Statistical modeling,forecasting and time series analysis of birch phenology in Montreal,Canada

The aim of this study was to analyse birch pollen time series observed in Montreal (Canada) in order to understand the link between inter-annual variability of phenology and environmental factors and to build predictive models for the upcoming pollen season. Modeling phenology is challenging, especially in Canada, where phenological observations are rare. Nevertheless, understanding phenology is required for scientific applications (e.g. inputs to numerical models of pollen dispersion) but also to help allergy sufferers to better prepare their medication and avoidance strategies before the start of the pollen season. We used multivariate statistical regression to analyse and predict phenology. The predictors were drawn from a large basin (over 60) of potential environmental predictors including meteorological data and global climatic indices such NAO (North Atlantic Oscillation index) and ENSO/MEI (Multivariate Enso Index). Results of this paper are summarized as follows: (1) an accurate forecast for the upcoming season starting date of the birch pollen season was obtained (showing low bias and total forecast error of about 4 days in Montreal), (2) NAO and ENSO/MEI indices were found to be well correlated (i.e. 44% of the variance explained) with birch phenology, (3) a long-term trend of 2.6 days per decade (p < 0.1) towards longer season duration was found for the length of the birch pollen season in Montreal. Finally, perturbations of the quasi-biennial cycle of birch were observed in the pollen data during the pollen season following the Great Ice Storm of 1998 which affected south-eastern Canada.     

Impact of 2003 heat waves on aerobiological indices of allergenic herbaceous family pollen season in Tuscany (Italy)

The aim of this study was to assess the current aerobiological situation and to investigate the influence of the hot and dry summer 2003 on pollen season (onset, end and duration of the pollen season, peak pollen day and value, total seasonal amount of pollen grains) of herbaceous family as Poaceae, Urticaceae and Compositeae. Heat wave of 2003 influenced the phenology of the main pollen families in Tuscany: the high temperatures occurred during 2003 affected pollen season of different family with different responses. This study confirms the role that the climate has on the flora species and in particular on herbaceous species phenology and the high variability of the pollination among different places, during extreme events. In general, high spring temperature induces an advance of the flowering period and a release of higher pollen quantity of Urticaceae and Poaceae; however, exceptional weather conditions (i.e., summer 2003) could exert an opposite effect, resulting in an impairment of flowering of Urticaceae during autumn. Compositeae species produced a low amount of pollen in 2003, even if the peak value was higher than the average in some stations.     

Study of the floral phenology of <Emphasis Type="Italic">Olea europaea</Emphasis> L. in Jaén province (SE Spain) and its relation with pollen emission

Phenological and aerobiological studies provide important information regarding the reproductive biology of cultivated species such as the olive. This article presents the results of an exploratory study of the floral phenology of Olea europaea L. at different altitudes in Jaén province (SE Spain) and an analysis of the main meteorological factors affecting flowering. As well, this study aimed to detect the relationship between phenology and olive pollen emission as a means of interpreting Olea pollen curves in the city of Jaén. Phenological observations were performed on olive trees at six sites, each at different altitudes and distributed over the whole area of olive cultivation in the province. Pollen data were obtained using a Hirst-type volumetric spore trap located within the city of Jaén. Phenological and aerobiological data were recorded in 2006 and 2007. This study shows that the chronology of the start of the flowering period depends on altitude. Statistical analyses indicate that the temperature, humidity, cumulative rainfall and cumulative solar radiation are the meteorological parameters that most affect olive floral phenology. The pollen season in Jaén generally lasts from May to June, with an annual total emission of over 40,000 pollen grains, the highest annual level of olive pollen emission in the world. The airborne pollen concentrations recorded in the city of Jaén are above all influenced by the olive groves located in the Guadalquivir valley.     

Pollen-landscape relationships in modern analogues of ancient cultural landscapes in southern Sweden — a first step towards quantification of vegetation openness in the past

This study aims to analyse how vegetation, and in particular the degree of openness of the landscape, is reflected in pollen assemblages from surface sediment in lakes. Modern analogues of ancient cultural landscapes in southern Sweden were selected. Surface sediments from 22 small lakes (0.5–20 ha) located mainly in the forest region of southern Sweden were collected and analysed for pollen in order to enlarge and complement an earlier data set of 13 lakes collected in the open, agricultural region of southernmost Sweden. The composition of the landscape surrounding the lakes was mapped within 1000-m and 500-m radii around the lakes using Colour InfraRed (CIR) aerial photographs. The pollen and landscape data were analysed using numerical ordination techniques. The results show that, despite the large variation of landscape openness, the variation in non-arboreal pollen (NAP) is low between the sites which was not the case for the 13 lakes of the previous study. It is hypothesised that this may be due to differences in the major characteristics of the two regions in which the sites were selected, i.e. mainly treeless and intensively farmed in the previous study and mainly forested in the present investigation. The difference in background pollen appears to play a decisive role on the relative representation of NAP. This implies that the background pollen should be estimated before NAP percentages can be used for quantitative reconstruction of past landscape openness. In the 22 lakes studied, Gramineae, Cerealia (excludingSecale),Filipendula andSalix are positively correlated to cultivated land within both radii, and with open land (tree cover not exceeding 20%) within the 1000-m radius.Quercus andFagus have some positive correlation with deciduous orest within 1000-m radius. We conclude that the landscape units cultivated land, open land and deciduous forest within 1000-m radius are reasonably well reflected in the pollen assemblages and could be predicted within this area.     

Mating dynamics of Scots pine in isolation tents

Seed orchards are forest tree production populations for supplying the forest industry with consistent and abundant seed crops of superior genetic quality. However, genetic quality can be severely affected by non-random mating among parents and the occurrence of background pollination. This study analyzed mating structure and background pollination in six large isolation tents established in a clonal Scots pine seed orchard in northern Sweden. The isolation tents were intended to form a physical barrier against background pollen and induce earlier flowering relative to the surrounding trees. We scored flowering phenology inside and outside the tents and tracked airborne pollen density inside and outside the seed orchard in three consecutive pollination seasons. We genotyped 5683 offspring collected from the tents and open controls using nine microsatellite loci, and assigned paternity using simple exclusion method. We found that tent trees shed pollen and exhibited maximum female receptivity approximately 1 week earlier than trees in open control. The majority of matings in tents (78.3 %) occurred at distances within two trees apart (about 5 m). Self-fertilization was relatively high (average 21.8 %) in tents without supplemental pollination (SP), but it was substantially reduced in tents with SP (average 7.7 %). Pollen contamination was low in open controls (4.8–7.1 %), and all tents remained entirely free of foreign pollen. Our study demonstrates that tent isolation is effective in blocking pollen immigration and in manipulating flowering phenology. When complimented with supplemental pollination, it could become a useful seed orchard management practice to optimize the gain and diversity of seed orchard crops.     

Prospects for improved off-crop habitat management for pollen beetle control in oilseed rape

There is an urgent need to develop sustainable and environmentally benign integrated pest management (IPM) strategies for arable crops. The enhancement and manipulation of naturally occurring populations of the natural enemies of crop pests through habitat management for ‘conservation biological control’, as well as habitat management to manipulate populations of the pests themselves, have the potential to become major components of successful IPM strategies. We review the studies that have contributed to our current understanding of how the crop margin, local landscape, and regional landscape can influence pollen beetle Brassicogethes aeneus (syn. Meligethes aeneus) (Coleoptera: Nitidulidae) abundance and damage to oilseed rape crops (Brassica napus), and the efficacy of their natural enemies. We also discuss how habitat management across these multiple scales may improve pollen beetle control, reducing the need for insecticide use and contributing towards sustainable production of this important crop which is grown on increasing areas for both food and fuel.     

Phenotypic selection on flowering phenology and size in two dioecious plant species with different pollen vectors

Dioecious plants may be pollinated biotically by animals or abiotically via wind or water currents. It has been hypothesized that these two types of pollen vectors might impose contrasting selective pressures on plant flowering phenology. In the present study we describe the flowering phenology of two sympatric dioecious species with contrasting pollination modes: Mercurialis perennis (wind‐pollinated) and Tamus communis (insect‐pollinated). We estimated selection differentials and gradients for flowering time and flowering synchrony. As flowering time might depend on the accumulation of enough internal resources, we also estimated direct and indirect selection on plant size. Both species have male‐biased sexual ratios, and males are bigger and produce larger flower displays than females, but only in T. communis do males bloom earlier and for longer than females. Selection gradients suggest that selection tends to favor early‐flowering females of T. communis. There is no evidence of direct current selection on the flowering phenology of M. perennis. Intersexual differences in phenology fit with sex allocation and sexual selection theories. As we hypothesized, phenology of the animal‐pollinated species is under stronger selection than that of the wind‐pollinated species and we discuss the potential role of pollen vectors in shaping the flowering phenologies of the study species.     

The effects of large-scale atmospheric fields on the cypress pollen season in Tuscany (Central Italy)

This research was performed for the purpose of analysing the relationships between large-scale meteorological information, in particular the North Atlantic Oscillation (NAO) index and the Sea Surface Temperature (SST), and the timing and magnitude of the Cupressaceae pollen season in the Pistoia district of Central Italy. The results demonstrated that in specific periods of the year, the NAO index, by partially determining the distribution of the main meteorological variables over the study area, is negatively correlated with the start and the end, as well as the peak day of pollen concentration. Pollen data were also correlated with the SST of the North Atlantic Ocean east of the Azores for the September–December period of the previous year, which is significant for exploring possibilities in terms of predicting the timing and magnitude of the cypress pollen season. The analysis of such meteorological variables and indices could be used to improve the existing forecasting systems of the phenology of the cypress pollen season. Moreover, the possibility of using meteorological information freely available on internet could cut costs and reduce spatial and temporal representativeness limitations relating to weather monitoring in loco.     

The role of landscape characteristics for forage maturation and nutritional benefits of migration in red deer

Large herbivores gain nutritional benefits from following the sequential flush of newly emergent, high‐quality forage along environmental gradients in the landscape, termed green wave surfing. Which landscape characteristics underlie the environmental gradient causing the green wave and to what extent landscape characteristics alone explain individual variation in nutritional benefits remain unresolved questions. Here, we combine GPS data from 346 red deer (Cervus elaphus) from four partially migratory populations in Norway with the satellite‐derived normalized difference vegetation index (NDVI), an index of plant phenology. We quantify whether migratory deer had access to higher quality forage than resident deer, how landscape characteristics within summer home ranges affected nutritional benefits, and whether differences in landscape characteristics could explain differences in nutritional gain between migratory and resident deer. We found that migratory red deer gained access to higher quality forage than resident deer but that this difference persisted even after controlling for landscape characteristics within the summer home ranges. There was a positive effect of elevation on access to high‐quality forage, but only for migratory deer. We discuss how the landscape an ungulate inhabits may determine its responses to plant phenology and also highlight how individual behavior may influence nutritional gain beyond the effect of landscape.     

The effect of the meteorological factors on the Alnus pollen season in Lublin (Poland)

Alder pollen seasons and the effect of meteorological conditions on daily average pollen counts in the air of Lublin (Poland) were analysed. Alnus pollen grains reach very high concentrations in the atmosphere of this city during the early spring period and the parameters of pollen seasons were very different in the particular years studied. The pollen season lasted on average one month. The highest variation was observed for the peak value and the Seasonal Pollen Index (SPI). The pollen seasons, which started later, had shorter duration. Peak daily average pollen counts and SPI value were higher during the shorter seasons. Similarities in the stages of pollen seasons designated by the percentage method depended on the start date of the pollen season. Season parameters were mainly correlated with thermal conditions at the beginning of the year. Regression analysis was used to predict certain characteristics of the alder pollen season. The highest level of explanation of the variation in Alnus pollen season start and peak dates was obtained in the model using mean temperature in February. The obtained regression models may predict 82% of the variation in the pollen season start date, 73% of the variation in the duration, and 62% in the peak date.     

The weak effects of climatic change on Plantago pollen concentration: 17 years of monitoring in Northwestern Spain

Plantago L. species are very common in nitrified areas such as roadsides and their pollen is a major cause of pollinosis in temperate regions. In this study, we sampled airborne pollen grains in the city of León (NW, Spain) from January 1995 to December 2011, by using a Burkard® 7-day-recording trap. The percentage of Plantago pollen compared to the total pollen count ranged from 11 % (1997) to 3 % (2006) in the period under study. Peak pollen concentrations were recorded in May and June. Our 17-year analysis failed to disclose significant changes in the seasonal trend of plantain pollen concentration. In addition, there were no important changes in the start dates of pollen release and the meteorological parameters analyzed did not show significant variations in their usual trends. We analyzed the influence of several meteorological parameters on Plantago pollen concentration to explain the differences in pollen concentration trends during the study. Our results show that temperature, sun hours, evaporation, and relative humidity are the meteorological parameters best correlated to the behavior of Plantago pollen grains. In general, the years with low pollen concentrations correspond to the years with less precipitation or higher temperatures. We calculated the approximate Plantago flowering dates using the cumulative sum of daily maximum temperatures and compared them with the real bloom dates. The differences obtained were 4 days in 2009, 3 days in 2010, and 1 day in 2011 considering the complete period of pollination.     

A systematic review of the effects of temperature and precipitation on pollen concentrations and season timing,and implications for human health

Climate and weather directly impact plant phenology, affecting airborne pollen. The objective of this systematic review is to examine the impacts of meteorological variables on airborne pollen concentrations and pollen season timing. Using PRISMA methodology, we reviewed literature that assessed whether there was a relationship between local temperature and precipitation and measured airborne pollen. The search strategy included terms related to pollen, trends or measurements, and season timing. For inclusion, studies must have conducted a correlation analysis of at least 5 years of airborne pollen data to local meteorological data and report quantitative results. Data from peer-reviewed articles were extracted on the correlations between seven pollen indicators (main pollen season start date, end date, peak date, and length, annual pollen integral, average daily pollen concentration, and peak pollen concentration), and two meteorological variables (temperature and precipitation). Ninety-three articles were included in the analysis out of 9,679 articles screened. Overall, warmer temperatures correlated with earlier and longer pollen seasons and higher pollen concentrations. Precipitation had varying effects on pollen concentration and pollen season timing indicators. Increased precipitation may have a short-term effect causing low pollen concentrations potentially due to “wash out” effect. Long-term effects of precipitation varied for trees and weeds and had a positive correlation with grass pollen levels. With increases in temperature due to climate change, pollen seasons for some taxa in some regions may start earlier, last longer, and be more intense, which may be associated with adverse health impacts, as pollen exposure has well-known health effects in sensitized individuals.

     

Trends and temperature response in the phenology of crops in Germany

The phenology of 78 agricultural and horticultural events from a national survey in Germany spanning the years 1951–2004 is examined. The majority of events are significantly earlier now than 53 years ago, with a mean advance of 1.1–1.3 days per decade. The mean trends for 'true phases', such as emergence and flowering, of annual and perennial crops are not significantly different, although more trends (78% vs. 46%) are significant for annual crops. We attempt to remove the influence of technological advance or altered farming practices on phenology by detrending the respective time series by linear regression of date (day number) on year. Subsequently, we estimate responses to mean monthly and seasonal temperature by correlation and regression in two ways; with and without removing the year trend first. Nearly all (97%) correlation coefficients are negative, suggesting earlier events in warmer years. Between 82% and 94% of the coefficients with seasonal spring and summer temperatures are significant. The conservative estimate (detrended) of mean temperature response against mean March–May temperature (−3.73 days °C⁻¹) is significantly less than the full estimate (−4.31 days °C⁻¹), the 'true' size of phenological temperature response may lie in between. Perennial crops exhibited a significantly higher temperature response to mean spring temperature than the annual crops.     

Pollen transport differs among bees and flies in a human‐modified landscape

Aim Dispersal distances of insect pollinators are critical in defining their contribution to landscape‐wide pollen movement and ultimately gene flow in natural and agricultural systems. We ask whether bee and fly pollinator taxa differ in their dispersal distances and transport of viable pollen in a human‐modified system. Location Canterbury and Otago region, South Island, New Zealand. Methods We captured pollen‐carrying insects travelling outside of a model mass‐flowering agricultural crop, Brassica rapa, using insect flight intercept traps at five distances (0, 100, 200, 300 and 400 m) from the pollen source. We examined pollen loads and pollen viability to determine whether pollen transport distance and viability differ among pollinator taxa. Results A total of 5453 insects were collected of which 717 individuals from 26 insect taxa were positively identified as dispersing pollen up to 400 m from the source. These taxa consisted of four species from two bee families (Hymenoptera: Apidae and Halictidae), and eight species from four fly families (Diptera: Bibiondae, Stratiomyidae, Syrphidae and Tachinidae). Apidae generally carried higher pollen loads and more viable pollen than most fly taxa. Taxa in the fly families Stratiomyidae and Syrphidae, however, carried pollen to 400 m, which is further than both bee families. Main conclusions A diverse array of wild and managed flower visitors can transport viable pollen from a pollen source to at least 400 m. Knowledge of the differences in transport distances among generalist pollinators in human‐modified environments is crucial to understand the potential extent to which (1) pollen transport can facilitate gene flow and (2) unwanted hybridization may occur between crops and related weeds.     

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.     

Specialty oilseed crops provide an abundant source of pollen for pollinators and beneficial insects

The continuing pollinator crisis is due, in part, to the lack of year‐round floral resources. In intensive farming regions, such as the Upper Midwest (UMW) of the USA, natural and pastoral vegetation largely has been replaced by annual crops such as maize (Zea mays L.), soyabean (Glycine max L.) and wheat (Triticum spp.). Neither the energy (nectar) nor protein (pollen) needs of pollinating and other beneficial insects are being met sufficiently by the new, high‐intensity, agricultural landscape. Several potentially useful oilseed crops can be grown in the UMW, and many of these oilseeds are highly attractive to beneficial insects. Prior research showed that some of these oilseeds produced abundant nectar, but their corresponding values for pollen production are unknown. Accordingly, the aim of our research was to document pollen (and protein) production per unit area of twelve oilseed crops grown in Minnesota and associate these values with levels of beneficial insect visitation during anthesis. Our results show that oilseed crops such as camelina (Camelina sativa L.), flax (Linum usitatissimum L.) and pennycress (Thlaspi arvense L.) produce relatively little pollen (≤40 kg/ha); borage (Borago officinalis L.), calendula (Calendula officinalis L.), canola (Brassica napus L.), crambe (Crambe abyssianica Hochst) and cuphea (Cuphea viscosissima Jacq. × Cuphea lanceolata W. T. Aiton) produce bountiful pollen resources (50–150 kg/ha); and oilseed echium (Echium plantagineum L.) generates massive amounts of pollen (>400 kg/ha), about 50% of which is protein. Our study is unique in presenting a season‐long perspective of pollen production in alternative oilseed crops, a resource valuable to pollen‐feeding insects such as managed and wild bees. Diversification of UMW landscapes that includes alternative oilseed crops such as oilseed echium and cuphea can potentially provide a ready source of pollen and protein to help combat pollinator decline.     

Sunlit mesocosms designed for pollen confinement and risk assessment of transgenic crops

To minimize concerns about the ecological consequences of wind and insect dispersal of pollen and the potential of gene flow from experimental genetically modified (GM) crops to compatible relatives, we have modified outdoor sunlit open top chambers (OTCs) for use with GM plants. We have redesigned 21 cylindrical OTCs, commonly used to study the effects of atmospheric pollutants, by adding (1) a pollen filter at the top of each unit to minimize the possibility of the escape of GM pollen; with pollen filters in place, the OTCs are referred to as mesocosms, (2) an evaporative cooler to help mitigate elevated temperatures during the summer months, and (3) an automated watering system that eliminates the need to enter a mesocosm for irrigation during pollination, thereby minimizing potential pollen escape and entry of insect pollinators. Each sunlit mesocosm contains three large plastic pots (each with 1.2-m² surface area) that simulate field plots and that contain a constructed plant community. For example, the community may consist of a GM and a non-GM cultivar of canola (Brassica napus), compatible weedy relatives, and non-compatible species that may be found in mesic disturbed areas such as roadsides or ditches beyond crop fields. The sunlit mesocosms provide a well-replicated outdoor testing system that confines pollen and that can be used to precede or supplement field tests that evaluate the potential ecological consequences of transgenic crops. The mesocosms are proposed as test systems in which transgenic crops and other plants (e.g., biofuel crops) that have been proposed to be grown in new geographies, or plants that produce novel compounds, may be studied to evaluate their potential effects on plant communities. The pollen confinement and insect exclusion features of our mesocosms may also minimize exposure of sensitive humans and insect pollinators to pollen and cellular debris from other plant parts.     

Crop–noncrop spillover: arable fields affect trophic interactions on wild plants in surrounding habitats

Ecosystem processes in agricultural landscapes are often triggered by resource availability in crop and noncrop habitats. We investigated how oilseed rape (OSR; Brassica napus, Brassicaceae) affects noncrop plants in managed systems and semi-natural habitat, using trophic interactions among wild mustard (Sinapis arvensis, Brassicaceae), rape pollen beetles (Meligethes aeneus, Nitidulidae) and their parasitoids (Tersilochus heterocerus, Ichneumonidae). We exposed wild mustard as phytometer plants in two cropland habitat types (wheat field, field margin) and three noncrop habitat types (fallow, grassland, wood margin) across eight landscapes along a gradient from simple to complex (quantified as % arable land). Both landscape and local factors affected the abundance of rape pollen beetles and parasitoids. Rape pollen beetle infestation and parasitism rates on these plants were lower in noncrop habitats and higher in wheat fields and field margins, whereas beetles and parasitoids responded differently to landscape scale parameters. We found the hypothesized spillover from OSR crop onto wild plants in surrounding habitats only for parasitoids, but not for pollen beetles. Parasitism rates were not related to landscape simplification, but benefited from increasing proportions of OSR. In contrast, rape pollen beetles benefited from simple landscape structures, presumably due to multi-annual population build-ups resulting from long-term OSR planting (as part of the crop rotation). In conclusion, we showed that spillover from cropland affects parasitism rates on related wild plants outside cropland, which has not been shown so far, but can be expected to be a widespread effect shaping noncrop food webs.     

Inadequate pollination services limit watermelon yields in northern Tanzania

Insect pollination plays a vital role for the yield of many crops, such as apples, strawberries and coffee, which are economically significant commodities on the global market. Yet, knowledge about the role of insect pollination is lacking for many cash crops that support the livelihoods of small-scale farmers in developing countries.To assess if yields of watermelon are pollen limited, we conducted a supplemental hand-pollinated experiment (using a pollen mixture of cross and self-pollen) in 13 small-scale farms in an agricultural landscape in the Kilimanjaro and Arusha regions in northern Tanzania. We assessed fruit set, fruit abortion and weight of the mature fruits stemming from hand pollinated and control flowers. To check if differences in yield responses between hand-pollinated and control treatments depended on resource availability, we also accounted for local soil conditions.We found that hand pollination (i) increased the probability of fruit initiation by 30%, (ii) reduced the probability of fruit abortion by 13%, (iii) increased the probability of flowers developing into mature fruits by 42% and (iv) increased average fruit weight by 1.3 kg (±0.15 SE). Our results indicate that our system is pollen limited, due to insufficient visitor frequency and/or inefficient pollinator species.Fruit initiation and fruit weight were positively related to soil carbon, irrespective of treatment. The influence of soil moisture was not consistent across the measured responses, and differed between hand-pollinated and the control treatments.We suggest that farmers in our focal area should focus on improving the quality of the landscape to sustain and enhance healthy pollinator communities ultimately improving yields. We also suggest that farmers should continue current practices with respect to fertilization. The role of soil moisture on fruit initiation and maturation should be investigated to ensure that the positive effects of pollen is not hindered by soil moisture conditions.     

Ambrosia pollen in the air of Lublin, Poland

Studies on Ambrosia pollen concentrations were carried out in Lublin in the period 1995–2004. The effects of a number of meteorological factors were analysed. In the first period of the study, the gravimetric method was used (1995–1999), while in the second period, the volumetric method was applied. The results show an increasing trend in the amount of airborne pollen. The Ambrosia pollen season in Lublin lasts from August to October. Over a period of 5 years, the highest number of pollen grains was recorded in September (53%), followed by August (44%) and October (3%). There were wide variations in annual totals. The annual total pollen counts was 167–1180 grains, with the peak value in 2002. Maximum daily pollen concentrations (56–312 pollen grains m⁻³) were recorded in the first half of August and in the first half of September. On the days when high Ambrosia pollen concentrations occurred, the temperature was above 21°C and the winds were mainly from the southeast, south and east. Maximum intradiurnal concentrations of pollen grains occurred in the afternoon hours. These results indicate, to some degree, that Ambrosia pollen is transported for long distances before descent.