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AN ECOLOGICAL AND PHYTOGEOGRAPHICAL ANALYSIS OF THE GRASSLANDS OF MEXICO
Author(s) -
Rzedowski J.
Publication year - 1975
Publication title -
taxon
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.819
H-Index - 81
eISSN - 1996-8175
pISSN - 0040-0262
DOI - 10.2307/1219002
Subject(s) - grassland , holarctic , ecology , edaphic , floristics , geography , endemism , flora (microbiology) , phytogeography , genus , species richness , biology , taxon , genetics , bacteria , soil water
Summary Grassland covers no less than 10–12% of the territory of Mexico. Its main types are briefly described and grouped according to their ecological determinism as climatic, edaphic, and anthropogenic. Ecological affinities of Mexican grasslands in relation to those of other parts of America are discussed, and 5 different communities dominated by grasses are analyzed as to the total geographical distribution of their genera and species, utilizing floristic lists available in the literature. The grassland characteristic of the semiarid areas of the High Plateau shows a high percentage of endemic species and genera. Its flora is similar to that of xerophilous scrubs of Mexico and has relatively little in common with the flora of the United States, in spite of the fact that ecologically this plant community is similar to the “short‐grass prairie” of western North America. The alpine grassland is also rich in species which are restricted to Mexico, but the analysis does not show any genus of limited area. On the other hand neotropical and holarctic influences in the flora are more or less even, although by its ecology and physiognomy the community is analogous to some “páramos” of the South American Andes. The savannas, or warm and humid climate grasslands, have few endemics in Mexico, and their floristic and ecological affinities are directed evidently to the south. The inland variant of the halophilous grassland shows moderate abundance of elements of restricted distribution, and the neotropical influence prevails slightly in its flora over the holarctic. The gypsophilous grassland, which does not seem to exist in America outside northern Mexico and adjacent areas of the United States, is rich in endemic genera and species, many of the last being obligate gypsophytes of very limited distribution. There is no direct evidence regarding the origin and the age of Mexican grasslands, but on the basis of data obtained from the analysis made, from the distribution of several grasses important in these grasslands, as well as from some paleogeographical and paleozoological data, it can be speculated that the existence of grasslands in Mexico may date from the middle or even from the early Tertiary. It is postulated that semiarid grasslands of this country, as well as the gypsophilous ones, had an “autochthonous” origin and a long evolutionary history. It is also possible that Mexico played an important role in the evolution of the halophilous grasslands of America. In contrast, the alpine ones seem to have a relatively recent origin, and the savannas possibly originated and evolved mainly in other sections of tropical America.