Short Dry Season Research Articles

Observed and simulated changes in precipitation seasonality in Argentina

Seasonality in Argentina is examined using precipitation observations from 56 weather stations north of 42°S and CRU gridded precipitation. The Walsh and Lawler Seasonality Index (SI) and Precipitation Concentration Index (PCI) are calculated to determine the different seasonality regimes. The main characteristic is an eastwest gradient, where precipitation tends to be more evenly distributed throughout the different months of the year in the east while rainfall in the west is concentrated in 3 months or less. High replicability values indicate that the wettest month generally occurs during a same period of months in central and northern Argentina. Several stations in eastern humid Argentina have significant positive changes in the mean of seasonality indices between 1961 and 1985 and 1986 and 2010, and increasing trend. In most cases this leads to a change in the regime from rather seasonal with a short dry season to a seasonal regime. Through a PAM Clustering technique a new regionalization of precipitation seasonality is obtained. The mean series in each cluster show a tendency towards more seasonal and highly seasonal regimes in all regions. The SI and PCI indices were calculated using the precipitation outputs of 18 global climate models (GCMs) from the Coupled Model Inter‐comparison Project Phase 5 (CMIP5) to examine the ability of these models to represent seasonality spatial distribution and changes in Argentina. To some extent the spatial distribution of seasonality is captured by models; however, there are considerable discrepancies in the location and extension of the eastwest gradient. The sign and location of trends and changes in the mean SI and PCI are adequately reproduced in only a few models. The low ability of GCMs to represent seasonality and its changes is a consequence of the difficulties GCMs have simulating precipitation characteristics in Argentina reported by different authors.

Global Analysis of the Role of Terrestrial Water Storage in the Evapotranspiration Estimated from the Budyko Framework at Annual to Monthly Time Scales

Abstract Recent studies have extended the applicability of the Budyko framework from the long-term mean to annual or shorter time scales. However, the effects of water storage change ΔS on the overall water balance estimated from the Budyko models (BM) at annual-to-monthly time scales were less investigated, particularly at the continental or global scales, due to the lack of large-scale ΔS data. Here, based on a 25-yr (1984–2008) global gridded terrestrial water budget dataset and by using an analytical error-decomposition framework, we analyzed the effects of ΔS in evapotranspiration (ET) predicted from BM at both grid and basin scales under diverse climates for the annual, wet-seasonal, dry-seasonal, and monthly time scales. Results indicated that the BM underperforms in the short dry (wet) seasons of predominantly humid (dry) basins, with lower accuracy under more humid climates (at annual, dry-seasonal, and monthly scales) and under more arid climates (at wet-seasonal scale). When the effects of ΔS are incorporated into BM, improvements can be found mostly at annual and dry-seasonal scales, but not notable at wet-seasonal and monthly scales. The magnitudes of ΔS are positively correlated with the errors in BM-predicted ET for most global regions at annual and monthly scales, especially under arid climates. Under arid climates, the variability of ET prediction errors is controlled mainly by the ΔS variability at annual and monthly time scales. In contrast, under humid climates the effect of ΔS on ET prediction errors is generally limited, particularly at the wet-seasonal scale due to the more dominant influences of other climatic factors (precipitation and potential ET) and catchment responses (runoff).

Une forte saisonnalité du climat et de la phénologie reproductive dans la forêt du Mayombe : l’apport des données historiques de la Réserve de Luki en République démocratique du Congo

En Afrique, la phénologie reproductive des arbres tropicaux, majoritairement annuelle, semble présenter une certaine régularité. Cette étude documente les variations intra- et interannuelles de la phénologie reproductive des arbres de la forêt du Mayombe à partir des données historiques de la Réserve de Luki (République démocratique du Congo). Le diamètre de reproduction des espèces exploitées pour le bois, encore largement méconnu, a été également examiné pour les espèces suffisamment représentées dans les données. Le suivi phénologique de 3 642 arbres appartenant à 158 espèces et 39 familles a été réalisé tous les 10 jours de 1948 à 1957. Les statistiques circulaires ont été utilisées pour tester le synchronisme de la phénologie entre arbres, à l’échelle de la communauté, pour la forêt dans son ensemble, et individuellement pour 87 espèces, dont 35 espèces bien représentées (n ≥ 20 arbres), 16 espèces commerciales et 36 autres espèces. Des régressions logistiques ont permis de déterminer le diamètre de fructification (minimum et régulier) de ces espèces. Pour la majorité des espèces, la floraison était régulière, annuelle et largement saisonnière (81,6 %, 71 espèces). Les pics étaient plus marqués pour la floraison que pour la fructification, plus étalée dans le temps, bien que significativement agrégée temporellement. La majorité des arbres et des espèces fleurissaient entre décembre et février, pendant la petite saison sèche, bien que des fleurs et des fruits étaient observables toute l’année à l’échelle de la communauté. Seules 13 espèces ont montré une relation significative entre le diamètre et la reproduction, parmi lesquelles sept espèces de canopée, cinq de sous-bois et une héliophile. Pour ces espèces, la moyenne du diamètre minimum de reproduction était de 17,3 cm.

Carry-Over Niches for Lepidopteran Maize Stemborers and Associated Parasitoids during Non-Cropping Season.

Sources of infestation are the key elements to be considered in the development of habitat management techniques for the control of maize stemborers. Several wild plants, grasses mostly, have been identified that serve as hosts for stemborers and their parasitoids during the off-season when maize is not present in the field. However, their abundance is much lower in wild plants compared to cultivated fields. Thus, the role of wild plants as a reservoir for cereal stemborers and their parasitoids is still controversial, particularly in agro-ecosystems with reduced wild habitat. We studied the occurrence of different maize stemborers and associated parasitoids in maize stem residues and wild grasses during non-cropping seasons as potential carry-over populations to subsequent early season maize plants. Surveys were conducted in the central region of Kenya during long and short dry seasons in maize residues and wild grasses as well as during the two rainy seasons in maize plants at earlier and late whorl stages during the years of 2017 and 2018. Wild habitat had a higher species diversity than maize residues habitat, but maize residues had a higher abundance of maize stemborer species, such as Busseola fusca, Sesamia calamistis, and Chilo partellus, and of associated parasitoid species (i.e., Cotesia flavipes and Cotesia sesamiae) than wild plants. Our surveys, complemented by field parasitoid releases of C. flavipes and C. sesamiae, indicated that maize residues constitute a better refugia reservoir not only of the maize stemborers but also of C. flavipes and C. sesamiae during non-cropping seasons as compared to wild plants and, thus, might constitute in this region the main source of both stemborers and C. flavipes/C. sesamiae carry-over in maize plants during the subsequent cropping season. Thus, systematic destruction of maize residues would not help the biological control of lepidopteran stemborers. This is particularly true in areas with reduced wild habitat.

Using Growth and Transpiration Phenotyping Under Controlled Conditions to Select Water Efficient Banana Genotypes.

Water deficit is one of the world’s major constraints in agriculture and will aggravate in the future. Banana (Musa spp.) is an important crop that needs vast amounts of water for optimal production. The International Transit Center of Bioversity International holds the world’s biggest collection of banana biodiversity (>1,500 accessions). The long-term aim of this research is to evaluate the potential within this collection for climate smart agricultural usage. Therefore, we developed a phenotyping setup under controlled environmental conditions and we selected 32 representatives of the Musa biodiversity (29 cultivars and 3 wild relatives) for evaluation. The best performing genotypes accumulated six to seven times more biomass than the least performing. Eight genotypes (five ABB, one AAB, and two AAA) invest under osmotic stress significantly more in root growth than in leaf growth. We predict therefore that these genotypes have potential for high productivity under rain fed conditions with a short dry season. To gain more insight in the transpiration physiology, we gravimetrically monitored individual plant transpiration over the diurnal period. All analyzed genotypes showed a marked reduction in transpiration rate in the afternoon. Moreover, the timing of this onset, as well as its impact on total transpiration, was genotype dependent. This phenomenon was more pronounced in 13 genotypes (eight ABB, two AAB, two AA, one BB). Banana is a crop originating from the humid tropics and has developed a strong root pressure to maintain an efficient water and nutrient transport even under saturated relative humidity conditions. Therefore, we hypothesize that the diurnal transpiration decline contributes to a higher water use efficiency without compromising the nutrient transport. Of the eight genotypes that had the best growth under osmotic stress, all analyzed ABB cultivars have a lower maximal transpiration rate, keep this maximal transpiration for a shorter time and therefore consume less water per day. We conclude that lab models are very useful to study the biodiversity and to identify different traits that contribute to a better drought tolerance/avoidance. We encourage researchers investigating other crops to start exploring their collections.

Climatology of coastal wind regimes in Benin

Using surface and lower-tropospheric wind observations at Cotonou (Benin), a comprehensive ten-year (2006–2015) climatology of coastal wind regimes at the West African Guinea Coast is presented for the first time. Four wind regimes are objectively identified: the monsoon and Harmattan winds, the nocturnal low-level jet (NLLJ) and the land-sea breeze (LSB) system. Amongst other things, these regimes are important for the occurrence of coastal squall line systems and for the redistribution of pollutants emitted from coastal cities. The seasonal cycle is split into the long (December–February) and short (July–September) dry seasons, the long (May–June) and short rainy (October–November) seasons, and the beginning of the long rainy season (March–April). In terms of the LSB, the lack of a diurnal reversal in wind direction obscures sea breeze activity at the height of the southwesterly monsoon flow in boreal summer and during a period of stronger winds in March-April related to large land-sea thermal contrasts. During these periods, the sea breeze manifests itself in a relative increase of the monsoon background flow during daytime, while early morning land breezes are infrequent. The latter expectedly, peak during the long dry season in December with a secondary peak during the long rainy season in May–June. The large–scale monsoon and Harmattan flows, mutually exclusive by definition, occur respectively, 88.2–98.4 % and 1.6–11.8 % per year with Harmattan days restricted to the long dry season and deepest monsoon flows of about 2.5 km confined to the long rainy season. The NLLJ is most prominent during the little dry season with, however, a similar and hitherto less documented peak in occurrence frequency during the beginning of the long rainy season. At this time of the year, the African Easterly Jet passes northward over Cotonou, causing the largest 3000–600 m vertical wind shear.

Exploring fine-scale human and livestock movement in western Kenya

Human and livestock mobility are key factors in the transmission of several high-burden zoonoses such as rift valley fever and trypanosomiasis, yet our knowledge of this mobility is relatively poor due to difficulty in quantifying population-level movement patterns. Significant variation in the movement patterns of individual hosts means it is necessary to capture their fine-scale mobility in order to gain useful knowledge that can be extrapolated to a population level. Here we explore how the movements of people and their ruminants, and their exposure to various types of land cover, correlate with ruminant ownership and other demographic factors which could affect individual exposure to zoonoses. The study was conducted in Busia County, western Kenya, where the population are mostly subsistence farmers operating a mixed crop/livestock farming system. We used GPS trackers to collect movement data from 26 people and their ruminants for 1 week per individual in July/August 2016, and the study was repeated at the end of the same year to compare movement patterns between the short rainy and dry seasons respectively. We found that during the dry season, people and their ruminants travelled further on trips outside of the household, and that people spent less time on swampland compared to the short rainy season. Our findings also showed that ruminant owners spent longer and travelled further on trips outside the household than non-ruminant owners, and that people and ruminants from poorer households travelled further than people from relatively wealthier households. These results indicate that some individual-level mobility may be predicted by season and by household characteristics such as ruminant ownership and household wealth, which could have practical uses for assessing individual risk of exposure to some zoonoses and for future modelling studies of zoonosis transmission in similar rural areas.

Implications of soils around domestic water points in the spread of intestinal parasites in the city of Yaounde (Cameroon).

To determine the role of soils in dissemination of enteric protozoan cysts and intestinal eggs and/or larvae of helminths, a study was carried out on muddy soils around springs and wells of six districts in Yaounde, Cameroon from February to July 2015. Protozoan cysts and helminth eggs and larvae were observed microscopically after concentration by standard scientific methods. Flagellated enteric protozoa cysts were detected at an average density of 245 ± 145 cysts/L for Giardia intestinalis, 308 ±190 cysts/L for Chilomastix mesnili, 105 ± 106 cysts/L for Enteromonas hominis and 96 ± 118 cysts/L for Retortamonas intestinalis. Cyst densities were higher during the short rainy season (277 ± 119 cysts/L) than in the short dry season (147 ± 60 cysts/L). The helminths identified were Ascaris sp., Enterobius sp., Necator americanus and/or Ancylostoma duodenale, Strongyloides sp., Taenia sp., Hymenolepis sp., Diphyllobothrium sp. and Fasciola sp. Size varied between 40 μm and 200 μm for eggs and between 100 μm and 600 μm for the larvae assessed. Densities of environmental forms of the helminths were also higher during the short rainy season (176 ± 77 agents/L) than during the short dry season (117 ± 49 agents/L). These results show that muddy soils could contribute to the contamination of wells and springs and should be considered in epidemiological studies of intestinal parasites.

Mass concentration, optical depth and carbon composition of particulate matter in the major southern West African cities of Cotonou (Benin) and Abidjan (Côte d'Ivoire)

Abstract. Air quality degradation is a major issue in the large conurbations on the shore of the Gulf of Guinea. We present for the first time PM2.5 time series collected in Cotonou, Benin, and Abidjan, Côte d'Ivoire, from February 2015 to March 2017. Measurements were performed in the vicinity of major combustion aerosol sources: Cotonou/traffic (CT), Abidjan/traffic (AT), Abidjan/landfill (AL) and Abidjan/domestic fires (ADF). We report the weekly PM2.5 mass and carbonaceous content as elemental (EC) and organic (OC) carbon concentrations. We also measure the aerosol optical depth (AOD) and the Ångström exponent in both cities. The average PM2.5 mass concentrations were 32 ± 32, 32 ± 24 and 28 ± 19 µg m−3 at traffic sites CT and AT and landfill site AL, respectively. The domestic fire site shows a concentration of 145 ± 69 µg m−3 due to the contribution of smoking and roasting activities. The highest OC and EC concentrations were also measured at ADF at 71 ± 29 and 15 ± 9 µg m−3, respectively, while the other sites present OC concentration between 8 and 12 µg m−3 and EC concentrations between 2 and 7 µg m−3. The OC ∕ EC ratio is 4.3 at CT and 2.0 at AT. This difference highlights the influence of two-wheel vehicles using gasoline in Cotonou compared to that of four-wheel vehicles using diesel fuel in Abidjan. AOD was rather similar in both cities, with a mean value of 0.58 in Cotonou and of 0.68 in Abidjan. The seasonal cycle is dominated by the large increase in surface mass concentration and AOD during the long dry season (December–February) as expected due to mineral dust advection and biomass burning activities. The lowest concentrations are observed during the short dry season (August–September) due to an increase in surface wind speed leading to a better ventilation. On the other hand, the high PM2.5 ∕ AOD ratio in the short wet season (October–November) indicates the stagnation of local pollution.

Breeding ecology of Kori Bustard Ardeotis kori strunthiunculus in the Serengeti National Park

The breeding ecology of the Kori Bustard Ardeotis kori strunthiunculus was studied in the plains of the Serengeti National Park, Tanzania in 2014 and 2015. Random transects were used to search for male courtship displays, nests, chicks and subadults. GPS satellite collars were used to locate nesting females. Linear regression analyses and post hoc tests were used to determine the predictors that contributed most to the variation of the dependent variables (courtship display, nest, chicks and subadults). The results indicate that courtship behaviour peaks during the short dry and short rainy season before the peaks in nests and chicks. The highest nest frequency was found in short grass habitats. Female Kori Bustard may undergo repeated nestings within a single breeding season. The adult sex ratio was female skewed during the breeding season. The Kori Bustard breeding season in the Serengeti plains is relatively long, lasting for almost nine months, and taking place during all seasons except for the long dry season. We recommend that management authorities conduct assessments of Kori Bustard recruitment as well as habitat suitability in the Serengeti ecosystem to develop future conservation strategies.

Stochastic modelling of tree architecture and biomass allocation: application to teak (Tectona grandis L. f.), a tree species with polycyclic growth and leaf neoformation.

For a given genotype, the observed variability of tree forms results from the stochasticity of meristem functioning and from changing and heterogeneous environmental factors affecting biomass formation and allocation. In response to climate change, trees adapt their architecture by adjusting growth processes such as pre- and neoformation, as well as polycyclic growth. This is the case for the teak tree. The aim of this work was to adapt the plant model, GreenLab, in order to take into consideration both these processes using existing data on this tree species. This work adopted GreenLab formalism based on source-sink relationships at organ level that drive biomass production and partitioning within the whole plant over time. The stochastic aspect of phytomer production can be modelled by a Bernoulli process. The teak model was designed, parameterized and analysed using the architectural data from 2- to 5-year-old teak trees in open field stands. Growth and development parameters were identified, fitting the observed compound organic series with the theoretical series, using generalized least squares methods. Phytomer distributions of growth units and branching pattern varied depending on their axis category, i.e. their physiological age. These emerging properties were in accordance with the observed growth patterns and biomass allocation dynamics during a growing season marked by a short dry season. Annual growth patterns observed on teak, including shoot pre- and neoformation and polycyclism, were reproduced by the new version of the GreenLab model. However, further updating is discussed in order to ensure better consideration of radial variation in basic specific gravity of wood. Such upgrading of the model will enable teak ideotypes to be defined for improving wood production in terms of both volume and quality.

Leaf phenological traits of the tree fern Cyathea praecincta (Cyatheaceae) in a Brazilian lowland tropical forest

Phenological studies are fundamental to our understanding of how the environment can influence plant growth and reproductive processes. Environmental triggers of fern phenology are poorly known. We investigated the leaf phenological traits of the tree fern Cyathea praecincta (Kunze) Domin in a Brazilian lowland tropical forest with a short dry season. We monitored 47 plants over an 18-month period, measuring leaf production, leaf fertility, leaf mortality and the relation of these variables with rainfall and temperature. Data on leaf expansion and lifespan were also presented. Full leaf expansion in C. praecincta took up to 3 months. The production of sterile and fertile leaves showed dissimilar interactions with climate, a common pattern among most tree ferns studied worldwide. Whereas production of sterile leaves of C. praecincta was not influenced by climatic variability, leaf fertility was driven by increasing rainfall. Some fertile plants (30%) produced exclusively fertile leaves and attained full maturity, playing a key role in the maintenance and growth of the population. The estimated leaf lifespan was 17.9±5.89 months. The finding that leaf mortality was driven by decreasing rainfall is in contrast with most tree ferns, which are not influenced by climate. None of the phenological variables was influenced by temperature. We demonstrated that rainfall plays a crucial role on leaf fertility and leaf mortality of C. praecincta in a tropical forest remnant with a short dry season and inversely related rainfall and temperature.

Seasonal glucocorticoid production correlates with a suite of small-magnitude environmental, demographic, and physiological effects in mandrills.

The activation of the hypothalamic-pituitary-adrenal axis is a neuroendocrine response to external and internal changes that animals face on a predictable or unpredictable basis. Across species, variation in glucocorticoid production has been related to such changes. In this study, we investigated the predictable, seasonal sources of variation in the levels of fecal glucocorticoid metabolites (fGCM) in a large natural population of mandrills (Mandrillus sphinx) in Southern Gabon. Using five years of regular behavioral monitoring and hormone analyses performed on 1,233 fecal samples collected on 99 individuals of both sexes and all ages and General Linear Mixed Models, we studied the three main seasonal predictors of fGCM concentrations: (i) weather conditions, (ii) number of adult males, and (iii) female reproductive status. These three predictors all vary seasonally in mandrills. We first showed an increase in fGCM concentrations during the short dry season while controlling for other factors. Pregnant females, which include the large majority of adult females at this time of the year, mainly drove this increase, although a combination of other small-magnitude, season-related effects linked to climatic events and demographic changes also partly explained this seasonal trend. Indeed, fGCM concentrations increased with both low temperatures (and low rainfall) and high numbers of adult males present in the group. These seasonal changes, while correlated, held true throughout the studied years and when restricting our analyses to a given season. Finally, we found that older mandrills showed on average higher fGCM concentrations than younger ones and that medium-ranked females exhibited the highest levels of fGCMs. The observed patterns suggest that plasticity in mandrills' metabolism in the form of glucocorticoid production allows them to adjust to predictable changes in climatic, demographic and physiological conditions by mobilizing and redirecting energetic resources toward appropriate, calibrated seasonal responses.

The Climate Change and Rwandan Coffee Sector

This paper provides a detailed overview of the current situation of the coffee sector in the Rwandan economy and identifies the possible challenges that the sector is currently facing. The study has identified the economic and the livelihood indicators for farmers who are engaged in coffee production and also gives the Rwandan coffee sector‘ situation and its position in the global coffee market. Also, the research has found out that in Rwanda, nearly 500,000 farmers produce coffee along with other crops, notably beans, savory banana and corn and found out that in 2012, coffee accounted for almost 30 percent of Rwanda‘s total export revenue. On the other hand, the study revealed that the sector throughout all the coffee production process, has undergone different challenges especially climate change as it is reported by the Ministry of Agriculture and Animal resources. A low yield was reported in 2007 and climate variability was quoted among the causes. Insufficient rainfall in the last three months of 2006 (the period of coffee flowering) proceeding the short dry season in the first two months of 2007 was recorded. The reduced rainfall was also poorly distributed across coffee growing regions in Rwanda. In addition, the research revealed that even though the area under coffee production is increasing, the coffee production is decreasing due to unexpected climate change and variability in current years and also the improper use of chemical fertilizers by coffee farmers is very critical. The study concluded that adding value to the coffee supply chain of Rwanda is adding direct economic benefits and important indirect social benefits to the lives of individuals and to the health of communities in Rwanda. Moreover, more effort should continue to raise the profile of the Rwandan coffee sector suggesting that proper use of chemical fertilizers, solid marketing channels and climate change adaptations measures would be the fair ways of making the sector more profitable and considering national targets to increase coffee export revenues, a few simple measures to improve the performance of the sector could have substantial effects on the country‘s economic growth.

Assessment of risk of dengue and yellow fever virus transmission in three major Kenyan cities based on Stegomyia indices.

Dengue (DEN) and yellow fever (YF) are re-emerging in East Africa, with contributing drivers to this trend being unplanned urbanization and increasingly adaptable anthropophilic Aedes (Stegomyia) vectors. Entomological risk assessment of these diseases remains scarce for much of East Africa and Kenya even in the dengue fever-prone urban coastal areas. Focusing on major cities of Kenya, we compared DEN and YF risk in Kilifi County (DEN-outbreak-prone), and Kisumu and Nairobi Counties (no documented DEN outbreaks). We surveyed water-holding containers for mosquito immature (larvae/pupae) indoors and outdoors from selected houses during the long rains, short rains and dry seasons (100 houses/season) in each County from October 2014-June 2016. House index (HI), Breteau index (BI) and Container index (CI) estimates based on Aedes (Stegomyia) immature infestations were compared by city and season. Aedes aegypti and Aedes bromeliae were the main Stegomyia species with significantly more positive houses outdoors (212) than indoors (88) (n = 900) (χ2 = 60.52, P < 0.0001). Overall, Ae. aegypti estimates of HI (17.3 vs 11.3) and BI (81.6 vs 87.7) were higher in Kilifi and Kisumu, respectively, than in Nairobi (HI, 0.3; BI,13). However, CI was highest in Kisumu (33.1), followed by Kilifi (15.1) then Nairobi (5.1). Aedes bromeliae indices were highest in Kilifi, followed by Kisumu, then Nairobi with HI (4.3, 0.3, 0); BI (21.3, 7, 0.7) and CI (3.3, 3.3, 0.3), at the respective sites. HI and BI for both species were highest in the long rains, compared to the short rains and dry seasons. We found strong positive correlations between the BI and CI, and BI and HI for Ae. aegypti, with the most productive container types being jerricans, drums, used/discarded containers and tyres. On the basis of established vector index thresholds, our findings suggest low-to-medium risk levels for urban YF and high DEN risk for Kilifi and Kisumu, whereas for Nairobi YF risk was low while DEN risk levels were low-to-medium. The study provides a baseline for future vector studies needed to further characterise the observed differential risk patterns by vector potential evaluation. Identified productive containers should be made the focus of community-based targeted vector control programs.

Darcy and Apparent Velocities of Groundwater in Phreatic Aquiferous Formations in Kumba– Cameroon: Determined by use of Trigger-Tube Tracer Test Method in Dug Wells

Kumba with a population of about 144,413 people is the capital of Meme Division, in the Southwest region is one of the largest cocoa cash crop producing areas in Cameroon. The inhabitants depend mostly on groundwater through dug wells. It has a hot and humid equatorial climate with annual rainfall 2298-3400 mm and annual temperature 27° C with a short dry season (December to March) and a long rainy season (April to November). There is a need for a good understanding of the hydraulic properties of the aquiferous formations for the planning and management of the groundwater resources of this area. Twenty-one hand-dug wells at different sites in Kumba were tested using sodium chloride (NaCl) as a conservative tracer, by use of the trigger-tube tracer test method. Field estimations of groundwater flow and groundwater velocities in the phreatic aquiferous formation in Kumba through by trigger tube tracer tests gave Darcy velocities ranging from 19.63 m/d at Krammar to 634.13 m/d at Dallas and apparent velocities ranging from 39.26 m/d at Krammar to 1268.27 m/d at Dallas. The trigger tube tracer tests carried out in some dug wells in Kumba reveals significant spatial variations in groundwater velocities and groundwater flow velocities which are relatively poor at Krammar and good at Dallas. The huge spatial variations in groundwater flows and groundwater velocities imply that groundwater flows at different rates, directions, and at different rates in different sections of the phreatic aquiferous formation in Kumba, probably due to spatial variations in permeability and existence fractures acting as groundwater conduits. Areas with low groundwater velocities like Krammar have lower permeabilities compared to those around PS Kumba Town, Dallas and CCAS. This suggests spatial variations in formation types, facies changes (transgressive and regressive), thickness and layering.

Kori bustard (Ardeotis kori struthiunculus) occurrence in the Serengeti grass plains, northern Tanzania

The kori bustard (Ardeotis kori struthiunculus) is indigenous to grasslands and lightly wooded savannahs of southern and eastern Africa. The species is categorized as near threatened in its entire range due to anthropogenic factors and low reproductive rates. The aim of this study was to analyse the impact of grass colour, grass height, season and location on the density/occurrence of this bird species in the Serengeti grass plains, Tanzania. Data were collected from January 2014 to June 2015 using transect counts in four seasons: (i) short dry, (ii) long rain, (iii) long dry and (iv) short rain seasons, respectively. The mean density of kori bustard in the grass plains was 0.25 ± 1.01 per 0.2 km2 with near-significant differences among the study sites. The occurrence of kori bustard was high in the medium height (11–30 cm) during the long rain and short dry seasons. The kori bustard density is relatively low, and the distribution varies with grass height and season. We suggest that conservation efforts should be directed at preventing its local extinction by protecting the habitat from excessive human activities, such as livestock grazing and illegal offtake.

System dynamics modelling approach to determine sustainable stocking rate for a sheep population in the Ethiopian highlands

A system dynamics approach was used to determine the sustainable stocking rate of the Menz sheep population in the Ethiopian highland. A model was developed to simulate stocking rate based on communal grazing land. The model is weather and resource (feed supply) driven. Pasture growth and dynamics was modeled using rainfall and temperature data. Herd dynamics was based on age groups of male and female animals from birth to herd exit, taking production and reproduction parameters into account. To simulate sustainable stocking rate, a common unit (Tropical Livestock Unit, TLU) was used to represent the various classes of sheep. A higher stocking rate was observed in the long rainy season when the green pasture supply is higher. However, stocking rate was decreased with decrease in green and dry standing pasture in the long and short dry seasons. Application of the sustainable stocking rate in reality can be challenging since farmers keep large flocks and the pasture land is owned by groups of farmers. More awareness creation, including practical show-cases of the benefits of variation of stocking rate based on available resources, is needed to convince farmers in this and many other regions of Ethiopia.

Prolonged drought results in starvation of African elephant (Loxodonta africana)

Elephant inhabiting arid and semi-arid savannas often experience periods of drought, which, if prolonged, may cause mortality. During dry periods, elephant aggregate around water sources and deplete local forage availability. However, the relationships between adult elephant mortality and both high local elephant density and forage availability close to water during dry periods remain unexplored. We hypothesized that elephant mortality is higher: a) when dry periods are longer, b) closer to water points, and c) in areas with higher local elephant density. Using nine years of elephant carcass data from Tsavo Conservation Area in Kenya, we analysed the probability of adult elephant mortality using maximum entropy modelling (MaxEnt). We found that elephant carcasses were aggregated and elephant mortality was negatively correlated with four months cumulative precipitation prior to death (which contributed 41% to the model), Normalised Difference Vegetation Index (NDVI) (19%) and distance to water (6%), while local elephant density (19%) showed a positive correlation. Three seasons (long dry, short dry and short wet seasons) showed high probability of elephant mortality, whereas low probability was found during long wet seasons. Our results strongly suggest that elephants starve to death in prolonged drought. Artificial water holes may lead to lower mortality, but also to larger populations with subsequent high browsing pressure on the vegetation. Our results suggest that elephant populations in arid and semi-arid savannas appear to be regulated by drought-induced mortalities, which may be the best way of controlling elephant numbers without having to cull.

Effect of fragmentation on the Costa Rican dry forest avifauna.

Deforestation and changes in land use have reduced the tropical dry forest to isolated forest patches in northwestern Costa Rica. We examined the effect of patch area and length of the dry season on nestedness of the entire avian community, forest fragment assemblages, and species occupancy across fragments for the entire native avifauna, and for a subset of forest dependent species. Species richness was independent of both fragment area and distance between fragments. Similarity in bird community composition between patches was related to habitat structure; fragments with similar forest structure have more similar avian assemblages. Size of forest patches influenced nestedness of the bird community and species occupancy, but not nestedness of assemblages across patches in northwestern Costa Rican avifauna. Forest dependent species (species that require large tracts of mature forest) and assemblages of these species were nested within patches ordered by a gradient of seasonality, and only occupancy of species was nested by area of patches. Thus, forest patches with a shorter dry season include more forest dependent species.