Local provenance produces more and lighter seeds even under drought stress
Alder buckthorne is a species of shrub common in Flanders. You can find the species in almost all of Europe, with the exception of most of Italy and Greece.
The INBO conducted a trial with three provenances: one Flemish, one Swedish and one Italian. Seeds harvested in these three regions were raised at INBO. From each provenance, we allowed one half of the plants to grow up under normal conditions, and one half underwent drought stress. Under both conditions, the Flemish provenance produced more berries than the other two provenances. In addition, the seeds of the Flemish provenance were lighter in weight.
The latter is what researchers also observed for beech: in the center of its range in Europe, beech nuts were somewhat lighter in weight than more on the edges. It seems that in less favorable regions, heavier seeds with more reserves are needed to germinate and grow well.
In the alder buckthorne trial, we also found that drought stress caused lower berry numbers, both in the year of the drought stress itself, and up to two years after the drought. Interestingly, however, the number of seeds per berry did not decrease and the weight of a berry did not change due to water deficit.
These results suggest that different provenances may behave differently. In order to estimate the effects of transporting such seeds to other regions on subsequent shrubs and trees, and by extension forests, it would be useful to test this in pilot plantings. To estimate responses to future climate in Flanders, controlled trials such as temperature and drought tests can help us.