Effects of Fire on Seedling Diversity and Plant Reproduction (Sexual vs. Vegetative) in Neotropical Savannas Differing in Tree Density

Little is known about the effects of fire on the structure and species composition of Neotropical savanna seedling communities. Such effects are critical for predicting long‐term changes in plant distribution patterns in these ecosystems. We quantified richness and density of seedlings within 144 plots of 1 m² located along a topographic gradient in long‐unburned (fire protected since 1983) and recently burned (September 2005) savannas in Brazil. These savannas differ in tree density and canopy cover. Sites along the gradient, however, did not differ in species composition prior to the fire. In recently burned savannas we also evaluated the contribution of vegetative reproduction relative to sexual reproduction by quantifying richness and density of root suckers. Finally, we tested seed tolerance to pulses of high temperatures—similar to those occurring during fires on the soil surface and below—of five dominant savanna tree species. Seedlings were more abundant and diverse in unburned than in burned savannas. Seedling species composition differed among unburned and burned savannas probably reflecting early differences in root: shoot biomass allocation patterns. In recently burned savannas, root suckers were more abundant and diverse than seedlings. Relatively long exposures (>10 min) of temperatures of 90 °C reduced seed germination in all studied species suggesting a negative effect of fire on germination of seeds located at or aboveground level. Because vegetative reproduction contributes more than sexual reproduction in burned environments, frequent fires are likely to cause major shifts in species composition of Neotropical savanna plant communities, favoring clonally produced recruits along tree density/topographic gradients.     

Savannas after afforestation: Assessment of herbaceous community responses to wildfire versus native tree planting

Afforestation and fire exclusion are pervasive threats to tropical savannas. In Brazil, laws limiting prescribed burning hinder the study of fire in the restoration of Cerrado plant communities. We took advantage of a 2017 wildfire to evaluate the potential for tree cutting and fire to promote the passive restoration of savanna herbaceous plant communities after destruction by exotic tree plantations. We sampled a burned pine plantation (Burned Plantation); a former plantation that was harvested and burned (Harvested & Burned); an unburned former plantation that was harvested, planted with native trees, and treated with herbicide to control invasive grasses (Native Tree Planting); and two old-growth savannas which served as reference communities. Our results confirm that herbaceous plant communities on post-afforestation sites are very different from old-growth savannas. Among post-afforestation sites, Harvested & Burned herbaceous communities were modestly more similar in composition to old-growth savannas, had slightly higher richness of savanna plants (3.8 species per 50-m²), and supported the greatest cover of native herbaceous plants (56%). These positive trends in herbaceous community recovery would be missed in assessments of tree cover: whereas canopy cover in the Harvested & Burned site was 6% (less than typical of savannas of the Cerrado), the Burned Plantation and Native Tree Planting supported 34% and 19% cover, respectively. By focusing on savanna herbaceous plants, these results highlight that tree cutting and fire, not simply tree planting and fire exclusion, should receive greater attention in efforts to restore savannas of the Cerrado.     

Post-fire dynamics of woody vegetation in seasonally flooded forests (impucas) in the Cerrado-Amazonian Forest transition zone

Fire disturbance alters the structural complexity of forests, above-ground biomass stocks and patterns of growth, recruitment and mortality that determine temporal dynamics of communities. These changes may also alter forest species composition, richness, and diversity. We compared changes in plant recruitment, mortality, and turnover time over three years between burned and unburned sites of two seasonally flooded natural forest patches in a predominantly savanna landscape (regionally called ‘impucas’) in order to determine how fire alters forest dynamics and species composition. Within each impuca, 50 permanent plots (20 m × 10 m) were established and all individuals ≥5 cm diameter at breast height (DBH) identified and measured in two censuses, the first in 2007 and the second in 2010. Unplanned fires burned 30 plots in impuca 1 and 35 in impuca 2 after the first census, which enabled thereafter the comparison between burned and unburned sites. The highest mortality (8.0 and 24.3% year⁻¹ for impuca 1 and 2) and turnover time (69 and 121.5 years) were observed in the burned sites, compared to 3.7 and 5.2% year⁻¹ (mortality), and 28.4 and 40.9 years (turnover), respectively, for the unburned sites. Although these seasonally flooded impuca forests are embedded in a fire-adapted savanna landscape, the impucas vegetation appears to be sensitive to fire, with burned areas having higher mortality and turnover than unburned areas. This indicates that these forest islands are potentially at risk if regional fire frequency increases.     

Habitat and fire heterogeneity explain the co-occurrence of congeneric resprouter and reseeder Hypericum spp. along a Florida pine savanna ecocline

The distribution of resprouting and reseeding woody plants may be limited by the frequency of disturbances. Such species have a high probability of persisting in frequently and rarely disturbed habitats and may co-occur at intermediate disturbance frequencies. Nonetheless, resprouters and reseeders of the genus Hypericum co-occur in frequently burned pine savannas of southeastern North America. We predicted that these congeners would sort along a fire frequency gradient resulting from fine scale variation in topography and soil moisture. We examined habitat associations of a resprouter (H. microsepalum), facultative reseeder/resprouter (H. brachyphyllum), and reseeder (H. chapmanii) that occur along Northern Florida pine savanna ecoclines. We sampled five belt transects of 50 continuous 1?×?1?m² plots for edaphic characteristics, fire spread, and densities of each species. Hypericum microsepalum was associated with upland, drier pine savannas where fires are frequent and typically burn uniformly across landscapes (2?C3?year fire frequency). In contrast, H. brachyphyllum and H. chapmanii were associated with intermediate mesic areas where fires burn increasingly patchily downslope along ecoclines from upland flatwoods to lowland wet depressions (10?C30?year fire frequency). Hypericum species of all life histories co-occur in intermediate areas where small changes in topography and edaphic characteristics generate a fire frequency gradient on a local scale. In pine savannas, fires vary from frequent to infrequent on a local within-landscape level as a function of elevation gradients. We conclude that the occurrence of such fire gradients along ecoclines should facilitate co-occurrence of plants with different life histories and thereby increase overall biodiversity.     

Patterns of herbaceous plant diversity in southeastern Louisiana pine savannas

Question: How diverse are Louisiana pine savanna plant communities and how is diversity affected by time since burn and removal of a competitively dominant species? Location: Lake Ramsay, southeastern Louisiana, USA. Methods: Species‐area curves were constructed from nine nested quadrats in open savanna differing in time since burn (6, 18 and 30 months). Species frequency was determined for 100 1 ‐m² quadrats. The dominant gras s, Andropogon virginicus, was removed with herbicide from moist and dry sites to test for possible effects of competition. Results: Slopes of log‐log species‐area relationships were steep (0.195 to 0.379). Time since burn did not affect the richness of herbaceous plants, only woody species. More than half of all species recorded (43/79, 54%) were infrequent (in < 10% of quadrats). After two years, there were no differences in species richness and composition for plots with and without A. virginicus. Conclusions: The high species diversity is typical of other savannas across the coastal plain. The large number of infrequent species indicates that the core‐satellite pattern of species occurrence found in temperate grasslands does not apply to southern pine savannas. The absence of effects due to removal of a dominant may be due to insufficient observation time, or low competition. Most species have traits, such as diminutive life forms, that suggest they are weak competitors for light in the presence of robust matrix grasses and in the absence of fire. Many species in Pinuspalustris savannas are likely either fugitive or peripheral species.     

Patterns and mechanisms of plant succession after fire on Artemisia-grass sites in southeastern Idaho

Cover data for plant species on eight environmentally similar sites that were each burned in a different year (from 2 to 36 years ago) were used to construct a composite sequence of vegetational change after fire on Artemisia-grassland sites in southeastern Idaho. Some species were early successional such as Lithospermum ruderale, and some late successional: Artemisia tridentata, A. tripartita, and Gutierreza sarothrae. But many species: Purshia tridentata, Symphoricarpos oreophilus, Amelanchier alnifolia, Chrysothamnus viscidiflorus, Achillea millefolium, Agropyron dasystachyum, and A. spicatum were present in both early and later stages. Shannon and Simpson indices of diversity and species richness indicated little change in alpha diversity through time. This was attributed mainly to the limited change in species composition from early to later stages. The general pattern of succession is compatible with the tolerance model of Connell & Slatyer (1977) in most respects. Species traits relating to persistence through a disturbance or re-establishment on the site, and tolerance of competition shape the course of succession on a site. Perennial grasses and forbs which sprout from the base after fire are the first species to dominate the sites. Sprouting shrubs, which require some years to regrow to their pre-fire form, are prominent by the sixth year. Shrubs which rely on dispersal become co-dominants in later stages, at which time some herbaceous species are reduced oreliminated. The pattern of succession can differ due to presence or absence of species with particular traits.     

Are the eucalypt and non-eucalypt components of Australian tropical savannas independent?

Eucalypts (Eucalyptus and Corymbia spp.) dominate (>60%) the tree biomass of Australia's tropical savannas but account for only a fraction (28%) of the tree diversity. Because of their considerable biomass and adaptation to environmental stressors, such as fire, the eucalypts may drive tree dynamics in these savannas, possibly to the exclusion of non-eucalypts. We evaluated whether the eucalypt and non-eucalypt components in tropical savannas are dependent so that changes in one component are matched by opposite trends in the other. Using tree inventory data from 127 savanna sites across the rainfall and fire frequency gradients, we found that eucalypt and non-eucalypt basal area and species richness had a negative relationship. This relationship was maintained across the rainfall gradient, with rainfall having a positive effect on the basal area and species richness of both components, but with a greater effect in non-eucalypts. Fire frequency negatively affected basal area, but not species richness, although basal area and species richness of eucalypts and non-eucalypts did not differ in their response to fire. Rainfall appears to set the upper bounds to woody biomass in these mesic savannas, while fire maintains woody biomass below carrying capacity and facilitates coexistence of the components. The magnitude of the component responses, particularly for non-eucalypts, is determined by rainfall, but their dependence is likely due to their differential response to both rainfall and fire, but not to competition for resources. Thus, while eucalypts dominate biomass overall, at high rainfall sites non-eucalypt basal area and diversity are highest, especially where fire frequency is low.     

When is a ‘forest’ a savanna,and why does it matter?

Savannas are defined based on vegetation structure, the central concept being a discontinuous tree cover in a continuous grass understorey. However, at the high‐rainfall end of the tropical savanna biome, where heavily wooded mesic savannas begin to structurally resemble forests, or where tropical forests are degraded such that they open out to structurally resemble savannas, vegetation structure alone may be inadequate to distinguish mesic savanna from forest. Additional knowledge of the functional differences between these ecosystems which contrast sharply in their evolutionary and ecological history is required. Specifically, we suggest that tropical mesic savannas are predominantly mixed tree–C₄ grass systems defined by fire tolerance and shade intolerance of their species, while forests, from which C₄ grasses are largely absent, have species that are mostly fire intolerant and shade tolerant. Using this framework, we identify a suite of morphological, physiological and life‐history traits that are likely to differ between tropical mesic savanna and forest species. We suggest that these traits can be used to distinguish between these ecosystems and thereby aid their appropriate management and conservation. We also suggest that many areas in South Asia classified as tropical dry forests, but characterized by fire‐resistant tree species in a C₄ grass‐dominated understorey, would be better classified as mesic savannas requiring fire and light to maintain the unique mix of species that characterize them.     

Effects of frequent fires and grazing on stable nitrogen isotope ratios of vegetation in northern Australia

The ratios of stable nitrogen isotopes expressed as δ¹⁵N values can indicate the openness of nitrogen cycles in ecosystems. Southwards through the Northern Territory, values of foliar δ¹⁵N in savanna trees increase as mean annual rainfall decreases from approximately 1800 mm to approximately 750 mm, with foliar δ¹⁵N thereafter decreasing toward arid central Australia. Recent literature argues that this pattern is caused by higher grazing intensity in semi‐arid savannas, but counter views have attributed the pattern more directly to variations in aridity. In this paper, grazed and ungrazed sites in a semi‐arid savanna are compared, and it is shown that grazing has a relatively small effect on the positive foliar δ¹⁵N values of grasses, but no effect on δ¹⁵N values of trees. This gives little support to the argument that variations in grazing pressure at the scale of hundreds of kilometres could result in detectable differences in the foliar δ¹⁵N values of trees. I then compare the semi‐arid savannas with mesic savannas, where fires are frequent, and with mesic rainforests, which are rarely burnt. Greater foliar δ¹⁵N values in rainforest and fire‐excluded mesic savannas than in frequently burnt savannas suggests that fire regimes affect foliar δ¹⁵N. The previously observed pattern in δ¹⁵N values along the rainfall gradient in the Northern Territory is consistent with trends in fire frequency and possible direct effects of fire, but further work is required to determine the relative impacts of aridity and fire. Within a particular rainfall regime, foliar δ¹⁵N values may indicate historical fire frequencies.     

Short‐term effects of herbicides and a prescribed fire on restoration of a shrub‐encroached pine savanna

Shrub encroachment occurring worldwide in savannas and grasslands has commonly been hypothesized to result from anthropogenically altered environments. Two disturbance‐based approaches to restoration have involved: (1) application of selective herbicides to reduce density/cover of shrubs; (2) reinstatement of natural fire regimes to generate environmental conditions favoring herbaceous species. We studied short‐term responses of native shrubs, vines, and grasses in a Louisiana pine savanna to herbicides followed by a prescribed fire and fire alone. Plots established in the summer, 2013, were hand‐sprayed in the fall with Imazapyr and Triclopyr, Triclopyr alone, or no herbicide, then prescribed burned the following spring. Numbers of species of shrubs and vines at scales of 1 and 100 m², numbers of stems and regrowth of stems produced by six common species of shrubs, and the number of flowering culms of perennial C₄ grasses were assessed postfire in 2014. Compared with fire alone, herbicides followed by fire resulted in (1) small reductions in species richness of shrubs and no effects on vines, (2) fewer stems comprising shrub genets, but similar postfire regrowth of resprouting shrub stems, and (3) fewer flowering culms of C₄ grasses. Underground storage organs of savanna shrubs and vines survived both aboveground disturbances. Thus, single applications of herbicides followed by fires reduced, but did not reverse shrub encroachment and negatively affected grasses. Because effects of herbicides overrode those of prescribed fires, these disturbances did not act synergistically, suggesting that reinstating natural fire regimes should be a priority in restoration of savannas and grasslands.     

Influence of fire on critically endangered Swartland Shale Renosterveld in the Cape Floristic Region

Questions

The degree to which renosterveld shrublands are fire‐dependent is currently unclear. To address this issue, the following questions were asked: (1) does smoke stimulate germination of soil‐stored seeds in renosterveld; (2) does recently‐burned renosterveld display changed composition and higher diversity than unburned vegetation; and (3) how do the species compositions of renosterveld soil seed banks and standing vegetation compare?

Location

Swartland, Cape Floristic Region, South Africa.

Methods

Soil seed bank samples from a north‐ and south‐facing slope were smoke‐treated and germinated to test for smoke‐stimulated germination. Burned standing vegetation was surveyed 16 months post‐fire, as was unburned vegetation on the same slopes. Seed bank species richness and density were compared between smoke‐treated and untreated samples within and between slopes. Burned and unburned standing vegetation were compared within and between slopes in terms of species richness, abundance and aerial cover. Compositional similarity of the seed banks and standing vegetation was assessed.

Results

Seed banks were dominated by annuals and graminoids. Smoke treatment had no effect, except for driving significantly higher species richness and seedling density in south‐facing slope perennial shrubs. Species richness and seedling density were significantly higher in seed banks on the south‐facing slope compared to the north‐facing slope. Burned standing vegetation exhibited significantly higher diversity than unburned vegetation. Annuals and graminoids displayed significantly higher species richness and aerial cover in burned renosterveld. The north‐facing slope contained less than half the number of species/m² compared to the south‐facing slope. The seed banks and standing vegetation showed low to intermediate similarity (Sørensen = 31%–53%), but grouped close together on an NMDS plot, suggesting intermediate similarity overall.

Conclusions

Elevated germination of perennial shrubs in smoke‐treated seed bank samples and increased diversity of post‐fire standing vegetation suggest the renosterveld in this study shows elements of a fire‐driven system. Certain species only recruited in burned sites, suggesting fire‐stimulated germination. Aspect had a major influence on plant community composition, with the mesic south‐facing slope being more diverse than the xeric north‐facing slope. The similarity between the seed banks and standing vegetation was higher than previously shown for renosterveld, and appears to be higher than for fynbos.     

Floristic composition,plant species abundance,and soil properties of montane savannas in the Gran Sabana,Venezuela

Floristic composition, species abundance, and soil properties were studied in slope, flat and disturbed savannas in the northern part of the Gran Sabana, Venezuela. All savannas presented shallow soils (<30 cm depth) with high content of sand and low content of clay. In general, the soils were poor in nutrients and strongly acidified. The major difference between the soils was the content of the stony fraction, which was significantly higher (P<0.05) in the slope savannas than in the flat savannas. A total of 57 dicot, 42 monocot, and 7 fern species were recorded in all studied savannas. In the flat and slope savannas predominated the monocot species, while in the disturbed savanna predominated the dicots. The families with the largest number of species were Poaceae (19.8%), Cyperaceae (13.2%), Asteraceae (10.4%) and Melastomataceae (8.5%). The number of species in the flat savannas was higher than that of the slope savannas. The lowest plant species richness was associated to slope savannas and their high content of stony fraction of the soils. The highest floristic similarity was found between slope savannas, and the lowest between disturbed savanna and slope savannas. The most abundant life forms in the studied savannas were perennial (42.4%) and annual (24.5%) herbs, followed by suffruticoses (16.0%) and shrubs (12.3%), and the less frequent was lianas (4.7%). The disturbed savanna showed the higher richness and diversity index. Trachypogon plumosum (Poaceae) was the most abundant species in all studied savanna.     

Woody Encroachment Removal from Midwestern Oak Savannas Alters Understory Diversity across Space and Time

Recovering biodiversity is a common goal during restoration; however, for many ecosystems, it is not well understood how restoration influences species diversity across space and time. I examined understory species diversity and composition after woody encroachment removal in a large-scale savanna restoration experiment in central Iowa, United States. Over a 4-year time series, restoration had profound effects across space and time, increasing richness at local and site-level scales. Restoration sites had increased α (within sample) Simpson's diversity and α and γ (site level) species richness relative to control sites, although γ and β (among sample) Simpson's diversity, β richness, and α species evenness were not affected. Changes in richness were driven by graminoids at the α and γ scales and woody species (and some evidence for forbs) at the α scale. Interestingly, indicator species analysis revealed that at least some species from all functional groups were promoted by restoration, although no species were significant indicators of pre-treatment or control sites. Both savanna and nonsavanna species were indicators of restored sites. Restoration promoted exotic species at both scales, although species with spring phenologies were unaffected. Woody encroachment removal may be a means to promote species establishment in savannas; however, in this study, it resulted in establishment and proliferation of native and exotic and savanna and nonsavanna species. Future work might consider reintroduction of key savanna species to supplement those that have established. Work like this demonstrates the utility of restoration experiments for conducting research on large- and multiscale processes, such as species diversity.     

Frequent burning promotes invasions of alien plants into a mesic African savanna

Fire is both inevitable and necessary for maintaining the structure and functioning of mesic savannas. Without disturbances such as fire and herbivory, tree cover can increase at the expense of grass cover and over time dominate mesic savannas. Consequently, repeated burning is widely used to suppress tree recruitment and control bush encroachment. However, the effect of regular burning on invasion by alien plant species is little understood. Here, vegetation data from a long-term fire experiment, which began in 1953 in a mesic Zimbabwean savanna, were used to test whether the frequency of burning promoted alien plant invasion. The fire treatments consisted of late season fires, lit at 1-, 2-, 3-, and 4-year intervals, and these regularly burnt plots were compared with unburnt plots. Results show that over half a century of frequent burning promoted the invasion by alien plants relative to areas where fire was excluded. More alien plant species became established in plots that had a higher frequency of burning. The proportion of alien species in the species assemblage was highest in the annually burnt plots followed by plots burnt biennially. Alien plant invasion was lowest in plots protected from fire but did not differ significantly between plots burnt triennially and quadrennially. Further, the abundance of five alien forbs increased significantly as the interval (in years) between fires became shorter. On average, the density of these alien forbs in annually burnt plots was at least ten times as high as the density of unburnt plots. Plant diversity was also altered by long-term burning. Total plant species richness was significantly lower in the unburnt plots compared to regularly burnt plots. These findings suggest that frequent burning of mesic savannas enhances invasion by alien plants, with short intervals between fires favouring alien forbs. Therefore, reducing the frequency of burning may be a key to minimising the risk of alien plant spread into mesic savannas, which is important because invasive plants pose a threat to native biodiversity and may alter savanna functioning.     

Changes of butterfly communities after forest fire

Fires change the diversity and composition of insects in forest ecosystems. In the present study, we examined the change of butterfly communities after a fire including the increase of butterfly richness, grassland species, and generalist species, and more changed communities. Butterflies were surveyed for 5 years after the big Uljin fire in 2007. During each year, butterflies were counted monthly by the line transect method from April to October at two sites (burned vs. unburned, ~ 1.5 km routes). Specialist grassland species decreased in the year of the fire but generalist species did not increase significantly. Butterfly richness did not change but butterfly diversity decreased due to a sudden increase of a species, Polygonia c-aureum. The butterfly community in the year of the fire was different from those in later years, showing temporary change of community in the year of the fire. Species composition was significantly different between burned and unburned sites, but this phenomenon cannot be interpreted as an influence of fire due to highly variable species composition of local butterfly assemblages and the non-repetitive sampling site of the present study.     

Loss of a large grazer impacts savanna grassland plant communities similarly in North America and South Africa

Large herbivore grazing is a widespread disturbance in mesic savanna grasslands which increases herbaceous plant community richness and diversity. However, humans are modifying the impacts of grazing on these ecosystems by removing grazers. A more general understanding of how grazer loss will impact these ecosystems is hampered by differences in the diversity of large herbivore assemblages among savanna grasslands, which can affect the way that grazing influences plant communities. To avoid this we used two unique enclosures each containing a single, functionally similar large herbivore species. Specifically, we studied a bison (Bos bison) enclosure at Konza Prairie Biological Station, USA and an African buffalo (Syncerus caffer) enclosure in Kruger National Park, South Africa. Within these enclosures we erected exclosures in annually burned and unburned sites to determine how grazer loss would impact herbaceous plant communities, while controlling for potential fire-grazing interactions. At both sites, removal of the only grazer decreased grass and forb richness, evenness and diversity, over time. However, in Kruger these changes only occurred with burning. At both sites, changes in plant communities were driven by increased dominance with herbivore exclusion. At Konza, this was caused by increased abundance of one grass species, Andropogon gerardii, while at Kruger, three grasses, Themeda triandra, Panicum coloratum, and Digitaria eriantha increased in abundance.     

Effects of fire on bird diversity and abundance in an East African savanna

Fire is an important determinant of many aspects of savanna ecosystem structure and function. However, relatively little is known about the effects of fire on faunal biodiversity in savannas. We conducted a short‐term study to examine the effects of a replicated experimental burn on bird diversity and abundance in savanna habitat of central Kenya. Twenty‐two months after the burn, Shannon diversity of birds was 32% higher on plots that had been burned compared with paired control plots. We observed no significant effects of burning on total bird abundance or species richness. Several families of birds were found only on plots that had been burned; one species, the rattling cisticola (Cisticola chiniana), was found only on unburned plots. Shrub canopy area was negatively correlated with bird diversity on each plot, and highly correlated with grass height and the abundance of orthopterans. Our results suggest that the highest landscape‐level bird diversity might be obtained through a mosaic of burned and unburned patches. This is also most likely to approximate the historical state of bird diversity in this habitat, because patchy fires have been an important natural disturbance in tropical ecosystems for millennia.     

The intermediate disturbance hypothesis does not explain fire and diversity pattern in fynbos

The intermediate disturbance hypothesis is a widely accepted generalization regarding patterns of species diversity, but may not hold true where fire is the disturbance. In the Mediterranean-climate shrublands of South Africa, called fynbos, fire is the most importance disturbance and a controlling factor in community dynamics. The intermediate disturbance hypothesis states that diversity will be highest at sites that have had an intermediate frequency of disturbance and will be lower at sites that have experienced very high or very low disturbance frequencies. Measures of diversity are sensitive to scale; therefore, we compared species richness for three fire regimes in South African mountain fynbos to test the intermediate disturbance hypothesis over different spatial scales from 1 m² to 0.1 hectares. Species diversity response to fire frequency was highly scale-dependent, but the relationship between species diversity and disturbance frequency was opposite that predicted by the intermediate disturbance hypothesis. At the largest spatial scales, species diversity was highest at the least frequently burned sites (40 years between fires) and lowest at the sites of moderate (15 to 26 years between fires) and high fire frequency (alternating four and six year fire cycle). Community heterogeneity, measured both as the slope of the species-area curve for a site and as the mean dissimilarity in species composition among subplots within a site, correlated with species diversity at the largest spatial scales. Community heterogeneity was highest at the least frequently burned sites and lowest at the sites that experienced an intermediate fire frequency.     

Tiger-Moths in Savannas in Eastern Amazon: First Assessment of Diversity and Seasonal Aspects

Biodiversity knowledge on insects is urgently needed due to the ever growing demand for food and the consequent deforestation process and loss of natural habitats in many understudied tropical regions. In this paper, we describe the outcome of a biodiversity research on tiger moths performed for the first time in a poorly studied Amazonian landscape—the savanna. We sampled tiger moths monthly with UV automatic light traps for 12 consecutive months in two sampling points in an area of savanna in eastern Amazon, and we compared our results to previously available data for eastern Amazon. We found a total of 91 species of which 80 were identified to species level. The most species-rich subtribes were Phaegopterina and Euchromiina with 32 species each. Species richness and abundance did not differ among sampling sites, but in general the species richness was higher during the dry season while abundance was higher during the wet season. This seasonal diversity pattern differs from the most common patterns recorded for savannas in other parts of the world. The species composition also changed in wet and dry seasons and correlated significantly with temperature and relative humidity. Our results suggest that the alpha diversity of the Amazonian savannas in our sampling area is lower than that in nearby rain forests and similar to that in agriculturally disturbed areas surrounded by rain forests. However, the species composition differed considerably from natural and disturbed areas. These results highlight the need of basic biodiversity surveys of insects in Amazonian savannas.     

Herbaceous vegetation responses to experimental fire in savannas and forests depend on biome and climate

Fire–vegetation feedbacks potentially maintain global savanna and forest distributions. Accordingly, vegetation in savanna and forest ecosystems should have differential responses to fire, but fire response data for herbaceous vegetation have yet to be synthesized across biomes. Here, we examined herbaceous vegetation responses to experimental fire at 30 sites spanning four continents. Across a variety of metrics, herbaceous vegetation increased in abundance where fire was applied, with larger responses to fire in wetter and in cooler and/or less seasonal systems. Compared to forests, savannas were associated with a 4.8 (±0.4) times larger difference in herbaceous vegetation abundance for burned versus unburned plots. In particular, grass cover decreased with fire exclusion in savannas, largely via decreases in C₄ grass cover, whereas changes in fire frequency had a relatively weak effect on grass cover in forests. These differential responses underscore the importance of fire for maintaining the vegetation structure of savannas and forests.