the donor trees of buds, the phenological status of the buds, and the anatomical characteristics of the scions and the rootstocks affect the survival and growth of Pinus engelmannii Carr. grafts. Scions were collected from two trees in each of three age classes (young, middle-aged, and old). Grafting was performed with buds in two physiological states (end of dormancy and beginning of sprouting). Cross-sections of the grafted organs were obtained for anatomical analysis. A Cox proportional hazards model was used to determine the effects of the variables that were considered. The age class of the scion donor trees, the total area of the cut surface of the scion, and the density of resin channels in the scions significantly affected (p &lt; 0.05) survival of the grafts. By contrast, the physiological state of the buds and the other anatomical characteristics of the grafted organs did not significantly affect graft survival. In P. engelmannii, grafting was most effective when scions from middle-aged trees were used. Graft survival was enhanced by a small total area of the cut surface of the scion and low density of resin channels in the scions. The area of the cambium of the scions directly influenced growth of the grafts.