Sprouting extends the lifespan of tree species in a seedling bank: 12-year study

Sprouting is an important way of extending the lifespan of trees. Persistence in low light conditions of the understory is the most important feature of a seedling bank. In this long-term study we showed how sprouting can extend the persistence of seedlings. Sorbus aucuparia (rowan), a tree species with multi-stemmed seedlings growing in subalpine spruce forest, was chosen for this study. The main aim of the study was to examine the persistence of seedlings and dynamics of sprouts within seedlings. Specifically, we sought to answer three main questions: (i) How long do individual seedlings and their sprouts live? (ii) How often do individuals produce sprouts? and (iii) Do individuals differ in their sprouting ability? It was found that rowan seedlings are very long-lived and it is achieved by the replacement of stems. The half-life of stems was 9.5 years. A mean height increase was 0.58 cm/year. New sprouts appeared in the population continuously. On average, the mean probability of sprouting was 0.16 per year. Individuals differed in their intensity of sprout replacement. Individuals with higher number of sprouts had more new and dead sprouts. After 12 years of study, 18% of individuals had replaced all their sprouts, i.e., lost all their sprouts that were present at the beginning of the study. The production of new sprouts was not a response to loss of biomass in the previous year. To conclude, our study showed that sprouting can be very effective mechanism of extending the lifespan of individuals suppressed in the forest understory. Such a prolonged lifetime should be taken into account when considering the probability of natural regeneration in forest areas with long intervals between successive disturbances. The sprouting process should also be taken into account when assessing the lifespan of a seedling bank under a forest canopy, as the lifespan of individuals can be many times longer than the lifespan of sprouts. (C) 2012 Elsevier B.V. All rights reserved.