Effects of time since invasion and control actions on a coastal ecosystem invaded by non-native pine trees

Invasive non-native trees cause structural and functional changes in plant
communities, which tend to increase over time since invasion. Native
vegetation responses after control operations provide important
information for restoration. We evaluated the effects of time since
invasion and of pine control on plant community structure and on
functional traits in a coastal open ecosystem in southern Brazil. We
compared richness, diversity, abundance and cover of woody and non-woody
native plant species, as well as species composition and
community-weighted means (CWM) based on functional traits (dispersal
syndrome, fruit type, maximum height, and shade tolerance) of plant
communities, in four conditions: a non-invaded area, an area where pines
were controlled (managed area), an area of recent invasion, and an area
invaded longer ago. Woody species abundance, richness and diversity
declined over time since invasion. However, while abundance recovered to
the point of not differing from the non-invaded condition in areas where
pines were controlled, species diversity and richness were lower in the
managed area than in the area that was never invaded. The effects of pine
invasion on richness and diversity of non-woody plants did not increase
over time, but plant cover progressively diminished. Woody and non-woody
species composition varied between the four conditions. Species
composition similarity was lower between conditions for non-woody than for
woody species. CWM differed between the older invasion and the other
conditions, determined especially by native plant height and shade
tolerance. Taller plants and more shade tolerant native species were
exclusively sampled in the older invasion. Synthesis and application. Pine
invasion reduced species abundance, plant cover, richness, and diversity,
altering the composition of plant community. The escalation of negative
temporal effects of pine invasion was observed on the composition of woody
and non-woody species and on functional traits. Although pine control
favored the natural regeneration of non-woody species, diversity of woody
species in the area submitted to pine control was lower than in the
non-invaded condition. Restoration activities are therefore required to
increase woody species diversity. These results provide relevant guidance
for the restoration of coastal ecosystems following invasive pine control.