Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : DESERT GRASSLAND MESQUITE AND FIRE

Auteur : Claveran Alonso, Ramon

Université de soutenance : University of Arizona

Grade  : Doctor of Philosophy (PhD) 1967

Résumé
A study was made of some ecological and physiological reactions of velvet mesquite (Prosopis Iuliflora (Swartz) DC. var. velutina (Woot.) Sarg., Emory oak (Ouercus emorvi Torr.). blue grama (Bouteloua gracilis (H.B.K.) Lag-), and sideoats grama (Bouteloua curtipendula (Michx.) Torr.) to high temperatures. These studies were made under field conditions near Cananea, Sonora, Mexico ; near Tucson, Arizona ; and in a greenhouse and laboratory at The University of Arizona. Individual blue grama plants were burned in the field using four fuel levels : the natural plant fuel, and the natural fuel to which had been added three, seven, and ten tons per hectare. Dry weight of the plant produced after burning was decreased by about one-half regardless of the amount of fuel used. Crude-protein content was slightly higher on the burned plants. No plants were killed by the fire. Greenhouse-grown blue grama and sideoats grama were subjected to temperatures of 50 C to 80 C in an oven for periods of one and three minutes. The dry weight produced by both grass species two months after treatment was inversely related to the temperature and length of the time applied. Protein conteritof the species was increased by high temperature treatments. Blue grama was more resistant than sideoats grama to high temperatures. Individual mesquite trees were burned with three, seven, and ten tons of fuel per hectare. An average of 86 percent of those with a basal diameter of 5 cm or less were highly damaged by fire. Of these 32 percent were completely killed. Only 3 percent of the mesquite with larger basal stem diameters were killed. Three, seven and ten tons of fuel per hectare produced an average mesquite damage of 52, 37, and 64, respectively. The following regressions were calculated from mesquite samples collected near Cananea : (a) bark thickness in relatioirto basal diameter, (b) basal stem diameter in relation to age, and (c) bark thickness in relation to age. A high degree of correlation was observed. Heat transmission in the bark of oak and mesquite trees was evaluated under field conditions. Oak bark was a better insulator than that of mesquite. This fact may largely explain the relatively high resistance of the oaks to grass fires. Heat resistance in young mesquites appears to be a function of age. Three- and 11-month-old greenhouse-grown mesquites were subjected to temperatures between 50 C and 85 C for a period of one minute in an oven. A temperature of 80 C severely damaged 99 percent of the three-month-old plants ; 80 percent of the 11-month-old plants were similarly damaged when heated to 85 C. Adenine was artificially supplied to 60-day-old blue grama and 76-day-old mesquite seedlings subjected for a period of three minutes to temperatures of 60 C and 70 C. As indicated by the dry weight produced by the plant after the treatment, blue grama did not show any effect from the addition of adenine. Mesquite, however, had less heat damage when adenine was supplied. These results suggest a deficiency of adenine in the plant as one reason for heat tissue damage, and that this metabolite can prevent heat lesions. Heat transmission into the desert grassland soil was very low ; the soil appears, therefore, to provide good protection for the underground buds of mesquite and grasses. These results suggest that fire is a potentially important ecological factor in the desert grassland. As a mesquite-control agent, fire appears to be most effective in the control of young mesquites (basal stem diameter of 5 cm or less) growing in desert grasslands with at least 700 kilograms of air-dry fuel per hectare and a continuous grass cover.

Mots clés : Mesquite. ; Burning of land. ; Fire

Présentation

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