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Accueil du site → Master → Etats Unis → 1988 → A survey of twenty-four grazed and non-grazed areas in southern New Mexico

New Mexico State University (1988)

A survey of twenty-four grazed and non-grazed areas in southern New Mexico

Herman, Hilary J.

Titre : A survey of twenty-four grazed and non-grazed areas in southern New Mexico

Auteur : Herman, Hilary J.

Université de soutenance : New Mexico State University

Grade : Master of Science (MS) 1988

Résumé
In southern New Mexico, a regional shift in vegetation is occurring, toward shrub desert (principle species Prosopis glandulosa, Larrea tridentata, Flouensia cernua and Gutierrezia sarothrae) and away from semidesert grassland (Bouteloua eriopoda, and other grasses). Many investigators feel livestock overgrazing in the early 1900’s, coupled with recurrent drought, was chiefly responsible. Recent grazing pressure has been light or moderate, however. Accordingly the role of livestock in the desertification process in southern New Mexico was assessed, to determine if recent livestock grazing influenced plant community attributes. Species frequency, lifeform category frequency, and average number of species per square meter (diversity) were examined at 24 exclosure sites in three plant communities (mixed grasslands, mixed brush and lowland communities). Exclosures examined ranged from 5 to 74 years in age. Results indicated few species exhibited any form of trend for higher or lower frequencies under grazing, versus under protection within exlcosures. Mixed grasslands exclosure sites had slightly higher species diversity under grazing. Mixed brush sites had slightly lower diversity under grazing. It therefore appears contemporary livestock grazing pressures are not directly causing further change from semidesert grassland to shrub desert. The survey also indicated protection from grazing here in souther New Mexico did not result in the development of a different flora within exclosures as compared to grazed areas, even within decades-old exclosures. Even so, the author suggests alteration of grassland structure and the vegetational mosaic has occurred. Interactions between livestock, native small herbivores and favorable weather patterns will further shrub stand establishment and spread. Ultimately the semidesert grassland will disappear unless appropriate measures are undertaken soon.

Mots Clés : cattle grazing, exclosures, cattle grazing, vegetation change, vegetation change, cattle grazing

Présentation (Jornada NMSU)

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