Functional diversity of herbaceous species under different fire frequencies in Brazilian savannas (original) (raw)
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1 Biodiversity, Fire, and Herbivory in Tropical Savannas
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Resource availability shapes fire‐filtered savannas
Journal of Vegetation Science, 2014
QuestionsHumid savannas can be considered fire‐filtered landscapes because fire is very frequent (<10 yr return intervals) and only fire‐resistant species can occur. This flammable vegetation can be functionally heterogeneous, structurally and floristically patchy. We hypothesized that resource availability (mainly water and nutrient availabilities) accounted for most of the functional and phylogenetic spatial structure of communities across these savanna landscapes.LocationEmas National Park, central Brazil.MethodsWe used individual‐based functional trait, phylogenetic and environmental data combined with spatial information to assess the main drivers and mechanisms of community functional change (turnover) in a large fire‐filtered savanna landscape. We used Mantel correlograms and a maximum rank correlation approach to assess the spatial structure and the subset of landscape factors that best predict compositional, phylogenetic, species‐based and individual‐based functional com...
Herbaceous and shrubby species co-occurrences in Brazilian savannas: the roles of fire and chance
Community Ecology, 2010
Competition and facilitation are expected to leave different signatures in the pattern of species co-occurrence. Competition may result in a given species pair occurring less often than expected by chance, whereas facilitation may result in a given species pair occurring more often than expected by chance. We assessed the co-occurrence of pairs of herbaceous and shrubby species in Brazilian savannas, asking (1) whether a given species pair occurs more often than expected by chance, (2) whether the number of species pairs in sites with frequent fires is higher than expected by chance, (3) whether the difference in the functional traits of heterospecific pairs is lower in sites with frequent fires, and (4) whether small environmental variations in each site instead of species interactions could explain the co-occurrence of species. We used null models to answer the first two questions, analyses of variance to answer the third question, and detrended correspondence analyses to answer the fourth question. In all studied sites, approximately half of the heterospecific pairs occurred more often than expected by chance. So, facilitation seems to be important in determining the co-occurrence of some species in Brazilian savannas. However, high fire frequencies changed the pattern of occurrence of the species pairs, resulting in a spatial signature indistinguishable from random. Frequent fires also promoted phenotypic clustering of species. Nevertheless, wherever fire frequency is reduced, competition may lead to phenotypic overdispersion of plant species. Thus, less harsh environmental conditions in savannas may increase the competition among plant species. support; to CNPq, for the scholarship granted to I.A.S. and M.A.B.; to Ibama, for research permission; to Emas National Park staff, for logistical assistance; to R. Moreira, M.B. Ramos-Neto, and Oreades Núcleo de Geoprocessamento for the ENP's satellite images; to A.T. Fushita for help in ENP's fire history map; to UnB and Unicamp herbarium staffs; to the taxonomists M.W. Ferreira, C. Proença and J. Semir, for their assistance in species identification; to P.K
Woody plant species co-occurrence in Brazilian savannas under different fire frequencies
Acta Oecologica-international Journal of Ecology, 2010
Fire plays an important role in determining the structure of the vegetation of savannas. Consequently, frequent fires are expected to assemble closely related plant species with very similar fire-related functional traits. We assessed the influence of different fire frequencies on patterns of co-occurrence of woody species at a fine spatial scale in Brazilian savannas. We used quantile regressions to test the relationship between co-occurrence indices and both phylogenetic distances and functional differences, calculated for every possible pair of species. Our results indicated that fire changes the pattern of co-occurrence of woody plants. Functionally different species co-occurred predominantly in a site protected from fire, whereas functionally similar species co-occurred predominantly in sites frequently burned. However, we did not find correlations between co-occurrence and phylogenetic distance of species, due probably to the random distribution of some functional traits in the phylogeny of savanna species. Thus, fire acts as an important environmental filter at fine spatial scales in Brazilian savannas, promoting functional -but not phylogenetic -clustering of plants.
Agriculture, Ecosystems & Environment (Elsevier), 2014
Tropical dry forests and savannas are important repositories of plant diversity and ecosystem services in the tropics. These ecosystems are also used extensively for grazing by livestock, and represent a critical element of the rural economy of many tropical countries. Fire is considered as a part of co-evolution in these ecosystems across the globe. However, in recent decades, there has been a shift in historical fire regime. Fire has become more frequent in these landscapes, and could be further enhanced under climate change. This poses threats to existing biodiversity, ecosystem processes, and rural economy. We asked how variability in fire frequency has influenced diversity and heterogeneity in grass species composition, and richness and abundance of grass species preferred by large herbivores (referred to as grazing accept- ability) in a South Indian tropical savanna forest. We assumed that an increase in fire frequency acts as the active constraint and limits an ecosystem from attaining the maximum heterogeneity, and the maximum grazing acceptability (maximum richness and abundance of grass species preferred by herbivores) in its native settings. We used MODIS active fire and burned area products to estimate fire frequency across the landscape. A nested sampling approach was used to collect information on vegetation and soil at different fire frequencies. Quantile regression analyses indicated that diversity and heterogeneity in grass species composition as well as grazing acceptability decreased with increasing fire frequencies. We found that livestock grazing intervened with the observed vegetation patterns; grass species diversity and hetero- geneity, and grazing acceptability increased with grazing intensity at lower quantiles. Other measured covariates, rainfall, and soil-fertility, alone were not able to explain the observed vegetation patterns in the landscape. The results show a need to control annual fires but allow and manage intermittent fires in this landscape. A complete suppression of fire is not desirable as fire releases nutrients from burning of deeper-rooted vegetation and thus acts as a periodic nutrient pump. It also played an important role in maintaining the grass cover by reducing shrub cover. Hence, it is important to consider the complex interactions between fires–grazers–soil–vegetation to develop effective management practices. We con- clude that fire frequency should be managed at low to intermediate levels (one fire in every 5–9 years, resembling the native settings), and grazing regulated, in order to sustain wild and domestic herbivores, biodiversity, and other key ecosystem processes and services over the long-term.
No Net Loss of Species Diversity After Prescribed Fires in the Brazilian Savanna
Frontiers in Forests and Global Change, 2020
Although savannas are fire-adapted ecosystems, prescribing fire for biodiversity conservation remains controversial at least in some regions where savannas occur. Faced with uncertainty, many decision makers and even scientists are still reluctant to prescribe fire for conservation purposes in fire-prone ecosystems, invoking the precautionary principle. Knowledge gaps on the ideal fire regime, such as how and when to burn, and especially the fear of biodiversity losses, are among the main arguments against fire management applied to remnants of native savanna vegetation. To inform this debate, we assessed the impact of prescribed fires on diversity of plants (different growth forms), ants, frogs, lizards, birds, and small mammals, in savannas and grasslands of the Brazilian Cerrado. We assessed the existing species richness, composition, and abundance in areas subjected to long periods of fire suppression and compared to that observed over a short period after prescribed dry-season fires, within each group of plants and animals. Whenever possible, we carried out separate analyses for grassland and savanna. Burning did not significantly reduce species richness of any of the groups analyzed, but had a positive effect on richness of graminoids in grassland. When analyzed at the species level, abundance of most animal groups did not show consistent responses to fire, except for a decrease in some frog populations in grasslands. Forbs, graminoids, and subshrubs increased in abundance after fire in grassland areas, though in savanna areas, abundance of forbs, and subshrubs tended to decline after fire. Species composition changed little in response to fire as indicated by low levels of dissimilarity between burned and unburned areas. These results confirm the high resilience of Cerrado biota to fire, as expected for savanna ecosystems in general. Besides, we demonstrate here that the risk of biodiversity losses cannot justify the objections to the use of prescribed fire for conservation purposes in the Cerrado.
2007
Contents 1. Introduction 2. Fire behavior in Neotropical savannas 3. The effects of fire on the herbaceous layer 4. The effects of fire on the woody layer 5. Fire and savanna physiognomy 6. Fire and the management of Neotropical savannas Related Chapters Glossary Bibliography Biographical Sketches Summary This chapter reviews the main characteristics of tropical savannas and their interactions with fire, a main factor involved in the dynamics of these ecosystems. Burning in savannas generally takes place by the end of the dry season, favored by the accumulation of dry biomass in the herbaceous layer. Several factors affect fire characteristics and behavior, such as quantity, quality and composition of the combustive matter, wind direction and velocity, relative humidity of air, and season of burning. Although fire is a mortality factor, common savanna plant species seem to be adapted to burning. Adaptations include underground reserves, protected meristems, re-sprout capacity, clonal multiplication, growth seasonality, thick cork layer, and sclerophyllous leaves. Deleterious effects of fire are greater in the younger or smaller size classes in the population. On the other hand, the passage of fire restores light and nutrients on the topsoil, that together with the return of rains create better conditions for seasonal growth. Under fire exclusion herbs escape from the direct mortality effects of burning but exclusion promotes shading and nutrient depletion which are harmful for the renewal of herbaceous growth. Species differ in their responses to fire regime, therefore the fire regime affects species composition. The fire regime is also important in terms of the physiognomy of the savanna. Frequent burning causes qualitative and quantitative changes in plant community structure and composition promoting open physiognomies with fewer woody elements. Conversely, fire exclusion has been shown to increase tree density in tropical savannas transforming open savannas in woodlands. In modern times, most fires are set by humans. However, natural fires by electric discharges during storms do occur although less frequently than human induced fires. Although fire has been used in savanna management since pre-Columbian times, it remains a complex issue that needs further research. Related Chapters Glossary Albedo: Fraction of incident shortwave radiation reflected by Earth. Biodiversity: The variability found in living organisms at various scales from genes to ecosystems. Cerradão: A type of savanna found in Brazil characterized by low species richness, a canopy higher and closer than the other savanna types. It also comprises deciduous and semi-deciduous tree species. Cerrado: the common word used in Brazil to designate savanna vegetation.
Journal of Biogeography, 2001
Aim We tested the hypothesis that exclusion from ®re and cattle is responsible for the increase in tree cover in open savanna vegetation. Location Four plots in open savanna vegetation from the Calabozo region in central Venezuela were studied. Plot A was located in a Biological Station (EBL) that was excluded from ®re and cattle between 1961 and 1991, with only two burning events in 1964 and 1968. The other plots (B, C, D) were located within 2 km distance from A, in neighbouring farms with soils similar to those in A but under various regimes of land use and ®re frequency. Methods We measured the cover of isolated trees, small tree groups and groves of each plot in 1960 and 1977 using geographic information system (GIS) and digitalized aerial photographs. Additionally, the plots were located in the ®eld and the open grassland was sampled in 1995 for species composition and density of stems above 20 cm height. Information on land use was obtained surveying people at the farms. Results There was an increase in the woody component of all plots during the 17-year interval (1960±1977). Total woody cover in the four plots as a whole increased from 4.5% to 17.9%. All three components measured, groves, tree groups and isolated trees, increased despite differences in land use and ®re frequency between plots. Contrary to our expectations, the ®eld survey performed in 1995 showed that ®re-sensitive species were abundant in the open savanna in plots B, C and D, which were not excluded. Plot B, with the most intense agricultural use showed the highest rate of woody increase, and plot C, under extensive cattle ranching, was second. The results also showed that woody cover increased by aggregation from single trees and small tree groups into groves. As a consequence of these changes, savanna physiognomy changed from open to dense savanna parkland with a woody cover reaching over 25% in one of the four plots. Conclusions The results agree with other reported increases in woody cover in savannas under exclusion or with annual ®res during the same time period in Africa (Dauget & Menaut, 1992). Our results support evidence from previous studies showing that ®re and grazing are only part of a complex system of interacting factors affecting the structure of savanna communities.