Fire-Induced Alterations in Soil Function and Regeneration Dynamics of Subtropical Chir Pine (Pinus roxburghii) Forests

Abstract

Sub-tropical chir pine (Pinus roxburghii) forests are highly susceptible to forest fires due to the resinous nature of the species and the accumulation of dry needle litter on the forest floor. Recurrent fires can significantly alter vegetation structure, soil properties, and natural regeneration processes, thereby affecting long-term ecosystem stability. This study aimed to evaluate the impacts of forest fire on soil physicochemical properties and natural regeneration in sub-tropical chir pine forests of District Buner, Khyber Pakhtunkhwa, Pakistan. The study was carried out in four naturally burnt forest patches and four adjacent unburnt patches. Soil samples were collected at a depth of 10–20 cm using an auger, with five representative samples obtained from each patch, resulting in a total of 40 samples. Laboratory analyses were conducted to assess soil potassium (K), phosphorus (P), pH, electrical conductivity (EC), water holding capacity (WHC), and organic nitrogen. To evaluate the effects of fire on regeneration, twenty circular plots (8.4 m radius) were established in both burnt and unburnt areas, yielding a total of 40 plots. Within each plot, all naturally regenerated chir pine seedlings with a height of 4 feet or less were counted. Soil physicochemical properties and regeneration dynamics were significantly changed by forest fire. Burnt soils exhibited significantly higher potassium concentrations (20.54 vs. 15.75 mg kg⁻¹), reduced water holding capacity (12.62% vs. 25.47%), lower electrical conductivity (0.06 vs. 0.46), higher pH (6.49 vs. 6.35), and lower organic carbon content (0.256% vs. 0.585%), while phosphorus showed no significant change (p = 0.145). Forest regeneration was also significantly reduced in burnt areas (34.6 vs. 44.0 seedlings). The findings highlight that forest fire has pronounced effects on soil health and regeneration dynamics in subtropical chir pine forests. Understanding these changes is essential for sustainable forest management and ecosystem restoration in fire-affected landscapes. The study recommends the implementation of firebreaks, fuel load reduction, erosion control measures, and community-based fire management strategies to mitigate fire impacts and promote long-term forest resilience.