The effect of varying fire regimes on soil biodiversity and physiochemical properties in the savannas of the Kruger National Park, South Africa

BACKGROUND

Savannas are one of the most extensive terrestrial biomes, covering about ~20% of the Earth’s land surface, roughly 50% of Africa, and up to 60% of southern Africa. In South Africa, the savanna biome is the largest, occupying more than one-third of the country. It is therefore central to regional biodiversity, carbon storage, and human livelihoods. Fire plays a key ecological role in these systems, helping to maintain the open tree-grass structure, support biodiversity, regulate woody encroachment, and control carbon and nutrient cycling. Because of this, fire is also widely used as a management tool. However, the long-term effects of different fire regimes on soil biodiversity and soil physical and chemical properties are still poorly understood, despite their importance for ecosystem productivity and resilience. Changes in fire regimes that alter soil biological and physio-chemical properties may thus have far-reaching consequences for overall ecosystem functioning.

This project uses the long-term Experimental Burn Plots (EBPs) in Kruger National Park, established in 1954, to investigate how different fire regimes; annual, triennial, sexennial, or no burning over more than 70 years affect soil health by integrating biological, physical, and chemical indicators. The main goal is to determine whether frequent burning reduces soil organic matter, nutrient availability, and biological integrity, and whether intermediate or less frequent fire regimes enhance soil stability and resilience. The study explicitly aims to connect soil fauna communities (their taxonomic composition and eco-morphological traits) with soil physics (structure, bulk density, porosity, water-holding capacity, moisture, texture) and soil chemistry (pH, salinity, nutrients, organic matter). By doing so, it addresses a key gap in savanna fire ecology and provides a comprehensive understanding of how different fire regimes influence soil function and overall ecosystem health in savanna landscapes.

OBJECTIVES AND HYPOTHESIS

• To determine the effects of contrasting fire regimes on soil biological quality and the composition of soil arthropod groups, and to examine changes in their eco-morphological functional adaptations using the QBS-ar approach.

H1: Contrasting fire regimes significantly alter soil biological quality, with higher fire frequency and intensity reducing soil arthropod diversity and lowering QBS-ar index values due to the loss of highly adapted euedaphic arthropod groups.

• To assess the extent to which different fire regimes alter key soil physical properties, including texture, bulk density, porosity, moisture content, water holding capacity, and soil structural forms.

H2: Frequent and high-intensity fire regimes increase soil bulk density and reduce soil porosity, moisture content, and water holding capacity compared to areas experiencing low frequency or low-intensity fires.

• To assess shifts in soil chemistry, including pH, salinity, organic matter, and nutrient availability across fire treatments.

H3: Different fire regimes significantly modify soil chemical properties, with burned areas showing increased soil pH and nutrient availability immediately after fire but reduced soil organic matter relative to unburned or low severity fire areas.

• To evaluate the relationships between fire regime attributes (frequency, intensity, and seasonality) and the combined biophysical and biochemical properties of soil.

H4: Fire regime attributes are significantly correlated with variations in soil biophysical and biochemical properties, with increasing fire frequency and severity leading to greater alterations in soil structure, chemistry, and biological quality.

METHODOLOGY

To achieve this goal, planned sampling will be randomly stratified within each fire treatment according to habitat type, based on topography and vegetation structure or cover. This approach ensures that any differences observed in soil properties and soil organisms can be attributed to the fire regime rather than to natural variation in the landscape.

Within each habitat type, four to six geo-referenced sampling points will be randomly selected using google earth Pro and GIS. All points will be located 50 m away from plot edges to maintain the integrity of the fire treatment and avoid edge effects. At each sampling point, soil will be collected from six depth classes between 0 and 30 cm. This depth range captures the main zone of soil biological activity and the soil layers most responsive to fire driven changes in organic matter inputs, temperature, and moisture.

• Biological indicators (soil fauna): Intact soil cores will be used to sample macro , meso , and microfauna. Soil fauna will be extracted using the Berlese-Tullgren strategy and preserved in ethanol for taxa identification and scoring with the Quotient of Biological Soil Quality (QBS) method. This approach will allow quantification of soil biological quality by measuring the presence and diversity of soil invertebrates such as mites, springtails, and insect larvae, which are directly linked to decomposition, soil aggregation, and nutrient cycling.

• Physical indicators: Bulk density, porosity, water holding capacity, moisture content, and aggregate stability and texture will be measured using standard gravimetric and core based methods. These metrics are chosen because fire induced changes in organic matter and vegetation cover are known to affect infiltration, compaction, and erosion risk key components of soil health in fire prone savannas.

• Chemical indicators: Soil pH, salinity (EC), organic matter (loss on ignition), total carbon and nitrogen (dry combustion using an elemental analyser), and plant-available macro and micronutrients (Mehlich-3 extraction with ICP-OES) will be analysed to capture fire driven shifts in soil acidity, ionic balance, nutrient availability, and soil C and N pools. This directly addresses the objective of understanding how fire regimes influence soil fertility and carbon storage.

SIGNIFICANCE

This project addresses major gaps in global fire-soil research, which often lacks long-term data and integrated biological-chemical-physical assessments. The EBPs provide a rare opportunity to quantify how decades of contrasting fire regimes influence soil biodiversity and ecosystem processes. The results will support evidence based fire management in Kruger National Park and contribute to broader conservation and climate adaptation strategies across Africa’s fire prone savannas.