According to the study, as the altitude increases from sea level, the number and diversity of species also increase. In lower altitudes, the forest cover is typically formed by only two or three species, while tree species increase at higher altitudes. These findings are consistent with the research of Mohammadi Zadeh et al. (2014), Hasanzadeh Navroudi and Safari (2018), and Rezaei Sangedehi et al. (2020).
As the altitude increases, the frequency of oak species decreases. Conversely, species such as Pistachio, Maple tree, Almond tree, and Italian Honeysuckle increase in frequency. Additionally, the frequency of hawthorn species is low in the lower band, but it increases in the middle altitude and decreases again at higher altitudes.
The status of the volume varies depending on the altitude. The volume is low in the lower altitude strata, reaches its maximum in the middle altitude, and then decreases again in the higher altitude. However, the northern and southern slopes studied do not follow the same pattern, mainly as a result of the direction of the slope.
The findings of this study are in agreement with the results obtained by Zhu et al. (2010), Gonmadje et al. (2017), and Mannan et al. (2018) regarding the decrease in volume along the altitude gradient. However, they do not align with the reports of Maza et al. (2022), Thokchom and Yadav (2017), and Cuni-Sanchez et al. (2017). Several factors could affect the increase or decrease in inventory along altitude gradients, including geographical latitude, forest type being studied, slope direction, soil type, and even the degree of slope (Soleimani et al., 2008).
Various factors have contributed to the reduction of forest inventory in the lower regions of the study area. These include drought and recent climatic variations in the Zagros region (Javanmiri Pour et al., 2023), intensified duration and severity of dust storms (Shahbazi et al., 2016), seasonal wildfires (Javanmiri Pour et al., 2022), soil compaction due to agricultural practices, livestock presence in forests (Javanmiri Pour et al., 2022), and destruction resulting from developmental activities (Alireza et al., 2020). These activities have caused reduced tree fertility, increased soil erosion, weakened trees, and made them susceptible to pest infestation and diseases. Alterations in rainfall patterns and changes in climatic parameters such as air temperature, wind speed, solar radiation, evaporation, transpiration, and dust have led to variations in tree species and associated characteristics across altitude gradients.
The distribution of trees across various altitude gradients has been observed to follow a distinct pattern of diametric classes, primarily adhering to a reversed normal model, which forms a U-shaped curve. This pattern holds true for elevations ranging from 1200–1475 m to 1475–1750 m and 2025–2300 m. However, at the elevation class of 1750–2025 m, the pattern intermittently transforms into a reversed J-shaped or a reversed U-shaped model. Furthermore, the distribution of trees across different altitude zones exhibits a Gaussian trend or a reversed U-shaped pattern in the lower and middle altitude classes ranging from 1200–1475 and 1475–1750 m. Contrastingly, the trend is declining in the middle and high-altitude regions (1750–2025 and 2025–2300 m).
It is worth noting that the inconsistent pattern observed at the elevation class of 1750–2025 m may be the result of various environmental factors, such as moisture and soil type, which may play a significant role in shaping the distribution of trees. Nonetheless, the pattern observed across different altitude gradients provides valuable insights into the natural patterns of forest growth and can help us understand the dynamics of forest ecosystems better.
Over the past two decades, natural and human-induced disturbances have caused deviations from the natural structure of forest ecosystems, resulting in significant impacts on the distribution of trees in terms of diameter and altitude classes. One of the most notable factors contributing to this phenomenon is the presence of livestock grazing in forest areas. The effects of this activity have led to the depletion of scarce regeneration and the forest's support base, both of which are necessary for its sustainability.
In the region under consideration, various types of shepherd camps exist, which are located in different altitude classes and significantly influenced by environmental factors, especially their altitude above sea level. These camps play a vital role in the life cycle of forest trees. In particular, shepherds utilize them during the autumn and spring seasons. Autumn is the season when seeds are produced, while spring marks the budding season for saplings. However, due to the presence of livestock in forest areas, seeds and saplings become fodder for the animals, leading to a negative impact on the forest's regeneration capacity.
In conclusion, the natural and human-induced disturbances in forest ecosystems have caused significant changes over the past two decades, leading to a deviation from their natural structure. The presence of livestock grazing in forest areas is a notable factor contributing to this. The negative impact of this activity on the forest's regeneration capacity and support base is crucial for its sustainability. Shepherd camps play a crucial role in the life cycle of forest trees, but their utilization during the autumn and spring seasons needs to be managed carefully to mitigate the negative impact on seed and sapling availability.
The present study aims to scrutinize the degree of dieback among trees in different altitude regions. The results indicate that the dieback status is more severe in lower-altitude regions compared to the mid-altitude regions. Moreover, within the mid-altitude areas, the degree of dieback is higher compared to the higher-altitude areas. These findings are consistent with the results presented by Karamian and Mirzaei (2020). However, the results are inconsistent with the findings of Mirzaei et al. (2019).
These findings have important implications for policymakers and environmentalists. The study highlights the need for effective measures to mitigate the impact of dead trees in lower-altitude regions. Moreover, it underscores the importance of monitoring the degree of dieback in mid-altitude areas, which are critical for the survival and growth of trees. Future research should focus on identifying the underlying causes of dieback in different altitude regions and developing targeted interventions to address this issue.
It has been observed that an elevation increase of every hundred meters from the sea level results in a reduction of approximately 0.6 degrees Celsius in air temperature. This temperature change, in turn, significantly affects the distribution of vegetation cover. It is noteworthy that the temperature change can cause a significant shift in the type of vegetation, as different species of plants have varying temperature requirements for optimum growth and survival. Therefore, an accurate understanding of the relationship between elevation, temperature, and vegetation cover is crucial for effective land management and environmental conservation.
Notwithstanding the pervasive issues related to global warming and climatic changes observed at larger scales, such as the ones under scrutiny in this study, the most significant factor in reducing dieback is the elevation from sea level. This is due to the fact that at higher elevations, the air temperature is lower, resulting in the ecological cold requisite for the physiological dormancy of trees and concomitantly, minimizing pest activities.
During the winter months, insect activity is inhibited by the presence of colder temperatures, which forces them into hibernation. This phenomenon results in a decrease in insect activity, particularly at higher altitudes, where the freezing winter temperatures often lead to casualties among specific insect populations. However, at lower altitudes, the absence of typical cold spells during the winter months means that damaging agents can persist, causing harm to Iranian oak trees.
It is essential to note that while insect hibernation is a natural occurrence, the absence of this process in lower altitudes can have severe consequences for the ecosystem. The impact of damaging agents on Iranian oak trees highlights the need for a proactive approach to mitigate such threats. The application of appropriate pest control measures can help prevent the destruction of these essential trees, which are vital to the ecosystem's health and biodiversity. The presence of colder temperatures during the winter months can have a significant impact on insect populations, forcing them into hibernation. However, this phenomenon is not universal, particularly in lower altitudes, where damaging agents can cause harm to trees. Therefore, it is necessary to implement preventive measures to protect the ecosystem and mitigate potential threats.
As altitude increases from sea level, due to the thinning of the air and less heat absorption, coupled with increased ground reflection at night, the reduction in air temperature occurs largely. The alteration of elevation from sea level is a crucial environmental factor that provides insight into the distribution of living organisms across temporal and spatial dimensions (Azizi et al., 2020). This factor exerts a significant influence on the quantity and type of precipitation, evaporation, transpiration, and solar radiation intensity, which, in turn, affects the type and density of vegetation cover (Roupioz et al., 2016). Alterations in elevation have been shown to reduce tree growth (Cooms and Allen, 2007). With an increase in altitude from sea level, the average air temperature decreases, resulting in the formation of distinct climatic regions in conjunction with other climatic factors. This, in turn, leads to the creation of regions with species diversity and adaptation to specific cold conditions (Magurran, 1988), which are less susceptible to drought stress during global warming and climate change.