Search Results (3)

Fire is a common disturbance in the Brazilian savanna (the cerrado), wherein high-frequency fires drive the vegetation structure, composition, function, and dynamics of savanna ecosystems. Under climate change pressure, further understanding of fire–vegetation relationships and interactions can provide new approaches for establishing integrated fire management strategies and can promote post-fire savanna vegetation recovery. To understand how 15 years of annually manipulated burning has affected vertical and horizontal structures of the vegetation, species composition and diversity metrics (species richness, Shannon’s diversity, and Pielou’s evenness), and aboveground carbon stocks, we surveyed all woody plant species with a diameter greater than three centimeters, in 15 plots of a typical Brazilian savanna (cerrado stricto sensu) at an experimental research station in central Brazil (the cerrado biome). The 15 plots (five plots per treatment) had been differently affected by fire events over a decade, and comprised three treatments: (i) annual fire, (ii) legacy fire (>15 years since the last fire event), and (iii) control (not burned in the past 30 years). A non-metric multidimensional scaling (NMDS) analysis indicated that fire had a significant effect on the species composition among the treatments; some species benefited from fire, such as Erythroxylum suberosum, whereas other species propagated better without fire, such as Roupala montana and Dalbergia miscolobium. Over a decade of annual fire events have led to decreases in Shannon’s diversity, species richness, and stem density, which were significantly lower in the annual fire treatment than in the control and legacy fire treatments. Stem density by diameter and height size classes (except for the 1–2 m class and above 8 m class) was higher in the control than that in the annual fire treatment, but the number of dead trees did not differ between the control and the annual fire treatment. Our results also showed that fire was a factor in changes in the evaluated parameters, such as in the annual fire treatment, where fire reduced the amount of biomass, and therefore the carbon stocks. This study suggests that, if burned yearly, typical Brazilian savannas can become less biodiverse in terms of woody plant species which negatively affects their fire resilience. Therefore, fire management practices should focus on determining the frequency of fire disturbances from which these ecosystems may benefit the most. Full article

Habitat fragmentation affects lichen communities by inducing edge effects, although the dispersal of pollutants by pesticide drift from commercial crops may also provoke alterations in community structure, due to the varying sensitivity of lichen morphotypes to pollutants. In this context, we tested the hypothesis that lichen morphotype richness and diversity, and the percentage area of the trunks covered by different lichen morphotypes are modified significantly at the edges of fragments of Cerrado vegetation inserted within the agricultural matrix. We evaluated habitat fragments representing different Cerrado formations (Cerradão, Cerrado sensu stricto, and seasonal semi-deciduous forest) as well as the Emas National Park, a prominent Cerrado conservation unit. We used Generalized Linear Mixed Models (GLMMs) to test the potential of the models compiled using a mixture of phytosociological and environmental parameters, including the species, the height of the host plant (H), the circumference of its stem at breast height (CBH), total chlorophyll (TC), bark fissuring (BF) and pH, and illuminance (Lum), to explain the observed variation in the lichen morphotype richness and the percentage cover of the trunks by corticolous lichen morphotypes at the center and edge of the fragments. The central areas invariably had a greater diversity of morphotypes in all the fragments. The morphotypes considered highly sensitive to disturbance were not observed in edge areas, confirming a clear edge effect, as well as the influence of pesticide drift from the adjacent farmland matrix, on the structure of the lichen community. At both the edge and center sites, the larger trees (higher CBH) with less fissured bark tended to have the greatest diversity of lichen morphotypes, and more acidic barks had the greatest lichen cover. The models tested indicated that the variable tree species is an important determinant of the observed patterns of lichen morphotype richness and cover, either on its own or in association with pH or CBH + pH. The analyses also indicated that all the variables tested are important in some way for the definition of the percentage cover of the host trunks. The present study contributes to the understanding of the diversity of the corticolous lichen communities in the remaining fragments of Cerrado vegetation and the effects of the agricultural matrix on this community. The lichen may thus play a role as indicators of impact on other species, these organisms may provide important insights for the further investigation of the disturbance caused by the agricultural matrix on the communities of other groups of organisms. Full article

In this study we assessed METRIC (Mapping Evapotranspiration at high Resolution with Internalized Calibration) model performance to estimate energy balance fluxes and evapotranspiration (ET) in two heterogeneous landscapes in the Brazilian Cerrado, including fluxes and ET in both agricultural and natural vegetation. The estimates were evaluated by comparing them to flux tower data collected over sugarcane (USR site), woody savanna (PDG site) and stricto-sensu savanna (RECOR site) areas. The selection of the study years (2005–2007 for USR/PDG sites and 2011–2015 for RECOR site) was based on the availability of meteorological data (to be used as inputs in METRIC) and of flux tower data for energy balance fluxes and ET comparisons. The broadband albedo submodel was adjusted in order to improve Net Radiation estimates. For this adjustment, we applied at-surface solar radiation simulations obtained from the SMARTS2 model under different conditions of land elevation, precipitable water content and solar angles. We also tested the equivalence between the measured crop coefficient (Kc_{_ec}) and the reference evapotranspiration fraction (ETrF or F), seeking to extrapolate from instantaneous to daily values of actual evapotranspiration (ETa). Surface albedo was underestimated by 10% at the USR site (showing a better performance for full crop coverage), by 15% at the PDG site (following the woody savanna dynamics pattern through dry and wet seasons) and was overestimated by 21% at the RECOR site. METRIC was effective in simulating the spatial and temporal variability of energy balance fluxes and ET over agricultural and natural vegetation in the Brazilian Cerrado, with errors within those reported in the literature. Net radiation (Rn) presented consistent results (coefficient of determination (R²) > 0.94) but it was overestimated by 8% and 9% in sugarcane and woody savanna, respectively. METRIC-derived ET estimates showed an agreement with ground data at USR and PDG sites (R² > 0.88, root mean square error (RMSE) up to 0.87 mm day⁻¹), but at the RECOR site, ET was overestimated by 14% (R² = 0.96, mean absolute error (MAE) = 0.62 mm.day⁻¹ and RMSE = 0.75 mm day⁻¹). Surface energy balance fluxes and ET were marked by seasonality, with direct dependence on available energy, rainfall distribution, soil moisture and other parameters like albedo and NDVI. Full article