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University of Arizona (1970)

Successional trends on protected versus grazed desert grassland ranges in Arizona

Smith, David Allen

Titre : Successional trends on protected versus grazed desert grassland ranges in Arizona

Auteur : Smith, David Allen,

Université de soutenance : University of Arizona

Grade : Master of Science (MS) 1970

Résumé
Two sets of line intercept data, taken over a 28-year period, were used to determine changes in vegetation on protected versus grazed desert grassland ranges in Arizona. Percentage intercept was used to determine changes for grouped grasses, forbs, and trees and shrubs. Percentages of cover, composition, and frequency were used to deter mine changes in individual species. Cover of grasses, trees and shrubs increased due to protection and with tim e, but the change in forb cover was not significant. Arizona cottontop (Trichachne califom ica (Benth.) Chase) increased most among grasses on the protected range. It was concluded that the increase was initiated by favorable clim atic conditions and perpetuated by protection. Red threeawn (Aristida long !seta Steud.) decreased on the protected range and increased slightly on the grazed range indicating an improve ment in climax status for the protected range. Buckwheat ( Eriogonum wrightii Torr.) increased in cover due to protection and with tim e. Burroweed (Haplopappus tenuisectus (G reene) Blake) decreased on both ranges but the rate was faster on the grazed range. The causes of this decline were concluded to be drought and competition with mesquite (Prosopis juliflora (Swartz) DC. var. velutina (W oot.) Sarg.). Cover of mesquite increased on both ranges but the rate was slower on the protected range. Snakeweed (Gutierrezia lucida (Greene) decreased with protection apparently due to increased grass competition.

Mots clés : Plant succession — Arizona. ; Rangelands — Arizona. ; Grassland ecology

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Page publiée le 13 juillet 2018