Abstract:
The negative effects of alien plant species on
ecosystem structure and functions are increasingly
recognised, and efforts to control these species are vital
to restore degraded ecosystems and preserve biodiver-
sity. However, we lack a full understanding of factors
that determine alien species invasions along spatial
gradients in herbaceous vegetation of tropical systems.
We therefore examined the effects of community prop-
erties, environmental variables and human-related dis-
turbance factors on the invasion of the alien grass
Echinochloa colona (L.) Link at small- and large scales in
the Kilombero Valley wetland, Tanzania. Generalized
additive mixed models showed that E. colona abundance
on a small scale was negatively related to above-ground
biomass and evenness of resident species, whereas E.
colona abundance was positively related to grazing
intensity. On a large scale, biomass (negatively related to
E. colona abundance) and distance to river (positive)
were important in explaining E. colona abundance.
These findings support the assertion that different fac-
tors may contribute to the invasion of alien plant species
at different spatial scales, as also reported in many
temperate systems. Overall, our results show that suc-
cessful invasion of alien species is a function of plant
community properties, human-related disturbance and
favourable environmental conditions. Effective man-
agement strategies should consider mitigations that can
increase the biomass and evenness of native species and
a reduction of grazing pressure to restore the wetland
and conserve biodiversity.
