The
invasion
of
non
-
indigenous
plants
is
considered
a
primary
threat
to
integrity
and
function
of
ecosystems
.
However
,
there
is
little
quantitative
or
____________________
evidence
for
ecosystem
impacts
of
invasive
species
.
Justifications
for
control
are
often
based
on
potential
,
but
not
presently
realized
,
recognized
or
quantified
,
negative
impacts
.
Should
lack
of
scientific
certainty
about
impacts
of
non
-
indigenous
species
result
in
postponing
measures
to
prevent
degradation
?
Recently
,
management
of
purple
____________________
(
Lythrum
salicaria
)
,
has
been
____________________
for
lack
of
evidence
demonstrating
negative
impacts
of
L
.
salicaria
,
and
management
using
biocontrol
for
lack
of
evidence
documenting
the
failure
of
conventional
control
methods
.
Although
little
quantitative
evidence
on
negative
impacts
on
native
wetland
biota
and
____________________
function
was
available
at
the
____________________
of
the
control
program
in
1985
,
recent
work
has
demonstrated
that
the
invasion
of
purple
loosestrife
into
North
American
freshwater
wetlands
alters
____________________
rates
and
nutrient
cycling
,
leads
to
reductions
in
wetland
plant
diversity
,
reduces
pollination
and
seed
output
of
the
native
Lythrum
alatum
,
and
reduces
habitat
____________________
for
specialized
wetland
bird
species
such
as
black
terns
,
least
bitterns
,
pied
-
billed
grebes
,
and
marsh
wrens
.
Conventional
methods
(
physical
,
mechanical
or
chemical
)
,
have
continuously
failed
to
____________________
the
spread
of
purple
loosestrife
or
to
provide
satisfactory
control
.
Although
a
number
of
generalist
insect
and
bird
species
utilize
purple
loosestrife
,
wetland
habitat
specialists
are
excluded
by
____________________
of
L
.
salicaria
.
We
conclude
that
negative
ecosystem
impacts
of
purple
loosestrife
in
North
America
justify
control
of
the
species
and
that
____________________
effects
of
purple
loosestrife
on
wetland
systems
and
biota
and
the
potential
benefits
of
control
____________________
potential
risks
associated
with
the
introduction
of
____________________
agents
.
Long
-
term
experiments
and
monitoring
programs
that
are
in
place
will
evaluate
the
impact
of
these
insects
on
purple
____________________
,
on
wetland
plant
____________________
and
other
wetland
biota
.
