نوع مقاله : مقاله پژوهشی

نویسنده

گروه جغرافیا و برنامه ریز شهری دانشگاه شهید باهنر کرمان

چکیده

نبکاها یکی از اشکال فرسایش بادی است که در اثر تجمع ماسه در اطراف گیاهان شکل می‌گیرد. این پژوهش سعی دارد با استفاده از مدل‌های آماری نقش پارامترهای مورفولوژی گیاهی را در تشکیل نبکاهای گونه کؤبر در کویر انار بررسی کند. پس ابتدا با ترسیم ترانسکت‌هایی نبکاهایی که در امتداد آن‌ها قرارگرفت شناسایی، سپس پارامترهای ارتفاع، قطر قاعده و شیب دامنه نبکا، همچنین طول و تعداد شاخه‌ها اندازه‌گیری و با استفاده از مدل‌های آماری روابط بین این پارامترها تحلیل شد. نتایج نشان می‌دهد که هرچند توسعه هوایی اندام‌های این گیاه محدود است، توسعه جانبی اندام‌های این گیاه بر روی زمین میزان خروجی را به حداقل رسانده است و به نسبت سایر گیاهان حجم بالایی از رسوبات بادی را به دام می‌اندازد. بنابراین، هرچند نبکاهای این گونه زیاد نیست، حجم ماسه تثبیت‌شده آن قابل توجه است، به‌طوری که این گونه قادر است به طور میانگین در حدود 25/0 مترمکعب رسوب را تثبیت کند. مقادیر بالای ضریب تبیین به میزان 88 درصد بین مؤلفه‌های ارتفاع نبکا با طول شاخه‌های گیاه و 83 درصد بین حجم نبکا و طول شاخه‌های گیاه بیانگر نقش مهم مورفولوژی این گیاه در انباشت رسوبات بادی است.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

The role of vegetation in Nebkhas formation and evolution in Anar desert

نویسنده [English]

  • Mohsen PurKhosravani

Department of Geography and Urban Planning, Shahid Bahonar University, Kerman

چکیده [English]

Introduction
Wind erosion is considered as the most important factor in degradation of Iran desert areas in Quaternary period and at the present time, 30 million hectares of surfaces are affected by the wind (Ahmadi and Feiznia, 1999: 429). Plains vast space, inadequacy or lack of vegetation, abundance of fine particles, looseness or detachedness of particles are some of the factors that have provided necessities for the wind to form interior plains (Alaei Taleghani, 2005: 295). Vegetation limits transportation of sediments by reducing wind speed. This action causes accumulation of wind sediments around vegetation and formation of Nebkha landscapes in result. In other words, Nebkha is the result of interaction between wind erosion and vegetation. Khalaf (1995: 275) argues that morphology of Nebkha is controlled by growth patterns of plant species to a large extent. Stallins (2006, 4) states that understanding of ecogeomorphological landscapes takes place by considering ecology and geomorphology processes and feedback between them. Therefore, the type of plant species forming the Nebkha and the connection among characteristics of plant ecology and Nebkha cones morphometry are the most important topics in Nebkha sediments morphology and systematic analyzes. This study tries to rely on quantitative characteristics in geomorphology. Also, relationships among factors of Nebkhas landscape will determine yielding Nebkhas. Since several factors are involved in Nebkha morphology, this study tries to investigate the importance of vegetation in the Nebkha morphology without changing some of the other factors. In other words, by selecting a limited area of study, climatic factors (wind, rain and ...), sedimentary factors (size, grading and ...) and time is assumed constant. Therefore, changes and communications made by performances of plant species forming Nebkha have investigated. The main purpose of the research is to investigate relationship between vegetation morphology and Nebkha morphometry characteristics based on statistical analyzes.
Materials and Methods
First, by using aerial region images, then by using field study, the study area and then the Nebkhas territory were determined. Sampling took place along transects that cover the entire area then the morphometric characteristics of Nebkha were measured along each transect. Sample size determined by Nebkhas locations along the deployed transects locations. Totally, 60 species of Capparis Spinosa were evaluated. In order to study characteristics of Nebkha, the morphological factors like attributes, height, slope (North, South, East and West mean slopes) and base diameter were measured and in order to evaluate the vegetation forming Nebkha, plant morphology factors such as mean length of the branches and number of branches were measured. The technique for measuring the relationship between plant traits and morphological traits has been stabilized by simple and multiple regression analysis using SPSS software. Regression equations such as linear, quadratic and cubic are tested for optimizing the results.
Results and Discussion
Pearson linear correlation analysis results between Nebkha morphometric characteristics and plant morphology characteristics suggest that the most correlation is between the branch numbers and Nebkhas height, to the extent level of 0.94 degree. Also, the correlation between the mean length of branches and Nebkha height is to the extent level of 88.0 degree. And also, the regression analysis results of comparison between Nebkha morphometric characteristics and plant morphology characteristics suggest that the largest relationship for linear, quadratic and cubic equations with probable error level of less than 0.01 is between the mean length of branches and Nebkha height to the extent level of 77 percent.
Results of multiple regression analysis have used to investigate the amount of all plant variables effect on the morphometric Nebkhas. Model 1 justifies multiple correlation analysis, between components of Nebkha height and the mean length of branches and the branch numbers with the mean coefficient of 0.89. Model 2 has designed for the relationship between two variables the mean length of branches and the branch numbers with Nebkha base diameter and the model coefficient is 0.743. Model 3 stated the relationship between the mean length of branches and the branch numbers with the mean slope cone. In this model, the regression coefficient is equal to 0.722.
Conclusions
In geomorphological studies, figures of the earth are reflections of surface processes and their systematic structure. Investigating structure and function of these systems would cause access to their past and also ability to draw their future evolutionary path. Research results show that a strong correlation between the components of Nebkha morphometry and plant morphology can be seen in the study area. Results indicate that the numbers of Capparis Spinosa species branches have the greatest impact on sedimentation of wind deposits.

کلیدواژه‌ها [English]

  • Anar desert
  • modeling
  • morphology
  • morphometry
  • Nebkha