جستجوی مقالات مرتبط با کلیدواژه « دندروژئومورفولوژی » در نشریات گروه « جغرافیا »

The annual loss of soil in the world is about 75 billion tons. In Iran, soil erosion is one of the most important environmental problems, and in Iran's catchments, soil erosion increased by 800% between 1951 and 2002. The significant decrease in the performance of Iran's catchments due to a large amount of erosion indicates the increasing necessity of monitoring and following up on this destructive phenomenon. Dendrogeomorphology is a technique that has been very successful in describing and determining geomorphological processes. Dendrogeomorphology is a very flexible method to assess soil erosion and can be used as a data source to determine the reliability of data obtained from direct estimation techniques. The purpose of this research is to investigate the state of sheet erosion in the Nachi watershed using the dendrogeomorphology technique on the oak tree's protruding roots as the region's dominant species. Considering the limited nature of such studies in Iran and the very fragile situation of the studied area, and the risk of filling up the reservoir of Zrebar Lake, which is very important from the point of view of the environment, it is necessary to study the situation of sheet erosion and soil wastage and sediment trans.

In order to achieve the research objectives, after collecting and preparing the primary information, including written information, statistical data, maps, and pictures, a preliminary area survey was carried out, and sampling sites were selected. The samples were prepared according to the program, based on the status of the catchment (according to the land use of the catchment and the direction of the range, the desired work units were selected in places with exposed roots). Based on this, different samples were taken in two different forests, agriculture uses, and western, eastern, and southern directions. All the samples were prepared from the oak tree species, which is the absolute majority in the study area. Finally, 64 samples were selected from the collected samples that could analyze the growth rings' anatomy. Discs harvested from the roots were used to reveal the vegetative rings of the discs by polishing and cutting the surfaces. Using a sanding machine, it was gradually polished with different grades to clear the growth ring border. Then, the disks were measured in the laboratory to determine the first year of root emergence and to determine the width of vegetative rings using a Lin-Tab 5 device equipped with a binocular microscope and specialized T-Sap chronology software with an accuracy of 0.01 mm.

This research showed that in the Nachi catchment, surface soil erosion in agricultural use (average erosion rate 2.43 mm per year) compared to forest use (average erosion rate 0.6 mm per year) is about 4 times. The results of the statistical tests also showed that the type of land use affects the average annual surface erosion rate in the studied basin. Also, this study found that different geographical directions do not affect the average annual surface erosion rate of the Nachi catchment. Comparing erosion values in agricultural and forest use shows the importance of natural covers' protective and important role in preserving the soil and preventing its erosion and wastage. Various studies in the world and Iran have shown that in recent decades, there has been an increasing increase in land use changes, that these changes have the basis of increasing runoff and affecting the amount of soil loss, comparing erosion in the agricultural area with the forest area, showing the protective and important role of the covers. Natural and forests have a valuable role in preserving the soil and preventing erosion and wastage of soil.

The results of this research reveal the necessity of paying more attention to studies on the possibility of modification and change of land use in these areas. The change in land use and the negative effects caused by human interference are not only in the basin itself but also in places outside the occurrence of erosion in the form of accumulation on high-quality agricultural lands, pastures, water storage sources, and irrigated canals. Also, the creation of pollution by sediments and heavy metals and accompanying chemicals, especially the threat to the very fragile ecosystem of Zrebar Lake, is more evident today than ever before. It is suggested to use another method parallel to this method in future works to validate the obtained erosion rate. In future studies, sampling should also be done from the northern slopes for a more detailed investigation of the effect of the slope directions on soil erosion.

Dendrogeomorphology is one of the most important techniques for determining the age of geomorphological processes such as slope movements, flooding, erosion, earthquakes and other processes. One advantage of application of dendrogeomorphology in the estimation of gully erosion is that it can estimate the annual rates of erosion. The aim of this research is to estimate the lateral and bed erosion of gully by dendrogeomorphological analysis of tree roots in Nilkooh catchment. To achieve this goal, a total of 50 samples from the roots of broadleaf trees, including Evangelical, wild persimmons, alder, oak, hornbeam, hawthorn and maple that have been exposed after erosion, were dated. The 35 samples were tested for lateral erosion of gully and 15 samples were also examined for gully bed erosion. During sampling, the information such as slope gradient, distance of the sample from the wall of gully and geographical coordinates were also recorded. Samples were dried in natural conditions and have been sanded for better clarity. In this study, exposed roots were sampled during 2013-2014. The minimum and maximum ages of roots were 3 and 14 years, respectively. The study reveals that the average rate of lateral and bed erosion of gully are 0.053 and 0.107 meter, respectively. The lateral erosion of gully has inverse correlation with elevation and gradient, whereas bed erosion of gully has positive correlation with elevation gradient.

  Flash floods are localized hydrological phenomena occurring in small catchments of a few to a few hundred square kilometers, with response times typically being a few hours or less As a result, they represent one of the most significant natural hazards with serious death tolls and economic damage at a worldwide level in general and in Mediterranean mountain catchments in particular.( Villanueva, 2010:383). Dendrogeomorphology is one of the subdivisions of dendrochronology (bah rami, 1389:1). Which is based on the analysis of the annual growth trees of trees for the age of geomorphic processes (Butler,2013:717). Geomorphic processes may influence trees in various ways The impact of rocks and boulders or abrasion processes may cause scars to the stem surface or even decapitate trees. Unilateral pressure of flowing material can result in a tilting of the stem. Finally material may bury the stem base when deposited. Affected conifer trees react to these impacts with callus tissue, tangential rows of traumatic resin ducts the formation of reaction wood or with an abrupt growth suppression or release gives an overview of the different impacts of debris flows on trees and their reactions to the disturbances(Bollschweiler,2007:340).
Methods and material
To collect tree samples (dendrogeomorphology), the following is done. Primary visits (from wounded trees in the main bed of the region) were carried out for sampling in April, June and July, 2014 and April, 2016. In field operations, instruments such as GPS to record sample locations, meters are used to measure sample diameter and hand saw for sample sampling. During the sampling operation, 15 samples of damaged trees were selected. During the sampling, the sample was attempted from the main canal to reduce the probable extent of other damage (human injury) and, of course, the damage was caused by the collision of the coarse sediments of the debris flow on the trees . After sampling, they were exposed to sunlight for drying for one month. After drying, each fifteen samples were polished by soft molding and transferred to the lab for examination, and their age was precisely determined using a microscope.

The purpose of this study was to determine the aging of floods with debris flow that occurred in pre-flood years in 2001 and 2002 in the region, as well as the reconstruction of debris flows in the catchment area of ​​Tangrah. Due to lack of station in the basin, the dendrogeomorphology method is the best method for accurate estimation of heavy floods in this area. The area under study is located in a mountainous forest covered area. During the years 2001 and 2002, with the advent of a sudden precipitation, the region experienced various currents. Because of this, trees and stones have been damaged by these currents. Due to these injuries, the precise age of these floods and floods that occurred in the past can be determined. Samples taken more than the original bedding, it is certain that these trees were most affected by the flood. Also, using the dendrogeodomorphological method of damaged tree rings and determining the age of wounds in the region, the maximum instantaneous flow of two flows was calculated using Manning method.

Discussion and
The results of this study indicate that the most injuries caused by the flow of debris flow in 2001 with Volumetric flow rate 840.68 m3/s. The analyzing of Fifteen samples showed that these flows were related to 2001-2002 debris flows. According to surveys on the gathered samples in the tan drainage basin and questionnaire for determining the debris flow occurrence in previous periods, we concluded that during the past seventy years, the debris flows of 2001 and 2002 are the only large in this debris floods the tangrah catchment

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.

the flood of December، 1964 on Coffee Creek، Trinity County، California. United States Geological Survey، professional Paper 422-K، 1-22 Stoffel، M. and Bollschweiler، M. 2007: Tree-ring based reconstruction of past debris-flow events and assessment of future risks in 32 torrents of the Valais Alps (Switzerland)، Quat. Int.، 167/8، 398– 399.

IntroductionDendrogeomorphology, which was first introduced by Alestalo (1971), is a subdiscipline of dendrochronology that, based on the analysis of annual tree rings and their growth morphology, addresses the spatial and temporal aspects of earth surface processes in Holocene period. The applications of dendrogeomorphology is dating and determining changes of various geomorphic processes such as floods, glaciers, storms, river channel migrations, mass wasting, earthquakes, volcanism and soil erosions, etc. Dendrogeomorphological research has mainly concentrated on tree trunks. Only to a lesser extent, roots have been studied for evaluation of sheet erosion rate and gully erosion. Estimating the rates of erosion based on the exposure of roots is based upon the changes in the wood anatomical pattern which occurs as soon as a root is exposed. Materials and MethodsThe study area is located in southern part of Gharachay catchment in Ramian County (Golestan province, Iran), between 36ْ 48ََ to 36ْ 57 N lattitude and 55ْ 6ََ to 55ْ 17 W longitude. Gharachay catchment drains an area of 143 km2. The altitudinal extend of the area ranges from 560 m in the northwest to 2650 m in the southwest. Geologically the studied area is a part of the Gorgan-Rasht zone in the Alborz mountains. The geological formation of this area includes Khosh Yeylagh (Kh), Lower part of Khosh Yeylagh (LKh), Mobarak formation (Cm1), Ghezel Ghaleh formation (Gh), Doroud formation (D), Lower Shemshak (Js1), Middle Shemshak (Js2), Upper Shemshak (Js3), and Old Alluvial Fans (Qt1). The aim of this research is a dendrogeomorphological analysis of tree roots for estimating the rate of sheet erosion in Gharechai (Ramian) Catchment. At first, DEM, slope and aspect map of the study area have been generated based on the topographic map at a scale of 1:50000 from Iranian National Geography Organization toposheets. Lithological formations were derived from the Geologic map of the studied area at a scale of 1:100000 by means of GIS (Integrated Land and Water Information System (ILWIS)). Before sampling of tree roots, the location of the exposed roots recognized by field observations and a detailed geomorphic mapping of the mentioned area. Before cutting each section, a detailed delineation of the spatial and morphological characteristics of the surroundings of the root-such as tree type, geographical location (UTM coordinates), altitude, aspect; slope of the specific root-was made. A total of 42 samples of tree roots from conifers and broadleaf species that were nearly and uniformly distributed in the catchment (Fig. 5) were obtained. Following detection of exposed roots, 38 sections of conifers (33 sections from yew, 1 section from cypress, 3 sections from juniper, and 1 section from pine) and 4 sections of broadleaves (2 sections from ash and 2 sections from oak) were provided during August 2008. During the cutting of tree root samples, sun-exposed part of outcropped root, contact of root and soil surface, the vertical distance between the upper part of the root and the present soil surface were measured for every section. Results and DiscussionIn this study, the height of eroded soil layer since the time of exposure (Er) has been calculated by Gartner method (2007, P. 248). Several parameters have been calculated for reconstruction of Er. At first, the exposed part (height) of the root (Ex) for samples was recorded. Reconstructing the first year of root exposure was carried out by analyzing the changes in the ring-growth pattern (from concentric to eccentric) and thereby the size of the root (excluding bark) at the time of exposure (R2) was determined. Then, the size -or height- of whole root (including bark) in cross section (R1), thickness of the upper (B1) and lower (B2) part of the bark were measured. Based upon the Gartner method (2007), Er has been calculated as follows: Er=R2+ (B1+B2) /2-R1+Ex (1) The value of Er was divided by the number of rings growing since the year of exposure (NRex) to calculate the annual erosion rate (Era): (2) Whereas conifers show more observable growth rings in comparison with broadleaves, most of the root cross sections of this study have been derived from conifers such as yew that have distinguishable growth rings. The mean sheet erosion of study area, based on sections of exposed tree roots, has been estimated 0. 541 mm/y. erosion rates in sections with 200-250, 150-200, 100-150, 50-100 and less than 50 years old are 0. 25, 0. 30, 0. 40, 0. 48 and 0. 86 mm/y respectively. ConclusionThis represents that the rate of erosion has been increased since the past 250 years. Analyzing the erosion rate in vegetation types reveals that the mean erosion rate is lower in denser forests than sparse forests. Evaluation of erosion rate in geological formation reveals that the mean erosion rate in soils over geological formations that have less dense forests, such as Lower Shemshak (Js1) and Middle Shemshak (Js2), is higher. This study also shows that conifers like Yew and Cypress that have more obvious and countable rings, have more capabilities in estimating erosion than broadleaf species like oak and ash.