The aim of this study was (1) to evaluate the importance of dormant bu
ds for the bud demography of the mountain birch Betula pubescens ssp.
tortuosa near the tree line and (2) to study whether sexual reproducti
on leads to costs for bud production rates. A bud population census wa
s taken in two consecutive years for six branches of each of 90 mounta
in birch trees. The trees were growing in a common garden and belonged
to 10 different progenies originating from different parts of Finnish
Lapland. The data were analyzed with matrix population models. The mo
st important transformations of the bud populations were between veget
ative short and long shoots. However, if most apparently dead buds are
actually latent dormants, they make an even more important contributi
on to the bud population growth rate than vegetative long and short sh
oots. Dormant buds may have considerable importance especially after e
vents such as herbivore outbreaks, in which short and long shoots are
damaged. Generative long shoots (with male catkins) and short shoots (
with female catkins) had approximately the same bud production rate as
the corresponding vegetative shoots, i.e., bud populations did not sh
ow any major costs due to sexual reproduction. Meristem costs, i.e., a
decrease in the number of buds due to sexual reproduction, may be rel
atively low in mountain birch, because new axillary buds develop and c
ompensate for lost shoot apices. This compensation capacity may be esp
ecially well developed under suboptimal conditions, where canopy expan
sion is limited by the harsh environment rather than by the availabili
ty of meristems. The resource cost of reproduction (e.g., in terms of
carbon or mineral nutrients) may also be partly compensated especially
when flowering intensity is sufficiently low.