Geoscience Reference
In-Depth Information
families are common in the understory along with the plants in the bean caper
(Zygophyllaceae) and wild cinnamon (Canellaceae) families. Groundcover is usu-
ally sparse in the closed canopy forest with bromeliads (Bromeliaceae), composites
(Compositaceae), aroids (Araceae), mallows (Malvaceae), purslane (Portulaceae),
and arrowroot (Marantaceae). Endemism can be high at the species level; however,
no endemic families and few endemic genera are present in the Neotropical expres-
sion of the biome.
Mesoamerican Dry Forests
Mesoamerican seasonal forests include tropical deciduous, tropical semideciduous,
and thorn forests. The legume family is the most species-rich family found in most
of these forests. Euphorbs and myrtle families are important components of the for-
est flora. Herbaceous and woody climbing vines are also present. Species in the
morning glory (
Ipomoea
spp.) squash, cactus, fig, legume, trumpet vine, and yam
(Dioscoreaceae) families are present. The few epiphytes present in these forests
include bromeliads, cactus, and orchids. The canopy is typically closed with little
understory biomass. Fire is problematic in these forests as few trees tend to be fire
adapted. Many have thin bark that is easily damaged, rather than the thick bark
commonly found on trees that evolved with fire. Less than 2 percent of these forests
are currently protected.
The dry forests of the Antilles tend to be short in stature and low in diversity.
They have a high density of short- and medium-size trees with an even canopy and
no emergent trees. The forests are typically found on limestone substrate or shallow
and rocky soils along the coasts and experience high winds and frequent hurri-
canes. They are able to recover more rapidly from these disturbances than the for-
ests on the mainland. The trees tend to be evergreen and sclerophyllous. Species in
the myrtle family tend to dominant the islands. Species in the cactus, euphorb, ca-
per, and bean caper families are also common. Since these forests occur on islands
they are vulnerable to human exploitation and degradation. The introduction of
nonnative species to the islands threatens the forests' survival.
The Gran Chaco
The Gran Chaco is the largest expanse of dry forest in South America. It lies
between 17
S latitude, occupying parts of northern Argentina, southeast-
ern Bolivia, and 60 percent of Paraguay, as well as a small portion of southwest
Brazil. The Chaco is a mosaic of vegetation, including dry forests and woodlands,
thorn scrub, palm savannas, grasslands, marshes, and salt flats. Gallery forests col-
onize along rivers and streams. The tropical thorn forest is the dominant forest of
the Chaco. Thorn forests are dense forests of opuntia cactus and mesquite trees
with bayonet bromeliads and star cactus in the understory. This makes it a rather
inhospitable place for large mammals (including researchers). The palo borracho
or drunken tree (kapok family) is a large evergreen tree in the Chaco, with a swol-
len trunk used to store water for survival during the dry season (see Figure 5.5).
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