orchids and orchidology in central america. 500 ... - lankesteriana.org

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on board of H.M.S Sulphur, who explored the Pacific
coast of Central America between 1836 and 1842, wrote
in 1843 about The regions of vegetation (Hinds, 1843,
cited in Jörgensen, 2003: 5). Schlechter cites Galeotti,
who in 1844, divided the climatic zones in Mexico in
“warm regions”, “temperate regions”, “temperate regions
rich in Cactaceae” and “cold regions” (Schlechter, 1918:
332). Somewhat later, Anders S. Oersted, who visited
Central America and the Caribbean about the middle of
the XIX Century, illustrated the vegetational zones of a
tropical island taking Jamaica as an example (Fig. 3A).
The phytogeography of Central America in general
has been considered by Grisebach, in 1884, based on
a few personal and a lot of foreign observations, in his
work Vegetation der Erde. Andreas Schimper published
his classic Plant geography upon a physiological basis
(Schimper, 1898). Richer in regional information than
the phytogeography of Grisebach (1872), Schimper’s
book divides the region from Mexico to Colombia into
monsoon rain forests, thin and monsoon forests, and
xerophilic vegetation (woodland savannas) (Gómez,
1986: 13). The progress in phytogeographical knowledge
in the XX Century is described by G. S. Hartshorn who,
in the case of Costa Rica 4 says: “The first essays for
the description of the phytogeography of Costa Rica
highlight a few floristic regions, based mainly on altitude.
Pittier recognizes three altitudinal bands: (1) a basal
zone from sea level to 1,000 m, with a mean temperature
between 28º and 21º C; (2) a montane or intermediate
zone from 1,000 m to 2,600 m with a mean temperature
between 21º and 14º C; and (3) a superior or Andine zone
above 2,600 m with mean annual temperatures between
15º and 5º C” (Hartshorn, cited in Janzen, 1991: 120).
In a very comprehensive essay about the phytogeographical
regions of Costa Rica, Wercklé described four
regions: (1) the Atlantic or Caribbean region from sea
level to 800 m; (2) The Pacific region, from sea level
to 800 m; (3) the temperate region from 800 to 1,500
m; (4) the cold region above 1,500 m. (Wercklé, 1909).
Standley followed the phytogeographical divisions
of Wercklé, but affirmed that the cold region had to
be subdivided into a low and a high band. In addition,
Standley was the first to point to the difficulty consisting
in assigning one single altitudinal limit to a particular
type of vegetation (Standley, 1937-38).
LANKESTERIANA
LANKESTERIANA 9(1—2), August 2009. © Universidad de Costa Rica, 2009.
Some decades later, L. R. Holdridge, who lived for
long years in Costa Rica, proposed in 1947 his system of
“Life Zones” (Fig. 3B) in which he assigned a primary
importance to temperature and rainfall and considered the
fluctuation and distribution of these climatic parameters
as the main determinants of the vegetation of the world.
The vegetation of each life zone has a physiognomy and
a particular structure that are present every time that
similar bioclimatic conditions occur (Holdridge, 1947).
To describe and illustrate in a simple manner the
Central American phytogeographical regions, we follow
Smith and Johnston (1945: 11) who, oversimplifying,
define for the region three basic zones: (1) the tropical or
subtropical rainforest; (2) the tropical deciduous forest;
y (3) the montane zone (Fig. 3C).
Tropical or subtropical rainforest: this zone extends
along the Atlantic coast, from Panama in the South
to the Yucatán peninsula in the North, although we
find similar forests in some points of the Pacific coast
(Darién in Panama, Osa peninsula in Costa Rica). It
corresponds to the “tierra caliente Atlántica” (= Atlantic
warm region) of Standley. The vegetation is determined
by high temperatures and rainfall and alluvial soils. On
its western limits, the rainforest ascends the mountain
sides until it merges with the premontane forest. A
certain monotony in the climatic conditions along the
year may be the cause for a relatively low biodiversity.
In Central America we find in this zone approximately
25% of all orchid species that are known for the region.
However, all generalizations are dangerous. As Smith
and Johnston warn, it is not to be assumed that the
rain-forests thus outlined are uniform in constitution.
On the contrary, they disclose a high degree of local
differentiation, being grouped together only because of
a superficial resemblance and because they are acted
upon by more or less similar climatic forces (Smith &
Johnston, 1945: 14). This is equally valid for all other
phytogeographical zones.
Tropical deciduous forest: for Central America,
this zone extends along the Pacific coastline and is
characteristic because of its two well differentiated
seasons. It corresponds to the “tierra caliente Pacífica”
(= Pacific warm region) of Standley. The appearance
of the vegetation undergoes striking changes during
the year. It is the zone where the variety of orchids is
4 Although each of the countries in the region shows phytogeographical differences, it is valid to generalize for Mesoamerica using
Costa Rica as a model.