Tabebuia rosea (Vertol.) DC.
Common Name: ROBLE DE SABANA, TRUMPET TREE
Common deciduous sub-canopy or canopy tree (20-30 m) found
preferentially on well to excessively drained soils such as those
present along the sandy coast. Roble de Sabana is an especially
notable tree thanks to the often spectacular displays of pink
blossoms that it produces during the height of the dry season.
This species shares much of its range with the Corteza tree (Tabebuia
chrysantha), a close relative whose similar - though more
ephemeral - shows of large yellow flowers are truly breathtaking.
Roble is the national tree of El Salvador.
Description: Roble de Sabana has
a mostly regular, straight, and cylindrical trunk that
may reach 70 cm or more in diameter. Large, rounded folds appear
in the bole near its base and these form stout but short buttress
roots at ground level. Roble bark is light gray or tan colored
and, in young trees, is marked by fine, vertical cracking. Older
individuals often have much thicker and rougher bark that is shallowly
etched by wide, vertical fissures. With stout, often angular limbs
that subdivide into a moderate number of stubby twigs, Roble has
a thin, single-layered crown that tends to be tall and relatively
narrow in shape. Roble foliage is unique and serves as an ideal
characteristic for identification purposes. Leaves are
palmately compound (25-35 cm in length) and oppositely arranged
along the twig. Each is composed of a long petiole (13 cm) supporting
five, smooth, elliptical leaflets of varying size: the three distal
leaflets (25 cm by 8 cm on 5 cm petioles) being about twice the
size of the proximal two (12 cm by 6 cm on 1 cm petioles). The
overall asymmetrical pattern produced by this leaflet configuration
(shared by all members of the Tabebuia genus) is memorable, making
this species easy to recognize. All foliage is shed at the start
of the dry season in late December and January and the trees remain
bare until late April when the first individuals begin to bud.
Re-foliation is complete by June. (The exact timing of these events
is strongly influenced by the microclimate experienced by individual
trees, with those found in wetter depressions or near streams
retaining their leaves longer into the dry season and being the
last to regenerate them.) Flowers (8 cm by 7 cm) are produced
in large, terminal panicles during the dry season. Ranging in
color from pink to white, each is dominated by a showy, trumpet-shaped
corolla that is formed from the five fused petals. Five stamens
and a central pistil adorn the blossom's yellow center and the
whole structure is supported by a cup-shaped, velvety-brown calyx.
Flowers are observable from late January through late April, however
there is often a very marked, dramatic, and highly synchronized
flowering peak that occurs in February. During this peak, the
trees - already leafless - are transformed into solid masses of
pink blossoms. Seen against the backdrop of the deep blue, dry-season
sky, this is a spectacular event - and one of the finest displays
of color that the tropical forest has to offer. Like most things
worth seeing, this spike in activity is short lived, lasting only
three or four days. When in flower, individual Roble trees can
easily be identified from a distance, brightly dotting the forest
with their canopies of pink. Fruits begin to grow immediately
after the perianths are shed, reaching full size within a couple
of weeks. They are long (30 cm or more), cylindrical, green or
brown capsules that can be seen hanging vertically from the ends
of the branches. After a month or two spent maturing and drying
in the hot summer sun, these capsules split along two longitudinal
seams that run down the sides of the pod. When this happens, hundreds
of neatly-packed, doubly-winged and very flat seeds (3-4 cm long)
are exposed. Seed wings angle outwards in precise columns on both
sides of the pod, and the whole structure takes on a herring-bone
pattern. Thus prone to the wind, the samaras are eventually plucked
from the pods and begin a spinning decent - usually traveling
some distance before settling on the forest floor. Harvests occur
from March through May. Seed germination coincides with the advent
of the rainy season in late April. By June, thousands of small
seedlings - consisting only of a pair of lobed cotyledons - blanket
the forest floor. These young trees grow rapidly at first, but
most succumb to the drought induced by the following dry season.
Should they survive, seedlings may be 15 cm tall by the end of
their first year.
Similar Species: The asymmetrical leaf pattern produced by Roble's five unequal leaflets is uniquely characteristic of, and common to, all of the five or so species of Tabebuia that are found in Costa Rica. The stunning, yellow-flowered Corteza tree (Tabebuia chrysantha) coexists with Roble in many other, mostly drier, Costa Rican landscapes. Corteza can be distinguished from Roble by noting the large quantity of rufous hairs that cover the foliage, petioles, and young shoots of this former species.
Natural History: The timing and sequence
of the fertility cycle demonstrated by Roble is common to a number
of tropical forest trees that grow in regions with short but pronounced
dry seasons. Flowers are often delicate structures that deteriorate
rapidly in the presence of rain and wind. Large, showy blossoms,
like those of Roble, suffer the most under these conditions. By
timing its flowering period to coincide with the dry summer months,
the Roble tree is demonstrating a behavioral adaptation intended
to maximize blossom life and help ensure pollination. Furthermore,
producing copious amounts of flowers at a time when obscuring
foliage has been shed enhances their visibility - increasing the
chances that pollinators (in this case mostly bees) will locate
them.
The dry summer season is also the most appropriate fruiting period
for a species that relies on the wind to disperse its seeds. Pods
dry well in the hot sun and the winged or cottony seeds are kept
light and buoyant by the arid conditions. Stiff summer breezes
then serve to carry the seeds great distances away from the parent
trees. Rainy weather would only serve to add weight to such seeds
and they would be pulled to the forest floor - through the stagnant,
wet-season air - with only minimal dispersal.
By the time fruition is complete and the seeds have been placed
in the soil, the dry season is nearly over. The first rains then
stimulate rapid germination and the young seedlings that emerge
are provided with a maximum amount of time get established before
the onset of the next dry season.
Roble's habit of disseminating large quantities of relatively
small seeds is representative of a general reproductive strategy
shared by many other forest species (see introduction). All plant
seeds contain similarly sized, tiny embryos accompanied by widely
varying amounts of stored food. The most important characteristic
in determining seed size, stored food is vitally important to
the embryo, since it represents the seedlings single source of
nourishment in the early days of its growth. Once this store is
exhausted, the rapid growth typical of germination ceases, and
the plant begins the slower process of providing food for itself
though photosynthesis. The small size of Roble seeds indicates
that their energy reserves are small. Each individual Roble embryo
will therefore grow less - and have less likelihood of surviving
its first year - than the embryo of a larger-seeded species. But
since smaller seeds require less energy to produce, the parent
tree is capable of generating far more of them. The diminished
survival rate of the individual embryo is apparently compensated
for by the vastly higher number of embryos disseminated into the
environment.
Uses: Roble de Sabana wood is hard, yellowish and easy to work. It is prized in the construction of furniture and veneer. Apparently, the common name "Roble" (meaning "Oak") derives from a similarity between the woods of these two species (Holdridge & Poveda, 1975). The bark contains tanins that have been used in home remedies (Deininger). Though a native of the Pacific lowland primary forest, Roble has been widely planted as an ornamental all over Costa Rica, where it thrives even in highly insolated, exposed sites. In the central valley - where it is commonly used to adorn busy roadsides - Roble demonstrates a high resistance to environmental pollution as well.
Distribution: Roble is native to the entire Pacific lowland region of Costa Rica, though it is most abundant in the northern and central part of this range. Significant populations of this species are found in Santa Rosa, Palo Verde, Manuel Antonio, Cabo Blanco, Carara, Curu, and Corcovado parks. Roble ranges from Mexico and the West Indies to Venezuela and Ecuador (Witsberger, 1982).
