S. Mcintyre et S. Lavorel, HOW ENVIRONMENTAL AND DISTURBANCE FACTORS INFLUENCE SPECIES COMPOSITION IN TEMPERATE AUSTRALIAN GRASSLANDS, Journal of vegetation science, 5(3), 1994, pp. 373-384
A distinctive feature of Australian vegetational history is the abrupt
ness of change since European settlement, involving the influx of exot
ic species and the imposition of exogenous disturbances which are nove
l in both intensity and character. This can produce two sources of hab
itat variability: the natural patterns arising from environmental vari
ation, as well as an overlying effect of disturbance. The relative imp
ortance of these two types of variables were compared in temperate her
baceous vegetation. Canonical Correspondence Analysis showed that envi
ronment and disturbance had similar contributions to floristic variabi
lity. Individually, lithology, altitude and soil disturbance were the
strongest variables while slope position, grazing and water enrichment
were slightly less important. Despite generally low levels of site sp
ecificity, groups of species associated with lithology, slope position
, altitude and different disturbance regimes were identified. Exotic s
pecies were associated with higher levels of disturbance, but showed l
evels of environmental specialization similar to the native component.
Through combination of this analysis with a previous analysis of spec
ies richness for the same data set, it became evident that environment
al variation mostly resulted in species substitutions while disturbanc
es led to losses of species, with partial replacement by exotics. Synt
hesizing these results, we identified three broad groups in relation t
o tolerance of levels of exogenous disturbance: (1) intolerant species
-native taxa intolerant of severe disturbances and constituting the sp
ecies-rich component of the vegetation; (2) tolerant species - exotic
and native taxa occurring at both disturbed and undisturbed habitats a
nd (3) disturbance specialists - predominantly exotic species, correla
ted with high levels of disturbance.