Ecological Effects of Fire Frequency on Soil, Microclimate, and Vegetation Dynamics in Secondary Forests at Nnamdi Azikiwe University Awka, Nigeria

Abstract

Anthropogenic fire is a pervasive agent of disturbance in tropical secondary forests, yet its specific impacts on ecosystem structure and function in West Africa remain inadequately quantified. This study assessed the effects of varying fire frequencies on soil physicochemical properties, microclimatic conditions, and vegetation composition in three secondary forest types within Nnamdi Azikiwe University Awka, Nigeria: frequently burned, periodically burned, and unburned (control). A completely randomized design was employed with three replicate plots (20 m × 20 m) per forest type. Standard analytical techniques were used to evaluate soil physicochemical properties. Vegetation was assessed via systematic sampling to determine species richness and Shannon diversity (H′). Data were analyzed using ANOVA and post-hoc Least Significant Difference (LSD) tests at p<0.05. The results demonstrated significant gradients of degradation with increasing fire frequency. Frequently burned sites exhibited severe depletion of SOM (1.04 ± 0.11%), N (0.062 ± 0.004%), and P (8.50 ± 1.40 mg/kg) compared to unburned (2.04 ± 0.11%, 0.154 ± 0.005%, 14.80 ± 1.30 mg/kg, respectively). Fire also induced soil acidification (pH: 5.26 in frequently burned vs. 6.08 in unburned). Microclimatic conditions were markedly altered, with frequently burned plots showing elevated soil temperature (33.5 ± 0.7 °C), reduced soil water potential (–1.2 ± 0.1 MPa), and diminished rainfall retention (45 ± 5%). Consequently, vegetation composition shifted dramatically, with species richness and diversity declining sharply from unburned plots (36.8 ± 2.15 species; H′=2.21) to frequently burned plots (8.4 ± 1.81 species; H′=0.92), indicating a successional arrest dominated by ruderal, fire-tolerant weed species. This study showed that frequent anthropogenic fire acts as a primary driver of ecosystem degradation in these tropical secondary forests, triggering a negative feedback loop of nutrient loss, microclimatic harshness, and biotic homogenization. A notable finding was the significant soil acidification under frequent burning, contrasting with the short-term alkalization often reported in other ecosystems. The findings underscore the critical need for implemented fire management strategies and targeted restoration interventions to mitigate biodiversity loss and promote ecological recovery in tropical forests globally.