The Amphibians and Reptiles of Sinaloa, Mexico - Smithsonian ...

56 UNIVERSITY OF KANSAS PUBLS., MUS. NAT. HIST.
Taxodium, Chlorophora, Pithecollobium, Haematoxylon and Caesalpinia.
Some of these trees reach a height of 30 meters or more.
Palms are locally abundant especially on the floodplains. Smaller
cacti are far less important in the composition of the vegetation of
the semi arid forest than in the plant formations to the north. The
slender Rathbunia alamosensis and the erect, dark green Opuntia
fuliginosa are frequently found, but never in large colonies (Sbreve,
1937:612). Most of the common cacti all seem to be shade-enduring
species.
A dense shrub vegetation occurs along the coast, especially bordering
lagoons. This vegetation consists primarily of mangrove
{Rhizophora mangle), which is found as far north as Tiburon Island,
Sonora. Various palms, especially Cocos nucifera, are common near
the beach. The dense and nearly continuous forest of this coastal
association occurs from Mazatlan southward. To the north of
Mazatlan the coastal association is more open and separated by long
stretches of sandy beach.
Some of the common plants of the semiarid forest are: Acacia
cymbispina, Ipomoea arborescens, Pachycereus pecten-arboriginum,
Caesalpima platyloba, Pitkecollobium sonorae> Cassia emarginata,
and Bursera simaruba.
Tropical Dry Forest
The Tropical Dry Forest, as used here, is homologous in part
with Brand's Humid Scrub (1936:26-27); Shreve's Thorn Forest
(1937:208-210); and Leopold's Tropical Deciduous Forest (1959:
34-35). The Tropical Dry Forest in Sinaloa occurs from sea level
to about 1000 meters elevation in the southern portion of the state
(Fig. 7). The differences between dry forest and semiarid forest
result from increase in mean annual precipitation. Greater rainfall
causes the more mesic plants to be major constituents of the flora,
whereas these same plants were restricted to water courses in the
northern, more arid portions of the state.
The physiognomy of the dry forest indicates a general overall
increase in height and density (Plate 6) of the component plants.
Shreve (1937:608) pointed out the marked increase of trees with
broad leaves in southern Sinaloa and northern Nayarit in contrast
to the xeromorphic leaves characteristic of trees in the thorn woodland
and semiarid forest. The vegetation is a relatively low forest,
15 to 25 meters high, of stocky, broad-leaved trees (Plate 7, Fig. 1).
Along water courses the dry forest assumes the dense character of