Search

City trees planted in parks and along streets are typically grown to large size in nurseries before being transplanted to their final growing sites. According to tendering rules within the European Union (EU), any business may compete for public contracts in any EU country, and this applies to purchases of valuable lots of nursery trees. There is however a risk of poor transplanting success if the trees are imported from very distant locations with a different pace of spring development. The aim of this study was to implement a Thermal Time model to predict the spring development of Tilia trees to find out in which geographical area the spring development is sufficiently similar to conditions in southern Finland, so that the success of transplantation of the trees is not unduly risked. We used phenological observations collected at the International Phenological Gardens (IPGs) over the whole of Europe, together with ERA-Interim weather data to estimate the model parameters, and then used the same date to predict the onset of leaf unfolding of Tilia during the years 1980 to 2015. Producing maps of phenological development of Tilia, we concluded that there are no large risks of frost damage if tree import area is limited to northern parts of Baltics or to the west coast of Scandinavia. [ABSTRACT FROM AUTHOR]

We conducted an experiment to find out how future climate conditions will impact the spring development of photosynthetic capacity of silver birch leaves. We had two greenhouse conditions. In the simulated future climate condition, we had both elevated temperatures and CO2concentration, while for reference we had trees growing under current climate conditions. We used two methods to measure the development of photosynthetic capacity: first, the maximum quantum efficiency of photosystem II with a fluorescence meter; and second, the CO2assimilation rate with gas exchange measurements. The development of full photosynthetic capacity took around two weeks following the bud burst. The maximum quantum efficiency developed slightly faster than the CO2assimilation rate. Both measurement methods showed that an elevated CO2concentration enhanced the development of photosynthetic capacity beyond the impact of temperature only. The enhancement under the conditions of our simulated climate change translates to achieving photosynthetic capacity up to five days earlier, which impact should be taken into account in simulations of photosynthetic productivity. [ABSTRACT FROM PUBLISHER]

We studied the photosynthetic activity of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies [L.] Karst) in relation to air temperature changes from March 2013 to February 2014. We measured the chlorophyll fluorescence of approximately 50 trees of each species growing in southern Finland. Fluorescence was measured 1-3 times per week. We began by measuring shoots present in late winter (i.e., March 2013) before including new shoots once they started to elongate in spring. By July, when the spring shoots had achieved similar fluorescence levels to the older ones, we proceeded to measure the new shoots only. We analyzed the data by fitting a sigmoidal model containing four parameters to link sliding averages of temperature and fluorescence. A parameter defining the temperature range over which predicted fluorescence increased most rapidly was the most informative with in describing temperature dependence of fluorescence. The model generated similar fluorescence patterns for both species, but differences were observed for critical temperature and needle age. Down regulation of the light reaction was stronger in spring than in autumn. Pine showed more conservative control of the photosynthetic light reactions, which were activated later in spring and more readily attenuated in autumn. Under the assumption of a close correlation of fluorescence and photosynthesis, spruce should therefore benefit more than pine from the increased photosynthetic potential during warmer springs, but be more likely to suffer frost damage with a sudden cooling following a warm period. The winter of 2013-2014 was unusually mild and similar to future conditions predicted by global climate models. During the mild winter, the activity of photosynthetic light reactions of both conifers, especially spruce, remained high. Because light levels during winter are too low for photosynthesis, this activity may translate to a net carbon loss due to respiration. [ABSTRACT FROM AUTHOR]

Abstract: The accurate prediction of the flowering period and the amount of released pollen of wind-pollinated trees is important for predicting the aerobiological pollen amounts and for estimating the intensity of background pollination of orchard seed production. Current phenological models, such as the commonly used temperature sum (thermal time) model, are efficient for predicting the timing of point events, e.g. the onset of flowering or leaf unfolding. However, the flowering period of boreal trees, including Betula pendula and B. pubescens, may last up to 5 weeks with widely varying flowering intensity. Therefore, the ability to predict the duration of the whole flowering period and the intensity of pollination is very important. In this paper, we present a new phenological model that predicts the whole flowering period and daily (normalized) variation of flowering intensity. The model is based on similar principles as the temperature sum model. The model was calibrated against pollen data recorded with pollen traps placed in several locations in Southern and Central Finland. Our new model predicted accurately the variation in the intensity throughout the flowering period. Moreover, it was able to predict the start and end of the pollination season with accuracy comparable to that achieved with an ordinary temperature sum model for point events. Due to limited amount of test data, the data-dependency of the model had to be tested with a bootstrapping approach. With this method, the model fit and parameter values showed to be independent of the parameter fitting data. The model can be used to predict the whole flowering period of wind-pollinated boreal trees for many different purposes, such as aerobiological forecasts of allergenic pollen, or generation of input data for models of long-range pollen transport. [ABSTRACT FROM AUTHOR]

Abstract: The timing of spring phenological events of boreal trees, such as flowering and leaf bud burst, is controlled to a great extent by the ambient air temperature, and these events are already showing an advancement that can be attributed to climatic warming. In this paper we utilised this phenomenon to verify direct observations of climatic warming. We constructed eight phenological time series using observations covering 160 years of the leaf bud burst of two species and of the flowering of six species of native deciduous trees growing in Finland. To eliminate the effect of urbanization on local temperature, we rejected the observations made in densely populated areas. When analyzing the trends in the timing of leaf bud burst and flowering we found an advancement of these phenological events ranging from 3.3 to 11.0 days per century. We then converted the observed phenological trends into temperature trends by using thermal time-type models that link the timing of bud burst and flowering to the temperature conditions during bud development. Warming estimates derived from the phenological trends suggested that the mean spring temperature increase in Finland has been 1.8°C per century, which is very close to the value of 1.5°C per century indicated by long-term temperature records. [Copyright &y& Elsevier]

The male flowering and leaf bud burst of birch take place almost simultaneously, suggesting that the observations of leaf bud burst could be used to determine the timing of birch pollen release. However, long-distance transport of birch pollen before the onset of local flowering may complicate the utilization of phenological observations in pollen forecasting. We compared the timing of leaf bud burst of silver birch with the timing of the stages of birch pollen season during an eight year period (1997-2004) at five sites in Finland. The stages of the birch pollen season were defined using four different thresholds: 1) the first date of the earliest three-day period with airborne birch pollen counts exceeding 10 grains m-3 air; and the dates when the accumulated pollen sum reaches 2) 5%; 3) 50% and 4) 95% of the annual total. Atmospheric modelling was used to determine the source areas for the observed long-distance transported pollen, and the exploitability of phenological observations in pollen forecasting was evaluated. Pair-wise comparisons of means indicate that the timing of leaf bud burst fell closest to the date when the accumulated pollen sum reached 5% of the annual total, and did not differ significantly from it at any site (p<0.05; Student-Newman-Keuls test). It was found that the timing of leaf bud burst of silver birch overlaps with the first half of the main birch pollen season. However, phenological observations alone do not suffice to determine the timing of the main birch pollen season because of long-distance transport of birch pollen. [ABSTRACT FROM AUTHOR]

We tested three theories predicting the timing of bud burst in mature birch (Betula pendula Roth) trees utilizing a 60-year phenological time series together with meteorological temperature observations. Predictions of the timing of bud burst based on light conditions in addition to temperature were more accurate than predictions based on dormancy development and temperature (prediction standard error of 2.4 days versus 4.3 days). The signal from light conditions, represented by fixed calendar date, determined the start of bud ontogenesis rather than dormancy release. We suggest that models developed to predict the timing of bud burst be utilized in the analysis of plant responses to climate change and of climate change itself. [ABSTRACT FROM PUBLISHER]

Collecting phenological data is a slow process. Although such data have been collected by a number of organizations, the reliability of these data is not known because the data-generating process cannot be repeated. No further observations to improve the reliability can be obtained. However, the data usually consist of several overlapping observation series and this overlap can be utilized to construct a combined phenological time series and to improve its reliability. We have developed two techniques for selecting the most reliable observations or observation series and thereby improve the reliability of the combined time series. Both techniques require that the method used to combine the separate phenological time series adjusts the individual series to eliminate possible systematic differences between them. A data set of bud burst in Betula pendula Roth collected in Central Finland during 1896–1955 was adjusted and used to test both techiques. Both techniques considerably improved the reliability of the combined time series; the mean of the confidence intervals of the annual means decreased by 12%. Despite the improvement in reliability, the resulting changes in the annual values of the combined time series were small, the largest change being 2.5 days. Removing outliers was the most effective method of improving reliability, i.e., it resulted in the greatest improvement with the smallest number of discarded observations. [ABSTRACT FROM PUBLISHER]