جستجوی مقالات مرتبط با کلیدواژه « بارندگی » در نشریات گروه « جنگلداری »

Comparative studies of river flows increase our understanding of the environmental effects of rivers on the vegetation along its borders. The riverine areas are particularly sensitive to the hydrological cycle, which is used as a suitable indicator to show environmental changes. Considering that the plant elements of the riparian forests are affected by river fluctuations and climatic variables. The current research focused on to investigate the effect of the Climate factors and river discharge rate on the growth of white poplar (Populus alba), Russian olive (Elaeagnus angustifolia), and tamarisks (Tamarix sp) .

three species from riparian forest of Aras selected for this research, after select trees, by using increment borer samples were extracted from the stem of the studied species. Tree-ring width of samples were measured and recorded after preparation with using of LINTAB measuring table. After cross-dating tree-ring series of individual samples, final, create general chronology for per species by use of standardization methods and tree-ring chronology obtained for Populus alba with 48 years, Elaeagnus angustifolia with 28 years, and Tamarix spp 23 years.

Investigating showed that Populus alba had a negative correlation to the maximum temperature in September and the average temperature in August and September. The Elaeagnus angustifolia had a positive correlation to the mean temperature in May and a negative to the minimum temperature in August. Elaeagnus angustifolia showed a positive relationship with the river flow in March and a negative relationship in September. The maximum temperature in October and the average temperature in October and December before the growing season had a negative effect on the Tamarisk radial growth. The total monthly precipitation in December and February before the growing season had a positive effect, and in September of the growing season and in January before the growing season showed a positive relationship with Tamarisk. The discharge values in December showed a negative relationship with Tamarisk.

The results of this research showed that the air temperature of the summer months and the low amount of rainfall and river flow in the dry months of the year are the factors that control of the growth of trees. Understanding the impact of climatic variables and river fluctuations on riparian forests can play an important role in planning its restoration, rehabilitation and management. Due to the recent droughts and the construction of dams on the Aras river upstream, the amount of flowing water in the river decreases and leads to a decrease in the level of vegetation on its banks. Therefore, it is necessary to consider affecting factors in the selection of native species in afforestation.

The aim of this study was to analyze the annual, monthly, and seasonal rainfall changes over a thirty-year period as well as before and after the emergence of declining oak. (Quercus brantii var. persica) trees (2000) in Ilam and Lorestan provinces. For this purpose, the authors used long-term data of daily rainfall in 1987–2017 period recorded by four synoptic meteorological stations; Ilam, Dehloran, Khoramabad, and Aligudarz. The Mann-Kendall non-parametric test was used to determine the rainfall trends. The decreasing trends of annual rainfall as well as mean differences in annual precipitation before and after emerging oak decline were not statistically significant at all meteorological stations. The average rainfall of four stations was 502 mm in the first decade (1987-1997), while it decreased to 422 and 371 mm in the second (1998-2007) and third decades (2008- 2017), respectively. The difference in the amount of annual rainfall before and after the emerging oak decline (442 against 401 mm) did not alter the mean rainfall event (̴7 mm). Although the thirty-year trends of seasonal rainfall were not significant, winter rainfall was decreased after emerging oak decline by 11% and spring, autumn, and summer rainfalls were increased by 5, 4, and 2%, respectively. Rainfall fluctuations in the Zagros vegetation region may act an accelerating factor for the emergence and extension of oak trees declining in the Zagros forests of Lorestan and Ilam provinces.

Among climatic factors, temperature and precipitation are of two particular importance, which directly and indirectly affects the uptake and transport of minerals. In order to study the relationship between climatic variables and chemical element concentrations in two groups of healthy and declined Iranian oak trees, three healthy trees and three declined trees were cut in Dadabad habitat of Khorramabad. A disk was selected from each tree. Then, growth rings over the last 35 years were determined including three five-years and two 10-years pieces. The samples were cut and extracted by using the wet digestion method, and the concentration of different elements (Ca, K, Mg, Fe, Na, Zn, Cu, Pb, Ni, Si, Cr) was measured by using atomic absorption apparatus. The result showed that there was no significant difference between concentration elements of healthy and declined wood trees. The Pearson correlation between concentration elements and the average of seasonal temperature and rainfall was significant; in healthy trees, potassium with autumn rainfall (-0.931), magnesium with winter rainfall (0.959) as well as spring temperature (-0.969) and summer (-0.967) had significant correlations, and in declined trees, potassium with spring temperature (-0.961) and summer (-0.949), calcium with autumn (-0.953), silicon with autumn (-0.686) and lead with spring (0.966) temperatures had significant correlations. The difference between element concentrations of two groups of trees regrading climatic factors can be caused by the difference between genetics and physiological characteristics of trees, environmental physiography (especially light regulation and moisture regime), and physiology of uptake.

Trees respond to environmental and climatic changes during their biological life. Tree rings study is one way to discover these responses called dendrochronology. The most effective climatic factors which affect tree rings are temperature and precipitation. Present study aimed at investigating the influence of temperature and precipitation on annual growth of oriental beach (Fagus orientalis Lipsky) and oak (Querscus castaneifolia C.A. Mey), which clearly illustrate climatic factors on their tree rings. Trees were selected in three altitudes (450, 900 and 1380 a.s.l), from forest part 2 of Neka and Haft Khal in central Alborz mountains of Iran. Core samples were extracted from two sides of trees with an increment borer. Growth rings widths were measured by using LINTAB6 table with accuracy of 0.1 mm. The measurement results were analyzed using time series analysis software TSAPWin. Results showed that growth pattern of oak and beech in three altitudes were not similar. Altitudes affect mean growth of these species significantly. In each altitude, oak and beech have shown different responses to temperature and annual precipitation. These differences could be depending on species’ nature. In response to climatic factors, oak was more sensitive than beech. In high altitude, previous growth season temperature of affect oak chronology negatively while had positive effect on mid and low altitudes. In all altitudes, oak positively affected by precipitation of June (of current growth year). Beech of high altitude showed positive correlation with March and summer precipitation. However, no significand correlation was detected in beech in low altitude

The aim of this study is to assess the effect of climatic parameters on diameter growth of Persian oak trees in Sarab-Karzan forests of Ilam. Climatic data of a 29-year period (1987-2014) was obtained from synoptic weather station of Ilam to extract some mean monthly parameters. For investigation of tree diameter growth, 15 individuals with diameter 20 to 25 cm were chosen and core samples were taken from north side of trees using increment borer. They were polishd with corse and soft sandpapers and dimater growth was measured using microscope model 1001. Pearson correlation was used to investigate the correlation between diameter growth and climate parameters. Independent sample t-test was conducted to evaluate the significance of the correlations. The results showed that mean diameter growth of trees was 2.44 mm over the 29-year period. The highest correlation was observed between diameter growth and relative humidity in July (Pearson coefficient of 0.501) and September (0.558) (P≤ 0.01). In general, higher correlations were observed between diameter growth with rainfall in May (0.273) and temperature in July (0.354).

The aim of this study was to investigate the relationships between vegetation changes and climate variables including rainfall and drought using MODIS satellite images during the years 2000-2014 in Chaharmahal and Bakhtiari Province. In order to evaluate the impact of rainfall and drought on vegetation changes in 32 synoptic, climatology and rain gauge stations in and around the province, SPI index was calculated in short time series (3, 6, 9 months) and long time series (12, 24 months). All the time scales were leading to early June in which the maximum growth of vegetation of the province is occurred. To this end, SPI drought maps and NDVI images were prepared at different time scales by kriging method and linear regression analysis was performed to define their relationships. Comparisons of NDVI and SPI over the study period showed that the vulnerability of vegetation to drought mostly depends on the life forms and plant species. In this study, depending on the type of vegetation, different correlation coefficients were observed between vegetation and SPI indices. Among different rangeland and forest vegetation types, higher correlations were found between NDVI and SPI in rangeland vegetation types compared to the forest ones and the highest correlations belonged to the annual grass and annual forb vegetation cover. This confirms the higher impact of reducing rainfall on the decline of rangeland cover compared to the forest vegetation. Overall, the findings of this study indicate that the MODIS NDVI can be used to study SPI in the assessment and monitoring of drought effects on vegetation cover. By studying and recognition of vegetation cover and applying NDVI index to assess changes in vegetation cover, vulnerable types of vegetation to drought could be identified.

Trees having long living are able to reflex long effects of climatic conditions on their spread of tree ring width. So, this research we tried to analyse the impact of climatic variables (rainfall & temperature) on radial growth in Ali Abad Catool, Gorgan. For this reason between 23 (Cupressus sempervirense var. horizontalis) trees increment cores in diameter of beast height (DBH) using an increment borer were extracted. The width of annual rings of samples after making ready by use of measuring table, with LINTAB6 program and correctness 0.01 mm was measured. The cross-date and adjustment were done between samples, and maximum and minimum amount of GLK between samples, 0.75 and 59.2 were obtained. Average amount of tree ring width has been standardized and index of (Cupressus sempervirens var. horizontalis) has been calculated. Length of chronology that is got 244 years has been determined. The relationship between growth and climate was figured using action response function. That minimum February’s temperature in the last growth season is most important factor of electable climate on growth of (Cupressus sempervirens var horizontalis). The analysis of pointer years showed that minimum chronological distance of eventual event of climatic arid phenomenon is one year and maximum six years in the region. This research was figured consistently the growth limiting factor isn’t raining in the low heights but the temperature also reveals its role in low heights. Although the necessity of more study on other species can proves or disprove the results.

Many characteristics of the trees including annual ring width are affected by climate variations. This research investigates the effect of temperature and precipitation on tree rings of Quercus infectoria. Twenty two healthy and thick trees were selected from oak forests located in the region near Javanrood in Kermanshah with geographical coordinations of 34° 47' 30"N and 46° 20' 6E". Samples were taken by increment borers. After preparing the sample surfaces, rings width were measured by binocular and LINTAB measurement table and TSAP software. Cross dating was carried out using TSAP software. Data of six trees were excluded because of low cross-dating indexes. ARSTAN software was used to develop the ring-width chronology. Data of temperature and precipitation were collected from the nearest meteorological station and their effect on tree-rings were investigated. The results showed that temperature had a negative effect whereas precipitation had a positive effect on rings width because of warm and dry condition of the region. Rings width was positively and significantly correlated with precipitation in March and May while temperature affected the rings width negatively and significantly in January, February and June. The effect of precipitation on tree growth was more significant than temperature.

By comparing the pattern of narrow and width rings among the trees in one area, the exact year of each rings could be determine. This is the base of Dendrochronology. In this study, according to the important role of Juniper (Juniperus polycarpos) trees, an investigation have been done on variation of tree rings in three sites of Iran; Lain (Khorasan), Firouzkouh (Tehran) and Zanjan. 15 trees have been cored in each sites and ring width of each core was measured. After crossdating and standardization, 3 ring width chronologies were prepared and compared with climate data. Lain's trees were older than the others and Zanjan was the worst site. In many cases, the chronologies had similarities, especially between Lain and Zanjan and in extreme years like 1902, 1917, 1961 and 1975. There were significant correlations between tree ring width and temperature and precipitation in the study areas. Some of the most important ones were the positive effect of precipitation during autumn and winter period before and during the current growing season. The temperature had mostly negative effect on juniper trees but the temperature during September had mostly positive effect concerning the improvement of latewood cell’s expansion. The results showed that the Juniper trees are appropriate trees in Iran for studying dendroclimatology.