Wet Savanna Research Articles

Long-Term Estimation of Rainfall Acidity in Major African Ecosystems

The paper examines the acidity of precipitation in three major ecosystems in Western and Central Africa, using data from 413 rainfall samples in the dry savanna of Banizoumbou, Niger; 1,056 samples in the wet savanna of Lamto, Ivory Coast; and 578 samples in the equatorial forest of Zoetele, Cameroon. Analyzed at the Toulouse Aerology Laboratory, the findings indicate that rain in Banizoumbou is alkaline (mean pH 6.19), while at Lamto and Zoetele it is acidic (mean pH 5.24 and 5.45, respectively). Despite significant potential acidity, actual acidity (measured by H+ ion concentration) remains low across all sites. The study highlights the importance of a multiphasic process in rainwater neutralization, involving the capture of acidic gases by mineral dust and gas-particle interactions primarily influenced by ammonia (NH3). Notably, the relationship between pH and the ratio of cations to anions varies: in Banizoumbou, they move inversely, whereas in Lamto and Zoetele, they change in the same direction. This suggests that terrestrial dust influences dominate in the dry savanna, while gas-particle conversion processes are more prominent in the wet savanna and equatorial forest.

Trends and seasonal variability in ammonia across major biomes in western and central Africa inferred from long-term series of ground-based and satellite measurements

Abstract. Ammonia (NH3) is the most abundant alkaline component in the atmosphere. Changes in NH3 concentrations have important implications for atmospheric chemistry, air quality, and ecosystem integrity. We present a long-term ammonia (NH3) assessment in the western and central African regions within the framework of the International Network to study Deposition and Atmospheric chemistry in Africa (INDAAF) programme. We analyse seasonal variations and trends in NH3 concentrations and total column densities along an African ecosystem transect spanning dry savannas in Banizoumbou, Niger, and Katibougou, Mali; wet savannas in Djougou, Benin, and Lamto, Côte d'Ivoire; and forests in Bomassa, Republic of the Congo, and Zoétélé, Cameroon. We use a 21-year record of observations (1998–2018) from INDAAF passive samplers and an 11-year record of observations (2008–2018) of atmospheric vertical column densities from the Infrared Atmospheric Sounding Interferometer (IASI) to evaluate NH3 ground-based concentrations and total column densities, respectively. Climatic data (air temperature, rainfall amount, and leaf area index), as well as ammonia emission data of biomass combustion from the fourth version of the Global Fire Emissions Database (GFED4) and anthropogenic sources from the Community Emissions Data System (CEDS), were compared with total NH3 concentrations and total columns over the same periods. Annual mean ground-based NH3 concentrations are around 5.7–5.8 ppb in dry savannas, 3.5–4.7 ppb in wet savannas, and 3.4–5.6 ppb in forests. Annual IASI NH3 total column densities are 10.0–10.7 × 1015 molec. cm−2 in dry savanna, 16.0–20.9 × 1015 molec. cm−2 in wet savanna, and 12.4–13.8 × 1015 molec. cm−2 in forest stations. Non-parametric statistical Mann–Kendall trend tests applied to annual data show that ground-based NH3 concentrations increase at Bomassa (+2.56 % yr−1) but decrease at Zoétélé (−2.95 % yr−1) over the 21-year period. The 11-year period of IASI NH3 total column density measurements show yearly increasing trends at Katibougou (+3.46 % yr−1), Djougou (+2.24 % yr−1), and Zoétélé (+3.42 % yr−1). From the outcome of our investigation, we conclude that air temperature, leaf area index, and rainfall combined with biomass burning, agricultural, and residential activities are the key drivers of atmospheric NH3 in the INDAAF stations. The results also show that the drivers of trends are (1) agriculture in the dry savanna of Katibougou; (2) air temperature and agriculture in the wet savanna of Djougou and Lamto; and (3) leaf area index, air temperature, residential, and agriculture in the forest of Bomassa.

Tracking Changes in Vegetation Structure Following Fire in the Cerrado Biome Using ICESat‐2

AbstractFires mediate grass and tree competition and alter vegetation structure in savanna ecosystems, with important implications for regional carbon, water, and energy fluxes. However, direct observations of how fire frequency influences vegetation structure and post‐fire recovery have been limited to small experimental field studies. Here, we combined lidar‐derived canopy height and canopy cover from NASA's Ice, Cloud, and land Elevation Satellite‐2 with over two decades of burned area data from the Moderate Resolution Imaging Spectroradiometer sensors to provide the first biome‐wide estimates of post‐fire changes in canopy structure for major vegetation types in the Cerrado (Brazil). Mean canopy height decreased with increasing burn frequency for all natural cover types, with the greatest decline observed for forests and savannas. The ability to separate changes in fractional canopy cover from height growth using lidar data highlighted the long‐time scales of vegetation recovery in forests and savannas after fire. For forests in medium and high precipitation areas, canopy cover returned to unburned values within 5 years following fire, whereas mean canopy height remained below unburned values, even in the oldest fires (14–20 years). Recovery times increased with decreasing rainfall, with average values of both fractional cover and canopy height below unburned areas after 14–20 years for savannas. We observed gradual recovery of vegetation height and cover over decades, even in mesic or wet savanna regions like the Cerrado. Infrequent fire activity, particularly in areas with greater land management, influences ecosystem structure across the biome, with important consequences for biodiversity conservation.

Web-sourced photographic methods reveal dietary composition and shifts in resident and migrant Coracias rollers in southern Africa

Closely related species coexisting in the same niche often have dietary overlap and interspecific competition can result in resource partitioning e.g., dietary shifts, migration or phenological changes. Traditional methods to study avian diets are typically costly, difficult, and invasive. Using web-sourced photographs is an emerging, non-invasive method to study avian foraging ecology. We used this approach, along with photographic road surveys, to study prey composition of migratory European Rollers Coracias garrulus and resident Lilac-breasted Rollers Coracias caudatus where they co-occur in southern Africa. These insectivorous sister species are frequently photographed with prey in their bills because of their conspicuous perch-and-wait foraging behaviour and bright plumage coloration. We collated over 250 photographs of rollers holding prey and identified prey items representing 15 animal orders. Lilac-breasted Roller diet contained six unique orders of prey during the Austral summer (when the European Roller is present), and only one during winter (when the European Roller has migrated north). This suggests that Lilac-breasted Rollers may broaden their diet seasonally to alleviate competition with European Rollers during summer. Additionally, Lilac-breasted and European Rollers had an 84% overlap in dietary composition, potentially representing high interspecific competition - even during wet savanna summers when resource abundance is high - that might have originally driven the evolution of migratory behaviour in the European Roller. Our findings expand the current knowledge of roller diets and highlighting the growing role of social media in ecological studies.

Mechanisms of fire‐maintained plant species diversity in species‐rich wet pine savannas

AbstractTemperate savannas and grasslands maintained by frequent, low‐intensity disturbances such as fire contain among the most species‐rich plant communities in the world. Precisely how these disturbances maintain such high fine‐scale diversity is poorly understood. This study examined the effects of the frequency of simulated fire (clipping combined with litter removal) and the relative importance of recruitment and survival on species diversity and trait and species composition at each of two pine savannas in southeastern Mississippi (USA) that had not been recently burned. Ten 2 × 2 m plots at each site were clipped/cleared annually from 2014 to 2019 and again in spring 2021 (annual frequency). The other 10 clipping plots were not clipped from 2018 to 2020 (reduced frequency). Vegetation in small subplots in annual frequency and reduced frequency plots was compared in August 2021 to test the effects of a short period without clipping on diversity and composition. To test the relative importance of recruitment and survival on diversity and composition, four 0.25 × 0.25 m quarter plots were established within each of 10 annual frequency plots per site following a clipping treatment in fall 2019 and assigned a 2 × 2 factorial arrangement of transplantation of sods from long‐unburned areas and herbicide application. Reducing the frequency of clipping reduced plant diversity and altered composition at both sites. A comparison of diversity and trait composition responses to transplant and herbicide treatments revealed how recruitment and survival combined to affect species diversity. Partial or complete recovery of diversity following clipping and litter removal at both sites was driven by rapid increases in short‐lived, resilient species that show fire‐stimulated emergence from a seed bank and the persistence of long‐lived species capable of surviving the prolonged period without fire or clipping. Species with reduced resilience and persistence were more likely to be lost in the reduced frequency treatment. Results are consistent with a model of short‐term coexistence of maximum species diversity maintained by the most frequent fire regime fuels will permit.

Linking resource- and disturbance-based models to explain tree-grass coexistence in savannas.

Savannas cover a significant fraction of the Earth's land surface. In these ecosystems, C3 trees and C4 grasses coexist persistently, but the mechanisms explaining coexistence remain subject to debate. Different quantitative models have been proposed to explain coexistence, but these models make widely contrasting assumptions about which mechanisms are responsible for savanna persistence. Here, we show that no single existing model fully captures all key elements required to explain tree-grass coexistence across savanna rainfall gradients, but many models make important contributions. We show that recent empirical work allows us to combine many existing elements with new ideas to arrive at a synthesis that combines elements of two dominant frameworks: Walter's two-layer model and demographic bottlenecks. We propose that functional rooting separation is necessary for coexistence and is the crux of the coexistence problem. It is both well-supported empirically and necessary for tree persistence, given the comprehensive grass superiority for soil moisture acquisition. We argue that eventual tree dominance through shading is precluded by ecohydrological constraints in dry savannas and by fire and herbivores in wet savannas. Strong asymmetric grass-tree competition for soil moisture limits tree growth, exposing trees to persistent demographic bottlenecks.

Growth and tissue nutrient responses of adults of Sarracenia alata to prey exclusion, nutrient addition, and neighbor reduction.

Carnivorous plants are often associated with nutrient-poor soils and fires. Fire can decrease available soil nitrogen (N) and increase light availability, thus potentially favoring carnivory if prey provide N. Prey can also be a source of phosphorus (P), however, and soil P-availability often increases and competition for prey can decrease following fire. Carnivory thus might be more advantageous before fire when prey and/or soil P are more limiting. We examined nutrient limitation of growth in a carnivorous plant, Sarracenia alata, in a wet pine savanna in southeastern Mississippi, USA. We measured growth and N:P tissue concentration responses of adult plants to a factorial arrangement of prey capture, neighbor reduction, and addition of N, P, and ash to the soil. We tested two hypotheses: (1) Prey provide N, and neighbor reduction and ash addition increase light and soil P and thus the benefit of carnivory; and (2) Prey provide P, neighbor reduction increases prey and/or P, and prey exclusion reduces growth the most when neighbors are not reduced. The exclusion of prey reduced growth more when neighbors were not reduced, an effect that was ameliorated slightly by the addition of P to the soil (the P-limitation hypothesis). Prey exclusion caused a decrease in tissue P when N was added to the soil. The results of this study with adult plants differed from those of a previous study using small juvenile plants, suggesting a shift from light limitation to P and prey limitation with increasing size.

Atmospheric Propagation Modelling for Terrestrial Radio Frequency Communication Links in a Tropical Wet and Dry Savanna Climate

Atmospheric impairment-induced attenuation is the prominent source of signal degradation in radio wave communication channels. The computation-based modeling of radio wave attenuation over the atmosphere is the stepwise application of relevant radio propagation models, data, and procedures to effectively and prognostically estimate the losses of the propagated radio signals that have been induced by atmospheric constituents. This contribution aims to perform a detailed prognostic evaluation of radio wave propagation attenuation due to rain, free space, gases, and cloud over the atmosphere at the ultra-high frequency band. This aim has been achieved by employing relevant empirical atmospheric data and suitable propagation models for robust prognostic modeling using experimental measurements. Additionally, the extrapolative attenuation estimation results and the performance analysis were accomplished by engaging different stepwise propagation models and computation parameters often utilized in Earth–satellite and terrestrial communications. Results indicate that steady attenuation loss levels rise with increasing signal carrier frequency where free space is more dominant. The attenuation levels attained due to rain, cloud, atmospheric gases, and free space are also dependent on droplet depths, sizes, composition, and statistical distribution. While moderate and heavy rain depths achieved 3 dB and 4 dB attenuations, the attenuation due to light rainfall attained a 2.5 dB level. The results also revealed that attenuation intensity levels induced by atmospheric gases and cloud effects are less than that of rain. The prognostic-based empirical attenuation modeling results can provide first-hand information to radio transmission engineers on link budgets concerning various atmospheric impairment effects during radio frequency network design, deployment, and management, essentially at the ultra-high frequency band.

Effect of intercropping on cassava bacterial blight caused by Xanthomonas axonopodis pv. manihotis in Togo

Bacterial blight is one of the biotic constraints to cassava production, affecting yield and cuttings. To contribute to preventing farmers from yield losses, the present study investigated the effect of intercropping cassava with common staple crops in Togo on the development of cassava bacterial blight under field conditions in four agroecological zones of the country. Cassava was intercropped with maize (Zea mays L.) in the forest-savanna transition zone at Davié, in the forest lowland zone at Adéta, in the forest highland zone at Danyi, and in the wet savanna zone in Sotouboua. Additionally, cassava was intercropped with taro (Colocasia esculenta (L.) Schott.) in the forest highland zone at Danyi. Border plants of cassava for each treatment were inoculated with a bacterial suspension of 107 cfu/ml. Bacterial blight severity was significantly reduced compared to sole cassava in the forest highland in cassava-taro and cassava-maize intercropping (p < 0.05 and p < 0.01 in 2000 and 2001, respectively), in the forest lowland in cassava-maize intercropping (p = 0.002 in 2001), and in cassava-maize intercropping in the wet savanna zone (p < 0.001 and p < 0.01 in 2000 and 2001, respectively), with generally no significant negative effect on cassava root yield. Though significant, disease reductions by intercropping generally were low (10 to 24%). Since no varieties with complete resistance to the disease had been identified among local and local improved varieties across ecozones in Togo, the combination of medium resistant varieties and an intercropping system, both adapted to the respective ecozone, can be recommended to farmers as part of integrated control measures against bacterial blight of cassava. Keywords: Cassava, bacterial blight, intercropping, control, Togo.

Soil organic carbon storage and contribution of management strategies to the “4 per 1000” target in a wet savanna, Côte d’Ivoire

Soil organic carbon storage and contribution of management strategies to the “4 per 1000” target in a wet savanna, Côte d’Ivoire

Distance sampling surveys reveal 17 million vertebrates directly killed by the 2020\u2019s wildfires in the Pantanal, Brazil

Anthropogenic factors have significantly influenced the frequency, duration, and intensity of meteorological drought in many regions of the globe, and the increased frequency of wildfires is among the most visible consequences of human-induced climate change. Despite the fire role in determining biodiversity outcomes in different ecosystems, wildfires can cause negative impacts on wildlife. We conducted ground surveys along line transects to estimate the first-order impact of the 2020 wildfires on vertebrates in the Pantanal wetland, Brazil. We adopted the distance sampling technique to estimate the densities and the number of dead vertebrates in the 39,030 square kilometers affected by fire. Our estimates indicate that at least 16.952 million vertebrates were killed immediately by the fires in the Pantanal, demonstrating the impact of such an event in wet savanna ecosystems. The Pantanal case also reminds us that the cumulative impact of widespread burning would be catastrophic, as fire recurrence may lead to the impoverishment of ecosystems and the disruption of their functioning. To overcome this unsustainable scenario, it is necessary to establish proper biomass fuel management to avoid cumulative impacts caused by fire over biodiversity and ecosystem services.

Short-term impact of fire on the total soil microbial and nitrifier communities in a wet savanna.

Savannas are characterized by the coexistence of grasses and trees. Fires are critical for their coexistence, because they decrease the survival of tree seedlings and saplings and their recruitment to the adult stage. In some humid savannas, perennial grasses inhibit nitrification and trees stimulate nitrification, which likely favors coexistence between trees and grasses. However, fires may influence plant capacity to control nitrogen cycling, which could subsequently influence tree–grass coexistence and savanna nitrogen budget. Therefore, we sampled soil in a humid savanna of Ivory Coast under the dominant nitrification‐inhibiting grass species and the dominant nitrification‐stimulating tree species and under bare soil before and after (i.e., 5 days) fire during the long dry season. We quantified the total microbial and nitrifier abundances and transcriptional activities and the nitrification enzyme activity. Fire decreased soil water content, probably by increasing evaporation and, maybe, by triggering the growth of grasses, and increased soil ammonium availability likely due to ash deposition and increased mineralization. Fire did not impact the total archaeal, bacterial, or fungal abundances, or that of the nitrifiers. Fire did not impact archaeal transcriptional activity and increased bacterial and fungal total transcriptional activities. In contrast, fire decreased the archaeal nitrifier transcriptional activities and the nitrification enzymatic activity, likely due to the often reported resumption of the growth of nitrification‐inhibiting grasses quickly after the fire (and the subsequent increase in root exudation). These results pave the way for a better understanding of the short‐term effects of fire on nitrogen cycling and tree–grass competition for nitrogen.

Assessing the Australian Termite Diversity Anomaly: How Habitat and Rainfall Affect Termite Assemblages

Termites are important ecosystem engineers in tropical habitats, with different feeding groups able to decompose wood, grass, litter, and soil organic matter. In most tropical regions, termite abundance and species diversity are assumed to increase with rainfall, with highest levels found in rainforests. However, in the Australian tropics, this pattern is thought to be reversed, with lower species richness and termite abundance found in rainforest than drier habitats. The potential mechanisms underlying this pattern remain unclear. We compared termite assemblages (abundance, activity, diversity, and feeding group composition) across five sites along a precipitation gradient (ranging from ∼800 to 4,000 mm annual rainfall), spanning dry and wet savanna habitats, wet sclerophyll, and lowland and upland rainforests in tropical North Queensland. Moving from dry to wet habitats, we observed dramatic decreases in termite abundance in both mounds and dead wood occupancy, with greater abundance and activity at savanna sites (low precipitation) compared with rainforest or sclerophyll sites (high precipitation). We also observed a turnover in termite species and feeding group diversity across sites that were close together, but in different habitats. Termite species and feeding group richness were highest in savanna sites, with 13 termite species from wood-, litter-, grass-, dung-, and soil-feeding groups, while only five termite species were encountered in rainforest and wet sclerophyll sites—all wood feeders. These results suggest that the Australian termite diversity anomaly may be partly driven by how specific feeding groups colonized habitats across Australia. Consequently, termites in Australian rainforests may be less important in ecosystem processes, such as carbon and nutrient cycling during decomposition, compared with termites in other tropical rainforests.

Functional diversity and coexistence of herbaceous plants in wet, species-rich savannas.

Trait differences among plant species can favor species coexistence. The role that such differences play in the assembly of diverse plant communities maintained by frequent fires remains unresolved. This lack of resolution results in part from the possibility that species with similar traits may coexist because none has a significant fitness advantage and in part from the difficulty of experimental manipulation of highly diverse assemblages dominated by perennial species. We examined a 65‐year chronosequence of losses of herbaceous species following fire suppression (and subsequent encroachment by Pinus elliottii) in three wet longleaf pine savannas. We used cluster analysis, similarity profile permutation tests, and k‐R cluster analysis to identify statistically significant functional groups. We then used randomization tests to determine if the absence of functional groups near pines was greater (or less) than expected by chance. We also tested whether tolerant and sensitive species were less (or more) likely to co‐occur by chance in areas in savannas away from pines in accordance with predictions of modern coexistence theory. Functional group richness near pines was lower than expected from random species extirpations. Wetland perennials with thick rhizomes and high leaf water content, spring‐flowering wetland forbs (including Drosera tracyi), orchids, Polygala spp., and club mosses were more likely to be absent near pines than expected by chance. C3 grasses and sedges with seed banks and tall, fall‐flowering C4 grasses were less likely to be absent near pines than expected by chance. Species sensitive to pine encroachment were more likely to co‐occur with other such species away from pines at two of the three sites. Results suggest that herb species diversity in frequently burned wet savannas is maintained in part by a weak fitness (e.g., competitive) hierarchy among herbs, and not as a result of trait differences among co‐occurring species.

Long-term atmospheric inorganic nitrogen deposition in West African savanna over 16 year period (Lamto, Côte d’Ivoire)

We present a long term assessment trend of atmospheric inorganic nitrogen deposition in Sub Saharan Africa (2000–2015) using observational and model data. This work proposes a compilation of International Network to study Deposition and Atmospheric chemistry in Africa wet and dry nitrogen deposition fluxes collected at the wet savanna site of Lamto (Côte d’Ivoire). Total deposition calculation takes in account: (a) gaseous (NO2, NH3, HNO3) dry deposition fluxes estimated by considering nitrogen compound concentrations at the monthly scale and modeling average monthly dry deposition velocities, (b) particulate PM10 (pNO3 −, pNH4 +) dry deposition fluxes calculated using the same inferential method and (c) wet deposition (WD) fluxes including ions concentration measurements (NO3 −, NH4 +) in rainwater combined with rainfall amount. We demonstrate for the first time the monthly and annual decreasing trends for dry nitrogen deposition of N-NO2 (−2.33% month−1 and −2.54% yr−1) and N-NH3 (−2.55% month−1 and −2.89% yr−1), but increasing trends for dry deposition of N-HNO3 (+1.00% month−1) and WD of N-NO3 − (+1.67% month−1 and +2.13% yr−1) and N-NH4 + (+2.33% month−1 and +3.36% yr−1). Dry season N-NO2 deposition flux decline shows agreement with long term trend in NOx emissions by biomass burning. Increasing trends for wet N deposition signals a gradual increase of nitrogen fertilizers use in agricultural practices in the Lamto area. Results also show no significant trend in total N deposition over the 16 year study period explained by the compensation of decreasing and increasing trends for dry and wet N deposition, respectively. However, at the annual scale, the mean total N deposition flux is estimated to 10.3 ± 1.2 kgN ha−1 yr−1 over the 16 year period, indicating an increase of 8% compared to the period 2000–2007.

Effects of Fire Frequency on Woody Plant Composition and Functional Traits in a Wet Savanna Ecosystem

The objective of this study was to assess the effect of fire frequency on vegetation taxonomic and functional diversity in a wet savanna ecosystem, eastern Zimbabwe. The study area was stratified into three fire frequency regimes using a 15-year fire history (2000–2014) across the landscape: high (HFF: burnt every 1-2 years), medium (MFF: burnt every 3-4 years), and low (LFF: burnt every 5-6 years). Data were collected from a total of 30 plots measuring 20 m × 20 m each between March and May 2018. In each plot, we recorded tree maximum height (Hmax), woody plant density, basal diameter, resprouting capacity, and bark thickness. We calculated species evenness, diversity, functional richness (FRic), Rao’s Quadratic Entropy (RaoQ), functional redundancy, and relative bark thickness. We recorded 1,031 individual trees belonging to 24 species across the three fire regimes. Significant differences across the three fire regimes were recorded for Hmax, woody plant density, and relative bark thickness P < 0.05 . Hmax and woody plant density were higher in LFF than HFF regimes while relative bark thickness was higher in HFF than in the LFF regimes. Species evenness was significantly higher in HFF and MFF regimes than LFF regime P < 0.05 , while FRic and functional redundancy significantly increased with decreasing fire frequency P < 0.05 . However, no significant differences were recorded for resprouting capacity, species richness, taxonomic diversity, and RaoQ P > 0.05 . Species like Cassia petersiana, Cussonia spicata, Vachellia spp., and Rhus lancea were associated with LFF, while species like Protea gaguedi, Brachystegia utilis, and Vangueria infausta showed a strong association with HFF to MFF. Our study demonstrated that a combination of taxonomic and functional diversity metrics is adequate to evaluate the response of savanna vegetation to fire. We recommend a further assessment on vegetation composition using other elements of fire regimes.

Floristic evidence for alternative biome states in tropical Africa.

The idea that tropical forest and savanna are alternative states is crucial to how we manage these biomes and predict their future under global change. Large-scale empirical evidence for alternative stable states is limited, however, and comes mostly from the multimodal distribution of structural aspects of vegetation. These approaches have been criticized, as structure alone cannot separate out wetter savannas from drier forests for example, and there are also technical challenges to mapping vegetation structure in unbiased ways. Here, we develop an alternative approach to delimit the climatic envelope of the two biomes in Africa using tree species lists gathered for a large number of forest and savanna sites distributed across the continent. Our analyses confirm extensive climatic overlap of forest and savanna, supporting the alternative stable states hypothesis for Africa, and this result is corroborated by paleoecological evidence. Further, we find the two biomes to have highly divergent tree species compositions and to represent alternative compositional states. This allowed us to classify tree species as forest vs. savanna specialists, with some generalist species that span both biomes. In conjunction with georeferenced herbarium records, we mapped the forest and savanna distributions across Africa and quantified their environmental limits, which are primarily related to precipitation and seasonality, with a secondary contribution of fire. These results are important for the ongoing efforts to restore African ecosystems, which depend on accurate biome maps to set appropriate targets for the restored states but also provide empirical evidence for broad-scale bistability.

Effects of fire frequency on savanna butterfly diversity and composition: A preliminary study

Fire plays a major role in many biomes, is widely used as a management tool and is likely to be affected by climate change. For effective conservation management, it is essential to understand how fire regimes affect different taxa, yet responses of invertebrates are particularly poorly documented. We tested how different fire frequencies influence savanna butterfly diversity and composition by using a long-term savanna fire experiment initiated in 1954 in the Kruger National Park (South Africa). We compared butterfly abundance, species richness and community composition across three fire frequencies: high (burnt annually), medium (burnt triennially) and low (burnt twice in 60 years). Plots with high fire frequency hosted higher abundance than medium- or low-frequency plots. Fire frequencies did not affect species richness, but they led to distinct communities of butterflies. Our findings suggest that, in view of the three fire frequencies tested, a spatial diversity of fire frequencies may increase butterfly diversity at the landscape level in wet savannas. Managers may need to promote a greater diversity of fire frequencies by increasing fire frequency in some areas to provide habitat for species requiring high fire frequency, and by decreasing fire frequency in a large proportion of the landscape to provide fire refuges. This study provides new insights for butterfly conservation in savannas and highlights several knowledge gaps, which further studies should address for insect responses to be given adequate consideration in fire management strategies.Conservation implications: A spatial diversity of fire frequencies may increase butterfly diversity. Managers may need to promote a greater diversity of fire frequencies by increasing fire frequency in some areas to provide habitat for species requiring high fire frequency, and by decreasing fire frequency in other areas to provide fire refuges.

Population Genetic Structure and Natural Establishment of Hybrids Between Sarracenia flava and Sarracenia minor in Francis Marion National Forest

We assessed population genetic structure and rate of hybridization in Sarracenia flava and S. minor in Francis Marion National Forest. The forest has an abundance of potential habitat for our study species and has suffered less human mediated disturbance than much of the county's longleaf pine savanna and wet pine savanna ecosystems. We examined 63 S. flava and 62 S. minor individuals, as well as one hybrid across a 486.02 km2 study site. We used eight nuclear microsatellite loci and one non-coding chloroplast marker to assess population genetic structure and describe the parentage of the hybrid. We found relatively little population genetic structure across many distinct field sites, even when those sites were separated by unsuitable habitat. In very small populations surviving in shrub-dominated longleaf pine savanna, genetic divergence was greater than in larger populations with more suitable habitat. The single hybrid discovered was an F1 hybrid for which S. flava served as the maternal parent. We found no signs of introgression. We hope that these data can help inform conservation decisions regarding Sarracenia species, as the low genetic structure seems to suggest a high degree of connectivity between geographically distinct populations of plants.

CERES-Maize model for simulating genotype-by-environment interaction of maize and its stability in the dry and wet savannas of Nigeria

When properly calibrated and evaluated, dynamic crop simulation models can provide insights into the different components of genotype by environment interactions (GEIs). Modelled outputs could be used to complement data from multi-environment trials. Field experiments were conducted in the rainy and dry seasons of 2015 and 2016 across four locations in maize growing regions of Northern Nigeria using 16 maize varieties planted under near-optimal conditions of moisture and soil nitrogen. The CERES-Maize model was calibrated using data from three locations and two seasons (rainy and dry) and evaluated using data from one location and two seasons all in 2015. Observed data from the four locations and two seasons in 2016 was used to create eight different environments. Two profile pits were dug in each location and were used separately in the simulations for each environment to provide replicated data for stability analysis in a combined ANOVA. The effects of the environment, genotype and GEI were highly significant (p = 0.001) for both observed and simulated grain yields. The environment explained 67 % and 64 % of the variations in observed and simulated grain yields respectively. The variance component of GEI (13 % for observed and 15 % for simulated) were lower but still considerable when compared to that of genotypes (19 % for observed and 21 % for simulated). From the stability analysis of the observed and simulated grain yields using six different stability models, three models (ASV, Ecovalence, and Sigma) ranked Ife Hybrid as the most stable variety. The slope of the regression (bi) model ranked Sammaz 11 as the most stable variety, while the Shukla model ranked Sammaz 28 as the most stable variety. Long-term seasonal analysis with the CERES-Maize model revealed that early and intermediate maturing varieties produce high yields in both wet and dry savannas, early and extra-early varieties produce high yields only in the dry savannas, while late maturing varieties produce high yields only in the wet savannas. When properly calibrated and evaluated, the CERES-Maize model can be used to generate data for GEI and stability studies of maize genotype in the absence of observed field data.