Termite mound emissions of CH4 and CO2 are primarily determined by seasonal changes in termite biomass and behaviour

Termites are a highly uncertain component in the global source budgets of CH₄ and CO₂. Large seasonal variations in termite mound fluxes of CH₄ and CO₂ have been reported in tropical savannas but the reason for this is largely unknown. This paper investigated the processes that govern these seasonal variations in CH₄ and CO₂ fluxes from the mounds of Microcerotermes nervosus Hill (Termitidae), a common termite species in Australian tropical savannas. Fluxes of CH₄ and CO₂ of termite mounds were 3.5-fold greater in the wet season as compared to the dry season and were a direct function of termite biomass. Termite biomass in mound samples was tenfold greater in the wet season compared to the dry season. When expressed per unit termite biomass, termite fluxes were only 1.2 (CH₄) and 1.4 (CO₂)-fold greater in the wet season as compared to the dry season and could not explain the large seasonal variations in mound fluxes of CH₄ and CO₂. Seasonal variation in both gas diffusivity through mound walls and CH₄ oxidation by mound material was negligible. These results highlight for the first time that seasonal termite population dynamics are the main driver for the observed seasonal differences in mound fluxes of CH₄ and CO₂. These findings highlight the need to combine measurements of gas fluxes from termite mounds with detailed studies of termite population dynamics to reduce the uncertainty in quantifying seasonal variations in termite mound fluxes of CH₄ and CO₂.     

Nutrient dynamics and plant assemblages of Macrotermes falciger mounds in a savanna ecosystem

Termites through mound construction and foraging activities contribute significantly to carbon and nutrient fluxes in nutrient-poor savannas. Despite this recognition, studies on the influence of termite mounds on carbon and nitrogen dynamics in sub-tropical savannas are limited. In this regard, we examined soil nutrient concentrations, organic carbon and nitrogen mineralization in incubation experiments in mounds of Macrotermes falciger and surrounding soils of sub-tropical savanna, northeast Zimbabwe. We also addressed whether termite mounds altered the plant community and if effects were similar across functional groups i.e. grasses, forbs or woody plants. Mound soils had significantly higher silt and clay content, pH and concentrations of calcium (Ca), magnesium (Mg), potassium (K), organic carbon (C), ammonium (NH₄⁺) and nitrate (NO₃⁻) than surrounding soils, with marginal differences in phosphorus (P) and sodium (Na) between mounds and matrix soils. Nutrient enrichment increased by a factor ranging from 1.5 for C, 4.9 for Mg up to 10.3 for Ca. Although C mineralization, nitrification and nitrification fraction were similar between mounds and matrix soils, nitrogen mineralization was elevated on mounds relative to surrounding matrix soils. As a result, termite mounds supported unique plant communities rich and abundant in woody species but less diverse in grasses and forbs than the surrounding savanna matrix in response to mound-induced shifts in soil parameters specifically increased clay content, drainage and water availability, nutrient status and base cation (mainly Ca, Mg and Na) concentration. In conclusion, by altering soil properties such as texture, moisture content and nutrient status, termite mounds can alter the structure and composition of sub-tropical savanna plant communities, and these results are consistent with findings in other savanna systems suggesting that increase in soil clay content, nutrient status and associated changes in the plant community assemblage may be a general property of mound building termites.     

Spatial heterogeneity in ecosystem structure and productivity in a moist Kenyan savanna

Topographic variations and disturbances are key sources of spatial heterogeneity in the ecosystem and may influence its functioning, productivity, and carbon (C) storage. In water controlled ecosystems, structural and functional heterogeneity become distinct during drought when the ecosystem processes are operating at their limits. We examined spatial heterogeneity arising from grazing, abandoned cropland, presence of Acacia trees, and termite mounds (termitaria). Soil water content (SWC) was significantly (P < 0.05) higher in termitaria and fenced (un-grazed) plots. Higher soil nitrogen (N) content occurred in the Acacia, termitaria, and fenced plots while total biomass was highest in the fenced plot. The termitaria plots showed the highest net ecosystem CO₂ exchange (NEE), ecosystem respiration (R _eco), and gross primary production (GPP) and were the only plots that were net CO₂ sinks. Except in fenced plots, maximum GPP was positively correlated with SWC and green biomass in all the other plots. Green biomass and R _eco were positively correlated with SWC. Shifting cultivation (abandoned farmlands) negatively affected soil quality, ecosystem CO₂ assimilation, and productivity. Removal of grazing (cattle) from the ecosystem negatively influenced GPP, while the presence of termitaria and Acacia trees facilitated soil water and N availability and ecosystem productivity. We concluded that soil water availability was responsible for most of the localized differences in the savanna and has a strong influence on ecosystem C capture and storage. We recommend that future studies on savanna productivity and ecosystem CO₂ fluxes should consider heterogeneity in the ecosystem in order to avoid bias and increase the accuracy of any estimates made.     

Termitaria vs. mistletoe: Effects on soil properties and plant structure in a semi-arid savanna

Termite mounds by creating patches of increased resource availability (e.g. water and nutrients) are a major source of spatial heterogeneity in savannas. Likewise, mistletoes via input of nutrient-rich litter alter nutrient and water availability increasing environmental heterogeneity in semi-arid savanna. Despite this recognition, the influence of termitaria and mistletoe on soil properties and plant community have not been investigated together. We established eight 100 m² plots each on termitaria, under mistletoe-infected trees and in the surrounding savanna and examined the soil properties and the structure of Securinega virosa (Euphorbiaceae) and Euclea divinorum (Ebenaceae) in semi-arid savanna, southwest Zimbabwe. Soil properties significantly differed among the sampling sites (p = 0.001) with soils of increasing clay, soil moisture, pH and phosphorus, calcium and ammonium concentrations occurring on termite mounds. Soils under mistletoe-infected trees were associated with silt, organic matter, sodium, potassium, magnesium and nitrate and the surrounding savanna was associated with soils of increasing sand content. Plant structure also differed significantly between sites with greater basal area of both S. virosa and E. divinorum on termitaria relative to mistletoe-infected trees and the surrounding savanna. However, the stem density of S. virosa was greater under mistletoe-infected trees than on termitaria and in the surrounding savanna. Plant structural variables of individuals of the same species were affected by different soil properties across treatments. The major patterns showed that plant structure was influenced positively by soil moisture and nitrate and negatively by phosphorus on termitaria; positively by clay, soil moisture and ammonium and negatively by potassium under mistletoe-infected trees; and by phosphorus and calcium in the surrounding savanna. These findings show that soil properties, plant structure and their relationships differ between termitaria, mistletoe-infected trees and surrounding savanna, and these differences are suggested to increase heterogeneity in soil resources availability and vegetation structure in semi-arid savanna.     

Effect of the replacement of a native savanna by an African Brachiaria decumbens pasture on the CO2 exchange in the Orinoco lowlands,Venezuela

In the Orinoco lowlands, savannas have been often replaced by pastures composed of the C₄ grass, Brachiaria decumbens Stapf. We addressed following questions: (1) How does the replacement of the native vegetation affect CO₂ exchange on seasonal and annual scales? (2) How do biophysical constraints change when the landscape is transformed? To assess how these changes affect carbon exchange, we determined simultaneously the CO₂ fluxes by eddy covariance, and the soil CO₂ efflux by a chamber-based system in B. decumbens and herbaceous savanna stands. Measurements covered a one-year period from the beginning of the dry season (November 2008) to the end of the wet season (November 2009). During the wet season, the net ecosystem CO₂ exchange reached maximum values of 23 and 10 μmol(CO₂) m^?2 s^?1 in the B. decumbens field and in the herbaceous savanna stand, respectively. The soil CO₂ efflux for both stands followed a temperature variation during the dry and wet seasons, when the soil water content (SWC) increased above 0.087 m³ m^?3 in the latter case. Bursts of CO₂ emissions were evident when the dry soil experienced rehydration. The carbon source/sink dynamics over the two canopies differed markedly. Annual measurements of the net ecosystem production indicated that the B. decumbens field constituted a strong carbon sink of 216 g(C) m^?2 y^?1. By contrast, the herbaceous savanna stand was found to be only a weak sink [36 g(C) m^?2 y^?1]. About 53% of the gross primary production was lost as the ecosystem respiration. Carbon uptake was limited by SWC in the herbaceous savanna stand as evident from the pattern of water-use efficiency (WUE). At the B. decumbens stand, WUE was relatively insensitive to SWC. Although these results were specific to the studied site, the effect of land use changes and the physiological response of the studied stands might be applicable to other savannas.     

The Importance of Termites to the CH<Subscript>4</Subscript> Balance of a Tropical Savanna Woodland of Northern Australia

Termites produce methane (CH₄) as a by-product of microbial metabolism of food in their hindguts, and are one of the most uncertain components of the regional and global CH₄ exchange estimates. This study was conducted at Howard Springs near Darwin, and presents the first estimate of CH₄ emissions from termites based on replicated in situ seasonal flux measurements in Australian savannas. Using measured fluxes of CH₄ between termite mounds and the atmosphere, and between soil and the atmosphere across seasons we determined net CH₄ flux within a tropical savanna woodland of northern Australia. By accounting for both mound-building and subterranean termite colony types, and estimating the contribution from tree-dwelling colonies it was calculated that termites were a CH₄ source of +0.24 kg CH₄-C ha⁻¹ y⁻¹ and soils were a CH₄ sink of −1.14 kg CH₄-C ha⁻¹ y⁻¹. Termites offset 21% of CH₄ consumed by soil resulting in net sink strength of −0.90 kg CH₄-C ha⁻¹ y⁻¹ for these savannas. For Microcerotermes nervosus (Hill), the most abundant mound-building termite species at this site, mound basal area explained 48% of the variation in mound CH₄ flux. CH₄ emissions from termites offset 0.1% of the net biome productivity (NBP) and CH₄ consumption by soil adds 0.5% to the NBP of these tropical savannas at Howard Springs.     

Mound building termites contribute to savanna vegetation heterogeneity

With biomass densities comparable to large ungulates and megaherbivores, termites play a key functional role in many tropical savanna ecosystems. This study focuses on vegetated termite mounds (termitaria) constructed by the Termitidae species Macrotermes herus. We studied how resource rich termitaria affect graminoid herbs (Poaceae and Cyperaceae), forbs and woody species composition and diversity. The density of termitaria explained 89% of the variation in dense thickets in the area. Fire tolerant Acacia species dominated the open savanna while fire sensitive species like Grewia spp. and the succulent Euphorbia candelabrum were restricted to termite mounds. Termitaria plots had four times the mean number of woody species and supported three times as many forb species as the adjacent savanna. For woody species, both the Shannon–Wiener index and the Shannon evenness index were higher on temitaria than on the savanna. There were no differences for graminoid herbs, except for the Shannon evenness index which was higher on termitaria. Our results indicate that graminoid herb richness peaks at lower productivity levels than trees and forbs in savanna ecosystems, as also recently found in temperate areas.     

Root foraging strategies and soil patchiness in a humid savanna

In Lamto (Côte d'Ivoire), the savanna is a patchy environment as far as soil is concerned: tree clumps and termite mounds lead to higher nutrient contents than in the surrounding savanna. Mature Borassus aethiopum (Mart.) specimens are tall palm trees dominating the community, with aerial parts located out of these nutrient-rich patches.Palm root densities were compared under tree clumps and in the surrounding savanna, and were also sampled along transects between palm trees and nutrient-rich patches (two clumps and one mound). Palm root densities were far higher (up to 10 times) in the nitrogen-rich soil of both clumps and termite mounds than in the surrounding savanna. Evidence is given that palm trees are able to extend their root system as far as 20 m towards these nutrient-rich patches where they proliferate. These results point out a particular root foraging strategy, which is one of the first known for a woody perennial. They also provide new insights for understanding nitrogen cycling and savannas high rate of primary production.     

Trophic interactions among invertebrates in termitaria in the African savanna: a stable isotope approach

Abstract 1. Termites (Isoptera) in tropical savannas are known as ecosystem engineers, affecting the spatial and temporal distribution of water, carbon, cations, and nutrients through their mound structures. Their mounds, however, also offer habitation to diverse taxa and feeding guilds of other invertebrates; a keystone role that has not been properly quantified. 2. The aim of this study was to explore the ecosystem role of termitaria in determining invertebrate diversity and their potential trophic interactions. We used stable isotopes to distinguish termite‐feeding invertebrates from invertebrates merely living in termite mounds under field conditions. 3. The results suggest that inquiline spiders (Arachnida) do not feed on termites directly, but on other invertebrates within the termitaria that are termitophagous, elevating the spiders three trophic levels higher than the termites. 4. This study is the first to demonstrate food web interactions among inquiline invertebrates with a stable isotope approach. It provides evidence that termites play a keystone role in the system by providing habitat for various, trophically interacting invertebrates. These results illustrate a rather unexplored ecosystem property of savanna termites.     

Geophagy by African ungulates: the case of the critically endangered giant sable antelope of Angola (Hippotragus niger variani)

The giant sable antelope (Hippotragus niger variani) is a critically endangered subspecies with a range restricted to a small area in the Angolan plateau. It is known to display geophagic behaviour, eating the soil of some Macrotermes termitaria. The aim of this study was to understand the importance of this behaviour for the giant sable and other ungulates sharing its range. We identified termite mounds used for geophagy based on local information confirmed by self‐triggering cameras. We collected and analysed soil samples of seven termitaria consumed by ungulates, the adjacent topsoil 50 m away from each, and seven control nonconsumed termitaria. Consumed termite mounds were richer in minerals than control mounds, and both were richer than the surrounding topsoil. Sodium levels showed the greatest contrasts and were about 20 times more abundant in consumed termitaria than in controls. The amount of sodium in background soil was extremely low (9.3 ppm), suggesting that this mineral is a limiting nutrient in the range of the giant sable. These results indicate that the observed geophagic habits may be driven by a need to compensate for a sodium deficiency. This situation should be considered in the planning of the species' conservation.     

Deciphering earth mound origins in central Brazil

Mound fields are a common landscape throughout the world and much of the evidence for their origin has been of a circumstantial nature. It has been hypothesized that earth mounds emerge over grasslands by termite activity; alternatively, they might be formed after erosion. We tested whether a mound field in central Brazil was generated by termite activity or erosion. We used soil organic matter isotopic composition, soil chemical, physical and floristic composition to determine the origin of a mound field. If the mounds emerged by termite activity in an established grassland the soil organic matter below the mound should have the isotopic signature of C₄ dominated grassland, which contrasts with savanna C₃ + C₄ signature. Additionally, soil traits should resemble those of the grassland. All markers indicate that the mounds were formed by erosion. The soil isotopic composition, chemical traits and texture below the mound resembled those of the savanna and not those of the grassland. Moreover, most of the species present in the mound were typical of savanna. Concrete evidence is provided that mound fields in the studied area were produced by erosion of a savanna ecosystem and not termite activity. The use of the techniques applied here would improve the assessments of whether analogous landscapes are of a biogenic nature or not.     

Termites facilitate and ungulates limit savanna tree regeneration

Both large herbivores and termites are key functional groups in savanna ecosystems, and in many savanna areas, large termite mounds (termitaria) are associated with distinct woody clusters. Studies on the effect of large mammals on tree regeneration are few, and the results are conflicting. Large herbivores have been found to be important seedling predators in some areas, but facilitate tree regeneration by outcompeting small mammals and reducing grass cover in other areas. Through the use of the experimental fencing of termite mounds and adjacent savanna areas in this study, we investigated how termites and large herbivores influence tree regeneration. Termite mounds had a higher number of seedlings, more species richness, more alpha diversity (OD) and lower evenness (E) than savanna plots. Large herbivores did not significantly affect overall seedling density, species richness, OD or E. Beta diversity was higher in savanna areas than on termitaria, and beta diversity decreased in savanna areas when herbivores were excluded. Herbivore exclusion increased the density of the 12 (40 %) most common seedling species, representing 79 % of all seedlings, and fenced plots had relatively taller seedlings than open plots. Thus, termites were the main determinants of tree regeneration in our study area, but large mammals regulated the most common species. Although our study confirms previous work suggesting that large herbivores affect tree regeneration, we found that termites were an even more important determinant. Termite impacts on tree regeneration deserve increased attention by savanna ecologists.     

Thicket clumps: A characteristic feature of the Kagera savanna landscape,East Africa

Question: What are the genesis and development of thicket clumps within a savanna landscape at geomorphically different locations and what are the driving forces? Location: The Kagera Region, in the border area of Rwanda, Uganda and Tanzania. Methods: The vegetation of 32 dry evergreen thicket clumps and their surrounding savannas have been analysed at different geomorphic locations. At each vegetation plot Na⁺, K⁺, Mg²⁺, Ca²⁺, Al³⁺, Fe^2+/3+, H⁺, P, C, N, bulk density and particle size were determined for each soil horizon. The impact of soil and termite mounds on thicket clump dynamics on seasonally waterlogged plains, gentle slopes and stony hillsides were assessed. Results: Thicket clumps and their surrounding savannas have a distinct structure and floristic composition. They also have distinct soil properties although parent materials are the same. On seasonally waterlogged plains, new thicket clumps can develop on Macrotermitinae mounds; on stony hillsides, Trinervitermes and Macrotermes show a uniform distribution pattern and may initiate the genesis of thicket clumps. Conclusions: Geomorphology broadly determines the significance and interactions of the main factors affecting site‐specific vegetation dynamics. On seasonally waterlogged plains, thicket clumps are restricted to termite mounds. Since intra‐species competition dictates a minimal distance between neighbouring Macrotermitinae colonies, thicket clumps do not coalescence. By contrast, on stony hillsides, the vegetation mosaic is highly dynamic and determined by the interplay of several factors. The growth of thicket clumps is mainly a function of the fire regime and the browsing intensity. At the present time, frequent cool, early dry season fires and the near absence of large browsers have favoured the advance and coalescence of thicket clumps and forest patches on stony hillsides.     

Influence of large termitaria on soil characteristics, soil water regime, and tree leaf shedding pattern in a West African savanna

Termitaria are major sites of functional heterogeneity in tropical ecosystems, through their strong influence on soil characteristics, in particular soil physico-chemical properties and water status. These factors have important consequences on nutrient availability for plants, plant spatial distribution, and vegetation dynamics. However, comprehensive information about the influence of termite-rehandled soil on soil water regime is lacking. In a humid shrubby savanna, we characterized the spatial variations in soil texture, soil structure and maximum soil water content available for plants (AWC max) induced by a large termite mound, at three deepths (0–0.10, 0.20–0.30 and 0.50–0.60 m). In addition, during a three month period at the end of the rainy season, soil water potential was surveyed by matrix sensors located on the termite mound and in the surrounding soil at the same depths and for the 80–90 cm layer. Concurrently, the leaf shedding patterns of two coexisting deciduous shrub species exhibiting contrasted soil water uptake patterns were compared for individuals located on termite mounds and in undisturbed control areas. For all the soil layers studied, clay and silt contents were higher for the mound soil. Total soil clods porosity was higher on the mound than in control areas, particularly in the 0.20-0.60 m layer, and mound soil exhibited a high shrinking/swelling capacity. AWC_max of the 0-0.60 m soil layer was substantially higher on the termite mound (112 mm) than in the surroundings (84 mm). Furthermore, during the beginning of the dry season, soil water potential measured in situ for the 0.20-0.90 m soil layer was higher on the mound than in the control soil. In contrast, soil water potential of the 0-0.10 m soil layer was similar on the mound and in the control soil. In the middle of the dry season, the leaf shedding pattern of Crossopteryx febrifuga shrubs (which have limited access to soil layers below 0.60 m) located on mounds was less pronounced than that of individuals located on control soil. In contrast, the leaf shedding pattern of the shrub Cussonia barteri (which has a good access to deep soil layers) was not influenced by the termite mound. We conclude that in this savanna ecosystem, termite mounds appear as peculiar sites which exhibit improved soil water availability for plants in upper soil layers, and significantly influence aspects of plant function. Implications of these results for understanding and modelling savanna function and dynamics, and particularly competitive interactions between plant species, are discussed.     

Termite mounds as browsing hotspots: an exception to the rule

In African savannas, termite mounds usually serve as browsing hotspots for mammals because of their soil fertility. Van der Plas et al., in this issue, describe that browsers avoid the unpalatable, evergreen tree species on mounds of Macrotermes natalensis in a mesic savanna, preferring mainly leguminous species with high leaf N and P concentrations in the matrix. This exception is probably a consequence of the fertile soils of the study area, and highlights the importance of environmental context for assessing ecological interactions.     

Termite mounds differ in their importance for herbivores across savanna types,seasons and spatial scales

Herbivores do not forage uniformly across landscapes, but select for patches of higher nutrition and lower predation risk. Macrotermes mounds contain higher concentrations of soil nutrients and support grasses of higher nutritional value than the surrounding savanna matrix, attracting mammalian grazers that preferentially forage on termite mound vegetation. However, little is known about the spatial extent of such termite influence on grazing patterns and how it might differ in time and space. We measured grazing intensity in three African savanna types differing in rainfall and foliar nutrients and predicted that the functional importance of mounds for grazing herbivores would increase as the difference in foliar nutrient levels between mound and savanna matrix grasses increases and the mounds become more attractive. We expected this to occur in nutrient‐poor areas and during the dry season when savanna matrix grass nutrient levels are lower. Tuft use and grass N and P content were measured along transects away from termite mounds, enabling calculation of the spatial extent of termite influence on mammalian grazing. Using termite mound densities estimated from airborne light detection and ranging (LiDAR), we further upscaled field‐based results to determine the percentage of the landscape influenced by termite activity. Grasses in close proximity to termite mounds were preferentially grazed at all sites and in both seasons, but the strength of mound influence varied between savanna types and seasons. In the wet season, mounds had a relatively larger effect on grazers at the landscape scale in the nutrient‐poor, wetter savanna, whereas in the dry season the pattern was reversed with more of the landscape influenced at the nutrient‐rich, driest site. Our results reveal that termite mounds enhance the value of savanna landscapes for herbivores, but that their functional importance varies across savanna types and seasons.     

Spatial variability and abiotic determinants of termite mounds throughout a savanna catchment

Termite mounds contribute to the spatial heterogeneity of ecological processes in many savannas, but the underlying patterns and determinants of mound distributions remain poorly understood. Using the Carnegie Airborne Observatory (CAO), we mapped the distribution of termite mounds across a rainfall gradient within a river catchment (～ 27 000 ha) of the Kruger National Park, South Africa. We assessed how different factors were associated with the distribution and height of termite mounds at three spatial scales: the entire catchment, among three broad vegetation types, and on individual hillslope crests. Abiotic factors such as the underlying geology and mean annual precipitation shaped mound densities at broad scales, while local hillslope morphology strongly influenced mound distribution at finer scales, emphasising the importance of spatial scale when assessing mound densities. Fire return period had no apparent association with mound densities or height. Mound density averaged 0.46 mounds ha^?1, and exhibited a clustered pattern throughout the landscape, occurring at relatively high densities (up to 2 mounds ha^?1) on crests, which are nutrient‐poor elements of the landscape. Mounds exhibited significant over‐dispersion (even spacing) at scales below 60 m so that evenly spaced aggregations of termite mounds are embedded within a landscape of varying mound densities. The tallest mounds were found in dry savanna (500 mm yr^?1) and were positively correlated with mound density, suggesting that dry granitic savannas are ideal habitat for mound‐building termites. Mound activity status also varied significantly across the rainfall gradient, with a higher proportion of active (live) mounds in the drier sites. The differential spacing of mounds across landscapes provides essential nutrient hotspots in crest locations, potentially sustaining species that would otherwise not persist. The contribution to biodiversity and ecosystem functioning that mounds provide is not uniform throughout landscapes, but varies considerably with spatial scale and context.     

Interannual variability in global soil respiration, 1980–94

We used a climate‐driven regression model to develop spatially resolved estimates of soil‐CO₂ emissions from the terrestrial land surface for each month from January 1980 to December 1994, to evaluate the effects of interannual variations in climate on global soil‐to‐atmosphere CO₂ fluxes. The mean annual global soil‐CO₂ flux over this 15‐y period was estimated to be 80.4 (range 79.3–81.8) Pg C. Monthly variations in global soil‐CO₂ emissions followed closely the mean temperature cycle of the Northern Hemisphere. Globally, soil‐CO₂ emissions reached their minima in February and peaked in July and August. Tropical and subtropical evergreen broad‐leaved forests contributed more soil‐derived CO₂ to the atmosphere than did any other vegetation type (～30% of the total) and exhibited a biannual cycle in their emissions. Soil‐CO₂ emissions in other biomes exhibited a single annual cycle that paralleled the seasonal temperature cycle. Interannual variability in estimated global soil‐CO₂ production is substantially less than is variability in net carbon uptake by plants (i.e., net primary productivity). Thus, soils appear to buffer atmospheric CO₂ concentrations against far more dramatic seasonal and interannual differences in plant growth. Within seasonally dry biomes (savannas, bushlands and deserts), interannual variability in soil‐CO₂ emissions correlated significantly with interannual differences in precipitation. At the global scale, however, annual soil‐CO₂ fluxes correlated with mean annual temperature, with a slope of 3.3 Pg C y^?1 per °C. Although the distribution of precipitation influences seasonal and spatial patterns of soil‐CO₂ emissions, global warming is likely to stimulate CO₂ emissions from soils.     

Strong positive effects of termites on savanna bird abundance and diversity are amplified by large herbivore exclusion

Vast areas of the African savanna landscapes are characterized by tree‐covered Macrotermes termite mounds embedded within a relatively open savanna matrix. In concert with termites, large herbivores are important determinants of savanna woody vegetation cover. The relative cover of woody species has considerable effects on savanna function. Despite the potentially important ecological relationships between termite mounds, woody plants, large herbivores, and birds, these associations have previously received surprisingly little attention. We experimentally studied the effects of termites and large herbivores on the avian community in Lake Mburo National Park, Uganda, where woody vegetation is essentially limited to termite mounds. Our experiment comprised of four treatments in nine replicates; unfenced termite mounds, fenced mounds (excluding large mammals), unfenced adjacent savanna, and fenced savanna. We recorded species identity, abundance, and behavior of all birds observed on these plots over a two‐month period, from late dry until wet season. Birds used termite mounds almost exclusively, with only 3.5% of observations occurring in the treeless intermound savanna matrix. Mean abundance and species richness of birds doubled on fenced (large herbivores excluded) compared to unfenced mounds. Feeding behavior increased when large mammals were excluded from mounds, both in absolute number of observed individuals, and relative to other behaviors. This study documents the fundamental positive impact of Macrotermes termites on bird abundance and diversity in an African savanna. Birds play crucial functional roles in savanna ecosystems, for example, by dispersing fruits or regulating herbivorous insect populations. Thus, the role of birds in savanna dynamics depends on the distribution and abundance of termite mounds.     

Soil Greenhouse Gas Emissions in Response to Corn Stover Removal and Tillage Management Across the US Corn Belt

In-field measurements of direct soil greenhouse gas (GHG) emissions provide critical data for quantifying the net energy efficiency and economic feasibility of crop residue-based bioenergy production systems. A major challenge to such assessments has been the paucity of field studies addressing the effects of crop residue removal and associated best practices for soil management (i.e., conservation tillage) on soil emissions of carbon dioxide (CO₂), nitrous oxide (N₂O), and methane (CH₄). This regional survey summarizes soil GHG emissions from nine maize production systems evaluating different levels of corn stover removal under conventional or conservation tillage management across the US Corn Belt. Cumulative growing season soil emissions of CO₂, N₂O, and/or CH₄ were measured for 2–5 years (2008–2012) at these various sites using a standardized static vented chamber technique as part of the USDA-ARS’s Resilient Economic Agricultural Practices (REAP) regional partnership. Cumulative soil GHG emissions during the growing season varied widely across sites, by management, and by year. Overall, corn stover removal decreased soil total CO₂ and N₂O emissions by -4 and -7 %, respectively, relative to no removal. No management treatments affected soil CH₄ fluxes. When aggregated to total GHG emissions (Mg CO₂?eq ha^?1) across all sites and years, corn stover removal decreased growing season soil emissions by ?5?±?1 % (mean?±?se) and ranged from -36 % to 54 % (n?=?50). Lower GHG emissions in stover removal treatments were attributed to decreased C and N inputs into soils, as well as possible microclimatic differences associated with changes in soil cover. High levels of spatial and temporal variabilities in direct GHG emissions highlighted the importance of site-specific management and environmental conditions on the dynamics of GHG emissions from agricultural soils.