خلاصة:
دانش اقلیم شناسی درختی» با مطرح کردن اثرات اقلیمی موجود در حلقه های سالیانه درختان» شناخت عناصر اقلیمی
ادوار گذشته را بویژه برای مناطقی که از داده های اقلیمی کوتاه مدتی برخوردارندء فراهم می سازد. از جمله این مناطق,
منطقه دنا است. به همین دلیل در این مطالعه, اقدام به بازسازی میانگین کمینه دمای ماهانه نیمه سرد سال منطقه دناء به کمک
پهنای حلقههای سالیانه گونه بلوط ایرانی» توسط رگرسیون خطی ساده و درجه دی شده است. با این هدفه سه ارتفاع
رویشی در جنگلهای منطقه دنا انتخاب و ۵۲ نمونه رویشی از ۲۹ پایه درخت., استخراج و پهنای دوایر رویشی سالیانه آنها
توسط نرم افزار اتوکد با دقت ۳ میکرون اندازه گیری شدند. بعد از مرحله تطابق زمانی, برای حذف اثرات غیراقلیمی تمامی
پارامترهای اقلیمی و سری زمانی حلقه های رویشی استاندارد شدند. از میان چهار گاه شناسی تهیه شده توسط نرم افزار
ARSTAN، گاه شناسی باقیمانده (RES) با کمینه دما طی دوره ۱۳۹۱-۱۳۹۰ واسنجی و همبستگی معنادار مثبت دما با
پهنای دوایر رویشی تایید شد. بر اساس روابط و همبستگی بین گاهشناسی باقیمانده و داده های اقلیمی دوره آماری مشترک»
کار بازسازی کمینه دمای ماهانه بیش از ۱۳۱ سال گذشته منطقه انجام و مشخص شد در سه دهه اخیر, کمینه دمای ماهانه
نیمه سرد سال, نسبت به یک قرن قبل از خودء یک روند افزایشی را داشته و تا حدودی از سرمای فصل سرد کاسته شده
است.
1. Introduction
One of the most important challenges in climatic studies of Iran is the lack of access to long-
term climatic data for all regions; among such regions, one can point to Dena region. This
region is in in the central Zagros, parts of Isfahan province, ChaharMahal and Bakhtiari, Fars
province and Kohkiluyeh and Boyer-Ahmad province. The longest reported climatic report of
the weather stations of the region is less than 30 years. On the other hand, dendroclimatology field provides information on temperature and rainfall of past periods through addressing climatic effects existing in annual rings of trees. This attempts aims to reconstruct minimum
monthly temperature of the past 131 years of Dena region based on the growth style of annual
growth rings of Quercus Persica.
2. Methodology
This study is divided into two parts:
2.1. Calculating the tree rings response to monthly temperature of cold seasons: to achieve
this goal, first, 3 dominant sites of Quercus Persica in the region were selected and 52 growth
samples were extracted from trees. Applying TSAP and ARSTAN, the index of sites'
chronology was prepared and the residual chronology was taken as the standard chronology and the statistical profile of this chronology was calculated. Then, applying Pearson moment
correlation, the response of growth rings to minimum monthly temperature of cold seasons
was specified for three stations of Yasooj, Pataveh and Dashte Room.
2.2. Reconstructing minimum monthly temperature of cold seasons from trees' growth
rings: in this section, applying a simple linear and quadratic regression, we reconstructed
minimum monthly temperature of cold months of the year (September-January) and the
validity and reliability of this construction was checked with the control station of
Shahrekord which is out of Dena region. 3. Discussion
The statistical features of the residual chronology of sites showed that the extracted samples
worth dendroclimatology studying. Some of such features include: internal correlation of
samples (0.529-0.574), the sensitivity of growth rings to minimum monthly temperature
(0.296-0.649), signal to noise ratio (9/52-10/16), and population signal (0.905-0.910). Also,
the results of Pearson correlation showed that the sensitivity of growth rings width to the
minimum monthly temperature of cold months is significant with positive correlation
coefficient and it is between 45 to 65 percent. In reconstruction stage, the mean coefficient of
determination of linear regression of reconstructed models, with confidence level above 95%,
was between 0.362 and 0.600 for the minimum monthly temperature for the stations except for February. Based on the reconstructed temperature, minimum temperature of October,
Geography and Environmental planning, 27th year, vol. 61, No. 1, April 2016
November, January and February of the last three decades has shown an increase of 1.7, 0.1,
0.3 and 0.2, respectively, in comparison to the previous century and the minimum
temperature of December has decreased about a tenth of a degree (-0.1). In addition, the
accuracy of reconstructed data of the region was confirmed with the control station
(Shahrekord).
4. Conclusion
The following conclusions are made based on this study:
Quercus Persica worth dendroclimatology study.
Quercus Persica is sensitive to the minimum of cold seasons of the year and this
sensitivity was significant with positive correlation coefficient.
Comparing the minimum monthly temperature of the cold seasons to the reconstructed
data of the previous century, it was found that the coldness of the cold months has been
decreased to some extent.
Studies show that the area of Quercus Persica forests of Dena region has been decreased
significantly in the last three decades and the results of this study show that due to the direct
correlation of minimum temperature with growth rings width, minimum temperature
probably has no significant effect on the decrease of the area of these forests.
It is probable that other climatic parameters and human interventions have more significant role in the decrease of Dena forests' area, which needs more investigations in this
field.
Reconstructing the minimum temperature of cold months of the year helps completion of
the climate database of Dena region and the country.