<s>
Detrended	B-Algorithm
correspondence	I-Algorithm
analysis	I-Algorithm
(	O
DCA	O
)	O
is	O
a	O
multivariate	O
statistical	O
technique	O
widely	O
used	O
by	O
ecologists	O
to	O
find	O
the	O
main	O
factors	O
or	O
gradients	O
in	O
large	O
,	O
species-rich	O
but	O
usually	O
sparse	O
data	O
matrices	O
that	O
typify	O
ecological	O
community	O
data	O
.	O
</s>
<s>
merged	O
into	O
Centre	O
for	O
Ecology	O
and	O
Hydrology	O
)	O
and	O
implemented	O
in	O
FORTRAN	B-Application
code	O
package	O
called	O
DECORANA	O
(	O
Detrended	B-Algorithm
Correspondence	I-Algorithm
Analysis	I-Algorithm
)	O
,	O
a	O
correspondence	B-Algorithm
analysis	I-Algorithm
method	O
.	O
</s>
<s>
When	O
such	O
data	O
are	O
analysed	O
by	O
a	O
standard	O
ordination	B-Algorithm
such	O
as	O
a	O
correspondence	B-Algorithm
analysis	I-Algorithm
:	O
</s>
<s>
the	O
ordination	B-Algorithm
scores	O
of	O
the	O
samples	O
will	O
exhibit	O
the	O
'	O
edge	O
effect	O
 '	O
,	O
i.e.	O
</s>
<s>
DCA	O
is	O
an	O
iterative	B-Algorithm
algorithm	I-Algorithm
that	O
has	O
shown	O
itself	O
to	O
be	O
a	O
highly	O
reliable	O
and	O
useful	O
tool	O
for	O
data	O
exploration	O
and	O
summary	O
in	O
community	O
ecology	O
(	O
Shaw	O
2003	O
)	O
.	O
</s>
<s>
It	O
starts	O
by	O
running	O
a	O
standard	O
ordination	B-Algorithm
(	O
CA	O
or	O
reciprocal	B-Algorithm
averaging	I-Algorithm
)	O
on	O
the	O
data	O
,	O
to	O
produce	O
the	O
initial	O
horse-shoe	O
curve	O
in	O
which	O
the	O
1st	O
ordination	B-Algorithm
axis	O
distorts	O
into	O
the	O
2nd	O
axis	O
.	O
</s>
<s>
No	O
significance	B-General_Concept
tests	I-General_Concept
are	O
available	O
with	O
DCA	O
,	O
although	O
there	O
is	O
a	O
constrained	O
(	O
canonical	O
)	O
version	O
called	O
DCCA	O
in	O
which	O
the	O
axes	O
are	O
forced	O
by	O
Multiple	O
linear	O
regression	O
to	O
correlate	O
optimally	O
with	O
a	O
linear	O
combination	O
of	O
other	O
(	O
usually	O
environmental	O
)	O
variables	O
;	O
this	O
allows	O
testing	O
of	O
a	O
null	O
model	O
by	O
Monte-Carlo	O
permutation	B-Algorithm
analysis	O
.	O
</s>
<s>
The	O
plot	O
of	O
the	O
first	O
two	O
axes	O
of	O
the	O
correspondence	B-Algorithm
analysis	I-Algorithm
result	O
on	O
the	O
right	O
hand	O
side	O
clearly	O
shows	O
the	O
disadvantages	O
of	O
this	O
procedure	O
:	O
the	O
edge	O
effect	O
,	O
i.e.	O
</s>
<s>
An	O
open	O
source	O
implementation	O
of	O
DCA	O
,	O
based	O
on	O
the	O
original	O
FORTRAN	B-Application
code	O
,	O
is	O
available	O
in	O
the	O
vegan	O
R-package	O
.	O
</s>
