جستجوی مقالات مرتبط با کلیدواژه « tree rings » در نشریات گروه « جغرافیا »

Wood is the long-term memory of the history of a tree which is records the environmental changes by anatomic and formic changes. denderocronology uses the trees as natural evidences or "silent witnesses" to reconstructing the past environmental characteristics. ‘dendrogeomorphology’ is one of the subfields of dendroecology which has been widely used for study of past geomorphic processes. dendrogeomorphology is detected of spatial and temporal aspects of the surface processes by analyzing of annual growth tree rings and disturbances in tree forms. Also dendrogeomorphology enables to precise the event occurrences in annual and even seasonal time scales. Based on the principle of dendrogeomorphology affected trees by geomorphic processes react to the events as disturbances in their ring and forms, in other words these reactions recorded in the series of their rings. Trees in temperate climates generate one growth ring in each year and Flood as a river geomorphic process influences on the trees morphology in margins and river bed, and lead to different growth responses in the series of tree ring. Tilted and scared trees thought the river bed and banks are the most common types of dendrogeomorphological evidences created by paleoflood events. These tree disturbances have been used for dating and reconstruction of past geomorphic events. Stem tree scars can be used as a paleostage indicators(PSI) to help researchers for reconstruction past flood events.
Study area: With approximately 3 km length, the study area is part of the mainstream Neka River in the south of Neka city. The beginning of the study reach is located in 36˚ 37ʹ 24˝ N latitude and 53˚ 21ʹ 52˝E longitude. The end point of the study reach terminated to Abloo convert dam which is located at 36…N latitude and 7778 E. Neka basin is an oblong basin with an area over 1903km2 started from northern slopes of Albborz mountain range and drains to Caspian sea in the north side of Neka city. The main stream originated from the Shahkooh Mountain in the south of Grogan and after receiving other tributaries creates the Neka River, after passing across the Neka City flows into the Caspian Sea. The length of main stream channel is 150km measured from the upstream until basin outlet in the Ablo gage station.
Material and Research method of this study is experimental- historical. We Firstly collected the basic data including book and articles, statistical data, satellite images and digital elevation models (DEM). Then we have analyzed the frequency of peak discharge records obtained from Iran ministry of power (IMP) for Abloo gage station. As well as we prepared the base maps including contour, slop, aspect, and geomorphological maps.
Sampling method of our study was selective as we extracted 18 cores through stem tree scars using a 300mm increment borer. The sampling trees are been located in the margin of stream channel and river banks. Also we were taken 6 reference samples from the trees without growth disturbances to make a cross dating with damaged trees. We used an identification card to record the characteristics of the sampled trees, including of tree type, tree diameter, tree height and tree scar dimensions as well as we marked the tree coordinates using an Etrex Vista portable GPS. We continued the study stages after sampling as following steps: 1- the cores were fixed on wood holders, then exposed the samples for drying in the laboratory atmosphere for several days. 2- the sample surfaces were smoothed by special sand paper to produce better clearness of number and widths of the rings. 3- The number of rings and ring widths were counted and matured using digital table LINTAB attached to the stereomicroscope (Leica stereomicroscope) and TSAPWIN software program. These laboratory equipments provided a 1:100mmof measuring accuracy. 4- Tree growth curves were drawn by TSAPWIN package and then analyzed to reconstructing of the flood event times. 5- In the last stage, the results obtained by dendrogeomorpholology method are compared with stream peak discharge records of Abloo gage station for period of 111111. Also we surveyed 4 stream channel cross- sections to use them for assessing the surface, mean velocity and discharge of past large floods in the study sites.
In this study, we analyzed the biologic paleo stage indicators and stream channel flood marks to reconstruct the past large hydrological events. We dated the large floods according to the sudden decreasing in the growth trend and growth pattern of tree rings. Then the results obtained from the tree ring analysis were compared and adjusted with systematic instrument data of Abloo gage station. According to the results of dendrogeomorphological analysis, we found out that most of scars have originated from the floods of 2008 and1999 with 130m3/sec and 2000 m3/sec respectively. Most scared trees are resulted from above floods in the study reach as the flood impacts obviously recorded in the tree ring series. Also the flood of 2003 with 361 m3/sec peak discharge causes greatest impacts on tree growth trends in the margin of river bed. We reconstructed two past large flood events in the study river which is occurred before establish of Abloo gage station. Based on changes in tree ring growth trends these two floods occurred in 1941 and 1955. With 270cm height from tree base, the largest stem tree scar in the study area relevant to Flood of 1941. Moreover the reconstructed floods by tree rings method were compared and coincidence with peak discharge data of Abloo hydrometric station and obtained results show that all of cases have coincidence and conformity with recorded data in the study station. We recognized the highest stem scar in the sample number 16 which is formed by a flood in 1935. The Scar height shows the flood mark of the largest paleo flood with 4277 m3/s in the study river. Reconstructed discharge has been calculated using the geometric data of study reach. We surveyed 4 channel cross-sections regarding to tree scar heights, then the area, perimeter, slope and bed roughness coefficient parameters determined in the cross- section sites. We used the manning equation for estimation of past flood discharges.
Based on the results of this study we reconstructed two largest floods in the Neka River which they are occurred in 1941 and 1955. With discharge of 4277 m/3, It seems these floods are been the largest floods of the study river during the last hundred years. Also flooding years reconstructed by the tree scars was in concordance with the flood discharges recorded in the Abloo hydrometric station. But the amount of flood discharges obtained by denderogeomorphology method is more than the recorded discharges by Abloo gage station. Then we can suggest that the analysis of trees rings and the height of scars in tree stem, are the very useful tools in the Neka River basin for reconstruction of the year of flood events and estimating of flood discharges.

Iran’s precipitation mainly affects by air masses that arrive to it from adjacent area directly or affects as teleconnection pattern due to remoteness from water sources. Due to irregular arrival of the air masses to Iran and far distance to teleconnection centers، occurrence of precipitation variations is one of the prominent characteristics of Iran’s climate. Also due to short period of instrumental data in the meteorological stations، there is no possibility for understanding of the climatic variations during the last centuries. Reconstruction of climatic variations based on current evidences، shows a more realistic understanding of the climatic variations of the region. Trees are the useful climatic evidences that experience different climatic situation of temperature and precipitation during their life period and the effects of these climatic variations is reflected in their tissues. In temperate climates، trees add a ring annually to their previous rings. Therefore، by studying of the tree-ring widths، useful climatic information can be obtained over the last centuries of the region. In the previous studies، relationship between the Southern Oscillation Index (SOI) and Iran’s precipitation only has been studied in a relatively short period due to the lack of instrumental data. In this study، we present a longer period of relationship between monthly precipitations of the region with Southern Oscillation Index (SOI) by reconstruction of precipitation based on Oak tree rings in the central Zagros region over the last centuries (1705-2010). In the present paper، three sites of Oak species with a short distance to the meteorological stations were selected in Lorestan (Shineh)، Kermanshah (Faryadras) and Ilam (Dalab) provinces. In Shineh and Faryadras sites Quercus infectoria species and in Dalab site Quercus Persica species used for sampling. Two increment cores at different sides of each tree were extracted by a Suunto increment borer at breast high. In each site 10 to 14 trees were sampled. After air drying، the surface of cores was prepared by a razor blade. The ring widths were measured with a LINTAB5 measuring system with a resolution of 0. 01 mm، and all cores were cross-dated by visual and statistical tests (sign-test and t-test) using the software package TSAP-Win. Raw ring widths were standardized by ARSTAN program to remove non climatic signals. Three site chronologies were obtained from the three sites. To increase the length of the chronology and due to the same trends and high correlations between the three site chronologies، all growth curves were combined and the regional chronology was calculated. The values of mean sensitivity (MS)، signal to noise ratio (SNR) and first auto correlation (AC1) were calculated for the regional chronology. Mean monthly precipitation of Khorramabad (1951-2010)، Kermanshah (1951-2010) and Ilam (1987-2010) meteorological stations were used to calibrate the tree-ring/climate relationship. Due to the high correlation (p<0. 01) between the regional chronology and mean monthly precipitation of the region، October-May، precipitation of the region was reconstructed using a linear regression model. For investigation of relationship between the reconstructed wet years and the El Nino events، Historical El Nino events from 18th century to present were obtained from NOAA database. The longest value of SOI (1876-2010) was obtained from Bureau meteorological station. Finally the relationship between October-May monthly values of SOI and the reconstructed October-May precipitation of central Zagros was investigated in the common period (1877-2010). Similar growth patterns of trees in the three sites indicate that they influence by the same growth factors. Relationship and correlations between monthly precipitation and the regional chronology showed that precipitation has positive effect on tree growths in the region. The positive correlation with precipitation during the pre-growing season show the fact that precipitation during these months provides moisture availability in semi-arid regions and favors formation of early wood cells، which account for the majority of the total ring-width (Liu et al.، 2011). Compression between the reconstructed precipitation and the actual precipitation of the central Zagros region shows some years with inconsistency between observed and reconstructed data. Most of the reconstructed wet years have been occurred coincidence with El Nino events. There is a negative relationship between the reconstructed October-May precipitation of central Zagros and Southern Oscillation Index (SOI). It should be noted that negative values of SOI indicate El Niño events and during the El Niño phases precipitation in most parts of Iran is above average. According to this، Southern Oscillation Index (SOI) during October to May has positive effect on precipitation in central Zagros. The highest correlation (p<0. 01) between SOI and the reconstructed precipitation was found on November and December which is supported by the results of Azizi (2000)، Yarahmadi and Azizi (2007) and Khoshakhlagh (1998). Also there is a significant correlation (p<0. 05) between SOI and the reconstructed precipitation in April and May. It may be due to the far distance between the study region and the El Nino origin. Therefore the study region during April-May influence by El Nino with a lag time. The length of the regional chronology is 305 years (1705-2010). Total and monthly precipitations from October to May have positive effect on tree growths in the region. The results showed that dry conditions occurred in 1730s، 1760s-1790s، 1810s، 1840s-1850s، 1870s-1880s، 1900s، 1920s، 1940s، 1960s and 1980s. Comparison of wet years and historical El Nino events showed that 77 of reconstructed wet years have occurred with El Nino events simultaneously. Investigation of relationship between the Southern Oscillation Index (SOI) and the reconstructed October-May precipitation of the central Zagros region showed that SOI has positive effect on precipitation in the region. The highest negative correlation between the Southern Oscillation Index (SOI) and the reconstructed precipitation was found in December. The highest correlation (p<0. 01) between SOI and the reconstructed precipitation of the region was found in November، December and January. There was a significant correlation (p<0. 05) between SOI and the reconstructed precipitation in April and May as well.

Long-term climate records are valuable for environmental planning، and tree rings allow records to extend to the time before the establishment of weather stations. For a better understanding of the past climate fluctuation and to mitigate the effect of climate fluctuation، dendroclimatic reconstructions have been applied in many parts of the world. Inter annual variations of climate have an intensive effect on water resources، agriculture، human settlements and regional ecosystems. The central Zagros region of Iran experiences different climatic situations over the seasons of a year. In recent years، dramatic changes in regional climate have damaged both local forests and agriculture. Weather stations cover a short time span of instrumental data in Iran. To overcome this challenge، tree rings can be used to put recent climate trends in a long-term context of climate variability. The central Zagros Mountains are one of the most important sites of oak forest in west of Iran. However، tree-ring based climate reconstructions are still scarce for this country. In this study، we present a reconstruction of temperature variations in the central Zagros Mountains using Quercus infectoria and Quercus persica tree rings over the last 250 years (1750-2010). The study sites are located in the central Zagros Mountain range in the west of Iran. Due to the climatic regime، there is a clear distinction between a dry (summer) and a wet (winter-spring) season in this region. Our sampling sites are covered by old-growth oak forests and have the shortest distance to meteorological stations. In this study 54 cores from two species of Quercus persica in Dalab site (Ilam province) and Q. infectoria Olive in Shineh site (Lorestan province) were extracted using an increment borer. After the sample preparation، annual ring widths were measured with a LINTAB5 measuring system. The TSAP-Win software was used for cross dating and correlations between the growth corves. The growth corves were standardized with ARSTAN program to remove none climatic effects. The Expressed Population Signal (EPS; Wigley et al، 1995) was calculated for the regional chronology (RC). Monthly and seasonal maximum temperature from Ilam (1987-2010) and Khoramabad (1951-2010) weather stations were used to calibrate the regional chronology (1750-2010) during the common period (1951-2010). Based on a linear regression model، seasonal maximum temperature of spring-summer was reconstructed over the 1840-2010 period. The results of the study show that the two site chronologies are strongly correlated with each other (p)