The influence of fire frequency on the structure and botanical composition of savanna ecosystems

Abstract

Savannas cover 60% of the land surface in Southern Africa, with fires and herbivory playing a key role in their ecology. The Limpopo National Park (LNP) is a 10,000 km 2 conservation area in southern Mozambique and key to protecting savannas in the region. Fire is an important factor in LNP's landscapes, but little is known about its role in the park's ecology. In this study, we explored the interaction between fire frequency (FF), landscape type, and vegetation. To assess the FF, we analyzed ten years of the Moderate resolution Imaging Spectroradiometer (MODIS) burned area product (2003–2013). A stratified random sampling approach was used to assess biodiversity across three dominant landscapes (Nwambia Sandveld‐NS, Lebombo North‐LN, and Shrubveld Mopane on Calcrete‐C) and two FF levels ( low —twice or less; and high —3 times or more, during 10 years). Six ha were sampled in each stratum, except for the LN versus high FF in which low accessibility allowed only 3 ha sampling. FF was higher in NS and LN landscapes, where 25% and 34% of the area, respectively, burned more than three times in 10 years. The landscape type was the main determinant of grass composition and biomass. However, in the sandy NS biomass was higher under high FF. The three landscapes supported three different tree/shrub communities, but FF resulted in compositional variations in NS and LN. Fire frequency had no marked influence on woody structural parameters (height, density, and phytomass). We concluded that the savannas in LNP are mainly driven by landscape type (geology), but FF may impose specific modifications. We recommend a fire laissez‐faire management system for most of the park and a long‐term monitoring system of vegetation to address vegetation changes related to fire. Fire management should be coordinated with the neighboring Kruger National Park, given its long history of fire management. Synthesis : This study revealed that grass and tree/shrub density, biomass, and composition in LNP are determined by the landscape type, but FF determines some important modifications. We conclude that at the current levels FF is not dramatically affecting the savanna ecosystem in the LNP (Figure 1). However, an increase in FF may drive key ecosystem changes in grass biomass and tree/shrub species composition, height, phytomass, and density.

Mining the Microbiome of Key Species from African Savanna Woodlands: Potential for Soil Health Improvement and Plant Growth Promotion

“…Sampling sites were selected during field trips to LNP and through map analysis based on accessibility, fire frequency, and the three dominant landscapes (C, LN, and NS) [ 15 ] ( Table 1 ; Figure S1a ). In each sampling site, eight circular 40-m-diameter plots arranged in two contiguous parallel transects (4 plots per transect) were surveyed ( Figure S1b ).…”

“…), although it is also associated with several other prominent trees and shrubs, such as the red bush willow Combretum apiculatum Sond. [ 15 ].…”

“…Altogether, these factors may affect the vegetation structure and composition, and thus the ecosystem’s stability [ 17 , 18 ]. Therefore, analyzing the history of fire regimes, as well as species’ adaptation to fire, is essential to understand key ecosystem processes and biodiversity dynamics for decision-making support [ 15 , 19 ]. However, studies that elucidate the interactions of African vegetation with ecological drivers are recent and still scarce [ 15 , 20 ].…”

“…Therefore, analyzing the history of fire regimes, as well as species’ adaptation to fire, is essential to understand key ecosystem processes and biodiversity dynamics for decision-making support [ 15 , 19 ]. However, studies that elucidate the interactions of African vegetation with ecological drivers are recent and still scarce [ 15 , 20 ]. Ribeiro et al [ 15 ] reported that while the current fire regimes in the Limpopo National Park (LNP, Mozambique) do not have a negative impact on the vegetation structure or composition, long-term fire frequencies may impose key changes on biodiversity dynamics.…”

“…However, studies that elucidate the interactions of African vegetation with ecological drivers are recent and still scarce [ 15 , 20 ]. Ribeiro et al [ 15 ] reported that while the current fire regimes in the Limpopo National Park (LNP, Mozambique) do not have a negative impact on the vegetation structure or composition, long-term fire frequencies may impose key changes on biodiversity dynamics. On the other hand, the work of Burbano et al [ 20 ] in the Kunene region of Namibia was the first extensive report on the diversity and structure of nitrogen-fixing bacteria associated with C. mopane , highlighting an outstanding diversity of PGP diazotrophic bacteria in legume tree roots, many of which are as yet uncultivated, as well as the difficulties in detecting symbiotic root nodules.…”