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INSTITUTE OF TROPICAL FORESTRY 
RIO PIEDRAS, PUERTO RICO 
FOREST SERVICE -
U.S DEPARTMENT OF AGRICULTURE 
December 1966 
HEIGHT GROWTH OF MAHOGANY SEEDLINGS, 
ST. CROIX, VIRGIN ISLANDS 
By 
R. w. Nobles an<l c. B. Briscoe 
Summary 
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. 
Resumen 
Los estudios de crecimiento de caoba en Santa Cruz, Islas 
V1rgenes, indicaron que durante los primeros dos afios 
las h1bridos de la caoba de hoja grande y de la caoba 
de hoja pequefia sobrepasaron la caoba de hoja pequefia, 
que a su vez sobrepaso la de hoja grande. 
Desde los 4 hasta las 7 afios, la altura alcanzada por la 
caoba de hoja grande y por el h1brido de los arboles 
portagranos de las dos especies fue esencialmente igual, 
y todos sobrepasaron en altura a la caoba de hoja pequefia. 
La caoba de hoja grande sufrio la mortalidad mayor segui<la 
por la caoba de hoja pequefia y finalmente por las dos 
h1bridos. 
* In cooperation with the University of Puerto Rico. 
LIBRA RY 
JUN 27 1967 
.RO.CKY MOUNTAIN STATION 
• 
., 
1/ 
Since the recogn1t1on of natural hybridization 
of small-leaf 
A 
(West Indies) mahogany (Swietenia rnahagoni Jacq.) with bigleaf 
W 
(Honduras) mahogany (~. macrophylla 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 begun on dry and intermediate sites 
on St. Croix, Virgin Islands. 
Four types of 1-0 seedlings 
were planted: 
Seedling 
Bigleaf 
Medium leaf 
Mediumleaf 
Small-leaf 
Mother-tree 
Bigleaf 
Bigleaf 
Small-leaf 
Small-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 more11. 
(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. 
!/ c. B. Briscoe and F. B. Lamb. 
1962. 
Leaf size in Swietenia. 
Car. For. 23:2:112-115. 
II c. B. Briscoe and R. w. Nobles. 
1962. 
Height growth of 
mahogany seedlings. 
Trop. For. Notes #13. 
2 
Because of prolonged dry spel~, 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. 
3 
Table 1.--Mean height growth in meters of mahogany seedlings, 1960-67 
Location 
New Works 
Thomas 
Sima Hill 
Betsy Jewel 
Cane Bay 
Ham Bluff 
Bodkin I 
Combined 
(1960-62) 
:Approximate: 
: 
Mediumleaf, : 
Mediumleaf, 
: 
:Mortality 
Rainfall 
:Bigleaf:Bigleaf mother:Small-leaf mother:Small-leaf:Percentage 
mm/Yr. 
700 
1100 
1100 
1200 
1300 
1300 
1400 
4.6 
6.6 
0.8 
6.3 
4.6 
(0.5) 
3.8 
5.1 
3.1 
7.5 
3.3 
5.6 
5.5 
4.8 
(1. 1) 
4.4 
4.7 
2. 7 
7.8 
2.6 
s.o 
6.0 
4.7 
(1.2) 
2 .1 
4.2 
1.2 
4.1 
1.7 
3.1 
5.0 
3.0 
(0. 8) 
33 
42 
78 
14 
53 
61 
31 
Mortality Percent 
63 
37 
32 
44 
43 
4