Aerobiological and meteorological factors’ influence on olive (Olea europaea L.) crop yield in Castilla-La Mancha (Central Spain)

Knowledge of the main biological and climate factors influencing final harvest is becoming increasingly necessary in order to obtain reliable crop estimates and, thus, ensure optimised, effective private crop management. This knowledge is also of great value to public agricultural institutions for the planning of government subsidies. Castilla-La Mancha (Central Spain) is the second largest olive-oil-producing region in Spain, the highest olive-oil-producing country in the world. This study sought to identify the main factors influencing olive fruit production in this region, including atmospheric pollen as an index of flowering intensity, and meteorological data over the flowering and fruiting seasons in two main olive-producing provinces of the region: Ciudad Real and Toledo. Statistical analysis indicated that the annual pollen index (PI) was the variable influencing most the final olive crop in both provinces. The maximum temperature in March was the meteorological variable affecting most the annual olive crop. Also, the rainfall registered in October influences the final fruit production. The integration of aerobiological and meteorological data represents an important step forward in the development of future crop forecasting models in the region of Castilla-La Mancha.     

Comparative study of the effect of distance on the daily and hourly pollen counts in a city in the south-western Iberian Peninsula

The airborne pollen concentration in the city of Badajoz was measured in two locations 2.9 km apart. The measurements were taken from January to June between 2009 and 2012 using Hirst-type volumetric aerobiological samplers. One sampler was placed at the Faculty of Science (FS) and the other at the Agricultural Engineering School (AES) of the University of Extremadura, Spain, on terraces located 16 and 6 m above ground, respectively. The two sets of hourly and daily pollen concentrations were compared regarding the meteorological parameters and the distribution of local pollen sources. A total of 46 pollen types were counted, with a mean total concentration of 43 pollen grains/m³ in the winter and 336 pollen grains/m³ in the spring. In the winter, pollen grains from (in decreasing order) Cupressaceae, Fraxinus–Phillyrea, Urticaceae spp., Alnus glutinosa and Urtica membranacea types represented 77 % of the total. In the spring, 89 % of the total was represented by pollen grains from (in decreasing order) Quercus, Poaceae, Olea, Pinaceae and Plantago. The FS/AES ratio was 0.57 in the winter and 1.31 in the spring. While a Wilcoxon test applied to the daily total concentration data showed statistically significant differences between the two sites, a correlation study based on the Spearman coefficient showed statistically significant correlations in both the winter and spring. The results were similar when comparing the separate pollen types, except for Urticaceae spp., which showed no statistically significant correlation. The meteorological data studied showed a statistically significant correlation with the daily concentrations. A comparison of the hourly concentration data showed no correspondence with the time of maximum concentration. The local distribution of pollen sources explained some of the differences found between the two sites. Overall, the results indicate that a single aerobiological sampler may be sufficiently representative to register the daily pollen grain data of an urban area of approximately 3 km or greater in diameter, although it underestimates the influence of heterogeneity in the distribution of the local flora.     

Airborne-pollen map for Olea europaea L. in eastern Andalusia (Spain) using GIS: Estimation models

Estimations based upon geostatistics and mapping have enabled the construction of a spatial model to predict the presence of biological particles in a particular region. This methodological proposal has been tested in a case study, at a regional scale, of airborne Olea pollen, using the data acquired from␣various sampling stations that are designed for the aerobiological monitoring of pollen levels. These sampling stations have been set up in cities throughout the region of Andalusia (southern Spain) at sites with very different characteristics in terms of biogeography, bioclimate, topography and vegetation. Pollen counts were made daily at all sites during 2003 using a volumetric spore-trap. Data were comparatively analysed in classical diagrams and by means of spatial-temporal maps. Space-time models were constructed using three coordinates, x, y (the UTM coordinates of each sampling station) and z, (the aerobiological data compiled for a specific period). The aerobiological data were interpolated by applying the traditional geostatistical method of Kriging. The introduction of the variable “space” into the model allowed us to predict pollen levels in different areas throughout the region. The interpolation method was used to make weekly estimations of Olea pollen values in areas where there was no aerobiological sampling station. In addition, the maps generated present a two-dimensional vision of the study area, showing that bioclimatic diversity of this region promotes a step-wise flowering of Olea.     

Airborne pollen sampling in Toledo, Central Spain

Toledo is one of the main tourist spots of Spain, attracting around two million visitors per year. Its geographical situation in the vast and scarcely monitored Region of Castilla La Mancha and the high number of tourists (especially in the spring) has resulted in the Spanish Aerobiology Network (REA) making this city a major study objective. Air monitoring studies carried out using REA sampling procedures commenced in October 2002. Thirty-two pollen types were identified during the sampling period (October 2002 to October 2004). The annual Pollen Index (PI) was 44124 for the agricultural year October 2002–October 2003, and 29666 in the same period of 2003–2004. The most abundant taxa were, in decreasing order of dominance: Cupressaceae, Quercus, Poaceae, Populus, Olea, Urticaceae, Platanus, Pinus and Ulmus. Other, less well-represented pollen taxa included Salix, Alnus, Fraxinus and Tamarix, which were characteristic of riverside areas, and Morus, Artemisia and Chenopodiaceae. The presence of Castanea pollen grains originating from chestnut crops far away from the city was clearly an example of long-distance transport. The highest concentrations of airborne pollen were detected from March to May and also in January, due to the flowering of Cupressaceae species. In general, there was a correlation between pollen and meteorological parameters: a positive correlation with temperature and a negative correlation with rainfall and humidity during the pre-peak period. A negative correlation between temperature and some tree pollen taxa was detected in the principal pollen period correlation analysis due to their long pollination periods.     

Intradiurnal variation of allergenic pollen in the city of Porto (Portugal)

This study reports the hourly distribution of the allergenic airborne pollen types more abundant in the atmosphere of Porto (Portugal) during the studied period. This knowledge will allow an adequacy daily routine for allergic patients during the hours of higher airborne concentrations. The airborne pollen concentration was continuously performed from January 2003 to December 2007 in the city of Porto using a Hirst-type volumetric sampler. Urticaceae, Cupressaceae, Acer spp., and Plantago spp. airborne pollen presented higher concentrations in the morning, while Alnus spp. and Betula spp. pollen were mainly present during the afternoon. Olea europaea and Platanus spp. pollen were regularly distributed along the day, while Poaceae and Pinus spp. pollen presented two diurnal maxima.     

Spring airborne pollen data in two sites in Trentino (Northern Italy): a comparison with meteorological data

In this paper airborne pollen concentration is compared to meteorological data of Trento and S. Michele all’Adige, two sites in the Adige Valley, in Trentino (North Italy). Pollen ofCorylus, Alnus, Betula andOstrya, four winter-spring flowering plants are considered. Pollen sampling was carried out in 1996 by volumetric Hirst-type samplers. For all pollen types considered, maximum pollen concentration coincided in both stations and there was a good overlap of the main pollen season length; the pollen curves of S. Michele a/A and Trento showed a highly positive correlation. The daily airborne pollen concentrations, defined as the number of pollen grains per cubic meter of air (P/m³), were compared to daily meteorological data: minimum and maximum air temperature (°C), average relative humidity (%), precipitation (mm), global incident radiation (cal/cm²), average wind direction (°) and wind speed (m/s). A highly positive correlation was found forCorylus and maximum temperature in both monitoring stations.Betula was positively, whereasOstrya was negatively correlated to relative humidity. With this first analytical approach sharp differences in the atmospheric pollen presence between the stations located at Trento and S. Michele all’Adige were not found.     

Phenological records as a complement to aerobiological data

Phenological studies in combination with aerobiological studies enable one to observe the relationship between the release of pollen and its presence in the atmosphere. To obtain a suitable comparison between the daily variation of airborne pollen concentrations and flowering, it is necessary for the level of accuracy of both sets of data to be as similar as possible. To analyse the correlation between locally observed flowering data and pollen counts in pollen traps in order to set pollen information forecasts, pollen was sampled using a Burkard volumetric pollen trap working continuously from May 1993. For the phenological study we selected the main pollen sources of the six pollen types most abundant in our area: Cupressaceae, Platanus, Quercus, Plantago, Olea, and Poaceae with a total of 35 species. We selected seven sites to register flowering or pollination, two with semi-natural vegetation, the rest being urban sites. The sites were visited weekly from March to June in 2007, and from January to June in 2008 and 2009. Pollen shedding was checked at each visit, and recorded as the percentage of flowers or microsporangia in that state. There was an association between flowering phenology and airborne pollen records for some of the pollen types (Platanus, Quercus, Olea and Plantago). Nevertheless, for the other types (Cupressaceae and Poaceae) the flowering and airborne pollen peaks did not coincide, with up to 1 week difference in phase. Some arguments are put forward in explanation of this phenomenon. Phenological studies have shown that airborne pollen results from both local and distant sources, although the pollen peaks usually appear when local sources are shedding the greatest amounts of pollen. Resuspension phenomena are probably more important than long-distance transport in explaining the presence of airborne pollen outside the flowering period. This information could be used to improve pollen forecasts.     

Influence of meteorological parameters on Olea flowering date and airborne pollen concentration in four regions of Portugal

For calculating the total annual Olea pollen concentration, the onset of the main pollen season and the peak pollen concentration dates, using data from 1998 to 2004, predictive models were developed using multiple regression analysis. Four Portuguese regions were studied: Reguengos de Monsaraz, Valença do Douro, Braga and Elvas. The effect of some meteorological parameters such as temperature and precipitation on Olea spatial and temporal airborne pollen distribution was studied. The best correlations were found when only the pre‐peak period was used, with thermal parameters (maximum temperature) showing the highest correlation with airborne pollen distribution. Independent variables, selected by regression analysis for the predictive models, with the greatest influence on the Olea main pollen season features were accumulated number of days with rain and rainfall in the previous autumn, and temperatures (average and minimum) from January through March. The models predict 59 to 99% of the total airborne pollen concentration recorded and the initial and peak concentration dates of the main Olea pollen season.     

A comparative study on the effects of altitude on daily and hourly airborne pollen counts

The concentration of pollen grains in the air was studied using two aerobiological volumetric Hirst-type spore traps, one at ground level and the other at a height of 16 m on a terrace. The study was carried out between 2009 and 2011, from March to June in Badajoz (SW Spain). Intradiurnal and daily pollen counts were compared with both, different meteorological parameters and the distribution of local pollen sources. Forty-six pollen types were identified and 89 % of the total grains corresponded to Quercus, Poaceae, Olea, Pinaceae and Plantago pollen types, in descending order. The mean height ratio of the daily pollen count was 1.02. Significant correlations were observed when comparing daily pollen counts for predominant pollen types at both levels. The comparisons have shown significant differences in the daily pollen count between the two samplers in the case of Olea and Pinaceae, but not for Quercus, Poaceae and Plantago. Similar results were obtained using the intradiurnal airborne pollen database. No significant correlation has been found between pollen count and the different meteorological parameters, showing no dependence on height. These differences of Olea and Pinaceae may be explained in part by the uneven distribution of the pollen sources and the disturbance by nearby buildings. The temporal variation patterns between the two sites were similar; however, taking into account the average of the data, the higher values were obtained first at the ground level and later at 16 m.     

A statistical approach to comparing the results from different aerobiological stations

The recent increase in the number of aerobiological stations means that it is possible to make comparative studies, not only to ascertain similarities and differences between pollen counts in different places, but also to ascertain the most suitable places for them to be situated and the most adequate distance which should be established between them. To this end, we present a statistical comparison of the results obtained for the pollen of the ten most abundant taxa, as recorded in the sampling stations of Malaga and Estepona (South of Spain) during 1995-97. The stations are 90km apart. The variables compared were the following: mean daily concentrations (for each year and the total period studied), the mean concentration of the three years for the same date (trend) and the deviation from this mean (for each year and taken as a whole). The interannual differences within and between stations were taken into account as regards the association, concentration and distribution of the variables. The results of the tests applied point that significant differences between the two stations were observed for most of the pollen types studied. Despite of this, a positive and significant correlation exists between the mean daily concentrations of the different taxa at the two stations, which is an important finding if we consider the possibility of making reliable predictions for one sampling site based on the data obtained at the other.     

Airborne behaviour of <Emphasis Type="Italic">Echium</Emphasis> pollen

Species of Echium are clearly entomophilous, but they release great amounts of pollen into the atmosphere with its consequent anemophilous transport, because their high pollen production, the smallness of the grains, and the exserted position of their anthers. Using three volumetric airborne sporetraps in Extremadura (SW of Spain) between 1994 and 1998, we found that Echium pollen reached pollen concentrations similar to or greater than other anemophilous plants. The main pollination period appeared from April to June. The maximum peak daily concentration reached 35.9 grains/m³ and the annual recorded totals showed interannual variations between 64.2 and 614.4. Correlations were calculated between the daily pollen concentrations and the meteorological parameters rain, temperature, wind direction and velocity and relative humidity. Wind direction seems to be significant, warm dry air seems to facilitate the release of pollen into the atmosphere and increase its concentrations. Hourly pollen concentration reached a maximum between 11:00 and 12:00 and a minimum at 07:00, and the patterns were very similar in the three localities studied. This would indicate that the presence of Echium pollen in the atmosphere is related to the processes of anthesis of the populations near the traps, and would not correspond to a model of transport from distant zones.     

Airborne olive pollen in Vigo (Northwest Spain): a survey to forecast the onset and daily concentrations of the pollen season

Temperature is one of the main factors affecting the start of flowering in tree species that flower at the beginning of spring. Knowledge of the chilling and heat needs required by plants to overcome the period of dormancy enables us to determine the onset of pollination, which is of great importance to allergy sufferers. This study attempted to obtain behaviour models with a view to determining both the onset of the olive pollen season and daily pollen concentrations during the pollination period in Vigo. Monitoring was carried out using a Lanzoni VPPS 2000 pollen trap, from 1995 to 2002 inclusive.

Olea pollen is mainly detected during the spring, principally in May. Given the geographical location, the very limited presence of this tree in the study area and the low Olea pollen concentrations detected in northern Spain as a whole, the values recorded here in the atmosphere of Vigo are particularly striking. A strong correlation was observed between total quantity olive pollen collected over the season and rainfall recorded during the second fortnight in February. According to the proposed model, an average of 680 Chilling Hours (CH) are necessary to overcome the chill period and break the state of bud dormancy, and 481 Growth Degree Days (GDD) °C are needed to induce flowering. Models for predicting daily mean pollen concentrations combine temperature and the previous days' pollen concentrations as predictor variables to provide a high level of prediction.     

Identification of potential sources of airborne Olea pollen in the Southwest Iberian Peninsula

This study aims to determine the potential origin of Olea pollen recorded in Badajoz in the Southwest of the Iberian Peninsula during 2009–2011. This was achieved using a combination of daily average and diurnal (hourly) airborne Olea pollen counts recorded at Badajoz (south-western Spain) and Évora (south-eastern Portugal), an inventory of olive groves in the studied area and air mass trajectory calculations computed using the HYSPLIT model. Examining olive pollen episodes at Badajoz that had distinctly different diurnal cycles in olive pollen in relation to the mean, allowed us to identify three different scenarios where olive pollen can be transported to the city from either distant or nearby sources during conditions with slow air mass movements. Back trajectory analysis showed that olive pollen can be transported to Badajoz from the West on prevailing winds, either directly or on slow moving air masses, and from high densities of olive groves situated to the Southeast (e.g. Andalucía). Regional scale transport of olive pollen can result in increased nighttime concentrations of this important aeroallergen. This could be particularly important in Mediterranean countries where people can be outdoors during this time due to climate and lifestyle. Such studies that examine sources and the atmospheric transport of pollen are valuable for allergy sufferers and health care professionals because the information can be incorporated into forecasts, the outputs of which are used for avoiding exposure to aeroallergens and planning medication. The results of studies of this nature can also be used for examining gene flow in this important agricultural crop.     

<Emphasis Type="Italic">Cyperaceae</Emphasis> and <Emphasis Type="Italic">Juncaceae</Emphasis> pollination measured in the air at two sites in SW Spain

The presence of airborne Cyperaceae and Juncaceae pollen was quantified using volumetric aerobiological traps over a 10-year period at two sites in SW Spain separated by 60 km (Badajoz 10 years, Mérida 3 years). The Pearson correlation coefficient was calculated between the daily and hourly concentrations. The values of the principal meteorological parameters—temperature, rainfall, relative humidity, and speed and direction of the wind—were calculated during the study period, and with the accumulated values corresponding to the period prior to pollination. The beginning and ending dates and the duration of the main pollen season (MPS) were also analyzed. Even though both families are anemophilous, the presence of their pollens in the air was low. The annual accumulated daily concentrations were in the range 1.8–15.8 for Juncaceae and 111.8–473.9 for Cyperaceae—values far lower than any other anemophilous pollen type. The Cyperaceae pollen concentration peaked between 09:00 and 12:00. The meteorological factor most closely related to its daily variations was found to be the wind direction, showing that location of the sources is of great importance. The results lend support to the hypothesis of a limitation of allogamous reproduction in favour of vegetative multiplication in both families. Nevertheless, the principal source of the airborne Cyperaceae pollen was found to be Scirpus holoschoenus, whose pollen is distinguishable from the rest. Hence, because of its large production of pollen, this species can be characterized as anemophilous and allogamous. Rainfall in the preceding autumn seemed to be responsible for the amount of Cyperaceae pollen in the air, since a lack of rain was found to be associated with lower densities in the traps. For the Juncaceae, it seems that the temperatures of the preceding December constituted the most limiting meteorological parameter.     

Comparative study of seasonal and intradiurnal variation of airborne herbaceous pollen in urban and rural areas

The content of herbaceous pollen in the atmosphere depends on the vegetal cover, climate and the weather and geographical conditions. The aim of the study reported here was to compare aerobiological data obtained from pollen monitoring stations located at sites differing with respect to their flora and microclimate – i.e. a town and a rural area. A volumetric method was used for sampling. In each microscopic preparation 12 vertical strips corresponding with 2-h intervals were analysed. A 90% method was used to determine the pollen season. The results were statistically verified using the u test and the Kolmogorov-Smirnov, Spearman and Wilcoxon tests. Higher values of the Seasonal Pollen Index (SPI), higher daily average concentrations and higher peak values were recorded in the rural area. An analysis of intradiurnal variations of airborne pollen showed that apart from the Poaceae the number of pollen grains in the air began to increase earlier in the day in the rural area; in the case of Rumex and Ambrosia, the maximum values also appeared a few hours earlier. For all the taxa investigated, the analysis of correlation showed a significant association between the daily average concentrations at both sites. The weakest association occurred for Plantago lanceolata; for all other taxa, the determination coefficients (R ²) were high. The results of the Wilcoxon test showed that, despite the strong positive association between daily concentrations of the pollen types investigated, there were differences in mean pollen concentrations in the overlapping pollen season. Mean concentrations of Poaceae and Rumex airborne pollen were significantly higher in the rural area in both years, and those of Urtica and P. lanceolata were significantly higher only in 2002.     

Aprpaoches to airborne pollen in SE spain. First survey in murcia: one year of pollen monitoring (1993–94)

First data from a pollen survey carried out in the city of Murcia (SE Spain) are given in this paper. Using a Burkard Volumetric Spore Trap, daily slides were prepared and 80 pollen types belonging to 51 families andAlternaria spores were identified and counted. Special attention was paid to 14 relevant taxa: Cupressaceae,Pinus, Genisteae,Olea, Morus, Acer, Platanus, Plantago, Quercus, Urticaceae, Poaceae, Chenopodiaceae,Artemisia andAlternaria. The main sources of airborne particles wereAlternaria (27.7%), Cupressaceae (13.5%),Olea (9.36%), Chenopodiaceae (8.31%) and Urticaceae (5.8%). Annual variations in pollen abundance and length of the flowering seasons are given for individual species and are related to environmental factors. Results indicate a main pollen season from March to June and a second minor season in September to October. The relatively high concentrations of Genisteae and the appearance of anArtemisia winter season were noted.     

Risk of pollen allergy in Nerja (southern Spain): a pollen calendar

An aeropalynological study was carried out in the atmosphere of the city of Nerja (southern Spain) during a period of 4 years (2000–2003), using a Hirst type volumetric pollen trap. An annual pollen index of 59,750 grains, on average, was obtained with 80–85% of the total pollen recorded from February to May, with Pinus, Olea, Urticaceae, Cupressaceae, Quercus and Poaceae being the principal pollen producers in abundance order. A total of 29 pollen types that reached a 10-day mean equal to or greater than 1 grain of pollen per m³ of air is reflected in a pollen calendar. The results were compared with those obtained for nearby localities and a correlation analysis was made between the daily fluctuations of the main pollen types and total pollen, and meteorological parameters (temperature, rainfall and hours of sun). The daily, monthly and annual values reached by the most important pollen types from an allergenic point of view (Olea, Urticaceae and Poaceae) confirms Nerja as a high-risk locality for the residents and the numerous tourists who visit the area.     

Oleaceae in Trieste (NE Italy): aerobiological and clinical data

Oleaceae pollen concentrations in the Trieste area are low (<10%) compared to the total number of airborne pollen grains, with only one pollination peak at the beginning of June when the Oleaceae concentration reached 62% of the total pollen count in 1992. This peak was due to an exceptionally high pollination of olive trees in 1992, when airborne pollen concentration rose to 1357 pollen grains/m³ on June 3. Sensitization toOlea increased from 1989 to 1993, when it was present in 23.4% of symptomatic patients, but the role ofOlea in inducing allergic respiratory symptoms is difficult to evaluate because almost all patients were sensitized to other pollens, and in particular to Gramineae: only four subjects were sensitized toOlea alone (1.4%). Despite the low Oleaceae pollen counts, this pollinosis is increasing, probably because of increased cultivation ofOlea in recent years. However, although skin prick test positivity is common in polysensitized patients, its role in inducing sensitization and symptoms is presently less important than that of other pollens.     

Pollen emission from olive trees and concentrations of airborne pollen in an urban area of North Sardinia

In this study the seasonal and daily variations in olive airborne pollen concentrations were measured in the atmosphere of Sassari (Italy) and the olive pollen emission was monitored in the countryside during the flowering period in 1995 and 1996, in order to detect the patterns of change in the atmosphere. The intensity and the timing of pollination was also studied in relation to phenological stages occurrence. In addition, the influence of the main meteorological parameters on pollen emission and airborne pollen dispersal in the city was assessed. Airborne pollen reached its highest concentration a few days before the peak of pollen emission in 1995 but several days after it in 1996 (6 days). Analysis of hourly concentrations shows that the maximum emission and dispersion recorded during the observation period occurred in the middle of the day. Significant regressions were found between hourly temperature and air humidity values and hourly pollen concentrations recorded in the olive grove for almost every day studied, indicating a negative correlation between humidity and pollen concentration and a positive correlation between pollen concentration and temperature. On the other hand, no significant correlation was observed between the meteorological parameters and pollen concentration recorded in the urban area.     

Dynamics and behaviour of airborne Quercus pollen in central Iberian Peninsula

Quercus pollen is one of the most abundant pollen types in the atmosphere of central Iberian Peninsula (Spain), as a consequence of the extensive representation of well-preserved forests and shrub communities dominated by species of the genus Quercus in this area. This paper analysed key features of the Quercus pollination season in the central Iberian Peninsula and the influence of weather-related variables on airborne Quercus pollen concentration through statistical techniques of correlation analysis and the use of a decision tree model for predicting pollen concentrations. Quercus species are very common in Spain and Portugal, dominating a number of ecosystems including Mediterranean forests. This gives rise to very high airborne Quercus pollen concentrations, particularly in spring. Sampling was carried out over a 6-year period using a Hirst volumetric sampler, and the sampling procedure established by the Spanish Aerobiology Network. Results show that between 92 and 98.5 % of total annual airborne Quercus pollen was recorded in the April–June period. Annual pollen index were high in all study years, averaging 12,344 grains, but it should be highlighted that pollen production was highly variable between years. Correlations between mean daily Quercus pollen concentration and weather-related variables showed that in the pre-peak period, a significant positive correlation was observed with the mean daily temperature and the hours of sunshine and a negative correlation was observed with the humidity and the rainfall. In the post-peak period, a significant negative correlation was found with the mean daily temperature and the hours of sunshine. The predictions obtained in the decision tree model showed a moderate significant correlation (r = 0.42) with the daily Quercus pollen concentration predicted and the one observed. Temperature is the most influential variable in the release of Quercus pollen.