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

Peter Makumbe,Gift Chikorowondo,Henry Ndaimani,Edson Gandiwa,Pride Canisia Dzamara,Daniel I Rubenstein

doi:10.1155/2020/1672306

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.

Highlights

Fire is a global phenomenon which influences vegetation structure and composition with implications on ecosystem functioning [23]
Hmax was significantly different among the fire frequency plots (P < 0.05) with the tallest trees found in low fire frequency (LFF) regime and shortest trees in high fire frequency (HFF) regime
Relative bark thickness significantly increased with increasing fire frequency with thicker barks in HFF than medium fire frequency (MFF) and LFF regimes (P < 0.05)

Summary

Introduction

Fire is a global phenomenon which influences vegetation structure and composition with implications on ecosystem functioning [23]. E influence of fire on plant structure, composition, and functional traits depends on the nature of the fire regime that include frequency, intensity, type, and season [19, 26]. In their study in Zimbabwean south eastern Lowveld, Gandiwa and Kativu [21] found that high fire frequency (return interval of one to two years) altered vegetation structure of Colophospermum mopane and Combretum apiculatum species. Devine et al [16] reported that increased fire frequency (annual return interval) resulted in greater proportion of multistemmed trees in a wet savanna. Fire has a strong influence on savanna woodland dynamics and function [52], the relationship between fire frequency and these ecosystem properties is still poorly understood in most of the wet savanna ecosystems. Fires tend to limit the productivity of woody species more than in dry savannas where cover is instead inhibited by water availability [8, 16]

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Results

Conclusion