Changes in Vegetation of Flooded Savannas Subject to Cattle Grazing and Fire in Plains of Colombia

Alejandro Huertas Herrera,Guillermo J Martínez Pastur,Brigitte L G Baptiste Ballera,María V Lencinas,Mónica D R Toro-Manríquez,Hugoberto Huertas Ramírez

doi:10.3390/land10020108

Abstract

Cattle grazing and fire are common types of management on natural ecosystems, generating several threats to the conservation of native vegetation (e.g., changes in species richness, cover, and abundance, mainly of bovine-palatable species). In this work, we analysed the response of the structure and composition of vegetation managed with different cattle stocking rates and fire in the savanna ecosystems of Colombia. The study was located in the eastern area of the Llanos region, where savannas were subjected to grazing and burning. Regarding grazing, we classified the area according to the cattle stocking rate (Bos indicus ~300 kg): NG = non-grazed, LS = low stocking rate (0.5 ind ha−1 yr−1), and HS = high stocking rate (1.0 ind ha−1 yr−1). Controlled artificial burning was applied in all the area at the beginning of the study, and surveys were conducted in the same plots at pre-burn (t0) and four post-burn times (t1, t2, t3, t4), at 15, 45, 75 and 105 days after burning. Vegetation composition (species list, life-form, palatability) and structure (bare soil and vascular plant ground covers, species height and richness) were recorded at each sampling. Data were compared through ANOVAs and multivariate analyses. We found 53 species in total: 26 in the pre-burn treatment and 44 in the post-burn treatments, detecting an increase of 18 species considering all treatments. Seven natives and two exotic species represented the dominant cover (>50%). LS and HS had the highest number of palatable species in t0 (seven species) compared with NG (two species), but this became similar after burning (14 species in NG, 12 in LS, and 11 in HS). ANOVAs and multivariate analyses showed that plant assemblages were significantly different according to the grazing treatment, and more homogeneous in pre-burn than in post-burn periods. Cattle grazing favored higher covers of dominant palatable species (e.g., Axonopus purpusii) compared with NG, but many native species with high palatability only recovered within the system after burning. In the context of the current management proposals, the search for new alternatives other than intensive cattle grazing and burning is needed to reconcile human production activities, international commitments against climate change and biodiversity conservation in the savanna landscapes.

Highlights

Fire management is a frequent practice applied in many tropical savannas to promote the vigorous regrowth of natural vegetation for cattle grazing [1,2]
Panicum versicolor was favored by burning, probably due to the removal of competition from other grass species with dense foliage (e.g., A. bicornis), facilitating the growth of suppressed species in the pre-burn condition, e.g., Adiantum obliquum, Hyptis mutabilis, Leptocoryphium lanatum, and Sida acuta. These changes in composition and dominance of species are important for land management, due to their contribution to the evidence the changes induced by burning could increase local diversity, e.g., I. brasiliensis is known for its rapid post-fire recovery and often becomes dominant after disturbances [35]
Substantial changes occur in vegetation composition and cover of several life-forms after burning, and due to previous grazing or the intensity of grazing

Summary

Introduction

Fire management is a frequent practice applied in many tropical savannas to promote the vigorous regrowth of natural vegetation for cattle grazing [1,2]. Many studies support that these vegetation communities need frequent disturbances to sustain the coexistence of trees and grasslands, such as savanna burning [3,4]. Many plant species in fire-prone vegetation have adaptive strategies to persist under recurrent burning events and grazing [5,6]. The use of fire is restricted in areas where it was considered harmful to nature [4,5,7]. The expansion of agriculture, intensive cattle production and forestry during recent decades has modified fire management practices and promoted the introduction of commercial grasslands and forest plantations [8,10]

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Discussion

Conclusion