Detection of seasonal variability in microclimatic borders and ecotones between forest and savanna

Along eight forest-savanna transects, the borders, the width of associated ecotones, and the depth-of-edge influence (DEI) towards the forest interior were determined on the basis of microclimatic parameters. The analysis focused on the seasonal variability of microclimate at the forest-savanna ecotone that has so far rarely been investigated. The study was located in an intact mosaic of semi-deciduous forests and savanna in the Comoé National Park (north-eastern Ivory Coast). The microclimatic parameters air temperature, air humidity, and vapor pressure deficit were measured from the dry season (February) until the rainy season (September) during five measurement periods (MP). Borders and ecotones including their confidence intervals were determined by a border-and-ecotone detection analysis, which is based on non-linear regression analysis. The ecotone limits were interpreted as DEI towards the two habitats. During the dry season, the microclimatic border between forest and savanna was located further towards the forest interior than during the rainy season. This may be caused by different foliation patterns of tree species at the forest interior and the forest boundary, with the latter being completely defoliated during the dry season. In addition, the variability of microclimatic parameters was higher and differences between forest and savanna were less pronounced during the dry season. The minimum DEI towards the forest interior was 27.4±15.5 m for air humidity in the rainy season (MP-5). The maximum DEI of 137.3 ±138.3 m occurred for air temperature in the dry season (MP-1). The average DEI for all microclimate parameters and MPs was 50.5 m. These DEI values are similar to observations from temperate and tropical forest boundaries in the literature. As microclimate borders proved to shift over the seasons, detailed knowledge of species’ responses to this variability appears to be essential for predicting concomitant dynamics of forest core areas.     

Monitoring and predictive mapping of floristic biodiversity along a climatic gradient in ENSO's terrestrial core region,NW Peru

The tropical dry forests of NW Peru are heavily shaped by the El Niño Southern Oscillation (ENSO), where especially El Niño brings rain to arid to semi-arid areas. However, the resulting effects on biodiversity patterns remain largely unknown as well as the effect of environmental variables on the floristic composition under varying rainfall patterns. Therefore, we studied the spatio-temporal effects of different ENSO episodes on floristic biodiversity along a climatic gradient ranging from the coastal desert to the Andean foothills. We sampled 50 vegetation plots in four years representing different ENSO episodes. To highlight the spatio-temporal changes in floristic composition and beta diversity across ENSO episodes, we predicted ordination scores with a Generalized Additive Model. We applied variation partitioning to test if topographic or edaphic variables gained in importance during more humid ENSO episodes. Additionally, we executed an irrigation–fertilization experiment to quantify the beneficial effects of the water–nutrient interaction under different simulated ENSO rainfall scenarios. Plant species richness increased under humid conditions during the humid La Niña (2012) and the moderate El Niño (2016), and slightly decreased under the very humid conditions during the coastal El Niño (2017). The spatial prediction revealed that specific vegetation formations became more pronounced with increasing water input, but that a large water surplus led to the disruption of the strict order along the climatic gradient. Edaphic and topographic variables gained in importance with increased water availability (2012 and 2016), however, this effect was not further amplified under very wet conditions (2017). The experiment showed that plant cover under Super Niño conditions was three times higher when fertilized. Overall, our spatial predictions concede detailed insights into spatio-temporal ecosystem dynamics in response to varying rainfall caused by different ENSO episodes while the results of the experiment can support farmers regarding a sustainable agrarian management.     

Effects of climate on historical fire regimes (1451–2013) in Pinus hartwegii forests of Cofre de Perote National Park,Veracruz, Mexico

Cofre de Perote National Park (CPNP) in Veracruz, Mexico is part of the Transmexican Volcanic Belt, and its Pinus hartwegii forests reflect a balance between the various natural factors that represent the region's climatology and hydrology. Like many other areas in this region, the historical fire regimes of these forests and their relationship with climate are unknown, but are needed for sustainable management plans. The main objectives of this study were to reconstruct the historical fire regime in a Pinus hartwegii forest and decipher the influenced of climate. Our investigation focused in two study areas, Valle la Teta (VT) and Barranca Honda (BH). The VT study area was divided into three sites based on humidity and elevation: 1) Humid (VTH), 2) Dry Low (VTDL) and 3) Dry High (VTDH). The approximated area for each site was ​​30, 30, 35 and 50 ha, for VTH, VTDL, VTDH and BH, respectively. We collected 162 fire scarred samples to reconstruct the fire history for the last 550 years (1461−2013). The fire scarred samples contained 1240 fire scars, with most fires occurring in spring (95 %) or summer (5%). Prior to 1973, these sites were characterized by a frequent surface fire regime. In all four sites, the mean fire intervals ranged from 5 to 6 years (for fires that scarred ≥ 10 % of the samples) and 13–23 years (for fires that scarred ≥ 25 % of the samples). Extensive fires (≥ 10 %) coincided with significantly dry conditions based on the Standardized Precipitation Index (SPI), influenced by El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation Index (PDO). We also found a significant relationship between fire occurrence and ENSO, both in its warm phase, El Niño (21 fires ≥ 10 %) and in its cold phase, La Niña (32 fires ≥ 10 %). Synchronization of the cold phase of ENSO (La Niña) with the cold phase of the PDO (negative), facilitated severe drought conditions, resulting in fires with the greatest spatial extent. Since 1973, extensive fires have been absent from the study area most likely due to anthropogenic activities including active fire suppression. These results show a strong climate-fire relationship in these high elevation forests. The lack of fire in the last four decades is concerning and could potentially lead to unnatural stand-replacing fires, unless the historical fire regime is restored to maintain natural processes and increase forest resilience.     

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.     

Preliminary Evidence of the Importance of ENSO in Modifying Food Availability for White‐tailed Deer in a Mexican Tropical Dry Forest1

The influence of El Niño/Southern Oscillation (ENSO) on rainfall and its possible effect on availability of food for white‐tailed deer (Odocoileus virginianus) in a tropical dry forest in the Pacific coast of Mexico was studied. From 1977 to 2003 there were three significant El Niño and La Niña events. During El Niño years rainfall decreased during the wet season ( June to October) and increased during the dry season (November to May), with the opposite effect during La Niña years. Plant diversity was monitored in permanent plots during the wet and dry seasons of 1989–1993. The results provide evidence that ENSO events affect deer food availability, particularly in the dry season.     

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.     

Large tree mortality and the decline of forest biomass following Amazonian wildfires

Surface fires in Amazonian forests could contribute as much as 5% of annual carbon emissions from all anthropogenic sources during severe El Niño years. However, these estimates are based on short‐term figures of post‐burn tree mortality, when large thicker barked trees (representing a disproportionate amount of the forest biomass) appear to resist the fires. On the basis of a longer term study, we report that the mortality of large trees increased markedly between 1 and 3 years, more than doubling current estimates of biomass loss and committed carbon emissions from low‐intensity fires in tropical forests.     

Edge influence on plant litter biomass in forest and savanna in the Brazilian cerrado

Edge influence, characterized by differences in ecosystem characteristics between the edge and the interior of remnants in fragmented landscapes, affects a variety of organisms and ecosystem processes. An important feature that may be affected by edges is the amount of plant litter, which provides important habitat for a large variety of organisms and influences ecological processes such as fire dynamics. We studied edge influence on plant litter and fine woody debris in the cerrado of São Paulo state, south‐eastern Brazil. We collected, sorted, dried and weighed plant litter along 180 m‐long transects perpendicular to three savanna and eleven forest edges adjacent to different anthropogenic land uses, with four to five transect per edge. There tended to be less biomass of the finer portions of fine woody debris at both savanna and forest edges. Graminoid litter at savanna edges was greater than in the corresponding interior areas, whereas other litter portions were either unaffected by edges or did not show consistent patterns in either savanna or forest. Edge influence was usually restricted to the first 20 m from the edge, was not influenced by edge characteristics and exhibited no clear differences between savanna and forest areas. Several mechanisms may have led to the variable patterns observed including variation in the plant community, plant architecture, and invasive species. The edge‐related variation in plant litter may putatively lead to, for example, increased fire frequency and intensity at the savanna edges and altered trophic dynamics at forest edges; the mechanisms and consequences of this edge influence should be addressed in future studies.     

Late glacial and Holocene vegetation,climate and fire history inferred from Lagoa Nova in the southeastern Brazilian lowland

The pollen and charcoal record of a 1,500-cm-long lake sediment core from Lagoa Nova allows a reconstruction of vegetation, climate and fire history in the Atlantic lowland of southeastern Brazil. Today the potential vegetation of the study region would be dense and tall semi-deciduous forest, related to a dry season of 4 months and 1,250 mm precipitation per year. The lowermost core section of Lagoa Nova is probably of late Glacial age and contains only few, poorly preserved pollen grains, indicating dry environmental conditions. Pollen preservation was good above 1,005-cm core depth. Extrapolating from four radiocarbon dates, this interval represents about the last 10,000 years. During the early Holocene (until about 8,500 b.p.), the landscape was dominated by savanna of the campo cerrado type (open shrub woodland), with frequent trees of Curatella americana and small areas of gallery forests along the drainage system. Savanna fires, probably natural, were frequent at that time. The palaeovegetation pattern is consistent with a long dry season of about 6 months and annual precipitation lower than today. Then, up to about 7,560 b.p., gallery forests expanded in the valleys, reflecting a shorter dry season of about 5 months and somewhat higher annual rainfall. Fire was less frequent during this wetter period. Between about 7,560 and 6,060 b.p., savanna expanded and gallery forests retreated, indicating a return to drier climatic conditions of probably between 5 and 6 months dry season and lower precipitation. Fire was again frequent, but not as frequent as during the early Holocene. During the mid to late Holocene period between about 6,060 and 2,180 b.p., the valleys were covered by semi-deciduous forest, but on the hills cerrado vegetation continued to grow. The dry season was probably around 5 months and rainfall was higher than in the preceding period. During the following period between about 2,810 and 600 b.p., the open cerrado on the hills changed to closed cerrado, reflecting wetter conditions with a shorter dry season than in the previous period. It was only after about 600 b.p. that dense semi-deciduous forests expanded throughout the study region, indicating the start of modern, wet climatic conditions with an annual dry season of about 4 months. Fire was nearly absent during this period. The reconstructed palaeoenvironment from the Lagoa Nova record is similar to that of Lago do Pires, indicating that changes in past vegetation, climate and fire frequency are regionally consistent in southeastern Brazil.     

Amazon drought and forest response: Largely reduced forest photosynthesis but slightly increased canopy greenness during the extreme drought of 2015/2016

Amazon droughts have impacted regional ecosystem functioning as well as global carbon cycling. The severe dry‐season droughts in 2005 and 2010, driven by Atlantic sea surface temperature (SST) anomaly, have been widely investigated in terms of drought severity and impacts on ecosystems. Although the influence of Pacific SST anomaly on wet‐season precipitation has been well recognized, it remains uncertain to what extent the droughts driven by Pacific SST anomaly could affect forest greenness and photosynthesis in the Amazon. Here, we examined the monthly and annual dynamics of forest greenness and photosynthetic capacity when Amazon ecosystems experienced an extreme drought in 2015/2016 driven by a strong El Niño event. We found that the drought during August 2015–July 2016 was one of the two most severe meteorological droughts since 1901. Due to the enhanced solar radiation during this drought, overall forest greenness showed a small increase, and 21.6% of forests even greened up (greenness index anomaly ≥1 standard deviation). In contrast, solar‐induced chlorophyll fluorescence (SIF), an indicator of vegetation photosynthetic capacity, showed a significant decrease. Responses of forest greenness and photosynthesis decoupled during this drought, indicating that forest photosynthesis could still be suppressed regardless of the variation in canopy greenness. If future El Niño frequency increases as projected by earth system models, droughts would result in persistent reduction in Amazon forest productivity, substantial changes in tree composition, and considerable carbon emissions from Amazon.     

Effects of fire and drought in a tropical eucalypt savanna colonized by rain forest

Aim This study documents the effects of multiple fires and drought on the woody structure of a north Australian savanna never grazed by domestic stock. Location The study was conducted in a 500 ha pocket of Eucalyptus‐dominated savanna surrounded by a late Quaternary lava flow. The flow is known as the Great Basalt Wall, located c. 50 km northeast of Charters Towers in semi‐arid north‐eastern Australia. This region was exposed to the largest 5‐year rainfall deficit on record between 1992 and 1996. Methods All individual woody plants were tagged within a 1.56 ha plot. Species were segregated into their habitat affinities (rain forest, ecotone, savanna) and regeneration strategy (resprouter, seeder). The survivorship of plants within these categories was analysed in relation to fire intensity from the first fire, and to each of four fires lit between 1996 and 2001. Results Before the first fire, the plot contained thirty‐one tree species including twenty‐one typical of the surrounding dry rain forest. These rain forest species were represented by small individuals and constituted <1% of the total basal area of woody plants. The basal area of savanna trees was 7.5 m² ha^?1 at the commencement of monitoring, although 31% had recently died and others had major crown damage. Further death of the drought debilitated savanna trees was substantial during the first year of monitoring and the basal area of live savanna trees declined to 1.1 m² ha^?1 after 5 years. Most species from both rain forest and savanna were classified as resprouters and are capable of regenerating from underground organs after fire. Species without this ability (rain forest seeders and ecotone seeders) were mostly eliminated after the first two consecutive fires. Among resprouters, survivorship declined as fire intensity increased and this was more pronounced for rain forest than for savanna species. Repeated burning produced a cumulative effect of decreasing survivorship for rain forest resprouters relative to savanna resprouters. Main conclusions The study provides evidence that savanna and rain forest trees differ in fire susceptibility and that recurrent fire can explain the restricted distribution of rain forest in the seasonally arid Australian tropics. The time of death of the savanna trees is consistent with the regional pattern after severe drought, and highlights the importance of medium term climate cycles for the population dynamics of savanna tree species and structure of Australian savannas.     

Seasonal variation in leaf traits between congeneric savanna and forest trees in Central Brazil: implications for forest expansion into savanna

The ecology of forest and savanna trees species will largely determine the structure and dynamics of the forest–savanna boundaries, but little is known about the constraints to leaf trait variation imposed by selective forces and evolutionary history during the process of savanna invasion by forest species. We compared seasonal patterns in leaf traits related to leaf structure, carbon assimilation, water, and nutrient relations in 10 congeneric species pairs, each containing one savanna species and one forest species. All individuals were growing in dystrophic oxisols in a fire-protected savanna of Central Brazil. We tested the hypothesis that forest species would be more constrained by seasonal drought and nutrient-poor soils than their savanna congeners. We also hypothesized that habitat, rather than phylogeny, would explain more of the interspecific variance in leaf traits of the studied species. We found that throughout the year forest trees had higher specific leaf area (SLA) but lower integrated water use efficiency than savanna trees. Forest and savanna species maintained similar values of predawn and midday leaf water potential along the year. Lower values were measured in the dry season. However, this was achieved by a stronger regulation of stomatal conductance and of CO₂ assimilation on an area basis (A _area) in forest trees, particularly toward the end of the dry season. Relative to savanna trees, forest trees maintained similar (P, K, Ca, and Mg) or slightly higher (N) leaf nutrient concentrations. For the majority of traits, more variance was explained by phylogeny, than by habitat of origin, with the exception of SLA, leaf N concentration, and A _area, which were apparently subjected to different selective pressures in the savanna and forest environments. In conclusion, water shortage during extended droughts would be more limiting for forest trees than nutrient-poor soils.     

Tropical and north Pacific teleconnections influence fire regimes in pine-dominated forests of north-eastern California, USA

Aim To assess the importance of drought and teleconnections from the tropical and north Pacific Ocean on historical fire regimes and vegetation dynamics in north‐eastern California. Location The 700 km² study area was on the leeward slope of the southern Cascade Mountains in north‐eastern California. Open forests of ponderosa pine (Pinus ponderosa var. ponderosa Laws.) and Jeffrey pine (P. jeffreyi Grev. & Balf) surround a network of grass and shrub‐dominated meadows that range in elevation from 1650 to 1750 m. Methods Fire regime characteristics (return interval, season and extent) were determined from crossdated fire scars and were compared with tree‐ring based reconstructions of precipitation and temperature and teleconnections for the period 1700–1849. The effect of drought on fire regimes was determined using a tree‐ring based proxy of climate from five published chronologies. The number of forest‐meadow units that burned was compared with published reconstructions of the El Niño/Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Results Landscape scale fires burned every 7–49 years in meadow‐edge forests and were influenced by variation in drought, the PDO and ENSO. These widespread fires burned during years that were dryer and warmer than normal that followed wetter and cooler years. Less widespread fires were not associated with this wet, then dry climate pattern. Widespread fires occurred during El Niño years, but fire extent was mediated by the phase of the PDO. Fires were most widespread when the PDO was in a warm or normal phase. Fire return intervals, season and extent varied at decadal to multi‐decadal time scales. In particular, an anomalously cool, wet period during the early 1800s resulted in widespread fires that occurred earlier in the year than fires before or after. Main conclusions Fire regimes in north‐eastern California were strongly influenced by regional and hemispheric‐scale climate variation. Fire regimes responded to variation that occurred in both the north and tropical Pacific. Near normal modes of the PDO may influence fire regimes more than extreme conditions. The prevalence of widespread teleconnection‐driven fires in the historic record suggests that variation in the Pacific Ocean was a key regulator of fire regimes through its influence on local fuel production and successional dynamics in north‐eastern California.     

Evapotranspiration of tropical peat swamp forests

In Southeast Asia, peatland is widely distributed and has accumulated a massive amount of soil carbon, coexisting with peat swamp forest (PSF). The peatland, however, has been rapidly degraded by deforestation, fires, and drainage for the last two decades. Such disturbances change hydrological conditions, typically groundwater level (GWL), and accelerate oxidative peat decomposition. Evapotranspiration (ET) is a major determinant of GWL, whereas information on the ET of PSF is limited. Therefore, we measured ET using the eddy covariance technique for 4–6 years between 2002 and 2009, including El Niño and La Niña events, at three sites in Central Kalimantan, Indonesia. The sites were different in disturbance degree: a PSF with little drainage (UF), a heavily drained PSF (DF), and a drained burnt ex‐PSF (DB); GWL was significantly lowered at DF, especially in the dry season. The ET showed a clear seasonal variation with a peak in the mid‐dry season and a large decrease in the late dry season, mainly following seasonal variation in net radiation (R_n). The R_n drastically decreased with dense smoke from peat fires in the late dry season. Annual ET forced to close energy balance for 4 years was 1636 ± 53, 1553 ± 117, and 1374 ± 75 mm yr^?1 (mean ± 1 standard deviation), respectively, at UF, DF, and DB. The undrained PSF (UF) had high and rather stable annual ET, independently of El Niño and La Niña events, in comparison with other tropical rainforests. The minimum monthly‐mean GWL explained 80% of interannual variation in ET for the forest sites (UF and DF); the positive relationship between ET and GWL indicates that drainage by a canal decreased ET at DF through lowering GWL. In addition, ET was decreased by 16% at DB in comparison with UF chiefly because of vegetation loss through fires.     

El Niño impacts on human-modified tropical forests: Consequences for dung beetle diversity and associated ecological processes

Our knowledge of how tropical forest biodiversity and functioning respond to anthropogenic and climate-associated stressors is limited. Research exploring El Niño impacts are scarce or based on single post-disturbance assessments, and few studies assess forests previously affected by anthropogenic disturbance. Focusing on dung beetles and associated ecological functions, we assessed (a) the ecological effects of a strong El Niño, (b) if post-El Niño beetle responses were influenced by previous forest disturbance, and (c) how these responses compare between forests impacted only by drought and those affected by both drought and fires. We sampled 30 Amazonian forest plots distributed across a gradient of human disturbance in 2010, 2016, and 2017—approximately 5 years before, and 3–6 and 15–18 months after the 2015–16 El Niño. We found 14,451 beetles from 98 species and quantified the beetle-mediated dispersal of >8,600 seed mimics and the removal of c. 30 kg of dung. All dung beetle responses (species richness, abundance, biomass, compositional similarity to pre-El Niño condition, and rates of dung removal and seed dispersal) declined after the 2015–16 El Niño, but the greatest immediate losses (i.e., in 2016) were observed within fire-affected forests. Previous forest disturbance also influenced post-El Niño dung beetle species richness, abundance, and species composition. We demonstrate that dung beetles and their ecological functions are negatively affected by climate-associated disturbances in human-modified Amazonian forests and suggest that the interaction between local anthropogenic and climate-related stressors merits further investigation.     

Climate regime shift and forest loss amplify fire in Amazonian forests

Frequent Amazonian fires over the last decade have raised the alarm about the fate of the Earth's most biodiverse forest. The increased fire frequency has been attributed to altered hydrological cycles. However, observations over the past few decades have demonstrated hydrological changes that may have opposing impacts on fire, including higher basin‐wide precipitation and increased drought frequency and severity. Here, we use multiple satellite observations and climate reanalysis datasets to demonstrate compelling evidence of increased fire susceptibility in response to climate regime shifts across Amazonia. We show that accumulated forest loss since 2000 warmed and dried the lower atmosphere, which reduced moisture recycling and resulted in increased drought extent and severity, and subsequent fire. Extremely dry and wet events accompanied with hot days have been more frequent in Amazonia due to climate shift and forest loss. Simultaneously, intensified water vapor transport from the tropical Pacific and Atlantic increased high‐altitude atmospheric humidity and heavy rainfall events, but those events did not alleviate severe and long‐lasting droughts. Amazonia fire risk is most significant in the southeastern region where tropical savannas undergo long seasonally dry periods. We also find that fires have been expanding through the wet–dry transition season and northward to savanna–forest transition and tropical seasonal forest regions in response to increased forest loss at the “Arc of Deforestation.” Tropical forests, which have adapted to historically moist conditions, are less resilient and easily tip into an alternative state. Our results imply forest conservation and fire protection options to reduce the stress from positive feedback between forest loss, climate change, and fire.     

El Niño,Host Plant Growth,and Migratory Butterfly Abundance in a Changing Climate

In the wet forests of Panama, El Niño typically brings a more prolonged and severe dry season. Interestingly, many trees and lianas that comprise the wet forests increase their productivity as a response to El Niño. Here, we quantify the abundance of migrating Marpesia chiron butterflies over 17 yr and the production of new leaves of their hostplants over 9 yr to test the generality of the El Niño migration syndrome, i.e., whether increased abundance of migrating insects and productivity of their food plants are associated with El Niño and La Niña events. We find that the quantity of M. chiron migrating across the Panama Canal was directly proportional to the sea surface temperature (SST) anomaly of the Pacific Ocean, which characterizes El Niño and La Niña events. We also find that production of new leaves by its larval host trees, namely Brosimum alicastrum, Artocarpus altilis, and Ficus citrifolia, was directly proportional to the SST anomaly, with greater leaf flushing occurring during the period of the annual butterfly migration that followed an El Niño event. Combining these and our previously published results for the migratory butterfly Aphrissa statira and its host lianas, we conclude that dry season rainfall and photosynthetically active radiation can serve as primary drivers of larval food production and insect population outbreaks in Neotropical wet forests, with drier years resulting in enhanced plant productivity and herbivore abundance. Insect populations should closely track changes in both frequency and amplitude of the El Niño Southern Oscillation with climate change.     

Guinean biodiversity at the edge: Rodents in forest patches of southern Mali

Southern Mali mainly belongs to the Sudanian savanna bioclimatic zone, but forest patches showing botanical affinities with Guinean humid forest remain as gallery forests or ravine forests. To characterize the rodent diversity of this area and check for the presence of some species of Guinean affinities in this group, rodent assemblages were sampled in four regions of southern Mali, using trapping and observational data in forest and surrounding habitats. Twenty-four species were recorded, comprising a representative sample of the expected overall diversity in this group according to rarefaction curves. Praomys rostratus was the dominant species in the most humid, closed lowland forest. Praomys daltoni was also present in this habitat type, being all the more abundant as habitat degradation was apparent. It became the dominant species in ravine forest on rocky substrate where P. rostratus was completely absent. In Sudanian savanna habitats and in herbaceous and cultivated areas, Mastomys erythroleucus dominated a diverse rodent community. A few species were found that testified for Guinean affinities of the most humid forest patches, especially in the extreme southeast of the country (region of Sikasso). Rodent assemblages of the Bafing and Mts Mandingues areas, in the western part of the study area, showed the highest similarity, in relation with environmental characteristics of this region representing an extension of the Fouta Djallon plateau in Guinea. The results obtained highlight the high biodiversity value of this forest-savanna mosaic, and provide new arguments in favour of the preservation of West African forest patches and their surrounding habitats.     

Causes of reduced leaf‐level photosynthesis during strong El Niño drought in a Central Amazon forest

Sustained drought and concomitant high temperature may reduce photosynthesis and cause tree mortality. Possible causes of reduced photosynthesis include stomatal closure and biochemical inhibition, but their relative roles are unknown in Amazon trees during strong drought events. We assessed the effects of the recent (2015) strong El Niño drought on leaf‐level photosynthesis of Central Amazon trees via these two mechanisms. Through four seasons of 2015, we measured leaf gas exchange, chlorophyll a fluorescence parameters, chlorophyll concentration, and nutrient content in leaves of 57 upper canopy and understory trees of a lowland terra firme forest on well‐drained infertile oxisol. Photosynthesis decreased 28% in the upper canopy and 17% in understory trees during the extreme dry season of 2015, relative to other 2015 seasons and was also lower than the climatically normal dry season of the following non‐El Niño year. Photosynthesis reduction under extreme drought and high temperature in the 2015 dry season was related only to stomatal closure in both upper canopy and understory trees, and not to chlorophyll a fluorescence parameters, chlorophyll, or leaf nutrient concentration. The distinction is important because stomatal closure is a transient regulatory response that can reverse when water becomes available, whereas the other responses reflect more permanent changes or damage to the photosynthetic apparatus. Photosynthesis decrease due to stomatal closure during the 2015 extreme dry season was followed 2 months later by an increase in photosynthesis as rains returned, indicating a margin of resilience to one‐off extreme climatic events in Amazonian forests.     

Impacts of El Niño-Southern Oscillation Events on the Distribution of Wintering Raptors

Abstract We report the effects of El Niño-Southern Oscillation (ENSO) events on the distribution and abundance of 3 raptor species at continental, regional, and landscape scales. We correlated values from the southern oscillation index (SOI), an index of ENSO phase and strength, with Christmas Bird Count data over a 30-year period. We investigated the relationship between the SOI and winter raptor distributions at 3 spatial scales: continental (central United States), regional (TX, USA), and landscape (3 roadside transects within TX). At the continental scale, ENSO events resulted in regional shifts for American kestrel (Falco sparverius), northern harrier (Circus cyaneus), and red-tailed hawk (Buteo jamaicensis) winter abundances. As expected, these shifts were northward during El Niño (warm) winters, and southward for red-tailed hawks and northern harriers during La Niña (cold) winters. Within Texas, northern harrier distributions shifted towards arid west Texas during wet El Niño winters but were restricted to mesic coastal Texas during dry La Niña winters. Red-tailed hawk abundance increased in eastern Texas during La Niña winters responding to cooler than normal temperatures throughout the northern Midwest. Data from local roadside transects over a 3-year period encompassing 2 El Niño winters and one La Niña winter supported the abundance patterns revealed by continental and regional data, and added evidence that fluctuations in winter abundances result from demographic pulses as well as spatial shifts for wintering populations. This study underscores the need for long-term monitoring at both local and regional spatial scales in order to detect changes in continental populations. Short-term or local studies would have erroneously assumed local population declines or increases associated with ENSO events, rather than facultative movements or demographic pulses supported by this study.