Zoning of Areas with Susceptibility to Oak Decline in Western Iran

In recent years, large-scale mortality and drought have occurred in the Zagros forests of western Iran, degrading thousands of oak trees (Zandebasiri et al. 2017, 2019, Hosseini et al. 2019, Ghanbari Motlagh et al. 2020, Jahanbazi Gojani et al. 2020). This phenomenon has been reported first time in the 2000s, especially in the forests of Ilam province, which has caused concern among foresters and authorities (Amir Ahmadi et al. 2015, Attarod et al. 2017, Kooh Soltani et al. 2018, Alesheikh and Mehri 2019, Mozafari et al. 2019). This is important because the forests of the Zagros cover 40% of the total forests of Iran, with an area of more than 5 million hectares (Ghadirian et al. 2018, Goodarzi et al. 2019, Zandebasiri et al. 2019).

Different species of Zagros oak including Quercus brantii Lindl., Quercus infectoria and Quercus libani are the most important and extensive forest ecosystems in Iran (Hosseini et al. 2017, 2019, Alesheikh and Mehri 2019, Mozafari et al. 2019). In addition, they play a very important role in water supply, soil protection, ecological balance and socio-economic status of residents (Costa et al. 2010, Ahmadi et al. 2014, Zandebasiri et al. 2019). Decline in tree species, especially oaks, is a function of various environmental parameters (Jurskis 2005, Gonzalez Alonso, Johansson 2008). These factors include droughts and climate change, reduced soil fertility, land use changes, pests and diseases, livestock grazing, etc., which have affected the health of trees and caused the phenomenon of decline globally (Oszako 2004, Eckhardt, Menard 2008, Gonzalez Alonso et al. 2008, Greenwood and Weisberg 2008, Kabrick et al. 2008, Costa et al. 2010, Ahmadi et al. 2014, Sohar et al. 2014, Keča et al. 2016, Amir Ahmadi et al. 2015, Attarod et al. 2017, Hosseini et al. 2017, Zandebasiri et al. 2017, 2019, Ghadirian et al. 2018, Alesheikh, Mehri 2019, Conte et al. 2019, Goodarzi et al. 2019, Mozafari et al. 2019, Touhami et al. 2019). Therefore, it is necessary to provide an appropriate model by considering these factors in order to prioritise declining forest areas to support decision-making by identifying susceptible areas and introducing preventive operations (Ghadirian et al. 2018, Kooh Soltani et al. 2018, Goodarzi et al. 2019, Mozafari et al. 2019). The decay of these forests has many irreversible ecological and socio-economic consequences for the future of the region (Kooh Soltani et al. 2018, Ghanbari Motlagh et al. 2020).

Today, with the development of new technologies and different patterns in zoning, some researches in this field would have been performed using different methods (Goodarzi et al. 2019). The most widely used among the methods are logistic regression models (Mahdavi et al. 2015a, Ghadirian et al. 2018), neural network models (Alesheikh, Mehri, 2019) and multi-criteria evaluation methods (Ahmadi et al. 2014, Kooh Soltani et al. 2018, Ghanbari Motlagh et al. 2020) in order to construct zoning maps of decline/dieback potential and determine the effective criteria. One of these methods is fuzzy logic, which has helped to solve many decision-making problems nowadays, and in most cases, it produces the best decision based on input data (Mohebbi Tafreshi et al. 2019). Fuzzy logic was first used by Professor Lotfi Asgarzadeh in 1965 to mean inaccurate, vague and ambiguous. In fuzzy logic, the degree of certainty or accuracy of a statement is expressed by a number between 0 and 1. Unlike Boolean or digital logic, the correctness of any statement is determined by two values, True and False (Zadeh 1965). Fuzzy is the spectrum between black and white, which allows modelling for real-world uncertain situations (Zadeh 1965). Fuzzy logic is one of the standard methods for selecting a suitable location and is basically a method of weighting the layers used because generally the parameters in the site selection are largely fuzzy in nature. This method is one of the most acceptable location methods (Lee 2007, Lewis et al. 2014, Mohebbi Tafreshi et al. 2019). Therefore, in this study, we used it to prepare a decline susceptibility map in the oak forests of Zagros in Ilam province in western Iran.

Standardised maps of the parameters were made based on the fuzzy functions defined in Table 1 (Fig. 2) and the final map of areas with susceptibility to oak decline was prepared (Fig. 3).

Fig. 2

Fig. 3

The present study has shown that all forests in the province are susceptible to decline. It is observed that 58.39% have severe susceptibility to decline, 19.85% have high susceptibility to decline, 16.71% have moderate susceptibility to decline and only about 6% have low susceptibility to decline.

A wide range of Zagros oak forests in Iran, especially in Ilam province, has suffered from susceptibility to oak decline and even ecosystem decline over the past decade. In this study, an attempt has been made to provide a zoning map of susceptibility to oak decline in this province based on a number of ecological, biological and socio-economic parameters using a fuzzy method based on GIS.

Oak decline is a phenomenon involving a set of factors that affect susceptible trees (Oszako 2004). Tree mortality reduces the quantity and quality of forest stands and negatively affects the performance of forest ecosystems. On the other hand, low species diversity in the context of these unfavourable conditions, beside events such as drought, cause deforestation (Keča et al. 2016). As a result, the regression process is accelerated and its structural changes are fully visible (Hamzehpour et al. 2011, Rostamnia and Akhoondzadeh Hanzaei 2016, Attarod et al. 2017, Jahanbazi Gojani et al. 2020). This issue has been mentioned in most studies related to the mortality of forest trees, especially oak species are very sensitive, worldwide (Jurskis 2005, Eckhardt and Menard 2008, Gonzalez Alonso, Johansson 2008, Costa et al. 2010, Sohar et al. 2014, Conte et al. 2019, Touhami et al. 2019).

The final map created is close to the fuzzy map of climatic factors. Especially areas with low rainfall indicate higher drought stress, because when rainfall decreases, evapotranspiration increases, and the possibility of weakening against stressors such as diseases, fungi and insects, which increase the possibility of decline (Eckhardt and Menard 2008, Kabrick et al. 2008, Sohar et al. 2014, Attarod et al. 2017, Hosseini et al. 2017, Pourhashemi et al. 2017, Conte et al. 2019, Goodarzi et al. 2019, Mozafari et al. 2019, Touhami et al. 2019).

Studies of Rostamnia et al., Akhoondzadeh Hanzaei (2016) and Hosseini et al. (2017) have shown that this province has been facing drought and rainfall changes in recent years, and especially oak species are very sensitive in response to these droughts. Data and a large number of trees have suffered from decline or physiological weakness and have been destroyed directly by drought or indirectly by pest outbreaks. Also studies of Hamzehpour et al. (2011), Ahmadi et al. (2014), Mahdavi et al. (2015a), Attarod et al. (2017), Goodarzi et al. (2019) and Mozafari et al. (2019) have revealed the relationship between climatic factors and oak mortality in the Zagros region.

Generally, weather conditions like high precipitation, low temperature, high farming land and low distance from streams favour the development of alien invasive oomycetes, especially Phytophthora genus (Woodward et al. 2005). Zoospores released, for example, after heavy rains can easily infect fine roots and interact with pathogenic fungi like Armillaria spp., which cause direct mortality of trees (Nowakowska et al. 2020). In such condition, the decline of trees becomes more severe when drought occurs after wet years. Damaged roots are not efficient in absorbing of water from dry soil. Climatic changes can even trigger this phenomenon in the future (Oszako et al. 2016).

Conversion of forest lands into agricultural lands in the vicinity of these forests in many areas of the Zagros basin leads to various problems. This allows more access and destruction of forests, soil erosion and even fires (Hamzehpour et al. 2011, Pourhashemi et al. 2017, Zandebasiri et al. 2017, 2019). As can be seen in the final map, the areas with proximity of agricultural land or greater access to roads is seen a higher potential for decline. In Mediterranean countries, the problem of changing the land use has affected the decline of oaks (Quercus suber) (Costa et al. 2010). Eucalyptus forests in Australia have also experienced decline due to human activities such as grazing and changes in forest land use (Jurskis 2005).

Among the topographic parameters, the highest compliance occurs in the elevation map. With increasing altitude and decreasing temperature and lack of access, the rate of deterioration increases (Eckhardt, Menard 2008, Greenwood, Weisberg 2008, Mahdavi et al. 2015a, Mozafari et al. 2019). Slope and aspect parameters act more locally and in many studies they are known as parameters affecting the decline of oaks in the forests of Zagros and the world (Eckhardt and Menard 2008, Ahmadi et al. 2014, Amir Ahmadi et al. 2015, Hosseini et al. 2017). Most mortality occurs in warmer, drier aspects (south and west) and steeper slopes. In these areas, more drought stress, less access to moisture and less soil depth cause trees to dry out and die (Eckhardt, and Menard 2008, Kabrick et al. 2008, Mahdavi et al. 2015a, Hosseini et al. 2017, Mozafari et al. 2019).

The phenomenon of oak decline has occurred in a large area of these forests where environmental parameters and habitat conditions such as climatic factors, topography, apart from socio-economic problems, are at the macro level. But at the local level and on a smaller scale, they have strengths and weaknesses and the appearance of the phenomenon of decline cannot be expected to be the same in different regions (Hamzehpour et al. 2011, Ahmadi et al. 2014, Jahanbazi Gojani et al. 2020).

In the final map of susceptibility to oak decline, which is made based on fuzzy gamma 0.9, more than 77% of the province's forests have high and severe susceptibility to decline. But the study Kooh Soltani et al. (2018) in Lorestan province showed that the fuzzy operator had the highest accuracy with 70% accuracy. This map is compared to the map of decline risk with three class presented based on the AHP (Analytical Hierarchy Process) method by Ahmadi et al. (2014) in which 51.7% of the area, 36.70% and 8.28% are at medium risk, and low respectively, it shows the conditions is much more critical. This situation indicates the need for emergency operations. The results of this study showed that GIS-based fuzzy logic can have great potential in solving complex spatial problems due to its speed, simplicity, and ability to provide acceptable results (Lee 2007, Lewis et al. 2014, Mohebbi Tafreshi et al. 2019) especially in the field of oak decline studies. Such zonings, which are prepared in very simple ways, can be used in the management of all forests in the Zagros region that are facing this problem and can be a guide for decision makers. But it must be considered that the mechanism and manner of relationship of environmental parameters is complex and nonlinear.