Going nowhere fast: a review of seed dispersal in eucalypts

Abstract

Abstract. 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 1-2 m per year, i.e.~70-140 m 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.

Landscape drivers of genomic diversity and divergence in woodland Eucalyptus

“…Strong IBD is likely a result of patterns of migration imposed by the reproductive ecology of eucalypts (Williams & Woinarski, ). Seed dispersal is limited in eucalypts, with pollen exchange accounting for the vast majority of migration among localities (Booth, ; Potts & Gore, ; Williams & Woinarski, ); recent analysis of chloroplast markers in box‐ironbark eucalypts supports this (Alwadani et al, ). Pollination is facilitated by generalist insect, bird and mammal pollinators in nearly all species (Potts & Gore, ; Williams & Woinarski, ).…”

“…Our findings of high genetic diversity imply a large pool of variation accessible to natural selection. However, the long generation time of these trees makes it unlikely that natural selection on local standing variation alone can outpace anthropogenic changes in climate and land use; therefore, migration of better‐adapted alleles is required (Booth, ; Booth et al, ). While we show pollen must have been exchanged over relatively large distances at a rate historically sufficient to prevent strong differentiation between localities, natural rates of migration are unlikely to prevent range contractions (Aitken & Bemmels, ; Booth, ; Prober et al, ).…”

Landscape drivers of genomic diversity and divergence in woodland Eucalyptus

“…Strong IBD is a result of by patterns of migration imposed by the reproductive ecology of eucalypts (Williams and Woinarski, 1997). Seed dispersal is limited in eucalypts, with pollen exchange accounting for the vast majority of migration among localities (Booth, 2017;Potts and Gore, 1995;Williams and Woinarski, 1997). Pollination is facilitated by generalist insect, bird, and mammal pollinators in nearly all species (Potts and Gore, 1995;Williams and Woinarski, 1997).…”

“…Andrew et al, 2005Andrew et al, , 2007Jones et al, 2007;Jordan et al, 2017;Rutherford et al, 2018;Steane et al, 2006Steane et al, , 2015Steane et al, , 2014Supple et al, 2018). Although eucalypts have very limited seed dispersal, they generally preferentially outcross and are pollinated by generalist bird and insect pollinators, both of which contribute to their spatial genetic structure (Booth, 2017;Potts and Gore, 1995;Williams and Woinarski, 1997). Spatial genetic autocorrelation is strong within populations, but tends to be weak at larger scales; for example, isolation by distance between localities is only apparent between localities separated by more than 500 km in E. melliodora (Supple et al, 2018).…”

Climate‐driven shifts in the distribution of koala‐browse species from the Last Interglacial to the near future

“…In reality, many eucalypt species have variable climatic tolerances and responses to climate change, such that some have the potential to persist beyond the extremities of the climate envelopes in which they currently thrive. In other words, we acknowledge that we have invoked an ‘equilibrium assumption’, which has its own particular problems (Varela et al 2009, Václavík and Meentemeyer , Saltré et al , 2015a, Booth ). Fortunately, all of our four models produced results for each species that generally corresponded well with the known distribution of koalas today (Supplementary material Appendix 1) (Adams‐Hosking et al ).…”