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Accueil du site → Doctorat → États-Unis → 1976 → GROWTH, DEVELOPMENT AND NUTRITIVE VALUE OF SOME ARIZONA CHAPARRAL SPECIES

University of Arizona (1976)

GROWTH, DEVELOPMENT AND NUTRITIVE VALUE OF SOME ARIZONA CHAPARRAL SPECIES

Pond, Floyd Williams

Titre : GROWTH, DEVELOPMENT AND NUTRITIVE VALUE OF SOME ARIZONA CHAPARRAL SPECIES

Auteur : Pond, Floyd Williams

Université de soutenance : University of Arizona

Grade : Doctor of Philosophy (PhD) 1976

Résumé
Seven species of shrubs from the Arizona chaparral were ob served, measured and analyzed between 1960 and 1963 to determine growth patterns, phenological development and nutritive values of foliage. The seven species were shrub live oak (Quercus turbinella Greene), hollyleaf buckthorn (Rhamnus crocea Nutt.), littleleaf mountainmahogany (Cercocarpus breviflorus Nutt.), birchleaf mountainmahogany (C. betuloides Nutt.), desert ceanothus (Ceanothus greggii Gray), Wright’s silktassel (Garrya wrightii Torr.), and skunkbush (Rhus trilobata Nutt). All were broadleaved schlerophylls except skunkbush. The shrubs were studied at three sites : Three-Bar at 1,000 m elevation with 60 cm of mean annual precipitation, Sierra Ancha at 1,500 m elevation with 53 cm mean annual precipitation, and Whitespar at 1,800 m elevation with 53 cm mean annual precipitation. Soils at Three-Bar and Whitespar were derived from granite and soil at Sierra Ancha was derived from diabase parent material. On all species, growth of stems was highly variable between years, seasons within years, species, site, and individual shrubs of the same species. Growth occurred each spring on all shrubs at all sites except in 1961. In 1961, winter moisture was below normal and pattern of rainfall evidently prohibited growth on all shrubs. Summer growth was limited to 1963 with a minor exception of a few millimeters of growth on one littleleaf mountainmahogany at Sierra Ancha in 1962. Summer rainfall in 1960 and 1962 was below normal and showers that did occur were late in the season. Summer rainfall appeared to be adequate in both 1961 and 1963, although summer growth did not occur in the summer of 1961 possibly due to low vigor resulting from no growth in the spring of that year. Growth started earliest in spring at Three-Bar, the lowest elevation, and began latest at Whitespar, the highest elevation. Desert ceanothus and birchleaf mountainmahogany began to grow earliest when minimum temperatures were near freezing, (28 to 36 F), shrub live oak and Wright’s silktassel began growth when minimum temperatures were still below 40 F (36 to 40 F) and hollyleaf buckthorn, littleleaf mountainmahogany and skunkbush began to grow after minimum temperatures were above 38 F. Production of seed was related to winter precipitation on all species except Wright’s silktassel. Although blooms were seen on most species each year even in the dry spring of 1961, the amount and pattern of rainfall determined maturation of seed. Seed production of Wright’s silktassel only occurred during summer while littleleaf mountain mahogany, at Sierra Ancha, produced seed in both spring and summer. The nutritive value of shrubs in the Arizona chaparral may not be as high as often supposed. Crude protein is generally high in early spring (15 to 20%), but rapidly declines to 5 to 8% as the season progresses and, in most species, is rarely higher than 7% during winter. Phosphorus is the element most likely to be deficient and, except in spring is often at or below the 0.18% required for adequate nutrition. Since calcium content is generally high, high calcium:phosphorus ratios often complicate the phosphorus assimilation. Calcium:phosphorus ratios are frequently above 7:1 in most species during fall and winter. Nutritive value alone appears to have little to do with grazing pref erence. Protein and phosphorus content in samples of skunkbush were comparable to those in littleleaf mountainmahogany, but grazing history shows that littleleaf mountainmahogany is much preferred over skunkbush by grazing animals.

Mots clés : Chaparral. ; Forage plants — Arizona.

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