Savanna Communities Research Articles

Post-fire temporal dynamics of plant-pollinator communities in a tropical savanna.

Fire is a major ecological and evolutionary factor promoting biodiversity and maintaining functioning of naturally fire-prone ecosystems. In tropical savannas, plant communities show a set of fire-adapted traits and both flowering and pollination services have the potential to rapidly regenerate after fire, but fire-suppression policies may disrupt this adaptability following potential woody encroachment. Understanding the effects of fire on plant-pollinator interactions are required to advance conservation of biodiversity and ecosystem functioning. We evaluated the dynamics of plant community assemblage, flower availability, composition of flower functional traits associated with attractiveness to pollinators, and activity and diversity of insect pollinator guilds over ten post-fire stand ages along a 14-year chronosequence in a naturally burned region in the Cerrado, a megadiverse savanna in Brazil. We expect to find a high resilience of plant-pollinator communities and a steady decline in the successional recovery as time-since-fire proceeds. Along the post-fire chronosequence, vegetation was dominated by subshrubs with tubular, white, and nectar flowers arranged in inflorescences, while bees were the predominant pollinators. Plant assemblage and flower number showed an initial significant increase but monotonically declined after 7-9years after fire. Accordingly, pollinator richness and abundance significantly reached highest peaks in interim periods and a steady decline over time. In contrast, the frequency of community-wide plant-life form, flower functional traits, and pollinator diversity remained unaltered over the post-fire chronosequence. We added compelling evidence of a high post-fire resilience of plant-pollinator communities and further understanding of how fire-suppression policies may affect pollination in the Cerrado.

Increasing agricultural land use in riparian networks negatively affects stream fish communities in a tropical savanna

Increasing agricultural land use in riparian networks negatively affects stream fish communities in a tropical savanna

Functional compensation in a savanna scavenger community.

Functional redundancy, the potential for the functional role of one species to be fulfilled by another, is a key determinant of ecosystem viability. Scavenging transfers huge amount of energy through ecosystems and is, therefore, crucial for ecosystem viability and healthy ecosystem functioning. Despite this, relatively few studies have examined functional redundancy in scavenger communities. Moreover, the results of these studies are mixed and confined to a very limited range of habitat types and taxonomic groups. This study attempts to address this knowledge gap by conducting a field experiment in an undisturbed natural environment assessing functional roles and redundancy in vertebrate and invertebrate scavenging communities in a South African savanna. We used a large-scale field experiment to suppress ants in four 1 ha plots in a South African savanna and paired each with a control plot. We distributed three types of small food bait: carbohydrate, protein and seed, across the plots and excluded vertebrates from half the baits using cages. Using this combination of ant suppression and vertebrate exclusion, allowed us explore the contribution of non-ant invertebrates, ants and vertebrates in scavenging and also to determine whether either ants or vertebrates were able to compensate for the loss of one another. In this study, we found the invertebrate community carried out a larger proportion of overall scavenging services than vertebrates. Moreover, although scavenging was reduced when either invertebrates or vertebrates were absent, the presence of invertebrates better mitigated the functional loss of vertebrates than did the presence of vertebrates against the functional loss of invertebrates. There is a commonly held assumption that the functional role of vertebrate scavengers exceeds that of invertebrate scavengers; our results suggest that this is not true for small scavenging resources. Our study highlights the importance of invertebrates for securing healthy ecosystem functioning both now and into the future. We also build upon many previous studies which show that ants can have particularly large effects on ecosystem functioning. Importantly, our study suggests that scavenging in some ecosystems may be partly resilient to changes in the scavenging community, due to the potential for functional compensation by vertebrates and ants.

Changes in Land Use through Eucalyptus Plantations Impact Soil Fauna Communities in Brazilian Savannas

Soil fauna is responsible for one-quarter of all species on Earth, and these organisms play crucial roles in many ecosystem functions and services; however, these communities are facing several threats related to human activities, especially in the Cerrado ecoregion, the second largest biome. We aimed to evaluate the soil mesofauna communities in a native savanna (Cerrado) and two l eucalyptus stands to verify differences and infer possible impacts on soil mesofauna abundance and diversity through land-use changes, as well as find correlations between soil chemical parameters and soil mesofauna groups. Pitfall traps were installed in each one of the 12 plots per land-use type to evaluate soil mesofauna abundance and diversity in the dry and rainy seasons, and soil chemical analyses were performed at 0–20 and 20–40 cm depth per plot. We found that Collembola, Isoptera, and Diptera during the dry season collections, and Formicidae, Isoptera, and Diptera in the rainy season collection were more abundant in the Cerrado. The eucalyptus plantations have reduced the abundance of these groups, in addition to also representing a possible loss of biodiversity promoted by these monocultures. The organic matter, Potassium, Calcium, Phosphorous, and pH contents can be used as good soil mesofauna indicators in the Cerrado.

Interactive roles of fire seasons and biological invasions in the short‐term dynamics of tropical savannas

AbstractAimChanges in fire regimes and biological invasions are major threats to tropical savannas. Fire is a key driver of community composition in these ecosystems and can be used as a management tool to control some invasive alien species, while being advantageous to native ones. However, we still do not fully comprehend the interactive effects of these threats on native plant communities. Here, we conducted an experiment in southeastern Brazil to investigate how variation in the composition of native communities invaded either by Melinis minutiflora or Urochloa brizantha is affected by fire in different seasons: early‐dry season, mid‐dry season and late‐dry season in comparison to fire suppression.LocationItirapina, state of São Paulo, southeastern Brazil (22°14′07″S 47°53′07″W).ResultsThe effects of fire seasons and invasive species were independent for species richness but interactive for species gains and losses. In general, the identity of the invasive species was a key factor driving community dynamics, with fire seasons playing a weaker role. Invaded communities changed gradually over time and the major changes happened over longer time lags. Communities invaded by M. minutiflora gained more species than those invaded by U. brizantha. Thus, communities invaded by M. minutiflora also had more variation in their species richness through time than those invaded by U. brizantha.ConclusionsAlthough biological invasions and fire seasons interacted as drivers of change in native savanna communities, the identity of the invasive species played a stronger role. Communities invaded by M. minutiflora gained more species and were more variable than those invaded by U. brizantha.

Influence of soil properties on woody vegetation structure, diversity and seasonality in Neotropical savannas

AbstractUnderstanding how savanna soil properties influence vegetation diversity and function is a major challenge in ecological studies. We investigated the effects of soil properties on woody species density, richness, composition, and vegetative phenology (inferred by the Normalized Difference Vegetation Index (NDVI)) in two alluvial and two interfluvial savanna sites (1 block of 10 plots of 20 × 50 m in each site), in the Brazilian Cerrado. We showed that plots in alluvial savannas present less fertile soils and have lower plant densities and species richness and higher seasonality of NDVI than plots in the interfluvial savannas. The species composition of the sites was associated with the P, Fe, K, and Mn content of the soil. Soil K, Fe, and Ca contents were the main variables associated with plant density in a linear mixed model (LMM) that explained 79% of data variability (r2c = 0.79%), and K, Fe, and Al were the main predictors to explain species richness (r2c = 0.81%). Soil K, pH, and Silt were the best predictors of the seasonality in NDVI (r2c = 0.14%). We highlight the all‐encompassing effect of K soil content on species density, richness, composition, and NDVI and argue that this macronutrient and a few other soil properties (e.g., P, Fe, Al, and Silt) are the main factors mediating plant responses to water and nutrient stress in woody savanna communities occurring in the Cerrado–Amazônia transition.

Tillage agriculture and afforestation threaten tropical savanna plant communities across a broad rainfall gradient in India

Abstract The consequences of land‐use change for savanna biodiversity remain undocumented in most regions of tropical Asia. One such region is western Maharashtra, India, where old‐growth savannas occupy a broad rainfall gradient and are increasingly rare due to agricultural conversion and afforestation. To understand the consequences of land‐use change, we sampled herbaceous plant communities of old‐growth savannas and three alternative land‐use types: tree plantations, tillage agriculture and agricultural fallows (n = 15 sites per type). Study sites spanned 457 to 1954 mm of mean annual precipitation—corresponding to the typical rainfall range of mesic savannas globally. Across the rainfall gradient, we found consistent declines in old‐growth savanna plant communities due to land‐use change. Local‐scale native species richness dropped from a mean of 12 species/m2 in old‐growth savannas to 8, 6 and 3 species/m2 in tree plantations, fallows and tillage agriculture, respectively. Cover of native plants declined from a mean of 49% in old‐growth savannas to 27% in both tree plantations and fallows, and 4% in tillage agriculture. Reduced native cover coincided with increased cover of invasive species in tree plantations (18%), fallows (18%) and tillage agriculture (3%). In analyses of community composition, tillage agriculture was most dissimilar to old‐growth savannas, while tree plantations and fallows showed intermediate dissimilarity. These compositional changes were driven partly by the loss of characteristic savanna species: 65 species recorded in old‐growth savannas were absent in other land uses. Indicator analysis revealed 21 old‐growth species, comprised mostly of native savanna specialists. Indicators of tree plantations (nine species) and fallows (13 species) were both invasive and native species, while the two indicators of tillage agriculture were invasive. As reflective of declines in savanna communities, mean native perennial graminoid cover of 27% in old‐growth savannas dropped to 9%, 7%, and 0.1% in tree plantations, fallows and tillage agriculture, respectively. Synthesis. Agricultural conversion and afforestation of old‐growth savannas in India destroys and degrades herbaceous plant communities that do not spontaneously recover on fallowed land. Efforts to conserve India's native biodiversity should encompass the country's widespread savanna biome and seek to limit conversion of irreplaceable old‐growth savannas.

The pivotal role of land cover around forest fragments for small‐mammal communities in a Neotropical savanna

AbstractWhile harboring the bulk of the planet's biodiversity, tropical ecosystems have experienced intense land conversion for agriculture. Studies examining the impacts of land‐use change on tropical biodiversity have primarily focused on forest cover loss but have overlooked the ecological potential of habitats surrounding forest fragments to modulate biodiversity loss. We examined whether small‐mammal communities changed with the land cover surrounding forest fragments, and how functional traits affected responses to land cover. Small mammals were sampled in the Brazilian Cerrado using live‐trap transects. Three landscape types were identified according to the surroundings of the transects (within 750‐m‐radius buffers): forest‐ (≥50% forest cover), pasture‐, and crop‐dominated landscapes (<50% forest cover, with predominance of pastures or crops, respectively). We examined the composition of functional traits across landscape types and used abundance models to analyze the response of small‐mammal communities to land cover. From forest‐dominated to pasture‐ and crop‐dominated landscapes, the abundances and/or species richness of the largest, forest‐specialist, frugivorous/granivorous, and terrestrial species decreased. In forest‐dominated landscapes, abundances and species richness were slightly affected by land cover surrounding forest fragments. In pasture‐ and crop‐dominated landscapes which represent the less‐preserved landscapes, increased proportions of native forests, open formations, and, to some extent, pastures, supported the increased abundance of small mammals. Land cover surrounding forest fragments is critical for maintaining the diversity of species and functional traits within small‐mammal communities. Our results emphasize the need to maintain native vegetation in human‐modified landscapes to maintain biodiversity and ecological functions.

Vegetation management shapes arthropod and bird communities in an African savanna.

Habitat heterogeneity is a key driver of the diversity and distribution of species. African savannas are experiencing changes in their vegetation structure causing shifts towards increased woody plant cover, which results in vegetation structure homogenization. Given the impact that increasing woody plant cover has on patterns of animal use, resource managers across Africa are implementing habitat management practices that are intended to reduce woody plant cover. To understand the ecological implications of various habitat management practices on arthropod and bird communities, we leveraged large-scale tree clearing and subsequent mowing in an African savanna to understand how changes in both the herbaceous layer and woody plant cover (i.e., structural heterogeneity) may shape arthropod and bird communities at the local scale. We focused on four replicated treatments: (1) annual summer mow, (2) annual winter mow, (3) >5 years since last mow (rest), and (4) an adjacent unmanipulated savanna to act as a control. We found that the mowing treatments significantly influenced vegetation structure both with respect to tree density and herbaceous layer. Both arthropod and bird community composition varied across treatments. Grass biomass was the best predictor of arthropod richness and abundance, with arthropods selecting for areas with high biomass. Insectivorous bird richness and abundance was driven by tree density (i.e., perching locations) and not arthropod abundance. Our results suggest that vegetation management practices contribute to habitat heterogeneity at the landscape scale and increase bird species richness through species turnover. However, we caution that if a single vegetation management practice dominates the landscape, it is plausible that it could lead to the simplification of the avian community.

Holocene fire regimes, fire‐related plant functional types, and climate in south‐coastal British Columbia forests

AbstractPaleoecological records of past fire events and forest composition provide long‐term ecological context for modern changes in fire regimes and forest dynamics. Here, we use pollen and contiguous macroscopic charcoal analyses of lake sediments from Pender Island, British Columbia, Canada to reconstruct changes in fire regimes over the last 10,000 years and investigate how these interact with changes in climate and forest composition with a focus on fire‐related plant functional types. The relatively warm and dry early Holocene was characterized by high charcoal accumulation rates, fire episodes of moderate severity, and a mean fire return interval of 100 ± 27 years. Forests at the time were open‐canopy Pseudotsuga menziesii forests with abundant fire endurer taxa (e.g., Pteridium aquilinum) that have a competitive advantage in regimes of frequent fire. Fire continued to occur every ~100 years, on average, during the establishment of Quercus garryana savanna communities; however, a decrease in charcoal peak magnitudes suggests the fire regime shifted to one characterized by smaller and/or lower intensity surface fires. As temperature and moisture deficits decreased in the mid‐ and late Holocene (i.e., after ~6000 calendar years before present), mean fire return intervals lengthened to 176 ± 54 years and increased variability in charcoal peak magnitudes suggests a mixed fire regime of low‐moderate‐intensity fires combined with infrequent crown or stand‐replacing fires. Relatively stable and moderate climate, longer fire return intervals, and mixed‐severity fires allowed P. menziesii (a fire resister) to dominate closed‐canopy forests and for fire avoiders to gradually become more common forest constituents. Millennial‐scale climate change has acted as the dominant driver of changes in both fire regimes and forest composition over the last 10,000 years; however, changes in fire‐related plant functional types highlight the important role that interactions between vegetation and fire play in long‐term fire regimes and forest dynamics.

Impacts of invasive alien species on riparian plant communities in South African savanna

Abstract Biological invasions are a threat to protected areas globally; however, the relative lack of studies quantifying the ecological impacts impairs informed decision-making. We selected three annual alien plants, widespread in the riparian habitats of the Kruger National Park, South Africa: Datura innoxia, Parthenium hysterophorus, and Xanthium strumarium, to examine their potential impacts on riparian plant communities. We identified 12–13 populations for each and placed a pair of invaded and uninvaded plots in each population. Species richness, Shannon diversity, and Pielou evenness were compared between the invaded and uninvaded plots using LMM models, and species composition was compared using ordination. The invaded vegetation showed lower species richness compared to the uninvaded, with the strongest effect observed for P. hysterophorus. The invaded plots also showed lower Shannon diversity and Pielou evenness due to the presence of alien dominants. For all three invaders, the invasion resulted in changes in the composition of native vegetation. Some native plants were more frequent and abundant in the invaded vegetation, possibly due to the habitats created in sandy river beds. The native species richness decreased with increasing invader cover, but the species richness of aliens accompanying the invasive dominants was not negatively affected by their cover. Our results confirmed the negative impact of invasive aliens on native plant diversity, with the most pronounced effect by Parthenium hysterophorus invasions.

Progress and challenges of Guinea’s national service of risk management in building climate-induced disasters’ resilience in Guinea Savanna communities

The increased frequency and magnitude of climate-induced disasters are a huge setback for the world’s economic growth and performance. Addressing such risks has long time motivated many governments to set up disaster-based management strategies, policies, and plans to strengthen their resilience. However, the implementation of such initiatives remains challenging in developing countries due to their specific internal development issues that require timely performance appraisals to offer suitable remedial actions. This motivated the present study to use the Risk Management Index (RMI), to measure Guinea’s risk management performance and effectiveness, focusing on its institutional progress and challenges encountered in building climate-induced disasters’ resilience in Guinea Savanna communities. Data were generated through semi-structured interviews with local authorities responsible for implementing prevention measures and emergency responses to disasters in Guinea Savanna, as well as inputs from academia with activities related to disaster risk management, combined with documentary research and field observations. Analyses of the RMI showed very limited progress in risk identification (RMIRI = 0.672 – 1.00), while almost no significant progress was made in financial provision (RMIFP = 0.124 – 0.487). On the contrary, policies of disaster management (RMIDM = 0.600 – 1.934) and Risk Reduction (RMIRR = 0.791 -1.606) have shown incipient progress. While all public policies need to be improved, urgent actions are needed in financial provision and risk identification policies. Therefore, the study suggests that local authorities should be more committed to risk identification and risk financing approaches to address the priority needs for effective disaster risk management in Guinea Savanna communities.

Substrate and low intensity fires influence bacterial communities in longleaf pine savanna

Bacterial communities associated with vegetation-soil interfaces have important roles in terrestrial ecosystems. These bacterial communities, studied almost exclusively in unburnt ecosystems or those affected by rare, high-intensity wildfires, have been understudied in fire-frequented grasslands and savannas. The composition of ground-level bacterial communities was explored in an old-growth pine savanna with a centuries-long management history of prescribed fires every 1–2 years. Using 16S metabarcoding, hypotheses were tested regarding differences in bacterial families of litter and soil surface substrates in patches of ground layer vegetation that were naturally burnt or unburnt during landscape-level prescribed fires. Litter/soil substrates and fire/no fire treatments explained 67.5% of bacterial community variation and differences, driven by relative abundance shifts of specific bacterial families. Fires did not strongly affect plant or soil variables, which were not linked to bacterial community differences. Litter/soil substrates and the naturally patchy frequent fires appear to generate microhabitat heterogeneity in this pine savanna, driving responses of bacterial families. Prescribed fire management may benefit from considering how fire-altered substrate heterogeneity influences and maintains microbial diversity and function, especially in these fiery ecosystems. Frequent, low-intensity fires appear ecologically important in maintaining the diverse microbial foundation that underlie ecosystem processes and services in fire-frequented habitats.

Legacy effects of nutrient addition reduces and displaces trophic niches in Collembola communities in a Brazilian woodland savanna

Ecosystems worldwide are being subjected to increasing rates of nutrient deposition. Additional nitrogen (N) and phosphorus (P) inputs and liming are common practices in agroecosystems that have long-term consequences for plant and microbial diversity and community structure during ecosystem restoration. However, legacy effects of nutrient deposition on multitrophic biodiversity and trophic interactions of soil organisms are poorly understood. Collembola is a good model group to study such effects. These small soil invertebrates are intimately linked to plants and microbes, and play an important role in soils by supporting soil fertility and energy channeling to higher trophic levels in soil food webs. Here, we studied the trophic niche structure of epigeic Collembola during a long-term (20 years) nutrient addition experiment in the Central Brazilian savanna (Cerrado), one of the tropical agricultural frontiers. We used descriptive isotopic metrics of Collembola communities based on stable isotopes of carbon and nitrogen to evaluate the legacy effects of fertilization (with N, P, and N + P additions) and liming on their trophic-niche structure. The strongest trophic niche shifts were observed under N addition, manifested in the form of (i) a reduction in trophic niche widththat is, decreased diversity of consumed basal resources available to the Collembola communityand (ii) in a more even distribution of Collembola taxa in trophic space. Community trophic niche was strongly displaced under P, N + P, and liming additions (i.e., it did not overlap with the control), reflecting intensified trophic links of Collembola to exotic C4 grasses. Overall, our results indicate that increased atmospheric N deposition simplifies the trophic structure of Collembola communities, which may affect the efficiency and pathways of energy channeling in soil food webs and soil functioning. In addition, the observed niche shifts suggests the need for flexibility in feeding by soil animals in savanna to persist under supplemental N + P and liming. Our study is among the first to explore the trophic structure of invertebrates in tropical soils and provides further evidence that nutrient deposition and agricultural fertilization and liming legacy effects have long-term consequences for soil organisms on multiple trophic levels.

Shade drives plant community changes of ground‐layer savanna vegetation: Short‐term changes under an experimental approach

AbstractAimWoody‐plant encroachment is a reality in many savannas worldwide, leading savannas to become replaced by forest ecosystems. As tree density and cover increase, increased shade and litter deposition may suppress the savanna's community of low‐lying plants. By using field manipulation, we tested shading and litter effects, alone and in combination, on the savanna's ground‐layer plant community. We investigated how changes in these environmental factors may affect the composition, structure, and above‐ground biomass in the plant community of a species‐rich Neotropical savanna.LocationSavanna patches in the Cerrado, southeastern Brazil.MethodsAnnual surveys of the herbaceous–shrub layer in a three‐year field manipulation experiment examining shading and litter deposition.ResultsShade negatively affected all evaluated parameters, while litter addition had only minor effects. The largest losses of richness, density, and cover occurred in forbs and grasses. Increased shade resulted in a sharp decrease in the above‐ground biomass of monocots.ConclusionsOur results show that light is a strong environmental filter for the ground‐layer community. The reductions in grass cover and biomass under shade treatments likely altered ecosystem functioning. Woody encroachment can thus be considered to represent a process that can alter the structure and functioning of savannas. Management interventions should therefore be taken to prevent woody encroachment or mitigate its harmful effects on savanna biodiversity and ecosystem functioning.

The Interactive Effects of Drought and Fire on Soil Microbial Communities in a Semi-Arid Savanna

The Interactive Effects of Drought and Fire on Soil Microbial Communities in a Semi-Arid Savanna

Relationships between soils and plant community composition and structure in a Neotropical savanna mosaic

Context How woody flora richness and composition in different vegetation communities in a Neotropical savanna are explained by chemical and physical soil properties? Objective Determinate the relationships between the topsoil properties, richness, and composition of woody flora in the following six vegetation communities of the Brazilian Cerrado: four non-waterlogged, one seasonally waterlogged and one permanently waterlogged. Methods We used rarefaction analysis to compare richness among vegetation communities and Canonical Redundancy Analysis to evaluate the relationships between soil and floristic composition. Key results We showed clear edaphic differences between Palm Swamps (higher organic matter), Gallery Forest (less fertile), Woodland Cerrado (finer soils texture) and Dense Cerrado, Typical Cerrado and Murundu Field (more fertile and coarser soils texture). The species richness was highest in the Gallery Forest and Typical Cerrado and lowest in Palm Swamps. The low species richness in Palm Swamps was caused by waterlogging, inferred by the high organic-matter content of the soil. The differences and similarities in species composition among vegetation communities were explained by waterlogging, fertility and texture of soils. Conclusions Changes in soil properties and woody species composition among vegetation communities can be abrupt, such as those among Palm Swamps, Gallery Forest and other vegetation communities, or gradual as those among Woodland Cerrado, Dense Cerrado, Typical Cerrado and Murundu Field. Implications The high local richness (alfa diversity) and clear species turnover between some vegetation communities (beta diversity) with difference in soil properties justify the necessity of conserving the complex vegetation mosaic in the studied region, once it is located on the Brazil’s agricultural frontier.

Evidence of nutrient translocation in response to smoke exposure by the East African ant acacia, Vachellia drepanolobium.

Fire is a major selective force on arid grassland communities, favoring traits such as the smoke‐induced seed germination response seen in a wide variety of plant species. However, little is known about the relevance of smoke as a cue for plants beyond the seedling stage.We exposed a fire‐adapted savanna tree, Vachellia (=Acacia) drepanolobium, to smoke and compared nutrient concentrations in leaf and root tissues to unexposed controls. Experiments were performed on three age cohorts: 2‐year‐old, 9‐month‐old, and 3‐month‐old plants.For the 2‐year‐old plants exposed to smoke, carbon and nitrogen concentrations were lower in the leaves and higher in the roots than controls. Less pronounced trends were found for boron and magnesium.In contrast, smoke‐exposed 3‐month‐old plants had lower root nitrogen concentrations than controls. No significant differences were found in the 9‐month‐old plants, and no significant shifts in other nutrient concentrations were observed between plant tissues for any of the three age cohorts. Synthesis: Our findings are consistent with smoke‐induced translocation of nutrients from leaves to roots in 2‐year‐old V. drepanolobium. This could represent a novel form of fire adaptation, with variation over the course of plant development. The translocation differences between age cohorts highlight the need to investigate smoke response in older plants of other species. Accounting for this adaptation could better inform our understanding of savanna community structure and nutrient flows under fire regimes altered by anthropogenic land use and climate change.

Floristic composition, diversity and edaphic effects in two rocky savanna communities in the Amazon and Cerrado, Brazil

Despite the uniqueness and reach of the flora from natural savannas in the Brazilian Amazon, and the existence of studies on its origin and diversity, there are no local studies associating floristic patterns with soil properties in savanna enclaves in the Amazon region of the state of Mato Grosso. Floristic composition and diversity were compared between a woody community from a rocky savanna inselberg in a transition region (RTS) between the two largest South American biomes (Cerrado-Amazon), and an enclave of rocky savanna in the Amazon (RAS), and the effects of soil properties were investigated. Floristic comparisons were also made between the two studied communities and two other rocky savanna communities near the Cerrado-Amazon transition. The flora and physical and chemical soil properties in twenty-five 20 × 20 m subplots (1 ha) in each community were sampled and georeferenced. An evident floristic distinction was found between the two studied communities, with low similarity values and a high number of indicator species. The observed and estimated richness and Rényi diversity profiles indicated lower species diversity in RAS than in RTS. Soils were found to be litholic, poorly drained, dystrophic, alic, extremely acidic, sandy and nutrient poor. Species composition and abundance was associated with soil properties in both communities. The clear difference in species composition and diversity between RTS and RAS seem to be shaped by soil properties, geographic isolation and floristic influence from the Cerrado and the Amazon. These results broaden the knowledge regarding the composition and diversity of woody plants of savannas in Amazonian enclaves and Cerrado inselbergs, and provide an important set of floristic and edaphic descriptors for the phytogeography of rocky savannas.

Fire does not change sprouting nor flowering, but affects fruiting phenology in a Neotropical savanna community

In fire-prone ecosystems, such as savannas, fire has been a common event for thousands of years. In these biomes, phenology is a functional trait characterizing the responses of plant communities to fire. In this study, we aimed to evaluate the effects of fire on the period of occurrence, seasonality, and number of species expressing vegetative and reproductive phenophases (sprouting, flowering, and fruiting) in a South American savanna community. We burned experimental plots in 2013, and during the subsequent year, we performed monthly evaluations of the presence and absence of vegetative and reproductive structures in 44 species of angiosperms in the control and burned plots. We described plant phenology at two levels: (i) considering all sampled plant species together (community); and (ii) separately considering the species found in the herbaceous-subshrub and shrub-tree layers (vegetation strata). We analyzed the data using circular statistics and generalized linear mixed models. At the community level, fire did not alter the mean period of occurrence of vegetative and reproductive phenophases; however, we observed changes in fruiting seasonality, which were mainly caused by the changes occurring in the shrub-tree layer. Except for those found in the shrub-tree layer, more species expressed the analyzed phenophases after fire compared to the “control” treatment. This study provides information regarding the responses of plants to burning at the end of the dry season, when most anthropogenic fires occur. Additionally, according to climate change predictions, the Southern Hemisphere is expected to experience longer dry seasons, which may contribute to an increased frequency of anthropogenic fires. Therefore, this phenological information can motivate subsidies that are important for the conservation of this biome and management plans related to the prescription of fires.