Leaving aside its presumed anthropogenic origin, which explains our use of
the term 'pseudo-savanna', the espinal (s.s.) in Chile can be viewed as a
complete, and relatively stable plant formation. Physiognomically, it consists
of an arboreal stratum of variable height and cover - consisting almost
exclusively of Acacia caven - which is complemented by an herbaceous cover
of synanthropic therophytes [Ovalle 1986; Ovalle and Avendafio 1987;
Ovalle et al. 1988].
The abundance and diversity of annuals is the second distinguishing
feature of the Chilean espinales and has engendered a number of practical
studies showing the positive effects of the tree stratum on annual pasture (see
section 3.0). The floral composition of this herbaceous stratum includes a
large number of coexisting species, mostly of circum-Mediterranean origin.
Between 90 and 95% of total herbaceous cover consists of invasive species
introduced to Chile within the past 300-400 years. In the Cauquenes area
alone (35°58'S 72°12'W; alt. 200m; mean annual precipitation 695mm),
more than 215 annual species have been identified in the espinales, of which
approximately 90% are recent immigrants [Ovalle et al. 1987]. This
represents about half the entire weed flora of Chile [Matthei et al. in prep.].
The dominant pasture species found in the espinales of the subhumid zone
are shown in Table 1.