Ochroma pyramidale Swartz
Common Name: BALSA
Common, evergreen subcanopy or canopy tree (20-30 m) always
found growing in disturbed sites where sunlight is abundant. As
such the species frequents secondary forests, light gaps, roadsides,
and the flanks of steep cliffs where landslides frequently clear
out the vegetation that manages to establish itself there. Balsa
also does well in shallow, droughty, and infertile soils where
most other species cannot survive. This tree is notable for its
unusual ecology as well as for its famous light - but strong -
wood.
Description: Balsa boles are very cylindrical
and usually quite straight, though it is not uncommon to find
gently curving (never angular) trunks. Reaching diameters
of up to 1 meter and clad in very smooth, light-gray or whitish
bark, even the biggest Balsas lack buttress roots. Branches in
this species are thick but they are relatively few in number and
the crown they produce is often narrow and always thin. Leaves
are very large, simple, and alternately arranged. The shallowly
lobed blades measure 30 cm across and are supported by stout petioles,
themselves 37 cm long. All parts of the leaves are covered with
reddish epidermal hairs, giving them a rough, sandpapery texture.
Leaves continue to be generated from the thick branch tips nearly
year round - with growth slowing or stopping only during the dry
season. Older foliage also continuously dies and is shed, turning
from green through yellow and then to brown in the process and
often making a considerable noise as they come crashing to the
ground. Balsa flowers are particularly unique and exotic.
They begin as large buds whose thick, leathery calyx is formed
from five fused sepals that completely cover the developing petals
with a protective dome. Soon, this calyx peals back, revealing
the white, still folded, hood of petals. Held perfectly upright
in the tree, these unopened flowers strongly resemble velvety
ice-creme cones - in size (12 cm long by 9 cm in diameter) as
well as in shape. When the flower finally opens, the five large,
thick, creamy-white petals bend backwards, covering the calyx.
Revealed in the center, a large fleshy ball, covered with hundreds
of short stamens, is perched at the end of a long, hollow tube
anchored deep within the corolla (similar in design to a common
Amapola flower). Over a period of several days, as the petals
slowly grade from white to yellow and then finally to burgundy,
the anthers shed their abundant stores of yellow pollen and die.
The ball that holds them finally twists open, exposing a long
pistil held safely within. Protected up until now, any pollen
deposited on the style is sure to come from a different flower.
Balsa trees blossom annually, during the months of December through
February, though individuals may only participate during a part
of this extended period. Fruits grow rapidly from the old
flower calyxes, appearing as long, ridged green rods (20 cm by
3 cm). When mature, the pods split lengthwise along several seams
and allow the tightly packed cotton within them to force its way
out. Expanding in the process, this soft material manages to cover
the entire structure, coating it in tan-colored fluff. Thus opened,
the mature fruit strongly resembles a large rabbit's foot (hence
its old scientific name: Ochroma "lagopus"). Embedded
within the cotton are many, small 3-4 mm seeds. Fruiting occurs
annually from mid-January through early April.
Similar Species: There are only
four common Pacific-coast tree species with extremely large,
simple leaves: Cecropia (Cecropia peltata), Panama (Sterculia
apetala), Vaco (Brosimum utile) and Balsa. The two
former species have three-dimensional, creased, and deeply-lobed
foliage, while that of Balsa is planar, only shallowly lobed,
and lacks creases. Elliptically shaped and devoid of lobes altogether,
Vaco leaves share only their large size with those of Balsa.
Natural History: Balsa is a bat
pollinated species: its flowers open for the first time only at
night. By day, flowers are eaten by Scarlet Macaws and visited
by assorted other parrots and Honeycreepers. Parrots also are
known to chew on the green pods, extracting the immature seeds
for consumption.
Balsa's small, light seeds are detached from the pods by gusts
of wind, clinging to pieces of 
fluff
as they fall. Wind dispersal of this nature necessitates a dry
season harvest. Once on the forest floor, seeds will apparently
not germinate unless soil temperatures are high enough to indicate
that direct sunlight is available. Allen
(1956) indicates that fire also aids in stimulating germination.
Otherwise, the seeds will remain dormant in cool soil, waiting
for a tree-fall, landslide, or even road-cut to provide them with
an opportunity to sprout.
Once germinated, Balsa seedlings grow rapidly. Their light but
sturdy wood allows them to make significant gains in height while
avoiding the time-consuming energy investments required of denser
building materials. It is not uncommon to see three year old Balsas,
already 7 meters tall and sporting 15 cm girths. Sexual maturing
is reached soon thereafter - with some individuals flowering and
reproducing in only their second year of life. Relatively short
lived trees, all the Balsa's will be gone before a century has
passed - and many of them will die much sooner. Balsa trees are
thus highly adapted to secondary forest conditions. True pioneer
species, they are able to colonize a damaged site quickly, taking
advantage of insolation levels, and droughty, infertile soil conditions
that would spell the demise of most primary forest trees.
Uses: The pale Balsa wood has been
used in rafts (hence the Spanish common name of balsa) and early
airplane construction, due to its light weight and relative strength.
Trees planted for this purpose need to be harvested before they
get too large, for older trees develop a water-storing capacity
in their cores - a condition known as "water-heart"
- that ruins the wood. In fact, it is said that when using drills
to remove core samples from older trees, spurts of water are often
ejected from the bore-hole after the borer is removed (Whitmore,
1983).
Large plantations of this tree were started during the Second
World War in what is now Corcovado National Park. They were never
used - due to the increased use of aluminum for aviation - and
the trees (and their descendants) can still be seen, surrounding
the park's Sirena post. The cotton produced by Balsa fruits has
been used as insulation and pillow stuffing, as has that of many
other members of the Bombacaceae family.
Distribution: In Costa Rica,
Balsa is found in all lowland, disturbed sites - on both coasts.
It ranges from southern Mexico to Bolivia and is present in the
West Indies (Whitmore, 1983).
Leaf Flower Fruit Flower
Bud Trunk Tree
Description: Balsa boles are very cylindrical
and usually quite straight, though it is not uncommon to find
gently curving (never angular) trunks. Reaching diameters
of up to 1 meter and clad in very smooth, light-gray or whitish
bark, even the biggest Balsas lack buttress roots. Branches in
this species are thick but they are relatively few in number and
the crown they produce is often narrow and always thin. Leaves
are very large, simple, and alternately arranged. The shallowly
lobed blades measure 30 cm across and are supported by stout petioles,
themselves 37 cm long. All parts of the leaves are covered with
reddish epidermal hairs, giving them a rough, sandpapery texture.
Leaves continue to be generated from the thick branch tips nearly
year round - with growth slowing or stopping only during the dry
season. Older foliage also continuously dies and is shed, turning
from green through yellow and then to brown in the process and
often making a considerable noise as they come crashing to the
ground. Balsa flowers are particularly unique and exotic.
They begin as large buds whose thick, leathery calyx is formed
from five fused sepals that completely cover the developing petals
with a protective dome. Soon, this calyx peals back, revealing
the white, still folded, hood of petals. Held perfectly upright
in the tree, these unopened flowers strongly resemble velvety
ice-creme cones - in size (12 cm long by 9 cm in diameter) as
well as in shape. When the flower finally opens, the five large,
thick, creamy-white petals bend backwards, covering the calyx.
Revealed in the center, a large fleshy ball, covered with hundreds
of short stamens, is perched at the end of a long, hollow tube
anchored deep within the corolla (similar in design to a common
Amapola flower). Over a period of several days, as the petals
slowly grade from white to yellow and then finally to burgundy,
the anthers shed their abundant stores of yellow pollen and die.
The ball that holds them finally twists open, exposing a long
pistil held safely within. Protected up until now, any pollen
deposited on the style is sure to come from a different flower.
Balsa trees blossom annually, during the months of December through
February, though individuals may only participate during a part
of this extended period. Fruits grow rapidly from the old
flower calyxes, appearing as long, ridged green rods (20 cm by
3 cm). When mature, the pods split lengthwise along several seams
and allow the tightly packed cotton within them to force its way
out. Expanding in the process, this soft material manages to cover
the entire structure, coating it in tan-colored fluff. Thus opened,
the mature fruit strongly resembles a large rabbit's foot (hence
its old scientific name: Ochroma "lagopus"). Embedded
within the cotton are many, small 3-4 mm seeds. Fruiting occurs
annually from mid-January through early April.
