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FOREST
SERVICE
-
INSTITUTE OF TROPICAL FORESTRY
'^'^H\0 PIEDRAS, i^UERTO RfGO
U.S
DEPARTMENT
OF
AGRICULTURE
}???
December
1966
HEIGHT GROWTH
OF MAHOGANY SEEDLINGS,
ST.
CROIX,
VIRGIN
ISLANDS,
/
By
R.
W.
Nobles, and
C.
B
Briscoe
Summary
AUG rZ 1957
CURRLNT SERlf-UECOROS
Small-leaf mahogany seedlings
grew more rapidly than
bigleaf and their hybrids
grew more rapidly than either
for
the
first
two years.
However,
by
age
4
and
conti-
nuing through
age
7,
both hybrids
and bigleaf were
significantly taller than
small-leaf.
Bigleaf suffered
the most mortality,
followed by
small-
leaf,
then
the
two hybrids.
Re sum en
Los
estudios
de
crecimiento
de caoba
en
Santa Cruz,
Islas
VIrgenes,
indicaron
que durante
los
primeros
dos
anos
los hibridos
de
la caoba
de hoja
grande
y
de
la
caoba
de hoja pequena sobrepasaron
la
caoba
de hoja pequena,
que
a
su vez
sobrepaso
la
de
hoja
grande.
Desde
los
4 hasta
los-
7
anos,
la altura alcanzada por
la
caoba
de hoja
grande
y por
el hibrido
de
los
arboles
portagranos
de
las
dos
especies
fue esencialmente
igual,
y todos
sobrepasaron
en altura
a
la caoba
de
hoja pequena.
La
caoba
de
hoja
grande
sufrio
la mortalidad mayor
seguida
por
la caoba
de hoja pequena
y finalmente
por
los
dos
hibridos
*
In cooperation with
the University
of
Puerto Rico
i/
Since
the
recognition
of natural hybridization
of small-leaf
(West
Indies)
mahogany
( Swieten ia mahagoni
Jacq.)
v.'ith bigleaf
(Honduras)
mahogany
(S.
macrophy 1 la
King)
there
has
been
con-
jecture
about
their relative
growth
rates.
One would
expect
small-leaf
to
be
the
fastest
growing
on
dry
sites,
the hybrids
to
be
fastest
on
intermediate
sites,
and bigleaf
to
excel
on
wet
sites.
In
1960
a comparison
was
begu
on
St.
Croix,
Virgin
Islands,
were
planted:
Seedl ing
Bigleaf
Medium leaf
Mediumleaf
Smal 1- leaf
on
dry
and
intermediate
sites
Four
types
of
1-0
seedlings
Mother-tree
Bigleaf
Bigleaf
Sma 1 1 - leaf
Sma 1 1 - leaf
Each
plot
contained
one
seedling
of each
type,
a total
of
4,
at
3-meter
(10-foot)
spacing.
There were
9 well-scattered
plots
at
each
of
11
locations.
Elevations
range
up
to
180 meters
(600
feet)
above
sea
level.
Mean
annual rainfall
varies
from
700
to
1400
mm
(29
to
54
inches)
per
year
for
the
7
locations.
Results
from
7
locations
are
given
in
Table
1.
The remaining
locations were
eliminated:
three because
of drouth mortality
and
one because
of destruction by bulldozer.
For the
first
two
years:
(a)
Both
types
of hybrid
seedlings
outgrew both
species
-
at
all
locations
but
one,
where small-leaf grew slightly more—
.
(b)
Small-leaf growth exceeded bigleaf growth.
(c)
The hybrids were not
different
from each
other.
After
7 years,
both hybrids
average
15
centimeters
(6
inches)
taller
than
the bigleaf,
but
the difference
is not
significant.
The bigleaf averages
1.5 meters
(5
feet)
taller
than
small-leaf,
a highly significant
difference.
y
C.
B,
Briscoe and
F.
B.
Lamb.
1962,
Leaf
size
in Swietenia .
Car.
For.
23:2:112-115.
y
C.
B.
Briscoe and
R.
W.
Nobles.
1962.
Height growth
of
mahogany seedlings.
Trop.
For.
Notes
#13.
2
Because
of prolonged
dry
spells, mortality
in
7
years
was
high:
109
of
252
trees
in
all
plots.
In
two
of
the wettest
sites,
Ham
Bluff and
Cane
Bay,
mortality jumped
44 percent
and
36 percent,
respectively,
in
the past
5
years.
As
expected,
mortality
was
highest
for bigleaf,
63 percent
for
all
sites.
Somewhat
surprisingly,
mortality
for hybrids
was
less
than
for
small-leaf,
37
and
32
percent
compared
to
44 percent.
The present
pattern
of development
was
established by
age
4,
and has
remained
constant
since,
Table
1.
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