Journal of Spatial Analysis

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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

Keywords: Ilam province, oak forest drought, drought, statistical models

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