Date:    Mon, 16 Nov 1998 13:29:07 EST
From:    C 
Subject: Natural disasters give invasive species greater foothold

ONCE A BULLY, ALWAYS A BULLY, INVASIVE NON-NATIVE PLANTS TEND TO
BE AGGRESSIVE WHEREVER THEY FIND THEMSELVES

12 NOVEMBER 1998
Contact: Nadine Lymn
 nadine@esa.org
 202-416-6182
 Ecological Society of America



 When Hurricane Andrew tore through tropical hardwood forests of
southern Florida in 1992, it uprooted trees, stripped off leaves,
fruits, flowers, and snapped off tree limbs. Opportunities for
plants to recolonize were numerous in the wake of this natural
disaster. But those most successful were invasive non-natives who
had already gained a foothold in the forests before the hurricane
struck.

In the November issue of Ecological Applications, researchers Carol
Horvitz and colleagues from the University of Miami report on
research that suggests that nature preserves may not be as safe
for conservation of native species as previously believed.

 "We found that in the aftermath of Hurricane Andrew, non-native
forest  species competed with native forest species for
regeneration  opportunities, exhibiting the same range of
ecological roles as native  forest species and competing for
particular kinds of regeneration  opportunities," said Horvitz.

 If invasive species can successfully compete with natives in areas
relatively free of human disturbance, explains Horvitz, they
present a  threat to biodiversity conservation and may considerably
alter ecosystem  processes.

 In the case of several non-indigenous vines, not only did they
form denser  "blankets" than native vines, but they also inhibited
the regeneration of  other natives by strangling native tree
seedlings and juveniles.

 Horvitz points out that Florida's invasive non-natives species
exhibit invasive behavior in other regions of the world, suggesting
that  understanding the ecological roles of such invaders in one
region may help  predict invasive roles in other areas.

 According to the researchers, the ecological roles of invasive,
non-indigenous species in forest ecosystems are poorly understood.
Some  analyses have proposed that such invaders become established
primarily in  human-disturbed areas. In contrast to these views,
Horvitz and her  associates suggest that successful invasion may
in fact occur in natural  habitats when invaders draw upon seeds,
juveniles, and other sources they  have sown prior to the
disturbance.

 Compared with native plants, the researchers found that non-native
species  were very similar in seed mass, and were also recruiting
from diverse  sources such as banks of pre-established juveniles,
dormant seeds, and  resprouts from pre-established adults. That
meant these non-natives were  not restricted to the pioneer type
of life history frequently thought to  be their primary option.

 Horvitz's article is part of a larger series of research presented
in this  issue of Ecological Applications. Entitled, "Ecological
Concepts in  Conservation Biology: Lessons from Southeastern U.S.
Ecosystems," the  series presents a collection of articles which
address the applicability  of ecological concepts to conservation
of Southeastern ecosystems.

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