Mid-wet Season Research Articles

Seasonal movements of small-island birds along habitat and elevation gradients highlights the conservation value of small-scale agroforests

Knowledge on species distributions and seasonal movement patterns within landscapes is important for understanding their ecology and roles in agroecosystems, and is critical for enabling their effective conservation and monitoring, particularly in small-island states where conservation resources are limited. We undertook bird surveys to examine species distributions across a range of agricultural land-use intensities and elevations on the Caribbean island of Grenada by collecting data over 6 repeated monthly surveys (3 wet season, 3 dry season) at sites located in a variety of habitats spread over 6–300 m elevation. We observed a gradual upslope increase in bird species diversity and abundance from the mid-wet season to the late-dry season, as well as a movement from reduced-canopy habitats to closed-canopy habitats in the dry season. The mid-elevation hillsides of Grenada consist of a diverse mosaic of closed canopy secondary forest patches, interspersed among more open agroforests and small-scale cropping and grazed areas. These agroecosystems appear to provide important habitats to birds throughout the year, especially open canopy agroforests in the wet season. We also found that open mixed agroforests contained a greater diversity of fruit, flower, and seed resources than closed canopy habitats such as secondary forest, cacao agroforests, young secondary forests, or dry forest scrub; and that plant food diversity was highest in the wet season. However, bird abundance significantly increased in closed canopy forest habitats during the dry season, suggesting that intact canopy forests provide important dry season habitat for many Grenadian birds, which may be particularly important for species in drier lowland areas experiencing more intensive agricultural land use and urban and resort development. Overall, this research demonstrates the importance of maintaining the functional connectivity of treed habitats at local and landscape scales for species conservation, as well as the contribution of diverse, small-scale agriculture to maintaining small-island bird communities.

Spatiotemporal distribution of microplastics in the Ganzhou section of the Ganjiang river: An insight into the source area impact

Field surveys for riverine microplastics (MP) are profoundly affected by background MPs from upstream cities, resulting in uncertainty when exploring the underlying mechanism of MP source and distribution. In this study, the Ganzhou Section of the Ganjiang River was surveyed because of its minor background effects and large anthropogenic influences. Relatively low MP abundance was found in the target rivers owing to the small background in the riverine source area. The average MP abundance in the dry season (10.9 ± 2.33 items L–1) was higher than that in the mid-wet season (3.47 ± 0.95 items L–1). The polymers were predominantly cellophane and polyethylene. The contribution of the functional areas to the predominant MP shape (fibre and fragment), size (0.125–0.5 mm), and colour (polychrome and white) distribution, was as follows: industrial > scenic > residential > natural areas. MP abundances fluctuated with different rainfall levels during the wet season, and varied synchronously with the river flow during a flow-controlled period, suggesting that land scouring and transportation played more critical roles than sediment release. The small watershed area in the upper reaches of the river caused a low terrestrial MP number, making it easy for the riverine MP content to reach a plateau. This work contributes to the understanding of MP distribution in freshwater and provides a potential guideline for MP control.

Delayed wet season increases soil net N mineralization in a seasonally dry tropical forest

Seasonal precipitation regime plays a vital role in regulating nutrient dynamics in seasonally dry tropical forests. Present evidence suggests that not only wet season precipitation is increasing in the tropics of South China, but also that the wet season is occurring later. However, it is unclear how nutrient dynamics will respond to the projected precipitation regime changes. We assessed the impacts of altered seasonal precipitation on soil net N mineralization in a secondary tropical forest. Since 2013, by reducing throughfall and/or irrigating experimental plots, we delayed the wet season by two months from April–September to June–November (DW treatment) or increased annual precipitation by 25% in July and August (WW treatment). We measured soil net N mineralization rates and assessed soil microbial communities in January, April, August and November in 2015 and 2017. We found that a wetter wet season did not significantly affect soil microbes or net N mineralization rates, even in the mid-wet season (August) when soil water content in the WW treatment increased significantly. By contrast, a delayed wet season enhanced soil microbial biomass and altered microbial community structure, resulting in a two-fold increase in net N mineralization rates relative to controls in the early dry season (November). Structural equation modeling showed that the changes in net N mineralization during the early dry season were associated with altered soil microbial communities, dissolved organic N, and litterfall, which were all affected by enhanced soil water content. Our findings suggest that a delayed wet season could have a greater impact on N dynamics than increased precipitation during the wet season. Changes in the seasonal timing of rainfall might therefore influence the functioning of seasonally dry tropical forests.

Effects of land use change, wetland fragmentation, and best management practices on total suspended solids concentrations in an urbanizing Oregon watershed, USA

While many different watershed management strategies have been implemented to improve water quality, relatively few studies empirically tested the combined effects of different strategies on water quality in relation to land cover changes using long-term empirical data at the sub-basin scale. Using 10 years of total suspended solids (TSS) data, we examined how the conversion of wetland, wetland fragmentation, beaver dams, and Best Management Practices (BMPs) affect wet season TSS concentrations for the 25 monitoring stations in the Tualatin River basin, USA. Geographic information systems, FRAGSTATS, and correlation analysis were used to identify the direction of land cover change, degree of wetland fragmentation, and the strength of the relationship between TSS change and explanatory variables. Improvement in TSS concentrations was tightly coupled with the aggregation of wetlands, presence of beaver dams, particularly during the mid-wet season when flows were highest. Other BMPs effectively reduced TSS concentrations for the early and late-wet seasons when flows were not as high as in the middle wet-season. Aggregated wetlands were more effective for improving water quality than smaller disaggregated wetlands of similar total area when combined with the presence of beaver dams and BMPs. These findings offer important scientific and practical implications for management of urbanizing watersheds that seek to achieve the dual goals of improving environmental quality and land development.

Phenology and litter production in the mangrove genus Xylocarpus along rainfall and temperature gradients in tropical Australia

We investigated how variation in climate influences the timing and intensity of phenological events in two species of the mangrove genus Xylocarpus. Leaf fall in Xylocarpus granatum was continuous in high rainfall sites but was seasonal at sites with long dry seasons. Xylocarpus moluccensis is deciduous, and leaf shedding occurred over 1–2 months at different times in dry season months. Budding and flowering were tightly coupled in X. granatum and occurred in the wet season. At the highest rainfall site, flower fall in X. moluccensis occurred in the mid-wet season, but occurred 9 months later at other sites with protracted dry seasons. For X. moluccensis, the quantities of leaves, buds, flowers and total litter fall were negatively related to annual rainfall, whereas bud fall was negatively related to air temperature. Variations in the quantity of litter produced by X. granatum were not explained by the environmental variables considered. Mean litter production was significantly greater for X. moluccensis than X. granatum (5.16 v. 3.37Mgh–1 year–1 respectively). Mixed forest litter production was greater in forests containing X. moluccensis than X. granatum (7.86 v. 5.95Mgh–1 year–1 respectively). X. granatum has a more plastic response to environmental drivers of canopy production than X. moluccensis.

Dynamics of wet‐season turbidity in relation to precipitation, discharge, and land cover in three urbanizing watersheds, Oregon

AbstractFrequent intense precipitation events can mobilize and carry sediment and pollutants into rivers, degrading water quality. However, how seasonal rainfall and land cover affect the complex relationship between discharge and turbidity in urban watersheds is still under investigation. Using hourly discharge, rainfall, and turbidity data collected from six stations in three adjacent watersheds between 2008 and 2017, we examined the temporal variability of the discharge–turbidity relationship along an urban–rural gradient. We quantified hysteresis between normalized discharge and turbidity by a hysteresis index and classified hysteresis loops during 377 storm events in early, mid, and late wet season. Hysteresis loop index and direction varied by site land cover type and season. Turbidity values peaked quicker in the watersheds with higher degrees of urban development than in a less urbanized watershed. The positive relation between discharge and turbidity was highest in two downstream stations in the mid wet season, whereas it was highest in two upstream stations in the early wet season. Correlation and regression analysis showed that maximum turbidity was best explained by discharge range, and the sensitivity of turbidity to discharge change was higher in the larger downstream watershed than in the small upstream watersheds. A flashiness index was negatively associated with the slope of turbidity versus discharge, suggesting that turbidity is difficult to predict solely on the basis of discharge in flashy urban streams. This paper contributes to a deeper understanding of the spatial and temporal variation of discharge–concentration relationship in urbanizing watersheds, which can help water managers increase the resiliency of water‐related ecosystem services to impacts of climate change.

Qualitative identification of hydrologically different water sources used by plants in rock-dominated environments

Sources of water used by plants in rock-dominated environments are far less clear than those in relatively homogeneous soils, largely because plants in rocky environments normally expose to more complex substrate conditions and their potential water sources are hard to locate and sample. In the current study, potential water sources for plants growing on cliff-face (a typical kind of rock-dominated environment) were roughly separated into two water pools based on their hydrological differences. A variable pool that is composed of water derived from recent precipitation that has rapid fluctuations in water content due to recharge by precipitation and depletion by transpiration, and a constant pool that is characterized by slower changes in water status because it can only be recharged by precipitation under certain conditions and depleted by transpiration of deep-rooted species. This study was conducted in a typical karst catchment of Northwest Guangxi, Southwest China. Stem water samples for the most common dominant tree species of cliff-faces and rainwater for each rain event were consecutively collected throughout the growing season. A co-occurring shrub species, which was identified to have a shallow root system, was further selected as a reference species. The reliance on different water pools was qualitatively identified based on the deviation of stem water isotope values between current and last sampling times, as well as its relationship to the isotope values of rainfall between these two sampling times. Our results showed that the shrub species continuously relied on water from the variable water pool, which was consistent with its shallow root system. While the dominant tree species shifted from the constant pool during the early wet season to the variable pool during the mid-wet season, then back to the constant pool during the early dry season. Moreover, the divergent reliance on different water pools by the two species was further supported by the species-specific dynamics in the efficiency in water use by various plants (reflected by leaf carbon isotope ratio). Our results provide new insights into the linkages between plant transpiration and hydrologically different water pools, which would be helpful in understanding the hydrological importance of different plant species.

Effect of Seasonality on Rates of Gregarine Infection in Workers of a Social Wasp Polybia Paulista (Hymenoptera, Vespidae).

Social insects face strong selection from parasites because the conditions of group living often favor the transmission of infection among nestmates. However, there is little detailed information on the effects of parasite infection in the host species. Workers of Polybia species, neotropical swarm-founding wasps, are commonly infected by gregarines, protozoans that are exclusively parasitic on invertebrates. Previous studies showed that high rates of gregarine infection in workers of Polybia occidentalis (Olivier) have negative effects on their colony performance. However, the effect of seasonality on infection rates throughout the year or between wet and dry seasons has not been examined. Host-parasite interactions cannot be understood without consideration of the overall population dynamic. We compared rates of gregarine infection in workers of Polybia paulista (Ihering) between wet and dry seasons and among months. The 35% rate was by far the highest of the four wet seasons sampled, but the rates declined in the mid-wet season and were very low during the dry season. Strong seasonal differences in infection rates were also observed between the dry and wet seasons. Several potential factors affecting the seasonal differences are discussed.

The significance of human respiratory syncytial virus (HRSV) in children from Ghana with acute lower respiratory tract infection: A molecular epidemiological analysis, 2006 and 2013-2014.

BackgroundAcute lower respiratory tract infection (ALRI) is a leading cause of childhood morbidity and mortality in developing countries. Globally, human respiratory syncytial virus (HRSV) is the most common pathogen of ALRI in infants and children. However, age-stratified HRSV disease burden data are largely absent from Africa, which is a key gap in informing an evidence-based recommendation for the introduction of an HRSV vaccine by the WHO.MethodsThis study investigated the presence of HRSV in respiratory specimens from 552 children <5 years old with ALRI from Accra, Ghana in 2006 and 2013–2014 by real-time PCR. Of HRSV-positive samples the second hypervariable region of the viral G protein gene was sequenced and analyzed for phylogeny, characteristic amino acid substitutions, and potential glycosylation patterns. Further, HRSV infections have been characterized by age, symptoms and timely occurrence.ResultsHRSV was observed in 23% (127/552) of the children with ALRI, with the highest incidence in infants younger than one year (33%, 97/295, p = 0.013). Within the observed seasonal circulation time of HRSV from June (mid-wet season) to December (beginning of the dry season) the incidence of ALRI due to HRSV was as high as 46% (125/273). HRSV disease was significantly associated with (broncho-) pneumonia, bronchiolitis, LRTI, and difficulty in breathing. Phylogenetic characterization of HRSV strains from Ghana identified the circulation of the currently worldwide prevailing genotypes ON1 and BA9, and shows evidence of an independent molecular evolution of ON1 and BA9 strains in Ghana resulting in potentially new subgenotypes within ON1 and BA9, provisionally named ON1.5, ON1.6, and BA9-IV.ConclusionThis study addresses important knowledge gaps in the forefront of introducing the HRSV vaccine by providing information on the molecular evolution and incidence of HRSV in Accra (Ghana, Africa).

Efficiency of rumen microbial protein synthesis in cattle grazing tropical pastures as estimated by a novel technique

The efficiency of microbial protein synthesis (EMPS) in cattle grazing a range of tropical pasture types was examined using a new method of intra-jugular infusion of chromium–EDTA to estimate urinary excretion of purine derivatives. Seven pasture types were studied in south-eastern Queensland, Australia, over a 13-month period. These included native tropical grass (C4) pasture (major species Heteropogon contortus and Bothriochloa bladhii) studied in the early wet, the wet–dry transition and the dry season; introduced tropical grass (C4) pasture (Bothriochloa insculpta) in the mid-wet season; two introduced tropical legume species (C3; Lablab purpureus and Clitoria ternatea); and the temperate-grass (C3) pasture, ryegrass (Lolium multiflorum). There was a large range in EMPS across pasture types, with a range of 26–209 g microbial crude protein per kilogram digestible organic matter intake (DOMI). Estimated rumen-degradable protein (RDP) supply (42–525 g/kg DOMI) was the major factor associated with EMPS across the range of pasture types studied. EMPS in steers grazing all tropical grass pastures was low (&amp;lt;130 g/kg DOMI) and limited by RDP supply. Negative linear relationships (P &amp;lt; 0.05) between EMPS and concentrations of both neutral detergent fibre and acid detergent fibre in extrusa were evident. However, non-fibre carbohydrate in extrusa, total non-structural carbohydrate concentration in plucked pasture leaf, rumen fluid and particle dilution rate, protozoal concentration in rumen fluid and rumen fluid pH were not correlated with EMPS. It was concluded that EMPS was well below 130 g microbial crude protein per kilogram DOMI when cattle grazed unfertilised, tropical grass pastures in south-eastern Queensland and that RDP was the primary limiting nutrient. High EMPS was associated with a very high RDP, vastly in excess of RDP requirements by microbes.

Annual age structure and reproduction in the Caatinga red-nosed mouse, Wiedomys pyrrhorhinos (Rodentia, Sigmodontinae)

Introduction: We analyzed the variation in the age structure, sex ratio, proportion of reproductive individuals, age and size at sexual maturity, and litter size in a population of the sigmodont rodent Wiedomys pyrrhorhinos. We compared the observed distributions with the monthly rainfall for the same period, to identify the reproductive period and to assess the effects of the rains on the age structure of the population during the ensuing months. We further compared our results with age structure patterns recovered from other documented rodent outbreaks to identify possible causes of a presumptive population outbreak represented by this series. Methodology: Museum samples had been obtained between July 1953 and February 1955 from 40 sites in Caruaru, Pernambuco, Brazil. Records from a total of 2280 individuals, 1834 of which represented by their skulls, were analyzed. Skulls were sorted into seven age classes based on molar eruption and wear. Monthly rainfall during the entire collecting period was analyzed for putative correlations with monthly frequencies of specimens and of indicators of reproductive condition, tabulated for each sex and age class. Results: Monthly frequency distributions of age classes presented separated and consecutive modal peaks, conforming to an age structured population. Monthly proportions of pregnant females were highly correlated with the amount of rainfall of the same and of the previous month, although records of pregnant females were obtained every month between July 1953 and December 1954. Pregnant females were found from age class 2 on. From January to April, 1954, reproductive females belonged to age classes 5 to 7. From May to September a wide range of age classes was documented among pregnant females, and from October to December only those of age classes 2 to 4 were recorded. Litter size varied throughout the year, with larger averages and ranges at midwet season (June-August) and was highly correlated with female weight, female length and with the amount of rainfall of the previous 30 days. Higher means in litter size were also in phase with higher proportions of pregnant females and with the age class 1 peak. Discussion and Conclusion: The population peak occurred four to six months after the rainfall peak (September – November) and was primarily comprised of young adults. After this period, the pregnancy rates were very low, ceasing completely by January, 1955, when most of the individuals belong to older age classes. This shift in age structure from younger to older individuals during population decline indicated that the samples documented an outbreak episode in 1954. This episode was possibly related to the unusual rainfall in November 1953, apparently sufficient to support two closely-spaced breeding seasons, with the second amplifying the effect of the first.

Implications of climate, land-use and land-cover changes for pastoralism in eastern Sudan

This study examines the changes in climate and land-use/land-cover (LULC) along the livestock seasonal migration routes in El Gedaref region (eastern Sudan). Analysis of temperature, rainfall and aridity index (ratio of rainfall to reference evapotranspiration) data during 1941–2009 shows significant warming of the climate, increasing rainfall variability and seasonality, and intensifying aridity conditions during the start and end of the wet season. The somewhat recent enhancement of the overall (annual) rainfall has reflected only in the mid wet season and were caused by few very wet days, indicating increased rainfall concentration and possible risk of soil erosion. Such climatic alterations and variability have inherent implications for land-use and land-cover over the region. LULC changes were investigated using multi-temporal satellite imagery from three sites along the livestock routes. The major trends were drastic conversions of natural vegetation areas into large-scale mechanized agricultural land. This resulted in a progressive loss and degradation of grazing area in the entire region. Overall, the documented LULC changes may cause an irreversible loss of biodiversity and a depletion of other ecological services provided by natural vegetation. The results of this study provide useful information when seeking to resolve complex land-management issues.

Influence of Climatic Variables on the Abundance of a Brazilian Salamander (Bolitoglossa paraensis) in Santa Bárbara Do Pará, Brazil

ABSTRACT. Very little is known on the ecological attributes of Neotropical salamanders. The aim of this study was to evaluate the effect of two abiotic factors on the temporal and spatial abundance of B. paraensis. Data were collected during four periods, in 23 plots of 250 m2 distributed randomly in Gunma Ecological Park, in the Brazilian state of Para. In each plot, temperature and relative humidity of the air were measured during searches, and abundance of salamanders was determined by active nocturnal searches. The abundance of salamanders varied significantly during the course of the year. The highest abundance (0–18) was recorded in the mid wet season, followed by the late wet season (0–7), early dry season (0–9), and late dry season (0–6). Spatial abundance of salamanders was influenced by climatic conditions only in the late dry season. Temporal and spatial variation in the abundance of the salamanders is associated with relative humidity, which was highest in the mid wet season, and lowest in the...

Life history, damage assessment and control of Trioza hopeae (Hemiptera: Psylloidea), a serious pest on Hopea odorata (Malvales: Dipterocarpaceae) in Vietnam

AbstractYoung plants of the commercially important timber species Hopea odorata Roxb. are seriously damaged by the psyllid Trioza hopeae Burckhardt &amp; Vu in nurseries in South Central and Southern Vietnam. Farmers routinely use Class 1 toxic insecticides to control the psyllids but these pose serious health risks in the urban environment. As a precursor to developing a pest management strategy, we studied the life cycle of T. hopeae and trialed several control measures. Trioza hopeae is polyvoltine with overlapping generations peaking in mid wet season. Females laid approximately 135 eggs; however, there was a natural attrition rate of about 80% in first‐instar nymphs due to the nymph's inability to find a suitable feeding site. Feeding nymphs induced pit galls on young H. odorata leaves and were present on all trees examined during the study. The pre‐adult life cycle lasted approximately 13 days and adult life span approximately seven days. Several toxic insecticides were found to be effective for controlling T. hopeae, but a novel non‐toxic alternative was equally as effective. We discuss these methods and potential biological control measures.

Tropical cyclones and reproductive ecology of Crocodylus acutus Cuvier, 1807 (Reptilia: Crocodilia: Crocodylidae) on a Caribbean atoll in Mexico

Crocodylus acutus, a coastal species nesting in sand beaches, could be affected by increasing tropical cyclone frequency. We studied key characteristics of C. acutus reproductive ecology on Banco Chinchorro atoll from 2006 to 2009, including the impact of two tropical cyclones. Hurricanes increased canopy openness causing earlier nesting the following year. Crocodiles nested at the beginning of the wet season with hatching in mid-wet season; this could represent a compromise between risking nest flooding and increasing freshwater availability for hatchlings. Tropical cyclones dramatically reduced nesting success by cooling and flooding clutches. Nursery sites were usually hypersaline, but heavy rainfall from tropical cyclones can likely benefit hatchling survival by decreasing salinity. While tropical cyclones have negative short-term impacts on crocodile nesting, they likely have an overall beneficial effect by creating and maintaining open sandy nesting areas used by C. acutus and they may explain its widespread distribution in Caribbean coastal areas.

Ruminal protein degradability of a range of tropical pastures

The rumen degradability parameters of the diet selected by two to four oesophageal-fistulated Brahman steers grazing a range of tropical pastures were determined by incubation of extrusa in nylon bags suspended in the rumen of rumen-fistulated (RF) Brahman steers. The effective protein degradability (Edg) was determined by measuring the rate of disappearance of neutral detergent insoluble nitrogen (NDIN) less acid detergent insoluble nitrogen (ADIN) in the incubated extrusa. Six to eight RF steers also grazed each of the pastures along with the oesophageal-fistulated steers, to allow determination of key rumen parameters and rumen particulate matter fractional outflow rates (FOR). The seven pastures studied included: native tropical grass (C4) pasture (major species Heteropogon contortus and Bothriochloa bladhii), studied in the early wet (NPEW), the wet/dry transition (NPT) and the dry (NPD) seasons; introduced tropical grass (C4) pasture (Bothriochloa insculpta), studied in the mid wet season (BB); the introduced tropical legumes (C3), Lablab purpureus (LL) and Clitoria ternatea (BP); and the temperate grass (C3) pasture, ryegrass (Lolium multiflorum, RG). Using the measured particle FOR values in calculations, the Edg estimates were very high for both C4 and C3 species: 0.82–0.91 and 0.95–0.98 g/g crude protein (CP), respectively. Substitution of an assumed FOR (kp = 0.02/h) for the measured values for each pasture type did not markedly affect estimates of Edg. However, C4 tropical grasses had much lower effective rumen degradable protein (ERDP) fractions (23–66 g/kg DM) than the C3 pasture species RG and LL (356 and 243 g/kg DM, respectively). This was associated with a lower potential degradability and degradation rate of organic matter (OM) in sacco, lower in vitro organic matter digestibility (IVOMD) and CP concentrations in the extrusa, and lower ammonia-N and branched-chain fatty acid concentrations in rumen fluid for the tropical grasses. As tropical grass pastures senesced, there was a decline in Edg, the ERDP and rumen undegradable protein (UDP) fractions, the potential degradability and degradation rate of OM and the IVOMD. These results provide useful data for estimating protein supply to cattle grazing tropical pastures.

DYNAMICS OF A SUBTROPICAL POPULATION OF THE ZEBRA LONGWING BUTTERFLY HELICONIUS CHARITHONIA (NYMPHALIDAE)

We studied the population dynamics of the zebra longwing butterfly, Heliconius charithonia (Nymphalidae), in a 0.05 ha garden in Miami, Florida, for 2 years to answer the following questions: (1) How stable is a suburban, subtropical population of this widespread neotropical butterfly? (2) What are the major factors influencing its population dynamics? (3) What are the implications of adult mobility regarding gene flow within and between fragmented urban populations of this species? A mark-recapture study indicated that adult population size averaged 59 individuals (range: 9-115 individuals). Peak numbers occurred in mid-wet season (September) in 1996 and in the late dry and early wet seasons (April through June) in 1997. Fluctuations in size of the adult population paralleled changes in biomass of the larval food plant, Passiflora incense. Population sex ratio was consistently male-biased (68% males). Reproduction occurred year-round, and parasitism by a trichogrammatid wasp killed about 50% of Heliconius eggs throughout the year. Recruitment of adults from chrysalises produced in the garden and deaths, rather than immigration and emigration, accounted for most numerical changes. Both males and females apparently adjust their home range locations in response to changes in the biomass of Passiflora plants. Females search these plants for suitable oviposition sites, and males search them for female pupae (mates). In addition to relatively high mortality from egg parasitism, fluctuations in the number of suitable oviposition sites and amount of larval food limited recruitment into the adult butterfly population. High adult mobility probably results in substantial gene flow within and between populations of this butterfly in urban south Florida.

Germinable soil seed banks in a tropical savanna: seasonal dynamics and effects of fire.

Abstract The germinable soil seed bank of a tropical eucalypt savanna of north‐eastern Australia was found to be dominated by grasses and forbs, with seed bank density ranging from 58 to 792 seeds per square metre, from a total of 53 species. Late dry season fires and the fire‐related cues, heat shock and smoke, broke the seed dormancy of a range of tropical savanna species. Heat shock promoted the germination of the species groups natives, exotics, subshrubs, ephemeral and twining perennial forbs, and the common species Indigofera hirsuta, Pycnospora lutescens and Triumfetta rhomboidea. Exposure to smoke at ambient temperature promoted germination from the soil seed bank of the species groups combined natives, upright perennial forbs and grasses, as well as the common grasses Digitaria breviglumis and Heteropogon triticeus. The germinable soil seed bank varied seasonally, increasing from the mid wet season (February) and early dry season (May) to a maximum in the late dry season (October). The effect of recent fire history on soil seed bank dynamics was limited to the immediate release of some seed from dormancy; a reduction in seed densities of subshrubs and monocots, other than grasses, in recently burnt savanna; and enhanced seed density of the ephemeral I. hirsuta in the year following fire. The seed banks of most savanna species were replenished in the year following burning.

Carbon monoxide, regional‐scale transport, and biomass burning in tropical continental Southeast Asia: Observations in rural Thailand

Surface CO variations from continuous measurements during 1997–2000 at a tropical site in rural Thailand are reported for the first time. The CO seasonal cycle at Srinakarin (14°22′N, 99°07′E, 296 m above sea level) shows a maximum during the late dry season (February–March) and a minimum during the midwet season (June–August) with a larger amplitude than other remote sites in the Northern Hemisphere. The 4‐year annual average, averaged monthly minimum, and averaged monthly maximum of CO mixing ratios are 260, 97, and 560 ppbv, respectively. The long‐range transport of air masses driven by the Asian monsoon and biomass burning activity in continental Southeast Asia are found to be the main factors controlling CO variation in Thailand. Trajectory analysis indicates that during the wet season when the southwest monsoon from the Indian Ocean prevails, relatively low CO mixing ratios of 101 ± 32 ppbv on average are observed. Meanwhile, an average of 306 ± 83 ppbv of CO is observed when the site is influenced by regionally polluted continental air transported by the northeast monsoon from East Asia during the early dry season. Air mass transport, however, cannot explain high CO mixing ratios during the late dry season. Analysis of fire hot spots from the Along Track Scanning Radiometer (ATSR) satellite data indicates that the seasonal cycle of biomass burning in continental Southeast Asia is regular and is at a maximum in March, coincident with the CO maximum. The good correlation between CO and the number of ATSR hot spots provides evidence that this high CO during the late dry season is due to biomass burning in continental Southeast Asia. In addition, we found possible influences from the 1997 Indonesian fires and the 1998 Siberian Fires on the CO variations at Srinakarin.

Grass composition and rangeland condition of the major grazing areas in the mid Rift Valley, Ethiopia

A range inventory and condition study was conducted in three altitude zones: lowland (1500-1700m), medium altitude (1700-2000m), and highland (2000-2500m). Each altitude zone was stratified into four or five important grazing areas. One area represented lightly grazed government ranches or parks which were used as benchmarks, another area represented the seasonal grazing areas with an intermediate grazing pressure and the remaining were the heavily grazed roadsides, lakeshores and other communal grazing lands. The range condition assessment was based on the composition of the herbaceous layer, basal cover, litter cover, relative number of seedlings, age distribution of grasses, soil erosion and soil compaction. Dry matter was sampled in the mid-wet season to assess the relationship between available dry matter and range condition. A total of 36 grass species, 3 legume species, 2 sedge species, 15 other herbs and 31 species of trees were identified. The palatable Cenchrus ciliaris was dominant in the benchmarks and seasonally grazed areas of the lowland while Hyparrhenia spp. dominated in the same areas of the medium altitude. Cynodon dactylon, and the non-palatable Eleusine floccifolia and Pennisetum schimperi were dominant on heavily grazed areas of the lowland, medium altitude and highland, respectively. The total score for range condition of the benchmarks (34 out of 50 points), was significantly higher than that of the seasonally grazed areas (26), the heavily grazed communal grazing areas (19), roadsides (16) and lakeshores (17) (P<0.05). The highlands showed a higher score for benchmarks and seasonally grazed areas only. There was a significant linear relationship between available dry matter of grasses and range condition (excluding unpalatable pioneer grasses, r2 = 0.56, P<0.01). Seasonally grazed areas were identified as key sites for pasture improvement since these are privately owned and managed. Pasture improvement will reduce the grazing pressure on the heavily grazed roadsides, lakeshores and other communally grazed areas.