Current issue: 57(2)
Under compilation: 57(3)
Budburst timing and the relationship to storage temperature and duration were investigated in four varieties (entries) of 1–2 metres tall silver birch (Betula pendula Roth) trees. A total of 2,160 shoots were sampled, and the material stores in darkness at 0, 3 or 6 °C from November 29, 1993. When the shoots were placed in storage, they had been through a period of 29 days with temperatures below 0°C (since October 15). By that time the autumn dormancy was assumed already broken, and the trees were expected to respond to increased temperature by bud development. On January 4, 1994, and on four subsequent dates, January 19, February 1, March 4 and March 17, shoots were taken out of storage and set in growth chambers at 9, 12 or 15°C. The time to budburst was recorded.
Duration of storage, storage temperatures and varieties were all highly significant for budburst. The interaction terms were of less statistical importance. Based on the contrast between the three different growth chamber environments, three different methods were used to calculate the threshold temperatures for each entry. In spite of the pre-selection of variable budburst performers, the threshold values, varying between 0°C to -2°C, could not be shown to be statistically different. According to the results, the time of budburst changes in accordance with both winter and spring temperatures, being extremely early after a mild winter and warm spring, given sufficient autumn chilling. The similarities in the threshold temperatures indicate that the ranking in earliness between varieties will most likely be the same from year to year without regard to climate change.
Temperature sums required for budburst in various Norway spruce (Picea abies (L.) H. Karst.) provenances were determined, and weather statistics were then used to predict the risk of potentially damaging frosts at 11 locations in Sweden. Frost risk was quantified as the probability of a frost occurring within 100 day-degrees (two weeks) after budburst. The examples provided show that a spruce seedling from central Sweden has to sustain almost twice as many frost occassions as a seedling from Belorussia, when planted in southern and central Sweden. The method presented here can be used for mapping early summer frost risk in Sweden and for supporting provenance transfer guidelines.
Male flowering was studied at the canopy level in 10 silver birch (Betula pendula Roth) stands from 8 localities and 14 downy birch (B. pubescens Ehrh.) stands from 10 localities in Finland in 1963–73. Distribution of cumulative pollen catches was compared to the normal Gaussian distribution. The basis for timing of flowering was the 50% point of the anthesis-fitted normal distribution. To eliminate effects of background pollen, only the central, normally distributed part of the cumulative distribution was used. Development was measured and tested in calendar days, in degree days (> 5°C) and in period units. The count of the parameters began in March 19.
Male flowering in silver birch occurred from late April to late June depending on latitude, and flowering in downy birch took place from early May to early July. The heat sums needed for male flowering varied in downy birch stands latitudinally but there was practically no latitudinal variation in silver birch flowering. The amount of male flowering in stands of the both species were found to have a large annual variation but without any clear periodicity.
The between years pollen catch variation in stands of either birch species did not show any significant latitudinal correlation in contrast to Norway spruce stands. The period unit heat sum gave the most accurate forecast of the timing of flowering for 60% of the silver birch stands and for 78.6% of the downy birch stands. Silver birch seems to have a local inclination for a more fixed flowering date compared to downy birch, which could mean a considerable photoperiodic influence on flowering time of silver birch. The species had different geographical correlations.
Frequent hybridization of the birch species occurs more often in Northern Finland than in more southerly latitudes. The different timing in the flowering causes increasing scatter in flowering times in the north, especially in the case of downy birch. Thus, the change of simultaneous flowering of the species increases northwards due to a more variable climate and higher altitudinal variation. Compared with conifers, the reproduction cycles of the two birch species were found to be well protected from damage by frost.
Anthesis was studied at the canopy level in 10 Norway spruce (Picea abies (L.) H. Karst.) stands from 9 localities in Finland was studied in 1963-74. Distribution of pollen catches were compared with the normal Gaussian distribution. The basis for the timing studies was the 50% point of the anthesis-fitted normal distribution. Development was characterized in calendar days, in degree days (>5°C) and in period units. The count of each unit began on March 19 (included). Male flowering in Norway spruce stands was found to have more annual variation in quantity than in Scots pine (Pinus sylvestris L.) stands studied earlier.
Anthesis in spruce in Northern Finland occurred at a later date than in the south. The heat sums needed for anthesis varied latitudinally less in spruce than in pine. The variation of pollen catches in spruce increased towards north-west as in the case of Scots pine. In the unprocessed data, calendar days were found to be the most accurate forecast of anthesis in Norway spruce. Locally, the period unit could be a more accurate parameter for the stand average. However, on a calendar day basis, when annual deviations between expected and measured heat sums were converted to days, period units were narrowly superior to days.
The geographical correlations respected to timing of flowering, calculated against distances measured along simulated post-glacial micgation routes, were stronger than purely latitudinal correlations. Effects of the reinvasion of Norway spruce into Finland are thus still visible in spruce populations just as they were in Scots pine populations.
The proportion of the average annual heat sum needed for spruce anthesis grew rapidly north of a latitude of ca. 63° and the heat sum needed for anthesis decreased only slightly towards the timberline. In light of flowering phenology, it seems probable that north-western third of Finnish Norway spruce populations are incompletely adapted to the prevailing cold climate. A moderate warming of the climate would therefore be beneficial for Norway spruce. This accords roughly with the adaptive situation in Scots pine
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Timing of anthesis in 21 Scots pine (Pinus sylvestris L.) stands from 14 localities in Finland was studied at the canopy level in 1963-74. Distribution of pollen catches were compared with the normal Gaussian distribution. The basis for the timing studies was the 50 per cent point of the anthesis-fitted normal distribution. Development was characterized in calendar days, in degree days (>5°C) and in period units. The count of each unit began on March 19 (included).
Period unit was found to be the most accurate delineation of development. Locally, calendar days were sometimes a more accurate parameter. Anthesis in Northern Finland occurred at a later date than in the south as was expected, but at lower heat sum. The variation in the timing of anthesis and the variation of pollen catches increased northwards. The geographical correlations calculated against distances measured along simulated post-glacial migration routes were stronger than purely latitudinal correlations. Effects of the reinvasion of Scots pine into Finland are thus still visible in pine populations.
The proportion of the average annual heat sum needed for anthesis grew rapidly above a latitude of 63° even though the heat sum needed for anthesis decreased towards the timberline. In light of flowering phenology, it seemed probable that the northern populations in Scots pine in Finland have still not completely adapted to the prevailing cold climate at these latitudes. A moderate warming of the climate would therefore be beneficial for Scots pine.
The PDF includes a summary in Finnish.
The timing of the tetrad phase of microsporogenesis in sixteen tree species, belonging to the genera of Abies, Larix, Picea, Pinus, Alnus, Betula, Corylus and Populus, was studied. The tetrad phase of microsporogenesis in conifers and in Populus tremula L. was reached from late March to early June including the yearly and latitudinal variation. The tetrad phase in Betulaceae was reached in late July to mid-August. The microsporogenesis in Betulaceae species differed in ecophysiological terms from the other species studied in that the timing in Betulaceae was rather day-length dependent than heat sum-correlated. In conifers and in Populus the timing of tetrad phase correlated with heat sums accumulated and did not correlate with day length or any kind of thermal threshold. This difference was, however, judged to be associated to seasonal adaptive strategies rather than taxonomic relationships.
The PDF includes a summary in Finnish.