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

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.

Pyric herbivory in a temperate European wood‐pasture system

“…Plant life forms were determined based on the TRY database (Kattge et al., 2020). We decided to test for an effect of fire and grazing on these life forms, since studies on pyric herbivory elsewhere in the world show that fire and grazing can strongly alter the relative cover of these life forms, especially in terms of the relative cover of grasses and shrubs (Fuhlendorf & Engle, 2004; Herrera et al., 2021; Pekin et al., 2012; Van Uytvanck & Hoffmann, 2009). In the below text, we refer to the different plant life forms as graminoids, forbs, ferns, shrubs and dwarf shrubs instead of the above categories.…”

“…This resulting heterogeneity ultimately increases biodiversity by varying effects on vascular plant species and life-form composition (Collins, 1992;Fuhlendorf & Smeins, 1999;Kirkpatrick et al, 2016;McGlinn & Palmer, 2019). Previous work has shown an increase in graminoids and a decrease in woody species under herbivory and fire (Fuhlendorf & Engle, 2004;Herrera et al, 2021;Pekin et al, 2012;Van Uytvanck & Hoffmann, 2009).…”