Going nowhere fast: a review of seed dispersal in eucalypts

Eucalypt species have several features that make them particularly well suited for climate change studies. A key assumption is that they have very limited powers of dispersal. If this is correct, it means that climate change analyses to the end of this century can concentrate mainly on assessing whether or not eucalypt species are likely to be able to survive at their existing sites. A recent major climate change study of more than 600 eucalypt species for the period 2014-2085 has used 5 km as a usual dispersal limit for the period to 2085, with the possibility of rare long-distance events. The review presented here considers how far natural stands of eucalypt species are likely to be able to migrate in the period to 2085. It is the first review to consider eucalypt seed dispersal as its major focus. It draws on evidence from millions of years ago to the present, and from eucalypt stands in Australia and around the world. Although rare long-distance events cannot be entirely ruled out, it is concluded that the great bulk of the evidence available indicates that the most likely potential dispersal rate is equivalent to about 1-2m per year, i.e. similar to 70-140m in the period to 2085. Over decades, this is likely to occur as a series of stepwise events, associated with disturbances such as bushfires. However, limitations such as inadequate remnant eucalypt stands and extensive agricultural developments may reduce actual migration rates below even this modest potential.