title: Temperature sum accumulation effects on within-population variation and long-term trends in date of bud burst of European white birch (Betula pendula).
abstract: Within-population variation in phenology of boreal trees indicates their adaptability to climatic variations. Although interannual variations in date of bud burst have been widely discussed, little is known about within-population variation, the key determinants for this variation and the effects of this variation on estimates of trends in bud burst date. Over a period of nine years, we monitored timing of bud burst daily in 30 mature white birch (Betula pendula Roth) trees in a naturally regenerated stand. Our results revealed not only large interannual variation but also considerable intraannual variation among individual trees in date of bud burst, the maximum within-population variation being four weeks. Bud burst can be accurately predicted by the date when a threshold value of temperature sum in spring is reached (base temperature +5 degrees C). Based on this temperature sum and past temperature records, we estimated the trend in date of bud burst. The linear trend estimate based on the years 1926-2005 is an advancement of 1.2 days per decade (95% confidence interval, +/- 0.7 days), which is much less than that predicted by time series based on coarser time intervals. We conclude that, because of large interannual differences, and large annual within-population variations in bud burst, estimates of bud burst date based on measurements made over a period of only a few decades are unreliable.
authors.affiliation: Finnish Forest Research Institute, Punkaharju Research Unit, Finlandiantie 18, Fin-58450 Punkaharju, Finland. matti.rousi@metla.fi
authors.forename: Matti
authors.initials: M
authors.lastname: Rousi
authors.forename: Jaakko
authors.initials: J
authors.lastname: Heinonen
mesh_terms: D029662:Betula / Q000254:growth & development* / Q000378:metabolism; D002980:Climate; D017752:Greenhouse Effect; D018519:Meristem / Q000254:growth & development; D018520:Plant Shoots / Q000254:growth & development*; D012621:Seasons; D013696:Temperature