## 4 Discussion  
### Analysis of Causes Affecting Spontaneous Grassland Fires in Qinghai Province  
The alpine meadow region, particularly the alpine swamp meadow area, experiences a high frequency of grassland fires in Qinghai Province [34]. Alpine meadow vegetation thrives, with high underground biomass and a substantial combustible load. Due to the high altitude and cold climate of the Tibetan Plateau, microbial decomposition of withered grasses, roots, and plant and animal residues occurs at a slower rate. The weak mineralization process and limited nutrient release result in insufficient soil nutrients, affecting vegetation growth and leading to significant organic matter accumulation. Consequently, swamping and humification processes intensify, forming thick layers of humus and peat underground, where underground fires predominantly occur near swamps and wetlands. Underground fires are primarily found near swamps and wetlands where soil pores are saturated with water [48]. In these anaerobic environments, bacterial activity increases, producing large amounts of flammable gases such as methane and phosphine, which can spontaneously combust at room temperature. Seasonal freezing and thawing in alpine swamp meadows contribute to the expansion of depressions between grass mounds [49]. During the summer half-year, these depressions are waterlogged, and in the winter half-year, ice forms. As spring arrives, the lower ice layers melt while the upper ice layer remains, creating enclosed cavities where combustible gases, such as methane, accumulate. Under strong solar radiation, these gases are heated, leading to spontaneous combustion and triggering surface grassland fires, a phenomenon consistent with the findings of [PERSON] [50]. Additionally, when large amounts of organic matter accumulate in poorly ventilated conditions, microbial decomposition generates heat, raising temperatures and triggering spontaneous combustion. If rat holes and soil fissures are present on both sides of the depression, they can form chimney-like channels, drawing air into the fire zone. This accelerates combustion, allowing the fire to spread rapidly along these pathways. Hot air and smoke are expelled through the openings, intensifying underground flames. Consequently, accurately detecting the fire's location and assessing suppression effectiveness becomes challenging, leading to the formation of underground grassland fires [51] (Figure 6). The humus or peat layer is the primary factor limiting the spatial distribution of underground fires. Studies by foreign scholars have shown a high incidence of underground fires in areas with extensive peat distribution [12; 52]. Climatic conditions play a crucial role in underground fires [53; 54], while their spread rate is influenced by vegetation recovery and moisture content [55]. [PERSON] [56] conducted indoor experiments comparing the effects of moisture content, ash content, and compactness on humus combustibility, concluding that compactness has a relatively minor impact. Once a subsurface fire reaches a certain scale, its spread becomes difficult to contain, even in peat with high moisture content [57]. In undisturbed North American forests and Indonesian peat wetlands, underground fires can persist for days or even weeks. Ignition can still occur in peat wetlands with a combustible moisture content exceeding 120% [58; 59]. In Qinghai Province, spontaneous underground fires primarily occur in alpine swamp meadows near rivers, where abundant combustible materials and thick peat layers provide fuel for combustion. These fires can still ignite despite the high moisture content, aligning with previous studies that explain the occurrence of underground fires in high-moisture alpine swamp meadows. Forest underground fires generally occur during dry seasons with high temperatures and low rainfall, whereas in Qinghai Province, underground fires are primarily concentrated in spring (March-May) when temperatures are lower.