© 1995 Heron Publishing—Victoria, Canada
Methods for combining phenological time series: application to bud burst in birch (Betula pendula) in Central Finland for the period 1896–1955
Risto Häkkinen (1), Tapio Linkosalo (1) and Pertti Hari (2)
1. The Finnish Forest Research Institute, Unioninkatu 40 A, FIN-00170 Helsinki, Finland / 2. Department of Forest Ecology, University of Helsinki, Unioninkatu 40 B, FIN-00170 Helsinki, Finland / Received August 18, 1994
Summary
We compared four methods for combining separate fragmentary phenological time series into a single long reliable series. The
systematic linear effect of differences in observers, genotypes, geography and climate at the observation points produces
disturbing variation in the observations and bias in the means of some time points. The three methods based on the adjustment
of individual series eliminated the disturbing variation and bias. The methods were compared based on phenological observations
of bud burst in birch (Betula pendula Roth). The method based on a linear mixed model of analysis of variance and the maximum likelihood estimation was considered
preferable to the other methods.
Keywords:
annual cycle, combined time series, phenological observations.
