Modeling of bud break of Scots pine in northern Finland in 1908–2014

Abstract

Bud break and height-growth of Scots pine (Pinus sylvestris L.) in the northern boreal zone in Lapland, Finland, was followed through the entire growing seasons in the periods 2001–2003 and 2008–2010 in sapling stands in two different locations in northern Finland set some 250 km apart along a latitudinal transect. Field measurements continued at the southern site also in 2011–2013. Air temperature was recorded hourly at the sites. A simple optimization algorithm (GA) was used to adjust parameters of the models predicting the timing of bud break of Scots pine in order to minimize the difference between observed and predicted dates. The models giving the best performance and century-long daily temperatures were used to reconstruct bud-break time series. The temperature observations were recorded for the period 1908–2014 in Sodankylä, which is located in-between the sapling stands in the north–south direction and for the period 1877–2014 in Karasjok, which is in Norway about 145 km north–west from the northernmost stand of this study. On average buds began to extend in the beginning of May in the southernmost stand and in mid-May in the northernmost stands, and the variation between years was in the range of 3 weeks. A simple day-length-triggered (fixed date) model predicted most accurately the date of bud break; root mean square error (RMSE) was 2 and 4 days in the northern and southern site, respectively. The reconstructed bud-break series indicated that based on temperature observations from Sodankylä, growth onset of Scots pine has clearly advanced since the 1960s, though it currently matches that of the early 1920s and early 1950s. The temperature record from Karasjok indicated a similar variation, though there was a weak linear trend advancing bud break by about 3–4 days over a 100-year period.

The Annual Phenological Cycle

“…The time series typically cover several decades (Lappalainen and Heikinheimo 1992;Häkkinen et al 1995;Linkosalo et al 1996). Long time series have been used for testing phenological models (Chuine et al , 1999Häkkinen et al 1998;Salminen and Jalkanen 2015) and for examining whether the effects of climatic warming are already observable in nature (Parmesan and Yohe 2003;Menzel et al 2006;Linkosalo et al 2009). …”

Spatiotemporal changes in the boreal forest in Siberia over the period 1985–2015 against the background of climate change

“…In addition, it can be seen from Figure 11(d) that Rbl responds positively to an increase in temperature, which indicates that broad-leaved forest is sensitive to warming and benefits from higher temperatures. A warming climate provides more favorable conditions for the growth and regeneration of plants that previously experienced harsh conditions, thus allowing broad-leaved forest species to survive in the cold north of the study area where they were previously unable to grow (Hoonyoung Park et al, 2015;Høgda et al, 2013;Salminen and Jalkanen, 2015). This pattern has also been observed in Finland (Kauppi et al, 2014).…”

Spring onset and seasonality patterns during the Late Glacial period in the eastern Baltic region

“…Phenological observations of B. nana budburst dates from the Kevo research station in Finnish Lapland suggest that the number of days from spring onset to MSW varies between 25 and 56 d, with a mean of 42 d. A modern dataset for B. pendula from several study sites in Finnish Lapland indicates that the number of days from spring onset to MSW ranges from 40 to 62 d; average spring onset date is 51 d before MSW (Pudas et al, 2008). The modern observations of the budburst dates of P. sylvestris in the Inari region in Finnish Lapland (Salminen and Jalkanen, 2015) suggest the spring onset range of P. sylvestris to be from 50 to 75 d before MSW. Compari-son of the modern phenological characteristics to the plant macro-remain data thus indicates that the major shift in vegetation composition was related to spring onset dynamics, which might have taken place earlier in the warmer periods of the Late Glacial.…”