Interannual Vari Research Articles

EFFET DES FACTEURS STATIONNELS SUR LA CROISSANCE RADIALE ET LA RÉPONSE DU PIN D’ALEP AU CLIMAT DANS LE MASSIF DE L’OUARSENIS, ALGÉRIE

Lesrelations entre leclimat et lacroissance radiale sur la période 1967-2010 de neuf populations de pin d’Alep dans le massif de l’Ouarsenis (Nord-Ouest de l’Algérie) ont été étudiées en fonction des facteurs stationnels (substrat, altitude, exposition et âge des arbres) à l’aide de méthodes de dendrochronologie. Les variations interannuelles des épaisseurs de cernes ont été analysées. L’étude rétrospective de la croissance radiale indique une forte variabilité interannuelle des épaisseurs des cernes à l’intérieur d’une même popu- lation. Les paramètres statistiques calcu- lés indiquent une forte variabilité de la croissance radiale entre les populations, cette variabilité étant liée aux facteurs sta- tionnels et à l’âge des arbres. L’âge joue un rôle négatif sur l’épaisseur moyenne des cernes et sur le phénomène de persis- tance. La sensitivité (sensibilité au climat) moyenne des arbres tend à être plus éle- vée sur les substrats gréseux ou schisteux que sur les substrats calcaires. L’analyse des relations cerne-climat montre que le pin d’Alep est réactif aux précipitations de la période précédant ou contempo- raine de la formation du cerne. Les tem- pératures interviennent négativement sur la croissance radiale, surtout par leurs valeurs maximales. Les relations du pin d’Alep aux conditions climatiques sont modulées par les facteurs stationnels, notamment le substrat. Les populations les plus réactives se localisent davantage sur un substrat gréseux. Ces résultats constituent un descriptif utile pour com- prendre la plasticité écologique du pin d’Alep et sa réponse aux changements cli- matiques, afin de proposer des mesures destinées à assurer une meilleure protec- tion des pinèdes menacées depuis plu- sieurs décennies.

Trend analysis of evapotranspiration and its response to droughts over India

Six temperature homogeneous regions of India were chosen to calculate evapotranspiration (ET) using Hargreaves and Samani method on a monthly basis. Break Trend Analysis has been applied to the annual and seasonal ETs of the respective homogeneous regions as well as for whole India and the factors contributing for the changes in ET have been analysed. By considering the data of Reconnaissance Drought Index (RDI), Rainfall, Advanced Very High Resolution Radiometer (AVHRR) Normalized Difference Vegetation Index (NDVI) for South West (SW) monsoon (June to September) and Rice yield (major Khariff crop yield) of All India, we investigated the variations in ET during drought years. The trend analysis of seasonal and annual ETover the test regions have shown significant (levels of 0.05 to 0.01) increase over the past 107 years of the study period (1901 to 2007). The enhancement in ET is found to be 2.9 mm/decade overIndia and with a maximum in West Coast India (6 mm/decade), followed by Northwest India (3.9 mm/ decade). The increasing trends in ET may be due to the increase in difference of maximum and minimum tempera- tures over these regions, which is of the order of 0.64 °C/ decade on all India scale. The analysis of ET in drought years consistently shows higher values in the years when India suffered under moderate and severe droughts. It is also ob- served that lower rainfall values in the drought years such as 1983, 1987 and 2002 were associated with the higher ETs accompanied by lower NDVI and Rice yields. The analysis has been extended to the comparison of ET with rainfall through wavelet spectrum to understand the interannual vari- ations which inferred the El Nino impact on ET. The correla- tionanalysis of ETover the Interior Peninsular regionwith the number of days falling in active and break spells of monsoon by which drought can be characterised, revealed the signifi- cant negative and positive values, respectively.

Grey seal diet analysis in Ireland highlights the importance of using multiple diagnostic features

Seals and humans are top predators in many marine ecosystems, often targeting the same food resource. With global declines in fish stocks, competition between these top predators is of increasing interest to scientists and resource managers. To understand and quantify this competition, robust data on the diet of seals are necessary. We present new information on the diet of grey seals Halichoerus grypus from a colony on Great Blasket Island, southwest Ireland, with particular reference to commercially important prey species such as salmonids. Inter-annual vari- ation in diet was investigated based on the recovery and identification of sagittal fish otoliths, bones and cephalopod beaks from faecal samples collected in 2009 and 2010. A total of 939 prey items were recovered, representing a minimum of 41 prey species. Thirty species were identified from otoliths while a further 11 species, including salmonids, were identified from additional diagnostic structures. The diet of grey seals was largely dominated by Gadiformes (21% corrected biomass), particularly Trisopterus spp., which contributed 7% in terms of corrected biomass and 52% by frequency of occurrence, while salmonids comprised over 36% of diet by corrected biomass. Inter-annual variation in sandeel (Ammodytidae) and blue whiting Micromesistius poutassou abundance was apparent, while the former was an important contributor to the diet in terms of corrected biomass (11%). The results support the principle that an 'all structures' approach to pinniped diet estimation can significantly increase the rate of detection for most fish groups, and result in improved estimation of seal diet.

Climatic variation affects clutch phenology in Agassiz’s desert tortoise Gopherus agassizii

There is concern about how climate change might affect Agassiz's desert tortoise Gopherus agassizii, a threatened species. We studied the effects of climatic variation on clutch phenology of a population at a wind energy generation facility for 7 field seasons between 1997 and 2011. Using X-radiography, we quantified the following phenophases based on the number of calendar days to each event from 1 January: appearance and disappearance of 65 first and 53 sec- ond clutches, and inter-clutch intervals between first and second clutches. Although third clutches were rare (n = 8), they were observed in 5 of 7 yr and were produced by 8 different females, all of which produced a third clutch only once during the study. Shelled eggs were visible from as early as 11 April to as late as 28 July, and the overall time span that eggs were visible differed among years. After controlling for maternal effects, we observed statistically significant inter-annual vari- ation in all phenophases except for inter-clutch interval. Clutch appearance was late in cool years relative to warm years and especially late after 2 consecutive cool years. Using degree day (DD) methodology, we calculated DD accumulation during the post-hibernation and nesting season for each year. We then used DD estimates for mean date of first clutch appearance to predict the mean date of first clutch appearance in subsequent years with 1 to 10 d accuracy for all but 1 yr (1998) with El Nino conditions. Clutch phenology appears to be correlated with inter-annual variation in climate and may be influenced by climatic events in previous years.

Inter-annual variability in diet of non-breeding pelagic seabirds Puffinus spp. at migratory staging areas: evidence from stable isotopes and fatty acids

During nesting periods, seabirds are known to exhibit considerable inter-annual vari- ability in diets, yet little is known about the diets of pelagic seabirds during non-breeding periods. Over 5 yr (2005 to 2009), we studied dietary partitioning between sympatric greater and sooty shear- waters, Puffinus gravis and P. griseus, during migratory staging periods in the Northwest Atlantic. Stable-isotope (SI; n = 253) and fatty-acid (FA; n = 127) signatures from blood samples were used to assess inter-annual patterns in diet and quantify prey choices. In addition to significant effects of year, capture site, and body condition, SI signatures revealed subtle, but consistent, dietary partition- ing between species. In all years, greater shearwaters fed at slightly higher trophic levels (overall mean δ 15 N = 13.6‰) and lower δ 13 C (-19.1‰) than sooty shearwaters (δ 15 N = 13.3‰, δ 13 C = -18.9‰). SI mixing models revealed that sooty shearwaters relied more heavily on euphausiids Meganyc- tiphanes norvegica, while greater shearwaters consumed more herring Clupea harengus, squid Illex illecebrosus, and, in some years, mackerel Scomber scombrus. In 2005/2006, bird diets consisted pri- marily of herring and krill, but demonstrated a shift towards krill and squid during 2007-2009. FA from bird plasma showed little inter-specific partitioning but a strong signal of annual variation for both species. We used a subset of prey FA and a modified multivariate approach to model bird diets and obtained dietary preferences broadly in agreement with SI results. The present study revealed inter-annual variability and dietary partitioning in sympatric species of pelagic seabirds, and high- lights potential shifts in prey availability to predators in the Bay of Fundy.

Evaluating uncertainty in climate change impacts on crop productivity in the Iberian Peninsula

Using a multi-model ensemble of climate-change impacts over the Iberian Peninsula, we identified regions and cropping options for which the uncertainty levels of projected impacts on crop productivity were either high or low. The ensemble consisted of 10 members per combination of scenario, climate model, location and cropping option, and was used to quantify the uncertainty of impacts on crop yield. CERES wheat and maize simulation models were linked to the control run and 1 scenario provided by 10 regional climate models (RCMs): control (1969-1990) and A2 future (2070-2100) climate. The contribution of RCMs, locations and cropping options to uncertainty on yield projections was analysed. Differences between the sign of the response and 30 yr time series of projections generated by each member of the ensemble were compared. The largest response to A2 scenarios also resulted in the smallest uncertainty, and vice versa. Low uncertainty was found for the sign of the yield response, which was mainly positive for spring and winter cropping options and neg- ative for the summer option. Uncertainty was lower for A2 than for control projections. Uncertainty was largest in northern, coastal and mountain regions, and smallest for inland southern regions, and depended on seasonal cropping options. Minimum and maximum uncertainty were found for maize and irrigated spring wheat, respectively. Water availability was the determinant for interannual vari- ability and its uncertainty. Choice of RCM contributed less to uncertainty than choice of location, and choice of cropping option contributed more to uncertainty than both of these factors. Interannual vari- ability showed larger uncertainty than mean impact magnitude, and this uncertainty was larger than that of the sign of the yield response. Regions with high uncertainty could benefit from higher-reso- lution simulations.

Nonparametric Simulation of Single-Site Seasonal Streamflows

Various parametric and nonparametric models have been suggested in literature for stochastic generation of seasonal streamflows. State-of-the-art nonparametric models are reviewed herein and their drawbacks identified. We developed a simple model that employs the k-nearest neighbor resampling algorithm with gamma kernel perturbation (denoted as KGK model), which enables generation of data that are not the same as the historical data. For preserving the annual variability two approaches are developed. The first one employs the aggregate variable concept (KGKA model), and the second one uses a pilot variable that leads the generation of the seasonal data (KGKP model). The pilot variable refers to the annual data that has been previously generated, but its role is not for disaggregation but rather for conditioning the state that guides the generation of seasonal flows. The proposed models have been compared with a currently available nonparametric model that considers the reproduction of the interannual vari...

Decadal changes in water temperature and ecological time series in Lake Geneva, Europe—relationship to subtropical Atlantic climate variability

We investigated connections between subtropical Atlantic climate variability, atmo- spheric conditions in the European Alpine region (45 to 47° N and 5 to 8° E) and the interannual vari- ability of the thermal conditions in the largest body of freshwater in Western Europe (Lake Geneva). The long-term water temperature was related to climate variability by means of a multivariate regres- sion model. Results revealed atmospheric connections that have been elusive so far, and showed that over the period from 1959 to 2000, summer thermal conditions in Lake Geneva appear tightly linked to the long-term variability of the subtropical Atlantic climate. The multivariate model revealed high skills and tight correlations, which suggest the possibility of assessing future thermal changes in Lake Geneva from the Atlantic climate variability. The implications of such climatic forcing on the function- ing of the pelagic ecosystem in Lake Geneva were illustrated by analysing the long-term changes in abundance of the summer-dominant carnivorous cladocerans Bythotrephes longimanus and Lep- todora kindtii during the period 1974 to 2000. Again, the multivariate model revealed high skills and excellent correlations between the interannual changes in abundance of these species and the variability of summer climate. Our approach provides a general understanding of the interrelations be- tween large- and regional-scale climates, local environmental conditions and the ecological responses in Lake Geneva during summer, and is therefore applicable to other retrospective studies.

Elemental composition of otoliths used to trace estuarine habitats of juvenile gag Mycteroperca microlepis along the west coast of Florida

The spatial relationships and relative contributions of known juvenile gag Myctero- perca microlepis habitats to specific fishery grounds and populations along the Florida west coast are virtually unknown. To determine if otolith composition is a valid tracer of specific nursery sites and can be used to classify adult fish to their nursery area, chemical concentrations in juvenile gag otoliths (Li, Na, K, Mg, Ca, Sr, Ba, Mn, Cu, Pb, δ 13 C and δ 18 O,) were measured for 4 nursery areas along the Florida west coast in 1992, 1995 and 1996. Classification of fish to nursery area was by para- metric discriminant function analysis and neural network simulation; both gave similar results in the spatial and temporal patterns of classification error and in identification of important classification variables (Mn, Sr and δ 13 C). Classification success rates ranged from 66 to 100%. Interannual vari- ability in otolith composition had a negative effect on classification success rate at the spatial scale of site separation ( 300 km) the year effect was reduced and class- ification success remained high without consideration of year class. Analysis of classification errors supports the separation of sites into northern and southern groups. The observed negative trend in otolith Sr and positive trend in otolith Mn with increasing latitude are positively correlated with cor- responding trends in groundwater Sr and sediment Mn, respectively, which are hypothesized to be the proximal causes for the otolith trends. Otolith composition is a valid technique for classifying juvenile gag to estuarine habitats along the west coast of Florida. Classification error rates of less than 10% are obtained when the year class of the fish is considered. Similar error rates were achieved across multi-year data at regional spatial scales.

Climate variability and vertical advection of nitrates in the Gulf of St. Lawrence, Canada

Using a modeling approach, we constructed a time series to examine interannual vari- ability in the spring nitrate concentrations in the surface layer of the Gulf of St. Lawrence (GSL) for the period 1947 to 2000. This 2-step modeling approach used the lower boundary of the cold inter- mediate layer (CIL), a persistent summer characteristic of the temperature profiles in the GSL, to infer interannual variations in the depth of the winter mixed layer. Using a linear model describing the dis- tribution of nitrates at intermediate depths, we estimated a time series of spring nitrate concentration in the surface waters of the GSL for the period 1947 to 2000. This early spring time series showed interannual fluctuations in nitrate concentrations of about 1 order of magnitude, attributable to vari- ability in winter convection. Such variability in the spring nitrate availability should have a significant impact on the ecosystem. Some elements that should be taken into account in any future attempt to validate this estimated nitrate time series are discussed.