Kruger National Park EBP carbon

Woody plant encroachment (WPE) is a global trend occurring in many biomes
including savannas and accelerates with fire suppression. Since WPE can
result in increased storage of soil organic carbon, fire management which
may include fire suppression can enhance ecosystem carbon sequestration in
savannas. At our study site in Kruger National Park, South Africa, we used
a long-term (~70-year) fire experiment to study the drivers and
consequences of changes in woody (trees and shrubs) cover and soil organic
carbon (C) sequestration. We surveyed four fire manipulation treatments
replicated at eight locations within the park, annual high-intensity burn,
triennial high (dry season) and low-intensity (wet season) burns and fire
exclusion, to capture the range of fire management scenarios under
consideration. Changes in woody cover were calculated over a period
similar to the experiment’s duration (~80 years) using aerial photographs
(1944–2018). Soils were analysed for soil organic C (SOC) and d13C to 30
cm, under and away from tree canopies to isolate local- and
landscape-level effects of WPE on SOC. The largest increases in woody
cover occurred with fire exclusion. We found that plots with greater
increases in woody cover also had higher SOC. Yet, trees were not the only
contributor to SOC gains, such that sustained high inputs of C4-derived
carbon (from grasses), even under canopies in fire suppression plots,
contributed significantly to SOC. We observed little difference in SOC
sequestration between the cooler triennial (wet season) burns and fire
suppression. Synthesis: Grass inputs to SOC remained high across the full
range of woody cover created by varying burning regimes. Total SOC stocks
stored from tree inputs only matched grass-derived SOC stocks after almost
70 years of fire exclusion. Our results point to C4 grasses as a resilient
contributor to SOC under altered fire regimes and further challenge the
assumption that increasing tree cover, either through afforestation
schemes or fire suppression, will result in large gains in C sequestration
in savanna soils, even after 70 years.