Using a botanic garden collection to test a bioclimatic hypothesis

Bioclimatic hypotheses are used to explain how climate regulates the occurrence of species. A derivative of these hypotheses is that plants moved between corresponding bioclimatic areas should thrive, whereas plants moved to a different zone should languish. This principle is routinely applied in forestry and horticulture but actual tests of the hypotheses seem scanty. We carried out a test on the Finnish system of bioclimatic vegetation zoning using the plant collection of Helsinki University Botanic Garden in Kumpula, which is situated at the northern limit of the hemiboreal zone. We aimed to test how the plants’ survival depends on their provenance with the expectation that plants from the hemiboreal or southern boreal zones should do best in Kumpula. Probability of survival was estimated using collection database information of 379 plant accessions of known wild origin, and logit models. Different growth forms were analysed separately. In most analyses accessions of temperate and hemiarctic origin showed lower survival probability than those originating from any of the boreal subzones, which among them exhibited rather evenly high probabilities. Trees were an exception showing an almost steadily increasing survival probability from temperate to northern boreal origin. In all, the results gave some support to the tested hypothesis, but the various factors that could not be controlled for produced results that were difficult to interpret. We conclude that botanic gardens should pay due attention to information management and curational practices to ensure widest possible applicability of their plant collections.