Climate and the complexity of migratory phenology: sexes,migratory distance,and arrival distributions

The intra- and inter-season complexity of bird migration has received limited attention in climatic change research. Our phenological analysis of 22 species collected in Chicago, USA, (1979–2002) evaluates the relationship between multi-scalar climate variables and differences (1) in arrival timing between sexes, (2) in arrival distributions among species, and (3) between spring and fall migration. The early migratory period for earliest arriving species (i.e., short-distance migrants) and earliest arriving individuals of a species (i.e., males) most frequently correlate with climate variables. Compared to long-distance migrant species, four times as many short-distance migrants correlate with spring temperature, while 8 of 11 (73%) of long-distance migrant species’ arrival is correlated with the North Atlantic Oscillation (NAO). While migratory phenology has been correlated with NAO in Europe, we believe that this is the first documentation of a significant association in North America. Geographically proximate conditions apparently influence migratory timing for short-distance migrants while continental-scale climate (e.g., NAO) seemingly influences the phenology of Neotropical migrants. The preponderance of climate correlations is with the early migratory period, not the median of arrival, suggesting that early spring conditions constrain the onset or rate of migration for some species. The seasonal arrival distribution provides considerable information about migratory passage beyond what is apparent from statistical analyses of phenology. A relationship between climate and fall phenology is not detected at this location. Analysis of the within-season complexity of migration, including multiple metrics of arrival, is essential to detect species’ responses to changing climate as well as evaluate the underlying biological mechanisms.     

Dendroclimatic potential of the Adesmia pinifolia shrub growing at high altitude in the Andes foothills

Highland ecosystems of western Andes foothills are currently poorly represented by dendrochronological information. The dendroclimatological potential of the Acerillo plant (Adesmia pinifolia), a shrub species well represented at these latitudes, was investigated. We reported the first ring width chronology of A. pinifolia growing at the central semi-arid Andes foothills of Argentina. We collected living and dead wood samples of Acerillo resulting in a chronology covering the period 1609–2020 (412 years) with a well replication from 1655 to present (> 13 samples). Bootstrapping correlation analysis revealed a strong positive relationship between our chronology and monthly precipitation and with the Standardized Precipitation Evapotranspiration Index (SPEI-12 months). For the last 40 years however, strong negative correlations with temperature are evidenced. The dendrochronological record also showed a negative relationship with sea surface temperatures from the Tropical Pacific, suggesting teleconnections with the El Niño Southern Oscillation (ENSO) phenomenon. The strong hydroclimatic signal recorded in the A. pinifolia chronology represents a high opportunity to produce long-term proxy climate data for the Central Andes foothills, an extensive region devoid of trees but of hydrological relevance for the support of important economic activities.     

Links between large-scale anomalies, rainfall and wine quality in the Iberian Peninsula during the last three decades

Recent strong El Niño‐Southern Oscillation (ENSO) signals have been identified in precipitation records from the Iberian Peninsula. Interannual association with ENSO accounts for more than half the total annual variance in selected stations of the south‐east, with ENSO leading rainfall by one year. In contrast, association with the North Atlantic Oscillation (NAO) at the Westernmost stations is much lower (25%). The potential of simple linear models is tested in the ENSO‐sensitive area, suggesting high capability of the Southern Oscillation Index (SOI) for predicting interannual rainfall fluctuations (mainly droughts and floods). Wine quality is associated with several factors, e.g. grape variety, soil type and processing, which can be considered invariable, mainly due to the strict regulations imposed by the quality regulating councils. Climate, however, has a great influence on resulting wine quality, and represents the most important source of variability at both short (day‐to‐day) and long (interannual) time scales. Over the last 30 years, high‐quality harvests in the five main wine regions in Spain, show a high probability (P < 0.0002) of being associated with an El Niño event occurring the same year or the year before. NAO influence is not significant during the same period. Thus, apart from considering the role of local climatic conditions in certain regions, which favour the production of excellent wines, larger‐scale climatic phenomena appear responsible for the year‐to‐year variations in quality.     

Climate–growth relationships of tropical tree species in West Africa and their potential for climate reconstruction

Most tropical regions are facing historical difficulties of generating biologically reconstructed long‐term climate records. Dendrochronology (tree‐ring studies) is a powerful tool to develop high‐resolution and exactly dated proxies for climate reconstruction. Owing to the seasonal variation in rainfall we expected the formation of annual tree rings in the wood of tropical West African tree species. In the central‐western part of Benin (upper Ouémé catchment, UOC) and in northeastern Ivory Coast (Comoé National Park, CNP) we investigated the relationship between climate (precipitation, sea surface temperature (SST)) and tree rings and show their potential for climate reconstruction. Wood samples of almost 200 trees belonging to six species in the UOC and CNP served to develop climate‐sensitive ring‐width chronologies using standard dendrochronological techniques. The relationship between local precipitation, monthly SST anomalies in the Gulf of Guinea, El Niño‐ Southern Oscillation (ENSO) and ring‐width indices was performed by simple regression analyses, two sample tests and cross‐spectral analysis. A low‐pass filter was used to highlight the decadal variability in rainfall of the UOC site. All tree species showed significant relationships with annual precipitation proving the existence of annual tree rings. ENSO signals could not be detected in the ring‐width patterns. For legume tree species at the UOC site significant relationships could be found between SST anomalies in the Gulf of Guinea indicating correlations at periods of 5.1–4.1 and 2.3 years. Our findings accurately show the relationship between tree growth, local precipitation and SST anomalies in the Gulf of Guinea possibly associated with worldwide SST patterns. A master chronology enabled the reconstruction of the annual precipitation in the UOC to the year 1840. Time series analysis suggest increasing arid conditions during the last 160 years which may have large impacts on the hydrological cycles and consequently on the ecosystem dynamics and the development of socio‐economic cultures and sectors in the Guinea‐Congolian/Sudanian region.     

Frugivory in sun bears (Helarctos malayanus) is linked to El Niño-related fluctuations in fruiting phenology, East Kalimantan, Indonesia

Sun bear ( Helarctos malayanus ) frugivory and fruiting phenology was investigated in a lowland dipterocarp forest in East Kalimantan, Indonesia. Two mast fruiting events, both coinciding with El Niño/Southern Oscillation events, occurred 4 years apart, resulting in large fluctuations in fruit availability. Sun bear fruit availability decreased from 13 trees ha⁻¹ fruiting month⁻¹ during the mast fruiting to 1.6 trees ha⁻¹ fruiting month⁻¹ during the intermast period. Almost 100% of sun bear diet consisted of fruit during mast fruiting period, whereas sun bear diet was predominantly insectivorous during intermast periods. The majority of sun bear fruit trees displayed 'mast-fruiting' and 'supra-annual' fruiting patterns, indicating sporadic productivity. Sun bears fed on 115 fruit species covering 54 genera and 30 families, with Ficus (Moraceae) being the main fallback fruit. The families Moraceae, Burseraceae, and Myrtaceae contributed more than 50% to the sun bear fruit diet. Sun bear fruit feeding observations were unevenly distributed over forest types with more observations in high-dry forest type despite fewer fruiting events, possibly due to a side-effect of high insect abundance that causes bears to use these areas more intensively. The possible evolutionary pathways of sun bears in relation to the Sundaic environment are discussed.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 489–508.     

Effects of climatic variation on field metabolism and water relations of desert tortoises

We used the doubly labeled water method to measure the field metabolic rates (FMRs, in kJ kg^?1?day^?1) and water flux rates (WIRs, in ml H₂O?kg^?1?day^?1) of adult desert tortoises (Gopherus agassizii) in three parts of the Mojave Desert in California over a 3.5-year period, in order to develop insights into the physiological responses of this threatened species to climate variation among sites and years. FMR, WIR, and the water economy index (WEI, in ml H₂O?kJ^?1, an indicator of drinking of free water) differed extensively among seasons, among study sites, between sexes, and among years. In high-rainfall years, males had higher FMRs than females. Average daily rates of energy and water use by desert tortoises were extraordinarily variable: 28-fold differences in FMR and 237-fold differences in WIR were measured. Some of this variation was due to seasonal conditions, with rates being low during cold winter months and higher in the warm seasons. However, much of the variation was due to responses to year-to-year variation in rainfall. Annual spring peaks in FMR and WIR were higher in wet years than in drought years. Site differences in seasonal patterns were apparently due to geographic differences in rainfall patterns (more summer rain at eastern Mojave sites). In spring 1992, during an El Niño (ENSO) event, the WEI was greater than the maximal value obtainable from consuming succulent vegetation, indicating copious drinking of rainwater at that time. The physiological and behavioral flexibility of desert tortoises, evident in individuals living at all three study sites, appears central to their ability to survive droughts and benefit from periods of resource abundance. The strong effects of the El Niño (ENSO) weather pattern on tortoise physiology, reproduction, and survival elucidated in this and other studies suggest that local manifestations of global climate events could have a long-term influence on the tortoise populations in the Mojave Desert.     

Reconciling the influence of global climate phenomena on macrofaunal temporal dynamics at a variety of spatial scales

Determining the relative importance of environmental forces on population dynamics is a fundamental question for ecologists. Growing concern over the ecological effects of climate change emphasizes the importance of defining whether broad-scale environmental forces uniformly act upon local populations (hierarchy theory) or cross-scale interactions influence local responses (multiscale theory). This study analyses 13 years of data on species abundances at six sites within a large harbour to determine the effect of the El Niño Southern Oscillation (ENSO). Environmental variables both directly and indirectly related to ENSO were observed to be important predictors of the temporal dynamics of abundance in many species, but the observed effects were not consistent across sites or species. While nearly all species were affected by large temporal and spatial scale variability, smaller temporal scale, location-specific environmental variables (such as wind-generated wave exposure and turbidity) were also generally important, increasing the variability explained by our models by up to 25%. As with many other broad-scale variables, generality of response to ENSO is affected by interactions across time and space with smaller scale heterogeneity. This study therefore suggests that the degree of interaction between broad-scale climatic factors, such as ENSO, with smaller scale variability, will determine the consistency of responses over large spatial scales, and control our ability to predict effects of climate change on coastal and estuarine communities.     

Spatial and temporal variability of net ecosystem production in a tropical forest: testing the hypothesis of a significant carbon sink

Tropical forest ecosystems play an important role in the global carbon balance. Depending on age and land use, they can act as carbon sources, sinks, or be in approximate balance, but it is uncertain if global environmental changes are forcing these ecosystems outside their natural range of variation. We asked the question of whether or not the net carbon flux of a tropical primary forest, which should be in balance over the long term, is within the expected range of natural variation. A simple Bayesian hypothesis testing method was used to address this question for primary forests in the Porce region of Colombia. Net ecosystem production (NEP) was measured in this forest in a set of 33 permanent plots from 2000 to 2002 in 2, 1‐year intervals. Our estimate of NEP ranged between −4.03 and 2.22 Mg C ha⁻¹ yr⁻¹ for the two intervals. This range was compared with a priori defined range of natural variation estimated from the ecosystem model STANDCARB, which estimated spatial and temporal variation due to gap dynamics. The prior range of variation was estimated between −1.5 and 1.5 Mg C ha⁻¹ yr⁻¹. The observed data on NEP did not provide sufficient evidence to reject the null hypothesis that these forests are in C balance. We concluded that the ecosystem is likely behaving within its range of natural variation, but measurement uncertainties were a major limitation to finding evidence to reject the null hypothesis. A literature review of C flux studies in the tropics revealed that about half of the observations could be explained by gap dynamics alone, while significant C sinks have only been observed during La Niña years, with contrasting results in other tropical forests. In conclusion, observational data of carbon fluxes do not appear to provide direct evidence for a significant carbon sink in some sites in the tropics.     

Vegetation responses to burning in a rain forest in Borneo

During the 1997/98 ENSO (El Niño Southern Oscillation) event more than 5 million ha of East Kalimantan, Indonesia burned. Here we quantify the initial stages of regeneration (19982001), both in forest that burned and in unburned controls. Sapling and seedling density and species richness remained significantly lower in burned than in unburned forest and community composition remained substantially different between both forest types throughout the sampling period. The only pronounced edge effect was a significantly higher density of seedlings in the interior of unburned forest. Sapling density increased and seedling density declined in both unburned and burned forest during the four-year study period. In the unburned forest, sapling and seedling species richness remained stable, but sapling species richness declined significantly with time in the burned forest. The pioneer community in the burned forest was, furthermore, characterised by higher growth and recruitment than in the unburned forest but mortality did not differ between both forest types. Differences in environment (burned versus unburned: 2965% of variation explained) and the distance between sample sites (1323% of variation explained) explained substantial amounts of variation in sapling and seedling community similarity. Similarity was, however, only marginally (< 1% explained) related to the edge position and temporal variation (difference among sample events). Our results, four years after the initial burn, indicate that burned forest still differed greatly from unburned forest in terms of density, species richness and community composition. There was also no clear trend of a return to pre-disturbance conditions, which indicates that the burned forest may remain in a severely degraded state for a prolonged period of time.     

Wood growth patterns of <Emphasis Type="Italic">Macrolobium acaciifolium</Emphasis> (Benth.) Benth. (Fabaceae) in Amazonian black-water and white-water floodplain forests

Macrolobium acaciifolium (Benth.) Benth. (Fabaceae) is a dominant legume tree species occurring at low elevations of nutrient-poor black-water (igapó) and nutrient-rich white-water floodplain forests (várzea) of Amazonia. As a consequence of the annual long-term flooding this species forms distinct annual tree rings allowing dendrochronological analyses. From both floodplain types in Central Amazonia we sampled cores from 20 large canopy trees growing at identical elevations with a flood-height up to 7 m. We determined tree age, wood density (WD) and mean radial increment (MRI) and synchronized ring-width patterns of single trees to construct tree-ring chronologies for every study site. Maximum tree age found in the igapó was more than 500 years, contrary to the várzea with ages not older than 200 years. MRI and WD were significantly lower in the igapó (MRI=1.52±0.38 mm year^?1, WD=0.39±0.05 g cm^?3) than in the várzea (MRI=2.66±0.67 mm year^?1, WD=0.45±0.03 g cm^?3). In both floodplain forests we developed tree-ring chronologies comprising the period 1857–2003 (n=7 trees) in the várzea and 1606–2003 (n=13 trees) in the igapó. The ring-width in both floodplain forests was significantly correlated with the length of the terrestrial phase (vegetation period) derived from the daily recorded water level in the port of Manaus since 1903. In both chronologies we found increased wood growth during El Niño events causing negative precipitation anomalies and a lower water discharge in Amazonian rivers, which leads to an extension of the terrestrial phase. The climate signal of La Niña was not evident in the dendroclimatic proxies.