Introducing the appropriate model of oak forest and drought relations



in Ilam province



Introduction

The forest ecosystems of the Zagros vegetation region have a very long history of exploitation in various

forms. The material of the Zagros vegetation region is Iranian oak. In recent years, a significant

proportion of oak forests have dried up or have experienced drought. Although the main cause of drought

in these forests has not been determined yet, in the preliminary studies, factors such as climate change,

increasing dust, increasing drought periods, pest infestation and disease, high user changes have been

cited as reasons for drought in the Zagros forests. (Hosseinzadeh and Pourhashemi, 1396). Iran's location

in the arid and semi-arid zone of the world (sub-tropical region) has often been associated with

fluctuations in climatic and atmospheric elements and under the influence of atmospheric currents,

synoptic patterns, irregularities in precipitation and temperature patterns (Rahmati, 2016; 1383).

Comparison of the effect of climatic variables on healthy masses and affected by the decline of oak in

Khorramabad city based on rainfall and temperature data using Pearson correlation coefficient, on annual

growth rings of oak trees Effectiveness of drought of oak trees from both series In general, healthy trees

have been more affected by monthly and seasonal temperatures and have shown the highest coefficient of

correlation with the temperature of the region (Naseri Karimvand et al., 2016). , And the Standardized

Rainfall Index (SPI) and the correlation between these two indicators in assessing and monitoring drought

in different areas of Isfahan province, the results showed that NDVI plant index can be a good alternative

to climatic indicators in drought assessment and monitoring) with the conclusion and colleagues, 2011:

79).

Data and Method

So from SPI and NDVI indicators and Moran index and statistical regression statistics and satellite

images of Modis and Landsat have used to analyze the relationship between dieback of Ilam forests and

happened drought in the region. The precipitation data of 93 rain gauge stations were analyzed during the

statistical period and according to the dry coefficients of SPI index, drought zoning layers of Ilam

province were prepared for two time series of 2000 to 2009 and 2010 to 2019. Greenery's raster layers

were prepared from Modis satellite imagery for the mentioned time series. The results of analysis of

Moran's statistical showed a significant correlation between the SPI index and the NDVI index in spatial

dimensions. By a simple random method, 143 points of oak dieback with dimension of 30 m 2 , which each

point was equivalent to a pixel-size, were recorded with a GPS device, and by simulating in satellite

imagery, the droplet layer of oak dieback was extracted.

Result and Discussion

What is debatable about the results of the implementation of methods for obtaining drought ranges and its

relationship with oak drought points or masses is that the results of the models show a statistically close

and direct relationship between drought and oak drought. . The general trend of oak drought and drought

in these two decades has been from the southeast to the northwest of Ilam province, with increasing

temperature and decrease in rainfall in the southern and eastern regions of the province and increasing

rainfall and decrease in temperature in the central and northwestern regions of Ilam province. The data of

the synoptic stations are consistent. Analysis of satellite imagery and declining greenery in the models

although the study was aimed at meteorological drought and precipitation fluctuations, but spatial

changes of arid points and masses in the province were adapted to field visits and human intervention,

especially in the southeast with agriculture. Under the rubble and the remnants of the dried trees, the ax

has been placed on the roots of these trees, and this trend is spreading in almost other parts of the arid

areas of the province. Therefore, due to the irregularity in the pattern of precipitation and temperature of

the research country (Rahmati, 2016; Zandi Army, 2004) and the effect of monthly and seasonal



نشریه تحلیل فضایی مخاطرات محیطی، سال نهم، شماره 1، بهار 1401 2

temperature on the growth and decline of oak trees in the study (Naseri Karimvand et al., 2016) and other

related research and The flooding situation in the basins of Ilam province, the rainfall, the impermeability

of the soil and their erosion, and finally the lack of moisture in the months before the oak trees grow in

the soil and the increase in temperature in the dry season, which leads to reduced humidity and eventually

greenery. Variables affecting oak drying in linear regression are not responsive, but more accurate results

will be obtained in multivariate regression, although regression analyzes are spatially empty, and X and Y

represent a one-way, quantitative analysis based on the number of dried trees with pixel counts. Drought

range is measured which this defect in SPI method despite its spatial and statistical analysis using Moran

statistical index due to non-compliance in the coefficients of this index with the range of changes in

Moran statistical analysis in statistical analysis is a more appropriate explanatory coefficient than The

regression models showed but at a lower level than the NDVI method it placed. The advantage of NDVI

method with Moran statistical analysis is the relationship between pixel and pixel, ie in spatial analysis,

all pixels that have green changes have been analyzed in the same domain of spatial changes with oak

trees. High results and higher statistical explanation coefficient were obtained than other models.

Conclusion

Although linear regression between extracted oak dieback points with SPI and Moran statistical indicators

was significant, but the relationship between NDVI index and Moran statistic has the effect of

independent variable of drought trend in spatial and temporal dimensions on the dependent variable

process of oak drought with spatial analysis. And nonlinear regression has a more appropriate and

accurate statistical significance and explanation. So this method as desirable method has been introduced

for analyzing of drought and oak dieback.

Keywords: Ilam province, oak forest drought, drought, Moran index