DOI: 10.5061/dryad.3r2280gjf
title: Low-intensity cattle grazing is better than cattle exclusion to drive secondary savannas towards the features of native Cerrado vegetation

description: Although livestock have been historically associated with land conversion
 and biodiversity loss, well-managed cattle grazing has been reported to
 contribute to conservation of open ecosystems. Knowing the balance between
 positive and negative effects of livestock (presence or exclusion) on
 different ecosystems is, therefore, crucial to support management
 decisions. We conducted an experiment in a secondary savanna with exotic
 grasses, used as pasture, to assess the effect of cattle presence in low
 density and cattle exclusion (in paired plots) on the trajectory of these
 ecosystems. Richness, composition and structure of the woody community,
 and exotic grass cover and biomass were compared between treatments in the
 beginning of the experiment and after seven years. At the end of the
 experiment, we also compared composition, richness, and density of the
 native ground layer. We verified that (a) cattle exclusion accelerates the
 undesirable woody encroachment, changes the species composition and leads
 to huge grass fuel accumulation, while (b) cattle grazing/browsing hinders
 changes in savanna structure and composition and reduces the exotic grass
 cover and biomass, thus favoring native herbaceous plants. By decreasing
 the grass biomass, cattle grazing also reduces the system flammability
 and, therefore, the risk and intensity of wildfires. Together, the
 positive effects of cattle presence and the negative effects of cattle
 exclusion lead to the conclusion that cattle should be maintained in these
 systems. Low-intensity cattle grazing limits woody and exotic grass
 invasion, improves native forb biodiversity, and help maintain composition
 and structural features of secondary savannas of the Cerrado.
description: In the year 2005, we set up 10
 pairs of 10 x 10 m permanent plots within a 6-ha fenced area used as
 pasture. Each pair comprised one open plot (grazed) and one exclusion plot
 (ungrazed). The ten pairs were haphazardly distributed in the area,
 keeping at least 50 m distance from each other. Around the exclusion
 plots, a barbed-wire fence was installed (12 x 12 m), keeping 1-m distance
 from the 10 x 10 m sampling plot inside. The paired plots were diagonally
 positioned, with a distance of 2 m between their closest corners to avoid
 excessive trampling in the grazed plot. We sampled the woody species and the exotic
 grasses within each plot immediately after fencing and once a year at the
 end of the dry season (September), up to 2012, comprising a 7-yr period of
 observations. In this study, we compared only data collected in 2005
 (initial) and 2012 (after seven years). In each plot, we counted (stems
 and individuals), tagged, identified and measured all woody plants (height
 ≥ 50 cm), and recorded stem diameter (from 3 cm minimum) at 50 cm above
 ground to estimate basal area. Using the line-intercept method (Canfield,
 1941), we estimated tree canopy cover and exotic grass cover percentage by
 sampling three 10-m parallel lines inside each plot. Biomass of the exotic
 grass (Urochloa decumbens) was sampled in two 50 x 50 cm randomized
 subplots within each 10 x 10 m plot, by clipping at 10 cm above ground.
 The grass biomass was dried at 70°C for 48 h and weighed. To support the
 interpretation of our results, using the same method for comparison, we
 collected 10 biomass samples of the ground layer (all plants below 50 cm
 in height) in uninvaded cerrado vegetation with similar canopy cover, as a
 reference ecosystem (at Santa Barbara Ecological Station,
 22°46′41′′S and 49°16′10W”). In the last sampling occasion,
 after seven years (2012), we also sampled (counting and identifying) all
 native plants (herbaceous as well as young woody plants) with height
 &lt; 50 cm in the whole area of each plot (100 m2), to verify the
 effects of each treatment on native plants of the ground layer. Native
 species sampled were functionally categorized as woody (shrubs, lianas and
 trees) or herb (graminoids and forbs). Native forbs and graminoids were
 virtually absent in the beginning of the experiment (see first-year
 pictures at Figure 1) and their spontaneous recovery was not expected.
 Considering the great importance of their return, we decided to include
 the native ground layer in the analyses, even without the initial
 information. In all samplings of native plants, multiple stems connected
 to the same underground structure were counted as a single individual.
 Rhizomatous and stoloniferous native plants were absent and exotic grasses
 were not counted, because it would be technically impossible.