Je. Anderson et al., Eucalypts forming a canopy functional type in dry sclerophyll forests respond differentially to environment, AUST J BOT, 48(6), 2000, pp. 759-775
Eucalyptus dives Schauer, E. mannifera Mudie, and E. rossii R.Baker & H.G.S
mith are sympatric trees that form a canopy functional type in dry scleroph
yll forests of south-eastern Australia. Although their ranges broadly overl
ap, distributions of the three species differ subtly within an abstract env
ironmental space defined by mean annual temperature and precipitation. We u
sed a combination of common environment and field studies to assess the ext
ent to which these eucalypts might respond differentially to environmental
conditions and to determine whether distributional differences are related
to physiological or morphological attributes of leaves. In three glasshouse
experiments, gas exchange characteristics of E. dives and E. rossii seedli
ngs were remarkably similar. However, data indicated that E. rossii makes m
ore efficient use of nutrients and, under some conditions, has higher water
-use efficiency than the other species. In five natural stands, there were
significant differences among sites and among species for leaf nitrogen and
phosphorus content, carbon isotope discrimination, and specific leaf area.
Significant site x leaf-variable interactions showed that the species resp
onded differentially to unique site conditions. At four of the five sites,
C-13 discrimination was significantly higher in E. mannifera than in the ot
her two species, and it was significantly higher in E. mannifera than in E.
rossii at all five sites. Lower water-use efficiency may restrict E. manni
fera to sites on the higher end of the precipitation gradient, whereas high
er water-use efficiency may give E. rossii an advantage on arid sites. Vari
ation in specific leaf area across sites was greater in E. mannifera and E.
rossii than in E. dives; in contrast, E. dives was more variable in 13C di
scrimination. Greater physiological plasticity could explain why E. dives o
ccupies a broader range of habitats than the other two species. Contrary to
expectations, no leaf variable was strongly correlated with the amount of
rainfall received at the sites, but C-13 discrimination was negatively rela
ted to mean annual radiation received, which may be a better index of water
availability. Despite similarities in gas exchange physiology, members of
this putative functional type clearly respond differentially to varying env
ironmental conditions, implying that accurate prediction of responses to en
vironmental change would require knowledge of attributes of each species. H
owever, differential responses might contribute to functional stability on
a site subjected to environmental variability.