This study tested whether fine particulate matter (PM_2.5) emissions from forest fuel combustion in the Xiao Xing’an Mountains are controlled by common or vegetation-category-specific factors. Six conifer, nine broad-leaved and seven shrub species were burned in a laboratory chamber (6966 measurements). Because the factors tested differed among categories, effects were analyzed within each category and compared across categories only for shared factors, using ANOVA, multiple linear regression, Random Forest and XGBoost. Fuel load was a primary factor in all three categories. In addition, PM_2.5 was controlled by moisture content, plant part and combustion mode in shrubs; by plant part, season and species in broad-leaved species; and by plant part and wind speed in conifers. Among the shared factors, moisture content had a clear effect only in shrubs (partial η² = 0.16 vs. ≤0.03 in trees). Smoldering tests produced 34% more PM_2.5 than flaming tests in shrubs (p < 0.001), and broad-leaved bark and branches had 89% higher PM_2.5 concentrations in April than in July. The mean shrub emission factor was 12.5 g/kg, without significant inter-species variation (p = 0.668). Under grouped five-fold cross-validation, Random Forest and XGBoost reached R² of 0.77–0.96, compared with 0.21–0.74 for linear models. The results support vegetation category as a stratification variable in regional forest-fire emission inventories.