Effects of Fire Frequency on Woody Plant Composition and Functional Traits in a Wet Savanna Ecosystem

Abstract

The objective of this study was to assess the effect of fire frequency on vegetation taxonomic and functional diversity in a wet savanna ecosystem, eastern Zimbabwe. The study area was stratified into three fire frequency regimes using a 15-year fire history (2000–2014) across the landscape: high (HFF: burnt every 1-2 years), medium (MFF: burnt every 3-4 years), and low (LFF: burnt every 5-6 years). Data were collected from a total of 30 plots measuring 20 m × 20 m each between March and May 2018. In each plot, we recorded tree maximum height (Hmax), woody plant density, basal diameter, resprouting capacity, and bark thickness. We calculated species evenness, diversity, functional richness (FRic), Rao’s Quadratic Entropy (RaoQ), functional redundancy, and relative bark thickness. We recorded 1,031 individual trees belonging to 24 species across the three fire regimes. Significant differences across the three fire regimes were recorded for Hmax, woody plant density, and relative bark thickness P < 0.05 . Hmax and woody plant density were higher in LFF than HFF regimes while relative bark thickness was higher in HFF than in the LFF regimes. Species evenness was significantly higher in HFF and MFF regimes than LFF regime P < 0.05 , while FRic and functional redundancy significantly increased with decreasing fire frequency P < 0.05 . However, no significant differences were recorded for resprouting capacity, species richness, taxonomic diversity, and RaoQ P > 0.05 . Species like Cassia petersiana, Cussonia spicata, Vachellia spp., and Rhus lancea were associated with LFF, while species like Protea gaguedi, Brachystegia utilis, and Vangueria infausta showed a strong association with HFF to MFF. Our study demonstrated that a combination of taxonomic and functional diversity metrics is adequate to evaluate the response of savanna vegetation to fire. We recommend a further assessment on vegetation composition using other elements of fire regimes.

Bird Functional Diversity in Agroecosystems and Secondary Forests of the Tropical Andes

“…According to our functional diversity metrics, agroecosystems have larger functional diversity values (in terms of RaoQ and functional richness) than secondary forests. This result agrees with the results of Morelli, Benedetti, Perna and Santolini [60], but contrasts with many other studies [6,31,[61][62][63][64]. Such differences may be due to community characteristics (e.g., species richness and abundance) or to environmental filters related to vegetation structure and landscape heterogeneity.…”

Vegetation composition on peatlands with different fire frequency in Musi Banyuasin, South Sumatra

“…A total of 10 species of saplings were found in the once-burnt, and then the number decreased to 5 species in the twice-burnt and again depleted to 2 species in the three and four-times-burnt. This shows that repeated fires could reduce the quality of structure and composition of the vegetation and increase species mortality (Malkisnon et al 2011;Balch et al 2013), that the constituent vegetations are dominated by fireresistant species (Makumbe et al 2020). The vegetation community similarity index (IS) at the sapling stage of each fire frequency class is presented in Table 3.…”

“…Each type of plant has a unique tolerance level to the environment to maintain its life, therefore, exceeds in the tolerance level will result in species mortality in a habitat. The fire frequency area is dominated by species that have fire resistance and the ability to grow quickly (Makumbe et al 2020). This study aims to explain the differences in vegetation that compose areas with different fire frequencies.…”

Precipitation gradients drive high tree species turnover in the woodlands of eastern and southern Africa

“…Fire regimes strongly influence woody vegetation structure (Smit et al 2010), but in savanna fire experiments, show little effect on both tree richness (Makumbe et al 2020) and grass composition (Andersen et al 2005). Browsing herbivores change woody plant composition in Kruger national park, South Africa, by preferentially eating species with high leaf nitrogen, decreasing their abundance outside of exclosures (Wigley et al 2014), whilst also promoting tree beta-diversity in East African savannas (Pringle et al 2016).…”