The C·I·B’s new director Dave Richardson and his long-term collaborator Marcel Rejmanek of the University of California Davis in the USA have been working on the invasion ecology of pine trees for many years. Due to their widespread use in forestry, pines have been introduced in large numbers to many areas where they do not naturally occur, primarily in the southern Hemisphere, and are a recognised model group in invasion biology.

Teaming up with former C·I·B postdoc, and now Professor at University of KwaZulu-Natal, Serban Proches, whose main research focus is global biogeography, and C·I·B member Dr John Wilson from the South African National Biodiversity Institute (SANBI), they have now investigated the global distributions of pine tree species, relating the size of invasive ranges to indigenous ranges and a whole range of other intrinsic and extrinsic characteristics.

The authors were at first surprised to discover that the relationship between indigenous and invasive ranges was very weak. Species with minute indigenous ranges like Pinus patula, P. elliottii, and P. radiata have attained remarkably large ranges in the regions they have invaded, whereas some of the species that are naturally most widespread, like P. sibirica and P. pumila, have not even become naturalised elsewhere. Incorporating the other variables, the authors showed that this weak relationship can be explained by the fact that intrinsic attributes such as trees’ reproductive strategies only explain part of their success as invaders. A much greater part has to do with how widely trees have been planted by humans. To rephrase this, if one tries hard enough, one has a shot of turning even intrinsically poorly prepared species into invaders. This is a rather disturbing thought, considering how many plant species are being introduced repeatedly to climatically-suitable regions, whether intentionally or accidentally.

Figure caption: The study was featured on the cover of the May 2012 issue of the journal Global Ecology and Biogeography. The image shows Pinus radiata invading fynbos near Swellendam in South Africa’s Western Cape province (Photo credit: D.M. Richardson).

Read the paper: Proches S, Wilson JRU, Richardson DM, Rejmanek M. 2012. Native and naturalized range size in Pinus: relative importance of biogeography, introduction effort and species traits. Global Ecology and Biogeography 21: 513–523.