Landscape drivers of genomic diversity and divergence in woodland Eucalyptus

Spatial genetic patterns are influenced by numerous factors, and they can vary even among coexisting, closely related species due to differences in dispersal and selection. Eucalyptus (L’Héritier 1789; the “eucalypts”) are foundation tree species that provide essential habitat and modulate ecosystem services throughout Australia. Here we present a study of landscape genomic variation in two woodland eucalypt species, using whole genome sequencing of 388 individuals of Eucalyptus albens and Eucalyptus sideroxylon. We found exceptionally high genetic diversity (π ≈ 0.05) and low genome-wide, inter-specific differentiation (FST = 0.15). We found no support for strong, discrete population structure, but found substantial support for isolation by geographic distance (IBD) in both species. Using generalised dissimilarity modelling, we identified additional isolation by environment (IBE). Eucalyptus albens showed moderate IBD, and environmental variables have a small but significant amount of additional predictive power (i.e., IBE). Eucalyptus sideroxylon showed much stronger IBD, and moderate IBE. These results highlight the vast adaptive potential of these species, and set the stage for testing evolutionary hypotheses of interspecific adaptive differentiation across environments.

Observations on roost use by the yellow-bellied sheathtail-bat (Saccolaimus flaviventris) in northern New South Wales, Australia

Hollow-bearing trees are recognised as essential habitat features for insectivorous bats and provide sites for mating, the rearing of young, hibernation, protection from predators, and social interaction. The characteristics of hollow-bearing trees used as roosts by insectivorous bats in Australia are poorly known. To help fill this gap, this note presents data on tree roost characteristics for the yellow-bellied sheathtail-bat (Saccolaimus flaviventris) obtained from northern New South Wales, Australia. Of the 19 roost trees observed, most were live Eucalyptus albens trees with an incomplete crown with substantial numbers of dead limbs. Roosts selected were, on average, 9.3 m high with an entrance diameter of 12.7 cm in trees with a mean diameter at breast height of 49.5 cm. All entrance hollows were located at the end of a rotten spout formed when a branch had broken off the tree. These observations are some of the first to document the characteristics of roost trees for this species in New South Wales and this information can be used by land managers to identify and retain suitable roosting habitat for S. flaviventris in the landscape.

Effects of soil disturbance, weed control and mulch treatments on establishment of Themeda triandra (Poaceae) in a degraded white box (Eucalyptus albens) woodland in central western New South Wales

Temperate grassy woodlands are endangered ecosystems in Australia, and many degraded remnants are in desperate need of understorey restoration. This experiment compared the effects of soil disturbance, weed control and mulch treatments on establishment of the original dominant grass, Themeda triandra Forssk., in a degraded white box (Eucalyptus albens Benth.) woodland at Cowra in central New South Wales (NSW). Awned Themeda seeds were surface-sown into replicated plots treated as follows: soil scalping, soil disturbance (by ripping), herbicide (simazine) application and retention of natural mulch. Scalping combined with soil disturbance best promoted Themeda establishment (47.8% after 40 days and 28% after 518 days), and also reduced broadleaf-herb densities. By contrast, scalping without soil disturbance had the worst effect on Themeda establishment (5.2% after 40 days and 4.5% after 518 days). Disturbance significantly enhanced Themeda establishment and decreased the density of annual grasses and the basal cover of non-Themeda species. By contrast, the retention of 500–800 kg of natural surface mulch had no apparent effect on Themeda establishment. Contrary to expectations, simazine reduced the density and basal cover of all species, including Themeda, which is normally resistant to this herbicide. All combinations of the mulched, disturbed and herbicide treatments (i.e. all treatments except scalping) gave similar results, ranging from 10.7 to 22.0 Themeda plants m–2 after 518 days. These results suggest that Themeda stands can be established in degraded box woodlands by using awned seed materials, with minimal seedbed preparation and simple sowing techniques. Further studies are required to determine whether established swards can resist weed invasion in the absence of ongoing weed management, and whether establishment success varies with soil conditions and landscape position.

The Dynamics of Callitris columellaris/Eucalyptus albens Communities Along the Snowy River and Its Tributaries in South-Eastern Australia

The vegetation in the rain shadow areas of the Snowy River region was studied. Five distinct woodland communities were recognised from a numerical classification, a community dominated by C. columellaris at lower altitudes on north and west aspects, three mixed C. columellaris/E. albens communities which are also aspect and altitude dependent, and a higher altitude, cool aspect, E. albens dominated community. Although C. columellaris and E. albens occupy separate niches, they compete strongly. Contrasting dispersal and germination behaviour between the two species may explain the current distribution and structure of these woodlands.