The El Niño southern oscillation and malaria epidemics in South America

A better understanding of the relationship between the El Ni?o Southern Oscillation (ENSO), the climatic anomalies it engenders, and malaria epidemics could help mitigate the world-wide increase in incidence of this mosquito-transmitted disease. The purpose of this paper is to assess the possibility of using ENSO forecasts for improving malaria control. This paper analyses the relationship between ENSO events and malaria epidemics in a number of South American countries (Colombia, Ecuador, French Guiana, Guyana, Peru, Suriname, and Venezuela). A statistically significant relationship was found between El Ni?o and malaria epidemics in Colombia, Guyana, Peru, and Venezuela. We demonstrate that flooding engenders malaria epidemics in the dry coastal region of northern Peru, while droughts favor the development of epidemics in Colombia and Guyana, and epidemics lag a drought by 1 year in Venezuela. In Brazil, French Guiana, and Ecuador, where we did not detect an ENSO/malaria signal, non-climatic factors such as insecticide sprayings, variation in availability of anti-malaria drugs, and population migration are likely to play a stronger role in malaria epidemics than ENSO-generated climatic anomalies. In some South American countries, El Ni?o forecasts show strong potential for informing public health efforts to control malaria.     

El Niño effects on the dynamics of terrestrial ecosystems

New studies are showing that the El Ni?o Southern Oscillation (ENSO) has major implications for the functioning of different ecosystems, ranging from deserts to tropical rain forests. ENSO-induced pulses of enhanced plant productivity can cascade upward through the food web invoking unforeseen feedbacks, and can cause open dryland ecosystems to shift to permanent woodlands. These insights suggest that the predicted change in extreme climatic events resulting from global warming could profoundly alter biodiversity and ecosystem functioning in many regions of the world. Our increasing ability to predict El Ni?o effects can be used to enhance management strategies for the restoration of degraded ecosystems.     

Disease resistance in Arabidopsisthaliana increases the competitive ability and the predicted probability of long‐term ecological success under disease pressure

Evidence is mounting that flowering by the mast-fruiting Dipterocarpaceae in Southeast Asia is triggered by ENSO events such that seeds are dispersed at the end of ENSO droughts. These droughts induce substantial defoliation and mortality of canopy trees, producing a favorable environment for seedling recruitment in the forest understory. Therefore, seedling release following droughts may have selected for synchronized, supra-annual fruiting in these rain forests. Currently, mast fruiting in Southeast Asia is generally regarded as an evolutionary response to seed predation by nomadic vertebrates. Separating the two causes for mast fruiting, seedling release and predator satiation, may be difficult if they are coupled in nature by ENSO droughts. Nevertheless, if the cue for masting is environmental, then the post-ENSO seedling environment should be considered a potential cause for masting, and if it operates in conjunction with predator satiation, then it may have provided the initial stimulus for supra-annual synchrony in fruiting.     

New cases of Diphyllobothrium pacificum (Nybelin, 1931) Margolis, 1956 human infection in North of Chile,probably related with El Niño phenomenon, 1975-2000

The effect of El Ni?o/ENSO on terrestrial atmosphere appears to be extremely clear. However there are outstanding evidences showing its effect on humans and their activities. In fact, prevalence of some parasitic infections have increased during El Ni?o phenomenon. The reasons for that are the migrations of sylvatic mammals, fishes and birds as well as by environmental contamination. In this report, we show evidence respect of new cases of human infection by Diphyllobothrium pacificum clearly associated with a cyclic manifestation of El Ni?o in the Chilean Pacific coast during 1975-2000.     

Observed relationships between El Niño‐Southern Oscillation,rainfall variability and vegetation and fire history on Halmahera,Maluku, Indonesia

A temporally high‐resolution palynological study of the uppermost section of core MD98‐2180 from Kau Bay, Halmahera, Indonesia, provides a vegetation and fire record covering the last 250 years. The record is compared with the Maluku Rainfall Index, Southern Oscillation Index (SOI) and southern hemisphere winter sea surface temperatures (SST) for the central Pacific Ocean based on instrumental data, as well as reconstructions of the SOI and the central Pacific SST and historically recorded El Niño events. The results show that significant El Niño events are generally associated with increased representation of Dipterocarpaceae pollen, probably reflecting the mass‐flowering of this taxon during El Niño‐Southern Oscillation (ENSO) droughts, and elevated charcoal levels, reflecting a greater incidence of fires during these extremely dry periods, while humid phases show increased fern numbers. Our findings demonstrate that pollen records ‘ecological’ in scale can provide useful additional proxy records of ENSO events.     

Mass flowering of dipterocarp forests in the aseasonal tropics

At irregular intervals of 2 to 10 years the aseasonal tropical rain forests in west Malesia come into heavy mass flowering, followed by mast fruiting. During a heavy flowering almost half the mature individuals and over 80% of the canopy and emergent tree Species in a forest may flower. This involves over 200 tree species in a forest flowering over a short period of 3–4 months. The pollination needs during a mass flowering appears to be overcome in several ways. A rapid increase in the number of pollinators seems to occur in the forest. This is partly caused by the migration of pollinators from the fringes of the forest to forage on the superabundance of flowers. At the same time, some groups of plants which share common pollinators appear to reduce pollinator competition by flowering in interspecific sequence. Many members of the family Dipterocarpaceae have evolved sequential flowering too. They also share unique pollinators, common flower thrips which appear to build up rapidly in numbers by feeding and breeding on the millions of dipterocarp flower buds which are present several weeks before the flowering. The environmental cue for this irregular, but widespread mass flowering can be traced to a small dip of about 2° C below mean night-time temperature for 4 or 5 nights. The conditions for such temperature drops occur during El Nino events.     

Effects of El Niño drought on seedling dynamics in a seasonally dry tropical forest in Northern Thailand

As El Niño is predicted to become stronger and more frequent in the future, it is crucial to understand how El Niño-induced droughts will affect tropical forests. Although many studies have focused on tropical rainforests, there is a paucity of studies on seasonally dry tropical forests (SDTFs), particularly in Asia, and few studies have focused on seedling dynamics, which are expected to be strongly affected by drought. Seedlings in SDTFs are generally more drought-tolerant than those in the rainforests, and the effects of El Niño-induced droughts may differ between SDTF and tropical rainforests. In this study, we explored the impact of El Niño-induced drought at an SDTF in northern Thailand by monitoring the seedling dynamics at monthly intervals for 7 years, including a period of strong El Niño. The effects were compared between two forest types in an SDTF: a deciduous dipterocarp forest (DDF), dominated by deciduous species, and an adjacent lower montane forest (LMF) with more evergreen species. El Niño-induced drought increased seedling mortality in both the forest types. The effect of drought was stronger in evergreen than in the deciduous species, resulting in higher mortality in the LMF during El Niño. However, El Niño increased seedling recruitment only in the DDF, mainly because of the massive recruitment of the deciduous oak, Quercus brandisiana (Fagaceae), which compensated for the mortality of seedlings in the DDF. As a result, El Niño increased seedling density in the DDF and decreased it in the LMF. This is the first long-term study to identify the differences in the impacts of El Niño on seedlings between the two forest types, and two leaf habits, evergreen and deciduous, in Southeast Asia. Our findings suggest that future climate change may alter the species composition and spatial distribution of seedlings in Asian SDTFs.     

El Niño-Southern Oscillation, rainfall, temperature and Normalized Difference Vegetation Index fluctuations in the Mara-Serengeti ecosystem

Understanding long-term climatic variability is basic to wise management and conservation of biodiversity. We analysed temporal variations in the local rainfall, temperature, Normalized Difference Vegetation Index and the hemispheric El Niño-Southern Oscillation (ENSO), using the Southern Oscillation Index and how they co varied in the Mara-Serengeti ecosystem of Kenya and Tanzania. Local rainfall showed a striking temporal variability and an evident 5-year quasi-periodicity in the ecosystem. Severe droughts were a recurrent/persistent feature of the ecosystem but extreme floods were relatively infrequent. The timings of droughts and floods coincided with strong episodes in the activities of the ENSO phenomenon. Above-average rainfall often accompanied cold ENSO episodes and below-average rainfall warm ENSO events, contrary to past generalizations suggesting that warm ENSO events are only associated with above-average rainfall whereas cold ENSO events with below-average rainfall in equatorial East Africa. Both minimum and maximum temperatures were below-normal during cold ENSO episodes and above-normal during warm ENSO events. Rising temperatures and declining rainfall throughout the 1990s and early 2000s, with unprecedently prolonged and strong ENSO episodes, engendered progressive habitat desiccation and reduction in vegetation production in the ecosystem. This exacerbated the debilitating effects of adverse weather on local plant and animal communities, resulting in high mortalities of ungulates.     

Population fluctuations of light-attracted chrysomelid beetles in relation to supra-annual environmental changes in a Bornean rainforest

In Southeast Asian tropical rainforests, two events, severe droughts associated with the El Ni?o-Southern Oscillation and general flowering, a type of community-wide mass flowering, occur at irregular, supra-annual intervals. The relationship between these two supra-annual events and patterns of insect population fluctuations has yet to be clearly elucidated. Leaf beetles (Chrysomelidae) are major herbivores and flower-visitors of canopy trees, affecting their growth and reproduction and, in turn, affected by tree phenology; but their population fluctuations in the Southeast Asian tropics have not been extensively investigated. We examined population fluctuation patterns of the 34 most dominant chrysomelid species in relation to the two supra-annual events by conducting monthly light-trapping over seven years in a lowland dipterocarp forest in Borneo. Our results showed large community variation in population fluctuation patterns and a supra-annual (between-year) variation in abundance for most of the dominant chrysomelids that was significantly larger than the annual (within-year) variation. Specifically, in response to a severe drought in 1998, chrysomelid species exhibited different population responses. These results show that population fluctuations of individual species, rather than the entire assemblage, must be analyzed to determine the effects of changes in environmental conditions on the structure of insect assemblages in the tropics, especially in regions where supra-annual environmental changes are relatively more important than seasonal changes.     

Potential impacts of a future persistent El Niño or La Niña on three subspecies of Australian butterflies

One of the major uncertainties of 21st century climate change is the potential for shifts to the intensity and frequency of the El Niño Southern Oscillation (ENSO) cycle. Although this phenomenon is known to have dramatic impacts on ecosystems regionally and globally, the biological consequences of climate change‐driven shifts in future ENSO events have been unexplored. Here, we investigate the potential impacts that a persistent El Niño, La Niña, or ‘Neutral' phase may have on species distributions. Using MaxEnt, we model the distribution of climatically suitable habitat for three northeast Australian butterfly subspecies (Doleschallia bisaltide australis, Hypolimnas alimena lamina, and Mycalesis terminus terminus) across the three ENSO phases. We find that the spatial extent and quality of habitat are lowest under conditions that would characterize a persistent El Niño (hot/dry). In contrast, suitable habitat is broadest under the warm/wet conditions associated with La Niña. Statistical analyses of the difference between pair‐wise combinations of suitability maps using Hellinger distance showed that projections for each subspecies and ENSO phase combination were significantly different from other combinations. The resilience of these, and other, butterfly (sub)species to changes in ENSO will be influenced by fluctuations in the strength of these events, availability of refugia, and life‐history characteristics. However, the population dynamics of wet‐ and dry‐season phenotypes of M. t. terminus and physiological limitations to high temperatures suggest that this subspecies, in particular, may have limited resilience should the strength and frequency of El Niño events increase.     

Resource-related variables drive individual variation in flowering phenology and mediate population-level flowering responses to climate in an asynchronously reproducing palm

Many tropical plant species show wide intra-population variation in reproductive timing, resulting in the protracted presence of flowering and fruiting individuals. Various eco-evolutionary drivers have been proposed as ultimate causes for asynchronous phenology, yet little is known about the proximate factors that control reproductive onset among individuals or that influence the proportion of trees producing new inflorescences within a population. We employed a nine-year phenological record from 178 individuals of the hyperdominant, asynchronously flowering canopy palm, Oenocarpus bataua (Arecaceae)¸ to assess whether resource-related variables influence individual- and population-level flowering phenology. Among individuals, access to sunlight increased rates of inflorescence production, while the presence of resource sinks related to current investment in reproduction—developing infructescences—reduced the probability of producing new inflorescences. At the population level, climate anomalies induced by El Niño Southern Oscillation (ENSO) affected the proportion of the population producing inflorescences through time. Moreover, the effects of ENSO anomalies on flowering patterns depended on the prevalence of developing infructescences in the population, with stronger effects in periods of low developing-infructescence frequency. Taken together, these results suggest that resource-related variables can drive phenological differences among individuals and mediate population-level responses to larger-scale variables, such as climate anomalies. Consequently, a greater focus on the role of resource levels as endogenous cues for reproduction might help explain the frequent aseasonal phenological patterns observed among tropical plants, particularly those showing high intra-population asynchrony.     

“El Niño” events recorded in dry-forest species of the lowlands of northwest Peru

The northwest coast of Peru (5°S, 80°W) is very sensitive to and impacted by the climate phenomenon El Niño-Southern Oscillation (ENSO). Though mainly desert, this warm, dry region contains an equatorial dry forest. We report the first dendrochronological studies from this region and identify several species that have dendrochronological potential. Short ring-width chronologies of Palo Santo (Bursera graveolens) show a well-developed response to the ENSO signal over the last 50 years and good inter-site correlations. Preliminary isotopic studies in Algarrobo (Prosopis sp.) also show evidence of the 1997–98 El Niño event. ENSO events have a strong effect on the variability in the growth of several species and thereby on the economy of rural communities where the wood is used for housing, cooking, furniture, tools, fodder and medicinal uses. The extensive use of wood in archeological sites also offers the possibility of ultimately developing longer records for some of these species.     

Phenological diversity in tropical forests

One of the most intriguing and complex characteristics of reproductive phenology in tropical forests is high diversity within and among forests. To understand such diversity, Newstrom et al. provided a systematic framework for the classification of tropical flowering phenology. They adopted frequency and regularity as criteria with priority, and classified plants in La Selva, Costa Rica, where most plants reproduced more than once a year irregularly. Many other studies have demonstrated annual cycles corresponding to rainfall patterns at the community level in Neotropical forests, including La Selva. On the other hand, supraannual flowering synchronized among various plant species, called general flowering, is known from aseasonal lowland dipterocarp forests in Southeast Asia. Within both forests, a wide spectrum of flowering patterns is found. This range of patterns suggests the great potential of tropical phenological studies to explore the selective pressures on phenology. Various abiotic and biotic factors can be selective agents. The shared pollinators hypothesis suggests that plant species sharing pollinators segregate flowering temporarily to minimize interspecific overlap in flowering times and thus minimize ineffective pollination or competition for pollinators, indicating strong phylogenetic constraints in timing and variation of flowering. Comparison of phenology within and among forests may help our understanding of phenological diversity. Attempts are now being made to develop a common language to communicate concepts and render interpretations of data more compatible among investigators and to create a network to promote comparative studies. Received: September 8, 2000 / Accepted: January 30, 2001     

Plant reproductive phenology over four years including an episode of general flowering in a lowland dipterocarp forest,Sarawak, Malaysia

The first systematic observation of a general flowering, a phenomenon unique to lowland mixed-dipterocarp forests in Southeast Asia, is presented. During general flowering, which occurs at irregular intervals of 3–10 yr, nearly all dipterocarp species together with species of other families come heavily into flower. We monitored reproductive phenology of 576 individual plants representing 305 species in 56 families in Sarawak, Malaysia. Observations continued for 53 mo from August 1992 and covered one episode of a general flowering cycle. Among 527 effective reproductive events during 43 mo, 57% were concentrated in the general flowering period (GFP) of 10 mo in 1996. We classified 257 species into flowering types based on timing and frequency of flowering. The most abundant type was “general flowering” (35%), which flowered only during GFP. The others were “supra-annual” (19%), “annual” (13%), and “sub-annual” (5%) types. General flowering type and temporal aggregation in reproductive events were commonly found among species in various categories of taxonomic groups, life forms, pollination systems, and fruit types. Possible causes for general flowering, such as promotion of pollination brought about by interspecific synchronization and paucity of climatic cues suitable for flowering trigger, are proposed, in addition to the predator satiation hypothesis of Janzen (1974) .     

Seasonal, El Niño and longer term changes in flower and seed production in a moist tropical forest

It has recently been reported that humid tropical forests are changing rapidly in response to global anthropogenic change and that these forests experience greater tree mortality and even fire during droughts associated with El Niño events. The former reports are controversial largely because a single method has been used – repeated censuses of tree plots. The latter reports focus on recent extreme El Niño events. Here, we show that flower and seed production both increase during El Niño events in an old-growth tropical forest in Panama. Flower production, but not seed production, has also increased over the past 18 years. The sustained increase in flower production was greater for 33 liana species than for 48 tree species. These results indicate that moderate El Niño events favour seed production, document long-term increases in flower production for the first time, and corroborate long-term increases in the importance of lianas using independent methods. Changes in levels of solar irradiance might contribute to all three patterns.     

“El Niño” events recorded in dry-forest species of the lowlands of northwest Peru

The northwest coast of Peru (5°S, 80°W) is very sensitive to and impacted by the climate phenomenon El Niño-Southern Oscillation (ENSO). Though mainly desert, this warm, dry region contains an equatorial dry forest. We report the first dendrochronological studies from this region and identify several species that have dendrochronological potential. Short ring-width chronologies of Palo Santo (Bursera graveolens) show a well-developed response to the ENSO signal over the last 50 years and good inter-site correlations. Preliminary isotopic studies in Algarrobo (Prosopis sp.) also show evidence of the 1997–98 El Niño event. ENSO events have a strong effect on the variability in the growth of several species and thereby on the economy of rural communities where the wood is used for housing, cooking, furniture, tools, fodder and medicinal uses. The extensive use of wood in archeological sites also offers the possibility of ultimately developing longer records for some of these species.     

Changes in rain forest butterfly diversity following major ENSO-induced fires in Borneo

Aims Throughout South‐East Asia, droughts associated with ENSO (El Niño Southern Oscillation) events have resulted in large‐scale fires affecting millions of hectares of rain forest. However, the long‐term impacts of these fires on the rain forest faunas are only poorly understood. Our aim was to study the recovery of rain forest butterfly assemblages following the 1997–98 ENSO event, which resulted in the largest‐scale fires in the recorded history of the region. Location A 420‐km² area in the Balikpapan‐Samarinda region of East Kalimantan, Indonesian Borneo. Methods Four landscapes were assessed after the 1997–98 ENSO event, including one landscape that was assessed prior to the event. Comparisons of species richness, species composition and guild abundance were made among landscapes and years. The relative importance of environment, geographical distance between sampling sites, and time between sampling years was quantified during the succession phase using a variance partitioning technique. Results The fires dramatically altered the butterfly community and resulted in a major decline in observed species richness within the landscape surveyed prior to the ENSO event. Following fires in 1998, butterfly assemblages in all landscapes were dominated by large‐winged generalist species. During 1999 and 2000, assemblages became increasingly dominated by smaller specialist species. Species endemic to Borneo that were present before fires were absent in 2000, despite intensive sampling over enhanced spatial and environmental scales. Community similarity was significantly dependent upon local environmental variables, geographical distance between sampling sites, and time between sampling years. Together, these explained over 52% of the observed variation in samples. Conclusions The importance of geographical distance between sampling sites indicates that recovery was dependent upon colonization from proximate habitats. Despite an apparent trend of return to pre‐ENSO community structure, low species richness throughout the survey area indicates that full recovery had not taken place by 2000.     

Teleconnection between tree growth in the Amazonian floodplains and the El Niño–Southern Oscillation effect

There is a limited knowledge about the El Niño–Southern Oscillation (ENSO) effects on the Amazon basin, the world's largest tropical rain forest and a major factor in the global carbon cycle. Seasonal precipitation in the Andean watershed annually causes a several month‐long inundation of the floodplains along the Amazon River that induces the formation of annual rings in trees of the flooded forests. Radial growth of trees is mainly restricted to the nonflooded period and thus the ring width corresponds to its duration. This allows the construction of a tree‐ring chronology of the long‐living hardwood species Piranhea trifoliata Baill. (Euphorbiaceae). El Niño causes anomalously low precipitation in the catchment that results in a significantly lower water discharge of the Amazon River and consequently in an extension of the vegetation period. In those years tree rings are significantly wider. Thus the tree‐ring record can be considered as a robust indicator reflecting the mean climate conditions of the whole Western Amazon basin. We present a more than 200‐year long chronology, which is the first ENSO‐sensitive dendroclimatic proxy of the Amazon basin and permits the dating of preinstrumental El Niño events. Time series analyses of our data indicate that during the last two centuries the severity of El Niño increased significantly.     

ENSO事件对中国森林火险天气的影响

ENSO事件影响中国的气候和森林火险天气,研究ENSO事件对中国各植被区火险天气的影响对于提高森林火险预报准确性有科学和实践意义。利用1951—2016年中国地面国际交换站气候资料的日值数据集(V3.0)数据计算每日的森林火险天气指数(FWI),根据MODIS过火区产品计算各植被区2001—2016年的森林过火面积,分别按事件情景(弱、中、强和超强厄尔尼诺事件以及弱、中和强拉尼娜事件)统计各植被区对应的火险期气温、降水、FWI和过火面积。结果表明: 1950—2016年,共发生19次厄尔尼诺事件和14次拉尼娜事件。受强或超强厄尔尼诺事件影响,西北地区春季火险期的日均最高气温明显升高,而中温带半干旱草原区春季火险期的日均最高气温在中厄尔尼诺年显著降低。厄尔尼诺年,南方和西南林区火险期的降水量一般会增加,中、低强度的拉尼娜事件会减少大部分区域的火险期降水量,但强拉尼娜事件导致大部分林区火险期的降水量增加。弱厄尔尼诺事件导致南方林区FWI降低;强或超强厄尔尼诺事件导致南方和西南林区的FWI有所降低,而北方林区的FWI有所升高。ENSO事件对各植被区FWI的影响存在显著的空间差异性。2001—2016年,当火险期的季节火险严重程度(SSR)显著变化时,暖温带湿润/半湿润地区落叶阔叶林区、中北亚热带湿润地区阔叶林区和热带南亚热带湿润地区阔叶林区的过火面积与SSR的变化一致,其他区域的过火面积受ENSO事件的影响不明显。     

Increased extreme drought events in south–central China since the last century：Evidence from oxygen isotope signatures preserved in tree ring cellulose

Tree-ring cellulose oxygen isotope ratios (δ¹⁸O) is a well-established proxy for hydroclimatic conditions in monsoon Asia. We reconstructed June–October relative humidity (RH_J–O) variations from 1808 to 2017, based on tree-ring cellulose δ¹⁸O data, which explain 46.2% of the actual RH variance in the Nanyue region, south–central China. Extreme wet events occurred frequently prior to the 1900s, but there have been more extreme dry events since the 1900s, apart from the late 1930s and early 1950s. Periodicity analysis revealed that the reconstructed RH_J–O records show obvious 15–30 years cycles from the 1830–1970s. The multi-decadal signals may reflect the effect of the Pacific Decadal Oscillation (PDO) on hydroclimate. In the positive PDO phase, there is drying in south–central China, which is related to a weaker East Asian summer monsoon (EASM) via the Pacific–Japan teleconnection. The decadal signal has weakened since the 1970s. In addition, the reconstructed RH_J–O record shows strong interannual variations, which may be related to the Central Pacific El Niño–Southern Oscillation (CP ENSO). During extreme CP El Niño events, there is a weaker EASM due to the Pacific–Japan teleconnection, and the study site experienced drought. Our reconstructed moisture record is characterized by a decreasing influence from the PDO and increasing influence from the CP ENSO in recent decades. Moreover, the frequency of CP ENSO events is projected to increase under anthropogenic warming. Consequently, more extreme droughts which are related to CP ENSO events may increase in the south–central China in near future.