Invasive species can alter the succession of ecological communities because they are
often adapted to the disturbed conditions that initiate succession. The extent to which this
occurs may depend on how widely they are distributed across environmental gradients and
how long they persist over the course of succession. We focus on plant communities of the
USA Pacific Northwest coastal dunes, where disturbance is characterized by changes in
sediment supply, and the plant community is dominated by two introduced grasses – the
long-established Ammophila arenaria and the currently invading A. breviligulata. Previous
studies showed that A. breviligulata has replaced A. arenaria and reduced community diversity.
We hypothesize that this is largely due to A. breviligulata occupying a wider distribution
across spatial environmental gradients and persisting in later-successional habitat than A.
arenaria. We used multi-decadal chronosequences and a resurvey study spanning 2 decades
to characterize distributions of both species across space and time, and investigated
how these distributions were associated with changes in the plant community. The invading
A. breviligulata persisted longer and occupied a wider spatial distribution across the dune,
and this corresponded with a reduction in plant species richness and native cover. Furthermore,
backdunes previously dominated by A. arenaria switched to being dominated by A.
breviligulata, forest, or developed land over a 23-yr period. Ammophila breviligulata likely invades
by displacing A. arenaria, and reduces plant diversity by maintaining its dominance
into later successional backdunes. Our results suggest distinct roles in succession, with A.
arenaria playing a more classically facilitative role and A. breviligulata a more inhibitory role.
Differential abilities of closely-related invasive species to persist through time and occupy
heterogeneous environments allows for distinct impacts on communities
during succession
