r. oladi

Globally, paulownia (Paulownia fortunei (Seem.) Hemsl.) is one of the most important wood species used in forestry. Despite extensive research on this genus, the influence of climatic factors on the growth and anatomical wood properties of paulownia has not been thoroughly investigated. Therefore, this research aims to examine how climatic factors—such as temperature, precipitation, relative humidity, and sunshine hours—affect radial growth and specific wood anatomical traits of cultivated paulownia trees in Gorgan County, Golestan Province, Northwest Iran.

Five 20-year-old Paulownia fortunei trees were selected from Hashemabad in Gorgan County. These trees were felled in late 2012, and a five-centimeter-thick disk was extracted from each stem base. Strips from the bark to the pith were cut radially from each disk, and the surfaces of the specimens were smoothed using a microtome blade before scanning. To enhance the contrast between the vessels and the background tissue, a charcoal blackening technique was employed prior to scanning. Using images obtained from image processing software, several features were measured: growth ring width, average vessel lumen area, porosity, vessel frequency, vessel area greater than 0.06 mm², radial and tangential diameter of vessels, and ray frequency in each growth ring. To eliminate the effect of juvenile wood—which consists of very wide rings in the early years of growth—five rings near the pith were excluded from measurements and analyses. Consequently, growth rings from 1998 to 2012 (15 years) were evaluated. Pearson correlation was used to investigate the relationships between climatic variables (monthly, bimonthly, seasonal, bi-seasonal, and tri-seasonal) and growth variables (growth rate and quantitative anatomical wood characteristics) from three months prior to growth until the end of the growing season. Additionally, internal relationships among the measured variables were assessed similarly.

The radial growth of paulownia exhibited a decreasing trend with age, particularly notable at seven and thirteen years. Other anatomical features (vascular traits and ray frequency) showed an increasing trend; however, vessel frequency did not exhibit a clear age trend. Correlation analysis revealed that all anatomical characteristics had an inverse relationship with growth rate; thus, as growth ring width increased, other characteristics (e.g., vessel area and vessel diameter) decreased. Vascular traits and ray frequency primarily showed positive correlations with each other, while the correlation between vessel frequency and other variables was weaker. Among climatic factors, total monthly rainfall and average sunshine hours in spring (especially May and June) significantly impacted radial growth and anatomical features of paulownia wood. Climatic factors from three months prior to the growth period (the previous winter) did not show significant correlations with anatomical characteristics; furthermore, correlations between anatomical traits and summer climatic factors were much weaker than those observed in spring. Increased spring rainfall enhanced radial growth while reducing anatomical features such as vessel size and ray frequency; average sunshine hours had a similar but less intense effect on these traits. Temperature and air humidity did not significantly affect the studied characteristics.

Overall, it can be concluded that paulownia has high water and light requirements but shows low sensitivity to temperature in the studied region. The months of May and June (mid to late spring) are particularly influential for radial growth and hydraulic architecture (water transport system) in paulownia trees. Increased precipitation and average sunshine hours promote radial growth but reduce vessel size. Additionally, ray frequency can be considered a valuable wood anatomical characteristic for studying the relationship between climate and tree physiology in future research. 

The Hyrcanian forests in northern Iran exhibit diverse rainfall and air temperature patterns. Altitude above sea level is a crucial topographical factor that influences plant growth and development, prompting trees to adopt different morphological, anatomical, and physiological strategies for survival and growth at varying elevations. This study aims to understand the impact of altitude on radial growth and tree-ring width by examining the rate of radial growth of Oriental beech (Fagus orientalis Lipsky) across different age classes in three altitude zones: low, middle, and high altitudes of the Hyrcanian forests in Kordkuy and Asalem habitats.

t three selected sites, located at approximately 700, 1400, and 2000 meters above sea level, tree-ring cores were extracted from 62 beech trees using an increment borer. Following core extraction, the holes on the trees were completely sealed with grafting wax. The surface of each core was prepared using a sequence of 100-, 400-, and 1000-grit sandpaper. Tree-ring widths (TRWs) were measured using LINTAB 5 and TSAP software. Measurements were taken from one side of the core and then from the other side. The obtained TRW series were analyzed using statistical parameters such as sign test, correlation coefficient, and Student's t-test. After cross-dating, average TRW chronologies were prepared for each tree. This method was then used to match the trees within each site. TRW chronologies for each site were verified using statistical methods. A one-way analysis of variance (ANOVA) test was performed to compare TRW chronologies. Meteorological data such as rainfall and temperature were obtained from the nearest weather stations. Meteorological data for Kordkuy and Asalem were obtained from the Gorgan and Astara meteorological stations, respectively.

The findings demonstrated that the elevation gradient had a significant impact on the radial growth of beech trees. TRW in the examined habitats is influenced by elevation above sea level in trees aged 50 to 150 years. The average radial growth of these trees in the middle elevations of Asalem and the lower elevations of Kordkuy is substantially higher than in other altitude areas. The mean growth of trees aged 100-150 years in the middle elevations of Asalem was the highest, amounting to 3.98 mm. Statistical analysis revealed a significant difference between the TRW of trees aged 100-150 years in the highland of Kordkuy with a mean annual growth of 1.94 mm and the lowerland of Kordkuy with a mean annual growth of 2.97 mm. During this age period, no significant difference was observed between trees from the upperland of Kordkuy and the moderate altitudes of Kordkuy, but there was a statistical difference between trees from moderate altitudes and the lowerland. A comparison of trees aged 200-250 years revealed a statistically significant difference between Kordkuy and Asalem moderate altitudes. The mean radial growth of trees aged 300-350 years in the upperland and moderate altitudes of Asalem is 1.25 and 1.32 mm, respectively. Statistical analysis demonstrated that there is no statistically significant difference between the mean radial growth of trees aged 300-350 years in the upper and middle altitudes of Asalem and the lowerlands of Kordkuy.

This study demonstrated that radial growth and tree-ring width of beech trees exhibited notable variations along an east-west transect across the Hyrcanian forests. The observed variations in beech radial growth and tree-ring sensitivity along the elevational gradient highlight the ability of beech trees to develop adaptive functional traits in response to environmental changes.

Vascular characteristics of the xylem determine the efficiency of the hydraulic system in broadleaved trees. To investigate the effects of elevation and longitude (temperature and precipitation gradient) on radial growth and vascular properties of common ash (Fraxinus excelsior) xylem, samples were taken from trees located in two wet sites in Ramsar (300 and 1300 m.a.s.l) and a semi-dry site in Sari (1260 m.a.s.l) of Hyrcanian forests. Tree-ring width (TRW), as well as early- and latewood width, average size (AVLA) and the number of vessels per area (VF), tree-ring porosity, relative specific hydraulic conductivity (RSC), and fiber length were measured and compared in the last ten growth rings of selected trees. According to the results, variations in vessel size were independent of other features and were affected by a different component. Compared with the highland of Ramsar, trees at low altitudes had wider annual rings while having lower RSC, VF, and porosity. Surprisingly, with a decrease in altitude (increasing temperature), the size of vessels shrank, which can be attributed to the inverse effect of over-threshold temperature on tree physiology. Despite the differences in AVLA and VF in the two highland sites of Ramsar and Sari, the combination of two features was in a way that the porosity, RSC, and TRW of trees in the two sites became comparable. In general, it can be concluded that in the western and central Hyrcanian forests, the effect of altitude – manifested in a decrease in temperature - on the radial growth and vascular system of ash trees is more pronounced than the effect of precipitation gradient (longitude).