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41 results for “tropical savannas”
DATASET : Thresholds of fire response to moisture and fuel load differ between tropical savannas and grasslands across continents
<p><strong>Abstract </strong></p> <p><strong>Aim:</strong> An emerging framework for tropical ecosystems states that fire activity is either ‘<em>fuel build-up limited</em>’ or ‘<em>fuel moisture limited</em>’ i.e. as you move up along rainfall gradients, the major control on fire occurrence switches from being the amount of fuel, to the moisture content of the fuel. Here we used remotely sensed datasets to assess whether interannual variability of burned area is better explained by annual rainfall totals driving fuel build-up, or by dry season rainfall driving fuel moisture.</p> <p><strong>Location:</strong> Pantropical savannas and grasslands</p> <p><strong>Time period:</strong> 2002-2016</p> <p><strong>Methods:</strong> We explored the response of annual burned area to interannual variability in rainfall. We compared several linear models to understand how <em>fuel moisture </em>and <em>fuel build-up effect </em>(accumulated rainfall during 6 and 24 months prior to the end of the burning season respectively) determine the interannual variability of burned area and explore if tree cover, dry season duration and human activity modified these relationships.</p> <p><strong>Results:</strong> Fuel and moisture controls on fire occurrence in tropical savannas varied across continents. Only 24% of South American savannas were <em>fuel build-up limited</em> against 61% of Australian savannas and 47% of African savannas. On average, South America switched from fuel limited to moisture limited at 500 mm yr<sup>-1</sup>, Africa at 800 mm yr<sup>-1</sup> and Australia at 1000 mm yr<sup>-1 </sup>of mean annual rainfall.</p> <p><strong>Main conclusions:</strong> In 42% of tropical savannas (accounting for 41% of current area burned) increased drought and higher temperatures will not increase fire, but there are savannas, particularly in South America, that are likely to become more flammable with increasing temperatures. These findings highlight that we cannot transfer knowledge of fire responses to global change across ecosystems/regions – local solutions to local fire management issues are required, and different tropical savanna regions may show contrasting responses to the same drivers of global change.</p>
Fire promotes functional plant diversity and modifies soil carbon dynamics in tropical savanna
<p>The dataset associated with the manuscript "Fire promotes functional plant diversity and modifies soil carbon dynamics in tropical savanna" (Teixeira et al.) includes 6 different datasets, for which we provided one metadata.<br> </p> <p><strong>Version 2</strong> includes an update of the biomass data set, including the correct transformation to g/m2 on fine roots biomass data.<br><br><strong>Version 3 </strong>includes an update of the belowground traits data set based on correcting formatting errors in the belowground traits data. <br><br><strong>Version 4 </strong>Sorry for the inconvenience. This version includes the correct updated belowground traits data file based on the correct formatting errors in the belowground trait data. <br><br>fluxes: it includes data related to net ecosystem C and water exchange. NEE and ET from each plot were measured using the LiCOR 7500 infrared gas analyzer (Li-Cor Inc.). See the method section in the manuscript for full details.</p> <p>soil_carbon: it includes carbon soil data.<br><br>biomass_v2: it includes data related to aboveground and belowground biomass. Aboveground data were collected in 0.5m2 subplot and belowground at 0.25m2 at 20cm depth both within 1m2 sampling plot. See the method section in the manuscript for full details.</p> <p>aboveground_traits: all aboveground functional traits from plant species. See the method section in the manuscript for full details.</p> <p>belowground_traitsv3: all roots functional traits from plant species. See the method section in the manuscript for full details.</p> <p>species_composition: plant community composition. See the method section in the manuscript for full details.</p> <p><br><strong>Abstract</strong><br>Fire is an evolutionary environmental filter in tropical savanna ecosystems altering functional diversity and associated C pools in the biosphere and fluxes between the atmosphere and biosphere. Therefore, alterations in fire regimes (e.g. fire exclusion) will strongly influence ecosystem processes and associated dynamics. In those ecosystems, C dynamics and functions are underestimated by the fire-induced offset between C output and input. To determine how fire shapes ecosystem C pools and fluxes in an open savanna across recently burned and fire excluded areas, we measured the following metrics: (I) plant diversity including taxonomic (i.e. richness, evenness) and plant functional diversity (i.e. functional diversity, functional richness, functional dispersion and community weighted means); (II) structure (i.e. above- and below-ground biomass, litter accumulation); and (III) functions related to C balance (i.e. net ecosystem carbon dioxide (CO<sub>2</sub>)<sub> </sub>exchange (NEE), ecosystem transpiration (ET), soil respiration (soil CO<sub>2</sub> efflux), ecosystem water use efficiency (eWUE) and total soil organic C (SOC). We found that fire promoted aboveground live and belowground biomass, including belowground organs, and coarse and fine root biomass, and contributed to higher biomass allocation belowground. Fire also increased both functional diversity and dispersion. NEE and total SOC were higher in burned plots compared to fire-excluded plots whereas soil respiration recorded lower values in burned areas. Both ET and eWUE were not affected by fire. Fire strongly favored functional diversity, fine root, and belowground organ biomass in piecewise SEM models but the role of both functional diversity and ecosystem structure to mediate the effect of fire on ecosystem functions remain unclear. Fire regime will impact C balance, and fire exclusion may lead to lower C input in open savanna ecosystems.</p>
Figure 8 in Diversity in Australia's tropical savannas: An integrative taxonomic revision of agamid lizards from the genera Amphibolurus and Lophognathus (Lacertilia: Agamidae)
Figure 8. Photos in life of species under revision: a, Lophognathus horneri sp. nov., adult male with breeding colouration, 80 mile beach, Western Australia (photo: R. Glor); b, Lophognathus gilberti, Katherine, Northern Territory (photo: R. Glor); c, Amphibolurus centralis, adult male with breeding colouration, West MacDonnell Ranges, Northern Territory (photo: J. Melville); d, Amphibolurus burnsi, adult male with breeding colouration, Westmar, Queensland (photo: S. Wilson); e, Tropicagama temporalis, Jabiru, Northern Territory (photo: S. Wilson); f, Gowidon longirostris, adult male with breeding colouration, Ormiston Gorge, Northern Territory (photo: R. Glor).
Figure 2 in Diversity in Australia's tropical savannas: An integrative taxonomic revision of agamid lizards from the genera Amphibolurus and Lophognathus (Lacertilia: Agamidae)
Figure 2. The distribution of Lophognathus sensu lato samples included in this study along the first three morphological principal components axes. Distribution of each taxon is delineated by a 95% confidence ellipse. Lophognathus gilberti has been separated into L. sp. nov., L. gilberti centralis, and L. gilberti.
Figure 6 in Diversity in Australia's tropical savannas: An integrative taxonomic revision of agamid lizards from the genera Amphibolurus and Lophognathus (Lacertilia: Agamidae)
Figure 6. Colour pattern variation in the lateral head views of Amphobolurus centralis, Lophognathus gilbert and L. horneri sp. nov. Museum registration numbers for the individual lizards photographed are provided.
Figure 7 in Diversity in Australia's tropical savannas: An integrative taxonomic revision of agamid lizards from the genera Amphibolurus and Lophognathus (Lacertilia: Agamidae)
Figure 7. Variation in white pigmentation on tympanums of Lophognathus sp. nov., L. gilberti and L. gilberti centralis. Orientation of the tympanums is provided under images. Museum registration numbers for the individual lizards photographed are also provided.
Figure 5 in Diversity in Australia's tropical savannas: An integrative taxonomic revision of agamid lizards from the genera Amphibolurus and Lophognathus (Lacertilia: Agamidae)
Figure 5. Primary type specimens: a,Amphibolurus centralis (MCZ 35207); b, Gowidon longirostris (BMNH 1946.8.28.73); c, Lophognathus gilbert (BMNH1946.8.28.69); d, Tropicagama temporalis (BMNH 1946.8.28.72).
Figure 3 in Diversity in Australia's tropical savannas: An integrative taxonomic revision of agamid lizards from the genera Amphibolurus and Lophognathus (Lacertilia: Agamidae)
Figure 3. Results from the integrative taxonomic approach to species delimitation. Genera are designated by a multicoloured horizontal bars at the top of the figure, and species within genera are designated by a number in black above a coloured vertical segment. Segment colours and species numbers correspond to those in fig.1.
Figure 1 in Diversity in Australia's tropical savannas: An integrative taxonomic revision of agamid lizards from the genera Amphibolurus and Lophognathus (Lacertilia: Agamidae)
Figure 1. MtDNA phylogenetic tree for the genera Lophognathus, Amphibolurus and Chlamydosaurus reproduced from Melville et al. (2011). Tree presented is a Bayesian 50% majority-rule consensus tree based on ~1200 bp mitochondrial DNA (ND2). Bayesian posterior probabilities and ML boostraps are provided on branches. Sample identification numbers are either Genbank accession numbers for previously published sequences or museum IDs (shown in brackets) for samples sequenced previously. Vertical bars indicate species following the taxonomic revision.
Data from: Landscape variation in defense traits along gradients of multiple resources in a tropical savanna plant
<p><span>Many plant species are widely distributed and consequently are exposed to multiple abiotic factors and diverse herbivores, each of which may distinctly affect the magnitude of different defense traits.</span><span> </span><span>Alternative theories for optimal allocation to plant defense traits predict both positive and negative associations between magnitude of defense and resource availability. These predictions may apply even within species. </span><span>This </span><span>suggests potential for a single species' patterns of association of defense traits and resources to vary with both the type of defense and identity of resource, but relatively few studies have explored intraspecific variation in multiple defense traits along several resource gradients simultaneously. </span><span>In order to address this gap, especially in an ecosystem dominated by large mammalian herbivores, we assessed relationships between multiple resources (rainfall, soil N, and soil P) and plant defense traits (prickle density, phenolics, and lignin content) using a widely distributed tropical savanna herb, <em>Solanum</em> <em>incanum</em>, growing in naturally occurring resource gradients within the Serengeti National Park. </span>We found substantial intraspecific variation in all three defense traits across sites (n =43). Variation in prickle density was positively associated with rainfall and soil P, but not soil N. In contrast to prickle density, phenolics and lignin were uncorrelated with all three resource gradients. This independent association of soil P with a carbon-based defense, prickle density, suggests potential for resources that are not components of defenses to influence allocation to defense traits. Such influence may reflect association between resource and herbivore abundance and/or preference. These varied patterns in resource-defense associations further emphasize the tremendous variation in anti-herbivore traits which may be influenced by different plant resources and highlight the need to consider multiple resource gradients in understanding evolution of plant traits.</p>
Data from: Landscape variation in defense traits along gradients of multiple resources in a tropical savanna plant
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Data from: Tropical biome switching: Ant communities transition from savanna to rainforest following cessation of burning
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Tropical riparian forests in danger from large savanna wildfires
<p>1. Tropical savannas are known for the fire-prone ecosystems, yet, riparian evergreen forests are another important landscape feature. These forests usually remain safe from wildfires in the wet riparian zones. With global changes, large wildfires are now more frequent in savanna landscapes, exposing riparian forests to unprecedented impact.</p> <p>2. In 2017, a large wildfire spread across the Chapada dos Veadeiros National Park, an iconic UNESCO site in central Brazil, raising concerns about its impact on the fire-sensitive ecosystems. By combining remote sensing analysis of Google Earth images (2003-2019) with detailed field information from 36 sites, we assessed wildfire impacts on riparian forests. For this, we measured the structure of trees, saplings and herbaceous plants, as well as topsoil variables.</p> <p>3. Since 2003, all riparian forests had canopy cover above 90 %, but after 2017, canopy cover dropped to 20 % in some forests, indicating large variation in wildfire damage. A closer look in the field revealed that, on average, the wildfire killed 52 % of adult trees and 87 % of tree saplings in flooded forests. In non-flooded forests, impacts on adult trees were negligible, but fire killed 75 % of tree saplings. Opportunistic vines and the invasive grass Melinis minutiflora were already present in severely disturbed flooded forests. In all forests, impacts on many ecosystem variables were related to canopy damage, a variable measurable from satellite. Overall, seasonally flooded riparian forests were the most severely impacted, possibly due to the relatively thinner barks of their trees.</p> <p>4. Synthesis and applications. Our findings reveal how riparian forests embedded in tropical savanna landscapes are in danger from large wildfires. The destruction of some forests has opened space for new plant species that may propel a shift to an alternative ecosystem state. Riparian forests are habitat of large savanna animals and their loss could affect entire trophic networks. Managing wildfires and invasive grasses locally is probably the best strategy to maintain riparian forests resilient. As wildfire regimes intensify in tropical savanna landscapes, our findings stress the need for an integrated management that considers riparian forests as a vulnerable element of the system.</p>
Not all trees can make a forest: tree species composition and competition control forest encroachment in a tropical savanna
<p>Forest encroachment into savannas is a widespread phenomenon, the rate of which may depend on soil conditions, species composition, or changes in stand structure. As savanna specialist trees are replaced by generalist species, rates of stand development may increase. Because generalists can persist in forests, they are likely to grow more quickly and survive longer in dense stands, compared to savanna specialists. Furthermore, the faster growth rates of generalists may allow them to overtop and outcompete savanna specialists, causing rapid species turnover.</p> <p>We measured growth and survival of 6147 individuals of 112 species of savanna and generalist tree species over a period of 10 years in an ecological reserve in Assis, São Paulo State, Brazil. We modeled growth and mortality as a function of soil texture and nutrients, tree size, competitive neighborhood, and membership in savanna or generalist (species which can persist in forests and savannas) functional groups.</p> <p>Tree growth and survival was strongly influenced by competition, as estimated by the basal area of trees taller than a focal tree. At the stand level, savanna species are unable to contribute basal area growth in closed stands, while generalist species continue to increase in basal area even at high stand basal area. This phenomenon is driven by differences in growth and mortality. Generalists grew faster than savanna species, both in height and diameter. This difference in growth rates led to savanna species becoming suppressed more rapidly than generalists. When suppressed, savanna species were more than twice as likely to die than were generalists. Soils had inconsistent and mostly weak effects which were difficult to separate from gradients of stand structure.</p> <p>Synthesis: We demonstrate that the presence of generalist trees accelerates rates of basal area accumulation due to their greater growth rates and tolerance of shading. Generalists outcompete savanna trees by growing faster in the open and overtopping savanna specialists. Due to the slow growth and high mortality of savanna species in the shade, they are unable to form closed-canopy stands. Accounting for differences among functional types and development of vegetation structure is critical for modeling forest encroachment.</p>
Figure 4 in Diversity in Australia's tropical savannas: An integrative taxonomic revision of agamid lizards from the genera Amphibolurus and Lophognathus (Lacertilia: Agamidae)
Figure 4. Distribution of study species included in this study, compiled from museum records.
Figure 9 in Diversity in Australia's tropical savannas: An integrative taxonomic revision of agamid lizards from the genera Amphibolurus and Lophognathus (Lacertilia: Agamidae)
Figure 9. Holotype of Lophognathus horneri sp. nov. (NTM R16472).
Tillage agriculture and afforestation threaten tropical savanna plant communities across a broad rainfall gradient in India
<p>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.</p> <p>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 (<em>n</em>=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.</p> <p>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/m<sup>2</sup> in old-growth savannas to 8, 6, and 3 species/m<sup>2</sup> 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. Reductions in native cover coincided with increased cover of invasive species in tree plantations (18%), fallows (18%), and tillage agriculture (3%).</p> <p>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 (9 species) and fallows (13 species) were both invasive and native species, while the 2 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.</p> <p><strong>Synthesis</strong>: 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.</p>
Data from: Rare frost events reinforce tropical savanna-forest boundaries
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Tillage agriculture and afforestation threaten tropical savanna plant communities across a broad rainfall gradient in India
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Tropical riparian forests in danger from large savanna wildfires
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