Flowering phenology of selected wind pollinated allergenic deciduous tree species

Systematic phenological observations have been carried out in the Dendrological Garden of Agricultural University of Poznañ, Park So3acki, Lasek Golêciñski, Przybyszewskiego Street, for two years (2003, 2004). The selected species of deciduous trees, as Betula pendula, Corylus avellana, Platanus x hispanica. There was interdependence between the course of flowering process and weather conditions. Long and frosty winter at the turn of 2002/2003 and subzero mean temperatures in the first quarter of 2003 delayed vegetation. Rapid coming of early spring in the year 2004 accelerate the development of generative organs. Each year spring ground frost during flowering did not inhibit this process. All the investigated tree species are anemophilous and produce large amounts of allergenic pollen grain. They cause allergic reactions throughout the whole period of pollen discharge. Male inflorescences in Corylus avellana, blooming very early, are one of the first plants causing allergic reactions. Betula pendula is the next to bloom, followed by Platanus x hispanica. Observations of phenological phases may provide useful information forecasting the beginning of the period of increased pollen concentration in air.


INTRODUCTION
The term phenology was introduced to science around mid-1850s by a Belgian botanist from Liège Carl Morren.However, already 100 years earlier Carl Linnaeus began systematic studies in that field, gave principles of phenology and developed its research methods (D z i u b a ³ t o w s k i et al., 1931).A fervent promoter of long-term phenological studies in Poland was £ a s t o w s k i (1948,1951), who devoted several separate studies to methodological issues in that field.Considerable services for the development of phenological studies in Poland are credited to S z af e r (1922,1959), who emphasized their importance for plant geography and ecology.The aim of this study was to follow flowering in selected wind pollinated tree species, producing large amounts of allergenic pollen grain.

MATERIAL AND METHODS
Observations were conducted in the North-Western part of the city of Poznañ, covering the area of the Dendrological Garden, the So³acki Park, the Golêciñski Wood and individuals growing in Przybyszewski Street.The aim of observations in the latter site was to study the effect of exhaust gas pollution on the course of phenophases.Three tree species were selected for phenological observations: common birch (Betula pendula Roth), hazel (Corylus avellana L.) and London plane (Platanus x hispanica Mill.ex Münchh.).These observations were conducted on 4-6 individuals of each species, located in various sites in the investigated area.
Phenological observations were conducted in 3-4 day intervals.Flowering phases were established according to £ u k a s i e w i c z (1984): 1. the emergence of first flower buds or buttons of flowers; 2. the emergence of first flowers (several fully opened flowers); 3. the beginning of full flowering (approx.25% opened blooming flowers); 4. the emergence of first overblown flowers (first flowers withered or fell); 5. the end of full flowering (approx.75% overblown flowers) ; 6. last buttons of flowers; 7. the end of flowering (the date when last flowers were overblown).If a given species has dioecious flowers; flowering phases of female and male flowers are presented separately.
Meteorological data were taken from the monthly survey Miesiêczny Prze-gl¹d Agrometeorologiczny (Table 1).While characterizing climatic conditions in the years of observations during flowering and in the period preceding it, it needs to be emphasized that the year 2003 was much cooler than 2004.Winter beginning the year 2003 was long and frosty.In the first quarter subzero mean monthly temperatures and low precipitation were observed.Minimal ground surface temperature dropped to -25°C.This resulted in a delayed vegetation of plants.The decrease in temperature in March together with March and April ground frosts had only a slight effect on plant development.In successive months no larger deviations were observed from the mean multiannual temperature of the month and precipitation totals.Summing up, precipitation total (345 mm) was much lower than the multiannual total (571.5 mm), and mean annual temperature was 9°C and was equal to the multiannual mean.Winter in 2004 was mild.Minimal ground temperature was not lower than -19°C.February was warmer than in the previous year, with large amounts of precipitation, which resulted

DISCUSSION
As was reported by W i t k o w s k a (1990), flowering depends on the temperature and the date of last ground frosts.In early flowering plants, the dates marking the beginning of the emergence are more varied than in late flowering species.
Information found in literature indicates that hazel begins flowering at the beginning or mid-March and this process is adversely affected by thawing weather in January and February followed by much cooler weather (S o k o ³ o w s k a , 1962).In this study in 2004 this species bloomed already towards the end of February.
K a c z m a r e k (1959,1964,1965) reported that in 1958 this process occurred around mid-February and in 1962 already in the third decade of January.This resulted from warm mild winters.In contrast, in the years 1963-65, as a result of very severe, frosty and long winters, flowering was delayed and started only in April.

CONCLUSIONS
1.In selected tree species the period of flowering, i.e. the phase of buttons of flowers and the phase of flowering, lasted from the beginning of early spring until the beginning of early summer.
2. The flowering phase was similar in all individuals of one species and no effect of pollutants on the course of this process was observed.4. As a result of mild and short winter at the turn of 2003/2004 early spring started earlier than usual, so vegetation, and thus also flowering, were accelerated.5.Each year spring ground frost during flowering did not inhibit this process.
6.All the investigated tree species are anemophilous and produce large amounts of allergenic pollen grain.They cause allergic reactions throughout the whole period of pollen discharge.
7. Male inflorescences in Corylus avellana, blooming very early, are one of the first plants causing allergic reactions.Betula pendula is the next to bloom, followed by Platanus x hispanica.
8. Observations of phenological phases may provide useful information forecasting the beginning of the period of increased pollen concentration in air.
Birch usually started flowering in the second decade of April (K a c z m a r e k, 1964; W i t k o w s k a, 1983).It was similar in the years 2003-2004.In 1974, due to considerably warmer weather in March and April, this phase occurred already in the beginning of April (W i t k o w s k a, 1983), while in 1958 and 1963 cold weather caused its delay until the beginning of May (K a c z m a r e k, 1959, 1964).
3. The long and frosty winter at the turn of 2002/2003 and subzero mean temperatures in the first quarter of 2003 delayed vegetation.